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MIRIGALDI, ALESSANDRO. "Power scaling of high power lasersystems." Doctoral thesis, Politecnico di Torino, 2022. http://hdl.handle.net/11583/2966325.
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Elliott, Stella N. "High power semiconductor lasers." Thesis, Cardiff University, 2010. http://orca.cf.ac.uk/54136/.
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Using red and near infra-red emitting quantum well and quantum dot based devices I have modelled the nearfield and farfield intensities and distribution in various waveguide structures. I compared the effect of various factors on the power density at catastrophic damage and found the greatest effect from the current pulse length and dot or well nature of the active region, for the first time in the AlGaInP material system. At short pulse length the quantum dot devices achieved a power density of 17 MW/cm
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Alvarez-Chavez, Jose Alfredo. "High-power fibre lasers." Thesis, University of Southampton, 2003. https://eprints.soton.ac.uk/15478/.
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This thesis reports on the experimental study of high-power, high-energy, cladding-pumped, rare-earth (Yb3+, Er3+/Yb3+)-doped fibre lasers. Some of the main capabilities of fibre lasers such as: High brightness and thermal properties were exploited for the development of a variety of continuous wave (CW) and Q-switched devices, whose characteristics also includes compactness. Our devices could already be considered an option for several applications. The 25-year long scientific and commercial evolution that fibre lasers have experienced is discussed in the first two chapters. The invention of Erbium-doped fibre amplifiers (EDFA's) and Internet were two major breakthroughs, which launched the need of WDM systems and laser sources. Fibre lasers, are now considered a flexible and powerful device whose technology has finally reached its maturity. Cladding pumping is the technique employed in these experiments in order to pump double clad fibre lasers using high power, broad stripes and bars. In this work, several inner cladding shapes have been used to overcome the normally high mismatch between diode laser beams and inner cladding areas of fibre lasers. Chapter Three consists of a review of cladding-pumped fibre lasers. It describes how inner cladding geometry and pump absorption limits the output power scalability of these devices. Nonlinear effects and amplified spontaneous emission are also studied due to their implication they have over fibre lasers performance. Results on conventional, continuous wave (CW) fibre lasers including fibre characterization and employed launching techniques are described in Chapter Four. A new method to obtain high intensity laser beam output from an Yb3+-doped, cladding-pumped, highly multimode fibre laser has been proposed. In this experiment, we propose the use of fibre tapers to increase intensity and improve beam quality. In CW regime, our results show an intensity increase of ~3.5 times with a low power penalty of ~1 dB. Also, without tapering, a maximum output power of 21-W was reached with a slope efficiency of >80%. Using a simple set of optic elements such as a l/2 waveplate, a polarizing beam-splitter and a bulk grating, we investigated the polarization characteristics of an Yb3+ fibre laser, from which we obtained 6.5 W of single polarization tunable output in the range of 1070 to 1106 nm. As a free running laser, the system produced 18 W at 1090 nm and showed a threshold of 1.8 Watts. The experiment is our first approach for developing a reliable high-power Yb3+-doped fibre source, that could be used in conjunction with optical parametric oscillators (OPO) and amplifiers (OPA) to frequency convert to a broad band of wavelengths. Using a new design of ytterbium-doped fibre made in-house with the conventional modified chemical vapor deposition (MCVD) process, we explored the possibilities of energy storage with such a large mode area (LMA) fibre. The fibre system was capable of delivering energetic pulses of >2 mJ, which could suggest the feasibility of a pulsed fibre laser in the region of tens of milli-Joules. The experiment is described in Chapter Six, on which the experiment that uses the tapered fibre laser in Q-Switched regime is also described and compared to LMA fibre laser. Gaussian-type pulses were obtained which reached pulse energies of 0.6 mJ at 4 kHz using a tapered fibre laser and 1.3 mJ at 500 Hz using conventional laser, corresponding to average powers of 2.1 Watts for the tapered laser and 0.8 watts for the conventional laser. Er3+/Yb3+-doped fibre lasers were part of our experimental work. This co-doping technique allows pumping of Yb3+ ions using broad-stripe high-power pump sources to reach much higher output power levels. Efficient energy transfer from excited Ytterbium ions into Erbium is achieved. From a preliminary study, the fibre laser showed a threshold of 160 mW and a slope efficiency of 49% with respect to absorbed pump power. The maximum output power was 6.2 watts at 1535 nm and a linewidth of 1 nm. One of our co-doped fibre devices produced 16.8 W of continuous wave, multimode laser power at the interesting wavelength of operation of 1550 nm. Finally, conclusions and future work are included in Chapter Eight.
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Abram, Richard Henry. "High power waveguide array lasers." Thesis, Heriot-Watt University, 1998. http://hdl.handle.net/10399/622.
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Park, Jung-Hyun. "High-gain, high-power free electron lasers." Thesis, Monterey, California. Naval Postgraduate School, 1991. http://hdl.handle.net/10945/30964.
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The Paladin FEL experiment is shown to exhibit clear and dramatic effects governed by the electron beam velocity distribution for the first time. The FEL integral equation is used to show that there is significant broadening of the gain spectrum due to the Gaussian velocity distribution, and also shows a plateau in the gain evolution along the undulator due to a triangular-shaped velocity distribution. The gain spectra and power evolution from simple, single- mode simulations are compared to the ELF experiments. The microwave power evolution along the undulator is compared as well for both the tapered and untapered undulators. In all cases, the agreement is found to be good.
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Voughs, Tyrone Y. "High-power amplifier free electron lasers." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2006. http://library.nps.navy.mil/uhtbin/hyperion/06Jun%5FVoughs.pdf.
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Thesis (M.S. in Applied Physics)--Naval Postgraduate School, June 2006.Thesis Advisor(s): William B. Colson, Robert L. Armstead. "June 2006." Includes bibliographical references (p. 57). Also available in print.
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Hastie, Jennifer E. "High power surface emitting semiconductor lasers." Thesis, University of Strathclyde, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399721.
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Wang, Jing. "High-average-power planar waveguide lasers." Thesis, University of Southampton, 2007. https://eprints.soton.ac.uk/50198/.
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Reported in this thesis is some progress towards high-average-power diode-pumped planar waveguide lasers. As a format of the laser active medium, planar waveguides take advantage of their extreme slab geometry, which is compatible with that of high-power diode lasers, offer a great degree of versatility of the pump arrangement, have excellent thermal handling capability, and deliver high optical gains per unit pump power. Pumped with different schemes, three kinds of planar waveguides are investigated herein: direct-bonded double-clad planar waveguides, ion-exchanged tapered waveguides, and thick films fabricated by pulsed laser deposition, of which a double-clad planar waveguide produced laser output power of up to 58W. PLD planar waveguides are investigated as a flexible alternative in high-power planar waveguide laser systems. As an initial demonstration, a slope efficiency of 11.2% was obtained from a diode-stack-pumped 50μm Nd:GGG PLD waveguide. The effect of self-imaging was observed with a 27μm Nd:GGG PLD waveguide.
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Pusino, Vincenzo. "High power, high frequency mode-locked semiconductor lasers." Thesis, University of Glasgow, 2014. http://theses.gla.ac.uk/5174/.
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Integrated mode-locked laser diodes are effective sources of periodic sequences of optical pulses, which have always been of great interest for a range of spectroscopy, imaging and optical communications applications. However, some disadvantages prevent their widespread use, such as the restricted tuning of their repetition rate and their output power levels never exceeding a few mW. This thesis reports on the work done to address those limitations. Two main findings are presented, the first being the generation of ultra-high repetition rate optical signals through external injection of two continuous wave signals. This mechanism is much simpler than other techniques previously proposed to increase the repetition rate of monolithic modelocked laser, and has proved successful in generating optical signals up to quasi-THz. It is based on injection of two continuous wave signals whose spacing is an integer multiple of the pulsed cavity free spectral range and whose injection wavelengths coincide with two of the monolithic laser modes. This technique allows discrete tunability of the repetition rate with a step equal to the injected cavity free spectral range, and the injected laser has been shown to lock up to a repetition rate of 936 GHz, corresponding to 26 times that of the free-running semiconductor laser (36 GHz). The presented scheme is suitable for integration, opening the way for a successful on-chip generation of ultra-high repetition rate optical signals exploiting coupled cavity phenomena. The second main finding of this thesis regards the changes induced on the pulsed operation of monolithic passively mode-locked lasers by a blue bandgap detuning applied to their saturable absorber. The quantum well intermixing technique has been used for attaining an area-selective bandgap shift on the fabricated chip, being fully postgrowth. The lasers with a detuned absorber were found to have an extended range of gain section currents and absorber voltages in which stable mode-locking operation took place. Furthermore, a comparison of mode-locked devices fabricated on the same chip, respectively with and without a bandgap detuned absorber, showed that the emitted pulses had greater peak power and were less affected by optical chirp when the bandgap of the absorbing section was shifted. A new intermixing technique has also been developed as part of this work to address some inconsistencies of the pre-existing one; the newly introduced approach has been found to provide better spatial resolution and a more precise control of the attained bandgap shift.
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Tisch, John William George. "Studies of high harmonic generation using high power lasers." Thesis, Imperial College London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309530.
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Jain, Deepak. "Novel optical fibers for high power lasers." Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/386233/.
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High power fiber lasers have several applications thanks to their outstanding features such as good beam quality, all fiberized compact device size, robustness, wavelength tuning, high wall-plug efficiency, and low cost. Due to these features high power fiber lasers are replacing other solid-state lasers for several applications. Fiber lasers are being used commercially for several applications such as surgery, material processing (cutting, drilling, polishing etc.), oil and gas sensing, pumping several other lasers, and space communication etc. However, nonlinear effects restrict the output power level of fiber lasers. Although reducing power density by using large core diameter fibers can increase the threshold of non-linear effects, however large core diameter leads to multimode behavior and is prone to bend-induced effective area reduction. Several novel large mode area fibers have been proposed to scale the output power level. However, the advantages of all-fiberized device and low cost disappear as most of these fibers involve complex fabrication and cannot be spliced to optical components such as conventional pump fibers. This thesis deals with novel large mode area fibers which are suitable for mass scale production and can offer low cost production compared to other competitive fiber designs thanks to their simple design. These novel fibers are all-solid and can be easily spliced to other fibers, thus can lead to an allfiberized device. Moreover, some of the novel fibers proposed in this thesis offer the delocalization of powers of the higher order modes outside the core. This delocalization of the higher order modes can be useful to ensure an effective single mode operation in a double clad configuration. The proposed novel fibers offer better or competitive mode area scaling performance compared to other competitive fibers. In this thesis, firstly conventional step-index fibers have been exploited for mode area scaling by reducing the refractive index of the actively doped core with respect to the cladding. Prior to this thesis, the lowest reported NA of a Yb-Al doped fiber was 0.048 corresponding to 0.0008 refractive index of core with respect to cladding. In this thesis, optimized solution doping process leads to a NA of 0.038 for a Yb and Al doped core corresponding to 0.0005 refractive index of core with respect to cladding. This reduction in NA of core leads to an effective area increase from ~450μm2 to ~700μm2 at 32cm bend diameter ensuring effective single mode operation. This is the lowest NA ever reported using cost-effective solution doping process to the best of author’s knowledge, which is widely used in manufacturing of rare-earth doped fiber. Further, in a 4%-4% laser configuration, a 35μm core diameter 0.038 NA fiber shows high laser efficiency (~81%) with good M2 (~1.1) value of output beam at 1040nm. Thesis also reports a novel fiber design known as single trench fiber, where a passive Ge-doped ring has been added around the core. This ring known as resonant ring facilitates the suppression of the higher order modes thanks to resonant coupling between modes of core and ring. The combination of ultra-low NA (~0.038) and a surrounding ring can lead to an effective single mode operation of fiber having a core diameter as large as of 50μm offering an effective area of ~1,500μm2 at ~40cm bend diameter. A 40μm core diameter single trench fiber has been successfully fabricated in house and shows robust effective single mode behavior. Further, a 30μm single trench fiber has been tested in a master oscillator power amplifier configuration delivering ~23.5ps pulses at 13.5MHz repetition rate carrying up to ~3.8μJ pulse energy corresponding to >160kW peak power and ~52.3W of average power, while maintaining ~76% slope efficiency. Numerical Performance of STF has also been reported at other wavelengths such as 1550nm and 2000nm. A detailed comparative analysis has been performed with other competitive fiber designs showing the advantages of single trench fiber over other fiber designs. Further, another fiber design known as multi trench fiber has also been proposed. Multi trench fiber can scale effective area as large as of 12,000μm2 in a rod-type configuration. Multi-trench fibers offer several advantages such as easy cleaving and splicing thanks to the all solid structure; however refractive index of active core has to be same as of passive cladding. Nevertheless, this fiber has shown a strong potential for applications in ultrafast rod-type fiber lasers. A 90μm core diameter passive fiber has been fabricated in house using rod-in-tube technique in conjunction with modified chemical vapour process. Experiments ensure an effective single mode operation. Furthermore, this fiber also shows the potential to be used for beam delivery applications with a small core diameter thanks to effective single mode operation over a wide range of bend radii. MTFs of 30μm and 20μm core diameter have been successfully fabricated and both ensure robust single mode operation over a wide range of bend radii at 1060nm and 632nm respectively. Numerical simulations show the possibility of a 10μm fiber to be effectively single moded at a wavelength of 300nm.
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Martin, Kevin Ian. "High power, diode pumped, single frequency lasers." Thesis, University of Southampton, 1996. https://eprints.soton.ac.uk/396626/.
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This thesis presents experimental and theoretical work on the development of high power (i.e. multi-Watt) single frequency lasers, with the main emphasis on using intra-cavity second harmonic generation to produce high power visible output. With such a laser, pumped by a beam shaped 20W diode bar, we have obtained over 3W of TEM00 single frequency output at 532nm. Because of the strong non-linear effects introduced into the resonator cavity by the frequency doubler, the behaviour of the laser can be significantly altered. In particular, there is the previously unreported phenomenon of mode-hopping suppression, where the non lasing modes are suppressed by the nonlinear loss (due to sum-frequency generation with the lasing mode). This allows the lasing mode to be smoothly tuned over many mode spacings simply by scanning the cavity length. Tuning ranges of up to 80GHz have been measured, and are in good agreement with theoretical calculations. There are also some less desirable consequences of the high nonlinear loss, such as parasitic lasing, self misalignment, and bidirectional lasing, that have had to be overcome in order to achieve efficient operation. Ring lasers can provide, arguably, the most robust and stable single frequency operation. However care must be taken in their design to minimise spatial hole burning. Even a small amount of residual spatial hole burning can cause multi-frequency operation in ring lasers. This thesis contains experimental measurements of spatial hole burning and compares these with a numerically calculated theory. Also, the technique of pump beam displacement to increase the single frequency performance of end-pumped ring lasers, suffering from residual spatial hole burning, is described. Thermal effects, such as thermal lensing and thermally induced birefringence often prove to be a major limiting factor in efficient operation of high power lasers. However these effects are dependent on several factors, such as the resonator design, and the heat sinking of the laser rod. Described in this thesis are the steps we have taken to minimize these effects in the designs of the high power lasers we have constructed.
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BRAGLIA, ANDREA. "High Power Fiber Lasers for Industrial Applications." Doctoral thesis, Politecnico di Torino, 2013. http://hdl.handle.net/11583/2506061.
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Fiber lasers can be considered a revolutionary technology in the laser field thanks to their
unique properties, such as high efficiency, simplicity, compactness and robustness. These
features have allowed in the last ten years their outstanding growth both in scientific and
industrial applications, eroding the market share of traditional laser sources like solid-state
and gas lasers. Fiber lasers power scaling to the kilowatt range is now well established
and, thanks to the fiber confinement, excellent output beam quality can be obtained,
with a remarkable benefit for applications. Today, high power laser sources are based on
ytterbium doped, large mode area fibers because ytterbium can be efficiently pumped in
the range 915nm − 975nm (where pump sources are widely available), generating laser
action at 1060nm − 1090nm. With this configuration, impressive power scaling has been
demonstrated in the last few years.
This Ph.D. thesis has been focused on the design and development of high power
fiber lasers for a wide range of industrial applications, like cutting, wending, drilling and
micro-machining. Both continuous and pulse wave fiber lasers have been demonstrated
and particular attention has been devoted to the development of critical technological de-vices like fused fibers combiner, strategic components either for pump light coupling into
the laser active fiber (pump combiner) and for power scaling through the beam combining
of several fibers lasers (signal combiner).
Ytterbium doped fiber lasers have been developed during the Ph.D activity and, in
particular, after a theoretical analysis devoted to the modeling of fiber laser cavities
and amplifiers, a continuous wave fiber laser and two pulsed laser systems have been
demonstrated. The CW fiber laser has been developed with a modular approach: 7
laser modules, capable of emitting hundreds of Watts each, have been coupled together
thanks to a fused fiber combiner. A multi-kilowatts output power has been demonstrated.
The photo-darkening effect in the active fiber of the laser modules has also been exper-imentally investigated. The pulsed architectures are instead a Q-switched MOPA and a
Seed MOPA fiber lasers. The first system is based on a fiber laser oscillator operating
in the Q-switching regime, followed by a power amplifier. This laser is capable of delivering 100ns pulses with 10W average power (2kW maximum peak power). The Seed
MOPA consists instead of a current modulated laser diode followed by two amplification
stages; 2W output average power with adjustable pulse widths from 10 to 100ns has been
demonstrated.
In the last part of the activity, a preliminary version of a thulium doped fiber laser
emitting at about 2000nm (i.e. in the so-called eye-safe region) has been developed. The
laser is a Seed MOPA system that has been tested in cw regime but in the near future
the pulsed behavior will be investigated.
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Naidoo, Darryl. "High brightness lasers." Thesis, Stellenbosch : Stellenbosch University, 2015. http://hdl.handle.net/10019.1/97044.
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Kheder, Abdul-Sameei Yaseen. "Starting high inertia, high friction loads from limited power sources." Diss., The University of Arizona, 1988. http://hdl.handle.net/10150/184455.
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At starting, electrical motors require large power and current. This may not be a problem in a large electrical system but it may be very severe for a limited power source like a solar array. If a direct approach is taken the array rating must be 5-6 times the motor rating in order to start the motor and its high inertia high friction load. Batteries have been used to store energy and supply that energy for starting. Batteries need maintenance and their low efficiency is a problem too. In this study a new type of controller has been suggested and developed for the use with D.C. motors. Computer simulation showed promising results. The controller uses the array power, which is equal to the rated power of the motor, for starting and for running condition. Experimental results showed that the theoretical results are applicable.
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Ottaway, David. "Medium power stable lasers for high precision metrology /." Title page, abstract and contents only, 1998. http://web4.library.adelaide.edu.au/theses/09PH/09pho89.pdf.
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Frist, Duane C. "Improved beam jitter control methods for high energy laser systems." Thesis, Monterey, California : Naval Postgraduate School, 2009. http://edocs.nps.edu/npspubs/scholarly/theses/2009/Dec/09Dec%5FFrist.pdf.
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Thesis (M.S. in Astronautical Engineering)--Naval Postgraduate School, December 2009.Thesis Advisor(s): Agrawal, Brij ; Kim, Jae Jun. "December 2009." Description based on title screen as viewed on January 28, 2010. Author(s) subject terms: High Energy Laser (HEL), beam control, Fast Steering Mirror (FSM), two axis gimbal, stabilization, video tracking, feedforward control, adaptive filter. Includes bibliographical references (p. 69). Also available in print.
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Murray, Paul R. "High peak power, pulsed, planar waveguide CO2 lasers." Thesis, Heriot-Watt University, 2000. http://hdl.handle.net/10399/1225.
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Scahill, Charlanne Mary. "Design of high power, single frequency semiconductor lasers." Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624851.
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Nikitichev, Daniil I. "High power ultra-short pulse quantum-dot lasers." Thesis, University of Dundee, 2012. https://discovery.dundee.ac.uk/en/studentTheses/b7cec111-5ed7-4020-9fad-794d817e8f61.
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In this thesis, novel multi-section laser diodes based on quantum-dot material are designed and investigated which exhibit a number of advantages such as low threshold current density; temperature-insensitivity and suppress carrier diffusion due to discrete nature of density of state of quantum-dots. The spectral versatility in the range of 1.1 µm – 1.3 µm wavelengths is demonstrated through novel mode-locking regimes such as dual-wavelength mode-locking, wavelength bistability and broad tunability. Moreover, broad pulse repetition rate tuning using an external cavity configuration is presented. A high peak power of 17.7 W was generated from the quantum-dot laser as a result of the tapered geometry of the gain section of the laser has led to successful application of such device for two-photon imaging. Dual-wavelength mode-locking is demonstrated via ground (?=1180 nm) and excited (?=1263 nm) spectral bands with optical pulses from both states simultaneously in the 5-layer quantum-dot two-section diode laser. The widest spectral separation of 83 nm between the modes was achieved in a dual-wavelength mode-locked non-vibronic laser. Power and wavelength bistability are achieved in a mode-locked multi-section laser which active region incorporates non-identical QD layers grown by molecular beam epitaxy. As a result the wavelength can be electronically controlled between 1245 nm and 1290 nm by applying different voltages to the saturable absorber. Mode-locked or continuous-wave regimes are observed for both wavelengths over a 260 mA – 330 mA current ranges with average power up to 28 mW and 31 mW, respectively. In mode-locked regime, a repetition rate of 10 GHz of optical pulses as short as 4 ps is observed. Noticeable hysteresis of average power for different bias conditions is also demonstrated. The wavelength and power bistability in QD lasers are potentially suitable for flip-flop memory application. In addition, a unique mode-locked regime at expense of the reverse bias with 50 nm wavelength tuning range from 1245 nm to 1290 nm is also presented. Broad repetition rate tunability is shown from quantum-dot external cavity mode-locked 1.27 µm laser. The repetition rate from record low of 191 MHz to 1 GHz from fundamental mode-locking was achieved. Harmonic mode-locking allows further to increase tuning up to 6.8 GHz (34th-order harmonic) from 200 MHz fundamental mode-locking. High peak power of 1.5 W can be generated directly from two-section 4 mm long laser with bent waveguide at angle of 7° at 1.14 GHz repetition rate without the use of any pulse compression and optical amplifier. Stable mode-locking with an average power up to 60 mW, corresponding to 25 pJ pulse energy is also obtained at a repetition frequency of 2.4 GHz. The minimum time-bandwidth product of 1.01 is obtained with the pulse duration of 8.4 ps. Novel tapered quantum-dot lasers with a gain-guided geometry operating in a passively mode-locked regime have been investigated, using structures that incorporated either 5 or 10 quantum dot layers. The peak power of 3.6 W is achieved with pulse duration of 3.2 ps. Furthermore, the record peak power of 17.7 W and transform limited pulses of 672 fs were achieved with optimized structure. The generation of picosecond pulses with high average power of up to 209 mW was demonstrated, corresponding to 14.2 pJ pulse energy. The improved optical parameters of the tapered laser enable to achieve nonlinear images of fluorescent beads. Thus it is for the first time that QD based compact monolithic device enables to image biological samples using two-photon microscopy imaging technique.
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Friel, Graham John. "Diode-pumped Nd:YLF lasers for high-power operation." Thesis, University of Southampton, 1998. https://eprints.soton.ac.uk/394397/.
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This thesis presents the results of investigation into a variety of high-power, miniature Nd:YLF lasers end-pumped by diode-lasers. Diode-pumping enables more compact, efficient and reliable operation than alternative laser sources. Three main areas of research have been investigated, namely mode-locking, novel laser-amplifiers and high-brightness end-pumping. The main motivation was to develop simple picosecond-oscillators, suitable for pumping synchronously-pumped optical parametric oscillators. These devices deliver widely tunable radiation and have applications in ultrafast spectroscopy. Ultrashort-pulse generation via mode-locking offers a particularly attractive way of scaling the peak-power output by many orders of magnitude above the average level. Nd:YLF lasers were chosen for investigation as they are suited to diode-pumping, have excellent thermal properties and are capable of generating pulses of ~1 ps duration. Different amplification techniques were studied as a means of further scaling the output power from these lasers. A novel technique termed mode-locked injection-seeding was demonstrated. A steady train of ~3.6 ps pulses, 135 MHz repetition rate, from an additive-pulse mode-locked laser was used to injection-seed a slave laser. The slave laser was pumped by a single 3 W diode-laser. An average signal-power of ~25 mW, at 1053 nm gave an amplified pulse duration of 5.2 ps and an average output power of 840 MW. This corresponded to a power gain of 34 (15.3 db) and a peak output power of 1.3 kW. Optimised resonator designs were investigated for a simple and scalable mode-locking technique known as Kerr-lens mode-locking. New resonator designs show improved Kerr-lens sensitivity but this technique is shown to be problematic in Nd:YLF. The first application of beam-shaping of broad-stripe diodes (4W) is described using a two-mirror device. This scheme does not significantly reduce the brightness of the diode-laser and allows focusing to intense circular spots. This reconfigured beam is used to investigate high-brightness pumping of a simple double-pass amplifier. Small-signal gains of 17 dB were demonstrated. Also two beam-shaped diode-bars, delivering a combined power of ~30 W were used to investigate pump-power scaling of an actively mode-locked laser. This laser produced 54 ps pulses (240 repetition rate) and 7.6 W average power.
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Vazquez, Zuniga Luis Alonso. "Ultrafast high power fiber lasers and their applications." Thesis, University of Southampton, 2012. https://eprints.soton.ac.uk/340703/.
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In this thesis I report experimental studies toward developing versatile, compact, and reliable ultrafast sources in the 1.5 micron wavelength region, and their power scalability. The first part of the thesis reports on the development of a stable all-fiberized wavelength-tunable frequency-shifted feedback (FSF) picosecond laser. Stability of the passive mode-locking mechanism is achieved by combining the effects of nonlinear polarization evolution and a frequency shifting mechanism carried out by an acousto-optic modulator. The novel configuration generates pulses in the range of ~ 34 to 66 ps, depending on the value of the frequency shift applied in the cavity. The cavity allows for continuous wavelength-tuning over 30 nm of the erbium gain bandwidth via a fiberized tunable filter. The stability of the laser cavity allows pulse analysis as a function of different parameters of the laser cavity. Additional extensive numerical analysis, combined with the experimental results, provide novel insights for understanding the dynamics of FSF lasers in the mode-locking regime, which have not been addressed in the literature before. The second part of the thesis reports on the development of a versatile, stable, compact mode-locked fibre laser using nonlinear polarization evolution and a semiconductor saturable absorber mirror(SESAM). The novel cavity can generate pulses with widths between ~ 2.7 and 11 ps over 25 nm of erbium gain bandwidth. This is achieved by integrating in the cavity state-of-the-art optical filters. The performance of this laser is compared to that of the FSF laser in terms of pulse energy, amplitude noise, timing jitter and power scaling. The third part of the thesis reports on the direct amplification of a mode-locked ~ 10 picosecond bandwidth-tunable laser source that I made by means of large-mode area (LMA) erbium-ytterbium co-doped and erbium-doped fibres. While cladding pumping amplification schemes have become a standard option for pulse amplification in the 1.5 μm region, core-pumped amplification in LMA erbium-doped fibres has been less studied. In this thesis, in addition to the amplification of picosecond pulses in an erbiumytterbium co-doped fibre; I present a novel scheme that uses a hybrid co-propagation core-pumped (1480 nm) and counter-propagation cladding-pumped (980 nm) scheme, which compensates for the low cladding absorption at 980 nm of the erbium-doped fibre. Picosecond pulses are amplified up to 1.5 W with peak powers exceeding 11 kW. The last part of this thesis reports on the study of a stable operating regime found in passive mode-locked lasers called noise-like pulses, which can generate broadband spectra directly from the main oscillator. Here, I report the record of a 135-nm bandwidth lineraly polarized noise-like pulse generation in an erbium-doped fibre laser by exploiting the birefringence of the cavity and the Raman gain of a highly nonlinear fibre (HNLF). Noise characterization of the source is carried out and compared to other commercial broadband sources in order to see its applicability in areas such as optical coherence tomography.
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Chard, Simon Peter. "Development of versatile high power bounce geometry lasers." Thesis, Imperial College London, 2010. http://hdl.handle.net/10044/1/6184.
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This thesis details an investigation into the development of bounce geometry lasers to achieve a more versatile range of laser characteristics. The bounce geometry has matured in recent years into a useful solid-state pumping scheme, but its performance has to date been limited by a number of factors, as well as largely restricted to neodymium systems. For real-world application, a more versatile range of laser characteristics would be desirable. A new design for a bounce geometry amplifier is presented that achieves a symmetric gain profile and thermal lens by control of the amplifier dimensions. The laser produces a circular stigmatic TEM00 (M2 < 1:11) beam with 14 W power. When Q-switched, the design permits versatile control over the repetition rate (single-shot to 480 kHz) with pulse energies up to 0.45 mJ. The stigmatic design also allows the direct generation of a Laguerre-Gaussian `vortex' beam, and proves favourable for modelocking with the nonlinear mirror method. Several designs are investigated to study power scaling in a master oscillator power amplifier (MOPA) configuration, including a stigmatic MOPA based on the amplifier described above, and a chain of multiple power amplifiers. A folded dual-pumped amplifier design is also demonstrated, which reduces the size and complexity of a multi-stage amplifier and allows power scaling to the 100 W level. Pulse amplification is also investigated, and a MOPA is optimised for energy extraction by a Q-switched oscillator. Finally a 3-micron bounce laser is presented using an erbium-doped YSGG gain medium. Different cavity designs are investigated, and a simple compact cavity is found to be optimum. Thermal effects are investigated and found to be a limiting factor on the laser's performance. Quasi-continuous wave pulse energies of up to 15 mJ are demonstrated, with an average power of up to 430 mW.
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Li, Hongbo. "Modeling Compact High Power Fiber Lasers and VECSELs." Diss., The University of Arizona, 2011. http://hdl.handle.net/10150/202712.
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Compact high power fiber lasers and the vertical-external-cavity surface-emitting lasers (VECSELs) are promising candidates for high power laser sources with diffraction-limited beam quality and are currently the subject of intensive research and development. Here three large mode area fiber lasers, namely, the photonic crystal fiber (PCF) laser, the multicore fiber (MCF) laser, and the multimode interference (MMI) fiber laser, as well as the VECSEL are modeled and designed.For the PCF laser, the effective refractive index and the effective core radius of the PCF are investigated using vectorial approaches and reformulated. Then, the classical step-index fiber theory is extended to PCFs, resulting in a highly efficient vectorial effective-index method for the design and analysis of PCFs. The new approach is employed to analyze the modal properties of the PCF lasers with depressed-index cores and to effectively estimate the number of guided modes for PCFs.The MCF laser, consisting of an active MCF and a passive coreless fiber, is modeled using the vectorial mode expansion method developed in this work. The results illustrate that the mode selection in the MCF laser by the coreless fiber section is determined by the MMI effect, not the Talbot effect. Based on the MMI and self-imaging in multimode fibers, the vectorial mode expansion approach is employed to design the first MMI fiber laser demonstrated experimentally.For the design and modeling of VECSELs, the optical, thermal, and structural properties of common material systems are investigated and the most reliable material models are summarized. The nanoscale heat transport theory is applied for the first time, to the best of my knowledge, to design and model VECSELs. In addition, the most accurate strain compensation approach is selected for VECSELs incorporating strained quantum wells to maintain structural stability. The design principles for the VECSEL subcavity are elaborated and applied to design a 1040nm VECSEL subcavity that has been demonstrated for high power operation of VECSELs where near diffraction-limited output over 20 W is obtained. Physical modeling of the VECSEL is also discussed and used to compare VECSEL subcavity designs on the laser level.
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Bai, Jinxu. "High Power High Energy Ytterbium-doped Fiber Amplifier System." Research Showcase @ CMU, 2016. http://repository.cmu.edu/dissertations/728.
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Fiber amplifiers with high power and high pulse energy are strongly in demand for both scientific research and industrial applications. Ytterbium-doped fiber has been an outstanding choice for its broad-gain bandwidth and excellent power conversion efficiencies. In this dissertation, we introduced a compact high power high pulsed energy laser system with chirally coupled core (3C) Yb-doped fibers as the gain media. Traditional standard fibers and photonic crystal fibers are not suitable for compact high power high pulse energy laser systems because of poor higher order modes (HOMs) management and complicated air-hole structure. Newly invented 3C silica fibers solve these problems. A helical side-core around the Yb-doped central core extracts the HOMs from the central core. By adjusting this chirally structure, the core of the 3C fiber can be enlarged and the transverse mode of the fiber can be single mode at certain wavelengths. To simulate the amplification process with high power high pulse energy better, a new modeling method based on a combination of the rate equations and the nonlinear Schrödinger equations is invented. The gain was calculated from rate equations and the pulse evolution was analyzed using nonlinear Schrödinger equation. The simulation provided a good guidance for building compact high power high pulse energy laser systems. To achieve high power and high pulse energy, the system is designed as a two-stage structure. The laser
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Sims, Robert. "Development of Thulium Fiber Lasers for High Average Power and High Peak Power Operation." Doctoral diss., University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5706.
Full textAbstract:
High power thulium fiber lasers are useful for a number of applications in both continuous-wave and pulsed operating regimes. The use of thulium as a dopant has recently gained interest due to its large bandwidth, possibility of high efficiency, possibility of high power and long wavelength ~1.8 – 2.1 [micro]m. The longer emission wavelength of Tm-doped fiber lasers compared to Yb- and/or Er-doped fiber lasers creates the possibility for higher peak power operation due to the larger nonlinear thresholds and reduced nonlinear phase accumulation. One primary interest in Tm-doped fiber lasers has been to scale to high average powers; however, the thermal and mechanical constraints of the fiber limit the average power out of a single-fiber aperture. One method to overcome the constraints of a single laser aperture is to spectrally combine the output from multiple lasers operating with different wavelengths into a single beam. In this thesis, results will be presented on the development of three polarized 100 W level laser systems that were wavelength stabilized for SBC. In addition to the development of the laser channels, the beams were combined using bandpass filters to achieve a single near diffraction-limited output. Concurrently, with the development of high average power systems there is an increasing interest in femotosecond pulse generation and amplification using Tm- doped fiber lasers. High peak power sources operating near 2 [micro]m have the potential to be efficient pump sources to generate mid-infrared light through supercontinuum generation or optical parametric oscillators. This thesis focuses on the development of a laser system utilizing chirped pulse amplification (CPA) to achieve record level energies and peak powers for ultrashort pulses in Tm-doped fiber. A mode-locked oscillator was built to generate femtosecond pulses operating with pJ energy. Pulses generated in the mode-locked oscillator were limited to low energies and contained spectral modulation due to the mode-locking mechanism, therefore, a Raman-soliton self-frequency shift (Raman-SSFS) amplifier was built to amplify pulses, decrease the pulse duration, and spectrally clean pulses. These pulses were amplified using chirped pulse amplification (CPA) in which, limiting factors for amplification were examined and a high peak power system was built. The primary limiting factors of CPA in fibers include the nonlinear phase accumulation, primarily through self-phase modulation (SPM), and gain narrowing. Gain narrowing was examined by temporally stretching pulses in a highly nonlinear fiber that both stretched the pulse duration and broadened the spectrum. A high peak power CPA system amplified pulses to 1 [micro]J energy with 300 fs compressed pulses, corresponding to a peak power >3 MW. High peak power pulses were coupled into highly nonlinear fibers to generate supercontinuum.Ph.D.
Doctorate
Optics and Photonics
Optics and Photonics
Optics
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Barber, J. R. "Variable-compression-ratio pistons for high power output diesel engines." Thesis, Brunel University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379249.
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Smith, Scott A. "High power infrared vertical external cavity surface emitting lasers." Thesis, University of Strathclyde, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.501809.
Full textAbstract:
The Vertical External Cavity Surface Emitting Laser (VECSEL) is now firmly established as an important category of semiconductor laser with many advantageous properties including high output power, excellent beam quality and wavelength flexibility. Thermal management of the optical pumped arrangement is of critical importance to ensure optimum operation, and crystalline heatspreader platelets have been successfully used in this role.
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Lee, Shinwook. "HIGH POWER MODE-LOCKED SEMICONDUCTOR LASERS AND THEIR APPLICATIONS." Doctoral diss., University of Central Florida, 2008. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3195.
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In this dissertation, a novel semiconductor mode-locked oscillator which is an extension of eXtreme Chirped Pulse Amplification (XCPA) is investigated. An eXtreme Chirped Pulse Oscillator (XCPO) implemented with a Theta cavity also based on a semiconductor gain is presented for generating more than 30ns frequency-swept pulses with more than 100pJ of pulse energy and 3.6ps compressed pulses directly from the oscillator. The XCPO shows the two distinct characteristics which are the scalability of the output energy and the mode-locked spectrum with respect to repetition rate. The laser cavity design allows for low repetition rate operation <100MHz. The cavity significantly reduces nonlinear carrier dynamics, integrated self phase modulation (SPM), and fast gain recovery in a Semiconductor optical Amplifier (SOA). Secondly, a functional device, called a Grating Coupled Surface Emitting Laser (GCSEL) is investigated. For the first time, passive and hybrid mode-locking of a GCSEL is achieved by using saturable absorption in the passive section of GCSEL. To verify the present limitation of the GCSEL for passive and hybrid mode-locking, a dispersion matched cavity is explored. In addition, a Grating Coupled surface emitting Semiconductor Optical Amplifier (GCSOA) is also investigated to achieve high energy pulse. An energy extraction experiment for GCSOA using stretched pulses generated from the colliding pulse semiconductor mode-locked laser via a chirped fiber bragg grating, which exploits the XCPA advantages is also demonstrated. Finally, passive optical cavity amplification using an enhancement cavity is presented. In order to achieve the interferometric stability, the Hänsch-Couillaud Method is employed to stabilize the passive optical cavity. The astigmatism-free optical cavity employing an acousto-optic modulator (AOM) is designed and demonstrated. In the passive optical cavity, a 7.2 of amplification factor is achieved with a 50 KHz dumping rate.Ph.D.
Optics and Photonics
Optics and Photonics
Optics PhD
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Holdsworth, Adrian Richard. "Brightness conserving optical systems for high power diode lasers." Thesis, Heriot-Watt University, 1999. http://hdl.handle.net/10399/583.
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Hayward, Robert Alan. "High-power diode-pumped solid-state 2 micron lasers." Thesis, University of Southampton, 2003. https://eprints.soton.ac.uk/41525/.
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Brightness scaling of diode-bar end-pumped solid-state lasers producing efficient output radiation in the 2 μm wavelength region is investigated. Problems and strategies for power scaling diode-bar end-pumped lasers in the 2μm region are also discussed. Thermal lens measure ments on Tm3+:YAG and Tm3+:(Lu,Y)AG were made. Thermal lens dependency on resonator loss is observed and attributed to heating from upconversion. High-power room temperature diode-bar end-pumped Tm3+:(Lu,Y)AG were developed. Efficient high power operation of the Tm3+:YAG laser producing 14.2W of output power at 2.013μm for 53.4W of incident pump power is demonstrated with M(2) values of 1.3 in orthogonal planes. The laser was then linearly polarised and compared with a similar laser using a scheme to compensate for the loss caused by thermally induced de-polarisation. Before the de-polarisation loss prevented lasing operation an output power of 8.4W was observed. Using the compensation scheme, the laser produced 11.5W of output power and was limited by pump power. The uncompensated de-polarisation loss was >5% reducing to <0.4% for the compensated laser. A high power Tm3+:(Lu,Y)AG laser producing 18W of output power at 2.022μm was demonstrated and compared with a Tm3+:YAG laser. High-power intracavity pumped Ho3+:YAG lasers were developed. A collinearly intracavity pumped Ho3+:YAG laser producing 8.4W of output power is demonstrated though application of the brightness scaling strategy was difficult to implement. A non-collinearly intracavity pumped laser showing 1.6W of output power is reported but showed alignment instability and was hard to replicate. Intracavity pumping schemes are discussed. A Tm3+:silica fibre laser produced 14.2W of output at 1.98μm for 38.3W of launched pump power with a slope efficiency of ~36%. This was the highest reported power from a Tm3+:silica fibre laser to the author's knowledge. A tunable Tm3+ fibre laser showed > 1.8W output power across a tuned wavelength range of 1870-2030 nm.
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Saadat, S. "Investigation of the generation of high-density matter using high power lasers." Thesis, Queen's University Belfast, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.373544.
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Strauss, Hencharl Johan. "Thermo-optical effects in high-power end-pumped vanadate lasers." Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/4007.
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Thesis (PhD (Physics))--University of Stellenbosch, 2010.ENGLISH ABSTRACT: The output power of end-pumped lasers is mainly limited by thermal effects in the bulk crystal gain material. The thermal effects either fracture the crystal or cause degradation in the laser beam quality and output power. This is especially pronounced in Nd:YVO4 and Nd:GdVO4 which exhibit strong thermal lensing. These two Nd3+ vanadate materials are of great value because of their high emission cross sections which makes them excellent gain materials for mode-locked, high repetition rate Q-switched and intra-cavity frequency doubled lasers. The two Nd3+ vanadates have very similar spectral properties but many publications claim that the more expensive Nd:GdVO4 is thermo-optically superior to Nd:YVO4. However, a debate ensued after theoretical calculations as well as measurements of the thermal conductivity and thermo-optical coefficients indicated that the opposite is true. To our knowledge there has never been a direct comparison of the thermal lensing of these two materials under identical pumping and lasing conditions. In order to contribute to the debate we did such measurements for different crystals of these two materials with equal low doping using three different measurement methods. We subsequently determined that Nd:YVO4 has slightly lower thermal lensing for the stronger gain -polarisation. One of the measurement methods we used is a novel more reproducible one that we developed for this purpose. It is more reproducible because it selectively measures only the focal length of the central, relatively unaberrated part of the thermal lens. Another measurement, utilising a probe beam through the laser crystal, found that there was almost no increase in the temperature when lasing is interrupted. This indicated that there is almost no upconversion present in the crystals which is probably due to their optimally chosen low doping. A further consequence of the vanadate debate is that there is still confusion about the value of the important thermo-optical coefficient for the higher gain -polarisation (dne/dT ) of Nd:YVO4. This parameter is of great importance in thermal calculations since the strength of the thermal lens is largely dependent on it. We therefore numerically modelled the thermal lensing in our crystals using different dne/dT values and found that the value given by Sato & Taira (2007) matches our experimental results the best. Our measurements also indicated that the thermal lens dioptric power increased nonlinearly with pump power. This appeared to contradict theory of thermal lensing since we knew that there was no upconversion in the crystals (which is the standard explanation for the nonlinear increase). We proceeded to use our numerical modelling to identify the main source of the nonlinear increase as the varying spectral output of the diode pump laser. The findings in this thesis therefore extend knowledge of the thermo-optical properties of the vanadates and increase understanding of the strongly aberrated thermal lenses formed inside them. Furthermore, the findings now enable the power-scaling of end-pumped vanadates lasers to higher levels.
AFRIKAANSE OPSOMMING: Die uitset drywing van longitudinale-gepompte vaste-toestand lasers word hoofsaaklik beperk deur termiese effekte in die laser kristal. Die kristal word of gekraak of die laser se bundel kwaliteit en uitset drywing verminder. Dit is veral ’n problem in Nd:YVO4 en Nd:GdVO4 kristalle waarin sterk termiese lense voorkom. Hierdie twee Nd3+ vanadaat kristalle is waardevol vanwee hulle ho¨e emissie deursnitte wat hulle uitstekend maak as versterkings materiale vir modus-gesinkroniseerde, ho¨e repitisie, Q-geskakelde en binne-resonator frekwensie-verdubbelde lasers. Die twee vanadate het baie soortgelyke spektrale eienskappe, maar verskeie publikasies beweer dat die duurder Nd:GdVO4 materiaal termo-opties beter is as Nd:YVO4. Onlangse teoretiese berekeninge asook metings van die termiese en termo-optiese kwaliteite van die twee kristalle toon egter die teenoorgestelde. Sover ons weet is daar nog geen direkte vergelyking van die termiese lens in hierdie twee materiale onder identiese kondisies gedoen nie. Ons het dus so ’n meting aangepak vir kristalle met identiese lae konsentrasie van die Nd3+ ioon deur drie verskillende meet metodes te gebruik. Een van die meet metodes is ’n nuwe, meer reproduseerbare metode wat ons ontwikkel het vir hierdie doel. Dit is meer reproduseerbaar omdat dit slegs die binneste deel van die termiese lens meet wat min sferiese aberrasie het. ’n Ander meeting, wat ’n toets-bundel deur die kristal stuur, het getoon dat daar byna geen verhoging in die die temperatuur van die kristal was toe ossilasie in die resonator onderbreek was nie. Dit is ’n aanduiding dat dat daar byna geen op-omskepping teenwoordig is in die kristalle nie wat te danke is aan hul optimale lae konsentrasie van die Nd3+ ioon. ’n Verdere gevolg van die debat is dat daar nog verwarring in die literatuur bestaan oor die waarde van Nd:YVO4 se termo-optiese dne/dT koeffisi¨ent. Hierdie parameter is van groot belang in berekinge van die termiese lens se fokale lengte vir die ho¨er wins -polarisasie. Deur numeriese modellering te gebruik het ons bevind dat die waarde wat verskaf word deur Sato & Taira (2007) ons eksperimentele data die beste pas. Ons metings het ook aangedui dat die dioptriese krag van die termiese lens nie linie¨er toeneem ten opsigte van die geabsorbeerde pomp krag nie. Dit was o¨enskynlik teenstryding met teorie oor termiese lense. Dit is omdat ons bevestig het dat daar geen op-omskepping in die kristalle teenwoordig was nie, wat die standaard verklaring vir die nie linie¨eriteit is. Ons het dus ons numeriese modellering gebruik om die hoofbron van die nie-lini¨ere toename te identifiseer as die veranderende spektrale uitset van die diode pomp laser. Die bevindings in hierdie tesis bou dus kennis op oor die termo-optiese eienskappe van die vanadate en versterk begrip van die sterk termiese lense binne hulle. Verder stel die bevindings ons nou in staat om die uitset drywing van longitudinale-gepompte vanadaat lasers na ho¨er vlakke te skaal.
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Bogan, Christina [Verfasser]. "Stabilized High Power Lasers and Spatial Mode Conversion / Christina Bogan." München : Verlag Dr. Hut, 2013. http://d-nb.info/1033041505/34.
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Zhang, Zhichao. "Numerical Modelling of High-Power Self-Organizing External Cavity Lasers." Thesis, University of Nottingham, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.523226.
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Jain, Apurva. "Applications of Volume Holographic Elements in High Power Fiber Lasers." Doctoral diss., University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5318.
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The main objective of this thesis is to explore the use of volume holographic elements recorded in photo-thermo-refractive (PTR) glass for power scaling of narrow linewidth diffraction-limited fiber lasers to harness high average power and high brightness beams. Single fiber lasers enable kW level output powers limited by optical damage, thermal effects and non-linear effects. Output powers can be further scaled using large mode area fibers, however, at the cost of beam quality and instabilities due to the presence of higher order modes. The mechanisms limiting the performance of narrow-linewidth large mode area fiber lasers are investigated and solutions using intra-cavity volume Bragg gratings (VBG) proposed. Self-pulsations-free, completely continuous-wave operation of a VBG-stabilized unidirectional fiber ring laser is demonstrated with quasi single-frequency (< 7.5 MHz) output. A method for transverse mode selection in multimode fiber lasers to reduce higher order mode content and stabilize the output beam profile is developed using angular selectivity of reflecting VBGs. By placing the VBG output coupler in a convergent beam, stabilization of the far-field beam profile of a 20 ?m core large mode area fiber laser is demonstrated. Beam combining techniques are essential to power scale beyond the limitations of single laser sources. Several beam combining techniques relevant to fiber lasers were compared in this study and found to be lacking in one or more of the following aspects: the coherence of the individual sources is compromised, the far-field beam quality is highly degraded with significant power in side lobes, spectrally broad and unstable, and uncertainty over scaling to larger arrays and higher power. Keeping in mind the key requirements of coherence, good far-field beam quality, narrow and stable spectra, and scalability in both array size and power, a new passive coherent beam combining technique using multiplexed volume Bragg gratings (M-VBGs) is proposed. In order to understand the mechanism of radiation exchange between multiple beams via these complex holographic optical elements, the spectral and beam splitting properties a 2nd order reflecting M-VBG recorded in PTR glass is experimentally investigated using a tunable single frequency seed laser. Two single-mode Yb-doped fiber lasers are then coherently combined using reflecting M-VBGs in both linear and unidirectional-ring resonators with >90% combining efficiency and diffraction-limited beam quality. It is demonstrated that the combining bandwidth can be controlled in the range of 100s of pm to a few pm by angular detuning of the M-VBG. Very narrow-linewidth (< 210 MHz) operation in a linear cavity and possibility of single-frequency operation in a unidirectional ring cavity of the coherently combined system is demonstrated using this technique. It is theoretically derived and experimentally demonstrated that high combining efficiency can be achieved even by multiplexing low-efficiency VBGs, with the required diffraction efficiency of individual VBGs decreasing as array size increases. Scaling of passive coherent beam combining to four fiber lasers is demonstrated using a 4th order transmitting M-VBG. Power scaling of this technique to 10 W level combined powers with 88% combining efficiency is demonstrated by passively combining two large mode area fiber lasers using a 2nd order reflecting M-VBG in a unidirectional ring resonator. High energy compact single-frequency sources are highly desired for several applications – one of which is as a seed for high power fiber amplifiers. Towards achieving the goal of a monolithic solid-state laser, a new gain medium having both photosensitive and luminescence properties is investigated – rare-earth doped PTR glass. First lasing is demonstrated in this new gain element in a VBG-stabilized external cavity.Ph.D.
Doctorate
Optics and Photonics
Optics and Photonics
Optics
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Tandoi, Giuseppe. "Monolithic high power mode locked GaAs/AlGaAs quantum well lasers." Thesis, University of Glasgow, 2011. http://theses.gla.ac.uk/2721/.
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In this thesis, approaches for increasing the output power in monolithically integrated semiconductor mode locked (ML) lasers were investigated. The wavelength range considered is the range of operation of low temperature grown GaAs photomixers, devices commonly used for THz generation. In particular, two GaAs/AlGaAs quantum well laser epistructures (operating at 830 nm and 795 nm) were considered, both with reduced optical confinement and elongated vertical optical mode size. In this work, such laser epistructures, commonly used by high power semiconductor laser manufacturers, were successfully employed, for the first time, for producing passively ML devices. Improved average powers (up to 48 mW) under ML operation were demonstrated, around ten times higher than values previously reported in monolithic GaAs/AlGaAs ML lasers. In continuous wave operation, the output power was limited by the catastrophic damage of the laser facets at around 50 mW. For this reason, facet passivation techniques were investigated, allowing for powers up to 124 mW to be achieved. In ML regime, the output power was instead limited by the catastrophic damage of the reverse biased section of the laser. This failure mechanism was investigated and explained considering thermal effects on the reverse biased section. Such effects limited the output power to around 27 mW in 830 nm devices, which was then improved by 70% in 795 nm devices with a 70% larger optical mode area. The larger mode size, combined to a small duty-cycle laser geometry, enabled a record peak power of 9.8 W to be achieved at 6.83 GHz. This particular repetition rate was specifically designed for coherent population trapping experiments in 87Rb vapors. Sub-picosecond transform limited pulses were achieved in both the laser materials considered, with a minimum duration of 0.43 ps at 126 GHz. With the values of peak power achieved, the developed devices may also be directly used for two-photon microscopy applications.
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Deile, Jochen. "Power scaling of high brightness multi-kilowatt coaxial CO2 lasers." Thesis, Heriot-Watt University, 2013. http://hdl.handle.net/10399/3297.
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The objectives of the work described in this thesis have been first, to develop a high brightness diffusion-cooled CO2 laser based on the annular discharge geometry and secondly, to scale up the output power to provide multi-kilowatt operation. A stable-unstable-hybrid resonator (helix-axicon resonator) serves as the starting point for the development. In order to address the brightness, polarization and temporal stability issues of this resonator several new features and concepts are introduced. High brightness is achieved by ensuring fundamental mode operation without truncating the mode in a free-space configuration. This is achieved by the introduction of shaped electrodes. The temporal stability problems are addressed by introducing a new resonator configuration in the unstable direction, by moving the unstable direction away from the boundary of stability in the ‘classical’ resonator stability diagram. The polarization issues are addressed by introducing a new beam shaping telescope that includes polarization correction based on the use of a dielectric coating, which transforms the azimuthal polarization emitted by the resonator into linear polarization. The overall outcome is the experimental demonstration of a laser with an output power of 2 kW, and a beam with M2 values < 1.1, exhibiting constant linear polarization and temporally stable beam characteristics. In the second part of the thesis, the power scaling laws for diffusion-cooled lasers with annular geometry and free-space propagation are derived and the scaling limits are investigated. A scaled-up version is realized by extending the discharge length and the introduction of distributed inductances to ensure a homogenous discharge distribution. A characterization of the laser confirms the conservation of all beam characteristics at higher output power levels. A maximum laser power level of about 4 kW was reached.
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Cooper, Laurence James. "Fabrication of novel geometry fibre lasers for high power applications." Thesis, University of Southampton, 2005. https://eprints.soton.ac.uk/38958/.
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This thesis details my work on the development of fabrication techniques for high power doped fibre lasers, using novel fibre geometries, and their demonstration. The main methods for increasing output power were using helical cores, multiple cores and large cores. A method for fabricating helical core fibres was proposed and implemented. Core and cladding pumped devices were successfully constructed, and were then tested in collaboration. A cladding pumped helical core fibre laser improved the beam from a 30μm core from an M2 of 3.3 to < 1.4, with a maximum output power of 64W and slope efficiency of 84%. A ribbon fibre with multiple laser emitting cores was fabricated. The difficulties in the fabri- cation of such a fibre required extensive research, and arise from the large aspect ratio of the preform and fibre, and the low size reduction during fibre drawing. Through many steps a ten core ribbon fibre was fabricated, which was used, in collaboration, to achieve an output laser power of 250W, with a slope efficiency of 65%. Using a spectral beam combination technique, 5 cores were locked together. The output from a number of cores within a circular fibre with no combination is a method for attaining stable high powers with moderate beam quality. A three core fibre was fabricated, and showed an M2 of 5 and slope efficiency of 75%. This fibre was then tapered down from 150μm in order to improve the beam quality further, and for 125μm and 100μm tapers, the M2 values measured were improved to 4.3 and 3.5, respectively. An Yb-doped rod was fabricated, with a large core of 140μm diameter, and machined flats to break the cladding symmetry. The power attained was only 13.4W with a slope efficiency of 20%, due to surface imperfections. A fibre created with altered fabrication techniques showed no surface defects and showed over 90% transmission for 800nm light. Experiments performed by a colleague showed a slope efficiency of 69% and an M2 of 11, indicating that the fabrication method could create an effective cladding pumped rod laser.
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Chen, Kang Kang. "High power pulsed ytterbium doped fibre lasers and their applications." Thesis, University of Southampton, 2011. https://eprints.soton.ac.uk/207735/.
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The aim of my project is to develop pulsed Ytterbium (Yb) doped fibre master oscillator power amplifier (MOPA) systems seeded by semiconductor lasers. I was principally focused on two specific projects aligned to sponsored programs of research within the ORC pulsed fibre laser group: the first project, TSB funded project LAMPS, aimed to develop an important class of next generation laser system capable of average output powers of more than 100 W when operating in both the nanosecond and picosecond regimes. The goal was to develop a fully fiberized, polarisation maintaining, single transverse mode system. The full project included the development of the necessary diode & micro-optic systems, fibre beam delivery technology and with application focused evaluations in collaboration with our industrial partners. The main project partners were BAE Systems, Selex, Ceram, Intense Photonics, ORC, Herriot Watt University, Power Photonics, OptoCap and Rofin Sinar. I contributed to the development of the single transverse mode Ytterbium (Yb)-doped fibre system and achieved the full target specifications of 100 W of output power with single mode and single polarisation operation in both the nanosecond and picosecond regimes. In addition, second harmonic generation pumped by the fundamental beam at 1.06 μm was also achieved. In order to transfer from picosecond pulses to nanosecond pulses it is only necessary to switch the seed laser, the power amplifier system remaining unchanged making for a highly flexible system. Both fundamental and second harmonic beam were successfully used to do material processing and various high power frequency conversion experiments (visible, broadband supercontinuum and mid-IR). The second project, called HEGAC (also funded by the TSB), was a collaboration with the University of Cambridge and SPI Lasers Ltd. The aim of the HEGAC project was to develop a high power nanosecond fibre laser with an active pulse shaping capability suitable for cutting metals. This project targeted mJ pulses with more than 100 W average power at the final output – with a 200 W stretch objective. We first achieved more than 310 W using a free space seeding and pumping configuration in our laboratories proving power scaling of our proposed approach. I subsequently rebuilt and improved this system and developed a fully- fiberized version (including all pump launches). The laser was capable of generating >100 W of output power and pulse energies up to 2.5 mJ. This project also involved spatial mode as well as temporal pulse shaping. Using a pair of axicon lenses the normal Gaussian beam profile was converted to a ring shaped profile as required and the system tested up to average powers of 100 W. In addition to the normal temporal pulse shapes required using our pulse shaping system (square, triangle and step), I also achieved high average power pulses with smooth shaped pulses (Parabolic and Gaussian) using an adaptive pulse shaping technique. The laser was transported and successfully used in materials processing experiments at Cambridge, proving the robustness of the design and implementation. I also did some novel experiments on high efficiency Raman conversion exploiting the square shaped pulses possible using this laser
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Wang, Tsuei-Lian. "High-Power Optically Pumped Semiconductor Lasers for Near Infrared Wavelengths." Diss., The University of Arizona, 2012. http://hdl.handle.net/10150/242398.
Full textAbstract:
Optically pumped semiconductor lasers (OPSLs) combine features including an engineerable emission wavelength, good beam quality, and scalable output power and are desirable for a wide variety of applications. Power scaling of OPSLs requires a combination of accurate epitaxial quantum design, accurate wafer growth and good thermal management. Here a fabrication process for OPSL devices was developed to ensure efficient OPSL device cooling and minimum surface scattering. A systematic thermal analysis was performed to optimize thermal management. Strategies for optimizing power extraction were developed; including increasing the gain/micro-cavity detuning that increases the threshold but also increases the slope efficiency and the roll-over temperature, recycling the excess pump via reflection from a metalized reflector at the back of a transparent DBR, anti-reflection coating at the pump wavelength while preserving the signal micro-cavity resonance. With optimized thermal management and the strategy of using large gain/micro-cavity detuning structure, a CW output power of 103 W from a single OPSL device was achieved. 42% optical-to-optical efficiency from the net pump power was obtained from the OPSL device with the double pass pump design and 39% optical-to-optical efficiency with respect to the total pump power was obtained with the new pump anti-reflection coating. For the fundamental mode operation, over 27 W of CW output power was achieved. To our knowledge, this is the highest 1 µm TEM₀₀ mode power reported to date for an OPSL. Finally, strategies for generating high peak power are also discussed. A maximum peak power of over 270 W was achieved using 750 ns pump pulses.
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Hempel, Martin. "Defect mechanisms in diode lasers at high optical output power." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2013. http://dx.doi.org/10.18452/16834.
Full textAbstract:
In dieser Arbeit wird der Catastrophic Optical Damage (COD) zeitaufgelöst untersucht um die beteiligten physikalischen Mechanismen zu identifizieren. Der COD Prozess konnte zeitlich in drei Phasen unterteilt werden, die Alterung, der thermische Runaway (selbst verstärkende Rückkopplung) und das Sekundärschadenswachstum. Die erste Phase konnte durch eine neu eingeführte Art der beschleunigten Bauteilalterung auf den Nanosekunden-Bereich reduziert werden. Die Rolle des Laser-Lichtfelds als Energiequelle des COD-Prozesses wurde experimentell bestätigt. Die genutzten thermographischen Techniken erlaubten eine in-situ Verfolgung des Defektwachstums. Diese direkte Messung der Ausbreitung, die Modellierung des Wärmeflusses und eine kristallographische Materialanalyse zeigen, dass das Material, welches von der Defekt-Front passiert wurde, innerhalb von Nanosekunden zu substanziell tieferen Temperaturen zurückkehrt. Verschiedene experimentelle Ansätze bestätigen das Vorhandensein einer Temperatur im Bereich von 1200°C-1500°C an der Schadensfront während des gesamten Degradationsprozesses. Dabei hat sich gezeigt, dass selbst wenn keine Laseremission mehr vorliegt, die verstärkte spontane Emission ausreicht, um den fortschreitenden Degradationsprozessmit Energie zu versorgen. Für den Start des thermischen Runaway muss ein bestimmter Temperaturunterschied zwischen der späteren COD-Position und dem übrigen aktiven Lasermaterial erreicht werden. Die vorliegende Arbeit zeigt verschiedene Mechanismen auf, die zu einer solchen Situation führen können. Dabei spielen auch physikalische Eigenschaften der verwendeten Materialsysteme und Schichtstrukturen eine entscheidende Rolle. Ein neu im Rahmen dieser Arbeit entwickeltes Modell zur Beschreibung der räumlichen Schadensausbreitung nutzt diesen Umstand, um die Defektkinetik ex-post zu rekonstruieren. Dies ermöglicht das Aufzeigen von Schwachstellen im Bauelement.The scope of this thesis is the time-resolved investigation of the catastrophic optical damage (COD) and the identification of the underlying physical mechanisms. The COD has been separated in three temporal phases: the aging, the thermal runaway (self-amplifying feedback mechanism), and the secondary defect growth. It was possible to reduce the first phase to a couple of nano-seconds by applying a new accelerated life test scheme. It was experimentally verified that the laser light is the primary energy source of COD. The applied thermographic technologies allowed an in-situ tracing of the defect growth. A fast thermo cycle during the passage of the defect front was confirmed by this direct measurement, a modeling of the heat flow, and a crystallographic material analysis. Different experimental setups indicate the presence of a temperature in the range of 1200°C-1500°C at the defect front, during the entire COD-degradation. Even if no lasing action is present anymore, the amplified spontaneous emission is sufficient to provide enough energy for further defect growth. In order to initiate the thermal runaway, a specific temperature difference is necessary between the COD-starting location and the remaining active laser material. This thesis provides an analysis of the mechanisms leading to such a situation. This kind of analysis was used to develop a new model of the geometrical defect growth. The ability to re-construct the defect dynamics based on ex-post analysis of the defect pattern allows for the identification of bottlenecks in the investigated device design leading to COD.
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Bouras, Vasileios. "High energy lasers for ship-defense and maritime propagation." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2002. http://library.nps.navy.mil/uhtbin/hyperion-image/02Dec%5FBouras.pdf.
Full textAbstract:
Thesis (M.S. in Applied Physics and M.S. in Electrical Engineering)--Naval Postgraduate School, December 2002.Thesis advisor(s): William B. Colson, Phillip E. Pace. Includes bibliographical references (p. 81-83). Also available online.
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Seifert, Frank [Verfasser]. "Power stabilization of high power lasers for second generation gravitational wave detectors / Frank Seifert." Hannover : Technische Informationsbibliothek und Universitätsbibliothek Hannover, 2010. http://d-nb.info/1008410470/34.
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Denvir, Donal Joseph. "Interaction of high power laser radiation with liquids." Thesis, Queen's University Belfast, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235828.
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Ure, K. A. N. "The generation of short, tunable high power optical pulses." Thesis, University of Southampton, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383874.
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Akbar, Jehan. "High power mode locked lasers monolithically integrated with semiconductor optical amplifiers." Thesis, University of Glasgow, 2012. http://theses.gla.ac.uk/3461/.
Full textAbstract:
This thesis is concerned with the design, fabrication and characterisation of high power semiconductor mode locked lasers (SMLLs), operating at ~ 1.5 μm. The devices are based on a novel epitaxial structure with three quantum wells (QW) in the active region. The novel epitaxial structure was based on a commercially available five-QW AlGaInAs/InP epitaxial structure, with the number of QWs reduced to increase the gain saturation energy and a farfield reduction layer (FRL), and a spacer layer were inserted in the n-cladding layer. SMLLs based on both the five-QW and three-QW material, were fabricated and comparatively investigated. The devices based on the three-QW material exhibited an increased average output power, as well as reduced RF linewidth and pulse widths. The average output power obtained in the mode locked operation from a 40 GHz MLL, based on this three-QW material was limited to 28 mW. Single mode ridge waveguide semiconductor optical amplifiers (SOAs) were monolithically integrated with the SMLLs, which increased the average output power to 130 mW. The devices performance was investigated at both the saturable absorber (SA) and SOA facets. Transform limited pulses with a minimum duration of 3.3 ps and a peak power of > 1 W were obtained at the SOA facet. To take advantage of the higher saturation output power of the tapered SOAs, SMLLs were monolithically integrated with 2° and 6° tapered SOAs, respectively. The devices integrated with 2° tapered SOAs were mounted on Aluminium Nitride (AlN) sub-mounts using Gold-Tin (AuSn) soldering for better heat sinking. These devices resulted in an average output power of 200 mW, with corresponding peak power > 1.2 W. The SMLLs integrated with 6° tapered SOAs, mounted on conventional brass sub-mounts resulted in a lower output power (105 mW), compared to the devices integrated with ridge waveguide and 2° tapered SOAs, respectively.
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Lee, Jason Robert. "High power, diode-pumped, planar waveguide lasers with excellent beam quality." Thesis, Heriot-Watt University, 2002. http://hdl.handle.net/10399/443.
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Kao, Tsung-Yu. "From high power terahertz quantum cascade lasers to terahertz light amplifiers." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/87923.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 201-208).
The terahertz (THz) frequency range (300 GHz to 10 THz, wavelength 30-1000 [mu]m), despite having many potential applications, is technologically relatively underdeveloped mainly because of the lack of suitable coherent radiation sources when compared with nearby electromagnetic radiation spectrum. The invention of the THz quantum cascade laser, a electronically-pumped semiconductor heterostructure which emits photons from electronic intersubband transitions, provides the first solidstate fundamental oscillator at the frequency range from 1.2 to 5.1 THz. Due to the subwavelength confinement nature of the metal-metal waveguide used in most of the THz QC lasers, far-field beam patterns from lasers with simple Fabry-Perot waveguides are divergent and far from ideal Gaussian beams. The first part of this thesis describes the development of single-mode THz QC lasers on metal-metal waveguides. Starting with the corrugated third-order DFB laser-a clever laser structure which utilizes end-fire array effect to achieve low divergence beam patterns-several applications using densely-packed third-order DFB laser arrays, such as frequency agile sources for THz swept-source optical tomography and local oscillators for THz heterodyne receivers with precise frequency control, have been investigated. With the improved design rules and fabrication techniques, 830 GHz single-mode frequency coverage on a monolithic multicolor DFB laser array has been achieved. The origin of the deterioration in far-field beam patterns and power outputs in long third-order DFB lasers is then identified. This finding leads to a modified third-order DFB laser structure which can achieve perfect phase-matching (PM) condition, resulting in scalable power output and even lower beam divergence when compared with that of a conventional third-order DFB laser. Radiations from up to 151 laser sectors are phase-locked to form a single-lobe beam pattern with divergence ~ 6 x 11° and ~13 mW pulsed power at the end-fire direction. This approach substantially increases the usable length of a third-order DFB laser while keeping a high slope efficiency (140 mW/A). Later development applies the concept of microstrip antenna-a structure commonly used in microwave engineering-to THz photonics devices. By coupling the microstrip antenna to each grating aperture of a perfectly phase-matched DFB laser, the radiation impedance of the laser can now be tuned to enhance the overall emission efficiency. This novel genre of DFB laser achieves > 8 mW pulsed power (10% duty-cycle) at 12 K with beam divergence as low as 12.5 x 12.5' and maximum lasing temperature Tmax = 109 K (pulsed) and 77 K (c.w.) with the highest slope efficiency (~450 mW/A) and wall-plug efficiency (0.57%) of all THz DFB laser sources. The second part of the thesis then focuses on the development of the first light amplifier in THz frequency under Fabry-Perot amplifier (FPA) scheme. Although amplification at terahertz frequency in quantum cascade structures has been demonstrated under the transient state or in a integrated platform, none of them is suitable for amplifying continuous-wave free-space THz radiations. The proposed amplifier is consisted of an array of short-cavity surface-emitting second-order distributed feedback lasers arranged in a two-dimensional grid which are operated marginally beneath their lasing thresholds. A overall system power gain of ~5.6x = 7.5 dB at ~3 THz is obtained with ~1 GHz bandwidth. The free-space THz light amplifier can be used as the pre-amplifier for a THz heterodyne receiver system to reduce the receiver system noise, or be placed on the focal plane of a THz imaging system to enhance the signal-to-noise ratio of the image and reduce the acquisition time. A new locking mechanism for two-dimensional phase-locked laser arrays based on antenna mutual-coupling is also proposed and then successfully demonstrated in the THz frequency using short-cavity DFB THz lasers. Up to 37 lasers are phase-locked to deliver 6.5 mW single-mode pulsed power (4% duty-cycle) at 3 THz with symmetric beam pattern (< 10 x 10°). This new coupling scheme can be extended to other electromagnetic systems with sub-wavelength confined elements such as plasmonic lasers and nanolasers. This thesis also reports the development of fabrication techniques required to bring the aforementioned novel THz cavity designs from concepts to reality which include a high aspect ratio (> 1:10) anisotropic reactive-ion etch on GaAs which is compatible with the metal-metal waveguide platform and the procedure to create airbridge structures by selectively removing the dielectric materials beneath the metal contacts.
by TsungYu Kao.
Ph. D.
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Daniel, Jae. "Wavelength selection and transverse mode control in high power fibre lasers." Thesis, University of Southampton, 2013. https://eprints.soton.ac.uk/371750/.
Full textAbstract:
In this thesis we explore the wide parameter space of thulium doped silica fibre lasers,looking at various techniques for the control of operating wavelength and bandwidth as well as transverse beam profile. We demonstrate the extremely broad tunability of thulium fibre sources. Through various device architectures we show wavelength coverage over a 450nm wavelength range from 1660nm to 2115nm. With a simple external cavity containing an electronically controllable acousto-optic tunable filter we construct a wavelength agile tunable fibre source. This source demonstrates rapid wavelength selection and coverage within the thulium gain band including multiple simultaneous wavelength selection. Under fixed wavelength operation we show the generation of high power and efficiency 1726nm light in a monolithic thulium fibre source with output powers of up to 12.6W and internal laser slope efficiencies of 69%. Exploiting the fast cavity dynamics of pulsed fibre sources we demonstrate the generation of a bandwidth and wavelength flexible ASE source. Under pulsed operation we generate peak powers of greater than 2kW with tunable bandwidth from 24nm to 0.28nm corresponding to a change in coherence length from ~5mm down to ~60μm. Applying this source to nonlinear frequency conversion, we show the ASE seeded supercontinuum generation at output powers of up to 1.5W, covering a wavelength range of more than one octave from 1000nm to greater than 2400nm. Looking further ahead with this ASE source, we investigate the effects of propagation and amplification within a multimode waveguide, highlighting the potentially detrimental effects of modal interference and through spectral bandwidth tailoring, successfully supresses these effects. Showing stable high peak power amplification within a multimode thulium fibre amplifier. Finally, we introduce a novel mode selection technique utilising multimode fibre Bragg gratings. Allowing the selection of individual modes within a multimode fibre oscillator. We experimentally demonstrate this technique within a multimode thulium fibre source showing the electronically controllable selection and arbitrary switching between the fundamental and next higher order mode at switching speeds of up to 20kHz and output powers of greater than 5W. Extending this technique, we show the generation of near arbitrary superpositions of the first two guided modes with electronically tunable beam ‘flatness’ and other parameters. The prospects for further core area scaling are also discussed.