Journal articles: 'Laser beams'

1

Singh, Arvinder, and Naveen Gupta. "Electron plasma wave excitation by beating of two q-Gaussian laser beams in collisionless plasma." Laser and Particle Beams 34, no. 2 (February 18, 2016): 230–41. http://dx.doi.org/10.1017/s026303461500097x.

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AbstractThis paper presents a scheme for excitation of an electron-plasma wave (EPW) by beating two q-Gaussian laser beams in an underdense plasma where ponderomotive nonlinearity is operative. Starting from nonlinear Schrödinger-type wave equation in Wentzel–Kramers–Brillouin (WKB) approximation, the coupled differential equations governing the evolution of spot size of laser beams with distance of propagation have been derived. The ponderomotive nonlinearity depends not only on the intensity of first laser beam, but also on that of second laser beam. Therefore, the dynamics of one laser beam affects that of other and hence, cross-focusing of the two laser beams takes place. Due to nonuniform intensity distribution along the wavefronts of the laser beams, the background electron concentration is modified. The amplitude of EPW, which depends on the background electron concentration, is thus nonlinearly coupled with the laser beams. The effects of ponderomotive nonlinearity and cross-focusing of the laser beams on excitation of EPW have been incorporated. Numerical simulations have been carried out to investigate the effect of laser and plasma parameters on cross-focusing of the two laser beams and further its effect on EPW excitation.

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Singh, Arvinder, and Naveen Gupta. "Beat wave excitation of electron plasma wave by coaxial cosh-Gaussian laser beams in collisional plasma." Laser and Particle Beams 33, no. 4 (July 14, 2015): 621–32. http://dx.doi.org/10.1017/s0263034615000646.

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AbstractThis paper presents a scheme for beat wave excitation of an electron plasma wave (EPW) by cross-focusing of two intense cosh-Gaussian (ChG) laser beams in an under dense collisional plasma. The plasma wave is generated on account of beating of two ChG laser beams of frequencies ω1 and ω2. Starting from Maxwell's equations, coupled differential equations governing the evolution of spot size of laser beams with distance of propagation have been derived by using Moment theory approach in Wentzel–Kramers–Brillouin approximation. The collisional nonlinearity depends not only on the intensity of first laser beam, but also on that of second laser beam. Therefore, dynamics of first laser beam affects that of other and hence cross-focusing of the two laser beams takes place. Numerical simulations have been carried out to investigate the effect of laser as well as plasma parameters on cross-focusing of laser beams and further its effect on power of excited EPW. It has been found that decentered parameters of the two laser beams have significant effect on power of EPW.

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Xiong, Liang Cai, Quan Sheng Zhou, and Peng Chen. "Vibration Analysis of Different Micro-Beams with Laser Ablation." Applied Mechanics and Materials 462-463 (November 2013): 428–31. http://dx.doi.org/10.4028/www.scientific.net/amm.462-463.428.

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The dynamic response of different micro-beams after laser excitation experiments have been investigated in this paper. The impact force that induces the vibration of micro-beams is the interaction of focused pulse laser and tested beams. The impact response of micro-beams after being excited is measured by Laser Doppler Vibrometer. Different beams such as cantilever beam, L-shaped beam are employed in our experiments. Comparisons of the vibration velocity and its frequencies of different beams have also been performed. Experimental results show that the mechanical effects of laser shock do really exist and can be utilized.

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Sharma, Prerana. "Cross Focusing of two Coaxial Gaussian Beams with Relativistic and Ponderomotive Nonlinearity." Zeitschrift für Naturforschung A 67, no. 1-2 (February 1, 2012): 10–14. http://dx.doi.org/10.5560/zna.2011-0064.

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This paper presents the cross focusing of two high power lasers by taking off-axial contributions of the laser beams in a collisionless plasma. Due to relativistic and ponderomotive nonlinearities the two laser beams affect the dynamics of each other and cross focusing takes place. The expressions for the laser beam intensities by using the eikonal method are derived. The contributions of the r2 and r4 terms are incorporated. By expanding the eikonal and the other relevant quantities up to the fourth power of r, the solution of the pump laser beam is obtained within the extended paraxial ray approximation. Filamentary structures of the laser beams are observed due to the relativistic and the ponderomotive nonlinearity. The focusing of the laser beams is shown to become fast in the extended paraxial region. Using the laser beam and the plasma parameters, appropriate for beat wave processes, the filaments of the laser beams are studied and the relevance of these results to beat wave processes is pointed out.

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Yang, Q. N., X. W. Zhang, and X. K. Dai. "A simulation and experimental study of dual-wavelength dye laser amplifiers." Journal of Physics: Conference Series 2147, no. 1 (January 1, 2022): 012011. http://dx.doi.org/10.1088/1742-6596/2147/1/012011.

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Abstract AVLIS requires a high average power laser beam of multiple wavelengths. There are two general ways to achieve such a beam. One is generating different wavelength laser beams by individual dye laser MOPA chains, then spatially combining them by a beam combiner. The other is combining different wavelength laser beams into one beam first, then co-amplifying it by a common MOPA chain. The latter one is more efficient. To further develop the method, this paper demonstrates a simulation and experimental study of dual-wavelength dye laser amplifiers. The one of the most critical parameters of a dual-wavelength laser beam is the power ratio of the two constituent beams, which can vary during the co-amplification. The simulation results show that for two laser beams with small wavelength difference, the spatial combination mismatches of two beams are the more dominant factor than the spectral differences in affecting the power ratio during the co-amplification. The result of the experiment is in good agreement with the simulation.

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Kumar, S., P. K. Gupta, R. K. Singh, R. Uma, and R. P. Sharma. "Self-compression of two co-propagating laser pulse having relativistic nonlinearity in plasma." Laser and Particle Beams 35, no. 4 (November 20, 2017): 722–29. http://dx.doi.org/10.1017/s0263034617000787.

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AbstractThe study proposes a semi-analytical model for the pulse compression of two co-propagating intense laser beams having Gaussian intensity profile in the temporal domain. The high power laser beams create the relativistic nonlinearity during propagation in plasma, which leads to the modification of the refractive index profile. The co-propagating laser beams get self- compressed by virtue of group velocity dispersion and induced nonlinearity. The induced nonlinearity in the plasma broadens the frequency spectrum of the pulse via self-phase modulation, turn to shorter the pulse duration and enhancement of laser beam intensity. The nonlinear Schrodinger equations were set up for co-propagating laser beams in plasmas and have been solved in Matlab by considering paraxial approximation. The propagation characteristics of both laser beams inside plasma are divided into three regions through the critical divider curve, which has been plotted between pulse width τ01 and laser beam power P01. Based on the preferred value of critical parameters, these regions are oscillatory compression, oscillatory broadening, and steady broadening. In findings, it is observed that the compression of the laser beam depends on the combined intensity of both beams, plasma density, and initial pulse width.

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Kotlyar, V. V., A. A. Kovalev, and E. G. Abramochkin. "Asymmetric hypergeometric laser beams." Computer Optics 43, no. 5 (October 2019): 735–40. http://dx.doi.org/10.18287/2412-6179-2019-43-5-735-740.

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Here we study asymmetric Kummer beams (aK-beams) with their scalar complex amplitude being proportional to the Kummer function (a degenerate hypergeometric function). These beams are an exact solution of the paraxial propagation equation (Schrödinger-type equation) and obtained from the conventional symmetric hypergeometric beams by a complex shift of the transverse coordinates. On propagation, the aK-beams change their intensity weakly and rotate around the optical axis. These beams are an example of vortex laser beams with a fractional orbital angular momentum (OAM), which depends on four parameters: the vortex topological charge, the shift magnitude, the logarithmic axicon parameter and the degree of the radial factor. Changing these parameters, it is possible to control the beam OAM, either continuously increasing or decreasing it.

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8

Lisiecki, A. "Comparison of Titanium Metal Matrix Composite Surface Layers Produced During Laser Gas Nitriding of Ti6Al4V Alloy by Different Types of Lasers." Archives of Metallurgy and Materials 61, no. 4 (December 1, 2016): 1777–84. http://dx.doi.org/10.1515/amm-2016-0287.

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Abstract The article presents the results of a comparative study of the nitriding process of titanium alloy substrate using two lasers with different characteristics of laser beams. One of the applied lasers was a high power diode laser emitting at a dominant wavelength of 808 nm, with a rectangular laser beam spot, and multimode energy distribution across the spot. The second laser was a solid state Yb:YAG disk laser emitting at a wavelength of 1.03 μm, with a circular beam spot, characterized by near Gaussian energy distribution across the spot. In a case of both lasers single stringer beads with a similar width and at similar energy input were produced. As a result of melting of the substrate with a laser beam in a pure gaseous nitrogen atmosphere composite surface layers with in situ precipitated titanium nitrides embedded in the metallic matrix of titanium alloy were produced, in both cases. However, the surface topography and structure is different for the surface layers produce by different lasers at the same processing parameters and width of laser beams.

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Safdar, Shakeel, Lin Li, M. A. Sheikh, and Zhu Liu. "An Analysis of the Effect of Laser Beam Geometry on Laser Transformation Hardening." Journal of Manufacturing Science and Engineering 128, no. 3 (December 6, 2005): 659–67. http://dx.doi.org/10.1115/1.2193547.

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The effect of transformation hardening depends upon both heating and cooling rates. It is desirable to have a slow heating rate and a rapid cooling rate to achieve full transformation. To date laser transformation hardening has been carried out using circular or rectangular beams which result in rapid heating and cooling. Although the use of different beam intensity distributions within the circular or rectangular laser beams has been studied to improve the process, no other beam geometries have been investigated so far for transformation hardening. This paper presents an investigation into the effects of different laser beam geometries in transformation hardening. Finite element modeling technique has been used to simulate the steady state and transient effects of moving beams in transformation hardening of EN 43A steel. The results are compared with experimental data. The work shows that neither of the two commonly used beams, circular and rectangular, are optimum beam shapes for transformation hardening. The homogenization temperature exceeds the melting point for these beam shapes for the usual laser scanning speeds and power density. Triangular beam geometry has been shown to produce the best thermal history to achieve better transformation and highest hardness due to slower heating without sacrificing the processing rate and hardening depths.

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Laksono, Pranoto Budi. "A STUDY OF THE INFLUENCE OF 650 nm LASER INTERFERENCE ON VISIBLE LASER LIGHT COMMUNICATION SYSTEM." TEKNOKOM 4, no. 2 (September 1, 2021): 60–65. http://dx.doi.org/10.31943/teknokom.v4i2.66.

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Visible Laser Light Communication System (VLLC) is a wireless communication system, using laser as the medium. In the data transfer process, it is possible to have optical interference where 2 laser beams coincide with one point on the reflector. Research on the effect of laser source interference has been carried out by several researchers including mitigation actions to reduce its effects. This experiment uses 2 optical distance sensors that produce a laser with a wavelength of 650 nm with a power <=4.1 mW and with the direction of the laser beam both of them cross each other. To determine the effect of the interference of two laser beams when crossing the communication process in the visible light communication system, a reflector is used which can capture the two laser beams and the reflector can be shifted gradually so that a condition can be obtained where the two laser beams meet at one point. From the measurements made at the points after the laser beam crossing, the measurements at the point where the beam crossed, and the measurements at the points before the beam crossing, it was obtained data, at the exact point where the laser beam crossed the interference occurred, which is indicated by unstable output voltage of the two lasers, so that communication at the point of intersection is disrupted. However, if outside the point of contact both before and after the point of contact, interference and communication systems will not occur.

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Jian, Chenhao, Ziyang Ye, and Andrea D. Pickel. "Laser heating with doughnut-shaped beams." Journal of Applied Physics 132, no. 24 (December 28, 2022): 245104. http://dx.doi.org/10.1063/5.0103369.

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Doughnut-shaped laser beams have applications in laser-based additive manufacturing, laser heating of diamond anvil cells, and optical super-resolution microscopy. In applications like additive manufacturing and heating of diamond anvil cells, a doughnut-shaped beam is frequently used to obtain a more uniform temperature profile relative to that generated by a conventional Gaussian beam. Conversely, in super-resolution microscopy, the doughnut-shaped beam serves to enhance spatial resolution and heating is an undesirable side effect that can cause thermal damage. Here, we develop analytical expressions for the temperature rise induced by a doughnut-shaped laser beam both alone and in combination with a Gaussian beam. For representative, experimentally determined beam radii and a wide range of thermal properties, we find that a doughnut-shaped beam results in a peak temperature rise no more than 90% and often less than 75% of that for a Gaussian beam with the same total power. Meanwhile, the region of the sample surface that reaches 80% of the maximum temperature rise is at least 1.5 times larger for a doughnut-shaped beam than for a Gaussian beam. When doughnut-shaped and Gaussian beams are applied simultaneously, the ratio of the maximum temperature rise for the two beams combined vs a Gaussian beam alone can be up to 2.5 times lower than the ratio of the doughnut-shaped vs the Gaussian beam power. For applications like super-resolution microscopy that require high doughnut-shaped laser beam powers, the doughnut-shaped beam intensity profile is thus advantageous for minimizing the total peak temperature rise when applied together with a Gaussian beam.

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12

Hagiwara, Toru, Mamiko Yagi, and Takuya Seo. "Visibility of Laser Beams and Illuminated Delineator as a Function of Fog Density." Transportation Research Record: Journal of the Transportation Research Board 1553, no. 1 (January 1996): 59–65. http://dx.doi.org/10.1177/0361198196155300109.

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In dense fog, adequate visibility of the delineator is important for providing the driver with road geometry cues. A new illuminated delineator that uses laser beams is proposed. Very few data have been published with regard to the visibility of laser beams in fog. However, laser beams can be expected to be highly visible in dense fog because of their high intensity, high energy, and directivity that is both monoclinic and strong. A study was conducted to evaluate the visibility of laser beams in fog. The effectiveness of two types of laser heads and an illuminated delineator containing two 10-W glow lamps was investigated in artificial fog. The dependent variables were luminance at a specific point on the laser beam and estimated brightness. The major independent variables were fog density and illuminance in the observation room. The laser beams were observed as sharp lines of light in dense fog. The visibility of the laser beams in fog had an inverse relationship to that of normal light. In addition, subjects reported that the directivity of the laser beams could effectively indicate the direction of the highway. However, the visibility of the laser beams was strongly affected by the illuminance in the observation room, and care must be taken to prevent drivers from looking directly at redundant laser beams. On the basis of these results, it is concluded that laser beams may be useful lighting sources in dense fog if this safety problem can be overcome.

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Kotlyar, Victor V., Alexey A. Kovalev, and Eugeny G. Abramochkin. "Topological Charge of Propagation-Invariant Laser Beams." Photonics 10, no. 8 (August 9, 2023): 915. http://dx.doi.org/10.3390/photonics10080915.

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If a vortex propagation-invariant beam is given by all its intensity nulls, then its topological charge (TC) can be defined easily: its TC is equal to the sum of topological charges of all optical vortices in these intensity nulls. If, however, a propagation-invariant beam is given as a superposition of several light fields, then determining its TC is a complicated task. Here, we derive the topological charges of four different types of propagation-invariant beams, represented as axial superpositions of Hermite–Gaussian beams with different amplitudes and different phase delays. In particular, topological charges are obtained for such beam families as the Hermite–Laguerre–Gaussian (HLG) beams and two-parametric vortex Hermite beams. We show that the TC is a quantity resistant to changing certain beam parameters. For instance, when the parameters θ and α of the HLG beams are altered, the beam intensity also changes significantly, but the TC remains unchanged.

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Nicola, Iulian, and Tudor Prisecaru. "Methods for Determining the Characteristics of Laser Beams and the Optical Transmission." Applied Mechanics and Materials 656 (October 2014): 345–50. http://dx.doi.org/10.4028/www.scientific.net/amm.656.345.

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The paper presents new methods and procedures to measure the characteristics of laser beams and their transmission through optical systems. The paper describes the work procedures and equipments used to measure the characteristics of laser beams and their transmission through optical systems. Using these working procedures, experimental measurement for the characteristics of the beam for a 1.54 µm laser rangefinder and the transmission of a 633 nm laser beam through laser protection glasses were made.

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Pawar, V. S., S. R. Kokare, S. D. Patil, and M. V. Takale. "Domains of modulation parameter in the interaction of finite Airy–Gaussian laser beams with plasma." Laser and Particle Beams 38, no. 3 (September 2020): 204–10. http://dx.doi.org/10.1017/s0263034620000270.

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AbstractIn this paper, self-focusing of finite Airy–Gaussian (AiG) laser beams in collisionless plasma has been investigated. The source of nonlinearity considered herein is relativistic. Based on the Wentzel–Kramers–Brillouin (WKB) and paraxial-ray approximations, the nonlinear coupled differential equations for beam-width parameters in transverse dimensions of AiG beams have been established. The effect of beam's modulation parameter and linear absorption coefficient on the self-focusing/defocusing of the beams is specifically considered. It is found that self-focusing/defocusing of finite AiG beams depends on the range of modulation parameter. The extent of self-focusing is found to decrease with increase in absorption.

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Ari-Izumi, Takashi, Ioana Gheorghe, Dan Filipescu, Satoshi Hashimoto, Shuji Miyamoto, and Hiroaki Utsunomiya. "Spatial profiles of collimated laser Compton-scattering γ-ray beams." Journal of Instrumentation 18, no. 06 (June 1, 2023): T06005. http://dx.doi.org/10.1088/1748-0221/18/06/t06005.

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Abstract The intensity and energy spatial distributions of collimated laser Compton scattering (LCS) γ-ray beams and of the associated bremsstrahlung beams have been investigated as functions of the electron beam energy, electron beam phase space distribution, laser optics conditions and laser polarization. We show that the beam halo is affected to different extents by variations in the above listed parameters. In the present work, we have used laser Compton scattering simulations performed with the eliLaBr code (https://github.com/dan-mihai-filipescu/eliLaBr) and real LCS and bremsstrahlung γ-ray beams produced at the NewSUBARU synchrotron radiation facility. A 500 μm MiniPIX X-ray camera was used as beamspot monitor in a wide γ-ray beam energy range between 1.73 MeV and 38.1 MeV.

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Urunkar, T. U., S. D. Patil, A. T. Valkunde, B. D. Vhanmore, K. M. Gavade, and M. V. Takale. "On the exploration of graphical and analytical investigation of effect of critical beam power on self-focusing of cosh-Gaussian laser beams in collisionless magnetized plasma." Laser and Particle Beams 36, no. 2 (June 2018): 254–60. http://dx.doi.org/10.1017/s0263034618000253.

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AbstractThe paper gives graphical and analytical investigation of the effect of critical beam power on self-focusing of cosh-Gaussian laser beams in collisionless magnetized plasma under ponderomotive non-linearity. The standard Akhmanov's parabolic equation approach under Wentzel–Kramers–Brillouin (WKB) and paraxial approximations is employed to investigate the propagation of cosh-Gaussian laser beams in collisionless magnetized plasma. Especially, the concept of numerical intervals and turning points of critical beam power has evolved through graphical analysis of beam-width parameter differential equation of cosh-Gaussian laser beams. The results are discussed in the light of numerical intervals and turning points.

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Leemans, Wim, Eric Esarey, Cameron Geddes, Carl Schroeder, and Csaba Tóth. "Laser guiding for GeV laser–plasma accelerators." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 364, no. 1840 (January 25, 2006): 585–600. http://dx.doi.org/10.1098/rsta.2005.1724.

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Guiding of relativistically intense laser beams in preformed plasma channels is discussed for development of GeV-class laser accelerators. Experiments using a channel guided laser wakefield accelerator at Lawrence Berkeley National Laboratory (LBNL) have demonstrated that near mono-energetic 100 MeV-class electron beams can be produced with a 10 TW laser system. Analysis, aided by particle-in-cell simulations, as well as experiments with various plasma lengths and densities, indicate that tailoring the length of the accelerator, together with loading of the accelerating structure with beam, is the key to production of mono-energetic electron beams. Increasing the energy towards a GeV and beyond will require reducing the plasma density and design criteria are discussed for an optimized accelerator module. The current progress and future directions are summarized through comparison with conventional accelerators, highlighting the unique short-term prospects for intense radiation sources based on laser-driven plasma accelerators.

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Cao, Hui, Xufei Xie, Yaohua Chen, Yunsong Dong, Liquan Wang, Zhurong Cao, Xu Chen, et al. "Laser repointing scheme for octahedral spherical hohlraums on the SGIII laser facility." Physics of Plasmas 30, no. 4 (April 2023): 042703. http://dx.doi.org/10.1063/5.0133806.

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The novel octahedral spherical hohlraum can provide an ideal and practical approach for the next generation of laser systems to support both direct and indirect drive to achieve predictable and reproducible fusion gain via multiple schemes. To demonstrate its advantage in a naturally high symmetry at a cylindrically configured laser facility, it requires to repoint the laser beams to approach as close as possible the ideal octahedral beam configuration with an injection angle (the angle between a beam and the normal direction of its laser entrance hole (LEH)) ranging from 50° to 60°. We report our investigation and experiment on the optimum repointing scheme at the SGIII facility, which uses 32 beams, with 8 beams entering each polar LEH at 49.5° and 55°, and 4 beams entering each equatorial LEH at 61.5° and 62.1°. It contains residual imbalance between the polar and equatorial beams, leading to an asymmetry dominated by the spherical harmonic Y20 mode, which can be remarkably reduced by the stronger backscatters of equatorial beams. Our experiment demonstrated the feasibility of the 32-beam optimum repointing scheme and generation of 175 eV under 86 kJ inside a 2.4-mm-radius octahedral hohlraum with 0.7-mm-radius LEHs, which provided a strong support for the later experiment on proof-of-concept of octahedral spherical hohlraum [Lan et al., Phys. Rev. Lett. 127, 245001 (2021)]. 2D simulations on LEH closure agree well with the observations. This work opens a novel way of realization of a quasi-spherical irradiation at a cylindrically configured laser facility without supplementary symmetry control.

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Apiputikul, Chatchalong, Kheamrutai Thamaphat, Monrudee Ranusawad, and Pichet Limsuwan. "Uncomplicated Setting Apparatus for Measurement of Fluid Flow Rate Using Laser Doppler Technique: Physics Teaching." Advanced Materials Research 770 (September 2013): 366–69. http://dx.doi.org/10.4028/www.scientific.net/amr.770.366.

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Laser Doppler velocimetry (LDV) or laser Doppler anemometry (LDA) is the technique of using the Doppler shift in a laser beam to determine the fluid velocity. In this work, dual beam mode (two incident beams, single observation location) was selected to use. A cost effective and easy module for measurement of water flow rate was designed and constructed. A He-Ne laser with a wavelength of 632.8 nm was used as a light source. The laser was passed through a beam splitter and divided into two beams with identical intensity and coherence. Subsequently, the two laser beams travelled to a focusing lens with a focal length of 100 mm and focused on a center of water flow channel in quartz cuvette with a dimension of 1 × 1 × 5 cm3. The beam angle was set at 4.96°. When the seeding particles, bubbles and microorganism in water, were moving through the intersection point of two beams, the light was scattered. The scattered light was collected by photodetector connected to processing system. The frequency of scatterred light is shifted according to the Doppler shift relations due to effect of Rayleigh scattering. The water flow rate can be calculated from Doppler shift frequency.

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Klein-Wiele, Jan-Hendrik, Andreas Blumenstein, Peter Simon, and Jürgen Ihlemann. "Laser interference ablation by ultrashort UV laser pulses via diffractive beam management." Advanced Optical Technologies 9, no. 1-2 (February 25, 2020): 41–52. http://dx.doi.org/10.1515/aot-2019-0068.

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AbstractThe fabrication of periodic surface patterns on various materials by ultrashort ultraviolet (UV) laser pulses is reviewed. Laser interference ablation using two or more coherent beams leads to deterministic, strictly periodic patterns. The generation of the interfering beams is accomplished by diffractive optical elements like gratings, grating systems or computer-generated holograms. The recombination of the diffracted beams is performed by optical imaging or diffractive beam management. Ultrashort UV pulses are especially suited for generating micron- to submicron-sized deterministic periodic patterns on metals and semiconductors.

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Chen, L., Y. Yan, and R. Zhang. "Effects of convection in laser-guided transportation." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 218, no. 7 (July 1, 2004): 775–82. http://dx.doi.org/10.1243/0954406041319536.

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Weak focusing laser beams can guide micrometre-sized beads to direct-write two-dimensional patterns or three-dimensional structures. Applications based on laser guidance have been found in many fields including biological research areas. This paper discusses the effects of convection, which is the main disturbance during laser-guided transportation. The heat generated by optical absorption causes the convection flow, as observed in experiments. To investigate this convection flow, a finite element analysis (FEA) model was set up and computation under different heat load conditions was carried out. The results show that the convection flow velocity at the laser beam centre has a direct proportional relation to the incident power and varies with the position of the laser beam.

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Sáenz, Juan José. "Laser tractor beams." Nature Photonics 5, no. 9 (August 30, 2011): 514–15. http://dx.doi.org/10.1038/nphoton.2011.201.

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Qiu, Jie, Liang Hao, Lihua Cao, and Shiyang Zou. "Collective stimulated Brillouin scattering with shared ion acoustic wave under the action of two overlapping laser beams." Plasma Physics and Controlled Fusion 63, no. 12 (November 12, 2021): 125026. http://dx.doi.org/10.1088/1361-6587/ac301d.

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Abstract The overlapping of multiple beams is common in inertial confinement fusion (ICF), making the collective stimulated Brillouin scattering (SBS) with shared ion acoustic wave (IAW) potentially important because of the effectively larger laser intensities to drive the instability. In this work, based on a linear kinetic model, an exact analytic solution for the convective amplification of collective SBS with shared IAW stimulated by two overlapped beams is presented. From this solution, effects of the wavelength difference, crossing angle, polarization states, and finite beam overlapping volume of the two laser beams on the collective SBS modes with shared IAW are studied. It is found that a wavelength difference of several nanometers between the laser beams has negligible effects, except for a very small crossing angle about one degree. However, the crossing angle, beam polarization states, and finite beam overlapping volume can have significant influences. Furthermore, the out-of-plane modes, in which the wavevectors of daughter waves lie in different planes from the two overlapped beams, are found to be important for certain polarization states and crossing angles of the laser beams. This work is helpful to comprehend and estimate the collective SBS with shared IAW in ICF experiments.

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Gagné, M. C., P. Galarneau, and S. L. Chin. "Photorefractive deflection technique using parallel and overlaping probe and pump beams." Canadian Journal of Physics 64, no. 9 (September 1, 1986): 1116–20. http://dx.doi.org/10.1139/p86-192.

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The present work provides an experimental study of a pulsed photorefractive technique to diagnose the interior of an irradiated region. Results obtained in a mixture of SF6 and Ar are presented to illustrate the experimental technique. Three distinct areas have been studied, (i) The two beams are parallel and their optical axes are coincident (collinear). At this particular position, the probe beam suffers a defocusing effect that is used to align collinearly two laser beams with a precision of ±3 μm. (ii) The two beams are parallel but slightly off axis. In this case, the probe beam suffers a deviation that is the sole result of a rarefaction in the irradiated region followed by the normal thermal equilibration. (iii) The two beams are parallel and slightly overlapping. The probe beam suffers a deviation similar to the preceding one. Moreover, it sees an initial outward-propagating acoustic (density) wave. It is in this particular region that the acoustic perturbation appears. Finaly, the gas mixture used under our experimental conditions is a good candidate for the collinear alignment of several laser beams. The only restrictions are that the pump laser must produce a beam with a symmetrical intensity profile, the other laser beams must be continuous-wave beams, and the gas mixture must be transparent to the latter.

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Yang, Tianli, Jing Yang, Wangzhe Zhou, Xuepeng Li, Yinan Zhou, Zongzhe Zhang, and Xiaojun Wang. "High-Power, High-Purity HG0n Hermite–Gaussian Laser Beam Generation in Cascaded Large Aspect Ratio Slabs." Applied Sciences 13, no. 19 (October 8, 2023): 11062. http://dx.doi.org/10.3390/app131911062.

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High-power, high-purity, nanosecond (ns) one-dimensional HG0n laser beams are proposed and demonstrated by using Nd:YAG cascaded slabs with a large aspect ratio. The HG0n laser beams are generated by adjusting the pump distribution, the intracavity apertures, and the tilt angle of the output coupler (OC). By controlling the gain and loss of HG0n modes of different orders, the high-purity, one-dimensional, high-order HG0n laser beams with orders 1 to 9 (HG01 to HG09) are produced, and their beam quality factors M2 align well with the theoretical predictions. Meanwhile, the large aspect ratio slab provides an ideal amplifier for the strip-shaped HG0n laser beams, and further power scaling is achieved by seeding the generated HG0n laser beams into an amplifier with an identical slab module. For the HG09 mode, the average power is amplified from 289 mW to 4.73 W with 294 ns pulse width, corresponding to a peak power of 32 kW. Moreover, above 5 W average power is achieved for all HG01 to HG08 modes. Hopefully, this scheme provides a solution for high-power and high-purity HG0n laser beam generation based on the slab-shaped configuration.

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SEMEROK, A., B. SALLÉ, J. F. WAGNER, and G. PETITE. "Femtosecond, picosecond, and nanosecond laser microablation: Laser plasma and crater investigation." Laser and Particle Beams 20, no. 1 (January 2002): 67–72. http://dx.doi.org/10.1017/s0263034602201093.

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Crater shapes and plasma plume expansion in the interaction of sharply focused laser beams (10 μm waist diameter, 60 fs–6 ns pulse duration) with metals in air at atmospheric pressure were studied. Laser ablation efficiencies and rates of plasma expansion were determined. The best ablation efficiency was observed with femtosecond laser pulses. It was found that for nanosecond pulses, the laser beam absorption, its scattering, and its reflection in plasma were the limiting factors for efficient laser ablation and precise material sampling with sharply focused laser beams. The experimental results obtained were analyzed with relation to different theoretical models of laser ablation.

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Kroupp, E., S. Tata, Y. Wan, D. Levy, S. Smartsev, E. Y. Levine, O. Seemann, et al. "Commissioning and first results from the new 2 × 100 TW laser at the WIS." Matter and Radiation at Extremes 7, no. 4 (July 1, 2022): 044401. http://dx.doi.org/10.1063/5.0090514.

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At the Weizmann Institute of Science, a new high-power-laser laboratory has been established that is dedicated to the fundamental aspects of laser–matter interaction in the relativistic regime and aimed at developing compact laser-plasma accelerators for delivering high-brightness beams of electrons, ions, and x rays. The HIGGINS laser system delivers two independent 100 TW beams and an additional probe beam, and this paper describes its commissioning and presents the very first results for particle and radiation beam delivery.

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WANG, SHUANGYI, ZHIWEI LÜ, DIANYANG LIN, LEI DING, and DONGBIN JIANG. "Investigation of serial coherent laser beam combination based on Brillouin amplification." Laser and Particle Beams 25, no. 1 (February 28, 2007): 79–83. http://dx.doi.org/10.1017/s0263034607070127.

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Based on transferring energy from multiple pump beams into one Stokes beam using Brillouin amplification, a serial coherent laser beam combination scheme is presented, which has many advantages, such as, simple structure, low cost, ease of adjustment, higher load capability, scalable easily, etc. Furthermore, it has been demonstrated that the combination of several beams using this method is theoretically possible. But in practice, the amplification of high power Stokes beam is a key problem to solve. In this paper, the amplification of Stokes beam whose power is higher than the pump beam is first studied and proved experimentally. Coupling the two laser beams by this method is proved experimentally, and the coupling efficiency reaches more than 80%. Then the feasibility of multiple beams combination based on Brillouin amplification is analyzed and tested theoretically.

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Batoo, K. M., S. M. Husein Kamona, Sh H. Zaki, H. A. Lafta, S. Hussain, W. M. Khazaal, A. H. M. Hamoody, et al. "Coherent control of parametric generation of laser beams via intersubband transitions in quantum wells." Laser Physics Letters 21, no. 2 (January 9, 2024): 026001. http://dx.doi.org/10.1088/1612-202x/ad1096.

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Abstract This paper investigates the propagation dynamics of laser beams within a semiconductor quantum well (QW) system. The study explores various scenarios involving different detuning values and spatially varying incident beams. The light–matter interaction within the QW system shows a complex interplay between detuning, spatial characteristics, and beam properties. In the resonant case, where the detuning values for probe and signal beams are zero, we observe exponential relaxation of both beams reaching a common value. Introducing detuning leads to oscillatory behaviors, with larger detuning values promoting more pronounced oscillations and an enhanced signal beam. The investigation takes an intriguing turn when we consider position-dependent incident beams. In these cases, the spatial patterns of the initial beam are transferred to the generated beam, leading to soliton-like propagation and the creation of beams with specific spatial dependencies. Remarkably, under substantial detuning, both incident and generated beams adopt periodic patterns in two dimensions, forming lattice structures with spot-like peak intensities. These findings underscore the versatility and controllability of the QW system, offering opportunities for engineered spatial and spectral properties in laser beams.

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31

BADZIAK, J., S. GŁOWACZ, S. JABŁOŃSKI, P. PARYS, J. WOŁOWSKI, and H. HORA. "Laser-driven generation of high-current ion beams using skin-layer ponderomotive acceleration." Laser and Particle Beams 23, no. 4 (October 2005): 401–9. http://dx.doi.org/10.1017/s0263034605050573.

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Basic properties of generation of high-current ion beams using the skin-layer ponderomotive acceleration (S-LPA) mechanism, induced by a short laser pulse interacting with a solid target are studied. Simplified scaling laws for the ion energies, the ion current densities, the ion beam intensities, and the efficiency of ions' production are derived for the cases of subrelativistic and relativistic laser-plasma interactions. The results of the time-of-flight measurements performed for both backward-accelerated ion beams from a massive target and forward-accelerated beams from a thin foil target irradiated by 1-ps laser pulse of intensity up to ∼ 1017 W/cm2 are presented. The ion current densities and the ion beam intensities at the source obtained from these measurements are compared to the ones achieved in recent short-pulse experiments using the target normal sheath acceleration (TNSA) mechanism at relativistic (>1019 W/cm2) laser intensities. The possibility of application of high-current ion beams produced by S-LPA at relativistic intensities for fast ignition of fusion target is considered. Using the derived scaling laws for the ion beam parameters, the achievement conditions for ignition of compressed DT fuel with ion beams driven by ps laser pulses of total energy ≤ 100 kJ is shown.

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Le, Hoang, Pavel Penchev, Anne Henrottin, David Bruneel, Vahid Nasrollahi, Jose A. Ramos-de-Campos, and Stefan Dimov. "Effects of Top-hat Laser Beam Processing and Scanning Strategies in Laser Micro-Structuring." Micromachines 11, no. 2 (February 20, 2020): 221. http://dx.doi.org/10.3390/mi11020221.

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The uniform energy distribution of top-hat laser beams is a very attractive property that can offer some advantages compared to Gaussian beams. Especially, the desired intensity distribution can be achieved at the laser spot through energy redistribution across the beam spatial profile and, thus, to minimize and even eliminate some inherent shortcomings in laser micro-processing. This paper reports an empirical study that investigates the effects of top-hat beam processing in micro-structuring and compares the results with those obtainable with a conventional Gaussian beam. In particular, a refractive field mapping beam shaper was used to obtain a top-hat profile and the effects of different scanning strategies, pulse energy settings, and accumulated fluence, i.e., hatch and pulse distances, were investigated. In general, the top-hat laser processing led to improvements in surface and structuring quality. Especially, the taper angle was reduced while the surface roughness and edge definition were also improved compared to structures produced with Gaussian beams. A further decrease of the taper angle was achieved by combining hatching with some outlining beam passes. The scanning strategies with only outlining beam passes led to very high ablation rates but in expense of structuring quality. Improvements in surface roughness were obtained with a wide range of pulse energies and pulse and hatch distances when top-hat laser processing was used.

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PUROHIT, GUNJAN, H. D. PANDEY, and R. P. SHARMA. "Effect of cross focusing of two laser beams on the growth of laser ripple in plasma." Laser and Particle Beams 21, no. 4 (October 2003): 567–72. http://dx.doi.org/10.1017/s0263034603214154.

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This article presents an effect of cross focusing of two laser beams on the growth of a laser ripple in laser-produced plasmas. The mechanism of nonlinearity is assumed to be ponderomotive force, arising because of the Gaussian intensity distribution of the laser beams. The dynamical equation governing the laser ripple intensity has been set up and a numerical solution has been presented for typical laser plasma parameters. It is found that the change in the intensity of the second laser beam can affect the growth of the laser ripple significantly.

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Wang, Guanxue, Keyu Chen, Xiaoyu Weng, Xinzhi Shan, Xiangyu Kang, Xiumin Gao, and Songlin Zhuang. "Laser cavity creation of one or dual orbital angular momentum vortex beams by edge diffraction regulation." Applied Physics Letters 122, no. 8 (February 20, 2023): 081104. http://dx.doi.org/10.1063/5.0127904.

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In the past three decades, a unique beam called vortex beam with orbital angular momentum has become the research focus of researchers. However, to date, almost all the methods for generating vortex beams are to adjust the phase distribution of the central part of the beam cross section. Is there a method to generate high-purity one or dual orbital angular momentum vortex beams based on the edge diffraction regulation? Specifically, it has been shown that a variety of complex laser modes can be generated in a special laser cavity, and these modes are difficult to control. How to create vortex beams from these complex patterns is an important scientific problem. This paper solves this scientific problem based on edge diffraction regulation in laser cavities. Only three variable aperture diaphragms are needed to realize the generation of one or dual orbital angular momentum vortex beams. Moreover, the topological charge of the beam is proved by interference experiments. This work can not only break the understanding of traditional vortex beam generation method and deepen the understanding of laser cavity regulation technology but also bring opportunities for optics, electromagnetics, and other related fields.

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35

Zhuo, Yi, Lina Ma, Sanyuan Li, Shaopu Su, and Lei Li. "Test Study on Strength of Laser Additive Manufacture AF1410 Steel I-Shaped Beam." Journal of Physics: Conference Series 2403, no. 1 (December 1, 2022): 012007. http://dx.doi.org/10.1088/1742-6596/2403/1/012007.

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Abstract The static and fatigue strength of laser additive manufactured AF1410 steel I-beam were tested by a four-point bending test, and the same method was used to test the conventional forged, machined AF1410 short steel beams. The fatigues test data of both short beams were analyzed by DFR method. The test and analysis results show that the static strength of laser additive short beams is close to conventionally fabricated short beams, and the fatigue performance is weaker than that of forged, machined short beams.

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Lee, Sang Won, Rhett Mayor, and Jun Ni. "Development of a Six-Degree-of-Freedom Geometric Error Measurement System for a Meso-Scale Machine Tool." Journal of Manufacturing Science and Engineering 127, no. 4 (March 11, 2005): 857–65. http://dx.doi.org/10.1115/1.2035692.

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This paper presents the development of a six-degree-of-freedom (DOF) geometric error measurement (6GEM) system that can be applied to the simultaneous measurement of six geometric error components of the moving axes of a meso-scale machine tool (mMT). The system consists of a laser module constructed by a cube beam splitter and a pigtailed laser diode, three two-dimensional position sensitive detectors (PSDs), and an additional cube beam splitter. The laser module moving with the positioning system of the developed mMT testbed generates two perpendicular laser beams, one of which is further divided into two laser beams at the second cube beam splitter. These three laser beams are detected by the three PSDs, and the full pose of the laser module is then calculated simultaneously by forward and inverse kinematic computations. The calculated full pose of the laser module is translated into six-DOF geometric errors of the mMT testbed. A series of experiments are performed to demonstrate the effectiveness and accuracy of the proposed 6GEM system. The experimental results show that the measurement accuracy of the 6GEM system was better than ±0.6μm for translational error components and ±0.6arcsec for angular error components.

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37

Jhu, Siou Jhun, Yi Hsien Liu, and Chung Wei Cheng. "Fabrication of Hybrid Micro/Nano Structures on Titanium by Vector Femtosecond Laser Beam." Nano Hybrids and Composites 42 (February 15, 2024): 11–19. http://dx.doi.org/10.4028/p-dyzdq8.

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The morphology of laser-induced periodic surface structures (LIPSS) and micro/nanostructures may be influenced by laser optics or process parameters. This study focused on two beam profiles, Gaussian and vector beams. Vector beam is an annular beam with a null intensity at its center. Radial and azimuthal polarization are the common states of polarization. We investigated Gaussian and vector femtosecond laser beams with the wavelength of 515 nm irradiated on titanium to analyze the ablation crater characterization and the ablation threshold of titanium. Finally, we conducted an experiment on the fabrication of the hybrid micro/nanostructures via spot-by-spot vector beam.

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Sharma, Prerana, and R. P. Sharma. "Generation of Longmuir turbulence and stochastic acceleration in laser beat wave process." Laser and Particle Beams 28, no. 2 (May 4, 2010): 285–92. http://dx.doi.org/10.1017/s0263034610000182.

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AbstractThis paper investigates the filamentation process of two co-axially propagating laser beams in collisionless plasma. On account of the ponderomotive nonlinearity, two laser beams affect the dynamics of each other, and cross-focusing takes place. The initial Gaussian laser beams are found to have non-Gaussian structures in the plasma. Using the laser beam and the plasma parameters, appropriate for the beat wave process, the filaments of the laser beams have been studied. Using these results, the Langmuir wave excitation at the beat wave frequency (when the laser beams are having filamentary structures) has been studied. The excited LW is modeled with the help of a driven oscillator and it is found that the excited Langmuir wave is not a plane wave; rather it has a turbulent structure. We have obtained the power spectrum of the excited beat wave (Langmuir wave), and calculated the spectral index. The stochastic electron acceleration has been studied in the presence of this Langmuir turbulence and relevance of these results to the beat wave process has been pointed out.

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39

Hüller, Stefan, Gaurav Raj, Mufei Luo, Wojciech Rozmus, and Denis Pesme. "Crossed beam energy transfer between optically smoothed laser beams in inhomogeneous plasmas." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 378, no. 2184 (October 12, 2020): 20200038. http://dx.doi.org/10.1098/rsta.2020.0038.

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Crossed beam energy transfer, CBET, in high-intensity laser–plasma interaction is investigated for the case of optically smoothed laser beams. In the two approaches to laser-driven inertial confinement fusion experiments, the direct-drive and the indirect-drive, CBET is of great importance because it governs the coupling of laser energy to the plasma. We use the two-dimensional wave-coupling code H armony to simulate the transfer between two laser beams with speckle structure that overlap in a plasma with an inhomogeneous flow profile. We compare the CBET dynamics for laser beams with spatial incoherence and with spatio-temporal incoherence; in particular we apply the smoothing techniques using random phase plates (RPPs) and smoothing by spectral dispersion (SSD), respectively. It is found that for laser beams (wavelength λ 0 ) with intensities ( I L ) above I L ∼ 2 × 10 15 W cm −2 ( λ 0 /0.35 µm) −2 ( T e /keV), both the so-called plasma-induced smoothing as well as self-focusing in intense laser speckles induce temporal incoherence; the latter affects the CBET and the angular distribution of the light transmitted behind the zone of beam overlap. For RPP-smoothed incident beams, the resulting band width of the transmitted light can already be of the same order as the effective band width of the SSD available at major laser facilities. We examine the conditions when spatio-temporal smoothing techniques become efficient for CBET. This article is part of a discussion meeting issue ‘Prospects for high gain inertial fusion energy (part 1)’.

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40

Anderson, Benjamin R., Natalie Gese, and Hergen Eilers. "Subsurface Spectroscopy in Heterogeneous Materials Using Self-Healing Laser Beams." Optics 5, no. 2 (June 20, 2024): 310–18. http://dx.doi.org/10.3390/opt5020022.

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Self-healing optical beams are a class of propagation modes that can recover their beam shapes after distortion or partial blockage. This self-healing property makes them attractive for use in applications involving turbid media as they can—in theory—penetrate further into these materials than standard Gaussian beams. In this paper, we characterize the propagation of two different self-healing beams (Bessel and Airy) through a solid scattering material with different scatterer concentrations and find that both beams do recover after scattering for samples below a threshold scatterer concentration. Additionally, we test the applicability of both beam shapes for improved sub-surface spectroscopy in heterogeneous materials using fluorescent particles and find that there is an average fluorescence intensity enhancement of 1.3× using self-healing beams versus a standard Gaussian beam.

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41

Singh, Vijay. "Modulation instability of two laser beams in plasma." Laser and Particle Beams 31, no. 4 (October 15, 2013): 753–58. http://dx.doi.org/10.1017/s0263034613000748.

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AbstractIn the present paper, spatial amplitude modulation instability arising due to relativistic self-phase modulation and relativistic cross phase modulation of two co-propagating, linearly polarized laser beams (with arbitrary relative polarization) interacting with homogeneous plasma, has been studied. Wave equations including finite perturbation length effects, group velocity dispersion, and coupled nonlinear source term have been set up. Coupled dispersion relation for the two laser beams has been derived and solved numerically. The growth rate of modulation instability has been obtained and compared with the growth rate of a single beam propagating in homogeneous plasma. It has been shown that modulation instability of a single beam may either be enhanced or suppressed by co-propagation of another laser beam having appropriate polarization.

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Sun, Xiaoyan, Fang Zhou, and Lian Duan. "An Annular Fresnel Zone Plate without Central Spots Fabricated by Femtosecond Laser Direct Writing." Micromachines 13, no. 8 (August 10, 2022): 1285. http://dx.doi.org/10.3390/mi13081285.

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In recent years, micro-annular beams have been widely used, which has expanded the possibilities for laser processing. However, the current method of generating an annular beam still has shortcomings, such as spot energy at the center of the produced beam. In this study, a Fresnel zone plate with an annular structure was machined using a femtosecond laser. After focusing, an annular laser beam without a spot in the center was obtained, and the radius and focal length of the annular beam could be easily adjusted. In addition, two annular Fresnel zone plates were concentrically connected to obtain a concentric double-ring beam in the same focal plane. The simulation and experimental results were consistent, providing effective potential for applications related to nontraditionally shaped laser beams.

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43

PEGORARO, F., S. ATZENI, M. BORGHESI, S. BULANOV, T. ESIRKEPOV, J. HONRUBIA, Y. KATO, et al. "Production of ion beams in high-power laser–plasma interactions and their applications." Laser and Particle Beams 22, no. 1 (March 2004): 19–24. http://dx.doi.org/10.1017/s0263034604221048.

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Energetic ion beams are produced during the interaction of ultrahigh-intensity, short laser pulses with plasmas. These laser-produced ion beams have important applications ranging from the fast ignition of thermonuclear targets to proton imaging, deep proton lithography, medical physics, and injectors for conventional accelerators. Although the basic physical mechanisms of ion beam generation in the plasma produced by the laser pulse interaction with the target are common to all these applications, each application requires a specific optimization of the ion beam properties, that is, an appropriate choice of the target design and of the laser pulse intensity, shape, and duration.

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Popa, Alexandru. "Accurate calculation of radiation damping parameters in the interaction between very intense laser beams and relativistic electron beams." Laser and Particle Beams 32, no. 3 (July 24, 2014): 477–86. http://dx.doi.org/10.1017/s026303461400041x.

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AbstractWe prove that the radiation damping force and the rate of change of the damping energy, in the Landau-Lifshitz forms, in interactions between very intense laser beams and relativistic electron beams, are periodic functions of only one variable, that is the phase of the electromagnetic field. The property is proved without using any approximation, in the most general case, when the degree of polarization of the electromagnetic field, the initial phase of the incident field and the initial energy of the electron have arbitrary values. This property leads to a strong simplification of the calculation of the radiation reaction parameters and of their dependence on the initial electron energy and angular frequency of the laser beam. Our analysis is performed in the proper inertial system of the electron. The radiation reaction is significant for laser beam intensities of the order 1022 W/cm2, and for electron energy greater than 1 GeV. The calculations reveal limitations of the method of generating hard radiations by interactions between laser beams and relativistic electron beams.

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45

L'Hermite, J. M., G. Rahmat, and R. Vetter. "Angular Selection of Products by Use of Saturated-Absorption Techniques in the Cs(7P)+H2→CsH+H Reaction." Laser Chemistry 10, no. 5-6 (January 1, 1990): 377–88. http://dx.doi.org/10.1155/1990/79301.

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The Cs(7P)+H2→CsH+H reaction is studied in a crossed-beam experiment with laser-induced fluorescence detection of CsH products. The usual flux (≈50mW/mm2) which is delivered by the C.W. tunable dye laser used in the experiment is enough to saturate the absorption by CsH products. Then, by crossing twice the laser beam through the collision volume (counterpropagating beams), one realizes the conditions of saturated-absorption experiments: when the laser frequency is tuned to a resonance frequency of CsH products, a defect to absorption occurs for these products which scatter in the collision plane and a "saturation dip" appears at the center of the corresponding fluorescence profile. Application of this technique to crossed-beam experiments can lead to the selection of product molecules which scatter in any definite plane. A different geometry of the laser beams (bent beams) is proposed to select molecules which scatter in any definite direction: it could be applied to detect an asymmetry in the scattering of the products with respect to the collision axis, when a particular preparation of the reagents is realized.

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46

Bulygin, Andrey, Igor Meglinski, and Yury Kistenev. "Non-Paraxial Effects in the Laser Beams Sharply Focused to Skin Revealed by Unidirectional Helmholtz Equation Approximation." Photonics 10, no. 8 (August 5, 2023): 907. http://dx.doi.org/10.3390/photonics10080907.

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Laser beams converging at significant focusing angles have diverse applications, including quartz-enhanced photoacoustic spectroscopy, high spatial resolution imaging, and profilometry. Due to the limited applicability of the paraxial approximation, which is valid solely for smooth focusing scenarios, numerical modeling becomes necessary to achieve optimal parameter optimization for imaging diagnostic systems that utilize converged laser beams. We introduce a novel methodology for the modeling of laser beams sharply focused on the turbid tissue-like scattering medium by employing the unidirectional Helmholtz equation approximation. The suggested modeling approach takes into account the intricate structure of biological tissues, showcasing its ability to effectively simulate a wide variety of random multi-layered media resembling tissue. By applying this methodology to the Gaussian-shaped laser beam with a parabolic wavefront, the prediction reveals the presence of two hotspots near the focus area. The close-to-maximal intensity hotspot area has a longitudinal size of about 3–5 μm and a transversal size of about 1–2 μm. These values are suitable for estimating spatial resolution in tissue imaging when employing sharply focused laser beams. The simulation also predicts a close-to-maximal intensity hotspot area with approximately 1 μm transversal and longitudinal sizes located just behind the focus distance for Bessel-shaped laser beams with a parabolic wavefront. The results of the simulation suggest that optical imaging methods utilizing laser beams with a wavefront produced by an axicon lens would exhibit a limited spatial resolution. The wavelength employed in the modeling studies to evaluate the sizes of the focus spot is selected within a range typical for optical coherence tomography, offering insights into the limitation of spatial resolution. The key advantage of the unidirectional Helmholtz equation approximation approach over the paraxial approximation lies in its capability to simulate the propagation of a laser beam with a non-parabolic wavefront.

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Li, Dongyu, Tang Yang, Minjian Wu, Zhusong Mei, Kedong Wang, Chunyang Lu, Yanying Zhao, et al. "Introduction of Research Work on Laser Proton Acceleration and Its Application Carried out on Compact Laser–Plasma Accelerator at Peking University." Photonics 10, no. 2 (January 28, 2023): 132. http://dx.doi.org/10.3390/photonics10020132.

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Laser plasma acceleration has made remarkable progress in the last few decades, but it also faces many challenges. Although the high gradient is a great potential advantage, the beam quality of the laser accelerator has a certain gap, or it is different from that of traditional accelerators. Therefore, it is important to explore and utilize its own features. In this article, some recent research progress on laser proton acceleration and its irradiation application, which was carried out on the compact laser plasma accelerator (CLAPA) platform at Peking University, have been introduced. By combining a TW laser accelerator and a monoenergetic beamline, proton beams with energies of less than 10 MeV, an energy spread of less than 1%, and with several to tens of pC charge, have been stably produced and transported in CLAPA. The beamline is an object–image point analyzing system, which ensures the transmission efficiency and the energy selection accuracy for proton beams with large initial divergence angle and energy spread. A spread-out Bragg peak (SOBP) is produced with high precision beam control, which preliminarily proved the feasibility of the laser accelerator for radiotherapy. Some application experiments based on laser-accelerated proton beams have also been carried out, such as proton radiograph, preparation of graphene on SiC, ultra-high dose FLASH radiation of cancer cells, and ion-beam trace probes for plasma diagnosis. The above applications take advantage of the unique characteristics of laser-driven protons, such as a micron scale point source, an ultra-short pulse duration, a wide energy spectrum, etc. A new laser-driven proton therapy facility (CLAPA II) is being designed and is under construction at Peking University. The 100 MeV proton beams will be produced via laser–plasma interaction by using a 2-PW laser, which may promote the real-world applications of laser accelerators in malignant tumor treatment soon.

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Lemos, N., W. A. Farmer, N. Izumi, H. Chen, E. Kur, A. Pak, B. B. Pollock, et al. "Specular reflections (“glint”) of the inner beams in a gas-filled cylindrical hohlraum." Physics of Plasmas 29, no. 9 (September 2022): 092704. http://dx.doi.org/10.1063/5.0099937.

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We report on the experimental measurement of specular reflection (“glint”) of laser beams off the hohlraum wall in inertial confinement fusion experiments at the National Ignition Facility. In a hohlraum, glinted light can escape the opposite laser entrance hole of the hohlraum and is a potential laser energy loss mechanism. The total measured glint on the inner cones of beams is measured to be less than 8 TW (when using the full National Ignition Facility laser), which is <2% of incident peak power. The simulated x-ray flux exceeds the measurement by 10%–20%, and glinted laser light is unable to account for this discrepancy. Similar inner beam glint was measured for ρ = 0.3 and 0.6 mg/cc gas fill hohlraums, but no glint was detected for 1.2 mg/cc densities. Inner beam glint is dominated by the lowest angle 21.5 beams within a 23.5 quad, and it is at most 30% sensitive to different quad polarization arrangements.

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CHAUHAN, P. K., S. T. MAHMOUD, R. P. SHARMA, and H. D. PANDEY. "Effect of laser ripple on the beat wave excitation and particle acceleration." Journal of Plasma Physics 73, no. 1 (February 2007): 117–30. http://dx.doi.org/10.1017/s002237780600465x.

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Abstract.This paper presents the effect of ripple on the plasma wave excitation process and acceleration of electrons in a laser produced plasma. The plasma wave is generated by the beating of two coaxial lasers of frequencies ω1 and ω2, such that ω1-ω2≅ωp. One of the main laser beams also has intensity spikes. The nonlinearity due to the relativistic mass variation depends not only on the intensity of one laser beam but also on the second laser beam. Therefore the behavior of the first laser beam affects the second laser beam, hence cross-focusing takes place. Owing to the interaction of ripple and the main laser beams, the ripple grows inside the plasma. The behavior of the ripple in the plasma affects the excitation of the electron plasma wave as well as the electron acceleration. The amplitude of the electron plasma wave and the electron energy are calculated, in the presence of ripple.

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McDevitt, T. E., G. H. Koopmann, and C. B. Burroughs. "Two-Channel Laser Vibrometer Techniques for Vibrational Intensity Measurements: Part 1—Flexural Intensity." Journal of Vibration and Acoustics 115, no. 4 (October 1, 1993): 436–40. http://dx.doi.org/10.1115/1.2930369.

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A laser technique which measures vibrational energy flow (intensity) via propagating bending waves is described. A pair of scanning laser beams from a two-channel laser vibrometer is used to provide a nonintrusive measurement of the intensity at various points on a vibrating beam. Results are shown to compare well with those of two additional techniques. These techniques, used for validation, employ a single laser beam and can only be used at resonance frequencies in beams or rods. The two-channel laser technique described can be applied to two-dimensional intensity measurements, is not limited to single frequency excitation, and has an inherent capability to facilitate phase error elimination via a photodetector switching technique which is also described.

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Journal articles on the topic 'Laser beams'

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