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1
Pityana, Sisa Lesley. "Second harmonic generation in waveguides." Thesis, University of Sussex, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239511.
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2
Nee, Phillip Tsefung. "Generation of squeezed light via second harmonic generation." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/34050.
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3
Trull, Silvestre José Francisco. "Second Harmonic Generation in Photonic Crystals." Doctoral thesis, Universitat Politècnica de Catalunya, 1999. http://hdl.handle.net/10803/6618.
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Photonic crystals emerged at the end of the last decade as a new frame to control the interaction between radiation and matter. The potential advances that such structures could report in photonics technology has lead to an increasing research focused on the implementation of photonic crystals possessing full photonic band gaps, hindering the fact that more simple structures, possessing band gaps in selected directions of space, may also provide strong control of the electromagnetic radiation leading to the observation of many new interesting phenomena. In fact, the scope of this control is not limited to a linear interaction and can be extended to nonlinear interactions of any order. In this work we present a study of the second order nonlinear interaction from nonlinear organic molecules placed within two different types of photonic crystals. First, we will discuss the enhancement and inhibition of the radiation at the second-harmonic frequency of a sheet of dipoles embedded in a 1D photonic crystal. The experimentally observed reflected second-harmonic intensity as a function of the angle of incidence shows sharp resonances corresponding to the excitation of the SH field in a local mode within the forbidden band in the structure, which position depends on the size of the defect, and additional resonance at the high angular band edge, which position is independent of the size of the defect. Comparison among these results and the SH intensity reflected by the same monolayer in free space (which presents a bell shaped radiation pattern as a function of the angle of incidence), shows an enhancement of the radiation at the resonances, and strong inhibition of the radiation at other angles within the gap. Theoretical simulation of the experiment shows a good agreement with the experimental results.
A detailed analysis of the enhancement and inhibition phenomena occurring in these structures shows a clear dependence of the resulting intensity with the position of the monolayer within the defect and with the dipole orientation. The change in phase difference between the oscillating dipoles and the field at the SH frequency at the monolayer as it is moved within the defect is found to play a determining role in the final energy transfer to the second-harmonic field. The resulting enhancement and inhibition of the radiation may be studied in terms of a nonsymmetric contribution of the different components of the field to the energy transfer process.
The second configuration studied in the present work consider the experimental demonstration of second-harmonic generation in a 3-dimensional macroscopically centrosymmetric lattice formed by spherical particles of optical dimensions. In such photonic crystals, the local breaking of the inversion symmetry at the surface of each sphere, allows for the existence of a nonvanishing second order interaction. The growth of the SH radiation is provided by the phase-matching mechanism caused by the bending of the photon dispersion curve near the Bragg reflection bands of this photonic crystal. Experimental evidence of this phase-matching mechanism, inherent of such crystals, is reported in this work. By measuring the SH intensity radiated from several crystals with different concentrations, we obtained the angular dependence of this type of emission and confirmed the surface character of the nonlinear interaction. A simplified theoretical model shows very good agreement with the experimental results. It is important to notice that in this mechanism of SHG, the nonlinearity of the molecule is independent of the phase-matching mechanism, that is inherent to the periodicity of the crystal.
In conclusion, the results obtained show a clear influence of the photonic crystals in the radiated SH intensity, resulting in enhancement and inhibition of the dipoles radiation.
4
Trzeciecki, Mikołaj. "Second harmonic generation from antiferromagnetic interfaces." [S.l. : s.n.], 2000. http://deposit.ddb.de/cgi-bin/dokserv?idn=96147792X.
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5
Crawford, Michael John. "Second harmonic generation from liquid interfaces." Thesis, University of Southampton, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261532.
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6
Trowbridge, Lynne. "Aligned composites for second harmonic generation." Thesis, University of Sussex, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283005.
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7
Galletto, Paolo. "Second harmonic generation of electrified metal surfaces /." [S.l.] : [s.n.], 2000. http://library.epfl.ch/theses/?nr=2262.
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8
Shen, Mengzhe. "Investigating second harmonic generation in collagen tissues." Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/54452.
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Collagen is the most abundant structural protein in the human body. When it is excited by femtosecond near infrared laser, second harmonic generation (SHG) signal at half the wavelength of the excitation wave is excited. For imaging thick tissues, the SHG signal is collected in the backward direction. The objective of this work is to elaborate the origin of the backward SHG in collagen at the fibril level and investigate some of its optic characteristics. The optic characteristics investigated include the wavelength dependence of SHG intensity, which is useful to analyze SHG in collagen tissues. However, the current published results are inconsistent. We study the microscopy system factors affecting the wavelength dependence and calibrate them by measuring the wavelength dependence of SHG intensity in a BaB₂O₄ crystal. With the proper calibration, typical wavelength dependence SHG spectra from mouse tail and Achilles tendon are investigated. The backward-collected SHG signal includes the backward generated SHG, and the forward generated but backward scattered SHG. Those two sources of the total backward SHG have different properties due to the difference in phase mismatch in the forward and backward directions. Here a non-invasive method is developed to separate them by using pinholes. By varying the pinhole size in a confocal multiphoton microscopy, the proportion of the backward scattered SHG to the total backward SHG can be obtained. Our results indicate that backward scattered SHG may not be the major source of backward SHG in the mouse tail tendon, which means significant SHG is purely generated in the backward direction. A large phase mismatch exists in generating backward SHG. Nevertheless, significant backward generated SHG has been observed in collagen tissues. We hypothesize that the periodic lattice structure of fibrillar collagen can provide a virtual momentum to assist the backward phase matching. Here the backward SHG phase matching is investigated in theory, simulation, and experiments, which are consistent and support the hypothesis. The various properties investigated in this thesis can provide a better understanding about SHG in collagen tissues and lead to new applications of SHG microscopy in diagnosing collagen related diseases in the future.Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate
9
Wang, Jing-Yi. "Nonlinear processes in intracavity second harmonic generation." Doctoral thesis, Universite Libre de Bruxelles, 1996. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/212351.
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10
Patrick, Brian Olivier. "Second-harmonic generation studies of organic salts." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq25133.pdf.
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11
Travers, Paul James. "Langmuir-blodgett films for second harmonic generation." Thesis, Coventry University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.254209.
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12
Wijeratne, I. "Second harmonic generation in novel optical waveguides." Thesis, City University London, 2013. http://openaccess.city.ac.uk/3015/.
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Second Harmonic Generation has traditionally been restricted to crystals; however, due to the development of highly sophisticated fabrication technology, poling and phase matching techniques, it has now become feasible in glass fibres and waveguides which are widely used in nonlinear optics. For instance, silica glass based Photonic Crystal Fibres (PCF) exhibit long coherence lengths and controllable optical properties such as chromatic dispersion despite low second order nonlinearity. Given such benefits, the numerical modelling and analysis of optical waveguides accurately and efficiently has become vital for the advancement of nonlinear optics. Hence, this thesis focuses on enhancing the Second Harmonic Generation in optical waveguides through the use of different structures and different materials, and demonstrating the same by numerical simulations. In this thesis, the accurate and numerically efficient Finite Element based Beam Propagation Method has been employed to investigate the evolution of Second Harmonic Generation in highly nonlinear SF57 soft glass Equiangular Spiral PCFs. Further, the H-field based Finite Element Method has been employed for the stationary analysis of Photonic Crystal Fibres. It is shown here that the second harmonic output power in highly nonlinear
13
Haslam, Steven. "Second harmonic generation from liquid-liquid interfaces." Thesis, University of Southampton, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266382.
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14
Fordyce, Adam James Graham. "Second-harmonic generation at liquid/air interface." Thesis, University of Southampton, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297873.
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Leeson, Paul. "Langmuir-Blodgett films for second harmonic generation." Thesis, Cranfield University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323931.
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16
Vecchi, Chiara. "Second harmonic generation in engineered silicon waveguides." Doctoral thesis, Università degli studi di Trento, 2021. http://hdl.handle.net/11572/298556.
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In the last years, Silicon becomes one of the most important technological platform for integrated photonics technologies. Nonlinear silicon photonics is a desired upgrade of this thecnology as it gives the opportunity to directly process the signal on the chip by using the wide spectrum of nonlinear phenomena. To have access to high order nonlinearities a large optical pump power is needed. Second order nonlinear effects are desirable due to the reduction of the used power with respect to third order nonlinearities. Moreover, it allows to achieve interesting efforts, such as wavelength conversion and generation of quantum states. Here the problem is that silicon has a diamond crystalline structure. Therefore, silicon is a centrosymmetric material. For a geometrical point of view, this property is reflected in a symmetry of the polarization vector P(E) = -P(-E) . The polarization vector is related to the electric field by: P = P^0 + P^(2) + P^(3) +... From equation 2, it is possible to see that, in order to respect the centrosymmetry, chi^(2) =0. So, in the dipole approximation, second order nonlinearities are inhibited in Silicon. Many efforts have been spent to induce second order nonlinearities in Silicon. At first, strained silicon, in which the centrosymmetry of Silicon crystalline structure is broken by an inhomogeneous strain, seemed to be the most viable solution. In strained silicon waveguides, the inhomogeneous strain is applied by a stressing layer of different materials with a different lattice constant deposited on top of the waveguide [4]. The first experiment based on Silicon waveguides was performed in 2006 by Jacobsen et al. that measured a nonlinear coefficient chi^(2) = 15 pm/V with a SiN stressing layer via DC electro-optic effect. This work was followed by many others, reaching values for the strain-induced second order nonlinear coefficient chi^(2) up to 340 pm/V. Few works gave a different interpretation of the chi^(2). It was demonstrated that during the deposition of the stressing layer there is the formation of
dangling bonds at the interface between the deposited layer and the silicon waveguide. These dandling bonds act as positive fix ions. The formation of this charges, indeed, determined an abundance of free-carriers in the core of the waveguide that, because of the free carrier dispersion, can affect the value of the effective measured nonlinear coefficient in the DC electro-optic effect. Azadeh et al. demonstrated for the firs time the crucial role of this phenomenon which overtakes the strain effect, also confirmed by Olivares et al. An upper limit of chi^(2) = 8 pm/V due to a strain effect was experimentally fixed. Other works investigated second order nonlinearities in Silicon looking at the Second Harmonic Generation (SHG). Cazzanelli et al. measured a value of chi^(2) = 40 pm 30 pm/V by SHG in multimodal waveguides using a pump wavelength above 2 um, without any phase matching mechanism. It was also demonstrated that stressing layers that induced the same value of strain but realized with different materials yield different SHG, making clear that not only strain but also charged defects play an important role in the generation of the SH signal. Indeed, it was demonstrated that charged defects can induce an electric DC field that interacts with the large chi^(3) of bulk silicon to give a dressed (effective) second order nonlinear coefficient chi^(2)_EFISH = 3 chi^(3) E_DC via electric-field-induced second harmonic (EFISH) generation. So in 2017 the effect of the strain on silicon waveguides was not clear. The aim of my PhD work is try to understand the origin of the dressed chi^(2) in silicon waveguide and propose a way to engineer and control it.
In order to understand the origin of second order nonlinearities in silicon, an experiment that can separate the role of the strain and the role of the trapped charged defects at the interface between the silicon waveguide and the stressing layer in an unambiguously way was performed. The sample used was composed by a set of strip silicon waveguides 243 nm thick with a SiN stressing layer of 140 nm deposited on the top of the waveguide. The waveguides were engineered in order to have intermodal phase matching condition between the TM1 mode for the pump wavelength and TE3 mode for the generated SH wavelength. Different widths of the waveguide have been used in order to tune the phase-matching condition wavelength. To investigate the role of the strain, the sample was mounted on a sample holder equipped with a screw to deformed the waveguide. Rotating the screw, a vertical displacement Delta_H is induced in the center of the sample orthogonal to its main plain. This displacement acts as an external load that increase the strain in the silicon waveguide. SHG was measured for different values of the Delta_H displacement. Increasing the load in the sample there is a red-shift of peak. Indeed, increasing the strain in the sample a change in the effective index is induced, and a change in the phasematching condition is obtained. However, SH power is always the same, revealing that the value of chi^(2) is not increasing with the strain. To investigate the role of the trapped defect at the Si/SiN interface, following the idea of Piccoli et al., the sample was exposed to UV irradiation to induce a passivation (i.e. neutralization) of the defects. Then, SHG was measured and no generation can be detected. These results clarify that the main causes of the SH in silicon waveguide is not given by the strain but by the charge defect and an upper limit of chi^(2) at 0,05 pm/V for the strain induced second order nonlinear coefficient was experimentally fixed. This result is also supported by an earlier theoretical estimation given by Khurgin et al. in 2015.
From these observations, the use of an applied electric field emerges as a way to induce a controlled effective chi^(2) in silicon waveguide suitable for technological application. The idea is based on the use of a controlled external E_DC field in order to obtain the desired value of chi^(2) where the electric field can be generated by placing lateral p-i-n junctions across the waveguide that can be reverse biased using metallic pads. In this way, chi^(2) can be enhanced increasing the applied bias and the only limitation is the breakdown field of silicon, that is known to be around V = 24 V. Timurdogan et al. demonstrated that it is also possible to use the periodicity of the p-i-n junctions to absorb the mismatch between the pump and the SH modes in order to obtain a quasi-phase matching condition. The sample used was a set of rib waveguides with different widths. Along the propagation direction of the waveguide p-i-n junctions have been grown. Since in the generation efficiency what matters is not the overall chi^(2) but the amplitude of its oscillations along the length of the waveguide, an interdigitated poling configuration was studied. In this configuration, regions of p-i-n junctions and regions of n-i-p junctions are periodically alternated. Second harmonic generation was observed in this poled waveguide and the
SH signal increased quadratically with both the pump power and the applied bias, according with the theory. It was also demonstrated that a larger conversion efficiency is obtained using this poling configuration instead of the poling configuration proposed by Timurdogan in 2017.
Also a modeling of the effect of the fabrication defects has been done. The pump P_p and the generated P_SH powers are related by P_SH = P_p^2|gamma^(2)|^2 L^2 S where S is the poling therm which describes what is happening along the length of the waveguide. S is a function of the geometry of the waveguide and of the periodicity of the p-i-n junctions: S=1/L^2 |int_0^L s(z) exp(i Delta beta z) dz|^2. During the fabrication, an unwanted variation of the geometrical parameters can be induced along the length of the waveguide both in the waveguide cross section and in the
poling period. The effect of this two kind of variations has been studied. Moreover, the coherence length of the process has been also studied, in order to have a clear understanding of the EFISH process. the developed model was compared with the experimental data. It is possible to extract the effective Delta chi^(2) of the EFISH process with an interdigitated poling configuration, when 24 V are applied to the junctions: Delta chi^(2)_eff=78 pm 3 pm/V.
Finally it was perform a study of microrings that can accomodate geometrical defects. Using a 4-bar symmetry of the chi^(2) tensor, a study of the conversion efficiency as a function of the different parameters of the microring has been performed. It was demonstrated that the most critical parameter is the thickness of the waveguide in the ring and it was shown a method to find a geometry that allows to have efficient conversion efficiency in a range of thickness of 16 nm around the nominal value. Moreover, this method is more general, since it is based only on the symmetry of the nonlinear tensor. Therefore, it can be easily applied to other materials.
17
Vecchi, Chiara. "Second harmonic generation in engineered silicon waveguides." Doctoral thesis, Università degli studi di Trento, 2021. http://hdl.handle.net/11572/298556.
Full textAbstract:
In the last years, Silicon becomes one of the most important technological platform for integrated photonics technologies. Nonlinear silicon photonics is a desired upgrade of this thecnology as it gives the opportunity to directly process the signal on the chip by using the wide spectrum of nonlinear phenomena. To have access to high order nonlinearities a large optical pump power is needed. Second order nonlinear effects are desirable due to the reduction of the used power with respect to third order nonlinearities. Moreover, it allows to achieve interesting efforts, such as wavelength conversion and generation of quantum states. Here the problem is that silicon has a diamond crystalline structure. Therefore, silicon is a centrosymmetric material. For a geometrical point of view, this property is reflected in a symmetry of the polarization vector P(E) = -P(-E) . The polarization vector is related to the electric field by: P = P^0 + P^(2) + P^(3) +... From equation 2, it is possible to see that, in order to respect the centrosymmetry, chi^(2) =0. So, in the dipole approximation, second order nonlinearities are inhibited in Silicon. Many efforts have been spent to induce second order nonlinearities in Silicon. At first, strained silicon, in which the centrosymmetry of Silicon crystalline structure is broken by an inhomogeneous strain, seemed to be the most viable solution. In strained silicon waveguides, the inhomogeneous strain is applied by a stressing layer of different materials with a different lattice constant deposited on top of the waveguide [4]. The first experiment based on Silicon waveguides was performed in 2006 by Jacobsen et al. that measured a nonlinear coefficient chi^(2) = 15 pm/V with a SiN stressing layer via DC electro-optic effect. This work was followed by many others, reaching values for the strain-induced second order nonlinear coefficient chi^(2) up to 340 pm/V. Few works gave a different interpretation of the chi^(2). It was demonstrated that during the deposition of the stressing layer there is the formation of
dangling bonds at the interface between the deposited layer and the silicon waveguide. These dandling bonds act as positive fix ions. The formation of this charges, indeed, determined an abundance of free-carriers in the core of the waveguide that, because of the free carrier dispersion, can affect the value of the effective measured nonlinear coefficient in the DC electro-optic effect. Azadeh et al. demonstrated for the firs time the crucial role of this phenomenon which overtakes the strain effect, also confirmed by Olivares et al. An upper limit of chi^(2) = 8 pm/V due to a strain effect was experimentally fixed. Other works investigated second order nonlinearities in Silicon looking at the Second Harmonic Generation (SHG). Cazzanelli et al. measured a value of chi^(2) = 40 pm 30 pm/V by SHG in multimodal waveguides using a pump wavelength above 2 um, without any phase matching mechanism. It was also demonstrated that stressing layers that induced the same value of strain but realized with different materials yield different SHG, making clear that not only strain but also charged defects play an important role in the generation of the SH signal. Indeed, it was demonstrated that charged defects can induce an electric DC field that interacts with the large chi^(3) of bulk silicon to give a dressed (effective) second order nonlinear coefficient chi^(2)_EFISH = 3 chi^(3) E_DC via electric-field-induced second harmonic (EFISH) generation. So in 2017 the effect of the strain on silicon waveguides was not clear. The aim of my PhD work is try to understand the origin of the dressed chi^(2) in silicon waveguide and propose a way to engineer and control it.
In order to understand the origin of second order nonlinearities in silicon, an experiment that can separate the role of the strain and the role of the trapped charged defects at the interface between the silicon waveguide and the stressing layer in an unambiguously way was performed. The sample used was composed by a set of strip silicon waveguides 243 nm thick with a SiN stressing layer of 140 nm deposited on the top of the waveguide. The waveguides were engineered in order to have intermodal phase matching condition between the TM1 mode for the pump wavelength and TE3 mode for the generated SH wavelength. Different widths of the waveguide have been used in order to tune the phase-matching condition wavelength. To investigate the role of the strain, the sample was mounted on a sample holder equipped with a screw to deformed the waveguide. Rotating the screw, a vertical displacement Delta_H is induced in the center of the sample orthogonal to its main plain. This displacement acts as an external load that increase the strain in the silicon waveguide. SHG was measured for different values of the Delta_H displacement. Increasing the load in the sample there is a red-shift of peak. Indeed, increasing the strain in the sample a change in the effective index is induced, and a change in the phasematching condition is obtained. However, SH power is always the same, revealing that the value of chi^(2) is not increasing with the strain. To investigate the role of the trapped defect at the Si/SiN interface, following the idea of Piccoli et al., the sample was exposed to UV irradiation to induce a passivation (i.e. neutralization) of the defects. Then, SHG was measured and no generation can be detected. These results clarify that the main causes of the SH in silicon waveguide is not given by the strain but by the charge defect and an upper limit of chi^(2) at 0,05 pm/V for the strain induced second order nonlinear coefficient was experimentally fixed. This result is also supported by an earlier theoretical estimation given by Khurgin et al. in 2015.
From these observations, the use of an applied electric field emerges as a way to induce a controlled effective chi^(2) in silicon waveguide suitable for technological application. The idea is based on the use of a controlled external E_DC field in order to obtain the desired value of chi^(2) where the electric field can be generated by placing lateral p-i-n junctions across the waveguide that can be reverse biased using metallic pads. In this way, chi^(2) can be enhanced increasing the applied bias and the only limitation is the breakdown field of silicon, that is known to be around V = 24 V. Timurdogan et al. demonstrated that it is also possible to use the periodicity of the p-i-n junctions to absorb the mismatch between the pump and the SH modes in order to obtain a quasi-phase matching condition. The sample used was a set of rib waveguides with different widths. Along the propagation direction of the waveguide p-i-n junctions have been grown. Since in the generation efficiency what matters is not the overall chi^(2) but the amplitude of its oscillations along the length of the waveguide, an interdigitated poling configuration was studied. In this configuration, regions of p-i-n junctions and regions of n-i-p junctions are periodically alternated. Second harmonic generation was observed in this poled waveguide and the
SH signal increased quadratically with both the pump power and the applied bias, according with the theory. It was also demonstrated that a larger conversion efficiency is obtained using this poling configuration instead of the poling configuration proposed by Timurdogan in 2017.
Also a modeling of the effect of the fabrication defects has been done. The pump P_p and the generated P_SH powers are related by P_SH = P_p^2|gamma^(2)|^2 L^2 S where S is the poling therm which describes what is happening along the length of the waveguide. S is a function of the geometry of the waveguide and of the periodicity of the p-i-n junctions: S=1/L^2 |int_0^L s(z) exp(i Delta beta z) dz|^2. During the fabrication, an unwanted variation of the geometrical parameters can be induced along the length of the waveguide both in the waveguide cross section and in the
poling period. The effect of this two kind of variations has been studied. Moreover, the coherence length of the process has been also studied, in order to have a clear understanding of the EFISH process. the developed model was compared with the experimental data. It is possible to extract the effective Delta chi^(2) of the EFISH process with an interdigitated poling configuration, when 24 V are applied to the junctions: Delta chi^(2)_eff=78 pm 3 pm/V.
Finally it was perform a study of microrings that can accomodate geometrical defects. Using a 4-bar symmetry of the chi^(2) tensor, a study of the conversion efficiency as a function of the different parameters of the microring has been performed. It was demonstrated that the most critical parameter is the thickness of the waveguide in the ring and it was shown a method to find a geometry that allows to have efficient conversion efficiency in a range of thickness of 16 nm around the nominal value. Moreover, this method is more general, since it is based only on the symmetry of the nonlinear tensor. Therefore, it can be easily applied to other materials.
18
Domínguez, Juárez Jorge Luís. "Whispering gallery microresonator for second harmonic light generation." Doctoral thesis, Universitat Politècnica de Catalunya, 2014. http://hdl.handle.net/10803/279215.
Full textAbstract:
In recent years, it has been proposed that circular microresonators may become an important element in the core of many photonic devices. The high Q-factors seen in fused silica micro-spheres and micro-toroids for light coupled in the whispering gallery modes (WGMs) inside the micro-resonator led to many new developments in a diversity of fields. Indeed, WGM micro-resonators have found applications in laser oscillation, optical filtering, bio and chemical sensing, frequency stabilization, quantum electrodynamics experiments, nonlinear parametric conversion and in many other light-matter interaction processes where light recirculation is an essential ingredient. For second and third order nonlinear optical phenomena a high-Q micro circular cavity is an ideal framework to lower the light intensity or material density and still obtain a measurable interaction. This may become particularly useful when the nonlinear interaction is considered on the sphere surface because at an interface centro-symmetry is always broken. In this thesis, we approach the problem of obtaining SHG with the smallest amount of material possible. Our goal is to demonstrate that WGMs in micro-sphere resonators are an optimal option to consider such type of non-linear interaction. SHG from a small amount of material may found interesting applications in high sensitivity unmarked detection of low numbers of very small objects such as molecules, viruses or other types of nano-particles.
The different experimental and theoretical developments we implemented to achieve such goal are reported in the four chapters of the current thesis. In chapter 1 we introduce basic concepts of spherical micro-resonators an their interest. Theoretical aspects of light propagation and nonlinear light generation in the whispering gallery modes in such micro-resonators are discussed in Chapter 2. A new method to obtain patterns of non-linear material is presented in Chapter 3. In Chapter 4, the developments presented in the previous chapters are combined to obtain second harmonic generation in the whispering gallery modes of microspheres. In this chapter we report the design and fabrication of a nonlinear spherical resonator to experimentally measure SHG from molecules deposited on its surface. Such nonlinear interaction is quasi-phase matched by implementing the periodical patterning reported in Chapter 3 on a molecular layer deposited on the surface of a micro-sphere. By coupling laser light pulses at the fundamental frequency into the whispering gallery modes of the high-Q spherical micro-resonators we demonstrate that a signal at the second harmonic (SH) frequency can be measured when less than 100 molecules contribute in the nonlinear interaction. Finally, applications of such type of generation in highly sensitive sensing are discussed.En años recientes los microresonadores circulares han sido propuestos como un elemento central para formar parte de muchos dispositivos fotónicos. El alto factor de calidad observado en microesferas o microtoroides de sílice cuando la luz se propaga en modos "whispering gallery" (WG) ha dado lugar a un gran número de nuevos desarrollos en campos muy diversos. En efecto, los micro resonadores con modos WG han encontrado aplicación en la oscilación laser, en el filtrado óptico, en sensores bioquímicos, como estabilizadores de frecuencia, en experimentos de electrodinámica cuántica, en la conversión paramétrica no lineal y en muchas otros procesos donde la recirculación de luz es un ingrediente esencial para su interacción con la materia. En fenómenos ópticos no lineales de segundo y tercer orden, la micro cavidad circular con un alto factor de calidad constituye una estructura ideal para poder obtener una interacción medible incluso cuando se consideran pequeñas intensidades de luz o bajas densidades de materia. Esto puede resultar particularmente útil en la superficie de la microesfera ya que en la interface entre dos materiales se rompe la simetría de inversión incluso cuando los materiales son centro simétricos. En esta tesis abordamos la generación de segundo armónico con una cantidad mínima de material. Nuestra meta es demostrar que los modos WG en resonadores de microesfera son una opción óptima para poder considerar este tipo de interacción no lineal. La generación de segundo armónico con una cantidad muy pequeña de material puede encontrar aplicaciones interesantes en la detección de muy pocos objetos pequeños tales como moléculas, viruses o cualquier otro tipo de nanopartículas. Los diferentes desarrollos experimentales y teóricos que implementamos para alcanzar nuestro objetivo están explicados en los cuatro capítulos de esta tesis. En el Capítulo 1 introducimos conceptos básicos de microresonadores esféricos y su interés. Aspectos teóricos de la propagación y generación no lineal de luz de los modos WG en dichos resonadores se discuten en el Capítulo 2. Un método nuevo para generar patrones de material no lineal se presenta en el Capítulo 3. En el Capítulo 4, los desarrollos de los capítulos previos presentados se combinan para implementar la generación de segundo armónico en los modos WG de las microesferas. En este capítulo reportamos el diseño y la fabricación del resonador esférico no lineal para llegar a medir experimentalmente la generación de segundo armónico de las moléculas depositadas en su superficie. Dicha interacción no lineal se obtiene en la configuración "quasi-phase matched" implementando el mecanismo de escritura de patrones reportado en el Capitulo 3, sobre una capa molecular depositada en la superficie de la microesfera. Mediante el acoplamiento de pulsos de luz láser a la frecuencia fundamental en los modos WG de un microresonador esférico con un alto factor de calidad Q, demostramos que la señal a la frecuencia de segundo armónico puede ser medida, menos de 100 moléculas contribuyen a esta interacción no lineal. Finalmente, se discuten aplicaciones de ese tipo de generación para la detección altamente sensible.
19
Shaw, Christopher P. "Polymeric materials for piezoelectricity and second harmonic generation." Thesis, Cranfield University, 1991. http://dspace.lib.cranfield.ac.uk/handle/1826/3674.
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Studies have been undertaken to utilise the possible potential of the rodlike, helical structures associated with polyglutamates and polyisocyanates for piezoelectric (PE) and nonlinear optical (second harmonic generation (SHG)) applications. Various techniques have been employed to form samples/films of these polymers containing oriented helices whose bulk structures are non-centrosymmetric, (an important criterium for the aforementioned applications). Owing to the poor yields obtained for certain intermediates in the synthetic stages of these polymers, only poly('S-benzyl-L-glutamate) (PBzLG) and poly(n- hexylisocyanate) (PHIC) were available for subsequent studies. Piezoelectric work was limited to hydrostatic measurements (d3h) made on electrically poled, composite (guest host), polymer samples. Phase separation was common in all the samples, but no piezoelectric response was observed. However, low concentration (not greater than 10% w/w) of active polymer (PBzLG or PHIC) and high conductivity during the poling stage, may have accounted for the lack of response. Electrically poled, homopolymer samples of PBzLG and PHIC were achieved using a solvent evaporation technique. Nonlinear optical studies of these poled samples revealed threshold fields above which detectable levels of SHG could be observed, (i.e. PBzLG > 40 V/mm, PHIC > 150 V/mm). The variation of SHG signal versus the angle of polarisation of the incident laser light (1064 nm) relative to the poling direction of the film, implied biaxial symmetry was present in the case of PBzLG, whereas the more conventional uniaxial symmetry was observed for PHIC. The variation in SHG signal observed for a fixed thickness was attributed to varying degrees of alignment, resulting from uneven poling. Although PHIC and PBzLG showed low SHG activity (less than value for urea), little ageing of this activity occurred over the 6 month testing period. Langmuir Blodgett studies carried out on chemically modified, low molecular weight PBzLG molecules showed poor transference of the monolayer to a quartz substrate once ten layers had been deposited. In addition, areas per molecule (or per residue) calculated from the pressure-area isotherms, proved inconclusive when deducing possible orientations for the PBzLG helices. No SHG signal was observed for the L.B. films.
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Baten, Shah Mohammad Abdul. "Optical second harmonic generation studies of electrochemical interfaces." Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/9321.
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Electrochemical oxidation of metal electrodes in aqueous media has been examined by in situ optical second harmonic generation (SHG), a nonlinear optical technique of second order. Simultaneous SHG and cyclic voltammetry experiments were carried out on Cu electrodes in alkaline media. The SHG response was found to be sensitive as Cu was oxidised first to Cu2O and then to CuO. The formation of Cu2O causes resonant contribution to the SHG signals due to the band-gap of Cu2O. As the upper layer, CuO is formed; it generates an electric-field induced second harmonic (EFISH) response. When the oxides layers are reduced, the SHG intensity changes markedly. The correlation of oxidation and reduction charge with the SHG signal intensity is found to be a useful method to investigate the oxide formation. The oxidation of Au electrodes in acidic media has been investigated. The initial growth of the compact (or α-) oxide causes a decrease in SHG intensity which is suggested to be the effect of the oxide growth on surface plasmons originated from the d-electrons in Au. When the thicker hydrous (or β-) oxide layers are formed at constant potentials on top of the α-oxide, the reductions of them are accompanied by remarkable sharp peak in the SHG response that appear just before any reduction charges begin to pass. As the β-oxide layer gets thicker with longer oxidation time and then reduced, the initial peak evolves into two before merging to form one broad peak. The SHG peaks are suggested to be linked to an order-disorder transition phenomenon at the α-/β-oxide interface; or it can also be due to the presence of the surface traps. These investigations have shown that the SHG technique with its inherent submonolayer sensitivity can be a useful technique to study electrochemical oxidation of metal electrodes.
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Stoller, Patrick C. "Polarization-modulated second harmonic generation microscopy in collagen /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2002. http://uclibs.org/PID/11984.
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Hamelin, Nicholas. "Second harmonic generation on ion implanted optical waveguides." Thesis, University of Sussex, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357681.
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Alexander, Alasdair Kiernan. "Investigation of interfaces by second harmonic ellipsometry." Thesis, University of Southampton, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.340524.
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Ctistis, Georgios. "Second harmonic Generation mittels Rasternahfeldmikroskopie Aufbau und erste Messungen." Berlin dissertation.de, 2006. http://deposit.d-nb.de/cgi-bin/dokserv?id=2863084&prov=M&dok_var=1&dok_ext=htm.
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Ripault, Quentin. "Second-Harmonic generation in helium-implanted 2D-PPLN waveguides." Paris 13, 2013. http://scbd-sto.univ-paris13.fr/secure/edgalilee_th_2013_ripault.pdf.
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The optical confinement for second-harmonic generation (SHG) by Quasi-Phase Matching (QPM) has the interest to highly improve the conversion performances from the periodically poled structures (PP). It allows the use of low pump-power. The originality of our works is that we have performed optical waveguides by helium implantation at MeV energies in congruent and MgO doped 2D-PPLN, having a square PP lattice and a periodicity of 6. 92 µm. Firstly, we have measured the linear properties of our samples by nondestructive methods. The refractive index profiles reconstruction by i-WKB method of the waveguides (no et ne) have been estimated from the effective indices measured at 532 nm, 633 nm and 1064 nm by prism-coupling method (m-line by reflection). We have also measured the overall losses of the samples in implanted PP zone with CCD-camera at these wavelengths. A SHG experimental setup has been built in order to characterise and compare the nonlinear properties of our 2D-PPLN in bulk and waveguide configurations (SHG at different QPM orders according to temperature, SHG emission angle, conversion efficiency). The nonlinear optical setup uses a microscope objective -coupling system - optical fibre-decoupling system and the pump is a cw-laser diode at 1064 nm, allowing a maximum optical power of 300 mW. We find a conversion efficiency of 6. 8 %/W in waveguide configuration and 0. 4 %/W in bulk configurationLe confinement optique dans le cadre de la génération second-harmonique (GSH) par Quasi-Accord de Phase (QAP) a l’intérêt d’améliorer grandement les performances de conversion de la structure Périodiquement Polarisée (PP), autorisant l’utilisation de sources lasers à faible puissance de pompe. L’originalité de notre travail est d’avoir réalisé ces guides d’ondes par implantation d’ions He+ à des énergies de l’ordre du MeV dans des PPLN 2D congruent non dopés et dopés MgO à 5%, de maille PP carrée et de période 6,92 µm. Dans un premier temps nous avons cherché à mesurer les propriétés linéaires de nos échantillons par des méthodes non-destructives. La reconstruction des profils d’indice de réfraction i-WKB de nos guides d’ondes (no et ne) ont été extrapolé a partir de la mesure des indices effectifs a 532 nm, 633 nm et 1064 nm, et en utilisant la méthode du couplage par prisme (m-line en réflexion). Nous avons également mesuré les pertes optiques globales des échantillons dans la zone PP implantée avec une camera CCD à ces longueurs d’ondes. Un dispositif expérimental de GSH a également été monté afin de caractériser et comparer les propriétés non-linéaires de nos PPLN-2D massifs et guides (GSH pour différents ordres du QAP et suivant la température, angle d’émission de la GSH, efficacité de conversion). Le banc de caractérisation d’optique non-linéaire utilise un système de couplage par objectif de microscope - découplage par fibre et utilisant comme source une diode laser à 1064 nm en continue, pouvant monter à une puissance optique de 300 mW. Nous avons trouvé une efficacité de conversion de 6. 8 %/W pour le guide et de 0,4 %/W dans le substrat
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Ciracì, Cristian. "Study of second-harmonic generation in nonlinear nanostructured materials." Thesis, Montpellier 2, 2010. http://www.theses.fr/2010MON20053.
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Au cours de ces 20 dernières années, une attention particulièrement soutenue a été donnée à l'étude et à la fabrication de matériaux nano-structurés permettant le contrôle de la lumière. Cependant, les propriétés de non-linéarité optique de ces nouveaux matériaux n'ont que très peu été explorées. Partant de ce constat, cette thèse se propose de pourvoir cette insuffisance. L'accent est mis en particulier sur le processus de génération de seconde harmonique à travers deux aspects fondamentaux: (i) le contrôle de l'émission de seconde harmonique pour des matériaux nano-structurés non-linéaires et (ii) l'augmentation de conversion dans des dispositifs photoniques intégrés. Nous présentons un nouveau phénomène de localisation non-linéaire qui a lieu dans des matériaux main-gauche et qui implique un accord de phase isotrope. Nous démontrons analytiquement le processus de localisation dans un milieu homogène main-gauche, avant de mettre en évidence un tel effet dans des cristaux photoniques non-linéaires à l'aide de simulations numériques. L'effet de localisation contra-propagative du second harmonique est utilisé pour le design d'une lentille de second-harmonique. Ce résultat théorique a été démontré numériquement pour une structure réalisable fonctionnant aux fréquences optiques. L'augmentation de génération de seconde harmonique constitue l'aspect complémentaire. En tirant parti de la forte localisation de lumière dans une chaîne de nano-tiges de dimension finie, nous montrons que, pris ensemble, le confinement transverse sub-longueur d'onde et la condition de résonance d'accord de phase contribuent de manière importante à l'augmentation de la génération de seconde harmonique. Les capacités de guidage sub-longueur d'onde de chaînes de nano-tiges sont mis en évidence en examinant leurs propriétés de propagation linéaire. Pour finir, nous nous penchons sur la condition d'accord de phase assurant l'interaction non-linéaire optimaleThe past twenty years have been exceptionally rich on the study and fabrication of nanostructured materials to control light, but no much attention was given to nonlinear optical properties of these novel materials. In this context, the present thesis would partially address this gap. In particular, we focus on the second-harmonic generation process, by considering two fundamental aspects: the second-harmonic emission control by means of nanostructured nonlinear materials and the conversion enhancement in integrated photonic devices. A novel nonlinear localization phenomenon occurring in left-handed materials and involving isotropic phase-matching is presented. We analytically demonstrate the localization process in a homogenous left-handed material and by numerical simulation we show the effect for nonlinear photonic crystals. The backward second-harmonic localization effect is used to design a second-harmonic lens. This interesting theoretical result is numerically shown for a feasible structure working at optical frequencies. The second-harmonic generation enhancement is the complementary aspect. By taking advantage of the strong light localization achieved in finite size dielectric nonlinear nanorod chains, we show that sub-wavelength transversal confinement, together with the resonant phase-matching condition, adds an important property to the second-harmonic generation enhancement. A study of linear propagation properties of nanorod chain structures first evidences its sub-wavelength guiding capabilities. Finally, the phase-matching condition that assures the maximal nonlinear interaction in this kind of structure is presented
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Wilson, Philip Trent. "Second harmonic generation spectroscopy using broad bandwidth femtosecond pulses /." Digital version accessible at:, 2000. http://wwwlib.umi.com/cr/utexas/main.
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Parkinson, Porshia Shane. "Silicon germanium growth kinetics and second harmonic generation studies." Digital version:, 2000. http://wwwlib.umi.com/cr/utexas/fullcit?p9992884.
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Fluck, Daniel. "Ion-implanted KNbO₃ waveguides for blue-light second-harmonic generation /." Zürich, 1995. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=11225.
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Letizia, Rosa. "Numerical Modelling of Photonic Crystal Devices for Second Harmonic Generation." Thesis, University of Leeds, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.509006.
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Airey, Robert James. "Second-harmonic generation from monolayer and multilayer Langmuir-Blodgett films." Thesis, Cranfield University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360221.
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Tancogne-Dejean, Nicolas. "Ab initio description of second-harmonic generation from crystal surfaces." Palaiseau, Ecole polytechnique, 2015. https://tel.archives-ouvertes.fr/tel-01235611v2/document.
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Plus de 50 ans après la première observation expérimentale de la génération de deuxième harmonique, la description théorique de la génération de deuxième harmonique est toujours sujette à débat, alors qu'elle est bien comprise d'un point de vue expérimental. C'est ce fossé que cette thèse vise à combler. Ce travail a pour but d'améliorer la description théorique ainsi que la compréhension de la génération de deuxième harmonique à la surface des cristaux semi-conducteurs. Lorsque l'on applique un champ électrique extérieur à un matériau diélectrique, des dipôles électriques se créent au niveau microscopique. Ces dipôles sont responsables de l'apparition, à l'intérieur du matériau, d'un champ induit. Les fluctuations du champ électrique à l'échelle microscopique, les fluctuations de la densité ou tout type d'inhomogénéités microscopiques doivent être pris en compte lorsque l'on décrit les propriétés optiques d'un système. Ces effets sont souvent appelés “effets des champs locaux”. Ces effets des champs locaux ont été largement étudiés par le passé et en particulier leurs effets sur les propriétés optiques des matériaux massifs est maintenant bien établi. Dans le cas des surfaces, la description théorique et les simulations numériques sont plus compliquées que pour les matériaux massifs. Le changement abrupt de la densité électronique conduit à une variation importante du champ électrique à l'interface avec le vide. Par conséquent, de forts effets dû au champ local sont attendus, en particulier dans la direction perpendiculaire au plan de la surface. Le but de cette thèse est de quantifier à quel point ces effets affectent les propriétés optiques linéaires et non-linéaires des surfaces. Une théorie macroscopique de la génération de deuxième harmonique à la surface des cristaux a été développée afin de tenir compte des effets dû aux champs locaux. Ces derniers sont calculés à partir des premiers principes, dans le cadre de la théorie de la fonctionnelle de la densité dépendante du temps (TDDFT). L'intérêt principal de cette thèse est la description de la réponse non-linéaire des surfaces, mais de nouveaux outils théoriques permettant une meilleure description des champs locaux et de leurs effets sur les propriétés optiques linéaires ont aussi été développé. Les simulations numériques se sont focalisées sur la surface Si(001), et le formalisme macroscopique développé durant cette thèse a été appliqué à trois reconstructions de surface, ici la surface propre Si(001)2x1, la surface monohydrique Si(001)2x1:H et la surface dihydrique Si(001)1x1:2H. Des comparaisons avec les résultats expérimentaux disponibles sont aussi présentéesMore than 50 years after the first experimental observation of second-harmonic generation, the theoretical description of second-harmonic generation is still under debate, whereas it is well understood from an experimental point of view. This is the gap that this thesis aims to fill. This work aims to improve the theoretical description and understanding of the generation of second-harmonic from the surfaces of crystalline semiconductors. When applying an external electric field to a dielectric material, electric dipoles are created at a microscopic level. These dipoles are responsible for the apparition, inside the material, of an induced field. The fluctuations of the electric field at a microscopic level, the density fluctuations or any kind of microscopic inhomogeneities must be taken into account when describing the optical properties of a system. These effects are often referred as “local-field effects”. These local-field effects have been widely studied in the past and in particular their effects on the optical properties of bulk materials are now well established. In the case of surfaces, the theoretical description and the numerical simulations are more intricate than for bulk materials. The abrupt change in the electronic density leads to a huge variation of the electric field at the interface with vacuum. As a result, strong effects of the local-field are expected, in particular in the direction perpendicular to the plane of the surface. The goal of this thesis is to quantify how important these effects are for the linear and second-order optical properties of surfaces. A macroscopic theory of second-harmonic generation from crystal surfaces has been developed in order to account for local-field effects. The latter are calculated from first-principles, in the framework of the Time-Dependent Density-Functional Theory (TDDFT). The primary interest is the description of non-linear optical responses of surfaces, but new theoretical tools for improving the description of local-field effects in the case of linear optics have also been developed. The numerical simulations have been focused on the Si(001) surface, and the macroscopic formalism developed during this thesis has been applied to three surface reconstructions, namely the clean Si(001)2x1, the monohydride Si(001)2x1:H and the dihydride Si(001)1x1:2H surfaces. Comparison with available experimental results is also reported
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SanGiorgio, Paul. "Measuring Electron Gas Relaxation in Gold through Second Harmonic Generation." Scholarship @ Claremont, 2001. https://scholarship.claremont.edu/hmc_theses/136.
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In a thermally equilibrated system, electron behavior in a metal is described by the Fermi-Dirac equation. With ultrafast lasers, electrons can be excited into temporary distributions which are not described by the Fermi-Dirac equation and are therefore not at a well-defined temperature. These nonthermal distributions quickly equilibrate through two primary processes: electron-electron scattering and electron-phonon scattering. In most situations, these effects are unnoticeable, since they are completed within 5 ps. A probabilistic numerical model for electron-electron scattering is presented. The model is robust, scaleable, and requires only one parameter. The success of the model suggests future work on a similar electron-phonon scattering model, which would provide a complete description of the elctron distribution during thermalization. Once complete, this model can be tested by measuring the amount of second harmonic light generated by an ultrafast laser in a pump-probe experiment.
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Andersen, Audrée. "Surfactants dynamics at interfaces a series of second harmonic generation experiments /." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=978991125.
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Viarbitskaya, Sviatlana. "Resonance-enhanced Second Harmonic Generation from spherical microparticles in aqueous suspension." Doctoral thesis, Stockholm University, AlbaNova University Center (together with KTH), 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-7517.
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Second harmonic generation (SHG) is a nonlinear optical effect sensitive to interfaces between materials with inversion symmetry. It is used as an effective tool for detection of the adsorption of a substance to microscopic particles, cells, liposomes, emulsions and similar structures, surface analysis and characterization of microparticles. The scattered second harmonic (SH) intensity from surfaces of suspended microparticles is characterized by its complex angular distribution dependence on the shape, size, and physical and chemical properties of the molecules making up the outer layer of the particles. In particular, the overall scattered SH intensity has been predicted to have a dramatic and nontrivial dependence on the particle size.
Results are reported for aqueous suspensions of polystyrene microspheres with different dye molecules adsorbed on their surfaces. They indicate that the scattered SH power has an oscillatory dependence on the particle size. It is also shown that adsorption of one of the dyes (malachite green) on polystyrene particles is strongly affected when SDS surfactants are added to the solution. For this system a rapid increase of the SH signal with increasing concentration of SDS was observed in the range of low SDS concentration.
Three different theoretical models are used to analyze the observed particle size dependence of SHG. The calculated angular and particle size dependences of the SH scattered power show that the models do not agree very well between each other when the size of the particles is of the order of the fundamental light wavelength, as here. One of the models - nonlinear Mie scattering - predicts oscillatory behaviour of the scattered SH power with the particle size, but fails to reproduce the position of the maxima and minima of the experimentally observed oscillations.
The obtained results on the size dependence of the SH can be used in all applications to increase the count rate by choosing particles of the size for which the SH efficiency was found to the highest. A new effect of cooperative malachite green and SDS interaction at the polystyrene surface can be employed, for example, in the areas of microbiology or biotechnology, where adsorption macromolecules, surfactants and dyes to polystyrene microparticles is widely used.
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Andersen, Audrée. "Surfactant dynamics at interfaces : a series of second harmonic generation experiments." Phd thesis, Universität Potsdam, 2005. http://opus.kobv.de/ubp/volltexte/2006/655/.
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Adsorption layers of soluble surfactants enable and govern a variety of phenomena in surface and colloidal sciences, such as foams. The ability of a surfactant solution to form wet foam lamellae is governed by the surface dilatational rheology. Only systems having a non-vanishing imaginary part in their surface dilatational modulus, E, are able to form wet foams. The aim of this thesis is to illuminate the dissipative processes that give rise to the imaginary part of the modulus.
There are two controversial models discussed in the literature. The reorientation model assumes that the surfactants adsorb in two distinct states, differing in their orientation. This model is able to describe the frequency dependence of the modulus E. However, it assumes reorientation dynamics in the millisecond time regime. In order to assess this model, we designed a SHG pump-probe experiment that addresses the orientation dynamics. Results obtained reveal that the orientation dynamics occur in the picosecond time regime, being in strong contradiction with the two states model.
The second model regards the interface as an interphase. The adsorption layer consists of a topmost monolayer and an adjacent sublayer. The dissipative process is due to the molecular exchange between both layers. The assessment of this model required the design of an experiment that discriminates between the surface compositional term and the sublayer contribution. Such an experiment has been successfully designed and results on elastic and viscoelastic surfactant provided evidence for the correctness of the model.
Because of its inherent surface specificity, surface SHG is a powerful analytical tool that can be used to gain information on molecular dynamics and reorganization of soluble surfactants. They are central elements of both experiments. However, they impose several structural elements of the model system. During the course of this thesis, a proper model system has been identified and characterized. The combination of several linear and nonlinear optical techniques, allowed for a detailed picture of the interfacial architecture of these surfactants.
Amphiphile vereinen zwei gegensätzliche Strukturelemente in einem Molekül, eine hydrophile Kopfgruppe und ein hydrophobe, meist aliphatische Kette. Aufgrund der molekularen Asymmetrie erfolgt eine spontane Adsorption an der Wasser-Luft Grenzfläche. Die Adsorptionsschicht verändert die makroskopischen Eigenschaften des Materials, z.B. die Grenzflächenspannung wird erniedrigt. Amphiphile sind zentrale Bauelemente der Kolloid- und Grenzflächenforschung, die Phänomene, wie Schäume ermöglichen.
Eine Schaumlamelle besteht aus einem dünnen Wasserfilm, der durch zwei Adsorptionsschichten stabilisiert wird. Die Stabilität der Lamelle wird durch die Grenzflächenrheologie entscheidend geprägt. Die wesentliche makroskopische Größe in diesem Zusammenhang ist das so genannte Grenzflächendilatationsmodul E. Es beschreibt die Fähigkeit des Systems die Gleichgewichtsgrenzflächenspannung nach einer Expansion oder Dilatation der Adsorptionschicht wieder herzustellen. Das Modul E ist eine komplexe Größe, in dem der Imaginärteil direkt mit der Schaumstabilität korreliert.
Diese Arbeit widmet sich der Grenzflächenrheologie. In der Literatur werden zwei kontroverse Modelle zur Interpretation dieser Größe diskutiert. Diese Modelle werden experimentell in dieser Arbeit überprüft. Dies erfordert die Entwicklung neuer experimenteller Aufbauten basierend auf nichtlinearen, optischen Techniken. Mit diesen Experimenten konnte eines der Modelle bestätigt werden.
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Linnenbank, Heiko [Verfasser]. "Second harmonic generation spectroscopy of plasmonic nanostructures and metamaterials / Heiko Linnenbank." Bonn : Universitäts- und Landesbibliothek Bonn, 2015. http://d-nb.info/1077290349/34.
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Kashyap, Raman. "Studies of second harmonic generation and optical damage in optical fibres." Thesis, University of Essex, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.253972.
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Timson, Andrew John. "Second harmonic generation of molecules located at the air/water interface." Thesis, University of Southampton, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326716.
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Lochun, Darren. "Towards a transparent Z-type multilayer film for second harmonic generation." Thesis, Cranfield University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309681.
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Handa, T. "Deposition and characterisation of Langmuir-Blodgett films for second harmonic generation." Thesis, Cranfield University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387644.
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Santiago, Condori Jordy Guilbert. "Non-collinear interaction of Laguerre-Gaussian modes in second harmonic generation." Master's thesis, Pontificia Universidad Católica del Perú, 2018. http://tesis.pucp.edu.pe/repositorio/handle/123456789/12114.
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Esta tesis aborda las interacciones no colineales de los modos Laguerre-Gaussianos.
Estas interacciones se utilizan para lograr la transferencia del momento angular orbital (OAM) en la mezcla de ondas no lineales. Esto se hace mediante conmutación controlada por polarización. Ajustando la geometría de los haces de entrada, es posible producir una salida OAM de tres canales con cargas topológicas arbitrarias que se generan simultáneamente y se resuelven espacialmente en la longitud de onda del segundo armónico. El uso de grados de libertad de trayectoria y polarización permite una conmutación óptica casi perfecta entre las diferentes operaciones OAM.
Se propone un modelo teórico que muestra un muy buena concordancia con los experimentos.Tesis
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Bertocchi, Matteo. "First principles Second-Harmonic Generation in quantum confined silicon-based systems." Palaiseau, Ecole polytechnique, 2013. http://pastel.archives-ouvertes.fr/docs/00/79/69/33/PDF/tesi-bertocchi.pdf.
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Dans cette thèse, je me suis interessé à la description ab initio du processus de génération de seconde harmonique (SHG), qui est une propriété optique non-linéaire des matériaux, et je me suis concentré sur les systèmes quantiques confinés, à base de silicium. Ces dernières années, les études ab initio ont suscité un grand intérêt pour l'interprétation et la prévision des propriétés des matériaux. Il est indispensable d'améliorer la connaissance des processus non-linéaires et de proposer une description de SHG, à partir des premiers principes. En raison de difficultés importantes, la description de l'optique non linéaire n'a pas encore atteint la précision des phénomènes linéaires. L'état de l'art des calculs ab initio SHG est représenté par l'inclusion des effets à plusieurs corps comme les champs locaux (LF) et l'interaction électron-trou, mais aujourd'hui, l'approche la plus utilisée est l'approximation de particules indépendantes (IPA), la seule en mesure d'aborder les calculs de structures complexes, tels que des surfaces et des interfaces. Alors que IPA peut être une bonne approximation pour les systèmes massifs, dans des matériaux discontinus d'autres effets peuvent être prédominants. L'objectif de ma thèse est de donner une analyse du processus de SHG dans des systèmes complexes comme les interfaces et les systèmes confinés à base de silicium, d'inférer de nouvelles connaissances sur le mécanisme physique mis en jeu et son lien avec la nature du système. J'utilise un formalisme fondé sur la théorie de la fonctionnelle de la densité dépendant du temps (TDDFT) où les effets à plusieurs corps sont inclus par un choix approprié des noyaux de la TDDFT. Le formalisme et le code ont été développés au cours de mon travail, permettant l'étude de matériaux complexes. Mes recherches ont porté sur l'étude de l'interface Si (111)/CaF2 (de type B,T4). Des études de convergence montrent l'importance du matériau semi-conducteur par rapport à l'isolant. La réponse est caractéristique d'une région profonde au-delà de l'interface Si, alors que CaF2 converge rapidement juste après l'interface. La réponse montre une sensibilité aux modifications électroniques, induites dans des états bien en-dessous de l'interface, et non à la structure ionique du silicium, qui retrouve rapidement la configuration du matériau massif. Une procédure de normalisation pour comparer avec l'expérience a été proposée. Les spectres de SHG ont été calculés en IPA, et en introduisant les interactions de champs locaux et excitoniques. De nouveaux comportements ont été observés par rapport aux processus SHG dans GaAs ou SiC, montrant l'importance des effets de champ locaux cristallins. Alors que IPA décrit la position des pics principaux de SHG et que les effets excitoniques modifient légèrement l'intensité totale, seuls les champs locaux reproduisent la forme spectrale et les intensités relatives des pics. Cela souligne combien les effets des différents acteurs dans le processus dépendent de la nature des matériaux. De nouvelles méthodes d'analyse de la réponse ont été proposées: en effet, le lien direct entre la position des pics et les énergies de transition est perdu dans les calculs de SHG : le signal provient d'une équation de Dyson du second ordre où les fonctions de réponse linéaires et non-linéaire pour des fréquences différentes sont mélangées. En outre, la complexité du matériau m'a permis d'obtenir des informations sur une grande variété de systèmes comme les multicouches et les couches de silicium confinées. Les résultats montrent un bon accord avec l'expérience, confirmant la structure de l'interface proposée. Cela souligne la précision du formalisme, la possibilité d'améliorer nos connaissances sur ces matériaux complexes. Les simulations ab-initio de SHG peuvent être utilisées comme une technique prédictive, pour soutenir et guider les expériences et les développements technologiques. Les résultats préliminaires sur les structures Si/Ge sont présentésIn this thesis I have dealt with the ab initio description of the second-harmonic generation (SHG) process, a nonlinear optical property of materials, focusing in particular on quantum confined, silicon-based systems. In the last decades, the accuracy and possibilities of ab initio studies have demonstrated a great relevance in both the interpretation and prediction of the materials properties. It is then mandatory to improve the knowledge of the nonlinear optical processes as well as the SHG first-principle description. Nowadays, due to nontrivial difficulties, nonlinear optics has not yet reached the accuracy and development of linear phenomena. In particular, the state of the art of ab initio SHG calculations is represented by the inclusion of many-body effects as crystal local fields (LF) and electron-hole interaction, but today, the mostly used approach is the independent particle approximation (IPA), the only one able to approach calculations of complex structures such as surfaces and interfaces. Whereas IPA can be a good approximation for bulk systems, in discontinuous materials other effects may be predominant. Hence their description is of great relevance although the lack of studies. My thesis tries to give a first analysis of the SHG process in more complex systems as the interfaces and the Si-confined systems, inferring new insights on the physical mechanism and its link with the nature of the system. I use an efficient formalism based on the Time Dependent Density Functional Theory (TDDFT) where many-body effects are included via an appropriate choice of the TDDFT kernels. Both the formalism and the code have been developed during the thesis work permitting the study complex materials. The research has been focused on the Si(111)/CaF2 (T4 B-type) interface case study. Convergence studies show the importance of the semiconductor material with respect to the insulator. The response is characteristic of a deep region beyond the Si interface whereas the CaF2 converges soon after the first interface layers. Moreover, the signal demonstrates to be sensitive to the electronic-states modifications that are induced far below the interface, and not to the Si ionic structure that recovers soon the bulk configuration. A normalization procedure to compare with the experiment has been proposed. The SHG spectra have been calculated in the IPA, introducing LF and excitonic interactions. New behaviors have been observed with respect to the SHG processes on strained silicon, GaAs or SiC showing in particular the importance of crystal local-field effects with respect to both the IPA and the excitons. Whereas IPA can describe the position of the SHG main peaks and the excitonic effects slightly modify the total intensity, only LF are able to correctly reproduce the spectral shape and the relative intensities of the peaks. This underlines how SHG and the different involved effects depends on the nature of the materials. New methods of analysis of the response have been proposed; actually, the direct link between the peaks position and the transition energies is lost in SHG calculations (i. E. The signal comes from a second order Dyson equation where linear and nonlinear response functions at different frequencies are mixed together). Furthermore, the complexity of the system allowed me to extend the study to a large variety of materials as the multilayers and the silicon confined slabs. The results show a good agreement with the experiment confirming the proposed T4 B-type interface structure. This underlines the accuracy of the formalism, the possibility of improving our knowledge on these complex materials going beyond the standard approaches, and confirms the possibility of SHG ab-initio simulations to be employed as a predictive technique, supporting and guiding experiments and technological developments. Preliminary results on Si/Ge superlattice are presented
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Sinclair, Bruce David. "Second harmonic generation in sodium vapour induced by a magnetic field." Thesis, University of St Andrews, 1987. http://hdl.handle.net/10023/13925.
Full textAbstract:
A high resolution study of magnetic-field-induced second harmonic generation in sodium vapour was performed using a single-frequency continuous-wave dye laser. Resonant enhancement was obtained by tuning the laser to the frequency of the 3S-40 two-photon transition of the sodium atoms. Coherent parametric emission of the second harmonic radiation ocurred in the presence of a symmetry-breaking magnetic field by means of a coherent electric-quadrupole emission at twice the laser frequency. A theoretical model of the second harmonic generation (SHG) was developed, and includes the roles played by atomic selection rules, Zeeman splitting and eigen function mixing in a magnetic field, and the effects of homogeneous and inhomogeneous broadening. The use of a single-frequency laser and an atomic nonlinear medium allowed an experimental investigation of a SHG process in unprecedented detail. This provided astringent test of the theoretical model developed to predict the properties of the nonlinear interaction in terms of fundamental atomic parameters. The excellent agreement obtained between theoretical and experimental results vindicated the theoretical methods used in the modelling.
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Bender, Frank Alexander. "Analysis of second harmonic generation at a free boundary for oblique incidence." Thesis, Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37308.
Full textAbstract:
This thesis investigates the generation of second harmonic bulk waves in the
presence of a free boundary. Second harmonic waves have proven to be useful in
the field of nondestructive evaluation to detect fatigue in a material at an early
stage. Since most experimental setups include a free surface, the influence of such a
boundary is of significant practical interest. As a result, the objective of this research
is to develop a quantitative understanding of the complete process of second harmonic
generation at a free boundary.
This research shows that the interaction of primary waves (with each other) in
the nonlinear framework leads to the generation of second harmonic bulk waves. We
distinguish between self-interaction of a single primary wave and the cross-interaction
of two different primary waves. The proposed approach uses the perturbation method
to solve the nonlinear equations of motion, and shows two fundamentally different
solutions. In the case of resonance, the secondary waves grow with propagation
distance. This is the most important practical case, since the growing amplitudes of
these waves should be easier to experimentally measure. In the second, non-resonant
case, the amplitudes of the secondary waves are constant.
The complete process of second harmonic generation is analyzed for an incident Pand
an incident SV-wave, with the primary and secondary fields given. Finally, the
degenerate case of normal incidence is presented. Normal and oblique incidence are
compared with regard to their feasibility in experimental setups. The specific behavior
of second harmonic waves propagating in aluminum is numerically determined. These
results enable a variety of physical insights and conclusions to be drawn from the
analytical and numerical investigations.
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Wu, Xiaohong. "Nonlinear optics in resonant cavities: second harmonic generation and far-infrared lasers." Doctoral thesis, Universite Libre de Bruxelles, 1987. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/213447.
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Teerenstra, Marcel Nicolaas. "Langmuir-Blodgett film formation and second-harmonic generation of poly(isocyanide)s." [S.l. : [Groningen : s.n.] ; University Library Groningen] [Host], 1995. http://irs.ub.rug.nl/ppn/292801947.
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Walker, James D. "Artificial surface mounted rotor systems: Experimental studies using surface second harmonic generation." Connect to online resource, 2007. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3256450.
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Murphy, Don M. "Synthesis and properties of novel carboranes and organometallics for second harmonic generation." Thesis, University of Oxford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303617.
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Matar, Omar. "Synthesis and characterisation of barium titanate nanoparticles for second harmonic generation applications." Thesis, University of Leeds, 2017. http://etheses.whiterose.ac.uk/18185/.
Full textAbstract:
This thesis presents findings of hydrothermally synthesised barium titanate nanoparticles for biomarker applications. Hydrothermal barium titanate (H-BT) and barium strontium titanate (H-BST) nanoparticles were successfully synthesised and were characterised for their second harmonic generation applications. X-Ray powder diffraction (laboratory and synchrotron) highlighted that H-BT and H-BST had a mixed tetragonal and cubic phase fraction present by Rietveld peak fitting analysis. Regardless of the phase fractions present, all nanoparticles emitted SHG (including a commercial cubic BaTiO3 sample that appeared cubic by XRD). The smaller sized H-BST nanoparticles (45 nm) required an increase in incident laser power compared to the H-BT sample (~140 nm). The phase of the nanoparticles and origin of SHG was investigated by electron diffraction, electron energy loss spectroscopy and high resolution HAADF-STEM imaging. In-situ electron diffraction of barium titanate showed that the tetragonal diffraction pattern transformed to a cubic pattern when heated above the Curie point. The phase transition was also investigated by EELS measurements of the Ti-L3 edge t2g-eg peak separation at room temperature and 400 oC showing the reduction in t2g-eg peak separation when the sample transforms from a tetragonal to cubic phase. The surface of the nanoparticles also showed an atomically rough layer with incomplete unit cells, and the ‘bulk’ of the nanoparticles showed random Ti-atom distortions by HAADF-STEM Ti-atom displacement analysis. This suggests the origin of SHG is likely to be both a cause of surface roughness and local asymmetric distortions in the nanoparticle bulk. The hydrothermally prepared and PLL-coated nanoparticles were measured to assess the cell viability and DNA damage of cells after a 24-hour exposure. The nanoparticles were measured by dynamic light scattering to understand the behaviour of uncoated and PLL-coated nanoparticles suspended in different media. The uncoated nanoparticles showed little reduction in cell viability and genotoxicity, whereas the PLL coated nanoparticles showed a reduction in cell viability and a failed comet assay at concentrations ≥10 µg/mL. The nanoparticles were confirmed to be taken up into the cells by electron microscopy of critically point dried and resin embedded cell sections. Cryo-TEM of the H-BT-PLL nanoparticles suspended at 100 µg/mL in complete cell culture media showed that some nanoparticles were coated with a calcium phosphate coating and others not. This resulted in, either cells having a direct exposure to PLL and positively charged nanoparticles, or all the calcium was removed from the media that is required for cell signalling pathways which could lead to a reduction in cell viability.