Photorefractive materials remain of interest as optically nonlinear elements, because of the large saturated nonlinear effects that they exhibit at low continuous wave optical power levels. They can be used to give large optical amplification to image bearing beams by utilising the nonlinear process of two-wave mixing. Four-wave mixing can also be achieved, and phase conjugate reflectivities of signal beams can be substantially greater than unity. Self-pumped phase conjugation is also possible in those photorefractive materials with nonlinearities that are suitably large.
{"title":"The Effect of Large Signals in Photorefractive Media","authors":"A. K. Powell, D. Fish, G. Barrett, T. J. Hall","doi":"10.1364/pmed.1991.tuc18","DOIUrl":"https://doi.org/10.1364/pmed.1991.tuc18","url":null,"abstract":"Photorefractive materials remain of interest as optically nonlinear elements, because of the large saturated nonlinear effects that they exhibit at low continuous wave optical power levels. They can be used to give large optical amplification to image bearing beams by utilising the nonlinear process of two-wave mixing. Four-wave mixing can also be achieved, and phase conjugate reflectivities of signal beams can be substantially greater than unity. Self-pumped phase conjugation is also possible in those photorefractive materials with nonlinearities that are suitably large.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"105 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128154813","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A method of solution for the scalar four wave mixing equations has been known for many years [1]. We show that these equations have an underlying symmetry in the form of the SU(2) group. This formulation identifies the conserved quantities of four wave mixing in an obvious sense rather than in the ad-hoc fashion used previously. The method also solves the equations in terms of beam amplitudes rather than beam ratios.
{"title":"Four-Wave Mixing Steady-State Solutions Utilising the Underlying SU(2) Group Symmetry","authors":"D. Fish, A. K. Powell, T. J. Hall","doi":"10.1364/pmed.1991.mc11","DOIUrl":"https://doi.org/10.1364/pmed.1991.mc11","url":null,"abstract":"A method of solution for the scalar four wave mixing equations has been known for many years [1]. We show that these equations have an underlying symmetry in the form of the SU(2) group. This formulation identifies the conserved quantities of four wave mixing in an obvious sense rather than in the ad-hoc fashion used previously. The method also solves the equations in terms of beam amplitudes rather than beam ratios.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"68 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133868168","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Klein, F. Strohkendl, B. Wechsler, G. Brost, J. Millerd, E. Garmire
Bi12TiO20 (BTO) is a photorefractive material in the same structural class (sillenite) as Bi12SiO20 (BSO) and Bi12GiO20 (BGO). However, BTO offers some unique advantages over BSO and BGO: (1) larger electro-optic coefficient (5.7 pm/V)1, and (2) lower optical activity (6°/mm at 633 nm)1, 2. Previous photorefractive measurements3,4 have shown that gain coefficients on the order of 10-15 cm−1 can be produced through the use of an applied AC field. In this work we show that the largest gain values can only be obtained for large values of the pump/probe intensity ratio β. As β approaches unity (large signal regime), higher spatial order gratings become prominent, and the gain is reduced from its large-β value.5−8 Our results are similar to those obtained by other researchers for BSO5 and GaAs6 with an applied field. We have analyzed this and related phenomena using a finite difference method to model the photorefractive grating formation. This method yields accurate numerical solutions which are valid for for all values of β.
{"title":"Large Signal Gain Effects in Photorefractive Bi12TiO20 at 633 nm","authors":"M. Klein, F. Strohkendl, B. Wechsler, G. Brost, J. Millerd, E. Garmire","doi":"10.1364/pmed.1991.tuc19","DOIUrl":"https://doi.org/10.1364/pmed.1991.tuc19","url":null,"abstract":"Bi12TiO20 (BTO) is a photorefractive material in the same structural class (sillenite) as Bi12SiO20 (BSO) and Bi12GiO20 (BGO). However, BTO offers some unique advantages over BSO and BGO: (1) larger electro-optic coefficient (5.7 pm/V)1, and (2) lower optical activity (6°/mm at 633 nm)1, 2. Previous photorefractive measurements3,4 have shown that gain coefficients on the order of 10-15 cm−1 can be produced through the use of an applied AC field. In this work we show that the largest gain values can only be obtained for large values of the pump/probe intensity ratio β. As β approaches unity (large signal regime), higher spatial order gratings become prominent, and the gain is reduced from its large-β value.5−8 Our results are similar to those obtained by other researchers for BSO5 and GaAs6 with an applied field. We have analyzed this and related phenomena using a finite difference method to model the photorefractive grating formation. This method yields accurate numerical solutions which are valid for for all values of β.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"113 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117277688","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Diode laser arrays provide a compact, high power, high efficiency source of monochromatic light and are finding many applications in all solid-state mini and micro-laser systems. Unfortunately, the preferred modes of operation of free-running, conventional gain-guided laser arrays involve the simultaneous oscillation of many array transverse modes1. This results in an undesirable broadened twin-lobe output in the far field which is generally several times the diffraction limit of the emitting region. This leads to poor focussability which in turn severely limits the efficiency of launching into optical fibers, coupling into planar waveguides and longitudinal pumping of solid-state micro-lasers.
{"title":"Phase conjugate techniques for diode laser brightness enhancement","authors":"S. Maccormack, R. Eason","doi":"10.1364/pmed.1991.tub1","DOIUrl":"https://doi.org/10.1364/pmed.1991.tub1","url":null,"abstract":"Diode laser arrays provide a compact, high power, high efficiency source of monochromatic light and are finding many applications in all solid-state mini and micro-laser systems. Unfortunately, the preferred modes of operation of free-running, conventional gain-guided laser arrays involve the simultaneous oscillation of many array transverse modes1. This results in an undesirable broadened twin-lobe output in the far field which is generally several times the diffraction limit of the emitting region. This leads to poor focussability which in turn severely limits the efficiency of launching into optical fibers, coupling into planar waveguides and longitudinal pumping of solid-state micro-lasers.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"172 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122854487","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The mobility of photoexcited charge carriers in photorefractive insulators can be measured with a holographic time-of-flight technique.1 By illuminating the crystal with two interfering 30 ps laser pulses at the wavelength of 532 nm, we create an instantanuous sinusoidal pattern of photoexcited charge carriers. A strong electric field E0 is applied across the crystal causing the sinusoidal pattern of charge carriers to drift with a velocity μE0, where μ is the mobility. With a proper choice of the interference fringe spacing Λ, the superposition of this drifting charge pattern on the complementary pattern of photo-ionized traps creates an observable oscillating space charge field. We probe this oscillation by diffracting a weak cw He-Ne beam from the refractive index grating that is created via the electro-optic effect. The period Pt of the observed oscillation is the time required for photoexcited charge carriers to drift over one spatial period Λ.
{"title":"Conduction band and trap limited mobilities in Bi12SiO20","authors":"P. Nouchi, J. Partanen, R. Hellwarth","doi":"10.1364/pmed.1991.tuc10","DOIUrl":"https://doi.org/10.1364/pmed.1991.tuc10","url":null,"abstract":"The mobility of photoexcited charge carriers in photorefractive insulators can be measured with a holographic time-of-flight technique.1 By illuminating the crystal with two interfering 30 ps laser pulses at the wavelength of 532 nm, we create an instantanuous sinusoidal pattern of photoexcited charge carriers. A strong electric field E0 is applied across the crystal causing the sinusoidal pattern of charge carriers to drift with a velocity μE0, where μ is the mobility. With a proper choice of the interference fringe spacing Λ, the superposition of this drifting charge pattern on the complementary pattern of photo-ionized traps creates an observable oscillating space charge field. We probe this oscillation by diffracting a weak cw He-Ne beam from the refractive index grating that is created via the electro-optic effect. The period Pt of the observed oscillation is the time required for photoexcited charge carriers to drift over one spatial period Λ.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116812698","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Since the observation of self-frequncy scaning with a passive phase-conjugate mirror coupled to a dye-laser cavity in 1984, much attention has been paid to frequency detuning in photorefractive (PR) wave mixing. Such a phenomenon has been widely studied in various photorefractive oscillators.(1) In this paper, we present the experimental results of frequency shift (f-shift) in our mutually pumed phase conjugator (Bridge conjugator)(2) and demonstrated to be dramatically dependent upon the power density of pumping beams.
{"title":"Frequency Shift in a Mutually Pumped Phase Conjugator of BaTiO3","authors":"Dadi Wang, Zhi-guo Zhang, P. Ye","doi":"10.1364/pmed.1991.wa5","DOIUrl":"https://doi.org/10.1364/pmed.1991.wa5","url":null,"abstract":"Since the observation of self-frequncy scaning with a passive phase-conjugate mirror coupled to a dye-laser cavity in 1984, much attention has been paid to frequency detuning in photorefractive (PR) wave mixing. Such a phenomenon has been widely studied in various photorefractive oscillators.(1) In this paper, we present the experimental results of frequency shift (f-shift) in our mutually pumed phase conjugator (Bridge conjugator)(2) and demonstrated to be dramatically dependent upon the power density of pumping beams.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"29 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123449104","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We have developed a technique to measure interferometrically charge-transport-induced refractive index gratings in photoconductive insulators. All four parameters needed to describe fully the interaction between the two beams Bragg matched to the grating can be determined. We use the method to find that the complex optical polarizability of an occupied charge trap equals that of an unoccupied trap plus (0.7 − i4.5 ± 0.7 ± i0.4) × 10−22 cm3 in photorefractive Bi12TiO20.
{"title":"Transport-induced-grating interferometry: application to photorefractive Bi12TiO20","authors":"P. Xia, J. Partanen, R. Hellwarth","doi":"10.1364/pmed.1991.tuc8","DOIUrl":"https://doi.org/10.1364/pmed.1991.tuc8","url":null,"abstract":"We have developed a technique to measure interferometrically charge-transport-induced refractive index gratings in photoconductive insulators. All four parameters needed to describe fully the interaction between the two beams Bragg matched to the grating can be determined. We use the method to find that the complex optical polarizability of an occupied charge trap equals that of an unoccupied trap plus (0.7 − i4.5 ± 0.7 ± i0.4) × 10−22 cm3 in photorefractive Bi12TiO20.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130475627","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this work photoinduced phenomenons in iron-doped (C= 0,01; 0,038; 0,05; 0,07 wt.%) and copper-doped (C =0,01; 0,025; 0,04 wt.%) lithium niobate and lithium tantalate single crystals have been investigated using the Raman scattering (RS) and IR-reflection speotroscopy. The following types of lasers were used as illumination sourses: YAG:Nd3+ (λ = 10640 Å); He-Ne (6328 Å); Ar+(5145, 4880 Å); He-Cd (4416 Å).
{"title":"Photogyration and Photoinduced Structure Distortions in Doped LiNbO3 and LiTaO3","authors":"S. Kostritskii","doi":"10.1364/pmed.1991.tuc15","DOIUrl":"https://doi.org/10.1364/pmed.1991.tuc15","url":null,"abstract":"In this work photoinduced phenomenons in iron-doped (C= 0,01; 0,038; 0,05; 0,07 wt.%) and copper-doped (C =0,01; 0,025; 0,04 wt.%) lithium niobate and lithium tantalate single crystals have been investigated using the Raman scattering (RS) and IR-reflection speotroscopy. The following types of lasers were used as illumination sourses: YAG:Nd3+ (λ = 10640 Å); He-Ne (6328 Å); Ar+(5145, 4880 Å); He-Cd (4416 Å).","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"46 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123103395","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Optical phase conjugation is an important nonlinear process, with many applications in the areas of optical communications and optical processing. This is as a result of the wave-front correction properties that phase conjugation offers and this has generated much interest in the area. A common method of producing phase conjugated wavefronts is the four-wave mixing interaction and many publications on the steady state solution to this problem have appeared over the last decade. More recently, however, interest has been focussed upon the temporal behaviour of four-wave mixing systems, with instabilities and chaos being both demonstrated by Gauthier et al [1] and predicted by Królikowski et al [2]. To date, the analysis for the temporal behaviour of anisotropic four wave mixing, in the transmission grating regime, has involved the direct numerical integration of the equations describing four wave mixing. This analysis however, does not utilise the symmetries of the four wave mixing process, and thus results in a more complex problem. Through exploitation of these symmetries the complexity of the problem has been reduced from one containing four complex variables, to one containing three real variables. This has been accomplished through the use of the Special Unitary Group 2, a group providing a two dimensional matrix, whose elements are functions of three real variables. The multiplication of this matrix, together with one containing the boundary conditions for the problem, thus enables the four complex beam amplitudes to be reexpressed in terms of three real quantities. Using this technique, the temporal nature of anisotropic four wave mixing has been studied, and shown under certain conditions, to exhibit chaotic behaviour when an electric field is present. The effect of any material absorption on the chaotic nature is also demonstrated.
{"title":"Dynamic Solutions and Instabilities of the Four-wave Mixing Interaction Utilising the Underlying SU(2) Group Symmetry","authors":"G. Barrett, A. K. Powell, T. J. Hall","doi":"10.1364/pmed.1991.tuc21","DOIUrl":"https://doi.org/10.1364/pmed.1991.tuc21","url":null,"abstract":"Optical phase conjugation is an important nonlinear process, with many applications in the areas of optical communications and optical processing. This is as a result of the wave-front correction properties that phase conjugation offers and this has generated much interest in the area. A common method of producing phase conjugated wavefronts is the four-wave mixing interaction and many publications on the steady state solution to this problem have appeared over the last decade. More recently, however, interest has been focussed upon the temporal behaviour of four-wave mixing systems, with instabilities and chaos being both demonstrated by Gauthier et al [1] and predicted by Królikowski et al [2].\u0000 To date, the analysis for the temporal behaviour of anisotropic four wave mixing, in the transmission grating regime, has involved the direct numerical integration of the equations describing four wave mixing. This analysis however, does not utilise the symmetries of the four wave mixing process, and thus results in a more complex problem. Through exploitation of these symmetries the complexity of the problem has been reduced from one containing four complex variables, to one containing three real variables. This has been accomplished through the use of the Special Unitary Group 2, a group providing a two dimensional matrix, whose elements are functions of three real variables. The multiplication of this matrix, together with one containing the boundary conditions for the problem, thus enables the four complex beam amplitudes to be reexpressed in terms of three real quantities. Using this technique, the temporal nature of anisotropic four wave mixing has been studied, and shown under certain conditions, to exhibit chaotic behaviour when an electric field is present. The effect of any material absorption on the chaotic nature is also demonstrated.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"15 3","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"120933473","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We present the results of a comprehensive electro-optic (EO) study of Sr0.61Ba0.39Nb2O6 at λ = 633 nm. The experiments are conducted in the transverse field configuration, hence the effective linear EO coefficient rc is measured. Uniformly poled samples yield rc = 230 ± 20 pm/V at 25°C and rc = 1600 ± 150 pm/V at 65°C. However, the EO behavior is found to substantially degrade when attempting domain reversal. Imaging a crystal through crossed polarizers during the reversal process shows a very non-uniform birefringence distribution in the vicinity of the original -c electrode face.
{"title":"Electo-Optic Effects and Domain Reversal in Sr0.61Ba0.39Nb2O6","authors":"J. Wilde, L. Hesselink","doi":"10.1364/pmed.1991.tua4","DOIUrl":"https://doi.org/10.1364/pmed.1991.tua4","url":null,"abstract":"We present the results of a comprehensive electro-optic (EO) study of Sr0.61Ba0.39Nb2O6 at λ = 633 nm. The experiments are conducted in the transverse field configuration, hence the effective linear EO coefficient rc is measured. Uniformly poled samples yield rc = 230 ± 20 pm/V at 25°C and rc = 1600 ± 150 pm/V at 65°C. However, the EO behavior is found to substantially degrade when attempting domain reversal. Imaging a crystal through crossed polarizers during the reversal process shows a very non-uniform birefringence distribution in the vicinity of the original -c electrode face.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"53 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132711416","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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