Recently, experiments with Bi12SiO20 (BSO) initiated by Mallick et al.[1] and continued by the Oxford group[2, 3, 4, 5, 6] have shown that, under certain conditions, one or more spatially subharmonic beams may arise between two pump beams (see Fig. 1).
{"title":"Analytic and Numeric Results on Subharmonics in BSO","authors":"A. Błȩdowski, B. Sturman, J. Otten, K. Ringhofer","doi":"10.1364/pmed.1991.wc22","DOIUrl":"https://doi.org/10.1364/pmed.1991.wc22","url":null,"abstract":"Recently, experiments with Bi12SiO20 (BSO) initiated by Mallick et al.[1] and continued by the Oxford group[2, 3, 4, 5, 6] have shown that, under certain conditions, one or more spatially subharmonic beams may arise between two pump beams (see Fig. 1).","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130711084","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}
DFWM as an useful tool to generate phase conjugate waves has recently been the subject of intensive study. In particular photorefractive crystals such as LiNbO3, KNbO3, BaTiO3 and SBN are widely used[1]. Among the published papers on DFWM most are concerned with backward phase conjugate waves and only a few with forward phase conjugate, waves.[2,3] In both of these papers the intensity of the forward phase conjugate wave has not been investigated. We report here a systematic study of the intensity of forward phase conjugate wave.
{"title":"Forward Phase-Conjugate Wave in Degenerate Four-Wave Mixing (DFWM) in Photorefractive Crystalline Slab","authors":"H. Zhang, X. H. He, S. Tang","doi":"10.1364/pmed.1991.tuc24","DOIUrl":"https://doi.org/10.1364/pmed.1991.tuc24","url":null,"abstract":"DFWM as an useful tool to generate phase conjugate waves has recently been the subject of intensive study. In particular photorefractive crystals such as LiNbO3, KNbO3, BaTiO3 and SBN are widely used[1]. Among the published papers on DFWM most are concerned with backward phase conjugate waves and only a few with forward phase conjugate, waves.[2,3] In both of these papers the intensity of the forward phase conjugate wave has not been investigated. We report here a systematic study of the intensity of forward phase conjugate wave.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"34 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131617565","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 papers 1-4 the possibility of new light beam generation by interactions of light waves in photorefrective crystals is shown. New beams appear due to the subharmonic formation of the main holographic grating. The analysis of subharmonic generation was carried out for crystals with nonlocal response2,3 and circular photogalvanic mechanism of grating recording4. The vector diagram illustrating the latter type of interaction is represented in Fig.1. Here, the generated beam 1(3) has polarization orthogonal to polarization of exciting waves 2,4.
{"title":"Spatial Subharmonic Generation at Intermode Interaction in Planar Waveguides","authors":"V. Popov, E. Shandarov, S. Shandarov","doi":"10.1364/pmed.1991.wc25","DOIUrl":"https://doi.org/10.1364/pmed.1991.wc25","url":null,"abstract":"In papers 1-4 the possibility of new light beam generation by interactions of light waves in photorefrective crystals is shown. New beams appear due to the subharmonic formation of the main holographic grating. The analysis of subharmonic generation was carried out for crystals with nonlocal response2,3 and circular photogalvanic mechanism of grating recording4. The vector diagram illustrating the latter type of interaction is represented in Fig.1. Here, the generated beam 1(3) has polarization orthogonal to polarization of exciting waves 2,4.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133052742","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 recently discovered effect of non-steady-state photo(EMF) is a powerful technique for the measurement of different parameters of photorefractive crystals [1-3]. The photoEMF is observed as an alternating electric current Jω through a short-circuited sample of photoconductor illuminated by a vibrating pattern of interference between two coherent waves, one of which is phase modulated with frequency ω (Fig. 1). It results from a periodic modulation of the spatial shift between the distribution of photoconductivity that followes movements of the interference pattern and the distribution of the space-charge electric field recordered through the conventional diffusion holographic mechanism in photorefractive crystals.
{"title":"Non-steady-state photoEMF in crystals with long relaxation times of photoconductivity","authors":"I. Sokolov, S. Stepanov","doi":"10.1364/pmed.1991.tuc6","DOIUrl":"https://doi.org/10.1364/pmed.1991.tuc6","url":null,"abstract":"The recently discovered effect of non-steady-state photo(EMF) is a powerful technique for the measurement of different parameters of photorefractive crystals [1-3]. The photoEMF is observed as an alternating electric current Jω through a short-circuited sample of photoconductor illuminated by a vibrating pattern of interference between two coherent waves, one of which is phase modulated with frequency ω (Fig. 1). It results from a periodic modulation of the spatial shift between the distribution of photoconductivity that followes movements of the interference pattern and the distribution of the space-charge electric field recordered through the conventional diffusion holographic mechanism in photorefractive crystals.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"24 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133839080","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}
Photorefractive media have been used for many novel applications in image processing. One interesting use is the novelty filter which is an all optical processor based on the response of two wave mixing (2-WM) or four wave mixing (4-WM) [1,2]. It is obvious that the temporal dymnamics of the wave mixing process is essential to understand such processes. However, since the overall photorefractive dynamics, including the wave mixing part, is described by complicated nonlinear partial differential equations, it is hard to obtain a general solution. The study has been largely limited to steady state behavior and the response of the photorefractive material only, without taking into account the dynamics of the wave coupling effects.
{"title":"On the Buildup and Decay of Photorefractive Wave Mixing Processes","authors":"M. Horowitz, B. Fischer","doi":"10.1364/pmed.1991.mb2","DOIUrl":"https://doi.org/10.1364/pmed.1991.mb2","url":null,"abstract":"Photorefractive media have been used for many novel applications in image processing. One interesting use is the novelty filter which is an all optical processor based on the response of two wave mixing (2-WM) or four wave mixing (4-WM) [1,2]. It is obvious that the temporal dymnamics of the wave mixing process is essential to understand such processes. However, since the overall photorefractive dynamics, including the wave mixing part, is described by complicated nonlinear partial differential equations, it is hard to obtain a general solution. The study has been largely limited to steady state behavior and the response of the photorefractive material only, without taking into account the dynamics of the wave coupling effects.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"325 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133956500","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 a photorefractive experiment the space-charge grating is built-up along a certain axis and it modulates the refractive indices via the linear electro-optic (EO) effect. In many of the works in the field there is an on-going dilemma which EO coefficient and also dielectric constants to use in order to model the photorefractive effect.[1] The relevance of the question lies in the fact that the unclamped (stress-free) and the clamped (strain-free) values typically differ by more than a factor of two. Experiments in KNbO3[2] and BaTiO3[3] tend to indicate that the unclamped values are more appropriate. In this contribution we show that neither the clamped nor the unclamped linear EO coefficients are to be used without caution but the appropriate effective coefficients must be calculated for every particular crystal symmetry and sample orientation.
{"title":"Elasto-optic and roto-optic contribution to the photorefractive effect","authors":"M. Zgonik, P. Günter","doi":"10.1364/pmed.1991.tuc13","DOIUrl":"https://doi.org/10.1364/pmed.1991.tuc13","url":null,"abstract":"In a photorefractive experiment the space-charge grating is built-up along a certain axis and it modulates the refractive indices via the linear electro-optic (EO) effect. In many of the works in the field there is an on-going dilemma which EO coefficient and also dielectric constants to use in order to model the photorefractive effect.[1] The relevance of the question lies in the fact that the unclamped (stress-free) and the clamped (strain-free) values typically differ by more than a factor of two. Experiments in KNbO3[2] and BaTiO3[3] tend to indicate that the unclamped values are more appropriate. In this contribution we show that neither the clamped nor the unclamped linear EO coefficients are to be used without caution but the appropriate effective coefficients must be calculated for every particular crystal symmetry and sample orientation.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"41 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114398887","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 photorefractive effect has now been identified and studied in many semi-insulating III-V compound semiconductors [1]. In general, it can be well described by a Single Defect Model (SDM) with one or two types of charge carriers. However, discrepancies arise between theory and the experimental results due to the presence of additional defects. In understanding the role of multiple deep defects in the photorefractive effect, temperature plays a key role. Each different defect has a specific energy position within the bandgap of the material. Thermal emission of carriers trapped at defect sites is a strong (exponential) function of defect energy and the sample temperature. The thermal relaxation of nonequilibrium defect occupancies, and the subsequent effect on the photorefractive effect, can be studied by monitoring the two-wave mixing (2WM) gain and four-wave mixing (4WM) diffraction efficiency as functions of temperature, providing a natural tool to characterize the material. We find that multiple defect levels in InP:Fe lead to dramatic changes in the photorefractive behavior. Reduced gain reported at room temperature can be shown to arise from an additional defect in InP other than isolated Fe.
{"title":"Electron-Hole Competition in InP:Fe -- The Role of Multiple Defects","authors":"R. S. Rana, D. Nolte","doi":"10.1364/pmed.1991.mc3","DOIUrl":"https://doi.org/10.1364/pmed.1991.mc3","url":null,"abstract":"The photorefractive effect has now been identified and studied in many semi-insulating III-V compound semiconductors [1]. In general, it can be well described by a Single Defect Model (SDM) with one or two types of charge carriers. However, discrepancies arise between theory and the experimental results due to the presence of additional defects. In understanding the role of multiple deep defects in the photorefractive effect, temperature plays a key role. Each different defect has a specific energy position within the bandgap of the material. Thermal emission of carriers trapped at defect sites is a strong (exponential) function of defect energy and the sample temperature. The thermal relaxation of nonequilibrium defect occupancies, and the subsequent effect on the photorefractive effect, can be studied by monitoring the two-wave mixing (2WM) gain and four-wave mixing (4WM) diffraction efficiency as functions of temperature, providing a natural tool to characterize the material. We find that multiple defect levels in InP:Fe lead to dramatic changes in the photorefractive behavior. Reduced gain reported at room temperature can be shown to arise from an additional defect in InP other than isolated Fe.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"113 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116081142","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 detection of the transient surface motion of objects is an area of far reaching practical importance. Applications include the vibration monitoring of many engineering structures (power plants, aircrafts, engines of various kinds...) and more recently the detection of ultrasound produced by pulse laser excitation. This technique, now in active development in our laboratory and elsewhere, extends ultrasonic inspection of materials to conditions otherwise difficult or impossible (complex geometries, hot products on a production line...). Various optical systems have been devised for detecting surface motion and have been recently reviewed1. We are reporting here the novel use of two wave mixing in a photorefractive crystal for detecting such a motion and in particular ultrasonic displacement produced by pulsed laser excitation. This approach has the merit of being applicable to a rough surface by integrating over many speckles and of having a very broad frequency detection bandwidth. The use of two-wave mixing for coherent homodyne detection of arbitrary wavefronts was previously reported and applied to the detection and amplification of an intensity modulated wave2. In the case of interest here of the detection of surface motion, the signal wave which has been scattered off the surface is instead phase modulated, and the scheme previously reported cannot be directly used since the transmitted signal wave and the diffracted pump wave, which acts as local oscillator, are in phase. Linear and sensitive detection of phase shifts requires instead the interfering light fields to be in quadrature. Before describing an optical configuration which satisfies this requirement, we analyze the effect of a small phase shift applied to the signal wave in a two-wave mixing configuration.
{"title":"Detection of the transient motion of a scattering surface by two-wave mixing in a photorefractive crystal","authors":"R. Ing, J. Monchalin","doi":"10.1364/pmed.1991.wc8","DOIUrl":"https://doi.org/10.1364/pmed.1991.wc8","url":null,"abstract":"Optical detection of the transient surface motion of objects is an area of far reaching practical importance. Applications include the vibration monitoring of many engineering structures (power plants, aircrafts, engines of various kinds...) and more recently the detection of ultrasound produced by pulse laser excitation. This technique, now in active development in our laboratory and elsewhere, extends ultrasonic inspection of materials to conditions otherwise difficult or impossible (complex geometries, hot products on a production line...). Various optical systems have been devised for detecting surface motion and have been recently reviewed1. We are reporting here the novel use of two wave mixing in a photorefractive crystal for detecting such a motion and in particular ultrasonic displacement produced by pulsed laser excitation. This approach has the merit of being applicable to a rough surface by integrating over many speckles and of having a very broad frequency detection bandwidth. The use of two-wave mixing for coherent homodyne detection of arbitrary wavefronts was previously reported and applied to the detection and amplification of an intensity modulated wave2. In the case of interest here of the detection of surface motion, the signal wave which has been scattered off the surface is instead phase modulated, and the scheme previously reported cannot be directly used since the transmitted signal wave and the diffracted pump wave, which acts as local oscillator, are in phase. Linear and sensitive detection of phase shifts requires instead the interfering light fields to be in quadrature. Before describing an optical configuration which satisfies this requirement, we analyze the effect of a small phase shift applied to the signal wave in a two-wave mixing configuration.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"45 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129052712","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}
Noise reduction techniques in photorefractive amplifiers are centrally important for numerous applications in image processing, pattern recognition and detection of ultra-low optical wavefronts. Recently original techniques for reducing the optical noise were proposed and experimentally demonstrated(1-3). Rotating the crystal is a very general method which successfully removes the amplified scattered noise and the multiple interface parasite reflections. In this paper, we propose an alternative for which no mechanical movement is required. As will detailed in the following, this new noise reduction method is mostly suited to photorefractive materials which exhibit a strong resonance of the two-wave mixing gain around the optimum angle between the injected signal and the pump beam.
{"title":"Detection of Low Intensity Optical Wavefronts Using Noise Reduction Techniques in Photorefractive Amplifiers","authors":"H. Rajbenbach, A. Delboulbé, J. Huignard","doi":"10.1364/pmed.1991.mc6","DOIUrl":"https://doi.org/10.1364/pmed.1991.mc6","url":null,"abstract":"Noise reduction techniques in photorefractive amplifiers are centrally important for numerous applications in image processing, pattern recognition and detection of ultra-low optical wavefronts. Recently original techniques for reducing the optical noise were proposed and experimentally demonstrated(1-3). Rotating the crystal is a very general method which successfully removes the amplified scattered noise and the multiple interface parasite reflections. In this paper, we propose an alternative for which no mechanical movement is required. As will detailed in the following, this new noise reduction method is mostly suited to photorefractive materials which exhibit a strong resonance of the two-wave mixing gain around the optimum angle between the injected signal and the pump beam.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128706466","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}
Recently, there are extensive studies on applying the photorefractive effect for optical data storage and processing[1][2]. One of the most important applications is for the volume holographic storage. In this paper we report theoretical derivations and experimental results on the important properties of the anisotropic diffraction in a photorefractive volume hologram in a BaTiO3. As we shall see, the diffraction efficiency, the angular sensitivity, and the optimal reconstructing angle for obtaining the maximum diffraction efficiency depend very much on the grating vector and crystal orientations. The crystal orientation and the light beam directions are shown in Fig.1. In order to avoid the beam coupling phenomena[3], we use S-polarized light for writing holograms and P-polarized light for reconstruction.
{"title":"Anisotropic Diffraction in Photorefractive Volume Hologram","authors":"Ching-Cherng Sun, M. Chang","doi":"10.1364/pmed.1991.wa7","DOIUrl":"https://doi.org/10.1364/pmed.1991.wa7","url":null,"abstract":"Recently, there are extensive studies on applying the photorefractive effect for optical data storage and processing[1][2]. One of the most important applications is for the volume holographic storage. In this paper we report theoretical derivations and experimental results on the important properties of the anisotropic diffraction in a photorefractive volume hologram in a BaTiO3. As we shall see, the diffraction efficiency, the angular sensitivity, and the optimal reconstructing angle for obtaining the maximum diffraction efficiency depend very much on the grating vector and crystal orientations. The crystal orientation and the light beam directions are shown in Fig.1. In order to avoid the beam coupling phenomena[3], we use S-polarized light for writing holograms and P-polarized light for reconstruction.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"2011 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125638093","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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