Huignard et al. presented a speckle-free imaging processor using a BSO crystal and four-wave mixing. The input beam passed through a diffuser screen which was mounted on a step by step rotation motor. Four-wave mixing generated a phase-conjugated beam which was time-integrated with a Polaroid camera [1].
{"title":"Time-Integrating Self-Pumped Phase Conjugator","authors":"E. Oldekop, A. Siahmakoun","doi":"10.1364/pmed.1991.wc11","DOIUrl":"https://doi.org/10.1364/pmed.1991.wc11","url":null,"abstract":"Huignard et al. presented a speckle-free imaging processor using a BSO crystal and four-wave mixing. The input beam passed through a diffuser screen which was mounted on a step by step rotation motor. Four-wave mixing generated a phase-conjugated beam which was time-integrated with a Polaroid camera [1].","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"43 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":"128292578","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}
E. V. Mokrushina, V. Prokof’ev, S. Sochava, S. Stepanov
There are two techniques of nonstationary holographic recording which are widely used for PRCs with long drift lengths of photocarriers. These are recording of a moving interference pattern in an external DC electric field [1] and recording of a fixed pattern in an AC field [21. Both of them allow the efficiency of the drift mechanism of recording in the external electric field to be increased and the recorded hologram to be transformed into a shifted one. The theory [3] predicts equal efficiencies of two-wave energy exchange for these two techniques. In practice, the "moving grating" technique is traditionally employed for Bi12SiO20 (BSO), but for Bi12TiO20 (BTO), recording in an AC field is in common use. Recent investigations of holographic recording in semi-insulating GaAs:Cr (λ=1.06 μm) [4,5] have demonstrated remarkable superiority of the moving grating mechanism.
{"title":"Experimental Comparison of the \"AC Field\" and \"Moving Grating\" Techniques for BTO and BSO Crystals","authors":"E. V. Mokrushina, V. Prokof’ev, S. Sochava, S. Stepanov","doi":"10.1364/pmed.1991.tuc1","DOIUrl":"https://doi.org/10.1364/pmed.1991.tuc1","url":null,"abstract":"There are two techniques of nonstationary holographic recording which are widely used for PRCs with long drift lengths of photocarriers. These are recording of a moving interference pattern in an external DC electric field [1] and recording of a fixed pattern in an AC field [21. Both of them allow the efficiency of the drift mechanism of recording in the external electric field to be increased and the recorded hologram to be transformed into a shifted one. The theory [3] predicts equal efficiencies of two-wave energy exchange for these two techniques. In practice, the \"moving grating\" technique is traditionally employed for Bi12SiO20 (BSO), but for Bi12TiO20 (BTO), recording in an AC field is in common use. Recent investigations of holographic recording in semi-insulating GaAs:Cr (λ=1.06 μm) [4,5] have demonstrated remarkable superiority of the moving grating mechanism.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"40 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":"114832432","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}
Consider the coupling between two trains of mode-locked pulses in a photorefractive crystal. Let each optical pulse be so weak that it takes a large number of pulses to built up a quasi-steady-state refractive-index grating in the crystal. In this case the shape of the pulses will change as the result of beam coupling.1 The temporal pulse shape changes for two reasons. First, interference between the diffracted pulse and the transmitted pulse alters the pulse shape, as shown in Fig. 1. Second, only a portion of each pulse's full frequency spectrum is diffracted by the volume photorefractive grating.
{"title":"Spectral Pulse Distortion from Two-Beam Coupling of Sub-Picosecond Pulses in a Photorefractive Crystal","authors":"X. Yao, J. Feinberg","doi":"10.1364/pmed.1991.wc4","DOIUrl":"https://doi.org/10.1364/pmed.1991.wc4","url":null,"abstract":"Consider the coupling between two trains of mode-locked pulses in a photorefractive crystal. Let each optical pulse be so weak that it takes a large number of pulses to built up a quasi-steady-state refractive-index grating in the crystal. In this case the shape of the pulses will change as the result of beam coupling.1 The temporal pulse shape changes for two reasons. First, interference between the diffracted pulse and the transmitted pulse alters the pulse shape, as shown in Fig. 1. Second, only a portion of each pulse's full frequency spectrum is diffracted by the volume photorefractive grating.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"79 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":"132264506","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}
G. Bouders, X. N. Phu, J. Lecoq, M. Sylla, G. Rivoire
A non linear medium is placed in the focal plane of a 4f set up (fig.1). The Fourier spectrum S(u) induces phase and amplitude changes inside the material [1].
在4f装置的焦平面中放置非线性介质(图1)。傅里叶谱S(u)引起了材料[1]内部的相位和幅度变化。
{"title":"An Imaging Method for Non Linear Medium Characteristic Measurements","authors":"G. Bouders, X. N. Phu, J. Lecoq, M. Sylla, G. Rivoire","doi":"10.1364/pmed.1991.tua1","DOIUrl":"https://doi.org/10.1364/pmed.1991.tua1","url":null,"abstract":"A non linear medium is placed in the focal plane of a 4f set up (fig.1). The Fourier spectrum S(u) induces phase and amplitude changes inside the material [1].","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":"129525899","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 phenomena of beam fanning and phase conjugation have been used to demonstrate such operations as optical limiting, interconnecting, tracking, and a wide variety of applications utilizing phase conjugate mirrors. Many other applications can be realized when two laser beams interact in a photorefractive crystal since one of the beams can be used to control the other. For example, it is possible to amplify, deplete, direct, switch, or modulate one of the beams with the other. The photorefractive effect provides the underlying mechanism for these demonstrations of all-optical light by light control. These applications depend upon the formation of particular photorefractive gratings and the perturbation of those gratings. Only recently has attention been given to the importance of the physical location of the gratings within the crystal.1,2,3
{"title":"Effects of Grating Erasure on Beam Fanning and Self-Pumped Phase Conjugation","authors":"G. Wood, W. Clark, E. Sharp, G. Salamo","doi":"10.1364/pmed.1991.wc14","DOIUrl":"https://doi.org/10.1364/pmed.1991.wc14","url":null,"abstract":"The photorefractive phenomena of beam fanning and phase conjugation have been used to demonstrate such operations as optical limiting, interconnecting, tracking, and a wide variety of applications utilizing phase conjugate mirrors. Many other applications can be realized when two laser beams interact in a photorefractive crystal since one of the beams can be used to control the other. For example, it is possible to amplify, deplete, direct, switch, or modulate one of the beams with the other. The photorefractive effect provides the underlying mechanism for these demonstrations of all-optical light by light control. These applications depend upon the formation of particular photorefractive gratings and the perturbation of those gratings. Only recently has attention been given to the importance of the physical location of the gratings within the crystal.1,2,3","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":"131307883","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}
Multiple-quantum-well structures in semiconductors have strong spatial inhomogeneity. Bandgaps in these multilayer samples vary by several tenths of eV over monolayer distances. These dramatic spatial changes in bandstructure have significant consequences for the photorefractive effect, creating new effects that have no analog in bulk photorefractive materials. The ability to design new materials and devices, and control desired photorefractive properties, has few limitations. Several processes give photorefractive quantum well structures unique advantages. Two charge separation processes, in particular, contribute to the novel effects: 1) bandgap energies can be selectively tuned to isolate optical absorption to some layers, but not others; 2) carriers in quantum wells tunnel into barrier regions with larger bandgaps, generating metastable defect occupancies with associated electric fields. These processes couple with one of the strongest advantages of quantum well structures: quantum-confined excitons. Quantum-confined excitons in semiconductors exhibit large quadratic electro-optic effects. The quadratic electro-optic effect combines with the charge separation processes to yield ultra-high sensitivity photorefractive effects with large diffraction efficiencies[1] and beam coupling gains. In this paper, we present the theory of photorefractive effects in quantum well structures, concentrating on the role of spatial inhomogeneity in the nonlinear optical behavior.
{"title":"The Photorefractive Properties of Quantum-Confined Excitons","authors":"D. Nolte, M. Melloch","doi":"10.1364/pmed.1991.ma8","DOIUrl":"https://doi.org/10.1364/pmed.1991.ma8","url":null,"abstract":"Multiple-quantum-well structures in semiconductors have strong spatial inhomogeneity. Bandgaps in these multilayer samples vary by several tenths of eV over monolayer distances. These dramatic spatial changes in bandstructure have significant consequences for the photorefractive effect, creating new effects that have no analog in bulk photorefractive materials. The ability to design new materials and devices, and control desired photorefractive properties, has few limitations. Several processes give photorefractive quantum well structures unique advantages. Two charge separation processes, in particular, contribute to the novel effects: 1) bandgap energies can be selectively tuned to isolate optical absorption to some layers, but not others; 2) carriers in quantum wells tunnel into barrier regions with larger bandgaps, generating metastable defect occupancies with associated electric fields. These processes couple with one of the strongest advantages of quantum well structures: quantum-confined excitons. Quantum-confined excitons in semiconductors exhibit large quadratic electro-optic effects. The quadratic electro-optic effect combines with the charge separation processes to yield ultra-high sensitivity photorefractive effects with large diffraction efficiencies[1] and beam coupling gains. In this paper, we present the theory of photorefractive effects in quantum well structures, concentrating on the role of spatial inhomogeneity in the nonlinear optical behavior.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"31 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":"125115748","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}
Among the variety of photorefractive crystals BaTiO3 distinguishes by its large nondiagonal electrooptic coefficient r42 = 1600pm/V which enables efficient anisotropic diffraction [1, 2].
{"title":"Holographic recording and parametric scattering due to orthogonally polarized beams in BaTiO3","authors":"L. Holtmann, E. Kratzig, M. Goulkov, S. Odoulov","doi":"10.1364/pmed.1991.tuc22","DOIUrl":"https://doi.org/10.1364/pmed.1991.tuc22","url":null,"abstract":"Among the variety of photorefractive crystals BaTiO3 distinguishes by its large nondiagonal electrooptic coefficient r42 = 1600pm/V which enables efficient anisotropic diffraction [1, 2].","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"11 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":"116715696","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}
C. Benkert, V. Hebler, Ju-Seog Jang, S. Rehman, M. Saffman
An important feature of neural network processing lies in a network’s ability to adapt to a given problem. The adaptation is accomplished by modifying its internal structure through some learning procedure. Neural network models may be classified in one of two types: The learning may be supervised by someone or something that indicates to the network what is expected of it, or the network may be governed by a self-organizing process in which it automatically develops an internal state that reflects the properties of its input environment. Self-organizing systems need no a priori knowledge supplied by a supervisor, and are particularly valuable when the task of the system depends only upon some property of the input data itself.
{"title":"Feature extraction by a self-organizing photorefractive system","authors":"C. Benkert, V. Hebler, Ju-Seog Jang, S. Rehman, M. Saffman","doi":"10.1364/pmed.1991.wc5","DOIUrl":"https://doi.org/10.1364/pmed.1991.wc5","url":null,"abstract":"An important feature of neural network processing lies in a network’s ability to adapt to a given problem. The adaptation is accomplished by modifying its internal structure through some learning procedure. Neural network models may be classified in one of two types: The learning may be supervised by someone or something that indicates to the network what is expected of it, or the network may be governed by a self-organizing process in which it automatically develops an internal state that reflects the properties of its input environment. Self-organizing systems need no a priori knowledge supplied by a supervisor, and are particularly valuable when the task of the system depends only upon some property of the input data itself.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"91 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":"126456202","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 in BaTiO3 has been the subject of extensive research in recent years. Because of very large electro-optic coefficients, BaTiO3 has become a unique candidate for a variety of nonlinear optical devices which operate at very low light intensities. Most of these devices use energy transfer between coherent optical beams that interfere inside the crystal while some devices use the extinction of a single beam through beam fanning1-3.
{"title":"Application of Beam Fanning in a Photorefractive BaTiO3 Crystal: Measurement of Light Scattering at Zero Degrees by a Single Glass Fiber","authors":"G. Padmabandu, C. Oh, E. Fry","doi":"10.1364/pmed.1991.wa4","DOIUrl":"https://doi.org/10.1364/pmed.1991.wa4","url":null,"abstract":"The photorefractive effect in BaTiO3 has been the subject of extensive research in recent years. Because of very large electro-optic coefficients, BaTiO3 has become a unique candidate for a variety of nonlinear optical devices which operate at very low light intensities. Most of these devices use energy transfer between coherent optical beams that interfere inside the crystal while some devices use the extinction of a single beam through beam fanning1-3.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"32 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":"125723243","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}
It is obvious that the homogeneity of the photorefractive sensitivity has strong influence on devices such as optically driven spatial light modulators (SLM) 1-3. These applications involve two-dimensional image information and need position-independent transfer functions. The photorefractive homogeneity is based on the distribution of the photorefractive donor centers and traps in the crystal. Therefore it is affected by the crystal growth conditions and subsequent crystal treatments such as poling and electro-chemical reduction 4, 5.
{"title":"Homogeneity of the photorefractive effect in reduced and unreduced KNbO3 crystals","authors":"P. Amrhein, P. Gunter","doi":"10.1364/pmed.1991.tua8","DOIUrl":"https://doi.org/10.1364/pmed.1991.tua8","url":null,"abstract":"It is obvious that the homogeneity of the photorefractive sensitivity has strong influence on devices such as optically driven spatial light modulators (SLM) 1-3. These applications involve two-dimensional image information and need position-independent transfer functions. The photorefractive homogeneity is based on the distribution of the photorefractive donor centers and traps in the crystal. Therefore it is affected by the crystal growth conditions and subsequent crystal treatments such as poling and electro-chemical reduction 4, 5.","PeriodicalId":355924,"journal":{"name":"Photorefractive Materials, Effects, and Devices","volume":"6 4","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132360133","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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