Models for the bulk photovoltaic effect in ferroelectric crystals

1988 ◽  
Vol 66 (8) ◽  
pp. 649-654 ◽  
Author(s):  
Fayez El Guibaly
Keyword(s):  
Electron Transport ◽  
Spatial Frequency ◽  
Interference Pattern ◽  
Photovoltaic Effect ◽  
Hologram Recording ◽  
Optical Interference ◽  
Intensity Pattern ◽  
Transport Length ◽  
Beam Coupling ◽  
Optical Pattern

Three models for the bulk photovoltaic effect in electrooptic crystals are discussed. All models produce the same results. First, the photocurrent responsible for hologram storage is spatially shifted relative to the optical pattern that produced it. Second, the efficiency of hologram recording decreases with increases in the spatial frequency of the optical interference pattern. Third, the efficiency of hologram recording decreases for crystals exhibiting a strong bulk photovoltaic effect. The effect of finite electron transport length on volume-phase hologram storage is analyzed. It is shown that the resulting holograms are spatially shifted relative to the optical-intensity pattern that produced it. This phase shift affects beam coupling during hologram reading; it can be an aid in studying the bulk photovoltaic effect and the relative importance of the various mechanisms of hologram writing. The analysis also points out that the finite electron transport length reduces the ability of the crystal to store holograms if the spatial frequency of the optical interference pattern is increased.

Hologram writing in lithium niobate: Beam coupling and the transport length in the bulk photovoltaic effect

1979 ◽  
Vol 50 (6) ◽  
pp. 4201-4207 ◽  
Author(s):  
L. Young ◽  
M. G. Moharam ◽  
F. El Guibaly ◽  
E. Lun
Keyword(s):  
Lithium Niobate ◽  
Photovoltaic Effect ◽  
Transport Length ◽  
Beam Coupling

The photorefractive sensitivity and the effective electron transport length in two-centre holographic recording

2006 ◽  
Vol 15 (12) ◽  
pp. 2977-2983 ◽  
Author(s):  
Zhou Yu ◽  
Liu Li-Ren ◽  
Liu De-An ◽  
Luan Zhu ◽  
Yan Ai-Min
Keyword(s):  
Electron Transport ◽  
Holographic Recording ◽  
Effective Electron ◽  
Transport Length

Optical Limiting with Lithium Niobate

1999 ◽  
Vol 597 ◽  
Author(s):  
Gary Cook ◽  
David C. Jones ◽  
Craig J. Finnan ◽  
Lesley L. Taylor ◽  
Tony W. Vere ◽  
...  
Keyword(s):  
Lithium Niobate ◽  
Diffusion Theory ◽  
Photovoltaic Effect ◽  
Optical Gain ◽  
Optical Limiting ◽  
Dark Conductivity ◽  
Simple Diffusion ◽  
Beam Coupling ◽  
Coupling Equations ◽  
Focusing Lens

AbstractIron doped lithium niobate (Fe:LiNbO3) in a simple focal plane geometry has demonstrated efficient optical limiting through two-beam coupling. The performance is largely independent of the total Fe concentration and the oxidation state of the Fe ions, providing the linear optical transmission of uncoated crystals is between 30% and 60%. Fe has been found to be the best dopant for LiNbO3, giving the widest spectral coverage and the greatest optical limiting. Optical limiting in Fe:LiNbO3 has been shown to be very much greater than predicted by simple diffusion theory. The reason for this is a higher optical gain than expected. It is suggested that this may be due to an enhancement of the space-charge field arising from the photovoltaic effect. The standard two-beam coupling equations have been modified to include the effects of the dark conductivity. This has produced a theoretical intensity dependence on the ΔOD which closely follows the behaviour observed in the laboratory. A further modification to the theory has also shown that the focusing lens f-number greatly affects the optical limiting characteristics of Fe:LiNbO3. A lens f-number of approximately 20 gives the best results.

Cortical Anatomy, Size Invariance, and Spatial Frequency Analysis

Perception ◽  
1981 ◽  
Vol 10 (4) ◽  
pp. 455-468 ◽  
Author(s):  
Eric L Schwartz
Keyword(s):  
Spatial Frequency ◽  
Human Vision ◽  
Second Step ◽  
Optical Pattern Recognition ◽  
Optical Pattern ◽  
Logarithmic Mapping ◽  
Size Invariance ◽  
Primate Vision ◽  
The Brain ◽  
Spatial Frequency Analysis

In a recent application of an algorithm developed in computer and optical pattern recognition, Cavanagh has suggested that a composite of spatial frequency mapping and complex logarithmic mapping would provide a translationally, rotationally, and size-invariant mechanism for human vision. In this work, Cavanagh has not made explicit the fact that this transformation is composite, that is, that the first step (global Fourier analysis) is perceptually, anatomically, and physiologically inconsistent with primate vision, but that the second step (complex logarithmic mapping) is actually embodied in the anatomy of the primate retinostriate projection. Moreover, it is the complex logarithmic remapping step which is entirely responsible for the computational simplification of the symmetries of size and rotation invariance. These facts, which have been extensively discussed in a recent series of papers, are briefly reviewed and illustrated. Furthermore, it is shown that the architecture of the retinostriate map may provide an example of computational anatomy in vision, such that the spatial representation of a stimulus in the brain may be of direct functional significance to perception, and to the nature of certain visual illusions.

scholarly journals Lateral photovoltaic effect and electron transport observed in Cr nano-film

2014 ◽  
Vol 22 (10) ◽  
pp. 11627 ◽  
Author(s):  
Shuai Liu ◽  
Xin Xie ◽  
Hui Wang
Keyword(s):  
Electron Transport ◽  
Photovoltaic Effect

Nonlinear Optical Properties of Organic Photorefractive Polymers

1992 ◽  
Vol 277 ◽  
Author(s):  
W. E. Moerner ◽  
C. A. Walsh ◽  
S. M. Silence ◽  
R. J. Twieg ◽  
T. J. Matray ◽  
...  
Keyword(s):  
Nonlinear Optical ◽  
Optical Nonlinearity ◽  
Intensity Pattern ◽  
Photorefractive Polymers ◽  
Beam Coupling ◽  
Epoxy Material ◽  
A Charge ◽  
Spatial Phase Shift ◽  
Index Modulation ◽  
Grating Formation

ABSTRACTThis paper describes the photorefractive properties of a new and growing class of materials exhibiting the effect, doped nonlinear organic polymers. We show directly using a PMMA-based copolymer with a pendant nonlinear nitroaminotolane chromophore doped with a charge transport agent that the presence of photoconductivity and optical nonlinearity are only necessary, but not sufficient to guarantee that a given materials system will yield measurable photorefractive gratings, rather than gratings due to some other process such as photochromism. To prove photorefractivity unequivocally, direct measurement of the spatial phase shift between the intensity pattern and the index modulation is best, and we summarize a convenient way to do this using two-beam coupling and sample translation. In addition to the photorefractive epoxy materials such as bisA-NPDA:DEH reported earlier (Phys. Rev. Lett. 66, 1846 (1991); Proc. SPIE1560, 278 (1992)), a new PMMA-based copolymer with pendant p-nitroaniline chromophores doped with DEH also shows photorefractive grating formation, with writing speed 100 times higher than that for the epoxy material.

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