Strong and fast phase modulation for quantitative analysis of photorefractive gratings

A new approach for studying photorefractive gratings in two-wave mixing experiments by a phase modulation technique is presented. The introduction of a large-amplitude, high-frequency sinusoidal phase modulation in one of the input beams blurs the interference pattern and provides powerful harmonic...

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Bibliographic Details
Published in:Applied physics. B, Lasers and optics Lasers and optics, 2006-05, Vol.83 (2), p.279-284
Main Authors: FRESCHI, A. A, DOS SANTOS, P. V, FREJLICH, J
Format: Article
Language:English
Subjects:
Beams (radiation)
Diffraction efficiency
Diffraction gratings
Exact sciences and technology
Fundamental areas of phenomenology (including applications)
Gratings
Gratings (spectra)
Harmonics
Mathematical models
Nonlinear optics
Optical elements, devices, and systems
Optics
Phase conjugation, optical mixing
photorefractive and kerr effects
Phase modulation
Phase shift
Physics
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Summary:A new approach for studying photorefractive gratings in two-wave mixing experiments by a phase modulation technique is presented. The introduction of a large-amplitude, high-frequency sinusoidal phase modulation in one of the input beams blurs the interference pattern and provides powerful harmonic signals for accurate measurements of the grating diffraction efficiency Delta *h and the output phase shift Delta *q between the transmitted and diffracted waves. The blurring of the light fringes can be used to suppress the higher spatial harmonics of the grating, allowing a space-charge field with sinusoidal profile to be recorded. Although the presence of such a strong phase modulation affects the beam coupling in a rather complicated way, it is shown that for the special case of equal intensity input beams, the effect of the phase modulation on Delta *h and Delta *q is reduced to a weakening of the coupling strength. The potentialities of the technique are illustrated in a study of refractive-index waves excited by running interference patterns in a Bi12TiO20 crystal. Expressions for the diffraction efficiency and the output phase shift are derived and used to match numerically calculated curves to the experimental data. The theoretical model is supported by the very good data fitting and allows the computation of important material parameters.
ISSN:0946-2171
1432-0649
DOI:10.1007/s00340-006-2145-x