We present analytical expressions for time-dependent space charge fields and two wave-mixing gains under the external applied fields accompanying with the grating translation. We analyzed the variations of complex space charge fields in a complex plane, and also obtained the explicit expressions for the resonance and optimum frequencies (or moving grating velocities), which maximize the magnitude and imaginary part of space charge fields. We also conducted two wave-mixing experiments with the grating translation technique without an external applied field in a BaTiO3 crystal. The transient behaviors of measured gains look like damped harmonic oscillations, showing excellent agreement with the theory for the entire time range.
© 2008 Optical Society of America
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