Detection of phase- and frequency-modulated optical signals using dynamic space-charge gratings in wide-bandgap crystals

The excitation of the non-steady-state photoelectromotive force and two-wave mixing signals is theoretically investigated for the case of uniformly accelerated motion of the recording light pattern. Such illumination is usually created by the linear frequency modulation of the interfering light beams. For the both effects we predict the pulsed response arising at the moments, when the velocities of the interference pattern and space-charge wave coincide. The application of the effects in laser Doppler velocimeters and accelerometers is discussed as well.We also study the excitation of the non-steady-state photoelectromotive force in semiinsulating SiC crystals illuminated by a phase-modulated light signal. Influence of an external ac electric field and shallow traps on the signal is revealed. Photoelectric parameters of the material and sensitivity of the detectors are estimated for the light wavelength λ = 532 nm.