Enhancement of the photorefractive gain in CdTe at 1.3-1.5 μm under alternating electric fields

Abstract

CdTe:V is a photorefractive material with high theoretical and measured sensitivities at wavelengths from the band edge (0.9 μm) to 1.5 μm. We report large enhancement of the two-beam-coupling gain in V-doped CdTe by using the applied alternating field method with square and sinusoidal wave forms. With nominally square wave forms, gain coefficients in excess of 10 cm−1 have been measured at 1.3 μm wavelength, which significantly exceed the absorption coefficient of 2 cm−1 in our sample. We have studied the effects of the ac voltage pulse shape using nominally square waves in the 100-230 kHz range and sinusoidal fields in the 3-7 MHz range. The exact shape of the internal electric field is measured by using the electro-optic field-induced birefringence and suggests a fast screening of the internal field. We will present a model that discusses the major effects of the alternating waveform shape and internal field screening on the beam-coupling gain. We have also measured the dependence of the gain on the pump-to-signal beam ratios and will present the results for both square and sinusoidal waveforms. Our observations suggest that large gain values are only attainable at very large beam ratios for the case of square waves.