Near-infrared sensitive two-wave mixing adaptive interferometer based on a liquid crystal light valve with a semiconductor substrate.

Two-wave mixing adaptive interferometer based on a liquid crystal light valve with a semiconductor GaAs substrate is realized and studied at 1064 nm wavelength. The local response of the dynamic hologram recorded in the liquid crystal layer of the light valve allows for detection of small phase modulations of the object beam. The characteristics of the interferometer are estimated experimentally. The temporal adaptability lies in the subsecond range. The large optical nonlinearity of the cell is favorable for measurements of small displacements with high sensitivity.

Infrared sensitive liquid crystal light valve with semiconductor substrate.

A liquid crystal light valve (LCLV) is an optically controlled spatial light modulator that allows recording of dynamic holograms. Almost all known LCLVs operate in the visible range of the spectrum. In the present work we demonstrate a LCLV operating in the infrared. The interaction of signal and pump waves is studied for different applied voltages, grating spacings, and intensities of the recording beams. A fourfold amplification of the weak signal beam is achieved. The amplitude of the refractive index modulation Δn=0.007 and nonlinear coupling constant n2=-1 cm²/W are estimated from the experimental results. External phase modulation of one of the recording beams is used for a further transient increase of the signal beam gain.

Characteristics of two-wave mixing adaptive interferometer with CdTe:Ge at 1.06 and 1.55 µm and improved temporal adaptability with temperature control.

We have characterized a two-wave mixing adaptive interferometer based on dc-biased photorefractive CdTe:Ge crystal at 1.06 and 1.55 µm. Excellent performance is shown at both wavelengths by demonstration of high sensitivity for measurement of small displacements and high cutoff frequency at low intensity. We have achieved a considerable reduction of the undesired low-frequency response using controlled heating of the crystal, which ensures depopulation of corresponding traps. The experimental data are used for measurement of the real and imaginary parts of the coupling constant, as well as the dielectric relaxation time of the crystal and the mobility-lifetime product of the free charge carriers.

High photorefractive gain at counterpropagating geometry in CdTe:Ge at 1.064 microm and 1.55 microm.

Recording of efficient reflection holograms is achieved in CdTe:Ge at lambda=1.064 microm and lambda=1.55 microm. The gain factor measured at both wavelengths for counterpropagating two-beam coupling considerably exceeds the absorption constant and transcends all values previously reported for semiconductors with no external field. The dependences of the gain factor on intensity and grating spacing are studied. Some crystal characteristics are estimated in the frame of a single band, one mobile species approximation of space-charge formation. The homogeneity of photorefractive properties in the crystal volume is demonstrated.