Stabilized recording and thermal fixing of holograms in photorefractive lithium niobate crystals

Abstract

Holograms are thermally fixed in photorefractive lithium niobate crystals, i.e., they are recorded at temperatures between 130 and 180 °C. The setup is actively stabilized during recording against movements or vibrations of the interference pattern which especially occur during long-period writing at enhanced temperatures. Two different techniques are investigated: (1) Interference of the recording beams using one crystal surface as a beamsplitter yields a signal for stabilization. (2) Alternatively, one of the beams is periodically phase modulated and the beam-coupling signal is used for stabilization. Reproducible refractive index changes of thermally fixed holograms up to 7.5×10−4 are obtained with both stabilization techniques. However, the second method is advantageous for multiplexing experiments, because no readjustment of the beam-coupling stabilization system is required if the angles of the recording beams are changed.

Photorefractive properties of lithium niobate crystals doped with manganese

“…The recording is stabilized utilizing an active feedback system. 30 From Fig. 6, we can see that a linear dependence of ⌬n s,o on the Mn concentration is still valid even for the highly doped crystal with a Mn concentration of 122 ϫ 10 24 m Ϫ3 .…”

Description of readout processes during strong beam coupling

“…This method employs a strong momentary phase modulation of one of the input beams which changes the position of the light fringes. The third important implication of the readout properties is the feedbackcontrolled beam coupling [7][8][9][10]. In this case, the readout characteristics obtained with the help of an auxiliary weak phase modulation are used to adjust the input phase via an electronic feedback loop.…”

Optimal recording wavelength for maximum diffraction efficiency of thermal fixing in LiNbO_3:Fe

“…The first is the low-high-low procedure (L-H-L procedure) or postfixing [8], which enables recording at room temperature, then compensating at high temperature, and finally developing at low temperature. The second is the high-low procedure (H-L procedure) or simultaneous fixing [9], which enables recording and compensating simultaneously at high temperature and finally developing at low temperature.…”