We have developed a model to explain the phenomena of electron focusing by pyroelectric and photogalvanic crystals. The pyroelectric crystals used to compare experiments with theory were Fe doped and un-doped LiNb0<sub>3</sub>. The crystals were either heated from the +z end or illuminated with a laser (to test photogalvanic effect). Heating the crystals by passing a current through a resistor attached to the +z end produced the pyroelectric effect: a change in polarization in response to a change in temperature. Illuminated with a CW solid-state diode pumped laser (532 nm, 100 mW) produces the photogalvanic effect: the build up of charge on the polar surfaces of the crystal. In both cases the polar ends of the crystal becomes electrically charged and produced self-focusing electron beams that were imaged on a ZnS screen. Using different targets we have produced x-rays, and demonstrated x-ray imaging of metal masks.
We have developed the all-optical EO-modulator using a pulsed photogalvanic power supply driven by light illumination (coherent and incoherent). Generated by ferroelectric crystal with the photogalvanic effect (Fe-doped LiNbO<sub>3</sub>), electrical pulses were used for driving a standard EO-modulator, based on transversal EO effect in Bi<sub>12</sub>SiO<sub>20</sub> (BSO) crystals. Both parallel and serial connections of photogalvanic crystal (LN), BSO and oscilloscope were tested. The depth of EO-modulation was very sensitive to the impedance of the connected cables, which implies the existence of transmission-line resonances. Secondly, a more compact version of EO self-modulation is realized with green (wavelength λ=532 nm, P=100mW) solid-state CW laser. In this case, reflection of the CW laser from the LN crystal was modulated in time. Pulsating optical reflection was correlated with the pulsating electrical signals. We report both modes of operation: (1) as pulsed high-voltage power supply, and (2) as compact-pulsed optical modulator. We have described these pulsations using model of photogalvanic effect and ferroelectric emission.
We have observed regenerative optical and electrical pulsations in Fe-doped photogalvanic/photorefractive crystals LiNbO<sub>3</sub> (LN). Rise time of the emitted electromagnetic pulses was 2 ns and amplitude of up to 10V for Continuous Wave (CW) laser power 50-200 mW. Optical pulsators, predicted by our theoretical approach were realized in LiNbO<sub>3</sub>:Fe crystals using Ar-ion laser, of wavelength 514 and 457 nm, and power P= 50-200 mW, with frequencies of pulsation ranging from sec to msec. The arrays of the Optical Photogalvanic Pulsators (OPP) may be constructed as a testing field for a novel parallel processing logic based on the pulsed-couple neural networks (PCNN). We have also tested the synchronous nature of the optical, electrical and piezoelectric signals.
We have observed the conversion of CW laser Ar-ion beam power into pulsating multi-channel outputs: optical, electric and piezoelectric with simultaneous dynamic pattern formation. Frequencies of multi-channel pulsations have characteristic sigmoidal dependence (with threshold) on laser intensity. We have also demonstrated the possibility of synchronization of two optical pulsators, through regulated optical coupling in a photorefractive LiNbO<sub>3</sub> crystal. Spatial distribution of scattered light is selforganized in different patterns (hexagonal and cross-type)