Two-dimensional, optical temporal bandpass filter using four-wave mixing in a BSO crystal: dynamic schlieren imaging system

Dynamic photorefractive Schlieren system

We present a dynamic Schlieren system that uses optical phase conjugation in a photorefractive crystal. The theoretical description of the system predicts that the square of the phase change in an object field is mapped as the intensity modulation in the system output. This is demonstrated experimentally with a He-Cd laser and a BaTiO(3) crystal arranged in the self-pumped phase-conjugator configuration.

Application of the BaTiO(3) beam-fanning optical limiter as an adaptive spatial filter for signal enhancement in pulsed infrared laser-excited photothermal spectroscopy

A method for obtaining a high-contrast visible-light signal from infrared absorption in low-absorbance samples is described. This method is based on a beam-fanning optical limiter in photorefractive BaTiO(3). The resulting signal is not linear but does exhibit an enhanced signal-to-background ratio that is 4 to 6 orders of magnitude better than that of conventional infrared absorption spectrophotometry in the shot-noise limit. A simple model for the beam-fanning, optical-limiter-based, pulsed-laser-excited photothermal spectroscopy detector is found to describe the experimental data adequately. This technique using photothermal spectroscopy detection may have advantages for rapid signal analysis and for two-dimensional visible imaging of infrared absorption.

Detection of subsurface defects using phase conjugate waves and forced vibration

In four-wave mixing in BSO crystal, a periodic forced vibration is applied to both the object under test and the standard object to provide signal and reference waves, respectively. The system images subsurface defects of the test object by converting the difference of vibration between the test and the standard objects into image intensity. The principle and basic experimental results are given.