REAL-TIME TWO-WAVELENGTH HOLOGRAPHIC INTERFEROMETRY WITH A BISMUTH-SILICON OXIDE CRYSTAL.

The Bismuth Silicon Oxide (BSO) single crystal can be obtained both in a large size and with good optical quality. It has been demonstrated that the BSO (Bi₁₂SiO₂₀) crystal is a practical holographic recording medium. BSO is a semiconductor and has a large electro-optic coefficient. These two properties of the BSO crystal are responsible for its capability to record. In this study, the linear and circular birefringence of the BSO crystal under an electric field were investigated. The measurement method is by passing a linearly polarized wavefield through the crystal. The transmitted wavefield is written in parametric expressions using Jones calculus, and the wavefield is probed by a simple ellipsometer. The two parameters in the Jones matrix, the linear and circular birefringence, are solved from the experimental data. The electro-optic coefficient is determined from the resulting linear birefringence to be 3.57 x 10⁻¹⁰ cm/V at λ = 632.8 nm. The diffraction efficiency and temporal response of the BSO crystal in the transverse electro-optic configuration were studied. The crystal was then coated with a single layer antireflection coating to investigate the effect of a multi-reflections inside the crystal. The result showed that although the visibility improved only about 20%, the diffraction efficiency and temporal response improved two times. The BSO crystal is used as the recording medium in a two-wavelength holographic interferometer. An optical edge filter is used in the interferometer to adjust the beam ratio, and a prism is used to incorporate tilt in the interferometer and to deviate the two wavelengths to satisfy the Bragg's condition for the volume hologram. The 488 and 514.5 nm lines of an argon-ion laser are used to give an equivalent wavelength of 9.45 μm. The interferograms obtained are of high contrast