Holographic technique for measurement of the kinetic constant and optical modulation of photosensitive materials.

We use a holographic technique to measure simultaneously and separately the temporal evolution of the refractive-index and the absorption coefficient modulations induced by light in a photosensitive material. The technique is phase sensitive, allowing separation of the signals from the phase and from the amplitude grating. The refractive-index and the absorption coefficient modulations as well as the kinetic constant of the photoreaction in the positive photoresist SC 1827 were measured at three different wavelengths. The results were compared with independent measurements, performed under homogeneous exposition. The good accord demonstrates the applicability of the technique to study photosensitive materials.

Measurement of phase differences between the diffracted orders of deep relief gratings.

Measurement of the phase difference between the 0th and the 1st transmitted diffraction orders of a symmetrical surface-relief grating recorded on a photoresist film is carried out by replacement of the grating in the same setup with which it was recorded. The measurement does not depend on lateral shifts of thereplaced grating relative to the interference pattern, on environmental phase perturbations or on the wave-front quality of the interfering beams. The experimental data agree rather well with theoretical results calculated for sinusoidal profiled gratings.

Avoiding hologram bending in photorefractive crystals.

Dynamic coupled-wave theory predicts the bending of recorded hologram phase planes in most photorefractive crystals. Bent holograms occur in LiNbO(3) and other photovoltaic crystals that are particularly interesting as holographic storage media and result in a reduced overall diffraction eff iciency. We show that hologram bending in LiNbO(3) can be avoided or at least sensibly reduced by use of an actively stabilized recording technique.

Adjustable phase control in stabilized interferometry.

We report an optoelectronic feedback loop that permits the active stabilization of an interferometric setup for any chosen value of the phase between the interfering beams. This method is based on phase modulation and homodyne detection techniques. The phase can be stabilized with a precision of better than 1 deg for our experimental conditions.

Phase-compensated holographic recording based on anisotropic photorefractive diffraction.

We report a simple actively stabilized setup for holographic recording on sillenite photorefractive crystals that is based on the anisotropic diffraction properties of these materials. The method is much simpler than previously published ones, requires neither phase modulation nor synchronous phase-sensitive detection, and needs no external reference. We describe the successful operation of this stabilization procedure for a Bi(12)TiO(20) crystal in a practical holographic interferometry setup, using the 632.8-nm wavelength of a He-Ne laser.