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Residual amplitude modulation (RAM) mechanisms in electro-optic phase modulators are detrimental in applications that require high purity phase modulation of the incident laser beam. While the origins of RAM are not fully understood, measurements have revealed that it depends on the beam properties of the laser as well as the properties of the medium. Here we present experimental and theoretical results that demonstrate, for the first time, the dependence of RAM production in electro-optic phase modulators on beam intensity. The results show an order of magnitude increase in the level of RAM, around 10 dB, with a fifteenfold enhancement in the input intensity from 12 to 190  mW/mm2. We show that this intensity dependent RAM is photorefractive in origin.

We report on the reversal of degradation of information masks stored in self-defocusing lithium niobate. After a long writing time, the image degradation appears as the splitting of refractive-index patterns stored in the medium. The reversal is achieved simply by illuminating the crystal with incoherent light from a halogen lamp. The reversal occurs because the refractive-index changes responsible for the splitting are of a smaller magnitude and are therefore erased first during incoherent illumination. Additionally, we gain insight into the storage, degradation, and erasure dynamics using a time-dependent numerical model of the photorefractive effect in this medium. Since the data can be recovered from a degraded state in which the original data are unrecognizable, this technique could be utilized in such applications as image scrambling or encryption.

The minimum quantities of the nine most abundant, isolated, atmospheric gases that are detectable with a refractometer are calculated. An examination of the applicability of refractometric techniques for detecting and analyzing gaseous mixtures is discussed and a comparison made against other established techniques. Traditionally, most gas analysis performed with an interferometer is in determining the dispersion or refractivity of a known sample, presented here is the inverse approach, where refractivities are measured to determine the concentrations of particular species within a gas. The method, and experimental results for determining the minimum quantities of a particular species detectable in a mixture has been explored, as well as the complications, such as the indistinguishability of dynamic polarizabilities of different gases and the subsequent demands for accurate pressure and fringe measurements of using interferometric techniques. It is shown that the concentration of a single (isolated) gas, in units of number density, can be determined to within approximately 1-10 x 10(18) m(-3), and a mixture of the three most abundant gases, N2, O2 and Ar, to within 3.4 x 10(4) parts in 10(6) (ppm) when a minimum detectable fringe shift of lambda/100 is assumed.

A theoretical model of modulation transfer spectroscopy (MTS) that includes pump beam depletion is presented and experimentally verified with data covering visible iodine transitions at 532, 543, and 612 nm. This model is used to determine the values for pressure, interaction length, and saturation intensity that yield maximum MTS signals for frequency locking to iodine transitions. The approach is demonstrated for iodine transitions at 532, 633, and 778 nm, with the results showing that theoretically the frequency instability scales inversely to the absorption coefficient.