Temporal diffraction by nonlinear interaction in optical fibers.

We describe an experiment in which two temporally stretched femtosecond pulses interact in a Kerr-like nonlinear medium. At high pulse energy, new, regularly spaced peaks appear in the autocorrelation of the recompressed output. The results are in quantitative agreement with numerical calculations of nonlinear propagation that show that both advanced and retarded pulses are present in the recompressed output and are comparable in duration with the input pulses. The results can be explained by drawing an analogy between four-wave mixing in real space and diffraction in the time domain.

Numerical and experimental comparison of spectral broadening of femtosecond optical asymmetric pulses in a monomode fiber.

The experimental self-phase-modulation spectra of 55-fsec optical pulses after propagation along 11 mm of monomode fiber are compared with the computed spectra obtained by a numerical solution of the nonlinear wave-propagation equation. We discuss the relative importance of the pertinent additional terms (third-order-disperson, shock, and reflection terms) and the importance of an asymmetric profile of the input pulses. This asymmetry is found to be a dominant parameter in the self-phase-modulation process. No other physical effect must be used in order to explain the observed spectra, which agree well with the numerical data.

Elastooptical antenna for detection of gravitational radiation.

Using the photoelastic effect in transparent solids to detect stresses induced by a gravitational wave is proposed. The induced birefringence is measured by a polarimeter. The phase difference is amplified by a Fabry-Perot cavity containing the medium. The sensitivity of this optical strain sensor is discussed, and that of the antenna is estimated.

Automatic measurement of the Stokes vector of light.

A system which measures the Stokes parameters of light automatically over a wide range of wavelengths is described. The method requires two piezooptic modulators, three lock-in amplifiers, and an on-line minicomputer for data processing. The absence of a static retardation plate provides an unprecedented insensitivity to beam wandering. Typical performance parameters such as response time, accuracy, and detectivity as a function of the incident polarization are given.

Pupil filters for moderate superresolution.

Some superresolving pupils, featuring a central maximum narrower than Airy's core and a first secondary maximum of a few percent, have been computed, following Frieden's formula and his criterion of maximum superresolution for circular symmetry. A superresolution factor of about 28% may be achieved without much sacrifice of illumination. Other pupils have been investigated where the SF reaches 35%. The behavior of the sidelobes in the point impulse image is examined. The corresponding encircled energy and point impulse response are given.