Multiple-path telescope: third-order design.

Exact results for the magnification and effective focal length of a multiple-path telescope are presented. We present analytical results for the third-order design of this system, using the Seidel sums for the five aberration terms. Numerical calculations are used throughout to corroborate these results. Third-order aberrations remain small or at least stable as the number of paths is increased.

Phase conjugation in amorphous selenium thin films.

We report phase conjugation in amorphous selenium thin films with a 25-mW He-Ne laser. The phase-conjugate signal exhibits a maximum efficiency of 18%. Gratings were recorded with spatial frequencies of 275 lines/mm. We have performed micro Raman spectroscopy measurements between and on the lines that form the grating, and the results reveal the presence of amorphous selenium only. Scanning electron microscopy together with profilometry measurements indicate induced variations of the film thickness. However, this relief does not seem sufficient to explain the observed effects.

Laser-induced diffraction patterns in germanium diselenide amorphous films.

We report the characterization of changes produced on germanium diselenide amorphous semiconductor thin films by a focused He-Ne laser beam. The diffraction pattern produced by the laser spot on the sample is studied as a function of the intensity and the irradiation time. At low intensities the state of polarization of the incident beam generates an asymmetry in the induced diffraction pattern. Moreover, if the polarization of the incident beam is rotated, the corresponding asymmetry rotates as well. These results show the difference between thermal and electromagnetic effects on the material. This system may be used as a high density recording medium.