Using short-pulse laser techniques, the formation time and absolute production efficiency of F centers in KCl have been investigated on the time scale of 10 " sec. The temperature-dependent yield of F centers observable at 46 psec following two-photon band-gap excitation has been determined over the range 12-880 K in crystalline KCl. The yield of F centers per ionizing event approaches unity near the melting point. The observation of transient 532-nm absorption resulting from ultraviolet pulse irradiation of molten KCl is reported. The formation time, production efficiency, and room-temperature decay time of self-trapped excitons in the lowest triplet state in NaCl have been investigated, as has the onset of 532-nm absorption in NaBr. The observations, in general, place upper limits of a few picoseconds on the time for capture of an electron by a hole in these alkali halides when capper densities are in the range of 5 X 10" cm '. Recently proposed mechanisms of F-center formation are, discussed in light of the present results. We develop mathematically convenient treatments for convolution of pulse shapes and intrinsic photochemical response in several kinetic models.

Temporal and spectral development of mode locking was investigated in a ring-cavity Nd : glass laser. It was found that whenever a mode-locked pulse formed in the ring cavity a satellite pulse would develop traveling in the opposite direction. The varying delay of the satellite pulse permitted time-resolved spectroscopy of the early stages of mode-locked oscillation. It was found that the spectral distribution broadens from 3 to 80 Å because of selfphase modulation inside the laser cavity.

We have measured the growth of F-band absorption at 532 nm in pure KC1 following two-quantum band-gap excitation by a 266-nm pulse. The rise time at T» 25 K is 11 ±9 psec. Spectral measurements confirm attribution of the early absorption to F centers. This absorption reflects the generation of new Frenkel defects with the F center created directly in its electronic ground state.

A novel method for determining thermal expansion coefficients has been devised. It is based on the dependence of Fabry-Perot resonances on the mirror separation. The expansion sample is formed into an etalon spacer, with highly reflecting endplates optically contacted to each end. The Fabry-Perot resonances are probed by variable radiofrequency sidebands derived from a frequency stabilized 633-nm He-Ne laser. A change in sample temperature DeltaT causes a change in interferometer length DeltaL, which shifts the resonance frequencies by Deltanu. Then alpha = (1/DeltaT)(DeltaL/L) = (1/DeltaT)(Deltanu/nu). alpha can be measured with precision limited ultimately by the stability of the stabilized laser (1:10(9) with presently available commercial lasers). alpha vs temperature has been measured for samples of Owens-Illinois Cer-Vit, Corning ULE silica, and Schott low expansion glass-ceramic.