Herbert Mahr

DIRECT MEASUREMENT OF PICOSECOND LIFETIMES

A lifetime in the picosecond range of a nonradiatively damped electronic transition in an organic dye was measured. The method utilizes picosecond pulses from a Q‐switched, mode‐locked Nd‐glass laser.

Time-resolved luminescence spectra in highly photo-excited CdSe at 1.8K

Abstract We report the first observation of very precise time-resolved luminescence from highly photoexcited platelets of CdSe at 1.8 K. The time dependence of both spontaneous and stimulated emission are presented. The results are taken as a further indication for the existence of an electron-hole liquid in CdSe at these excitation densities.

NONCOLLINEAR PARAMETRIC SCATTERING OF VISIBLE LIGHT

Experimental observations of noncollinear parametric interactions in ADP pumped by 3472‐A laser light are reported for a wide variety of signal and idler frequencies, crystal orientations, and observation directions. The results provide the first confirmation of the predictions of newly extended theory.

Stimulated Emission of Polaritons

The gain of optically pumped CdS lasers is calculated assuming that stimulated emission occurs with photonlike polaritons created in inelastic exciton‐exciton collisions; it is shown that gain constants of the recently observed magnitude can be expected from this mechanism.

A new, versatile, three-pulse technique for the measurement of picosecond duration luminescent decay

Abstract We present a new, versatile, three-pulse method for the measurement of picosecond duration time decay of luminescence with an example.

Cavity‐length stabilization technique for synchronously pumped mode‐locked lasers

We demonstrate a technique for active stabilization of the cavity length of synchronously pumped mode‐locked lasers. The technique is general and relies on the ultrashort‐pulse forming process itself. It can be implemented in a variety of nonparasitic ways, has high sensitivity to changes in true optical path length of the cavity, and offers the possiblity of long‐term stabilization.

Photoluminescence of CdSe with picosecond time resolution

Abstract The temporal evolution of luminescence of CdSe at He-temperature is studied after picosecond-pulse photo excitation with a Kerr shutter technique capable of 15 psec resolution.

Optical Filament Formation in Nitrobenzene Resulting from Laser Intensity Inhomogeneities

An experiment was performed in nitrobenzene with a multimode ruby laser to study filament formation as a function of beam aperture size. A theory which assumes that optimum‐size intensity spikes of the incident‐laser‐beam self‐focus first can explain the experimental results with one adjustable parameter.

Fine structure of two-photon absorption in CdS

Abstract We have observed the fine structure of the P -excitons ( A , n = 2) in Cds through two-photon absorption. The strengths of absorption peaks of P -excitons and their dependence on the polarization of the light agree with predictions of a four-band model of two-photon absorption. Additional two-photon absorption peaks were identified as phasematched two-step two-photon processes involving second harmonic polarizations.

Picosecond Luminescence Spectroscopy of Highly Photo-Excited Semiconductors

Over the past few years we have used a picosecond time resolution luminescence spectrometer [1–4] for the study of time resolved luminescence spectra of highly photo-excited semiconductors. At He-temperatures in CdSe single crystals, we find a single, broad luminescence band, centered at about 6820A (Fig. 1). The width of the band changes with time after excitation [4]. The total emission in this band decays with a nearly exponential, but distinctly non-exponential time dependence over a time span of about 500 psec. Considerable effort was spent in identifying the mentioned luminescence band as an intrinsic property of highly photo-excited CdSe. Samples of various types and origins were found to give rise to bands of similar location and width, particularly at early time delays. Considerable care was exercised to identify and stay clear of stimulated emission [4] which was clearly present in some samples. We are fairly confident, then, that the emission band shown in Fig. 1 is an intrinsic, spontaneous emission phenomena originating in highly photo-excited CdSe. The luminescent shape of Fig. 1 is, however, influenced by self-absorption. Luminescence spectra taken with the E-vector of the emitted light parallel to the c-axis of CdSe can be different from luminescent spectra taken for Elc.