R. C. C. Leite

Long‐Transient Effects in Lasers with Inserted Liquid Samples

Buildup and decay transients were observed when polar or nonpolar liquid cells were placed within the resonator of a helium—neon laser operating in the red at 6328 A. Similar but smaller effects were also observed with two solids. Time constants were the order of a few seconds for all materials, which suggests a thermal phenomenon, but general heating effects were ruled out by the strong localization of the phenomenon. Transverse motion of the cell by about one beam width caused new transients similar to the initial ones.It is believed that the effects are caused by absorption of the red light in the material, producing a local heating in the vicinity of the beam and a lens effect arising from the transverse gradient of refractive index. Absorptions of 10−3 to 10−4 parts per centimeter are sufficient to produce the effects, and are believed to be reasonable values for the materials studied. One of the most important applications may in fact be for the measurement of small absorbancies.The experiments are ...

THE THERMAL LENS EFFECT AS A POWER‐LIMITING DEVICE

Due to residual absorption, a self‐induced negative lens is formed when molecular liquids are inserted in the path of a CW laser beam. This lens has a power‐dependent focal length which allows for its application as a power controller. Experimental results show that control under 3% is obtained for a CW argon laser.

DIELECTRIC‐WAVEGUIDE MODE OF LIGHT PROPAGATION IN p‐n JUNCTIONS

The condition for coherent laser emission from forward-biased p-n junctions [1-3] can be written as [4] [equation 1]... In order for the reported values [1-3] of Ic/A to agree with Eq. (1), must must use values pf d ~50 μ [4]. The question arises as to the nature of the mechanism which could confine the light generated near the junction to such small distances.

Photoexcited hot LO phonons in GaAs

Abstract We report the observation of photoexcited “hot” LO phonons in GaAs. We also obtain an order of magnitude estimate of LO phonon lifetime which agrees reasonably well with the estimate from the linewidth in Raman scattering. Finally we compare our results with the recent experiments by Vella-Coleiro in which a large magnetic field is essential for the observation of “hot” LO phonons.

Super Radiant Narrowing in Fluorescence Radiation of Inverted Populations

The effect of resonance reabsorption of fluorescent radiation on the spectral distribution has been considered as early as 1913 by Laudenburg and Reivhe [1]. Schein [2] and Zemansky [3] recognized that the reabsorption causes a broadening of the light emitted by resonance lamps. In this note we report an experimental and theoretical study of the complementary effect, i.e., of resonance radiation originating in a system in which the population of the upper level of the resonance transition is made to exceed that of the lower one (inverted population system).

OBSERVATION OF THE DIELECTRIC‐WAVEGUIDE MODE OF LIGHT PROPAGATION IN p‐n JUNCTIONS

Theoretical considerations of the propagation of electromagnetic energy near a p-n junction (1) show that the “sandwich” formed by having a depletion layer bounded by the p and n regions can act as a dielectric waveguide. (1,2)

Resonant Raman Effect in CdS and ZnSe

Preliminary studies of lattice Raman scattering from CdS[1] disclosed a large enhancement of the Raman cross-section as the excitation photon energy approached that of the band gap. Predictions of this resonance effect were common in the literature, but different theories[2–4] yielded rather different quantitative results. In an effort to discriminate among the several theories we have measured the absolute percentage increase of Raman cross section of transverse and longitudinal optical phonons, as well as polaritons, in CdS and ZnSe. While we have been unable to explain in detail the empirical results of our experiments, we are motivated in our present communication by the belief that their novelty and complexity will prompt others to hypothesize explanations.

Absorption Measurements and Impurity Assignment of Bound Exciton Complexes by Self‐Absorbed Luminescence

It is shown that self‐absorbed emission lines due to a bound exciton and its phonon satellite may be used to determine (1) the absorption coefficient at the wavelength of bound exciton emission line and (2) the nature of the impurity binding the exciton. The technique is described and is illustrated by experimental results on CdS.

PHONON‐ASSISTED AND PHONON‐FREE RADIATIVE TRANSITIONS IN SULFUR‐DOPED GaAs DIFFUSED JUNCTIONS

In the course of electroluminescence studies of GaAs junctions we investigated the emission spectra of sulfur-doped zinc-diffused diodes. The peaks in the spectra correspond to three main transitions and their associated phonon emission satellites.