Gordon Lasher

GaAs Injection Laser with Novel Mode Control and Switching Properties

The effects of nonuniform current densities on the properties of GaAs injection lasers are investigated. The structure studied is an injection laser with a channel etched on the p side of the junction parallel to the reflecting ends. It is found that the threshold current is higher for nonuniform currents than for uniform currents. The mode in which the laser oscillates depends on the distribution of current. A simple model of the transition and the energy vs density of states for the semiconductor is presented to explain these effects. Bistable operation of the structure has been observed.

Laser‐induced recrystallization and damage in GaAs

We have investigated the recrystallization of ion‐implanted amorphous GaAs using a frequency‐doubled 10−8‐s pulsed Nd : YAG laser. The best results were obtained by spatially overlapping laser pulses at 20 MW/cm2. At power densities above 20 MW/cm2, not only does the GaAs surface begin to show uneven solidification, but also an increasing degree of disorder is revealed in Raman scattering and by a broad hump in the spectrum of channeled He‐ion backscattering. This laser‐induced damage is similar for single‐crystal and ion‐implanted GaAs samples. We attribute the damage at high power densities to the loss of arsenic and subsequent rapid cooling of a gallium‐rich liquid.

A method for predicting soft X-ray emission from supernovae

This paper gives a set of predictions of the properties of the soft X-ray flare from supernovae based on the energy of the explosion and the characteristics of the envelope of the star. The effects of the absorption of the interstellar medium are included to determine the photon flux, time duration, and average photon energy of the received radiation. The method is expressed in a number of simple approximate relationships which can be used to find the predicted quantities for any set of input values.

Laser induced damage and recrystallization of ion implanted GaAs by frequency‐doubled Nd:YAG laser

We have investigated the recrystallization of ion‐implanted amorphous GaAs using a frequency‐doubled, 10−8 s pulsed Nd:YAG laser. The best results were obtained by spatially overlapping laser pulses at 0.2 J/cm2. The recorder GaAs samples were examined by He‐ion backscattering and Raman scattering. At power densities above 20 MW/cm2 (0.2 J/cm2), not only does the GaAs surface begin to sow uneven solidification, but also an increasing degree of disorder is revealed by the presence of the density‐of‐states background in the phonon spectra, and by a broad hump in the spectrum of channeled backscattering. This laser induced damage is similar for single crystal as well as ion‐implanted GaAs samples. Therefore, we attribute the damage at high power densities to the loss of arsenic and subsequent rapid cooling of a gallium‐rich liquid. Our calculated temperature profile places the liquid‐solid interface in the neighborhood of the disordered layer.

The winding number of three complexes in SU(3)

Abstract The Phillip-Stone algorithm for the topological charge of a lattice gauge field requires the computation of the winding number of certain 3-complexes in the space of the group. The extension of the computational procedure for the SU(2) gauge group to SU(3) requires an understanding of the SU(3) geometry. An important issue is the behavior of a 3-cell in SU(3) as it approaches a critical configuration, i.e., one at which the cell is a discontinuous function of its vertices. A measure of the proximity of a cell to critically is found and a method for computing its contribution to the winding number is recommended.

Winding numbers for SU(3) lattice gauge fields

Abstract A method for finding the winding numbers of simplicial complexes in the group space of SU (3) has been developed and tested on 10,000 random complexes. The method may be extended to find the winding numbers of the cell complexes of the Phillips-Stone algorithm for the topological charge of lattice gauge fields. This paper gives the physical motivation for studying the topological aspects of lattice gauge fields, discusses the geometry of the SU (3) group space, and explains the method of finding the winding numbers of complexes in SU (3).

Density, velocity, and temperature profiles for the extended envelope model of type I Supernovae

The early light curve of Type I Supernova has been fitted by a model in which the low density envelope of a supergiant is exploded by the sudden release of energy at its center. This paper supplements previous publications on this model by giving information about the model which is necessary for the computation of the emitted spectrum, namely, the density, temperature and velocity profiles of the expanding shell.

The Early Type I Supernova Light Curve: The Effect of Hydrogen Abundance

Since the early days of Colgate and White (1965), most researchers working with numerical models of supernovae have specialized in either the inside or the outside parts of the supernova. This development is a reasonable one. The gravitational collapse of a dense core is completed in a second or two, but the passage of a shock wave through a stellar envelope may take half a day. To model the shock wave and the subsequent observable emission of radiation one only needs to know the energy, momentum and material deposited in envelope by the inner processes. This paper reports our most recent progress in modelling the early part of Type I light curves.