Marvin Hass

Infrared lattice reflection spectra of III–V compound semiconductors

Abstract The fundamental lattice reflection band of InSb, InAs, GaSb and GaAs has been measured at liquid helium temperature with a grating spectrometer. By comparing the observed spectrum with that calculated using a single classical dispersion oscillator, the following values of the transverse ( v 0 ) and longitudinal ( v l ) optical frequencies for long wavelength vibrations and Szigeti effective ionic charge ( e ∗ 8 / e ) are obtained: InSb, v 0 = 184.7 ± 3 cm −1 , v l = 197.2 ± 2, e 8 ∗ e = 0.42; InAs , v 0 = 218.9 ± 3 cm −1 , v l = 243.3 ± 2, e 8 ∗ e = 0.56; GaSb , v 0 = 230.5 ± 3 cm −1 , v l = 240.3 ± 2, e 8 ∗ e = 0.33; GaAs , v 0 = 273.3 ± 3 cm −1 , v l = 297.3 ± 2, e 8 ∗ e = 0.51; InP , v 0 = 307 ± 8 cm −1 , v l = 351 ± 5, e 8 ∗ e = 0.68; AlSb , v 0 = 318 ± 8 cm −1 , v l = 345 ± 5, e 8 ∗ e = 0.53 The values for InP and AlSb were obtained by a reanalysis of earlier room temperature data. An empirical dependence of e 8 ∗ e on the difference between the atomic polarizabilities of the group III and group V atoms has been observed.

Raman spectra of vitreous silica, germania and sodium silicate glasses☆

Abstract The polarized Raman spectra of vitreous silica, germania, and sodium silicate glasses have been obtained in the frequency shift region extending from 10 to 1300 cm −1 . The observed spectra of silica and germania have been compared with recent calculations of the vibration spectrum and with the i.r. spectrum. The Stokes-Raman spectrum at low temperatures of vitreous silica decreases markedly in intensity at low frequencies (less than 100 cm −1 ), but only slightly at higher frequencies (greater than 300 cm −1 ). The temperature dependence of the Stokes-Raman spectrum is consistent with first-order processes.

Measurement of Very Low Absorption Coefficients by Laser Calorimetry

Laser calorimetric or thermal rise techniques are useful for the determination of very low absorption coefficients in solids. A number of improvements in this technique are described of which the most important is a means of separating surface and bulk absorption. These techniques have been applied to study alkali halides in the ir but are applicable where laser sources of sufficient power are available.

Sheet Infrared Transmission Polarizers

The production and properties of sheet infrared transmission polarizers of the parallel wire-grating type are discussed. These polarizers are produced by evaporation of a metal conductor on one side of the grooves of an infrared-transmitting plastic film echelette diffraction grating and were first described by Bird and Parrish in 1960. The principal advance in technique given here lies in the use of a commercially available plastic film grating (which is the critical component) and in the fabrication of film gratings of polyethylene which have fewer absorption bands. The degree of polarization is above 98% and the transmission is above 70% in most of the spectral region between 50 cm−1 and 600 cm−1. In the region from 600 cm−1 to 5000 cm−1, the degree of polarization is above 95%, but some plastic absorption bands limit the coverage.

Infrared absorption in low‐loss KCl single crystals near 10.6 μm

The infrared absorption in KCl single crystals near 10.6 μm has been studied using calorimetric techniques with fixed‐frequency and tunable CO2 laser sources. By use of crystals grown in a reactive CCl4 atmosphere, with surfaces carefully prepared by chemical polishing, it is possible to obtain absorption coefficients of 0.0002 cm−1 or less in samples several centimeters thick. This residual absorption is composed of a surface and a bulk part. It is possible to show that the bulk absorption approaches the estimated intrinsic limit of 0.00008 cm−1. An absorption band near 9.8 μm is present in all samples examined and appears to be largely associated with the surface.

Analysis of laser calorimetric data

Adiabatic laser calorimetry, which is the most widely used method for studying the absorption coefficients of low-loss materials, can be adapted to study both the bulk and surface absorption by using a long rod sample geometry. In the limiting case of small heat losses, calculations of the thermal rise curves obtained in laser calorimetry indicate that two regions of constant slope can be expected. The first of these can be identified with the bulk absorption coefficient only and the second with the sum of the surface and bulk absorptions. Experimental data illustrating this two-slope behavior are presented.

Absorption coefficient of pure water at 488 and 541.5 nm by adiabatic laser calorimetry

The absorption coefficient of pure water was found to be 0.00017 cm−1 at 488 nm and 0.00029 cm−1 at 541.5 nm using adiabatic laser calorimetric techniques. These values are in good agreement with the generally accepted long-path transmission spectra of Clarke and James.

Temperature dependence of the Raman spectrum of vitreous silica

Abstract A large temperature dependence of the Stokes-Raman spectrum of vitreous silica is observed for low frequency shifts, while there is a much smaller temperature dependence for frequency shifts greater than 200 cm−1. The data is consistent with an analysis involving first order processes only.

Residual absorption in infrared materials

The sources of the residual absorption of ir materials in their transparent region between 2microm and 10microm are reviewed with emphasis upon recent developments. On the longer wavelength side of this spectral region, many insulating crystals are limited by intrinsic multiphonon absorption, and, on the shorter wavelength side, all insulating crystals are limited by extrinsic effects associated with impurities, defects, and surfaces. During the last few years, the general character of the intrinsic multiphonon absorption has become sufficiently well understood so that its frequency and temperature dependence can be accounted for in both ionic and covalent crystals. The nature of extrinsic absorption is more complicated as it arises from a number of sources. In some cases, the measured absorption coefficient can be attributed with some certainty to a specific origin. In others, especially for the ionic crystals at shorter wavelengths, the origin of the extrinsic residual absorption is not known and may be limited by the experimental measurement techniques, at least in some of the better crystals.

Infrared lattice reflection spectra of LiCl, LiBr, KF, RbF, and CsF

The infrared lattice reflection spectra of LiCl, LiBr, KF, RbF, and CsF were measured in the spectral region from 95 to 1500 cm/sup -1/ and were analyzed by the KramersKronig method. The following fundamental dispersion frequencies were obtained: LiCl, 191 plus or minus 2 cm/sup -1/; 4 cm/sup -1/; KF, 190 plus or minus 2 cm/sup -1/; RbF, 156 plus or minus 2 cm/sup -1/; CsF, 115(?) cm/sup -1/. The effective charges and compressibilities were computed with the aid of the Szigeti relations. (auth)