Showing papers by "Solid State Physics Laboratory published in 1975"

Transversely excited 337 μm HCN waveguide laser.

Abstract: Theory, construction and performance of the first transversely excited HCN 337 μm waveguide laser are presented. The first part of this paper reviews the theory of the particular waveguide structure. Losses, fields and resonance conditions are calculated with the Maxwell equations by analytical approximation.

Electrical resistivities and phase separation of liquid lithium-sodium alloys

Abstract: The resistivities of liquid lithium-sodium alloys have been determined as a function of temperature for alloy compositions covering the entire concentration range. When the resistivity is plotted as a function of concentration, the nonlinear terms corresponding to the Nordheim rule appear to be remarkably small. A shallow minimum was found at the lithium-rich end of the composition range. As the measurements were carried out from 500°C down to temperatures below the phase separation temperature, the temperature coefficient of the resistivity could be calculated. Additionally, the immiscibility loop of the phase diagram has been determined. Calculations along the lines of the diffraction model provide satisfactory agreement with experiment but appear to be rather sensitive to one of the input parameters.

Influence of the coriolis coupling on angular correlation functions of rotating molecules

Abstract: In this paper, the influence of the Coriolis coupling of first order on angular correlation functions of symmetric-top and spherical-top molecules in gases and liquids is studied. The theories of St. Pierre and Steele, and of McClung on molecular reorientation processes are revised to include Coriolis coupling. The theoretical angular correlation functions show drastic changes for a varying Coriolis coupling constant ξ. They are compared with experimental data obtained by Fourier transforming vibration-rotation spectra of chloroform, carbonyls and methanes, in the gaseous and the liquid state. The effect of Coriolis coupling on the angular correlation functions of linear molecules is also provided by the above theory. As an example the experimental correlation function of the perpendicular transition of OCS in a dense medium is presented

Wall processes and radial gain of the cw HCN laser

Abstract: The measurement of the degree of dissociation and a discussion of the formation of excited laser-active HCN molecules are presented. It is shown that HCN molecules formed by chemical reactions on the wall of the discharge tube contribute significantly to the laser gain and cause the experimentally observed constant gain over the resonator.

Far-infrared solar brightness measured with a balloon-borne lamellar-grating interferometer

Abstract: The solar brightness temperature was measured at wavelengths between 208μ and 660μ with a lamellar-grating interferometer. In order to avoid terrestrial absorption due to water vapor the measurement of the absolute spectral brightness was performed at altitudes of 30 km and 35 km with a balloon borne gondola. A cylindrical black body radiation source served as absolute calibration standard. Its wall temperature lay between 1100 K and 1300 K. Since the box of the interferometer and the black body could not be evacuated for the calibration, the air in the system was replaced by dry nitrogen. Nevertheless, residual water vapor absorption lines hampered the precision of the absolute calibration. The corresponding error could not be reduced to less than ±100 K. The present experimental temperature profile is compared to results obtained from other measurements. The results agree with the empirical HSRA model and with those of other research groups in the spectral range between 208μ and 660μ.

Axially non-symmetric hole centers in calcium-chlorapatite

Abstract: EPR-spectra of X-irradiated “oxygen-poor” calciumchlorapatite single crystals have been analysed. The spectra can be associated with a new type of (OCl)2−molecular ion. The magnetic parameters deduced from rotational EPR experiments are compared with those of heteronuclear molecular ions in other materials. Mit EPR wurden durch Rontgenstrahlen erzeugte Farbzentren in synthetischen, sauerstoffarmen Einkristallen von Chlorapatit untersucht. Die Spektren ruhren von neuen Typen von (OCl)2−-Molekularionen her. Die magnetischen Parameter werden mit Hilfe von Rotationsexperimenten bestimmt. Sie werden mit Parametern von heteronuklearen Molekularionen in anderen Materialien verglichen.

Epr of bacl2-eu2+ and bacl2-gd3+

Abstract: Paramagnetic resonance spectra of Eu2+ and Gd3+ ions at Ba2+ sites in BaCl2 were measured at room temperature and liquid nitrogen temperature. There was little difference between the spectra of the same ion taken at the different temperatures. The important parameters in the spin Hamiltonian are: Eu2+(300 °K): b=24 × 10−4 cm−1, b = −450 × × 10−4cm−1; Eu2+ (77 °K): b = 33 × 10−4cm−1, b = −467 × 10−4cm−1; Gd3+(77 °K): b = 84 × 10−4cm−1, b = −461 × 10−4cm−1; g =1.992. The corresponding theoretical values are: Eu2+: b = 104 × 10−4cm−1, b = −357 × 10−4cm−1; Gd3+: b =99 × × 10−4cm−1, b = −334 × 10−4cm−1; g = 1.993. Die Spektren der paramagnetischen Elektronenresonanz von Eu2+ - und Gd3+-Ionen auf Ba2+ -Platzen werden bei 300 und 77 °K gemessen. Der Unterschied zwischen den Spektren desselben Iones bei verschiedenen Temperaturen ist gering. Die wichtigsten Parameter im Spin-Hamilton-Operator sind: Eu2+ (300 °K): b02 = 24 × 10−4 cm−1, b = −450 × × 10−4 cm−1; Eu2+ (77 °K): b = 33 × 10−4 cm−1, b = −467 × 10−1 cm−1; Gd3+ (77 °K): b = 84 × 10−4 cm−1, b = −461 × 10−4 cm−1 g = 1,992. Die entsprechenden berechneten Werte sind: Eu2+: b = 104 × 10−4 cm−1, b = −357 × 10−4 cm−1; Gd3+: b = 99 × × 10−4 cm−1, b = −334 × 10−4 cm−1; g = 1,993.

Effect of piezoelectric potential scattering on the microwave faraday effect in n-CdS

Abstract: The theory of free-carrier Faraday effect in semiconductors previously developed by Donovan and Webster for lattice and impurity scattering is extended to the case of n-type CdS, taking into account piezoelectric and deformation potential scattering. The high frequency magnetoconductivity tensors are derived considering the detailed structure of the conduction band of CdS. The Faraday rotation measurements in n-type CdS along the c-axis are performed at liquid nitrogen temperature and room temperature at 24 GHz. The experimental results are found to agree well with the theory, for β = p/a = 1.9, where a and p being the deformation potential and piezoelectric scattering coefficients at T = 90 °K, respectively. Die kurzlich von Donovan und Webster fur Gitter- und Storstellenstreuung entwickelte Theorie des Faraday-Effekts freier Trager in Halbleitern wird auf n-eitendes CdS erweitert, wobei piezoelektrische und Deformationspotentialstreuung berucksichtigung wird. Die Tensoren der Hochfrequenz-Magnetoleitfahigkeit werden unter Berucksichtigung der detaillierten Leitungsbandstruktur von CdS abgeleitet. In n-leitendem CdS werden Messungen der Faraday-Drehung in Richtung der c-Achse bei Zimmertemperatur und Stickstofftemperatur bei 24 GHz durchgefuhrt. Es wird gefunden, das die experimentellen Ergebnisse fur β= p/a = 1,9 gut mit der Theorie ubereinstimmen, wobei a und p die Koeffizienten der Deformationspotential- bzw. piezoelektrischen Streuung bei T = 90 °K sind.

F-centers in calcium-chlorapatite doped with nacl

Abstract: EPR and optical absorption experiments at 300 K on X-irradiated synthetic calcium-chlorapatite single crystals doped with NaCl are presented. Two different EPR signals due to electron-excess centres have been observed. The signals are assigned to two types of F-like colour centres, for which models are given. Es wurden bei 300 K durch Rontgenstrahlen erzeugte Farbzentren in synthetischen Ein- kristallen von Kalziumchlorapatit, dotiert mit NaCI, mit EPR und optischen Absorptions- messungen untersucht. Zwei verschiedene EPR-Signale, die von ElektronenuberschuO- zentren stammen, werden beobachtet. Die Signale werden zwei verschiedenen F-artigen Farbzentren zugeschrieben, fur die Modelle aufgestellt werden..

Modification of phonon distribution in degenerate semiconductors by high electric fields: Effect on transport coefficients

Abstract: Drift mobility, Hall mobility, and Hall coefficient of a degenerate semiconductor at very low temperatures and high electric fields are calculated. Following Paranjape's approach the modified distribution of phonons are taken into account in the calculation of the transport coefficients for arbitrary degeneracy of simple model semiconductors. The electron scattering due to ionized impurities as well as due to acoustic phonons have been considered. The calculations show that the inclusion of the modified phonon distribution in the theory reduces the theoretical values of drift and Hall mobilities of degenerate semiconductors by a factor of two or more; its effect on Hall coefficients is to decrease the theoretical value slightly (20%). Die Driftgeschwindigkeit, Hallbeweglichkeit und der Hallkoeffizient eines entarteten Halbleiters werden bei sehr niedrigen Temperaturen und hohen elektrischen Feldern berechnet. Der Behandlung von Paranjape folgend, werden die modifizierten Phononenverteilungen bei der Berechnung der Transportkoeffizienten fur beliebige Entartung eines simplen Modellhalbleiters berucksichtigt. Dabei wird sowohl Elektronenstreuung durch ionisierte Storstellen als auch durch akustische Phononen angenommen. Die Rechnungen zeigen, das die Einbeziehung der modifizierten Phononenverteilung in die Theorie die theoretischen Werte der Drift- und Hallbeweglickeiten von entarteten Halbleitern um einen Faktor von zwei oder mehr reduziert, wobei sich auch der theoretische Wert des Hallkoeffizienten leicht (20%) verringert.

Role op atomic number of elements, band gap and refractive index on the electrical susceptibilities of AII-BVI compounds

Abstract: Some correlations of electrical susceptibilities (χE) with physical parameters such as atomic numbers of elements, band gaps and refractive indices, have been established for the group II–VI compounds. For Ca, Sr and Ba chalcogenides,χE is inversely proportional to Eg. Such a behaviour is also noticed for Zn and Hg chalcogenides; sulphides being the exceptions. For most of the compounds, the variation of electrical susceptibilities and refractive indices is governed by the relationχE=n−3/2.χE increases almost linearly for many of the binary compounds with the corresponding increase in the atomic number of anion or cation, keeping the atomic number of the other member element to be constant.

Infrared absorption study of Cr/CN/6/n-/ complexes doped in KCl crystals

Abstract: Infrared absorption spectrum of Cr(CN)63− doped in KCl crystals show that the site symmetry of the ion is predominantlyC8 corresponding to one cation vacancy in the nearest neighbour and the other in the next nearest neighbour position with respect to Cr3+ ion X-irradiation produces complexes of the type Cr(CN)64− and Cr (CN)65−