摘要:

A photoacoustic method has been applied to the quantitative measurement of optical absorption at 10.6 &mgr;m in coated and uncoated alkali halide samples having a spatially varying optical absorption. Photoacoustic signals were measured as a function of the chopping frequency of a CO2laser source. The dependence of the signals on chopping frequency and an absolute electrical calibration of the cell were used to interpret the data. The results are in good agreement with laser calorimetry or infrared transmission measurements on the same samples. Signal fluctuations identified with thermal and source‐coherence effects are reported and discussed. The experiments reported here confirm the utility of the photoacoustic technique in the general investigation of optical properties of highly transparent materials.

ISSN:0021-8979    

DOI:10.1063/1.324532

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Auger‐recombination lifetimes of the excess carriers inp‐type III‐V alloys are calculated as functions of the chemical composition. The Auger transition involving the conduction band, the heavy‐hole band, and the spin split‐off band is analyzed. The mixing of ans‐like state into the valence band, which is induced by disorder in alloys, is taken into account on the basis of the tight‐binding picture. It is shown that the disorder effect is especially significant in alloys whose band‐gap energy is small, as in InAs1−xSbx. A plot of the lifetime against the chemical composition of GaSb1−xAsxshows a prominent valley at the composition, where the band‐gap energy is nearly equal to but a little larger than the spin‐orbit splitting.

ISSN:0021-8979    

DOI:10.1063/1.324533

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A general formalism is developed that describes the generation of short‐ and long‐range echoes in an ensemble of independent nonlinear oscillators such as exemplified by piezoelectric powder particles. The basic physical model is one of self‐parametric interaction in which a parameter of the oscillating system is modulated by the oscillation in the system itself. The resulting formalism, which is similar to the one used in holography, correctly describes the observed echo phenomena. Moreover, it implies the possibility of more general signal storage, analogous to holography. To test the theory, a model has been built consisting of 20 nonlinearLCcircuits. Experimental results confirm the existence of both short‐ and long‐range echoes; some of the more detailed implications of the formalism that concern pulse shape are also borne out by the experiment.

ISSN:0021-8979    

DOI:10.1063/1.324534

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Photoinduced changes in refractive index and thickness in evaporated As2S3films have been measured by means of a prism‐coupling technique. The irreversible and reversible structural transformations are associated with increases in the refractive index of 0.133 and 0.029, respectively, at a wavelength of 633 nm. Additionally, a dynamical change in refractive index by 0.003 appears under the band‐gap illumination of about 10 mW/cm2. The origin of this change is attributable to a result from photoelectronic excitation. In the irreversible process, the films expand first and subsequently contract as the refractive index increases monotonically, whereas any change in thickness was not detected within an experimental error of ±10 A˚ for the reversible process.

ISSN:0021-8979    

DOI:10.1063/1.324525

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The laser resonance absorption technique has been used to determine the relaxation rate of electronically excited neodymium vapor during its expansion into vacuum. Significant increases of population into ground and 1128‐cm−1levels were found. Analysis shows that interaction between excited metastable atoms and electrons are much more important for relaxation than atom‐atom collisions. The final population of neodymium appears to be frozen at a temperature lower than the surface temperature of melt.

ISSN:0021-8979    

DOI:10.1063/1.324535

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Low‐temperature (3.5<T<77 °K) measurements of the dielectric constant and dissipation of ZnO ceramic varistors are presented for frequenciesfin the range 30<f<105Hz. A loss peak and dispersion in &egr; observed at 4 °K are identified as resulting from the two‐phase structure of the ZnO varistor (Maxwell‐Wagner model). We find the zinc oxide grain resistivity &rgr;ZnO∼106&OHgr; cm in a typical commercial varistor at 4.2 °K. The physical origin of a second loss peak observed in measurements around room temperature is discussed. We show the latter dispersion is not interpretable using a Maxwell‐Wagner model for an inhomogeneous conductor.

ISSN:0021-8979    

DOI:10.1063/1.324536

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The electric dipole moment displacement currents which are to be expected from the change with time of the electric dipole moment of the potassium conductance channels in squid axon membrane with change in transmembrane potential are compared with the displacement currents observed in frog skeletal muscle cell membrane. The parameters needed to describe the muscle displacement currents—the resting potential, the dipole moment magnitudes, and the channel surface densities—are remarkably similar to those needed to describe the observed voltage‐dependent potassium ion conductance in the squid membrane. The smaller relaxation rates in muscle membrane can be accounted for by increasing by 5% the potential hindering conformation relaxation of the conductance system. It is also concluded that tetraethylammonium and tetracine modify the system permeability rather than the dipole moments of the configurations of the potassium conductance system.

ISSN:0021-8979    

DOI:10.1063/1.324537

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A mathematical formalism is developed whereby the expected signal from a delayed fission neutron uranium logging experiment can be calculated efficiently. An assumption that the logging geometry can be approximated by one‐dimensional spherical geometry is made in order to facilitate the calculation of neutron‐transport results that are needed to evaluate the formalism. Sample results from these calculations are used to form a comparison of the magnitudes of prompt and delayed fission neutron logging signals, respectively, for various observation times and amounts of water in the logging borehole.

ISSN:0021-8979    

DOI:10.1063/1.324538

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

An electrostatic lens for electron microscopy was devised in which a dielectric was charged with electrons in order to give rise to an electrostatic field. The lens performed well when an electron beam was steadily running through it. It was possible to obtain a diffraction pattern from an object suitable for observation by electron microscopy.

ISSN:0021-8979    

DOI:10.1063/1.324539

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Characteristics of surface acoustic waves (SAW) on fresnoite (Ba2Si2TiO8) single crystals are calculated using published and recently measured data. It is found that Ba2Si2TiO8is located between LiNbO3and LiTaO3in the SAW characteristics. No sets of temperature‐compensated propagation planes and directions are found among major singly rotated cuts in Ba2Si2TiO8.

ISSN:0021-8979    

DOI:10.1063/1.324540

出版商:AIP    

年代:1978

数据来源: AIP