摘要:

The resistivity of CdSe thin films, vapor deposited on insulating substrates, has been reduced by more than two orders of magnitude by irradiation with a cw argon‐ion laser. A threshold power density of about 0.6 W for a beam diameter of 250 &mgr;m is necessary to cause a measurable decrease in the resistivity of a 0.4‐&mgr;m‐thick film; above this value, the resistivity decreases rapidly with increasing power to a minimum value. Electron and x‐ray diffraction analyses show that there is an increase in film grain size by only a factor of 2 on annealing, but SEM and Auger studies indicate that there are significant changes in the surface topography and composition. Calculations show that the power absorbed by the CdSe film is sufficient to cause melting. The decrease in resistivity can be attributed to the effect of Se vacancies created by preferential loss of Se from the film surface at these elevated temperatures.

ISSN:0021-8979    

DOI:10.1063/1.326736

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

A type of sustained oscillations that can occur in the output of semiconductor injection lasers are studied analytically. The frequency of oscillations and the conditions of instability are deduced from the nonlinear differential rate equations. This model raises the possibility that, at least in some if not many cases, the stability of a laser above threshold is determined by the degree of saturation of the optical gain. If the gain saturates, the laser is stable, and disturbances become damped oscillations. If the gain increases above the standard value, there will be some current level above threshold at which oscillations become sustained. Furthermore, the condition for critically damping the transient ringing in laser output is also derived analytically. The results of the analysis are compared with the limited experimental results available and the agreement is reasonable. The analysis also provides general guidelines for the design of injection lasers that will be less susceptible to instabilities in their optical output.

ISSN:0021-8979    

DOI:10.1063/1.326737

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

By means of two‐ and three‐photon comparative luminescence measurements, carried out utilizing a ruby and neodymium laser, we show how the &ggr;3three‐photon absorption coefficient can be determined. The technique used is presented and applied for the CdS and PbI2. The &ggr;3experimental values obtained are compared with the theoretical predictions and with previous experimental data.

ISSN:0021-8979    

DOI:10.1063/1.326738

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The time development of optically induced refractive‐index hologram gratings in photrefractive electro‐optic crystals such as lithium niobate and bismuth silicon oxide is analyzed allowing arbitrary electron‐transport lengths and nonsinusoidal grating shapes. In this analysis, diffusion and drift in applied and space‐charge fields as well as the bulk photovoltaic effect (when applicable) are included. Results for the photoinduced space‐charge field are presented for a range of realistic experimental conditions. It is shown that the spatial phase of the space‐charge field and therefore the beam coupling is strongly dependent on the electron‐transport lengths, whereas the magnitude of the field and therefore the diffraction efficiency is not dependent. It is shown that for paraelectric materials (such as BSO) the results of short‐ and long‐transport‐length analyses must converge for long recording times (saturation).

ISSN:0021-8979    

DOI:10.1063/1.326739

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Nanosecond pulses of 10‐&mgr;m radiation can be generated by switching the output of a low‐pressure CO2laser with a N2‐laser‐controlled semiconductor reflection switch. These pulses have been used to injection mode lock the ∼50 J output of a 5‐liter TEA CO2oscillator. The 10‐&mgr;m reflectivity of the optically generated charge carriers is found to be a function of the wavelength of the switching laser, while 10‐&mgr;m transmission data has been used to monitor surface recombination before and after laser annealing of a germanium sample.

ISSN:0021-8979    

DOI:10.1063/1.326740

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

A high‐power microwave propagating through a plasma‐filled waveguide gives rise to the generation of second and third harmonic waves because of ponderomotive force and energy‐dependent collisions, respectively. The generated harmonics possess a very different kind of intensity distribution than that of the normal modes. The efficiency of second harmonic generation is resonantly enhanced at some optimum size of the waveguide such that 2&bgr;1=&bgr;2, i.e.,n2&pgr;2/b2+(m2−4) &pgr;2/a2= 3&ohgr;p2/c2where &bgr;1and &bgr;2are the propagation constants of fundamental and second harmonic modes. This effect might account for the observed high yield of second harmonic generation in laser‐produced plasmas. The third harmonic power, however, shows a monotonic rise (tending towards a saturation value) with the width of the waveguide.

ISSN:0021-8979    

DOI:10.1063/1.326741

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The problem of surface‐wave reflection at thin‐strip overlays occurs frequently in signal‐processing devices. Grooved array reflectors employ strip overlays of the same material as the substrate, while metallic transducers incorporate strips of a material different from the substrate. A simple model for calculating the reflection coefficient of thin overlays is described, based on the normal‐mode analysis developed by Auld. Calculated values are in close agreement with reported experimental values for grooves inST‐Xquartz andY‐Zlithium niobate, and for aluminum onST‐Xquartz.

ISSN:0021-8979    

DOI:10.1063/1.326742

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The hydride precipitation in the Nb‐H system has been studied by the acoustic‐emission technique varying the temperature between 330 and 225 K at hydrogen concentrations ranging from 3.8 to 5.8 at.%. Concomitantly, elastic‐modulus and internal‐friction measurements have been conducted in order to reveal the hydride‐precipitation temperatures and the plastic‐deformation phenomena occurring during the formation of the hydride misfitting precipitates. In the virgin material, acoustic emission is absent during evolution of the precipitation although the dislocation‐multiplication processes are operative. When, due to a severe precipitation, a certain degree of deterioration of the material has been reached, acoustic activity characterized by discrete bursts is then stimulated by the hydride formation and definitively persists also after the high‐temperature annealing. The temperatures of the onset of the acoustic emission are lower than those corresponding to the hydride precipitation and may fit a line parallel to solvus. The data clearly indicate that neither the phase transformationpersenor the plastic‐deformation processes accompanying the precipitation can be the sources of the observed acoustic emission. The results suggest that the measured emissivity may be attributed to the nucleation and growth of nonrecoverable defects. According to the proposed model, during hydride precipitation, acoustic‐emission activity should be detected when a progression of irreversible deterioration of the material is occurring.

ISSN:0021-8979    

DOI:10.1063/1.326743

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The mass transfer of particulates of silica and germania is characteristic of the MCVD process for preparing optical fiber preforms. Here, after considering a number of alternatives, it is suggested that the dominant mechanism of mass transfer is thermophoresis, i.e., diffusion due to a large temperature gradient. Analytical arguments are given which support this assertion and compare favorably with experiments carried out in a MCVD apparatus.

ISSN:0021-8979    

DOI:10.1063/1.326744

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

A solar‐powered solid‐state heat transfer device capable of operating in either a refrigeration or a heat‐pump mode is proposed. The device’s operation is based on the combined utilization of the photovoltaic and Peltier effects.

ISSN:0021-8979    

DOI:10.1063/1.326745

出版商:AIP    

年代:1979

数据来源: AIP