摘要:

Enrichment of the carbon isotopes by photodissociation or photochemical reaction of Freon (CF2Cl2) induced by a TEA‐CO2laser has been reported recently by several authors. The present work shows that large effects on the chlorine isotopes are also induced. Their laser‐wavelength dependence has been measured, and some complementary information on the carbon isotopic effects has been collected. Excitation around 930 cm−1yields an enrichment in37Cl in the residual CF2Cl2, and excitation around 1085 cm−1has an opposite effect, while13C enrichment is found around both 1090 and 922 cm−1and12C enrichment is found around 1065 cm−1. These effects can be qualitatively explained with the known fundamental vibrations &ngr;1(922 cm−1, stretching mode) and &ngr;6(992 cm−1, rocking mode) of CF2Cl2. The efficiency of the photodissociations of CF2Cl2induced by a CO2laser is evaluated, and an effective threshold energy density of 3 J/cm2is found at 1089 cm−1.

ISSN:0021-8979    

DOI:10.1063/1.324586

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

We have measured the amount of vibrational energy transferred to translation inV‐Vcollisions between SF6and helium or argon. We used precise mass‐spectrometric measurement of the change in SF6density in a flow of He or Ar and SF6through a focused cw CO2laser beam under conditions where the number of collisions in the beam was much less than the collision number forV‐Tdeactivation. We have determined the ratio of energy lost &Dgr;? to the number of collisions forV‐VrelaxationZVVto beZ−1VV&Dgr;? =13±6 cm−1/collision for helium and 4±2 cm−1/collision for argon. These values are independent of temperature over the range 150–300 K.

ISSN:0021-8979    

DOI:10.1063/1.324587

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Molecular‐beam epitaxy (MBE) with ion beams as dopants is proposed, and experiments with Zn ions in GaAs and AlxGa1−xAs are reported. In conventional MBE, impurities with low sticking coefficients have not been used because doping into MBE layers involves simultaneous evaporation. In this paper, a method of ionizing the dopant molecular beam and increasing its effective sticking coefficient is proposed. By means of ionization, an effective sticking coefficient of ∼0.03 for Zn ions in GaAs and AlxGa1−xAs is obtained as compared with a value of ∼10−7for neutral Zn. This value does not vary even with the mole fraction of AlAs in the system AlxGa1−xAs. A strong ion acceleration is not essential for increasing the sticking coefficient, and ionized dopants arriving at the substrate even without enough kinetic energy for penetration beneath the surface react and bond with the surface atoms sufficiently to prevent reevaporation. Crystallographic characteristics of ion‐doped GaAs and AlxGa1−xAs films are as good as for undoped MBE layers and the Hall mobilities are comparable to those of LPE and VPEp‐type layers. Other electrical and optical characteristics are reported here, and the results show that this modification of MBE can be applied to many other dopants and is a useful method to fabricate various electron devices, especially with complicated structures.

ISSN:0021-8979    

DOI:10.1063/1.324588

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Cross sections for momentum transfer and for rotational, vibrational, and electronic excitation were obtained from an analysis of experimental data for electron drift velocity, characteristic energy, and ionization coefficient. Recently measured data in the range 1×10−16?E/N?4×10−15V cm2were included in the analysis.

ISSN:0021-8979    

DOI:10.1063/1.324589

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A perturbation method was given recently for solving electrostatic problems involving a conducting torus which is freely charged or influenced by a uniform field parallel to its axis. It was forseen that one limitation of the method, the fact that no external influence other than the one just mentioned is allowable, could be removed in the case of a circular torus (anchor ring) by means of the Kelvin transformation and superposition, and the present paper develops this aspect. A number of presumably new results are given for a torus influenced by a given charge located on its axis, and it is shown how the procedure can be extended for a very general axisymmetric situation involving a given charge distribution.

ISSN:0021-8979    

DOI:10.1063/1.324590

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Guided‐wave acousto‐optic diffraction has been demonstrated on a silicon substrate for the first time. The surface acoustic wave is launched from a ZnO/Tab2O5/SiO2/Si multilayered structure, while a Ta2O5/SiO2/Si optical waveguide is used for the acousto‐optic interaction. The measured diffraction efficiency is 3.3% per milliwatt of acoustic power. An order‐better performance is possible with improved transducer geometry. The silicon‐based guided‐wave acousto‐optic technology is preferred for eventual integration of both optical and electronic components for integrated optical applications such as rf spectrum analyzer and fiber‐optical terminals. Experiments with a similar structure on a glass substrate is also reported.

ISSN:0021-8979    

DOI:10.1063/1.324591

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The spontaneous radiation generated in the active region of (Al,Ga)As double‐heterostructure (DH) proton‐delineated stripe‐geometry lasers has been studied by measuring the luminescence (Ls) emitted from a window fabricated in the metallization on the substrate. Observations of the intensity of this luminescence with an image converter provide an effective means for detecting growth‐, processing‐, and aging‐induced defects. In addition, these measurements provide a simple procedure for separating changes in optical loss from changes in radiative‐recombination efficiency. Thus,Lsobservations are useful for quality control and laser‐aging analysis. For lasers with 8% aluminum in the active region,Lsis shown to be principally radiation reemitted from a very thin layer of GaAs substrate at the interface with then‐type ternary layer. Reasonably high spatial resolution (∼3 &mgr;m) of the radiation from the active stripe region is retained in this absorption‐reemission process. For devices with no aluminum added to the active layer, the luminescence is mostly single pass radiation from the active region. Quantitative current and spatial dependences ofLshave been obtained which probe the carrier concentration in the active volume. It has also been shown that the threshold current is easily measured by an abrupt change indLs/di(saturation) and that this slope also characterized the slope of the intensity of the stimulated emission (L) above threshold. In addition, abrupt changes indLs/diat threshold current have been measured near the edges of the stripe showing that saturation‐induced effects are observable over the entire stripe width. In the current increment in which near‐field examination ofLshowed spatial motion of a filament significant spatial changes inLswere observed (although only for lasers without aluminum in the active layer). Thus, spatial motion of lasing filaments can be correlated with changes in the steady‐state spatial carrier‐concentration profiles. Many lasers exhibited a decrease inLsabove threshold, most pronounced about the central axis of the lasing stripe. This decrease in the steady‐state carrier concentration does not seem to be consistent with a model based on saturable optically absorbing traps.

ISSN:0021-8979    

DOI:10.1063/1.324592

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

It has been proposed that the technique of angular multiplexing could provide an efficient scheme for extracting short pulses from a high‐gain laser with a high degree of spatial and temporal control of the extracted laser beam. The scheme of angular multiplexing proposes to amplify short laser pulses (∼1 nsec) by sequentially passing these pulses through the amplifier at slightly different angles. The intensity of each pulse must be sufficient to control amplified spontaneous emission and to extract a significant fraction of the available energy. The experimental demonstration of this technique on the high‐gain xenon laser is described here. The measurements were made for a two‐pulse train with each pulse width shorter than the amplifier gain period. The results of this experiment indicate that for an optimum pulse separation and input pulse intensity, a major fraction of the available laser energy could be extracted efficiently by the pulse train without significant pulse distortion.

ISSN:0021-8979    

DOI:10.1063/1.324593

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Absorption loss in barium sodium niobate (BSN) crystals at both the 1.064‐&mgr;m fundamental and 0.532‐&mgr;m SH wavelengths perturbs the SHG phase‐matching condition, thereby coupling the circulating and SH power with the nonlinear loss. Discrete transitions in circulating power, hysteresis in the intracavity SHG temperature phase‐matching signature, and bistable operation are the direct result of this absorption loss. Extensive analytical and experimental results were obtained and are reported.

ISSN:0021-8979    

DOI:10.1063/1.324594

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

We extend the work of a previous paper to give a long‐wavelength approximation for elastic wave scattering by an elliptical flat crack. Explicit formulas for the far‐field scattered amplitudes in this approximation are given for various experimental configurations. These formulas are then applied to give a simple inversion procedure. The orientation and eccentricity of the crack are readily determined from unnormalized scattering data. The size may be determined from an absolute intensity measurement.

ISSN:0021-8979    

DOI:10.1063/1.324579

出版商:AIP    

年代:1978

数据来源: AIP