摘要:

The deflection of light by acoustic surface waves in multimode waveguides is studied in the present work. Conditions on deflection of single‐mode and multimode optical power are derived, and expressions are presented for the number of resolvable spots and the efficiency that may be obtained with these scattering processes. A description of the waveguide analog to anisotropic Bragg scattering is given, and the advantages and disadvantages of this approach are discussed in detail.

ISSN:0021-8979    

DOI:10.1063/1.1663488

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Photoluminescence and laser data (77°K) are presented, clarifying the role of the NN pair states in above‐gap radiative transitions. Heavily Te‐doped (1019/cm3) and N‐doped (≳ 1019/cm3)x=0.24 vapor phase epitaxial GaAs1−xPxsamples are prepared to ensure a large doped‐in supply of electrons in NN pairs states. Identical samples, but without N+doping (N+‐doped layer etched off), are examined for comparison. Nitrogen‐free samples lase at energies as high as 60 meVabove Eg(&Ggr;); the N+‐doped samples lase at significantly higher threshold and at energieshv≲Eg(&Ggr;), where resonance enhancement is large. The addition of Zn (via diffusion) to convert then‐type N‐doped crystal toptype removes the built‐in electron supply from the NN pair states and permits laser operation on the donor band tail at relatively low energy and low threshold, which shows that the N impurity does not damage the crystal. While the N trap is most useful in GaAs1−xPxin the region near the direct‐indirect transition (x≡xc≈0.46, 77°K) and in the indirect range (x>xc), these and related data indicate that the N trap detracts from the radiative recombination process in the direct range (x≪xc).

ISSN:0021-8979    

DOI:10.1063/1.1663489

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Glow‐discharge mass spectrometry, in which an rf glow discharge is used both to sputter etch the sample undergoing analysis and to ionize the neutral sputtered species, is shown to be a promising new technique for the elemental analysis of thin solid layers or bulk solids. A description of the method is given followed by some examples of its application to composition profiling. The influence of some parameters is shown and opinions as to the advantages and disadvantages of the method are given.

ISSN:0021-8979    

DOI:10.1063/1.1663490

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A proposed relation between spontaneous and coherent properties of injection lasers is applied to several published results. On experimental and theoretical grounds it is shown that the parameter 1+X, the ratio of conventional gain coefficient to prorated loss for the strongest cavity mode, can be determined from the spontaneous emission. Over a limited range above unity, 1+Xis the ratio of spontaneous intensity at the operating point to its value at threshold. This supplies a needed experimental connection between spontaneous studies at frequencies higher than the lasing band and the coherent properties. Published data of the current dependence of spontaneous emission are discussed in this framework, and the information needed to intercompare their internal state is pointed out. In general, fundamental differences in laser dynamics should be evidenced by radically different values of the critical parameterP* of the nonlinearity associated with the power dependence ofX. All published values ofP* are of order 5 mW per cavity mode, as predicted, indicating a similarity in the nonlinearity for quite different types of material. The recent observation thatP* is independent of facet area gives strong support to the idea that the source of the nonlinearity is saturable optical absorption in a strongly interacting system.

ISSN:0021-8979    

DOI:10.1063/1.1663491

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The photocurrent kinetic response and the photocurrent spectral response at 300 K are reported for Bi12SiO20in the optical range 1.0–2.0 eV. In this range trap occupancy dominates the response. The kinetic response of the transient‐trap‐filled photocurrent provides values of the electron trap density and the optical absorption coefficient for the photoionization of the electron trap. The optical ionization energies of the traps are provided from the trap‐filled spectral response. Combining these quantities with previously determined thermal ionization energies of the electron traps provides a value for the electron effective mass of m*=14 m and a value for the effective density of states in the conduction band ofNc=1×1017T3/2. Using this value for the effective mass, an optical absorption coefficient for the photoionization process is calculated, and found to be in good agreement with the experimentally observed value.

ISSN:0021-8979    

DOI:10.1063/1.1663492

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

This paper presents parametric studies of the performance of a 10‐liter atmospheric‐pressure CO2laser system controlled by a 4‐&mgr;sec pulse of electrons from a cold‐cathode gun. The experimental results are compared to the predictions of a theoretical model described in this paper. For various laser gas mixtures and values ofE/Pthe peak small‐signal‐gain coefficients range up to 4.7% cm−1. Measurements of gain uniformity across the laser medium and of the time dependence of the small‐signal gain are also presented. Operation of the device as an oscillator over a range of parameters has shown that the output pulse typically consists of a sharp gain‐switched spike followed by a longer tail with energies up to 30 J in the spike and 200 J in the entire pulse. The theoretical model generally predicts peak small‐signal gain well for gas mixtures containing nitrogen; the largest discrepancy is for pure CO2gas. The model also predicts the shapes of oscillator pulses satisfactorily.

ISSN:0021-8979    

DOI:10.1063/1.1663493

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

When making photographs in x rays or &ggr; rays with a multiple‐pinhole camera, the individual images of an extended object such as the sun may be allowed to overlap; then the situation is in many ways analogous to that in a multiplexing device such as a Fourier spectroscope. Some advantages and problems arising with such use of the camera are discussed, and expressions are derived to describe the relative efficacy of three exposure/postprocessing schemes using multiple‐pinhole cameras.

ISSN:0021-8979    

DOI:10.1063/1.1663494

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Studies of the doping profile characteristics of molecular‐beam epitaxy (MBE) of GaAs on GaAs substrates are reported. Highly resistive regions at the substrate—epitaxial‐layer interface, and within the epitaxial layer, may occur if the growth is interrupted. It is shown that almost any arbitrary voltage dependence of the capacitance of such structures can be achieved by varying the dopant deposition rate during epitaxy. To illustrate the versatility of this growth technique, voltage‐variable capacitors have been prepared with Schottky barriers on MBE GaAs layers with precisely controlled doping profiles. Low‐frequency measurements (up to 100 MHz) demonstrate that capacitance variations in excess of a factor of 10 have been achieved by varying the applied bias voltageVfrom 0.3 V (with no significant forward conduction) to −1.0 V. The feasibility of frequency tuning diodes withC−1/2[sine wave]&jgr;−V, where &jgr; is the effective barrier height, is shown. At ‐3 V bias, cutoff frequencies >40 GHz have been measured. With an improved diode design, cutoff frequencies in excess of 200 GHz are expected at similar bias voltages.

ISSN:0021-8979    

DOI:10.1063/1.1663495

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A small hydrogen fluoride mixing laser has been developed which produces cw radiation with excellent short‐term amplitude stability (variation less than ±1.5%) and requires only 14 liter/sec pumping capacity. Using a grating and a semitransparent mirror mounted on a piezoelectric crystal for laser cavity optics, the laser has been made to operate on a single molecular transition and also on a single cavity mode. By varying the cavity length it was possible to tune the laser over about 300 MHz. The gain of the laser was established at about 30% by measurement of mode pulling and also by direct gain measurement.

ISSN:0021-8979    

DOI:10.1063/1.1663496

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

An intense electron beam has been used to initiate HF lasing in mixtures of SF6and C2H6. Parametric studies of this highly superradiant chemical‐laser system were performed to determine optimum composition of the SF6/C2H6mixture. The maximum laser energy measured was 5.5 J in a pulse width (FWHM) of 45 nsec. The efficiency for conversion of deposited electron‐beam energy to laser energy was approximately 4%. The chemical reactions and the limits on the production of fluorine atoms and of vibrationally excited HF are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1663497

出版商:AIP    

年代:1974

数据来源: AIP