摘要:

High‐speed one‐ and two‐dimensional spatial light modulation may be carried out using the electroabsorption (Franz‐Keldysh) effect in a GaAs buried‐channel charge‐coupled device (CCD). For photon energies slightly lower than the energy gap, the transmission through or along the surface of a CCD structure may be controlled by the signal charge in the wells, through the change of electric field with charge. The modulator is thus electrically addressable and it promises optical quality sufficient for coherent applications. Experimental measurements on a specially designed GaAs CCD structure with semitransparent gates have verified the predicted performance.

ISSN:0003-6951    

DOI:10.1063/1.93548

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Laser‐induced desorption has been demonstrated for strongly optically absorbing molecules on nominally transparent substrates. Both H2O and hydrocarbon contaminants were desorbed using a pulsed HF/DF laser source at 2.8 and 3.7 &mgr;m. Following laser desorption of H2O, the 2.8‐&mgr;m damage threshold in CaF2roughly doubled. Surface mapping of H2O desorption with a 120‐&mgr;m‐diam focal spot showed considerable variation with spatial position on polished CaF2, indicating localized concentrations of adsorbate.

ISSN:0003-6951    

DOI:10.1063/1.93556

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The mutual interaction between a 70‐kA intense relativistic electron beam and a passive structure increased the kinetic energy of electrons from 4.2 to 7.4 MeV. This process (known as autoacceleration) should be capable of generating electron beams with even higher particle energy and with currents ≳ 100 kA.

ISSN:0003-6951    

DOI:10.1063/1.93557

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The spatial dependence of electron beam deposition was measured for a 320‐kV beam propagating into argon, guided by a magnetic field of 1 kG. Deposition was monitored using the HgBr (B‐X) fluorescence at 502 nm, which is believed to arise from the recombination of HgBr+2.

ISSN:0003-6951    

DOI:10.1063/1.93558

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The small‐signal gain and the output power of air breathing electric discharge CO2laser have been measured in the absence of He gas. A maximum gain of 4.9 m−1was observed at a gas composition of CO2:air = 120:80 (l/min, at normal state), and a 45‐W output power was obtained with an energy conversion efficiency of 5.1%. The corresponding specific power was 7.4 J/g.

ISSN:0003-6951    

DOI:10.1063/1.93559

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Effects of impurities on the characteristics of high‐voltage glow discharges are theoretically studied. These glow discharges are established during a few microseconds between two plane parallel electrodes separated by a few centimeters under a deuterium pressure of about 0.1 mmHg, at currents of the order of 1–10 A, and voltages of about 100 kV. With tritium‐loaded cathodes, high‐voltage discharge tubes produce neutron pulses. In a one‐dimensional theoretical treatment of the discharge, we take into consideration complex processes: charge exchange, ionization of gas by ions, and ion dissociation. Our model shows that some gaseous impurities increase the neutron emission level. Computed variations of neutron output and discharge characteristics as a function of impurity partial pressure are in good agreement with experimental values.

ISSN:0003-6951    

DOI:10.1063/1.93560

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Flash x radiography of ablatively accelerated planar foils has provided quantitative measurements and qualitative observations regarding several parameters of critical interest to direct illumination laser fusion. A 1.05‐&mgr;, 3.3‐ns driver beam was focused onto carbon foils in a large (0.7–1‐mm diameter) spot to reduce edge effects. From images produced by a backlighting x‐ray flash, we have measured overall coupling efficiency, smoothing of laser nonuniformities, target velocity, and ablation pressure. The high velocity targets maintain a localized, high density (≳3% of solid). In contrast to other workers’ recent measurement of pressure from x‐ray imaging, our x‐radiographic results, including pressure, are in general agreement with earlier NRL studies. Our results have also provided further insights into double foil interactions and planar target preheat measurements.

ISSN:0003-6951    

DOI:10.1063/1.93561

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The Boltzman equation, for energy deposited by fast electrons in the presence of an applied magnetic field, is solved in the diffuse beam approximation. The solution is obtained by a simple coordinate transformation which is valid both when &lgr;/rL⩽0.25 (&lgr; = mean free path,rL= Larmor radius) and when &lgr;/rL⩾4.5. The half‐space solution is used to determine the dose in a gas. The theoretical results are compared with experiments. It is found that agreement is better than *10% for cases of interest.

ISSN:0003-6951    

DOI:10.1063/1.93562

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The optical constants (nandk) and dc resistivity have been measured for black chrome particulate solar absorbing coatings for the purpose of defining the applicability of various inhomogeneous medium theories in the description of the black chrome optical response. It has been shown that percolation‐type behavior does exist in the films and hence of the various theories, only those exhibiting percolation at the 0.3 packing fraction value determined for the black chrome films are applicable. The two valid approaches are an effective medium theory first proposed by Bruggeman and a modified Maxwell Garnett theory which includes a particle shape distribution.

ISSN:0003-6951    

DOI:10.1063/1.93563

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The effect of substrate surfaces on the formation of the nematic phase at the isotropic→nematic transition of a mixture of 4‐cyano‐4′‐n‐pentylbiphenyl and hexamethyl‐benzene was studied by observing the textures with a polarizing microscope and measuring the birefringence induced by the substrate in the isotropic phase for two typical homogeneous aligning surface treatments: (1) polyvinylalcohol coating followed by rubbing and (2) SiO oblique evaporation. The two treatments resulted in completely different textures at the transition depending on the magnitude of the ordering, or equivalently the birefringence, induced by the substrate in the isotropic phase.

ISSN:0003-6951    

DOI:10.1063/1.93564

出版商:AIP    

年代:1982

数据来源: AIP