摘要:

A 16‐&mgr;m CO2‐N2downstream‐mixing gasdynamic laser, where a cold CO2stream is mixed with a vibrationally excited N2stream at the exit of the nozzle, is studied theoretically. The flow field is analyzed using a two‐dimensional, unsteady, laminar and viscous flow model including appropriate finite‐rate vibrational kinetic equations. The analysis showed that local small‐signal gain up to 21.75 m−1can be obtained for a N2reservoir temperature of 2000 K and a velocity ratio of 1:1 between the CO2and N2mixing streams.

ISSN:0003-6951    

DOI:10.1063/1.96575

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

High electrical and high chemical efficiencies were simultaneously achieved for the multikilojoule HF chemical laser using a Lambda‐type (inclined type) electron beam initiation scheme. The optimum addition of NF3or SF6fluorine donor could increase both efficiencies and could reduce the total pressure of the laser gas mixture. The laser output obtained from the low‐pressure mixture of H2/F2/O2/NF3=30/208/62.5/70 (Torr) was 4.5 kJ in a 50‐ns FWHM pulse width with an electrical laser efficiency of 226% and a chemical efficiency of 18.5%.

ISSN:0003-6951    

DOI:10.1063/1.96576

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The light scattering and electro‐optic response of new material with display potential are investigated. The materials consist of microdroplets of nematic liquid crystals which are spontaneously formed in a solid polymer at the time of its polymerization. Droplet size, spacing, and distribution are readily controlled in these materials to allow optimization of displays based upon electrically controlled light scattering from the liquid crystal droplets. Preliminary experimental and theoretical studies of the light scattering properties show these materials to offer new features suitable for many display applications.

ISSN:0003-6951    

DOI:10.1063/1.96577

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Nonlinear optical coupling to planar GaAs/AlGaAs waveguides has been observed at 1.06 &mgr;m using a grating coupling technique. At an input intensity of 100 MW/cm2, intensity dependent nonlinear switching to the waveguide mode occurs. The results indicate a fast nonlinear response time.

ISSN:0003-6951    

DOI:10.1063/1.96578

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We report the first observation of strong magnetic field tuning of laser emission from Cd1−xMnxTe/Cd1−yMnyTe multiple quantum well structures. The spectral peak of the stimulated emission shifts to lower energy with increasing field at a rate of 3.4 meV/T to a maximum shift of 34 meV at 10 T. This is about five times slower than in bulk Cd1−xMnxTe with a comparablexvalue. Stimulated emission was observed for samples cooled to 1.9 K when optically pumped with a Nd:YAG laser.

ISSN:0003-6951    

DOI:10.1063/1.96579

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We report time‐resolved electrical‐resistance measurements obtained during pulsed‐laser melting of a metal. Through heat‐flow calculations and solute‐diffusion measurements, the measured resistances are correlated with the thresholds for partial and full melting of a thin film of aluminum. Furthermore, simultaneous time‐resolved reflectance measurements establish that, in this geometry, melting and solidification proceed via the motion of a well‐defined, planar liquid/solid interface, whose position can be deduced from the resistance measurements. These measurements permit, for the first time, real‐time determinations of melt‐depth histories in fundamental studies of rapid solidification processing of metals.

ISSN:0003-6951    

DOI:10.1063/1.97015

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Raman spectroscopy has been used to study strains in GaAs‐In0.2Al0.8As strained‐layer superlattices with a fixed layer thickness (100–100 A˚) and various InxAl1−xAs buffer layers [x=0 (GaAs in place of AlAs), 0.1, and 0.2]. Strain‐induced frequency shifts of the longitudinal optic phonon modes depend on the alloy composition (lattice constant) of the buffer layer. For the GaAs buffer layer (x=0) the mismatch between the superlattice and the buffer layer is accommodated by dislocations near the interface region, while for the In0.2Al0.8As buffer layer the mismatch is accommodated by the tensile strain in the GaAs layers.

ISSN:0003-6951    

DOI:10.1063/1.96580

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Spectral absorption characteristics in InGaAsP/InP double heterostructure epitaxial crystal layers have been investigated by using stimulated Raman scattering light from silica fiber excited with neodymium:yttrium aluminum garnet laser and by examining the transmitted guided light. The method proved useful in measuring wavelength‐dependent optical absorption ranging between 0.1 and 20 cm−1in epitaxial layers with waveguiding structures as well as characterizing loss in optical waveguides in the wavelength region between 1.06 and 1.7 &mgr;m.

ISSN:0003-6951    

DOI:10.1063/1.96581

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We report the result of the study on the electrically active deep level defects in Si films grown by molecular beam epitaxy. A deep level defect atEc−0.58 eV is consistently obtained for samples grown on substrates with purposely contaminated surfaces. The observed defects are all located within 3000–5000 A˚ of the epilayer‐substrate interface with concentrations in or below 1014cm−3range. Secondary ion mass spectroscopic study results indicate the correlation between the substrate surface residual carbon concentration and the observed defect concentration. These defects appear to be higher order defects rather than the single level defects, as evidenced by the asymmetry of the deep level transient spectra. For samples grown on the substrates cleaned using an established surface cleaning method, no deep level defects within the detection limit (∼1012cm−3in our case) are observed.

ISSN:0003-6951    

DOI:10.1063/1.96582

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Photoluminescence (PL) studies have been carried out on 120 A˚ InGaAs/InAlAs single quantum well structures grown by molecular beam epitaxy. Three types of samples were grown with the growth being interrupted before interface formation. The interruption times were 0, 2, and 3 min. The corresponding linewidth of the main excitonic transition associated with the quantum well was found to be 20, 16, and 10 meV, respectively, while the PL intensity changed by the ratio 1:0.4:0.1. We believe this behavior is due to a steady improvement in the interface quality due to interruption accompanied by impurity accumulation during the interruption. Analysis of the 10 meV linewidth, which is among the smallest ever reported, suggests that the InAlAs/InGaAs interface can be described by two‐dimensional InAlAs and InGaAs islands which have a height of two monolayers and a lateral extent of about 100 A˚.

ISSN:0003-6951    

DOI:10.1063/1.96583

出版商:AIP    

年代:1986

数据来源: AIP