摘要:

Spectral analysis of high‐power pulsed D2O lasers has been accomplished using SAW dispersive delay lines. Both the contributions of longitudinal modes and the tuning of the stimulated Raman line at 385 &mgr;m have been observed.

ISSN:0003-6951    

DOI:10.1063/1.90720

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

An implementation of the chirp transform algorithm for performing a real‐time Fourier transform is described. The implementation is based upon an acousto‐optic convolver with a large time‐bandwidth product An instantaneous bandwidth of about 75 MHz was achieved for the Fourier transformer with a dynamic range in excess of 60 dB for a cw time‐gated waveform. By using an almost‐uniform light‐beam intensity across the device, the measured sidelobe amplitudes were within 0.5 dB of the theoretical values. The corresponding measured phase errors were less than 5°. The adaptability of this acousto‐optic implementation is demonstrated by the ease with which one can vary both the sidelobe weighting function and the time rate of the transform.

ISSN:0003-6951    

DOI:10.1063/1.90721

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Electromagnetic‐acoustic transducers (EMAT’s) can excite and detect elastic shear waves with electronically controlled elliptical polarizations. These can be used to construct an ellipsometer for precise measurement of mechanical properties of solids, in analogy to devices presently used in optical studies. The elastic‐wave case differs from the optical case in two important ways. Longitudinal as well as transverse waves will, in general, exist, and the propagation medium, as well as the surfaces, play an important role in determining the system response. A device is described which is designed to avoid the former mode conversion effects on thin plates. The results of two simple experiments to demonstrate its performance are then reported. In one, measurement of the texture of a metal plate demonstrates the ability to sense bulk property changes which alter the relative velocities of the two‐wave components. In the second, measurements of the effect of a fluid on one side of the plate demonstrates the ability to sense surface changes which alter the relative attenuation of the two‐wave components. The technique appears likely to find future application in the high‐precision measurement of a number of elastic properties, particularly in view of the fact that it requires no couplant and hence can perform well under various adverse conditions.

ISSN:0003-6951    

DOI:10.1063/1.90722

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Electrostatic modes on non‐neutral electron clouds confined in a magnetic mirror field have been investigated. The cloud contains 2×1011electrons at an average kinetic energy of 0.3 MeV for a magnetic field with a peak intensity of 9 kG at the midplane. It was found that the cloud is moving azimuthally as well as longitudinally. The azimuthal motion has anm=1 spatial nature. The longitudinal modes have a more complicated nature, but their frequency equals that of the azimuthal mode.

ISSN:0003-6951    

DOI:10.1063/1.90723

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

A multipole magnetic field is applied in a multifilament plasma source. By changing the strength of the magnetic field, the instability of the discharge, the change of the density profile, and the increment of the ion density are investigated. It is shown that the stable plasma with a rather high density on the order of 1012cm−3and with a uniform density profile within ±5% over the 9‐cm diameter is obtained in the lower discharge current compared with the discharge without the magnetic field, and the total heater current of the filament can be reduced by about 10%. The ratio (0.93) of the discharge current to the heater current without a magnetic field is improved to 1.8 with the field.

ISSN:0003-6951    

DOI:10.1063/1.90724

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Transient gain has been observed on theC→Atransition of XeF*. Measurements made at 488.0 and 475.9 nm showed a peak gain of 8&percent; through a short cell filled with Ar/Xe/NF3mixtures and excited by a short electron‐beam pulse. A stimulated emission cross section of 5×10−18cm2is derived, consistent with the measured linewidth and radiative lifetime of theC‐Atransition. Weaker amplification was observed at 514.5 nm.

ISSN:0003-6951    

DOI:10.1063/1.90725

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Experimental and theoretical results are presented for the Brillouin spectrum of single‐mode optical fibers in the 180° scattering geometry. It is shown that for core diameters less than 10 &mgr;m both the Brillouin frequency shift and spontaneous linewidth are influenced by the nature of the normal acoustic‐mode spectrum and wave‐vector nonconservation in the acousto‐optic interaction. The velocity and lifetime of longitudinal phonon excitations in the core are evaluated, and the consequences to stimulated Brillouin scattering assessed.

ISSN:0003-6951    

DOI:10.1063/1.90726

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

A laser calorimeter has been used to measure two‐photon absorption in solids. This new technique provides greater sensitivity than is possible in nonlinear transmission measurements. The two‐photon absorption coefficients of CdTe and CdSe at 1.06 &mgr;m using ∼16‐nsec (FWHM) pulses are 0.13±0.04 and 0.050±0.014 cm/MW, respectively.

ISSN:0003-6951    

DOI:10.1063/1.90706

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

We have devised a new nonlinear spectroscopic technique, photoacoustic Raman spectroscopy (PARS), which uses acoustic methods to detect energy deposited in a molecular gas by the process of stimulated Raman scattering. The technique was demonstrated by stimulated Raman excitation of the 2916.7‐cm−1&ngr;1symmetric stretch vibrational mode of CH4using two cw laser sources (an argon ion laser at 514.5 nm and a tunable dye laser near 605.4 nm). Excellent agreement between calculated and experimentally observed PARS signals was obtained for CH4.

ISSN:0003-6951    

DOI:10.1063/1.90707

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Efficiencies of 25% have been obtained with 1‐cm‐diam AlGaAs/GaAs heteroface concentrator solar cells utilizing an ultrathin AlGaAs window layer design. A low specific resistance (<0.005 &OHgr; cm2) Ohmic contact is achieved by direct contact to thep‐GaAs active layer. Liquid phase epitaxy has been developed to grow <500‐A˚ thick window layers on large‐area (3.3×3.3 cm) GaAs substrates. Four 1‐cm‐diam cells are produced from each wafer and demonstrate the potential for larger‐scale production.

ISSN:0003-6951    

DOI:10.1063/1.90708

出版商:AIP    

年代:1979

数据来源: AIP