摘要:

Optically induced laser action has been achieved at room temperature with a structure consisting of a pumped double‐heterostructure (DH) GaAs active layer taper coupled to a low‐loss passive AlxGa1−xAs waveguide incorporating a second‐order Bragg‐reflection grating which served as a feedback component. In terms of injection pumping, the lasing threshold is equivalent to approximately 8 kA/cm2. In contrast to optically pumped conventional DH GaAs‐AlGaAs lasers, the output has a spectral width reduced to 2 A˚, its wavelength is insensitive to the pumping geometry, and the lasing always occurs in time at the peak intensity of the pump. Additional relevant active and passive data are also given.

ISSN:0021-8979    

DOI:10.1063/1.324666

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A picosecond dye laser system has been developed which utilizes the 265‐, 355‐, and 530‐nm pulse harmonics of a mode‐locked Nd+3glass laser to pump transversely several dyes which emit tunable picosecond pulses from 340 nm to near infrared. The psec dye laser pulses are amplified in a specially designed dye cell pumped by aQ‐switched Nd/glass laser to energies of ∼4 mJ per picosecond pulse with a pulse width of 7 psec.

ISSN:0021-8979    

DOI:10.1063/1.324667

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Recent measurements of radiation from certain rare gas–halogen mixtures have indicated the efficient production of broadband emitters in the visible. This paper reports a gain measurment at 4416 A˚ in mixtures containing the two emitters tentatively identified as Kr2F* (&lgr;max=4000 A˚ and FWHM=900 A˚ and ArXeF* (&lgr;max=4600 A˚ and FWHM=900 A˚). Attenuation of the 4416‐A˚ probe laser during electron‐beam and electron‐beam‐sustained discharge excitation of 2–3 atm pressure mixtures of argon‐krypton‐fluorine and argon‐xenon‐fluorine indicates absorption only. The fluorescence signals from ArXeF* and XeF* (Ar/Xe/F2mixture), and KrF* and Kr2F* (Ar/Kr/F2mixtures) were monitored simultaneously with the absorption of the probe laser. Since the absorption was not proportional to the fluorescence of these species, it is tentatively concluded that it is due to another transient species. Typical absorptions of 10−3cm−1were observed at pump levels of 105W cm−3. A knowledge of the absorption mechanism will be required to assess the efficiency with which such lasers can be made to operate, if at all.

ISSN:0021-8979    

DOI:10.1063/1.324668

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The intensities of the Cd 2288‐ and 2981‐A˚ and Cd+2144‐ and 2265‐A˚ lines have been measured as a function of Cd vapor pressure in the Cd‐Ar discharge. Except for the 2981‐A˚ line, the intensities are highest at Cd vapor pressures in the range 5–30 mTorr. The 2981‐A˚ line increases in intensity with increasing Cd vapor pressure in the 5–200‐mTorr range. Absolute radiant flux densities have been determined by calibrating the spectrometer response using a low‐pressure mercury discharge.

ISSN:0021-8979    

DOI:10.1063/1.324669

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The problem of the scattering of an obliquely incident plane electromagnetic wave by a rotating dielectric column is discussed on the basis of Maxwell’s equations and the constitutive relations of the Minkowski type for rotating media. Consider a homogeneous isotropic nondispersive dielectric column rotating at constant angular velocity around its axis, with its peripheral velocity assumed to take an arbitrary value smaller than the vacuum velocity of light. Then, the scattering properties of the rotating dielectric column are investigated in detail with the aid of numerical examples. From the numerical examples for the scattering pattern and the backscattering cross section, it is found that the scattering of electromagnetic waves by a dielectric column is modified in an interesting manner by its rotational motion.

ISSN:0021-8979    

DOI:10.1063/1.324678

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The first‐ and the second‐order Bragg interactions in an unbounded active medium having a sinusoidally varying permittivity or gain in the direction of progression of the interacting waves are investigated. In the first‐order Bragg interaction, there is absolute instability of the participating waves. In the second‐order Bragg interaction, the waves are convectively unstable with their spatial amplification reduced in the Bragg region by the destructive interference of the two interacting waves. The nature of these instabilities are analyzed and physical explanations for the various characteristics are provided. When the gain of the medium is an order magnitude smaller than the modulation index, the absolute instability, instead of taking place in the first, occurs, in the second Bragg region. The importance of incorporating the gain in a manner that is consistent with the material dispersion law is emphasized.

ISSN:0021-8979    

DOI:10.1063/1.324679

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

It is often difficult and unpractical, in the acoustic imaging area, to insert a focusing lens between the observed object and the ultrasonic receiver. Furthermore, the focal length must, in the B scan mode, be varied very fast in order to keep the line sources lying at different depths well focused. A spatial‐sampling scheme may be used for circumventing these problems by taking off the possibly complex processing unit from the element contacting the observed object, without additional complexity or degradation in the flexibility and usefulness of the apparatus. The sampling is done using a receiving transducer array to convert the acoustic signals into electrical ones, which may be amplified before being applied to another reemitting transducer array: an acoustical field identical to the original one is so reconstructed. The sampling operation will, however, alter the image quality by introducing parasitic images. The dependence of the perturbations upon the system parameters is studied in this paper and criteria are derived for limiting them.

ISSN:0021-8979    

DOI:10.1063/1.324680

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The acoustic field focused by a spherical solid‐water interface has been computed and the results have been used to optimize the geometry of a transmission acoustic microscope. An experimental study has been performed, which enables the sampling of the focused acoustic field, as may be realized by using the Fourier‐transform‐operation concept for an ideal lens.

ISSN:0021-8979    

DOI:10.1063/1.324681

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Using theR‐line fluorescence of trace Cr3+in sintered Al2O3as an example, a method of analysis is outlined for determining the residual microstress and macrostress in a polycrystalline aggregate. It uses the shift and broadening, induced by residual stress, of a line due to a transition in an atomic system dissolved in the aggregate. For sintered Al2O3from three different manufacturers, but made for the same purpose, the isotropic and shearing components of the residual microstress and macrostress are listed in tabular form. For the isotropic component of the microstress a distribution is found, with a mean value of ∼2 kbar, in which tension and compression are equally probable.

ISSN:0021-8979    

DOI:10.1063/1.324682

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Volume ionization produced in Ar by uv photoions was measured using a fast rotating Langmuir probe. The uv radiation was obtained from an electric discharge and collimated to produce a cylindrical plasma. Measurements were performed for pressures of 100, 200, 400, and 600 Torr and distances of 2.5–10.2 cm from the discharge. Plasma decay was observed from 50 to 350 &mgr;s after the discharge was fired and was attributed to radial expansion by ambipolar diffusion and volume recombination. By an extrapolation process, the initial photoion density can be obtained; its distance dependence suggests two‐photon ionization of Ar. The results are also compared to other measurements found in the literature.

ISSN:0021-8979    

DOI:10.1063/1.324683

出版商:AIP    

年代:1978

数据来源: AIP