摘要:

An integrated hydrodynamic inhomogeneous spherical model is used to describe the temporal evolution of thin targets under heating by a laser beam. Computer analysis gives temperature laws as a function of characteristic parameters of both target and laser beam. The results indicate a change in the scaling laws for such laser‐created plasmas.

ISSN:0021-8979    

DOI:10.1063/1.1662810

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Stopping cross sections of &agr; particles for silicon and germanium have been measured for 0.3 ≤E&agr;≤ 2.0 MeV. The experimental method consists of the elastic scattering of &agr; particles either from a thick Ta backing onto which the stopping element has been evaporated, or directly from the film of stopping element evaporated onto a thick Al backing. The results were analyzed using a three‐parameter formula for stopping cross section recently suggested by Brice. With the parameters obtained from a least‐squares fit, the formula was found to be useful in calculating the stopping cross sections for energies outside the measurements, at least up to 10 MeV.

ISSN:0021-8979    

DOI:10.1063/1.1662811

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The evolution of a picosecond optical pulse in a mode‐locked Nd : glass laser is primarily affected by the construction of the resonator components. By paying attention to what have been thought of as minor details in the design of the laserhead, such as mounting of the flashlamps and laser rod, virtually 100% reliability and remarkable reproducibility have been achieved. Furthermore, we have studied how the pump power, mirror alignment, and saturable dye concentration affect the reliability and have found that these parameters must be critically controlled if reproducibility is desired.

ISSN:0021-8979    

DOI:10.1063/1.1662812

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A mathematical formalism is presented for calculating the mode spectrum and threshold condition for a corrugated distributed‐feedback laser. The procedure is applied to the case where the active medium is bounded by metallic walls. An expression for the coupling constant &kgr; which measures the amount of feedback per unit length is obtained. The complex transcendental equations relating the key parameters are shown to be of the same form as those deduced by Kogelnik and Shank for a periodic index variation.

ISSN:0021-8979    

DOI:10.1063/1.1662813

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Various aspects of the propagation of an intense laser beam through the atmosphere are considered. The basic laser‐fluid equations are presented and a linearized analysis of these equations is given which predicts a very low power threshold for Brueckner‐Jorna‐type convective instabilities. Another class of instabilities is predicted to be of more practical importance than the convective instabilities and an effective Reynolds number is derived which may help to characterize these turbulent instabilities. In the following paper by the same authors a computer solution of the full set of nonlinear equations is described and the initial development of the laser‐fluid interaction is investigated.

ISSN:0021-8979    

DOI:10.1063/1.1662814

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A numerical solution of the nonlinear macroscopic laser‐fluid equations for propagation of a Gaussian laser pulse in air is described. The concept of ``utility analysis'' of numerical differencing schemes is introduced. With the computation scheme used, the laser pulse could be followed for only 10−5sec; so enormous energy was put into the pulse to enhance the interaction with the fluid. Thus the initial pulse distortion could be observed. Analytical evaluation of the computer results produces a detailed quantitative check and suggests that a combination of analytic and numerical methods would allow a pulse to be conveniently followed for much longer periods of time. The preceding paper by the same authors describes various types of instabilities to be anticipated for propagation over long periods of time or with large powers.

ISSN:0021-8979    

DOI:10.1063/1.1662815

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Single crystals of ZnxCd1−xTe solid solutions have been grown from a melt under an Ar pressure of about 50 atm. The crystals of uniform composition were grown over the whole range of molar composition, when the crystal growth was performed in excess Zn and/or Cd. A grown boule of 30 × 15 mm &phgr; contained several single‐crystal domains of size 7 × 5 × 5 mm. On the basis of Vegard's law, the molar compositionxwas determined from x‐ray measurements of lattice constants. The variation ofxthroughout a single‐crystal domain was found to be less than ± 1%. Optical experiments including transmittance and reflectance measurements have been made on the cleaved (110) planes at room temperature. The variation of the lowest band gap withxwas determined from the peak positions in the reflectivity spectra. The bowing parameter, which is a measure of the deviation from the linear change, of this gap was found to be 0.33 eV.

ISSN:0021-8979    

DOI:10.1063/1.1662816

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

In order to study the influence of statistical effects on the microwave behavior of polar semiconductors, power reflection and transmission measurements have been performed onn‐type InSb with the aid of a modified reflectometer at 134 GHz in the temperature range from 83 to 170 K. The carrier concentration and the dc mobility were measured by the van der Pauw method. The Boltzmann equation was numerically solved for low dc and ac electric fields. The calculated dc mobility vs temperature curve was adjusted to the experimentally determined curve by a proper choice of the total ionized impurity concentrationNi. Using this value ofNithe power reflection and transmission at 134 GHz were calculated. Good agreement is obtained between experiment and theory, especially for the temperature dependence. It is shown that at 134 GHz the ac behavior ofn‐InSb cannot be described accurately by Drude's theory.

ISSN:0021-8979    

DOI:10.1063/1.1662817

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

An electrostatic velocity analyzer of the Mo¨llenstedt type is described in detail, featuring in particular a high efficiency (through‐put) and a resolution adjustable from about 0.2 to 30 eV (or more) full width at half‐maximum (FWHM). The construction is kept simple by using several commercially available parts. A sweep generator together with a multichannel scaler is utilized to record spectra over an energy range from 0 to 16 000 eV. An experimental calibration technique is described and two energy‐loss spectra obtained by electron impact are given to demonstrate the performance of the analyzer.

ISSN:0021-8979    

DOI:10.1063/1.1662818

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The response of materials to ≈5‐ms pulses of 10.6‐&mgr; laser radiation at peak power densities of 1 to 2 MW/cm2has been observed with simultaneous determination of (i) both front and back surface temperature rises, (ii) pressure delivered to the specimen as a function of time, (iii) total impulse delivered to the specimen, and (iv) absorption wave effects via high‐speed framing camera coverage. The materials studied are 2024 aluminum alloy, 304 stainless steel, graphite, a Fiberglas‐epoxy composite, alumina, MgO, and Pyroceram. It was found that Fiberglas‐epoxy and graphite exhibit continuous coupling of the laser energy during the entire pulse, whereas the metals showed strong initial coupling which gradually diminished to near zero and then recoupled at the end of the pulse. The ceramics exhibited repetitive decoupling and recoupling during the entire pulse. The photographic evidence indicates the formation of laser‐supported plasmatrons in the case of the metals and laser‐supported combustion waves with the ceramic materials.

ISSN:0021-8979    

DOI:10.1063/1.1662819

出版商:AIP    

年代:1973

数据来源: AIP