摘要:

Ion‐beam mixing at Ni‐Si interfaces was studied as a function of dose, temperature, and dose rate. In the temperature range 10–443 K, the thickness of the mixed Ni‐Si layer grew proportionally to the square root of dose for 250‐keV Ar+and 280‐keV Kr+irradiations. The apparent diffusion coefficient for mixing during irradiation comprises temperature‐dependent and independent contributions. The activation enthalpy for the temperature‐dependent part is ∼0.09 eV. Varying the dose rate by a factor of ∼20 had little effect upon mixing at either 80 or 368 K. Analysis of these results using chemical rate theory showed that the low activation enthalpy for diffusion was not associated with point‐defect motion. More likely the temperature dependence of mixing in Ni‐Si is associated with the effect of temperature on compound formation. The results for mixing at 10 K in Ni‐Si were compared with those in Ni‐Al, at 10 K, to study the effect of crystal structure on displacement mixing.

ISSN:0021-8979    

DOI:10.1063/1.330624

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Techniques used currently to determine bulk and surface laser absorption coefficients of highly transparent materials have drawbacks both inherent and practical that limit their accuracy. Conventional bar calorimetry attempts a two‐coefficient characterization of nine separate physical absorption sites. Photoacoustic techniques requireinsitucalibration sensitive to sample geometry and material. This paper proposes a new technique in which a set of conventional ballistic laser calorimetry measurements are made on a single prismatic sample. Systematic changes in the polarization and direction of propagation of the laser beam can lead to an explicit determination of individual surface and bulk absorption coefficients. An equilateral prism sample provides a set of independent measurements sufficient to establish the bulk absorption in each of three internal paths and two absorption components on each of the three surfaces. This geometry can be used, in principle, for materials with refractive indices less than 2; more practically, for indices less than 1.7. For higher indices, a truncated prism is proposed which allows seven independent measures to deduce eight absorption components. As assumption of constant surface anisotropy is proposed to complete the analysis. Design criteria for the prism shape are presented, along with analytical expressions for all relevant absorption experiments, and for the simplest cases of uniform, isotropic high and low index materials.

ISSN:0021-8979    

DOI:10.1063/1.330625

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A Na2dimer laser which is excited longitudinally by a single‐frequency Ar+‐ion laser at 488.1 nm exhibits a very narrow gain profile in forward direction of the pump beam. Using linear resonators with lengths ≲2 m, the gain profile can be appreciably narrower than the spacing of adjacent axial resonator modes. Only if a resonator mode coincides with the gain profile, laser oscillation is shown to occur. This leads to a very unstable emission with low efficiency. Possibilities to achieve controlled emission are demonstrated.

ISSN:0021-8979    

DOI:10.1063/1.330626

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

As a novel alternative to the conventional Xe flash lamps, a surface‐spark‐discharge ultraviolet (UV) flash with a poly‐tetra‐fluoroethylene (Teflon) resin was utilized to an initiation of a H2/F2chemical laser. Because we employed a high‐voltage and low‐inductance power supply to drive a surface‐spark flash, a stabilized surface discharge in a high pressure (≃1 atm) laser gas and high efficiency power input to an UV flash have been realized. We have obtained a maximum HF laser output energy of 8.5 J/pulse (14.6 J/ ∂) at an electrical efficiency of 9.7%. A surface‐spark light source is experimentally found to be able to uniformly initiate a large‐volume laser gas mixture.

ISSN:0021-8979    

DOI:10.1063/1.330627

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Results of a study of the electrical derivative characteristics of InGaAsP buried heterostructure lasers are presented. By considering current‐leakage paths and electrical contact nonlinearities, an equivalent circuit model appropriate to the buried heterostructure laser has been developed. Solutions for the theoretical electrical derivatives of series‐parallel‐reducible networks have been obtained and applied to the equivalent circuit model of the buried heterostructure laser. Comparison of experimentally measured and calculated electrical derivative characteristics provides both qualitative and quantitative information concerning the distribution of current and voltage in buried heterostructure lasers. By combining the techniques of electrical‐derivative measurement and equivalent‐circuit modelling, an improved understanding of the properties of buried heterostructure lasers has been established.

ISSN:0021-8979    

DOI:10.1063/1.330628

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The time dependence of the reflection of the output mirror for a two‐level pulsed laser is determined for an arbitrary time‐dependent pumping rate. The result derived using the methods of optimal control theory is given as an explicit function of time. The optimal reflectivity eliminates relaxation oscillation spikes so that the output is a smooth function of time. Moreover, the peak instantaneous intracavity photon density of the optimal solution is significantly reduced relative to the photon density using constant reflectivity, thereby increasing the fluence without reaching the damage threshold. Numerical examples for a Nd+3/YAG system is provided. A practical feedback mechanism for controlling the output mirror reflectivity as a function of time that well approximates the optimal solution is proposed.

ISSN:0021-8979    

DOI:10.1063/1.330629

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The irradiance from a low‐gain argon‐ion laser is observed to be self‐modulated at harmonics of the longitudinal mode spacing (82 MHz). The laser is made to oscillate at five discrete frequencies between 408 and 737 MHz by controlling resonator losses.

ISSN:0021-8979    

DOI:10.1063/1.330630

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The amorphous to polycrystalline transition in thin silicon layers is accompanied by a large change in optical transmission in the visible. By inducing this transition by laser annealing, high‐resolution optical recording and visible‐light readout have been demonstrated. As an optical recording material, amorphous silicon layers offer characteristics of high information‐storage density, long‐term stability, and negligible degradation upon repeated readout. Such an optical image in a thin silicon layer can be converted to a relief pattern by taking advantage of the difference in etch rate between amorphous and polycrystalline silicon, thus providing a method of producing patterns in silicon layers without use of intermediate photo‐resist steps.

ISSN:0021-8979    

DOI:10.1063/1.330631

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The fabrication of photoresist gratings on reflecting surfaces is considered both theoretically and experimentally. We show that it is important to take into account the actual phase shift of the waves reflected from the surface. It is found that the intensity at the photoresist‐surface boundary may be significantly larger than that at the standing‐wave minimum. The theory is confirmed by the examination of the profiles of photoresist gratings made on PbSnTe, in comparison to GaAs. This phenomenon may have wider applications when the photolithographic fabrication of fine features on reflecting surfaces is considered.

ISSN:0021-8979    

DOI:10.1063/1.329868

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Utilizing the second Stokes line of the stimulated Raman scattering in a multimode, graded‐index optical fiber pumped by a 1.32‐&mgr;m Nd:YAG laser, we have first demonstrated an optical time domain reflectometry at a wavelength of 1.5 &mgr;m for a multimode fiber. As a result, the maximum detectable fault location length of 28 km was successfully obtained. The present technique is applicable to the fault location in ultralong length.

ISSN:0021-8979    

DOI:10.1063/1.329869

出版商:AIP    

年代:1982

数据来源: AIP