摘要:

A thermodynamic calculation is conducted to determine the distribution of hydrogen atoms absorbed in a one‐dimensional palladium rod, along which a temperature gradient is imposed. The rod is assumed to be completely sealed, so that the total number of the hydrogen atoms is conserved regardless of its thermal conditions. A model calculation based on a zeroth‐order interaction model predicts that upon the imposition of the gradient, the hydrogen distribution will significantly change from its initial uniformity. The profile of the redistributed hydrogen can be discontinuous at one point on the rod. The concentration gap developed at this point of temperatureTimplies that the two‐phase region in the palladium hydride phase under the thermal equilibrium is nonexistent under the nonequilibrium condition. Similar to the disappearance of the two‐phase region above the critical temperature, the concentration gap is reduced with an increase of the temperature gradient.

ISSN:0021-8979    

DOI:10.1063/1.353318

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The use of small apertures or sharpened tips as sensing elements in scanned‐probe optical sensing devices has led to the development of a number of instruments that provide lateral spatial resolution much finer than that available in conventional optical imaging instruments. Such a device might generally be classified as a scanning optical microscope, or SOM. One particular mode of SOM operation involves the use of a sharpened optical fiber to collect light emanating from a surface. The lateral spatial resolution of such a collection‐mode SOM is discussed in terms of the electromagnetic mode solutions of the probe tip. Numerical results indicate that, though bound modes solutions exist for increasingly fine unclad tips, classical diffraction effects limit resolution to a finite fraction (approximately 1/3) of the source wavelength &lgr;. A second mechanism for signal transduction is shown to involve molecular scattering at the probe tip. An analysis of signal collection efficiency demonstrates that at tip radii below &lgr;/5 for metallic‐clad probes, and &lgr;/10 for probes in a dielectric ambient, scattering dominates and imaging resolution scales with tip size, thus defeating limits imposed by diffraction.

ISSN:0021-8979    

DOI:10.1063/1.353319

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The nonmonotonic relation between the increasing wavelength and the noncritical phasematching (NCPM) temperature are analyzed in detail for temperature‐tuned as well as the phase matching angle for angle‐tuned second harmonic generation in a LiB3O5(LBO) crystal. This relation was called ‘‘the phase matching retracing behavior.’’ Because of the retrace, LBO is the unique nonlinear optical crystal that can produce the spectra through blue to near infrared by NCPM. It has been shown that the retracing wavelengths (∼1.3 &mgr;m), and furthermore, the conjugation relation for phase matched wavelengths are approximately independent of the tuning means. There exist at the retracing wavelengths not only the retrace for the tuning curves but also for the beam walkoff, group velocity mismatch, and the angular and spectral acceptances. The spectral noncritical phase matching is achieved and the group velocity mismatch is zero at the retracing points. The temperature acceptances are also very large. These properties of LBO, combining its high damage threshold, high transparency, nonhygroscopicity, and the availability of the large and high quality crystal, make LBO the best choice in doubling, either by type I or type II, by temperature‐tuned or angle‐tuned, the radiations (including ultrafast pulses) in the vicinity of 1.3 &mgr;m, such as those from some diode lasers, optical parametric oscillator/amplifier, and Nd:YAG/YAP/YLF lasers working at4F3/2–4I13/2transition.

ISSN:0021-8979    

DOI:10.1063/1.354084

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Wavelength tunability in three‐section distributed feedback laser diodes has been studied under pulsed and continuous biasing. In both cases comparably large modejump‐free tuning ranges (2.5 and 3.7 nm, respectively) were obtained for devices operated with two injection electrodes. Several effects are discussed in terms of a possible explanation of the enhanced tunability in these devices.

ISSN:0021-8979    

DOI:10.1063/1.353320

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Clean thin samples of silicon (111) have been irradiated by 350–400 ns dye‐laser pulses of 590 nm radiation under ultrahigh vacuum (UHV) conditions. Results obtained using a UHV transmission electron microscope on the thermal shock cleavage of these samples are reported. Classic cleavage along {111} planes was observed at relatively low fluences (less than 0.04 J/cm2). The observations on the sample morphology before and after laser irradiation demonstrate that under the conditions that yield to cleavage, there is no long range diffusion of point defects and there is no tendency for the cleavage to occur at pre‐existing defects. Although in some cases, cleavages occur at locations that are logically weak, in general, there appears to be no correlation between the cleavage sites and the three‐dimensional crystal structure.

ISSN:0021-8979    

DOI:10.1063/1.353321

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Metal‐coated, nanometer‐size particles are modeled with a realistic distribution of coating thicknesses. General expressions are given for the local‐field enhancement, absorption, and nonlinear optical response. In addition, heuristic arguments are used to determine the effects of a diffuse, rather than a sharp interface. The linear and nonlinear optical properties are discussed within the context of the effective medium theory for small volume fractions. An efficient method of solution is used with the flexibility to handle an arbitrary number of coatings.

ISSN:0021-8979    

DOI:10.1063/1.353290

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

It is well known that the signal output intensity from a dye laser oscillator depends directly on the pump intensity. The opposite effect, the dependence of the transmitted pump intensity on the signal intensity, is studied in detail. The theoretical results are compared with experimental data obtained using an argon‐laser‐pumped rhodamine 6G dye laser.  

ISSN:0021-8979    

DOI:10.1063/1.353291

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Light‐scattering and transmission properties of aligned nematic droplets dispersed in a solid polymer are studied. Theoretical evaluations of the differential and total cross sections are performed in the anomalous diffraction approximation. The corresponding attenuation coefficients are calculated in a single scattering approximation. The effect of interdroplet interference is discussed as well. Theoretical calculations are in agreement with experimental data obtained from thin films of polymer dispersed nematic droplets of micron size, aligned by an applied electric field.

ISSN:0021-8979    

DOI:10.1063/1.353292

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Simple expressions were derived for the temperature rise at the surface of a thick medium under sustained laser irradiation. These were employed to estimate the thermal contributions to property measurements in a few simple representative scenarios.

ISSN:0021-8979    

DOI:10.1063/1.353293

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The response of a radio‐frequency discharge in an electronegative gas to laser‐induced photodetachment is considered. The discharge is described by a numerical fluid model, including the electron energy balance. The detachment event is simulated by transforming instantaneously all or part of the negative ions into electrons in the region of the discharge passed by the laser beam. In order to avoid severe restrictions on the computational time step, the evolution of the electron density and of the electric field is solved with a fully implicit numerical method. It turns out that the relaxation towards the periodic quasisteady state is mainly governed by a simultaneous increase of the production rate of negative ions and decrease of the ionization rate. The qualitative behavior of the calculated electron decay rate is in accordance with experimental observations.

ISSN:0021-8979    

DOI:10.1063/1.353294

出版商:AIP    

年代:1993

数据来源: AIP