摘要:

The mechanism of darkening of standard silver halide photochromic glass is studied by electron paramagnetic resonance (EPR) of photogenerated divalent copper ions. A time resolution of the EPR spectra was obtained by recording the evolution with the irradiation time of the EPR intensity at various magnetic‐field strengths. It is shown that only one copper species is photogenerated during darkening. This species is a CuII‐silver vacancy complex oriented along a [110] direction. The electron ground state has a predominantlydz2character. The activation energy of the formation of this complex,E=0.06±0.01 eV, is controlled by the migration of interstitial silver ions. It is also shown that the silver vacancy of the complex is generated during the hole trapping by the monovalent copper ion.

ISSN:0021-8979    

DOI:10.1063/1.351400

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The effects of the beam divergence of the input pump laser beams on the nonlinear frequency mixing process in a dielectric medium is discussed. The divergent laser beams have finite angular spreads so that all of the interactions between the two input beams can never satisfy the phase‐matching condition exactly. A numerical model is developed to investigate the effects of input beam divergence on conversion efficiency. The angular spread of each of the input beams is represented by a set of plane waves having a distribution of propagation directions. Each of the plane‐wave components from one input beam is allowed to interact with all the plane‐wave components of the second input beam. This model is applicable to processes such as sum frequency generation, difference frequency generation, and optical parametric amplification. Second‐harmonic generations as a special case of sum frequency generation is used as an example in the numerical studies. Results indicate that the conversion efficiency is dependent on the amount of beam divergence, the input intensity, and the length of the nonlinear medium. These parameters must be optimized with respect to one another to maximize the conversion. The optimization is especially critical in high‐power systems where high conversion efficiency is sought.

ISSN:0021-8979    

DOI:10.1063/1.351272

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We have carried out a generalized perturbation analysis of the second‐order nonlinear equation for photon density for semiconductor lasers. The second‐order equation is obtained with minimal approximations, from the single‐mode semiconductor laser rate equations, which unlike previous work, include both the effect of gain compression and the coupling of the spontaneous emission to the lasing mode. After deriving the general perturbation formula, expressions for second harmonic distortion as well as third‐order intermodulation distortion are obtained. Unlike previous work which is restricted to two subcarriers, the present work gives results for an arbitrary number of subcarriers.

ISSN:0021-8979    

DOI:10.1063/1.351273

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A time‐dependent and three‐dimensional dye laser amplifier simulation is presented. Its amplified spontaneous emission (ASE) is simulated by distinguishing the propagating directions of the angularly divided ASE, which makes it possible to simulate both the laser and ASE. Strong generation of the ASE is seen from the part of the excited volume where there is no input signal, indicating that ASE greatly depends on the input‐beam geometrical profile, as well as its temporal matching with the pumping beam.

ISSN:0021-8979    

DOI:10.1063/1.351274

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Thermal diffusion from a single colloidal sphere suspended in an aqueous medium that is heated by a laser pulse is examined. The temperature field as a function of position and time arising from the cooling of a hot colloidal sphere suspended in an infinitely extended aqueous medium is obtained by solving the heat conduction equation with initial, asymptotic, boundary conditions using a Laplace transform technique. A polymethylmethacrylate sphere of 83 nm diameter is calculated to cool in water within 7 ns. The cooling time is found to decrease quadratically with the particle diameter. We discuss the use of arrays of dyed polymethylmethacrylate spheres suspended in a refractive‐index‐matched aqueous medium as a fast (ns) optical switching device which acts as an optical monostable.

ISSN:0021-8979    

DOI:10.1063/1.351275

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The effects of strong turbulence (C2nup to 3×10−9m−2/3) on laser beam propagation were measured. Beam broadening of a factor of 2, and wander over several hundred microradians were observed. Long‐term beam broadening agrees with values calculated from simplified analytic models.

ISSN:0021-8979    

DOI:10.1063/1.351276

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

An extension of the classical thermal Stefan problem by incorporating the dependence of the phase transition temperature on pressure generated by the flow of the liquid phase due to a density change in the transition process is presented. Two prototypical planar situations are considered. The first is the onset of freezing in an incompressible liquid layer of finite thickness in a gravity field. Asymptotic solutions developed for this problem demonstrate that the initial singularities of the interface velocity and acceleration, typical for the solutions of the classical Stefan problem with an instantaneous temperature drop at the fixed boundary, are regularized by the dynamic pressure effect. The second problem addressed is the freezing or melting of a saturated porous half‐space with a flow governed by the Darcy law. Exact similarity solutions (accounting for compressibility of the fluid in the case of freezing) are developed. They indicate that the pressure dependence of the transition temperature may affect significantly the propagation of the phase‐change front.

ISSN:0021-8979    

DOI:10.1063/1.351277

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

An interesting and useful analogy can be drawn between the equations of static poroelasticity and the equations of thermoelasticity including entropy. The correspondence is of practical use in determining the effective parameters in an inhomogeneous poroelastic medium using known results from the literature on the effective thermal expansion coefficient and the effective heat capacity of a disordered thermoelastic continuum.

ISSN:0021-8979    

DOI:10.1063/1.351278

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

This paper is devoted to the calculation of the electric tractionPeacting at every point on the surface of a charged gas or liquid bubble immersed in an insulating liquid and subjected to an electric field between parallel‐plate electrodes. It is shown that the deformation of a bubble charged or situated near the electrodes is not symmetric. This dissymmetry has been verified experimentally. The expression forPeused in a previous work [C. G. Garton and Z. Krasucki, Proc. R. Soc. London Ser. A280, 211 (1964)] represents a particular case (bubble uncharged or electrically neutral) of the one we have established. In this case, the shape of the distorted bubble is that of a prolate spheroid. This deformation of bubbles also depends on their concentration and positions in the electrode gap.

ISSN:0021-8979    

DOI:10.1063/1.351279

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Simultaneous pulsing of two, closely spaced discharge tubes inhibits the ignition of one of the discharges. Such cross‐talk is prominent for discharge tubes having a floating cathode potential (i.e., with an impedance attached to the cathode), driven by short duration pulses, and having a long discharge path. The cross‐talk originates from at least two mechanisms. First, a voltage jump at the cathode, induced by a capacitive coupling with another cathode, makes the anode‐cathode potential smaller, and hence discharge ignition is inhibited. Second, wall charges induced by a discharge in a neighboring tube also inhibit ignition. The cross‐talk can adversely affect the operation of gas discharge displays. It is demonstrated that cross‐talk in the panel can be eliminated by adopting a dephasing drive technique.  

ISSN:0021-8979    

DOI:10.1063/1.351280

出版商:AIP    

年代:1992

数据来源: AIP