摘要:

The performance of Kr*2as a 146 nm fluorescence or laser source when pumped by a low‐current, long‐pulse electron beam has been determined. The fluorescence efficiency of Kr@B|2is near the theoretical limit of ∼46% at modest pressures over a range of pump rates up to 3×105W/cm3. Lasing could not be achieved under the conditions studied here. An improved kinetics and extraction code has been developed to model the performance of the Kr*2system. A key component of the model is a more detailed treatment of the interactions between secondary electrons and excited atomic and molecular xenon states. Estimated rates for these processes are presented. With this model, good absolute agreement of model predictions with experimental results has been obtained at pressures as low as 0.5 atm.

ISSN:0021-8979    

DOI:10.1063/1.341762

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The nonlinear, lossy optical waveguide coupler employing GaAs/GaAlAs multiple quantum well structure has been analyzed. Using properly defined distributed circuit parameters, we model a system of coupled waveguides with a system of coupled transmission lines. The equivalent transmission line system parameters are derived in terms of the rectangular coupled waveguide system parameters. The coupled‐mode theory, developed for the study of the nonlinear lossy transmission line system, is then applied to the equivalent transmission line system. The coupled‐mode equations are solved numerically with the aid of the Runge–Kutta method, and the mode powers are calculated. It is shown that the variation of output power of the coupler and the division of powers between the two guides of the coupler depend strongly on the input power. The minimum input power required for the coupler to switch from the cross‐over state to the straight‐through state depends upon the losses of the guide as well as on the separation between the two guides of the coupler.

ISSN:0021-8979    

DOI:10.1063/1.341763

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Several Ti:LiNbO3waveguides have been fabricated in dry and wet atmosphere, varying the diffusion time. The effect of water vapor on the diffusion process has been investigated. Effective indices and attenuation at &lgr;=0.6328, 1.15, and 1.52 &mgr;m have been measured. In the dry case, the Ti in‐diffusion proceeds more rapidly than in the wet case, and the two diffusion coefficients have been calculated. Also, it has been observed that the presence of water vapor in the atmosphere does not completely prevent the phenomenon of Li2O out‐diffusion, while the importance of the boat and the furnace materials in this process has been verified. Attenuation measurements showed that particular care must be taken, when working with waveguides diffused for short times, for two reasons. (1) The ratio diffusion length/wavelength, i.e., the normalized frequencyv, decreases, and modes approach the cutoff, becoming more lossy. Of course, this is more evident working at long wavelength. (2) The surface roughness can strongly affect the attenuation value.

ISSN:0021-8979    

DOI:10.1063/1.341764

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The parametric dependence of the output energies and efficiencies for the Raman conversion of the radiation from a long‐pulse 1‐J XeCl excimer laser in Pb vapor was investigated. The effects of atom depletion and buffer gas on the stimulated Raman scattering output were discussed in detail. Multipeak structures of the waves of the Raman‐shifted pulses were observed which could be attributed to the coherent effects in Raman scattering. A computer model was introduced to explain the multipeak structures of the stimulated Raman scattering waveforms.

ISSN:0021-8979    

DOI:10.1063/1.341765

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Some characteristics of reversible phase‐change optical data storage based on an amorphous‐crystalline transformation in InSbTe alloys are given. The reversible phase change was observed in a wide region of composition. The laser amorphized spot of a ternary compound In3SbTe2film could be crystallized using a diode laser pulse of less than 100 ns with an incident laser power of more than 10 mW. The crystallization temperature of the amorphized spot was 280 °C and the activation energy was about 1.8 eV which shows that long‐term data retention at room temperature is possible. The repetition number of static write and erase using the pulse of 50 ns reached above 105. These data show that the ternary compound film has potential for reversible optical data storage media with high‐speed erasing and long‐term data retention.

ISSN:0021-8979    

DOI:10.1063/1.342502

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Output characteristics of the short‐pulse electron‐beam excited ArF (193 nm), KrF (248 nm), XeF (351 nm), KrCl (222 nm), and XeCl (308 nm) lasers were experimentally investigated at the same time on the same device for various mixtures all pumped at a high excitation rate of 2.3 MW/cm3. The optimum pressure of rare gas forming its rare‐gas halide excimer increased for the sequence of ArF, KrCl, KrF, XeCl, and XeF, indicating that rare‐gas halides were more quenched by the heavier rare gases, such as Xe, even at near‐atmospheric pressures. At nearly atmospheric pressures the Ar‐buffered mixtures gave higher laser energy than Ne‐buffered mixtures except for the XeF laser. Through a series of measurements, the ArF laser showed the best result on the output energy of 96 J (5 J/l ) with an intrinsic efficiency of 3.4%.

ISSN:0021-8979    

DOI:10.1063/1.341766

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The temperature variation of the nonlinearity constant in silicon has been studied for longitudinal waves along the [110] axis and for shear waves along the [110] axis with polarizations along the [11¯0] and [001] axes in the range 73–273 K. The temperature dependence of the nonlinearity constant estimated from the second‐ and third‐order elastic constants has been further used to evaluate the acoustic attenuation in the Akhieser region at 475 MHz. The estimated values of acoustic attenuation have been compared with the measured values available in the literature and are found to be in good agreement. The nonlinearity constant showed a positive temperature coefficient for the longitudinal waves, whereas it showed a negative temperature coefficient for the shear waves. These results resemble those obtained for germanium and copper.

ISSN:0021-8979    

DOI:10.1063/1.341767

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Laser‐excited thermal‐wave image magnitude and phase were acquired by photoacoustic detection in the 10–1000‐Hz modulation frequency range on epoxy/aluminum interface systems with surface (black) and bulk (white) laser‐absorbing epoxy, different planar interface distances, surface and subsurface flaws, and different surface angle boundaries. The following conclusions were reached from the thermal‐wave results: (1) thermally thin epoxy on aluminum layer thicknesses can be estimated from variable modulation frequency data; (2) planar and subsurface defect interface structures of epoxy/aluminum systems are best studied by examining both magnitude and phase images; (3) thermal‐wave images are more straightforward to interpret for the systems that absorb light at the irradiated surface rather than in the bulk. These conclusions are consistent with thermal diffusion length and thermal‐wave reflection effects predicted by theory for surface light‐absorption conditions.

ISSN:0021-8979    

DOI:10.1063/1.341768

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

In a previous paper the authors initiated studies of fully developed laminar liquid‐metal flows, currents, and power losses in a rectangular channel with a moving perfectly conducting wall and with a skewed homogeneous external magnetic field for high Hartmann numbers, high interaction parameters, low magnetic Reynolds numbers, and different aspect ratios. The channel had insulating side walls that were skewed to the external magnetic field, while the perfectly conducting moving top wall with an external potential and the stationary perfectly conducting bottom wall at zero potential acted as electrodes. These electrodes were also skewed to the external magnetic field. A mathematical solution was obtained for high Hartmann numbers by dividing the flow into three core regions, two free shear layers, and six Hartmann layers along the channel walls. The free shear layers were treated rigorously and in detail with fundamental magnetohydrodynamic theory. The previous work, however, left the solution for the velocity profiles in terms of a complex integral equation which was not solved. In the present work the integral equation is solved numericallyby the method of quadratures to give the velocity profiles, viscous dissipation and Joulean losses in the free shear layers. In addition, expressions for the viscous dissipation in the six Hartmann layers are presented. The best approximation to the viscous dissipation in the channel is the sum of theO(M3/2) contributions from the two free shear layers, theO(M3/2) contributions from the two Hartmann layers separating the free shear layers from the insulators, and theO(M) contributions from three of the Hartmann layers separating core regions from the walls. The best approximation to the Joulean power losses in the channel is the sum of theO(M2) contribution from the central core region which carries anO(1) current between the electrodes and theO(M3/2) contributions from the free shear layers. The expressions for the viscous dissipation and Joulean losses in each region involve the products of universal constants, electrical potentials and geometric factors. The theoretical magnetohydrodynamic model presented here was developed to provide data to help in the design of liquid‐metal current collectors.

ISSN:0021-8979    

DOI:10.1063/1.341769

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

We have carried out an experiment to measure the heating of a dense carbon plasma,ne∼1018–1019cm−3, by a relativistic electron beam. Using spectroscopic methods, the temperature of the plasma was measured. By taking into consideration the heat loss mechanisms in the plasma, the amount of energy deposited into the plasma by the beam was determined. The results are consistent with theoretical predictions.

ISSN:0021-8979    

DOI:10.1063/1.341770

出版商:AIP    

年代:1988

数据来源: AIP