摘要:

Barrier penetration is attributed to energy fluctuations expected from the uncertainty principle. Numerical simulations are made by calculating the traversal time and action for a large number of possible velocity profiles. Distributions of traversal time are determined by assuming that the probability of each velocity profile decreases exponentially with the action of the fluctuation it requires. Distributions of traversal times are reported for rectangular barriers having different sizes. For large barriers the distributions are leptokurtic and centered at the semiclassical traversal timeT0=d&sqrt;m/[2(V0−E)], wheredandV0are the length and height of the barrier andmandEare the mass and energy of the particle. The kurtosis decreases and the mode shifts to shorter durations with decreasing barrier size.

ISSN:0021-8979    

DOI:10.1063/1.354844

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Nuclear‐magnetic‐resonance spin‐lattice relaxation measurements were conducted in a Bentheimer sandstone sample for drainage experiments involving gas‐liquid fluid phases with ten different saturation levels ranging from complete water saturation (Sw=1) down toSw=0.14. A monotonic decrease in relaxation times was observed as the water saturation was lowered over this broad saturation range. This phenomenon is explained by considering that for a drainage process the liquid (wetting) phase was drained from different‐sized pores at different saturations with larger pores being drained first. The relaxation decay curves corresponding to each saturation state were analyzed using both stretched exponential and discrete multiexponential functions. In particular, the effect due to bulk fluid relaxation was eliminated so that a more appropriate relationship between pore size distribution and the relaxation rate is obtained. From these analyses, the relative variation of pore size distributions corresponding to different saturation levels was obtained. A power‐law dependence of saturation with relaxation times is observed which indicates that the relaxation analysis can be used to characterize fluid saturations.

ISSN:0021-8979    

DOI:10.1063/1.354845

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Intense ultraviolet emission bands around 340 nm were measured in microwave (MW) and rf glow discharges of GeF4. The bands are due to excited GeF2and identical with the 340 nm bands in the rf discharges of GeH4‐CF4‐H2mixtures which were published earlier. The emitting species drastically changed from GeF in matched MW discharges to GeF2in rf discharges by way of an intermediate case in mismatched MW discharges. Selective excitation of GeF in MW plasma and GeF2in rf plasma is discussed on the basis of a difference in electron energy between both plasmas and the energy is estimated in each case.

ISSN:0021-8979    

DOI:10.1063/1.354846

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A method is described by which the optical properties of asymmetric Einzel lenses may be measured. This method uses the technique of grid shadows. For the measurement of cardinal elements as well as spherical aberration coefficients, two independent measurements are required. For chromatic aberration coefficients, measurements are required as a function of lens voltage ratio. No extra lens is required for the measurements. An experiment is described in which the optical properties of an asymmetric lens are measured. Within the errors of the measurement, the technique is demonstrated to produce good agreement with theoretical calculations.

ISSN:0021-8979    

DOI:10.1063/1.354847

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The nonlinear phenomenon of polarization rotation in Ti:LiNbO3optical channel waveguides was investigated using Raman microprobe microscopy. Polarization sensitive Raman selection rules permitted the identification of polarization rotation of the propagating transverse electric or transverse magnetic waveguide mode. From an analysis of the Raman scattered light collected orthogonal to the waveguide surface the threshold power necessary to initiate the process of mode conversion could be determined. In addition, the Raman microprobe was used to determine waveguide loss coefficients by collecting inelastically scattered light. The values obtained by this method were compared to those measured by collecting the elastically scattered light. A value for the asymmetric component, &bgr;15, of the photovoltaic tensor was calculated to be 7.8×10−13A/W for theX‐cut,Y‐propagating and 3.8×10−14A/W and 1.2×10−14A/W for the rapid thermally annealedZ‐cut,Y‐propagating channel waveguides, respectively.

ISSN:0021-8979    

DOI:10.1063/1.354848

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A unique property of the free‐electron laser (FEL) is its capability to be tuned continuously over a wide spectral range. This is a major difference with all other high‐power lasers. However, the tunability of first‐generation FELs used to be quite poor (typically 10% or less), due to constraints imposed by the accelerator and the undulator. The free electron laser for infrared experiments (FELIX) uses an undulator with an adjustable gap, which permits wavelength scans over an octave in typically 2 min without the need for any readjustment of the electron beam. Results obtained in operation of the long‐wavelength FEL of the FELIX facility are presented. These involve measurements of the spectral range covered (16–110 &mgr;m), the output power, and the influence of the cavity desynchronism. The results are compared with numerical simulations.

ISSN:0021-8979    

DOI:10.1063/1.354849

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Various types of InP-based semiconductor lasers, Fabry–Perot (FP), and distributed feedback (DFB), in different wavelength regions of 1.3, 1.48, and 1.55 &mgr;m have been subjected to human-body-model electrostatic discharge (ESD) testing. The reverseV-Icharacteristics of these diode lasers were found to be generally most sensitive in detecting ESD damage than the forward characteristics (e.g., threshold current) of the laser. The laser ESD failure voltages were much lower for the reverse than the forward polarity and DFB lasers were found to be more vulnerable to ESD than FP lasers. The failure mechanism was found to be due to localized melting—a thermal effect—in both polarities of ESD testing. We also report the study of the latent ESD effects on the long-term aging rates of semiconductor lasers.  

ISSN:0021-8979    

DOI:10.1063/1.354850

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A new type of Si guided‐wave electro‐optic modulator is proposed and analyzed. The modulator makes use of the impact‐ionization mechanism for carrier generation, and the carrier‐dispersion effect for electro‐optic conversion. Both electrical and wave propagation properties of the modulator were examined by a two‐dimensional device simulator and a three‐dimensional waveguide simulator, respectively. Numerical estimates of phase modulation due to refractive‐index change and intensity modulation due to optical absorption and radiation loss were obtained. One of important features of the prospected modulator is speed. The simulated turn‐on and turn‐off time of the modulator was less than 1 ns. GHz modulation is, therefore, possible for this class of modulators with device structure and doping profiles optimized for fiber coupling.

ISSN:0021-8979    

DOI:10.1063/1.354851

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Loss characteristics of potassium and silver double‐ion‐exchanged glass waveguides are studied. Low propagation losses (less than 0.25 dB/cm) at 1.296 &mgr;m wavelength are measured, although aluminum as a mask and inexpensive multipurpose glass as a substrate are used in the fabrication process. The losses are compared to the losses of waveguides made by one‐step aluminum masked silver ion exchange and by silver ion exchange with ionic masking (dielectric mask). The reasons for the loss reduction in double‐ion‐exchanged waveguides compared to one‐step silver ion‐exchanged waveguides are discussed.

ISSN:0021-8979    

DOI:10.1063/1.354852

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The explosion or rapid vaporization of a liquid film on an opaque surface by a pulsed laser is studied experimentally. Using a probe‐beam deflection sensing (PDS) scheme, together with a previously developed transmission monitor, the distortion of the PDS signal due to the generation of shock waves by the exploding liquid is investigated. Various liquids, including alcohols and pure water in contact with substrates such as polyimide, amorphous carbon, and silicon, are studied for a wide range of excimer laser fluences. It is concluded that the present PDS technique is highly sensitive to the explosion threshold.

ISSN:0021-8979    

DOI:10.1063/1.354853

出版商:AIP    

年代:1993

数据来源: AIP