摘要:

We describe a new noncontacting method for measuring the temperature of electrically conducting objects by sensing the magnetic field noise. When a high‐Qantenna is placed close to a conductive material, e.g., a hot metal plate, the effective noise temperature of the antenna becomes proportional to the temperature of the material. Contrary to the conventional noise thermometer in which a resistor is embedded in the material, the method requires neither galvanic nor thermal contact. If the antenna impedance at different frequencies is known, the temperature of the object can be calculated from the total voltage noise of the antenna. We show, however, that for high‐Qantennae the knowledge of the impedance at resonance is adequate to determine the unknown temperature. Consequently, the temperature of moving objects can be measured via synchronous monitoring of the total noise of the antenna and its impedance at resonance. Since only electrically conductive objects create magnetic field noise, the method is immune to nonconductive contamination of the surface.    

ISSN:0021-8979    

DOI:10.1063/1.354865

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

This article presents a simple, yet general and exact analytic‐numerical method of solving one‐dimensional quantum mechanics problems. It is based on the concept of dividing an arbitrary potential into convenient segments and analyzing the multiple reflection of a plane matter wave between neighboring potential walls. Amplitude reflection and transmission coefficients of each segment are the basis for the analysis. A simple iterative technique for calculating them by a square barrier approximation is given. This method is applicable to various potential barriers, wells, and periodic structures including continuous variations of potential energy and particle effective mass.

ISSN:0021-8979    

DOI:10.1063/1.355329

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The low‐temperature four‐wave mixing (FWM) photorefractive response was investigated in undoped Bi12GeO20(BGO) crystals. The FWM diffraction efficiency increases as the temperature is lowered until a local maximum is reached after which it decreases. The temperature where the maximum intensity FWM signal occurs depends on the write conditions. A model assuming both electron and hole gratings was used to describe the observations. Two shallow trap levels of 0.015 and 0.08 eV were identified as being responsible for the fast decay (<1 s) components of the FWM signal in undoped BGO.

ISSN:0021-8979    

DOI:10.1063/1.354866

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A comprehensive investigation on the spectroscopic properties and laser performance of Nd3+doped GdLiF4(GLF), a new laser crystal, is reported. Our high resolution absorption and emission spectra for GLF are nearly identical to those of Nd:LiYF4(YLF), a well known laser crystal, strongly suggesting that the two crystals are isostructural. The laser performance of Nd:GLF is very similar to that of Nd:YLF. A maximum laser‐pump‐laser slope efficiency of 68% and 67% was obtained for low (1.0 at. %) and high (4.0 at. %) Nd concentration GLF respectively. Concentration quenching of the fluorescence decay time was observed and appears to be due to the dipole‐dipole interaction between the isolated Nd3+ions and Nd3+ion pairs.  

ISSN:0021-8979    

DOI:10.1063/1.354867

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Data are presented on the 300 K (and 77 K) continuous photopumped laser operation of AlyGa1−yAs‐GaAs‐InxGa1−xAs quantum‐well heterostructures (QWHs) that have been oxidized (H2O vapor+N2, 425 °C) selectively along the high‐band‐gap heterolayers located on either side of a GaAs waveguide (WG) region with an InxGa1−xAs QW in its center. Transmission electron microscope images show that the oxide‐embedded GaAs‐InxGa1−xAs WG+QW active region remains unoxidized and thus is sandwiched between electrically insulating AlyGa1−yAs native oxide layers. The thresholds for photopumped 300 K continuous laser operation of the as‐grown and oxide‐embedded QWHs are approximately equal after differences in the Ar+‐laser photopumping efficiencies are considered.

ISSN:0021-8979    

DOI:10.1063/1.354868

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Intractable low‐mode nonuniformities caused by power imbalance or pointing error of beams are studied quasi‐analytically based on Skupsky’s axially symmetric model [S. Skupsky and K. Lee, J. Appl. Phys.54, 3662 (1983)]. These nonuniformities can be improved by decreasing the imperfections &sgr;P&OHgr;, or by increasing the number of laser beamsNB: deteriorated irradiation uniformity is shown to be proportional to &sgr;P&OHgr;/&sqrt;NB. Criteria of these imperfections for high irradiation uniformity [≤1% root‐mean square (rms)] are then presented in terms ofNB. The model is further extended to treat general asymmetric beam patterns. Optimization of beam pattern is also a central issue.

ISSN:0021-8979    

DOI:10.1063/1.354869

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

In high‐power AlGaAs window structure lasers with a window grown on facets (WGF) structure, dependence of window effects on Al content of the window layer is examined. When the Al content of the window layer is more than that of the cladding layer, the window effects are found. But, in other cases, the window effects do not occur. A calculation of a carrier leakage from the active layer to the window layer is performed. From the result, we deduce that the reduction of the window effects is caused by the carrier leakage. In the WGF laser with the confirmed window effects, a maximum output power of 350 mW is achieved and highly reliable operation under 100 mW at 50 °C beyond 10000 h is attained.

ISSN:0021-8979    

DOI:10.1063/1.354870

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A model to describe fanning effects in photorefractive crystals is presented. The intensity distribution of the fanning beam for one incident beam and two incident beams in 45°‐cut BaTiO3crystals has been studied theoretically and experimentally, with good agreement. The theoretical results suggest that, when there is a fanning effect, only at intermediate effective interaction lengths does the signal beam have a high gain in two‐wave mixing. The transient behavior of the fanning beam in a 45°‐cut BaTiO3crystal has also been studied theoretically and experimentally.  

ISSN:0021-8979    

DOI:10.1063/1.354871

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

GaInP/AlInP quasi‐quaternary (QQ) compounds grown by gas‐source molecular‐beam epitaxy were systematically investigated. Quasi‐quaternary properties were obtained with GaInP/AlInP short‐period superlattices when the thickness of the AlInP layers was less than 3 ML. Equivalent band‐gap values of QQ compounds were defined in terms of the layer thickness ratios of the GaInP and AlInP layers. Using GaInP/AlInP quasi‐quaternary compounds, 607–640‐nm wavelength QQ lasers with 20‐nm QQ active layers were fabricated. Threshold current densities as low as 1.5 kA/cm2were attained for QQ lasers emitting at 635 nm without the presence of strain or quantum‐well effects.

ISSN:0021-8979    

DOI:10.1063/1.354872

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

In this paper a model of charged particle behavior in a low‐pressure oxygen plasma is developed, and compared with experimental results. Agreement is excellent. It is demonstrated that the extremely high temperature (≳1 eV) of electrons in these plasmas results in diffusion totally dominating the transport of charged species. It is also shown that charged particle recombination on the walls of a quartz reactor is insignificant. Finally, the influence of the electron temperature profile must be fully considered for accurate results. This work complements an earlier model of radical behavior in these plasmas. Both are needed to fully understand materials modification in these plasmas, which has been shown to involve a synergism between radicals and charged species.

ISSN:0021-8979    

DOI:10.1063/1.354873

出版商:AIP    

年代:1993

数据来源: AIP