摘要:

High resolution calorimetric detection of single particles in magnetic fields up to 8 T at temperatures <0.1 K is reported. A careful study of heavily doped Si and Ge thermistors reveals an extremely large positive magnetoresistance in the variable range hopping conductivity regime. This phenomenon is used to optimize the impedance and the temperature sensitivity of a calorimetric detector. Initial experiments show an energy resolution full width at half maximum of 800 eV for 62.5 keV conversion electrons and an energy threshold of <400 eV. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361806

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We report the observation of optical switching in a CdTe etalon at room temperature using 11 ns pulses at 1.064 &mgr;m radiation. We have also observed optical limiting and pulse compression. The switching was attributed to the nonlinear change in the index of refraction induced by two‐photon absorption. The thermal effect was found to have a negligible contribution to the nonlinearity. The transmission of the etalon was studied as a function of its initial detuning and the input intensity. The switching times were found to be in the range of 1.5–3.7 ns. A theoretical model was developed in the plane‐wave approximation assuming both nonlinear absorption and refraction and was found to be in good agreement with the experimental results. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361807

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Optical injection effects and all‐optical set‐reset operations in two‐segment strained multiquantum‐well (MQW) distributed feedback (DFB) bistable lasers were experimentally investigated. The optical bistable characteristics under detuned optical injection, of strained MQW DFB bistable lasers, show the effect of the residual Fabry–Perot side modes of the DFB structures; optimizing the input wavelength and the input power is suggested for applications. The switching properties of dynamic optical set‐reset operations with pulsed optical injection were reported, which appear to be related to the optical bistable characteristics under cw optical injection; however, the switching transients are found to be essential to full understanding of these switching properties. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361808

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We derive formulas for the optical confinement factor &Ggr; from Maxwell’s equations for TE and TM modes in the slab waveguide. The numerical results show that the formulas yield correct mode gain for the modes propagating in the waveguide. We also compare the formulas with the standard definition of &Ggr; as the ratio of power flow in the active region to the total power flow. The results show that the standard definition will underestimate the difference of optical confinement factors between TE and TM modes, and will underestimate the difference of material gains necessary for polarization insensitive semiconductor laser amplifiers. It is important to use correct optical confinement factors for designing polarization insensitive semiconductor laser amplifiers. For vertical cavity surface‐emitting lasers, the numerical results show that &Ggr; can be defined as the proportion of the product of the refractive index and the squared electric field in the active region. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361809

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The transversal mode properties of vertical cavity surface emitting lasers (VCSELs) are studied by spectrally resolved scanning near‐field optical microscopy. In contrast to classical optical microscopy techniques, our method is able to simultaneously decompose lasing transversal modes by their wavelength with lateral superresolution. As the tip‐sample distance is controlled by the well‐established shear‐force detection, additional topographical information showing the surface structure of the laser is provided. Therefore, near‐field spectroscopy allows the detailed analysis of the spatial light distribution emitted by the laser with respect to the current injection contact, making it a promising tool for the characterization and optimization of VCSELs. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361810

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Absorption characteristics of metal powders for 10.6 &mgr;m CO2laser radiation were examined. Using a calorimetric method, absorptance measurements were performed on four different powder materials, including aluminum, copper, iron, and titanium aluminide. The experimental results showed that laser absorptance depends on powder porosity and material. The measured absorptance values at low laser intensities ranged between 28% and 43%. The titanium aluminide powders showed the highest absorptance values, and aluminum powders the lowest. As laser intensity was increased, the copper and iron powders showed strong signs of oxidation when irradiated in air, resulting in an increase in absorptance. Neither oxidation nor increased absorptance were observed when helium or argon were used as shielding gas. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361811

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The interaction of laser radiation from a Nd/glass laser with single crystals of cyclotrimethylene trinitramine (RDX) secondary explosive and RDX slices (cleaved from larger crystals of RDX) has been studied by high‐speed framing photography with microsecond interframe times. Decomposition and deflagration were recorded following ignition at localized regions or ‘‘hot spots.’’ ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361812

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The axial distributions of electrons, atomic and molecular ions as well as metastable atoms in an argon ultrahigh frequency (UHF) discharge at a moderate pressure sustained by a traveling electromagnetic wave have been theoretically obtained. The dependence between the absorbed wave power and the electron density necessary for plasma modeling has been numerically derived by taking into account both direct and step‐wise ionization processes. The inclusion of step‐wise ionization process leads to a lower electron temperature comparing to that calculated under the assumption that only the direct ionization takes place. The results have been compared with the experimental data for an UHF argon plasma at 1.8 Torr. A better agreement is achieved when the ionization by metastable–metastable collisions is taken into account together with the step‐wise ionization. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361802

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The spatial and temporal evolution of the components of a plasma surrounding a 90° convex and a 90° concave electrode whose potential is suddenly decreased in a three‐component plasma is numerically investigated. The quasineutral plasma consists of positive ions and various proportions of negative ions and electrons. The results are compared and contrasted with those that are obtained in a normal two‐component plasma. The transient or ion matrix sheath is identified and its subsequent evolution is investigated. Effects of perturbations in the electrode are investigated. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361803

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have performed a series of space‐independent, electron Boltzmann calculations for the determination of electron‐driven rate coefficients in helium/xenon glows for a variety of He/Xe mixture ratios. The present work was performed in support of research efforts involving plasma display panels. Our Boltzmann calculations do not involve any term‐expansions of the electron velocity distribution function (EVDF) and, in principle, incorporate the exact EVDF. Legendre decompositions of our complete EVDFs suggest that the more common two‐term approximation methods may be unreliable for the determination of certain rates in gas mixtures. More generally, this data can be used to provide the rate and transport coefficients necessary for fluid simulations involving He/Xe glows under a limited range of discharge conditions. For each mixture ratio considered, polynomial fits to the resulting, steady‐state rate coefficients, electron drift velocities and average energies, as functions of E/N are presented. As expected, the data is very sensitive to the mixture ratio of the two gas components. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361804

出版商:AIP    

年代:1996

数据来源: AIP