摘要:

This paper presents a new calibration of the pressure shift of the7D0−5F0fluorescence line ofSrB4O7:Sm2+, in hydrostatic medium (helium) up to 124 GPa and in nonhydrostatic medium (H2O) up to 130 GPa. There is no quenching of the luminescence, in contrast to that observed in similar compounds. We show that this line permits more accurate pressure measurements at very high pressure than the commonly usedR1emission line of ruby because it remains intense, sharp, well isolated from the other lines, and weakly dependent on nonhydrostaticity. The wavelength pressure shift of the7D0−5F0line is found to be very well represented by the nonlinear relation:P=4.032&Dgr;&lgr;(1+9.29×10−3&Dgr;&lgr;)/(1+2.32×10−2&Dgr;&lgr;)withPin GPa and&Dgr;&lgr;=&lgr;−685.41in nm. High temperature experiments up to 900 K at room pressure were also performed. The negligible temperature dependence and the small thermal line broadening are further advantages for high pressure–high temperature studies in diamond anvil cells. A metrology forin situmeasurements of pressure and temperature, based on the combined use of this compound with ruby is also presented, along with a new calibration of the rubyR1frequency shift with temperature from 300 to 800 K. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365025

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Motivated by the possibility of using condensed gas moderators to produce very slow (epithermal) polarized muons we have studied the moderator properties of rare gas solids and solid N2thin films as a function of the growing parameters (deposition temperature and rate, heat treatment) and of the film thickness. For Ar and Kr moderators the moderation efficiency is found to depend on the growth temperature and an annealing effect is observed. The dependence can be interpreted in terms of the changes in granularity and porosity of the condensed gas layers when the growth parameters are varied. From the thickness dependence of the moderation efficiency the escape depth of the very slow muons was determined. Its large value indicates a suppression of electronic energy loss mechanisms for the epithermal muons. The time dependent decay properties of the moderators were also investigated and found to depend solely on the rest gas pressure. At a pressure of10−10mbar the moderation efficiency remains stable over a period of days. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365027

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The steady-state and transient behavior of the photoconducting electro-optic polymer, PVK:TNF:DR1:ECz, was analyzed with various writing and reading beam polarization configurations to elucidate the contribution of various effects including the photoisomerization process on the diffraction phenomenon at the wavelength of 632.8 nm. The effect of the applied field on the diffraction efficiencies was observed to be strongly dependent on the polarization states of the writing and reading beams. It was found that the electro-optic contribution dominated the diffraction phenomenon for thep-polarized writing and reading beams while the molecular reorientation effect dominated for thes-polarized writing and reading beams and when the writing beams are cross polarized. The diffraction grating formed via the photoisomerization process was confirmed to be refractive index grating instead of an absorption grating. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365028

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Transmission loss characteristics of a fluorophosphate fiber was investigated in 200–800 nm wavelength region. The transmission loss was found to be primarily dominated by extrinsic absorption due to transition metal impurities. The total scattering is the next most important loss factor which is in fact Rayleigh in character exhibiting a&lgr;−4dependence, and the ultraviolet absorption tail is the least significant loss factor. Radiation resistance characteristics of the bulk glasses corresponding to the core and cladding have also been investigated. Upon exposure to ultraviolet radiation from a 1 kW Hg-Xe lamp, the radiation-induced defect centers leading to additional absorption bands in the ultraviolet region result mainly from the photoionization processes ofFe2++h&ngr;=Fe3++e−and2Cl−+h&ngr;=Cl2−+e−for theCl−doped glasses, and the former one is also responsible for the glasses without doping ofCl−. The electron capture centers in the glasses are the[PO4]and/or[P2O7]groups. If the irradiation is carried out with a KrF excimer laser having high-energy density, the formation of radiation-induced defect centers is due not only to the photoionizable multivalent ions, but also to the photoionization of phosphate groups in the glasses. The latter process gives the purple color to the irradiated glasses. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365029

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The primary coating in real optical fiber applications is a soft polymer with a low Young’s modulus that is used as a strain buffer to minimize microbending loss. The secondary coating and jacket are hard polymers with higher Young’s moduli and sufficient thicknesses to sustain the mechanical force. The buckling of optical fibers causes additional transmission loss, thereby necessitating that it be minimized. The optical fiber’s spring constant is a critical factor in the buckling phenomenon. Moreover, a higher value of the spring constant corresponds to a higher resistance to buckling. A closed form solution of the spring constant in the buckling of tightly jacketed double-coated optical fibers is presented. The effects of polymeric coatings on the spring constant are also considered. To obtain a higher value of the spring constant and adhere to optical fiber applications, the thickness of the primary coating was decreased, and the Poisson’s ratio of the primary coating and the Young’s moduli and Poisson’s ratios of the secondary coating and jacket were increased. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365030

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We investigate herein the propagation and tunneling of monochromatic light through a tapered fiber tip, modeled as a tapered perfectly conducting waveguide. The opening aperture of the waveguide is much smaller than the wavelength of light. The transmission rate through the tip as well as the profiles of electric fields are obtained. A detailed formulation for calculating the fluorescent spectra of a single molecule under near-field excitation is also presented. In addition, the limitations of fluorescence measurement for obtaining near-field pattern is discussed on the basis of the present formulation. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365031

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The desire to fabricate very small semiconductor lasers requires that we address problems associated with surface recombination. We have proposed and demonstrated a segmented quantum well active region in which lateral diffusion is intentionally reduced. Such a structure should prevent the transfer of electrons and holes from the interior of a laser device to the edges. The supply of carriers to surface-related carrier traps can thus be eliminated, and we need not concern ourselves with the electrical quality of the surfaces. In this work we present calculations which predict laser performance for various lateral diffusion conditions. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365032

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Using a comprehensive numerical model, we analyze the first long-wavelength (1.55&mgr;m) vertical-cavity surface-emitting lasers operating continuous-wave at room temperature (up to 33 °C). These double-fused lasers employ strain-compensated InGaAsP multi-quantum wells sandwiched between GaAs/AlGaAs distributed Bragg reflectors that are fused on both sides of the InP spacer. The two-dimensional model includes drift and diffusion of electrons and holes, finite-element thermal analysis, calculation of the internal optical field at threshold, andk⋅pband structure computations. The simulation shows excellent agreement with a large variety of experimental characteristics. Internal laser parameters like optical losses and injection efficiency are obtained. The thermal conductivity of the multilayer mirror is found to be only one third of the value expected. Temperature dependent absorption and Auger recombination within the active region as well as lateral leakage currents are identified as dominating loss mechanisms. The analysis shows great potential for high-temperature operation of double-fused vertical-cavity lasers. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365033

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A method for the calculation of optical modes in disk-like resonant cavities is presented. The eigenvalue equation for resonant wavelengths and threshold optical gain as well as the optical field distribution is established. The characteristics of the optical modes in microdisk lasers are studied using this method. Numerical calculations are carried out for some long wavelength microdisk lasers. The theoretical analyses and numerical results show that the optical modes in a microdisk laser with a very small thickness can be approximately classified into transverse electric and transverse magnetic modes, but the lasing modes and other lower threshold modes are transverse electric polarized, and a spontaneous emission coefficient between 0.2 and 0.3 can be achieved in long wavelength semiconductor microdisk lasers. The possibility of a microdisk laser to lase in a surface emitting mode is also demonstrated. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365034

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

For more than ten years [J. Bisognano, I. Haber, L. Smith, IEEE Trans. Nucl. Sci.NS-30, 2501 (1983)], the longitudinal wall impedance instability was thought to be a serious threat to the success of heavy-ion driven inertial confinement fusion. This instability is a “resistive wall” instability, driven by the impedance of the induction modules used to accelerate the beam. Early estimates of the instability growth rate predicted tens ofe-folds due to the instability which would modulate the current and increase the longitudinal momentum spread and prevent focusing the ion beam on the small spot needed at the target. We have simulated this instability using anr−zparticle-in-cell code which includes a model for the module impedance. These simulations, using driver parameters, show that growth due to the instability is smaller than in previous calculations. We have seen that growth is mainly limited to one head to tail transit by a space-charge wave. In addition, the capacitive component of the module impedance, which was neglected in the early work of Lee [E. P. Lee, Proc. Linear Accelerator Conference, (UCRL-86452), Santa Fe, NM, 1981] significantly reduces the growth rate. We have also included in the simulation intermittently applied axial confining fields which are thought to be the major source of perturbations to seed the longitudinal instability. Simulations show the beam can adjust to a systematic error in the longitudinal confining fields while a random error excites the most unstable wavelength of the instability. These simulations show that the longitudinal instability must be taken into account in a driver design, but it is not the major factor it was once thought to be. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365035

出版商:AIP    

年代:1997

数据来源: AIP