摘要:

A study of an electro‐optic response in a free‐standing ferroelectric liquid crystal film has been carried out. The response time becomes shorter with increasing electric field and, especially at a certain threshold of electric field, it changes in stepwise by three orders of magnitude. The response time of the faster kind of response that appears in the higher field region is several hundred milliseconds and is about one thousand times faster than the slower kind of response at lower fields. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117985

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Nanocrystalline Ge particles embedded in a SiO2layer, directly formed by an excision process from a SiGe strained layer during low temperature ultraviolet‐assisted oxidation are shown to exhibit visible photoluminescence. The emission maxima of the photoluminescence spectra are situated at around 2.18 eV, a value that corresponds, according to recent data to an average particle size of 5 nm, in excellent agreement with our previous Raman and transmission electron microscopy measurements of particle size. It is proposed that stress effects associated with the oxidation of small spherical particles allow the formed nanocrystalline Ge to survive during prolonged ultraviolet oxidation of the SiGe layer. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117986

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have found that the application of light to strontium barium niobate (SBN) during electrical repoling stabilizes the newly formed domains. This stabilization becomes apparent when repoling the crystal back into its original domain direction as a change in the distribution of displacement current as a function of voltage. This appears to be the process underlying the other recent work in the area of optical control of domain structures for quasi‐phase‐matching of nonlinear processes. We present an explanation for this effect in terms of the microdomain structure of SBN. This model should aid in the search for new materials for optical periodic poling. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117987

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We report on the evolution of the excitonic optical features from two dimensions (2D) to one dimension (1D) in GaAs/AlAs fractional‐layer‐superlattice (FLS) wire structures. We demonstrate for the first time how the excitonic optical properties continuously evolve from 2D to 1D by introducing the FLS lateral compositional modulation in an AlGaAs quantum well. We also present a theory numerically analyzing the optical absorption properties in the FLS wires. Present theory accurately reproduces the experimental results using the AlAs/GaAs FLS wires and clarifies the main optical features associated with excitons in the intermediate quantum‐confinement regime between 1D and 2D. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117988

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Frequency‐stable, narrow linewidth oscillation of a 638 nm AlGaInP diode laser has been achieved with an external photorefractive BaTiO3phase conjugator in a novel configuration. The mechanism of the phase conjugation in this configuration is the stimulated photorefractive backscattering process with the measured phase‐conjugate reflectivity of <1.8×10−3%. With this new phase‐conjugate feedback method, the laser linewidth was reduced to ∼0.1 nm (within the resolution limit of the spectrum analyzer used) and the oscillation frequency was highly stabilized, while it was impossible with a conventional cat conjugator. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117989

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We demonstrate lasing action in a novel microcavity laser device based on vertical cavity surface‐emitting laser technology. This laser can be used for intracavity spectroscopy, high contrast imaging of small (10 &mgr;m) structures, and is well suited for use in micro‐optical mechanical systems for analysis of particles or fluids. Here, we investigate spectra of intracavity polystyrene spheres. Lasing threshold, single‐mode operation, and multimode operation are all studied. Transverse mode separation in the multimode regime is found to be effective for sizing of the spheres.

ISSN:0003-6951    

DOI:10.1063/1.117990

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

An electro‐optic polymer intensity modulator designed in the heavily multimode region but operating as a quasi‐single mode waveguide has been demonstrated. The device relaxes much of the trade‐off relationship between the modulation voltage and coupling efficiency without the sacrifice of the modulation extinction ratio. The device poled at 1.5 MV/cm shows half‐wave voltage–length product of 7.2 V cm, modulation extinction ratio better than 20 dB, and mode diameters of about 4 and 9 &mgr;m in vertical and lateral directions, respectively. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117991

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Time‐resolved luminescence data from heavily nitrogen doped ZnSe (total N concentration exceeding mid‐1018/cm3) is presented. The luminescence exhibited a decay time and a rise time which increased with decreasing energy of observation. Furthermore, both the decay times and rise times decreased with increasing temperature. These observations are consistent with the following model: (i) a band of states is created due to fluctuations in the ionized impurity concentrations; (ii) a portion of the carriers captured by the shallower impurity states are transferred to deeper states prior to recombination. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117992

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A method for optimized generation and detection of thermoelastic stress waves for the measurement of tissue optical properties and structure is investigated. The stress waves are formed by short pulsed irradiation of an absorbing dye solution with aQ‐switched Nd:YAG laser at 532 nm. An optical transducer based on pressure‐induced reflectivity changes of a continuous laser beam at a glass‐water interface detects the stress wave in front of the irradiated sample surface. It is shown theoretically and experimentally that this kind of detector, where the active area is a small spot close to the irradiated surface, minimizes signal distortion due to acoustic diffraction. Comparisons of absorption coefficients measured acoustically and from optical transmission show a good agreement between the two methods. The high sensitivity of the detector (1.5 mV/bar) makes it possible to keep the temperature and pressure rise in the investigated target low, which enablesinvivoapplications of the optical transducer. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117993

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Monolithic polycapillary focusing optics can collect a large solid angle of x rays from a point source and form intense focused beams for microbeam x‐ray fluorescence (MXRF) analysis. Such an optic was tested and characterized in a MXRF setup. For the Cu K&agr;line, the measured focal spot size of the optic was 43 &mgr;m full width at half‐maximum (FWHM). With the 16 W microfocusing x‐ray source (50 &mgr;m×10 &mgr;m), the average Cu K&agr;intensities over the focal spot was measured to be 8.9×104photons/s/&mgr;m2. When compared to a straight single channel capillary optic with approximately the same output beam size, an intensity gain of 44 was obtained. The optic was applied to the MXRF setup to analyze trace elements in various samples and a minimum detection limit (MDL) of about 2 pg was achieved for the transition elements (V, Cr, Mn, and Fe). The optic was also used to map the distributions of trace elements in various samples. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117994

出版商:AIP    

年代:1996

数据来源: AIP