摘要:

The successful application of the stochastic optimization method known as simulated annealing can depend very much on the appropriate annealing schedule. While determining optimal schedules for arbitrary complex optimization problems is beyond the current scope, we here determine optimal schedules for a special class of systems with known properties. The state spaces of these special systems have the structure of self similar trees. Using methods of optimal control theory, we are able to predict the optimal schedule analytically for two distinct optimization criteria. These predictions are shown to be in good agreement with numerical results. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359253

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We calculate the intensity of far‐infrared absorption of a single electron and two electrons in a square‐well quantum dot under an external electric field. The intensity is effectively modulated by an applied electric field in different ways, according to the number of electrons in the quantum dot. The difference is due to the effect of Coulomb interaction between electrons. The Stark effect on optical transition of interacting electrons confined in a quantum dot is discussed. When a quantum dot is selected out of an array of quantum dots by a local electric field, we can detect the number of electrons in it using electric‐field‐induced far‐infrared absorption spectroscopy. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359254

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Near‐field scanning optical microscopy is used to determine the field structure within a noncircularly symmetric optical fiber. The output from an elliptical core fiber is measured and found to be in good agreement with the field predicted using a point matching method and fiber parameters determined from the preform. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359255

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Third‐order nonlinear optical properties of As2S3‐based glass fibers are studied at a wavelength of around 1.55 &mgr;m. Through time‐resolved pump‐probe measurements and analysis of spectrum broadening due to self phase modulation, it is confirmed that As2S3‐based glass fibers are capable of instantaneous nonlinear refractive response to a subpicosecond pulse. Stimulated Raman scattering (SRS) with a Stokes shift &Dgr;k=344 cm−1is observed using a picosecond pump pulse. The Raman gain coefficient was estimated to be 4.4×10−12(m/W), which is two orders of magnitude higher than that for silica fiber. The relaxation time of the Raman contribution to nonlinear refraction is estimated to be 97 fs and the influence of the SRS on subpicosecond pulse propagation is observed as a low‐frequency Raman gain. The two‐photon absorption (TPA) coefficient is estimated to be &agr;2=6.2×10−15(m/W) through a transmission change measurement. The TPA figure of merit for As2S3glass at a wavelength of 1.55 &mgr;m is estimated to be low enough for all‐optical switching applications. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359256

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Aninsitustudy of the effects of ionizing radiation on the strength of the Raman and photoluminescence signal of high OH, low OH, and fluoride core fibers has been performed with 514.5 nm laser excitation. The fibers were irradiated with a60Co source at a constant dose rate of 560 rads/h. The high OH fiber displayed a much slower decay of the fiber Raman intensity than the other two fibers during irradiation. The fluoride fiber exhibited the quickest decline in Raman signal with the intensity dropping by a factor of 1000 in less than 20 min. The Raman intensity of the low OH silica fiber recovered to greater than 90% of its pre‐irradiation value after a post‐irradiation photoanneal with 488 nm laser light. The silica fibers displayed an increase in intensity of a broad photoluminescence feature centered at 650 nm. However the fiber photoluminescence intensity remained much weaker than the Raman intensity throughout the irradiations. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359596

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Guided acoustic waves propagating in transparent and isotropic solids are studied by optical interferometry via the photoelastic effect. Unlike the photoelastic technique, the interferometric method permits the measurement of the phase shift rather than the polarization change of the light passing through an acoustic field. By analyzing the acoustically induced change in the index ellipsoid of refraction, it is demonstrated that the optical phase shift is proportional to thedilatationor the relative change in volume of the material. The dilatation fields of the symmetric and antisymmetric Lamb modesS0andA0, as well as that of the Rayleigh wave, were calculated. Experiments performed in fused quartz by the interferometric method are in good agreement with theoretical predictions. Compared to the conventional photoelastic technique, the interferometric measurement of acoustic wave is phase sensitive and quantitative. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359592

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Two‐dimensional, relative measurements of the argon 1s5metastable density distribution were obtained in a low‐pressure, 13.56 MHz, parallel‐plate, Gaseous Electronics Conference reference cell discharge using planar laser‐induced fluorescence imaging. For the conditions examined (pure argon, 75–300 V, 13.3–133.3 Pa), the measured density fields show significant radial and axial variations that depend more strongly on pressure than applied voltage. Generally speaking, the metastable density increases radially from the center to the edge of the discharge by ∼10%–30%. As the pressure is increased, the peak metastable density increases by ∼4 times and the axial distribution changes from a center‐peaked parabolic‐like profile to an asymmetric profile peaked near the powered electrode. Comparisons of centerline metastable and excited‐state emission profiles indicate that, while the metastable distribution is largely determined by the spatially dependent electron‐impact excitation function, variations in quenching can significantly affect the resulting metastable density profile at some conditions. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359193

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The properties of a proton source developed for use in a pulsed high power magnetically insulated ion diode have been determined. The source is created from a sliding gas discharge on the surface of a thin double layer of TiH and Pd deposited on an insulating substrate. By driving a short (<20 ns) high current pulse through the metal films hydrogen is released from the Ti store and a multichannel electrical breakdown is created in the desorbed gas layer. The uniformity of this breakdown depends on the capacitance per area of the multilayer setup. It has been found that the breakdown always occurs after the same areal gas density has been released. The density as well as the temperature of the plasma depend on a continuous influx of hydrogen from the reservoir and on the expansion. The electron temperature decreased from up to 12 early in the pulse to less than 3 eV late in the pulse. Over a distance of 1 mm the plasma density falls from 1017at the surface to 1015cm−3. The plasma expansion is stopped by a strong magnetic field parallel to the surface; however, the neutral hydrogen density increased with increasing magnetic field. Carbon ions are the most important contaminant of the hydrogen plasma. However, their fraction is smaller than 10%. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359194

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

GaP1−xNxalloys (x=0.02–0.07 andx&bartil;0.99) have been formed by ion implantation of Ga+and N+into GaP. X‐ray diffraction measurements proved that both a wurtzite structure and a zincblende structure of the crystals have been formed within the implanted layers. They are similar to but not the same as GaN and GaP, respectively. An emission band at an energy higher than the energy gap of GaP appeared on the photoluminescence (PL) spectra of the implanted layers and consists of several components. Formation of the alloy and origins of the PL components are discussed. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359195

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The early stages of thin film formation are studied on atomic scale by scanning tunneling microscopy imaging. Gold is sputter deposited on a graphite substrate using Cs+ion bombardment of a gold target at a few keV energy. Stable gold nuclei are formed at defect sites which are produced by the impact of gold atoms with energy larger than 180 eV. This energy is needed to displace a carbon atom from the lattice in a binary collision. Three‐dimensional clusters grow by attachment of additional gold atoms to the nuclei. The fraction of gold atoms with energy larger than 180 eV depends on Cs+ion energy and typically is less than one percent of the incident gold flux. After 1 s of deposition, the average size of the clusters is 10 atoms. Cluster density is 1012clusters per cm2, and a few percent of the incident flux is condensed in the clusters. These phenomena are a consequence of the weak interaction strength between gold and graphite. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359196

出版商:AIP    

年代:1995

数据来源: AIP