摘要:

Very high conversion efficiency (6.5 dB for 23.4 nm down-wavelength shift and 4.5 dB for 16 nm up-wavelength shift) is reported, using four-wave mixing in a bulk semiconductor optical amplifier. Based on a dual pump configuration where wavelength conversion is achieved by shifting one of the pumps, superior performance has been achieved in terms of both efficiency and the converted signal-to-background amplified spontaneous emission noise ratio, especially for very large wavelength shifts. Simple theoretical considerations are also discussed for the explanation of the improved performance of the converter. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121399

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Direct formation of surface relief gratings at modest intensities on azobenzene polymers has recently been accomplished. Unusual optical erasure of these surface relief gratings was observed. It is found that the optical erasure is dependent on the polarization state of the erasing beam as well as that of the recording beams used to form the gratings. Thus, gratings when formed memorize the polarization states which created them and influence their erasure behaviors accordingly. Direct transfer of patterns by photoprinting through a phase mask has been achieved. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121400

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Opposite signs of nonlinear refraction in chloroaluminum (ClAl) phthalocyanine (Pc) dissolved in methanol are observed using theZ-scan technique with two output modes of a frequency-doubled,Q-switched, mode-locked Nd:YAG laser operating at 10 Hz. Using the single picosecond (ps) pulses switched out of the pulse trains, positive nonlinear refraction is observed and attributed to population transitions among ClAlPc’s singlet states. Using the full nanosecond pulse trains, a sign change of nonlinear refraction relative to that of single ps-pulse excitation is observed, and is attributed to the heat-induced temperature rise and the population relaxing to ClAlPc’s triplet states. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121401

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The nonreciprocal wave number shift of a TE-like mode propagating along a normally magnetized gyrotropic rib waveguide supporting a domain lattice is predicted theoretically using perturbation theory. The electromagnetic fields are calculated by the effective index method and by a more rigorous numerical method. Preliminary estimations for Bi-substituted iron garnets show that the maximum nonreciprocal phase shift of a TE-like mode may be comparable to that of a TM-like mode in a tangentially magnetized waveguide. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121402

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

This letter presents a way to overcome ultrasonic focusing degradations through strongly diffracting nondissipative layers. A first set of experiments shows that, using finite aperture transducer arrays, neither the time-reversal technique, nor other focusing techniques are able to achieve proper focusing through this kind of aberrator. These experimental results show the limits of a finite aperture time-reversal mirror compared to the theoretical behavior of a time-reversal cavity. To simulate a time-reversal cavity, totally reflecting walls are set between the time-reversal mirror and the aberrator. The experiments and numerical simulations presented in this letter show that as soon as we introduce these reflecting boundaries, the time-reversal focusing becomes optimal and the spatial resolution is strongly improved. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121403

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A sonochemical procedure for the preparation of cadmium sulfide (CdS) nanoparticles coated on submicron spherical silica particles has been described. Ultrasonic irradiation of a slurry of silica microspheres, cadmium sulfate, and thiourea in an aqueous medium for 3 h under ambient air yields cadmium sulfide–silica (CSS) composite. Heating the initial amorphous CSS nanocomposite at 150 °C for 1 h under aN2atmosphere yields diffraction peaks assignable to the CdS phase. The transmission electron microscopy image of CSS shows that the CdS nanoparticles homogeneously coated on the silica(SiO2)carrier. The infrared spectroscopy illustrated the structural changes that occur when the amorphousSiO2is coated with CdS nanoparticles ultrasonically. The photoluminescence spectrum of the CdS and CSS shows a broadband with a maximum centered around 560 nm, which is similar to that of quantum CdS particles. The sharp onset of a CSS emission band compared to that of the CdS emission band in the red region indicates that theSiO2carrier provides a medium for controlling the aggregation of CdS nanoparticles. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120624

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Diamond nucleation on Si(100) surfaces can be promoted by a dc-glow discharge process, using aCH4/H2gas mixture. However, the phase composition and structure of the carbon film deposited during the dc-glow discharge pretreatment are still unclear. In the present work, we report on a combined study of near edge x-ray absorption fine structure (NEXAFS), and high resolution scanning electron microscopy (HR-SEM) of this film as a function of substrate temperature. NEXAFS measurements of the films deposited by the dc-glow discharge process render unambiguous evidence of diamond phase formation in the 880–900 °C substrate temperature range. It is determined from HR-SEM measurements that in this temperature range, nanosize diamond particles are formed. At lower and higher substrate temperatures the NEXAFS results indicate the predominant formation of graphitic carbon. The changes in the film composition as a function of substrate temperature during the dc-glow discharge process is expressed in terms of relative graphitic character (RGC) of the precursor film. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121404

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The density of states in the energy region near Fermi level for hydrogenated amorphous carbon thin films is presented. The different types of states are identified in their origin and the problem of their detection is considered. It is shown that only some of these states are accessible to detection by electron spin resonance. A quantitative correlation between their density and the quantum efficiency of the room temperature photoluminescence process is achieved. Such correlation applies to films having a wide range of physical properties deposited by different techniques. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121405

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Thin films of boron nitride were deposited by unbalanced magnetron sputtering at pressures between 0.065 and 1.32 Pa in order to study the effects of pressure and negative substrate bias on the energy of the bombarding plasma ions and subsequent stabilization of the cubic phase. It was found that the threshold bias voltage for nucleation of films with a high percentage of the cubic phase increases with the product of the pressure and sheath thickness. This trend is explained in terms of the changes in the average energy of the particles bombarding the growing film produced by pressure-dependent charge-exchange collisions in the plasma/substrate sheath. This energy modification process has predictable consequences in complex deposition processes. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121407

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A torsional actuator generating angular displacement from piezoelectric shear strain was developed. The actuator is a tube consisting of an even number of segments poled along the length, which are adhesively bonded together, and the joints act as electrodes to apply the driving voltage. The experimental data measured on the prototype actuator: (i) prove the proposed concept of the torsional actuator, (ii) show that the actuator functions well under the torque load, and (iii) demonstrate that it has superior characteristics compared to previously reported designs of torsional actuators. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121408

出版商:AIP    

年代:1998

数据来源: AIP