摘要:

The optical limiting performances of seven asymmetric pentaazadentate porphyrin-like cadmium complexes have been measured at 532 nm with nanosecond pulses. In af/38geometry, with sample transmission of 0.51–0.80 in a 2 mm cell, the limiting thresholds for these complexes were1.4–3.0 mJ/cm2.The throughputs of these complexes were limited to0.31–1.13 J/cm2for incident fluences as high as3.5 J/cm2.The limiting throughput was strongly influenced by the nature of the ligand. Lower bounds for the ratio of triplet excited-state to ground-state absorption cross sections have been estimated at 3.4–5.7. The lower limiting thresholds, lower limiting throughputs, as well as the ease of modification of the ligands, make these complexes promising candidates for optical power limiters. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122366

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Recent experiments claim that subwavelength resolution can be obtained with an optical scanning microscope using uncoated optical fiber probes. In these experiments, linearly polarized light is sent down the fiber which is reflected and depolarized in the tip-sample region. The internally reflected signal in the orthogonal polarization is detected. Here, numerical solutions of the vector Maxwell equations for a model are discussed. In this model, subwavelength resolution can indeed be obtained in the above mode, while this is not possible without polarization sensitivity. The influence of parameters such as polarization, different scanning modes and tip-sample distance is discussed. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122118

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

This letter introduces a method to perform frequency dependence of radar cross section for either simple or complex scatters in terms of model measurement. To do so, the expressions of physical scale factor based on the electromagnetic similarity are suggested by means of dimensional analysis, geometric and physical optics approximation. Using the results of model measurement within a small range of frequency, the frequency dependence of an arbitrarily shaped scatterer can be obtained. For the purpose of verification and comparison, some measurements of simple and complex shapes have been carried out. The calculated results agree well with the experimental data on the prototype itself. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122119

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Fused silica plates were implanted with Co ions at room temperature at the energy of 50 keV and to the fluence of4×1016 ions cm−2.The formation of metal nanoclusters was observed by transmission electron microscopy. The cluster size distribution is narrow with a mean-diameter value of about 3 nm. Atomic in-depth distribution was determined by Rutherford backscattering spectrometry, whereas the cobalt chemical state was characterized by electron spectroscopies. Nonlinear refractive indexn2is of the order of0.2 cm2 G W−1,as determined by theZ-scan technique at a wavelength of 770 nm for 130 fs long pulses at a 76 MHz repetition rate. Zero-field-cooled and field-cooled magnetization curves at the liquid-helium temperature exhibit features of superparamagnetic behavior that are characteristic of assemblies of single-domain nanoparticles. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122120

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We demonstrate the epitaxial lateral overgrowth (ELO) of GaN from narrow stripes with triangular cross sections by atmospheric pressure metal organic chemical vapor deposition, and characterize the optical properties of these stripes at each stage of the growth using spatially resolved cathodoluminescence spectroscopy, wavelength imaging, and line scans. An improvement of the optical quality of the GaN materials grown by the ELO technique is clearly shown by the appearance of a free exciton peak, the enhancement of bandedge emission, and the weakening of the yellow emission. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122121

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

By incorporating a broad transverse waveguide (1.3 &mgr;m) in 0.97-&mgr;m-emitting InGaAs(P)/InGaP/GaAs separate-confinement-heterostructure quantum-well diode-laser structures we obtain record-high continuous-wave (cw) output powers for any type of InGaAs-active diode lasers: 10.6–11.0 W from 100-&mgr;m-wide-aperture devices at 10 °C heatsink temperature, mounted on either diamond or Cu heatsinks. Built-in discrimination against the second-order transverse mode allows pure fundamental-transverse-mode operation(&thgr;⊥=36°)to at least 20-W-peak pulsed power, at 68×threshold. The internal optical power density at catastrophic optical mirror damage (COMD)P¯COMDis found to be 18–18.5MW/cm2for these conventionally facet-passivated diodes. The lasers are 2-mm-long with 5&percent;/95&percent; reflectivity for front/back facet coating. A low internal loss coefficient(&agr;i=1 cm−1)allows for high external differential quantum efficiency&eegr;d(85&percent;). The characteristic temperatures for the threshold currentT0and the differential quantum efficiencyT1are 210 and 1800 K, respectively. Low differential series resistanceRs:26 m&OHgr;; leads to electrical-to-optical power conversion efficiency values in excess of 40&percent; from 1 W up to 10.6 W cw output power, and as much as 50&percent; higher than those of 0.97-&mgr;m-emitting Al-containing devices. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122122

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Cathodes made with Al–LiF or Al–CsF composites are found to greatly enhance the performance of organic light-emitting devices (OLEDs). With a composite cathode, devices based on an organic bilayer structure have shown lower operating voltage, higher efficiency, and better forward light output than devices with LiF/Al, Mg, or Al cathode. Unlike devices with an Al and Li alloy cathode, OLEDs with a composite cathode can be made with good reproducibility. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122367

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The optical properties ofn-type GaN grown by hydride vapor phase epitaxy, with intentional Si doping levels ranging from nominally undoped toND−NA=4×1017 cm−3,are investigated using low temperature photoluminescence. We identify free and neutral donor-bound exciton transitions and two-electron satellites (TES) at 1.7 K. The energy difference between the principal neutral donor-bound exciton peak and its TES yields a Si donor binding energy of 22 meV. The intensity of the Si-related TES increases with increasing Si concentration. The Si donor is much shallower than the two residual donors, which have binding energies of 28 and 34 meV. This result suggests that the main residual donors in this material (and possibly in many layers grown by metal organic chemical vapor deposition and metal organic molecular beam epitaxy as well) are not Si. Silicon doping also introduces an acceptor level with a binding energy of about 224 meV. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122123

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The antireflection coating of PbSe laser diodes is crucial for external resonator lasers.In situdetermination of the threshold current in cryogenic temperature operation is used in order to optimize the thickness of evaporated layers for minimum reflection. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122368

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We report on Raman spectra ofBaFe12O19thin films. These thin films have been deposited by injection chemical vapor deposition on three different substrates:Al2O3(001),Gd3Ga5O12(111), and Si (100). The observed Raman-active vibrations of the films are compared with recently published Raman spectra from bulk compounds. Surprisingly, we observed nearly the same spectra for all the films, although x-ray diffraction indicates polycrystalline (Si), textured(Gd3Ga5O12),and epitaxial(Al2O3)structure. We interpret these results by supposing the coexistence of well oriented regions and randomly oriented microcrystallites, which are not detectable by x-ray diffraction. Furthermore, by Raman spectroscopy we identified an additional phase for the films deposited onAl2O3which has not been observed by x-ray diffraction either. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122124

出版商:AIP    

年代:1998

数据来源: AIP