摘要:

In this letter we present a hard x-ray phase contrast microscope based on the divergent and coherent beam exiting an x-ray waveguide. It uses lensless geometrical projection to magnify spatial variations in optical path length more than 700 times. Images of a nylon fiber and a gold test pattern were obtained with a resolution of 0.14 &mgr;m in one direction. Exposure times as short as 0.1 s gave already visible contrast, opening the way to high resolution, real time studies. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119324

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The behavior of bright, efficient, low-driving-voltage blue organic light-emitting diodes based on amino-oxadiazole-fluorenes (AODFs) withAl2O3/Alcathodes is described. It is shown that the thinAl2O3buffer layer sharply enhances current injection, increases the device efficiency, and reduces the driving voltage; the performance of devices with the optimal oxide buffer layer thickness approaches those withMg0.9Ag0.1cathodes. The effects of theAl2O3buffer layer are believed to result from the removal of interface gap states induced by defects and chemical bonds between the AODF and Al, which trap carriers and quench singlet excitons nonradiatively. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119325

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A multilayered electroluminescent device was constructed with epitaxially oriented films ofp-sexiphenyl with its molecular axis lying or standing next to the substrate surface. The films with the lying and standing orientations were prepared by vapor deposition onto the KCl (001) surface kept at 20 and 150 °C, respectively. After successive depositions of electron-transport layer and Al cathode, the films were removed from the KCl substrate and transferred on an indium tin oxide coated glass anode. The cell with lying molecules emitted a higher electroluminescence with a narrowed spectrum at remarkably low driving voltages, as compared to one with standing molecules. This electroluminescent behaviors depend upon anisotropic distribution of the polarized emission light as well as efficiency of the carrier transport in the ordered molecular arrays with different orientation modes. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119331

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

An optically pumped waveguide structure has been fabricated with methyl substituted conjugated laddertype poly(paraphenylene) as the active material. The choice of the device parameters allows one to observe a high directionality, a small beam divergence, a complete linear polarization, and a linewidth with an upper limit of 1.7 nm at a considerable low threshold of3 kW/cm2at room temperature. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119332

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Time resolved intracavity gain, saturable absorption dynamics, intracavity intensity pulse profiles, and their corresponding spectrograms, were measured in an external cavity hybrid mode-locked semiconductor diode laser. These measurements were performed to obtain fundamental information of the mode-locking dynamics and to determine their role in the pulse shaping and chirping dynamics. The results of these experiments show that the integrating nonlinearity associated with gain depletion, coupled with group velocity dispersion, leads to asymmetric intensity pulse profiles with predominantly cubic temporal phase, while saturable absorption coupled with group velocity dispersion tends to linearize the chirp. Exploitation of these dynamics may allow researchers to generate optical pulses with higher peak intensities than previously reported. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119333

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The absorption coefficient for a 0.4-&mgr;m-thick GaN layer grown on a polished sapphire substrate was determined from transmission measurements at room temperature. A strong, well defined exciton peak for theAandBexcitons was obtained. TheA,B, andCexcitonic features are clearly defined at 77 K. At room temperature, an energy gapEg=3.452±0.001 eVand an exciton binding energyExA,B=20.4±0.5 meVfor theAandBexcitons andExC=23.5±0.5 meVfor theCexciton were determined by analysis of the absorption coefficient. From this measured absorption coefficient, together with the detailed balance approach of van Roosbroek and Shockley, the radiative constantB=1.1×10−8 cm3/swas obtained. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120191

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Characteristics of lasing in optically pumped, vacuum deposited organic semiconductor thin films of tris-(8-hydroxyquinoline) aluminum doped with DCM laser dye are studied as a function of DCM concentration and ambient temperature. In contrast to inorganic laser diodes, the lasing wavelength, output power, differential quantum efficiency, and threshold pump energy of organic lasers are found to be independent of temperature in the range from 0 to 140 °C. In addition, no degradation in laser performance was observed at temperatures approaching 160 °C. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120186

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Two-photon optical beam induced current (TOBIC) images were acquired through the polished backsides of integrated circuits. An excitation beam with a photon energy below the band gap can traverse even thick substrates virtually unattenuated. At the focus—and only there—two-photon absorption generates electron-hole pairs very efficiently when using a sub-picosecond light source. An additional advantage of TOBIC is a significant increase in spatial resolution. With high numerical aperture objective lense features smaller than 1 &mgr;m are easily discernible. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119334

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have observed saturation of photoluminescence peak at extremely low pump intensities in growth-interrupted and undoped asymmetric-coupled quantum-well structures. We believe the saturation is due to filling of the exciton states localized at the interface islands. The exciton density required to completely fill the localized exciton states at the interface islands for one of the samples is two orders of magnitude lower than that for the previous sample. We have demonstrated that even under the same growth condition, two samples with the same structure exhibit distinctly different photoluminescence spectra and saturation characteristics. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119335

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Bound-free vacuum uv emissions from rare-gas alkali ionic excimers were observed by relativistic electron beam pumping of gas mixtures of Xe or Kr with hot cesium vapor. The observed two diffuse emission bands centered at 159 and 131 nm are assigned to be the2 1&Sgr;+→1 1&Sgr;+transition of(XeCs)+and(KrCs)+ionic excimers, respectively. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120187

出版商:AIP    

年代:1997

数据来源: AIP