摘要:

The measurements of photocurrent as a function of depletion layer or Schottky barrier width have been performed to determine the exciton diffusion length (L) in microcrystalline chlorophyll a (Chl a). This method of determiningLis particularly advantageous in that it does not require a prior knowledge of the absorption coefficient of the material as is usually the case with other, e.g., constant surface photovoltage or constant photocurrent techniques. A value of 180 A˚ has been obtained forLin Chl a. While this value is comparable to those for many organic semiconductors, it is much inferior to that for the minority carriers in inorganic photoconductors. The smaller diffusion length may, in part, explain the feeble power conversion efficiency of Chl a and other organic photovoltaic cells. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117445

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Cross‐sectional information on low electron density materials can be obtained by probing a sample with a 60 keV coherent synchrotron x‐ray beam in an in‐line holography setup. Such objects are practically transparent to high energy x rays and create a phase shift of the wave front only. Images of a 100 &mgr;m diameter boron fiber were recorded in the extreme near field region, where contrast occurs only at interfaces between regions with different decrements of refractive index. Theoretical simulations are in good agreement with the measured intensities. In a tomographic reconstruction the 15 &mgr;m diameter core of the fiber is clearly visible, demonstrating the possibility of reconstructing three dimensional interfaces between low density materials. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117446

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have determined the far‐field patterns and beam parameters of vertical‐cavity surface‐emitting lasers (VCSELs) with different structures. The results show that the window diameter and the active‐layer aperture of VCSELs strongly influence laser far‐field distributions and beam characteristics; for VCSELs with small window &ohgr;=5 &mgr;m, only one dominant lobe has been observed in the far‐field profiles, even though injected current was increased up to 2Ith; and the smaller the ratio of the window diameter to the active‐layer aperture, the larger is the far‐field divergence. The laser structure dependence of theKfactor has also been studied. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117447

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Light‐induced enhancement of the third‐order nonlinear optical susceptibility of a heterodimer consisting of two different porphyrin monomers, a zinctetra(4‐sulfonatophenyl)porphyrin and a zinctetra(4‐N‐methyl‐pyridyl)porphyrin, was observed when the sample was optically pumped by a 30 ps, 532 nm pump pulse. The temporal behavior of the enhancement was studied. It was found that the enhancement was due predominantly to the population of the charge‐separated state with a large electronic third‐order nonlinear optical susceptibility ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117448

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We report on the demonstration of all‐optical switching in a 110 &mgr;m diam, 1 cm long Fabry–Perot cavity defined in a dye‐doped polymer optical fiber waveguide. Such a device is a basic building block of optical logic. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117449

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We report holographic, real time, depth‐resolved image acquisition, storage, and reconstruction in photorefractive GaAs/AlGaAs multiple quantum wells under high background radiation conditions. Reconstructed images of 50 &mgr;m transverse and depth resolution have been achieved using this device as a coherence gate to image through 9 mean free paths of turbid scattering medial ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117450

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Vertical‐cavity surface emitting lasers (VCSELs) were grown by molecular beam epitaxy over openings in a SiN4mask, deposited on a GaAs wafer. We obtained ready to use lasers and laser arrays, laterally defined by the polycrystalline, highly resistive material grown over the SiN4laser. The performance of the lasers (e.g., 20×20 &mgr;m2by size) were similar to that of VCSELs defined by post growth processing methods. Special transverse modes characteristics and a well defined polarization were observed in square shaped lasers and it was attributed to selective growth induced anisotropy. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117451

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We report the performance of a micromachined, photoconductive‐sampling probe that is fabricated on low‐temperature‐grown GaAs and mounted on a single‐mode optical fiber. The epitaxial probe has a temporal resolution of 3.5 ps, a spatial resolution of 7 &mgr;m, and a sensitivity of 15 nV/(Hz)1/2when integrated with a high impedance, junction field‐effect transistor source follower. The fiber, which couples short laser pulses to the interdigitated detector pattern on the probe, also provides flexible support and mobility. The probe’s compact cross section makes it ideal for applications as an internal‐node, picosecond‐response, photoconductive sampling probe or wave form launcher for test and characterization of integrated circuits. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117452

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We present a novel and simple double‐pass fiber Raman laser in the visible and near‐IR regions, based on the use of a fiberoptic autocollimation technique with Littrow‐prism‐tuned emission. When the Raman medium is a 40‐m‐long 68‐&mgr;m‐core‐diam graded‐index multimode fiber with powerful (above 100 kW pulse power coupled into the fiber) nanosecond pumping using the second harmonic of a Nd:YAG laser (&lgr;p=532 nm), we obtain widely tunable generation in both the visible and near‐ IR. By using the double‐pass fiber Raman laser with various lengths of the multimode fiber, continuously tunable generation over a wide spectral range (0.54–1.01 &mgr;m) is obtained. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117453

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We present the operating characteristics of a two‐cavity third harmonic gyroklystron experiment. The input cavity utilizes a 9.854 GHz TE011mode which is driven by a 100 kW magnetron. The TE031output cavity has a resonant frequency of 29.57 GHz. The nominal beam voltage and current are 435 kV and 210 A, respectively. The pulse length is about 1 &mgr;s and the average ratio of parallel to perpendicular velocity is near one. Peak powers above 1.8 MW are achieved with an efficiency of about 2% and a gain of 14 dB. The theoretical simulations are in good agreement with the experimental results. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117454

出版商:AIP    

年代:1996

数据来源: AIP