摘要:

Cs–K–Te films have been fabricated under ultrahigh vacuum by vapor deposition of Te, K, and Cs onto a Mo substrate into the preparation chamber of the free electron laser of the University of Twente. Their photoemission properties are reported in this letter. The average quantum efficiency at 259 nm measured on 5 evaporated Cs–K–Te photocathodes is 22.5&percent;, whereas the best quantum efficiency obtained at 259 nm is 23.4&percent;. To our knowledge, this is the highest quantum efficiency at 259 nm reported so far, being about twice that of Cs2Te photocathodes. The reported results demonstrate that Cs–K–Te photocathodes are very promising for the use in photoinjectors. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118362

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Transfer of temporal fluctuations between the signal and pump beams in diffusion dominated photorefractive two-beam coupling is studied experimentally. The dependence on the gain, beam intensity ratio, and frequency of the fluctuations is found to agree well with a linearized analysis. The transfer of perturbations is frequency dependent at low frequencies, and becomes constant at frequencies large compared to the inverse material time constant. We discuss the possibility of pump noise suppression when amplifying weak signals. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118640

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have observed extreme-ultraviolet (XUV) “line-free” continuum emission from laser plasmas of high atomic number elements using targets irradiated with 248 nm laser pulses of 7 ps duration at a power density of∼1013 W/cm2. Using both dispersive spectroscopy and streak camera detection, the spectral and temporal evolution of XUV continuum emission for several target atomic numbers has been measured on a time scale with an upper limit of several hundred picoseconds limited by amplified spontaneous emission. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118364

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The mechanical resonance behavior of near-field optical microscope probes is examined with a simple experiment on a flat pyrex sample. While our tapered-fiber probe is locked on the second resonance for servo control, the vibration characteristics around the first resonance are investigated. We find that the overwhelming cause of decreased vibration amplitude as the tip approaches the sample is an increase in damping presumably due to a fluidlike layer on the sample. A small additional effect is also observed that could be due to force derivatives. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118365

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report the second harmonic generation and electroluminescent (EL) properties of a soluble metal complex polyurethane (PU). The PU was prepared by the reaction of a zinc Schiff base with 4,4′-diphenylmethane-diisocyanate. The polymer film has been effectively poled under a corona field and its linear and nonlinear optical (NLO) properties were characterized. The results indicated that the NLO effects of the polymer are mainly originated in the distorted coordination tetragonals formed by the central zinc atoms and coordination atoms. The polymer shows strong photoluminescence under a ultraviolet-lamp illumination and can be used as a luminescent material for EL devices. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118366

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We perform measurements of the differential gain of modelocked semiconductor quantum well lasers over a wide spectral range employing a modified “electrical pump-optical probe” technique. We find that the two-dimensional density of states expresses itself significantly in the spectral dependence and value of the differential gain. Contributions of the second electronic level are observed in the high-energy range with an increasing in the differential gain, whereas a slightly decreasing differential gain with decreasing wavelength is observed in spectral regimes, where only the first quantized level contributes. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118363

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A novel technique for measuring temperature, based on pulsed photothermal radiometry and analysis of the spectral and temperature dependence of Planck’s blackbody equation, is described. In this technique a body is irradiated by a laser pulse and its temperature inferred from the time dependence of the emitted infrared signal curve. This technique was used for near ambient temperature measurements using aCO2laser, an infrared detector, and infrared transmitting silver halide optical fibers. The experimental results are consistent with theory. This technique is independent of changes in emissivity or geometric factors and it will be useful for accurate and fast noncontact temperature measurements. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118602

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The excess linewidth broadening of continuously tunable InGaAsP/InP laser diodes at 1.5 &mgr;m wavelength is investigated. Terminal electrical and FM noise measurements indicate that the recombination processes in the forward biased tuning region produce significant 1/fcarrier noise. Below 1 MHz the 1/fnoise dominates yielding a noise enhancement of about 30 dB at 1 kHz. The discrepancy observed so far between theoretically expected and measured spectral linewidth can be well resolved by taking into account this additional noise source. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118603

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A novel photorefractive polymer composite is reported which exhibits a high two-beam coupling gain coefficient (&Ggr;=200cm−1at 120 V/&mgr;m, fast response time (&tgr;g=50 ms at 1W/cm2), overmodulation of diffraction efficiency, and high sensitivity. The composition and processing have been altered to yield greatly improved material stability. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118604

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have examined in detail the formation of surface relief structures in azobenzene polyesters formed by polarization holography with orthogonally circularly polarized laser beams. We show that it is possible to separate the contribution to the diffraction efficiency into an anisotropic part and a surface relief part by examining the polarization content of the first order diffracted beam. By studying the dynamics of the growth of the grating, we show that the gratings due to anisotropy and surface relief appear at the same time. Atomic force microscopic investigations of the film after irradiation reveal a strongly polarization dependent surface relief pattern. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118605

出版商:AIP    

年代:1997

数据来源: AIP