摘要:

In this letter, terahertz (THz) pulse measurements with a chirped probe pulse are analyzed. The method of stationary phase is used to explore the relation between the temporal waveform of an input THz pulse and spectral distribution of an output probe pulse on a detector array. The dependence of the temporal resolution on the chirp rate, the spectrum of the chirped probe beam, and the spectral resolution of the spectrometer is discussed. We confirm that the temporal resolution of the chirped pulse technique is equal to the square root of the product of the original unchirped probe pulse duration and the chirped pulse duration. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121685

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

An adaptive heterodyne interferometer is configured as a line receiver using wave mixing in photorefractive bismuth silicate crystal. The line receiver is directionally most sensitive to ultrasound impinging normal to the line, and is significantly less sensitive to ultrasound impinging in other directions. Such a system is attractive in situations where the ultrasonic scatter from a specific direction is to be selectively pulled out in the presence of scatter from other “noise” sources. It is also demonstrated that the line probe system can be used to bridge the sensitivity gap that optical detection thus far has suffered vis-a`-vis piezoelectric detection. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121687

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have observed stable single-mode oscillation of optically pumped vertical-cavity surface-emitting lasers (i.e., without fabricated aperture) in several high-order daisy modes. The surprising stability of the nodal lines of a daisy mode is explained as being due to the combined action of many microscopic defects; when a daisy mode is moved across the wafer, the effective correlation length of the orientation of the pinning is of the order of 1 &mgr;m. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121688

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Laser action was observed in GaN pyramids under strong optical pumping at room temperature. The pyramids were laterally overgrown on a patterned GaN/AlN seeding layer grown on a (111) silicon substrate by metal–organic chemical vapor deposition. Each pyramid had a 15-&mgr;m-wide hexagonal base and was on average 15 &mgr;m in height. The pyramids were individually pumped, imaged, and spectrally analyzed through a high-magnification telescope system using a high-density pulsed excitation source. Under high levels of optical pumping, multimode laser at room temperature was observed. The integrated emission intensity for both spontaneous and lasing peaks was studied as a function of excitation power density. The effects of pyramid geometry and short-pulse excitation on the multimode nature of laser oscillations inside of the pyramids is discussed. This study suggests that GaN microstructures could potentially be used as pixel elements and high-density two-dimensional laser arrays. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121689

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Systematic studies of polaritons in single stepped quantum wells are performed, and the presence of forbidden transitions in optical spectra are taken as a fingerprint of nonhomogeneous indium concentration. The large intensities of such transitions for well thicknesses in the range of quasi-two-dimensional exciton behavior are pointed out. Finally, second harmonic generation excited at half gap is found to be enhanced with respect to the bulk contribution as suggested by the theory. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121690

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The dielectric response of epitaxialBaTiO3thin films deposited on MgO was measured through surface electrodes as a function of applied bias, frequency, and temperature. The room temperature value of the dielectric constant was ∼500 with a dissipation factor,tan(&dgr;),of 0.05 at 100 kHz. Measurements varying the bias field showed hysteresis of the dielectric response and a tunability of 30&percent; for a maximum applied field of ∼7 MV/m. The frequency response of the dielectric constant is well described by a Curie–von Schweidler power law with an exponent ∼0.04 in the range 1 kHz–13 MHz. The films undergo a diffuse phase transition at temperatures higher than the bulk Curie temperature. The behavior of the dielectric response is attributed to the presence of residual strain in the epitaxial thin films. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121691

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

ZnSTe-based Schottky barrier photovoltaic detector arrays were fabricated on GaP(100) using a two-step molecular beam epitaxy growth approach. These detectors exhibit visible blind and ultraviolet (UV) sensitive response with a peak UV responsivity of 0.13 A/W and1.2×106 V/Wat 320 nm. The built-in potential of these detectors was determined to be 1.7 V. The temporal photocurrent response of a400×400 &mgr;m2detector was measured to be 1.2 ns, limited apparently by the resistance-capacitance (rc) constant of the detector structure. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121692

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Efficient organic light emitting devices (OLEDs) using methyl substituted ladder-type poly (paraphenylene)(m-LPPP)and tris(8-hydroxy) quinoline aluminum(Alq3)as active materials are presented. For bilayer OLEDs the emissive region is found to be in both layers adjacent to them-LPPP/Alq3interface. The performance of these hybrid devices with constantm-LPPPthickness and varyingAlq3thickness is compared to that of a single layerm-LPPPdevice by investigating the relative spatial distribution of the light emission. The relation between the intensity of the light emitted from each layer and the distance to the cathode metal is discussed. Furthermore, them-LPPPemission is also affected by the internal electric field at the interface. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121693

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We report on intracavity white-light continuum generation in a Ti:sapphire oscillator at an average repetition rate of 200 kHz. A spectrally resolved pump-probe experiment is performed in order to demonstrate the potentialities of these continuum femtosecond pulses. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121694

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Near-field scanning optical microscopy, in which an uncoated fiber tip is used for delivering excitation light and picking up photoluminescence, is applied for diagnosing defects in semiconductor devices. Using this high resolution, potentially subdiffraction limited, and fast acquisition time scanning &mgr;-photoluminescence (PL) technique, we are able to locate nonluminescing defects in a multiple quantum well grown by molecular beam epitaxy. Near-field characteristics of the measured spectral PL intensity are also discussed. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121695

出版商:AIP    

年代:1998

数据来源: AIP