摘要:

Atomic force microscope images reveal a root-mean-square roughness&Dgr;d=16 nmfor InGaN/GaN double-heterostructure laser structures with cleaveda-plane facets. Thec-plane sapphire substrate cleaves cleanly along both theaandmplanes. A theoretical model is developed which shows that the power reflectivity of the facets decreases with roughness by a factor ofe−16&pgr;2(n&Dgr;d/&lgr;0)2,wherenis the refractive index of the semiconductor and&lgr;0is the emission wavelength. Laser emission from the optically pumped cavities shows a TE/TM ratio of 100, an increase in differential quantum efficiency by a factor of 34 above threshold, and an emission line narrowing to 13.5 meV. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122172

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We demonstrate an optically pumped InGaN/GaN-based multiquantum well distributed feedback laser in the blue spectral region. The third-order grating providing feedback was defined holographically and dry etched into the upper waveguiding layer by chemically assisted ion-beam etching. When aligning the stripe-shaped pump beam either parallel or perpendicular to the grating grooves, we found a considerably lower pumping threshold, higher slope efficiency, a slightly longer emission wavelength, and a much narrower linewidth for the geometry with the pump beam orthogonal to the grating lines. A nearly constant emission wavelength of 400.85 nm and a linewidth of 0.7 Å were observed under various pump intensities. To the best of our knowledge, this is the narrowest linewidth ever reported for an optically pumped device in this material system. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122325

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Cubic GaN/AlGaN double heterostructure was grown on semi-insulating GaAs (100) substrate by metalorganic vapor phase epitaxy. Strong stimulated emission was observed from the cleaved edge of the optically pumped cubic GaN/AlGaN heterostructure at 15 K. The cavity was formed simply by cleaving the substrate. The stimulated emission was demonstrated by the superlinear increase of the output intensity and the highly transverse electric polarized nature. The stimulated emission showed an obvious redshift compared with the spontaneous one. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122326

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Nonlinear spectral filtering provides a simple method for reducing noise in optical pulses to below the shot noise level. We show its effectiveness for excess noise reduction in an ultrafast optical pulse train by demonstrating 23 dB reduction of low frequency1/fnoise in pulses from a passively mode-locked erbium-doped fiber laser. The noise reduction is achieved by spectrally filtering pulses propagated as solitons through a 1.5 km length of optical fiber. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122327

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We report the device performance of normal-incidence (In, Ga)As/GaAs quantum dot intersubband infrared photodetectors. A primary intersubband transition peak is observed at the wavelength of 13 &mgr;m(E0→E1)and a secondary peak at 11 &mgr;m(E0→E2).The measured energy spacing in the conduction band of the quantum dots is in good agreement with low temperature photoluminescence measurement and calculations. A peak detectivity of1×1010 cm Hz1/2/Wat 13 &mgr;m was achieved at 40 K for these devices. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122328

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We report large polarization state rotations of a weak pulsed beam in CdTe/CdMnTe quantum wells photoinduced by intense circularly polarized pulsed pump beam. Time-resolved analysis of the effect shows that, at moderate pump fluences, the polarization state rotation is due to the combined effect of many-body interactions and spectral hole burning at early times and to photoinduced magnetization at longer ones. At higher pump fluences, space filling and degenerate four-wave mixing become important. At low pump fluences (few&mgr;J/cm2) already the polarization rotation photoinduced at early times can be as large as a few degrees making these multiple quantum wells potential candidates for applications. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122329

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We present two methods for generating numerically a one-dimensional random surface, defined by the equationx3=&zgr;(x1),that has a prescribed probability density function of slopes. This problem arises in the design of a diffuser that scatters light uniformly within a range of scattering angles and produces no scattering outside this range. Numerical calculations of the scattering of light from random surfaces generated by these approaches show that the scattered intensity, indeed, has a rectangular distribution as a function of the scattering angle. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122330

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

An integrated optical isolator is demonstrated based on efficient nonreciprocal conversion from a fundamental TM mode to a deep TE radiation mode away from the cutoff. The isolator is realized using a single-mode rib channel waveguide in Ce-substituted yttrium iron garnet, which has a very large Faraday rotation. 27 dB isolation is obtained at a wavelength of 1535 nm. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122331

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The picosecond time-resolved emission spectrum of the cyanine dye 1,1′-diethyl-3,3′bis-(3-sulfopropyl)-5,5′,6,6′-tetrachlorobenzimidazolocarbocyanine (also known as BIC) adsorbed onto colloidal silver was examined as a function of laser pulse energy at room temperature. BIC is found to aggregate on colloidal silver, and the number of coherently responding molecules involved in the one-exciton state (i.e., the coherence length) was estimated to involve 8–9 molecules. Lasing at a remarkably low incident pulse energy threshold was found for this system and explained in terms of a mechanism involving superradiant states created in coherently coupled adsorbed molecules that emit photons which stimulate emission from other spatially distributed superradiant states. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122563

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A direct determination of the Poisson’s ratio in 150 nm polycrystalline tungsten thin films deposited by ion-beam sputtering on Duralumin substrates has been performed by combining x-ray diffraction measurements within situtraction on the sample. X-ray diffraction experiments using thesin2 &psgr;method have been done at LURE, the French synchrotron facility (Orsay, France) on a four-circle diffractometer. The method described in this letter allows us to extract in a simple way and with a good precision the Poisson’s ratio of thin films on substrates from the evolution of thesin2 &psgr;curves as a function of applied strains. In the case of tungsten thin film, the value obtained is close to the bulk material one. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122332

出版商:AIP    

年代:1998

数据来源: AIP