摘要:

Differential microscopy is realized by conventional off‐axis electron holography with an electron biprism behind the specimen. Two phase images reconstructed from two holograms which are obtained with slightly different potentials of the electron biprism are utilized to make a one‐dimensional differential image. Polystyrene latex particles which are charged by electron irradiation are used to demonstrate that the differential image is independent of the distortion of a reference wave. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117555

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Active mode locking achieved at a 50 GHz repetition frequency by modulation at half (25 GHz) the cavity resonance frequency using a monolithic mode‐locked InGaAsP laser integrated with an electroabsorption modulator is described. A pulse width of around 3 ps and a high suppression ratio of more than 33 dB of the intensity modulation at the driving frequency are obtained. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117556

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We propose and demonstrate a novel corona discharge method for the fabrication of bulk periodically poled MgO‐LiNbO3substrates. The bulk periodic domain inversion has been successfully formed with a first‐order modulation period of 5.2 &mgr;m for a wavelength of 980 nm over a 6.5 mm interaction length in aZ‐cut 0.4‐mm‐thick MgO‐LiNbO3substrate for the first time. It was found that MgO‐LiNbO3crystal is capable of forming domain inversion under a low applied voltage of no more than 6 kV/mm, which is lower than the case of LiNbO3and LiTaO3. A 490 nm blue light power of 6.7 mW was achieved in a single pass through periodically poled MgO‐LiNbO3, by using a high‐power monolithically integrated flared master oscillator power amplifier of 790 mW as a fundamental source. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117540

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

An optical method for vibration detection and spectral analysis based on photorefractive frequency domain processing is presented. The method utilizes the photorefractive effect in selected materials (bismuth silicon oxide) for synchronous detection of the optical phase shift of an object beam scattered from a vibrating specimen surface. Four‐wave mixing and lock‐in detection allow measurement of both the vibration amplitude and phase. Narrow‐bandwidth detection can be achieved at frequencies from the photorefractive response limit to the reciprocal of the photoinduced carrier recombination time. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117541

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The effect of reverse bias voltage on optical transmission through a waveguide semiconductor saturable absorber is measured for various optical input pulse energies. Reverse bias voltage dependent pulse shape narrowing after a single pass through the device is also observed. Experimental results show that the transmission through the device can be controlled very effectively by modulating the reverse bias voltage on the device when the input pulse energy is low so that the absorption of the saturable absorber is unsaturated. We believe that this kind of controllable semiconductor saturable absorber can be used for many laser systems or modulator and limiter applications in optical communication systems. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117542

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Two‐dimensional photonic band‐structure effects have been observed in the visible and near‐uv regions, between 350 and 800 nm. These effects appear in all‐solid‐state arrays of glass cylinders in a glass matrix. The arrays have center‐to‐center nearest‐neighbor separations between 0.188 and 0.278 &mgr;m, perfect long‐range order, and low refractive index contrast. For light propagating perpendicular to the cylinder axes, very narrow attenuations appear in the transmission spectra as a result of the photonic band structure. The positions of these attenuations are determined by the periodicity, composition, and symmetry of the arrays. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117543

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Transmission experiments are performed on high porosity reticulated polyurethane foams saturated by different gases at ultrasonic frequencies up to 800 kHz. An excess attenuation is observed at high frequencies, when the wavelength is not sufficiently large compared to the lateral dimensions of the fibers. At lower frequencies, these experiments lead by using classical models of equivalent fluids, to a fast and reliable method for determining the characteristic length &Lgr;. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117544

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

An apparatus including a robot manipulated optical system has been built to provide absolute emission data from an inductively coupled plasma operating in argon in non‐equilibrium conditions. Data for the two‐dimensional population densities of one of the excited states of neutral argon ArIare presented together with the Langmuir probe data for electron density and plasma potential. Measurements were performed at 500 mTorr and 50 mTorr and with 100 sccm flow of argon under the constant power condition, 100 W. The data show that excitation profile is almost identical to the radial profile of electron density. At higher pressure maximum excitation and electron density are produced close to the walls, while at low pressure maximum excitation is at the center of the vessel and a high field is formed close to the walls. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117545

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Thermally induced disordering of ZnCdSe/ZnSe superlattices was studied by secondary‐ion‐mass‐spectroscopy and cathodoluminescence. The structures were grown by molecular beam epitaxy and annealed in Zn, H2, or Se atmosphere. In Zn atmosphere the superlattice was found to be stable up to 500 °C, whereas a heat treatment in H2and Se atmosphere leads to a complete intermixing at temperatures of 450 and 430 °C, respectively. A Si3N4stripe was used to protect the superlattice locally from the annealing atmosphere and to achieve a laterally structured intermixing. The disordering area is controlled to better than 600 nm. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117546

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The donor impurity distribution in a GaN epitaxial layer was studied using Raman imaging. TheA1(LO) Raman line at 735 cm−1is found to be inversely correlated to the presence of silicon in GaN due to phonon interaction with the free carrier plasma associated with donor impurities in the material. The spatial variation of theA1(LO) signal was imaged directly using newly developed instrumentation. Features with dimension of about 0.5 &mgr;m are observed in faceted GaN crystallites. This variation in free carrier concentration is attributed to preferential donor impurity incorporation during growth. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117547

出版商:AIP    

年代:1996

数据来源: AIP