摘要:

An optically resonant periodic electrode structure designed as a combined waveguide coupler/Bragg reflector can function as an optical or optoelectronic switch. We present experimental results showing self-modulation of the reflectivity from such a structure using Nd:YAG laser pulses, and show self-modulation at lower intensities using an optically resonant periodic electrode structure equipped with a central phase shift. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119670

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report photopumped operation of a monolithic coupled semiconductor microcavity laser. The structure consists of two &lgr;-sized GaAs vertical cavities, one on top of the other, coupled together through a common mirror. Due to a wedge induced into each cavity, the detuning between the cavities can be continuously varied when moving across the sample. Depending on the detuning, laser action is simultaneously achieved at two different wavelengths or occurs only at one wavelength. At resonance, we observe coupled dual-wavelength laser emission at two widely spaced wavelengths (13 nm) with the same threshold and same dependence on pump power. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119671

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The nonlinear optical properties for the PbO,TiO2,K2O,andSiO2system have been measured by theZ-scan method. The magnitude and sign of the nonlinear refractive indexn2were determined, as was the negative sign, which indicated a self-defocusing optical nonlinearity. Two optical absorption bands at 540 and 660 nm, respectively, are observed in the optical absorption spectra. The sources of the absorption bands are attributed to the3d-shell electronic transitions ofTi3+ions from the ground state to the excited states. The origin of the negative nonlinear refractive index was the contribution of resonant electronic transition processes, which can cancel the positive nonresonant refractive index that mainly resulted from the hyperpolarizabilities of the Pb–O and Ti–O pairs. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119672

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

GaN photoconductive detectors have been fabricated on sapphire substrates by metal organic vapor phase epitaxy and gas-source molecular beam epitaxy on Si (111) substrates. The photodetectors showed high photoconductor gains, a very nonlinear response with illuminating power, and an intrinsic nonexponential photoconductance recovery process. A novel photoconductor gain mechanism is proposed to explain such results, based on a modulation of the conductive volume of the layer. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119673

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We measure at different wavelengths the linear and nonlinear optical properties of a new chromophore for photorefractive applications by means of frequency-dependent ellipsometry experiments. We show that the optical dispersion of the refractive index modulation responsible for the high diffraction efficiency in lowTgpolymers can be described by a two-level model. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119674

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report the use of a 5-mm-long planar Nd:yttrium aluminum garnet waveguide grown by liquid-phase epitaxy as an amplifier at 1.064 &mgr;m. In a double-pass configuration pumped by a 1.2 W diode laser, small signal gains of 686 (28 dB) have been observed and efficient power extraction demonstrated with output powers of up to 290 mW being obtained. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119675

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have demonstrated that transmission through a fiber grating can increase the system response of a directly modulated semiconductor laser by over 7 dB at all modulation frequencies up to 25 GHz. When combined with dispersive optical fiber, the grating produced a system response that was larger, flatter, and had a larger bandwidth, providing a frequency-domain demonstration of dispersion compensation through an unchirped grating. The effect can be understood as frequency modulation to amplitude modulation conversion by the grating, and was accurately predicted by a Fourier domain analysis of the laser signal and grating. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119676

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We initiate micro-explosions inside fused silica, quartz, sapphire, and other transparent materials using tightly focused 100 fs laser pulses. In the micro-explosions, material is ejected from the center, forming a cavity surrounded by a region of compacted material. We examine the resulting structures with optical microscopy, diffraction, and atomic force microscopy of internal cross sections. We find the structures have a diameter of only 200–250 nm, which we attribute to strong self-focusing of the laser pulse. These experiments probe a unique regime of light propagation inside materials at intensities approaching1021 W/m2,the electron ionization that accompanies it, and the material response to extreme pressure and temperature conditions. The micro-explosions also provide a novel technique for internal microstructuring of transparent materials. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119677

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have found that terrace contrast of oxidized Si(001) substrate observed with a scanning reflection electron microscopy (SREM) is reversed by progress in thermal oxidation by one atomic layer of Si. The cause for such terrace contrast reversion is that reflection electron intensity depends on Si-bond direction at oxide/Si interface. This fact was confirmed by calculations based on a multiple scattering theory. The motion of oxide/Si-bulk interface can be, thus, observed by SREM. The reversion and continuous change of the terrace contrast indicate that oxidation occurs monolayer by monolayer on Si(001) substrate. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120567

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We show the possibility to measure the effective tip shape and the lateral resolution of a scanning force microscopy (SFM) probe on the nanometer-scale directly from SFM images of SiC(0001). On this surface there are grooves 10–100-nm-wide related to cleavage planes. The SFM tip penetrates the groove but does not reach the bottom since its side walls touch both rims. The width of the narrowest groove resolved is the lateral resolution. The apparent topography across a groove yields directly the tip radius of curvature in excellent agreement with the values estimated from scanning electron micrographs. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119678

出版商:AIP    

年代:1997

数据来源: AIP