摘要:

We have used the inherent surface sensitivity of second-harmonic generation to develop an instrument for nonlinear optical microscopy of surfaces and interfaces. This optical technique is ideal for imaging nanometer-thick, chromophoric self-assembled monolayers (SAMs), which have been patterned using photolithographic techniques. In this paper, we demonstrate the application of second-harmonic generation microscopy to patterned SAMs of the noncentrosymmetric molecule calixarene and discuss the resolution and sensitivity limits of the technique. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364284

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present images of the source of extreme ultraviolet (XUV) harmonic emission at a wavelength of 220 Å from the interaction of a 20 TW, 1.053 &mgr;m Nd:glass laser beam focused to intensities up to 4×1018W cm−2onto a solid target. From these measurements we determine an upper limit to the source size and brightness of the harmonic emission to show its efficacy as a novel source of short-pulse, coherent XUV radiation. We also demonstrate the empirical scaling of the harmonic generation efficiency with irradiance up to 1019W &mgr;m2 cm−2, and extrapolate to estimate the possible source brightness at higher irradiances. These source brightnesses are compared to those available from an x-ray laser system. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364362

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Aging properties of AlGaAs high power laser arrays were monitored by photocurrent (PC) measurements. We demonstrate that this method allows a quantitative analysis of the aging process and provides insight into the microscopic degradation mechanisms. In graded index separate confinement heterostructures, the PC spectra in the spectral range of the laser transition display a substantial current decrease with aging. This is attributed to enhanced rates of surface recombination and defect generation in the graded gap region. In contrast, step index structures exhibit a much smaller change of PC. The PC results are complemented by measurements of low-frequency laser current noise and front facet temperature. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364256

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Light emission from a ridge waveguide1.3 &mgr;mInGaAsP/InP semiconductor laser pumped both electrically and optically was analyzed by polarization- and time-resolved measurements. The electric and the optical excitation was realized with a dc-bias current and with 150 ps pulses from aQ-switched Nd-YAG laser at1.064 &mgr;mwavelength, respectively. The pump light was introduced into the InGaAsP/InP laser through a window opened in the substrate gold contact. The steady-stateP–Icharacteristics of the semiconductor laser exhibited a transition from TM- to TE-polarized light emission if the injection current surpasses a certain value that depends on the heatsink temperature. Depending on the dc-bias current and the optical pulse power, a variety of different emission characteristics of the semiconductor laser were observed: pure TE or TM pulsations, in combination with a background cw emission in some cases; simultaneous emission of TE and TM pulses and switching between TM and TE emission states with switching times as short as 30 ps. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364257

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A two-dimensional time-dependent analysis is presented to describe photorefractive recording in a film with anisotropic transport parameters. The solution of the rate equations together with suitable boundary conditions on the film faces has been obtained by numerical methods for a parallel recording geometry. The recording curves very markedly depend on the anisotropy ratioai=&mgr;z/&mgr;x(zbeing the axis perpendicular to the film faces), the grating period, and the ratio between film and buffer permittivities. Forai=1, the solution coincides with that previously obtained using an analytical approach. Approximate analytical solutions forai≠1 have also been worked out and compared to the numerical results. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364258

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A transient, two-dimensional drift-diffusion model is developed for optically addressed spatial light modulators made with quantum-well materials. The transport of free and well-confined carriers is considered along with nonlinear transport effects such as velocity saturation, field-dependent carrier escape from quantum wells, and resonant absorption. In addition to full numerical solutions to the transport equations, analytical and simplified numerical solutions are developed to describe basic screening behavior and to give estimates of speed and resolution performance. In particular, a self-consistent small signal model is developed to justify the surface-charge picture often used to describe device operation. This model is also used to simulate grating formation and decay. It is found that the maximum screening rate and peak grating amplitude are achieved using vertical drift lengths much longer than the device length. A detailed analysis of resolution performance is also given in which the effects of transit time, carrier lifetime, and free and confined transport along the wells are simulated. For typical device parameters, the two main limitations to resolution performance are found to be anisotropic drift in the interior due to the quantum wells and transverse drift along the device interfaces. Two device designs are compared to assess the ability to optimize device performance by changing experimentally accessible parameters such as carrier lifetime and quantum-well escape rates. Resolutions down to 7 &mgr;m and frame rates of 100 kHz at 10 mW/cm2are achieved. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364259

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The dynamic emission of screw dislocations from a propagating crack tip has been investigated. The crack velocity and velocity of each dislocation are assumed to be proportional to the third power of the stress intensity factor and the effective stress, respectively. The stress intensity factor for theith dislocation emission is derived according to the spontaneous emission criterion. It is found that the stress intensity factor for dislocation emission is independent of crack mobility but the number of dislocations emitted decreases with increasing crack mobility. The number of emitted dislocations and the size of the plastic zone decrease but the maximum stress intensity factor for dislocation emission increases with increasing initial crack length. The size of the dislocation-free zone increases with increasing initial crack length for steady state. The dislocation–crack system reaches the steady state when the dislocations and crack tip move at the same velocity. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364260

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Gas flow in long, narrow, very shallow, micromachined silicon dioxide–quartz glass channels was studied with the use of a mass spectrometric system. The channel bottom was partly covered with an evaporated, 10-Å-thick platinum film along its whole length, and the channel was inserted as the only leak between a gas mixing chamber and an ultrahigh vacuum mass spectrometer chamber. At a wide pressure range upstream of the channel (10–1000 Torr), the steady state flow through the channel was characterized as being close to molecular. At a pressure buildup of either H2or O2in the gas mixing chamber, the mass spectrometer response was delayed more than what can be explained by molecular diffusion. A total restriction of the diffusion due to adsorption on platinum is suggested. The assumption is in accord with different validation experiments. A model for the adsorption delay time is presented and discussed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364261

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The particular feature of the point-to-ring corona has been utilized in order to carry out measurements of the mobility of large positive ions by balancing their drift in a known electric field against a known air flow velocity. The experimental results have provided evidence of ionic-mobility values of the order of 10−6m2/V s. These are typical values of the so-called intermediate ions which normally consist of some 4000 water molecules surrounding singly charged ionized atoms such as H+and Na+. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364293

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Spatial profiles of electron density and temperature of electron cyclotron resonance discharge plasmas have been successfully measured using laser Thomson scattering. The results, thus obtained, were valuable for quantitative comparison with results of a computer simulation. Measurements were performed for two cases with different locations of the electron cyclotron resonance zones. Simulation results obtained from a hybrid code, which treats ions and neutral particles as discrete particles and electrons as a fluid, were fitted to the experimental profiles of the electron density and temperature by adjusting the microwave power deposition profiles. From these comparisons and an analysis of other simulation data, it was found that the large difference of radial electron density profiles for two discharge conditions was caused by the difference of radial space-charge electric-field distributions. The radial electron temperature distribution determined the radial electric field that drove the ions radially and also resulted in a peaked electron density profile for one case and a more uniform profile for the other case. It is also shown that Coulomb collisions of electrons with ions as well as electron–neutral collisions are important for the analysis of electron behavior along the magnetic field lines. ©1997 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.364262

出版商:AIP    

年代:1997

数据来源: AIP