摘要:

In magnetic resonance force microscopy (MRFM) experiments, magnetic forces couple to the motion of microscale cantilever beams. Extension of MRFM to the detection of single electrons will require both unprecedented force sensitivity and motional stability of the cantilever. We describe the principles and performance of optimal cantilever motion control. The method accounts for inherent noise processes and practical application of control forces. We show that active feedback control improves cantilever motional stability, enabling instrument designs of much higher sensitivity and faster imaging than passive designs. Experimental results of implemented cantilever control systems are presented in Part II. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363085

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We describe the implementation of optimal controllers for damping the motion of cantilevers used in magnetic resonance force microscopy. We demonstrate that optimal control is achievable and that torsional magnetic coupling provides an effective actuation method. Cantilever Brownian vibrational amplitude was reduced from 2 to 0.16 A˚ and resonant quality was reduced from 2000 to 5. Applied control fields were sufficiently small that they would not affect magnetic resonance phenomena. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363086

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Much more intense ultraviolet (UV) and blue upconversion fluorescence of Tm3+was observed in a new stable fluoroindate glass compared with other fluoride or oxide glasses. The intense upconversion intensity and high thermal stability of these fluoroindate glasses indicate a high possibility for the realization of a UV and blue upconversion laser. It is reported that the compositional dependence of the fluorescence intensity is largely dependent on the phonon energy of the host glass. The dependence of the phonon energy of the host glasses on contributions from multiphonon decay on the fluorescence intensity is also discussed. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363087

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A theoretical self‐consistent investigation of optically pumped mid‐infrared intersubband semiconductor laser with hot electron effects is presented. Electron dynamics under optical pumping are investigated within a rate equation formulation where particle and energy flow equations are derived from Boltzmann’s equation using Fermi statistics. Electron‐polar optical phonon interactions with suitable screening are calculated by using a macroscopic model with slab and interface phonon modes. Our calculations show that despite hot electron effects, population inversion between the first and second excited states can occur at low temperatures under intersubband optical excitation. It is anticipated that lasing in the mid‐infrared can be achieved with asymmetric quantum well structures optimized for electron concentrations exceeding 1011/cm2. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363088

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Lead borotellurite glasses of the systemxPbO:(80‐x)TeO2:20B2O3(x=20–70) are submitted to open‐apertureZ‐scan measurements at 532 nm. Degenerate two‐photon absorption coefficient of the glass ranges from 7.4±1.2 to 21.9±3.6 cm/GW; larger value is observed for the glass with higher PbO content. The proportional relationship between the PbO content and the two‐photon absorption coefficient in the ternary glass is explained tentatively in terms of the Pb‐associated absorption band existing in the deep ultraviolet region. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363089

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

In Appl. Phys. Lett.67, 1990 (1995), we proposed a particularly simple four‐domain (4‐D) twisted nematic(TN) liquid crystal display(LCD) device, which is composed of two left‐handed and two right‐handed TN subpixels. The two members of each pair of same handedness subpixels are rotated 180° with respect to each other, resulting in four domains that spatially average one another optically to provide a wide angle of viewing with no gray scale inversion. The optical performance of the 4‐D TN LCD was confirmed by studies of a test cell fabricated by a two‐step SiOxoblique evaporation technique. In this article, we report the realization of our four‐domain TN display by a reverse rubbing technique that should be suitable for mass production in the display industry. The optical simulation of our 4‐D TN cell was performed and the effect of disclinations at subpixel boundaries on display contrast investigated. A simple model was developed to evaluate the stability of our 4‐D structure. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363090

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Polymer dispersed liquid crystal (PDLC) materials based on poly(polyethyleneglycol methacrylate) are prepared by ultraviolet light induced polymerization. Microphase structure of PDLC films is observed by scanning electron microscopy. It reveals that reversed morphology type PDLC is obtained. The liquid crystal (LC) is a continuous phase and fills up the irregular space of the polymer network. A comprehensive investigation is performed on the electro‐optical properties of PDLC films. The light scattering and transmittance properties of PDLC films are studied. The effects of LC domain size, light wavelength, applied voltage, frequency, temperature, incident angle, and film thickness on electro‐optical properties of PDLC films are discussed. The results show that size and shape of LC domain seriously affect the electro‐optical properties of PDLC film. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363091

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The effects of a cylindrical cavity in a metal surface on the energy coupling of a laser beam with the solid were investigated by using a photothermal deflection technique. The photothermal deflection of a probe beam over the cavity was measured while the bottom of the cavity was heated with a Nd–YAG laser with a wavelength of 1064 nm. Cavities in three different materials and with two different aspect ratios were used for the experiment. Temperature distributions in the solid and the surrounding air were computed numerically and used to calculate photothermal deflections for cavity heating and for plane surface heating. Reflection of the heating laser beam inside the cavity increased the photothermal deflection amplitude significantly with larger increases for materials with larger thermal diffusivity. The computed photothermal deflections agreed more closely with the experimental results when reflection of the heating laser beam inside the cavity was included in the numerical model. The overall energy coupling between a heating laser and a solid is enhanced by a cavity.

ISSN:0021-8979    

DOI:10.1063/1.363092

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The present study discusses cw CO2‐laser cutting of wire‐wound resistors. Based on the three‐dimensional mathematical model developed, we computed the evolution of the temperature field in the sample and the phase change, as functions of the laser beam power and processing speed. The temperature dependence of the thermophysical coefficients and the dependence of light‐absorption coefficient on the laser beam angle on incidence are taken into account. Experimental results are presented for the minimum laser power that provides cutting of the sample at different speeds. A reasonable agreement between the experimental and theoretical results is found. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363093

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The acoustic wave most commonly transmitted and detected in the high‐porosity absorbent materials used in noise control is generally the air‐borne slow compressional wave. In a new experiment, the air saturating the sample is replaced by helium and the transmission is studied at ultrasonic frequencies (70–600 kHz). The experiment is quite easily performed using standard ultrasonics and vacuum equipment. The main purpose of this work is to propose a method to determine simultaneously both the viscous and thermal characteristic lengths with the same precision. These two parameters characterize the viscous and the thermal interactions between the frame and the fluid at high frequencies. The characteristic lengths are deduced from the high‐frequency asymptotic behavior of either the velocity or the attenuation curves obtained in the sample saturated by air and by helium. It also appears that due to the properties of helium, the discrepancy previously observed between predictions and measurements is shifted toward higher frequencies. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363817

出版商:AIP    

年代:1996

数据来源: AIP