摘要:

A versatile fiber‐optic confocal Raman microscope has been developed. Fiber optics provide remote capabilities for the microscope and the ability to use multiple excitation sources and detection schemes. The horizontal and vertical resolutions of the instrument have been determined by monitoring spectral changes while scanning known interfaces and microparticles. The mini‐ mum detectable particle size has been determined via the spectroscopic analysis of calibrated polystyrene microspheres. The horizontal resolution has additionally been tested in the imaging of a 10 &mgr;m glass fiber embedded in an epoxy matrix. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146555

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The potential of a diagnostic technique to provide quantitative three‐dimensional (3D) density distributions of species in a low temperature laser‐produced plume is shown. An expanded, short pulse, tunable dye laser is used to probe the plume at a set time during the expansion. Simultaneous recording of two‐dimensional in‐line absorbance maps and orthogonal recording of laser induced fluorescence permits the 3D density mapping by scanning the dye laser frequency. Preliminary data, supported by a simple model, is presented for the case of Ba IIions in a YBCO plume heated by a KrF laser. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146556

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

This paper discusses a technique which uses Compton scattered gamma radiation to obtain high contrast, highly spatially resolved, three‐dimensional images in optically opaque objects. A highly desirable property of this technology is that this method allows the acquisition of radiographs without the necessity of placing the object between the source and detector. This paper describes a prototype apparatus which is capable of obtaining images with a spatial resolution of about 1 mm at a depth of 25 mm in steel of normal density with the source and detector both on the same side of the object. Some modeling calculations, reconstruction algorithms, and data verifying the performance of this technique will be presented as well as details of how the efficiency and throughput of this system could be increased by over two orders of magnitude. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146557

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A dual purpose sensor acquisition and experimental control system which functions in the demanding environment of a nuclear magnetic resonance imaging (NMRI) spectrometer is described. The system ensures accurate sensor readings during imaging and protects sensitive electronic equipment from the effects of the intense radio frequency pulses and magnetic field gradient switches in NMRI. A homebuilt isolation network was constructed with isolation transformers and optoisolators. A variety of hardware and software methods are implemented to ensure accurate sensor data. The system also allows for the ready incorporation of external events into the NMRI pulse sequence. LabVIEWTM, a graphical programming environment, is the heart of our acquisition/control system. LabVIEW’s graphical interface and modular design enables flexible programs to be constructed which are easily understood and modified by the user. Applications of the system, monitoring photopolymerization and controlling ultrasonic cavitation in conjunction with NMRI, are outlined. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147585

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Metallic point contacts and tunnel junctions with a small and adjustable number of conduction channels have been obtained in the last few years using scanning tunneling microscope and break junction techniques. For conventional break junctions, the reported drift of the interelectrode spacing in the tunnel regime is typically of the order of 0.5 pm/min (1 pm=10−12m). We have nanofabricated break junctions which display a drift smaller than 0.2 pm/h. The improvement results from the scaling down by two orders of magnitude of the device dimensions. We describe the nanofabrication process, which can be adapted to most metals. We have performed measurements on Al, Cu, and Nb devices. The results illustrate the ability of the technique to explore phenomenalike conductance quantization and two level fluctuations. These new adjustable atomic size contacts and tunnel junctions can be integrated in complex circuits. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146558

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Uncooled infrared sensors are important for a number of technological and scientific measurements. We have designed, built, and tested a new uncooled infrared sensor which is made by silicon micromachining. This infrared sensor uses a tunneling displacement transducer to detect the thermal expansion of a small volume of trapped gas. Prototype devices based on this design have been operated with NEP better than 3×10−10W/&sqrt;Hz at 25 Hz, which is competitive with the best comparably sized uncooled sensors available. This article will describe the design, fabrication, and operation of all elements of this sensor. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146559

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have observed linear ‘‘crystals’’ of up to tens of laser‐cooled199Hg+ions in a linear rf ion trap. The trap operates at liquid‐He temperature and is designed for use as a prototype 40.5 GHz frequency standard with high accuracy and stability. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146560

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

This paper describes the design and tests of an ultrahigh vacuum apparatus built for the study of particle surface interactions, with emphasis on ion scattering experiments. The system was designed to provide facilities for angle resolved electron spectroscopy, ion scattering spectroscopy (ISS), Auger electron spectroscopy (AES), and ultraviolet photoelectron spectroscopy (UPS). It has provisions for photon spectroscopy and fixed angle time‐of‐flight (TOF) scattering and recoiling spectrometry. Mass selected ion beams in the energy range from a few eV to a few keV can be produced in a continuous or pulsed mode. Two independent, parallel plate tandem electrostatic analyzers, which can rotate around the sample are employed. The angular range spanned is analysis‐type dependent and varies from 0° to 135°. One of the analyzers was designed for low energy secondary electron spectroscopy (0–100 eV) and the other one for ISS and AES measurements in the energy range from a few eV to 5 keV. The system disposes of a Czerny–Turner monochromator for optical spectroscopy in the visible. TOF analysis can be performed for 7° and 38° scattering angles and a flight length of 2.2 m. Alternatively, a large area detector set at 20 cm from the collision center allows TOF and charge fraction measurements over an angular range from 0° to 110°. We describe various tests of the different components of the apparatus and some results of experiments on ion scattering. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146561

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We present data demonstrating the influence of an applied electric fieldEoriented normal to the input surface of a microchannel plate (MCP) detector on the critical operating parameters of the detector, including the quantum detection efficiency, the spatial resolution, and pulse height distribution. The MCP detector response is characterized using 20 keV protons as the primary radiation. An applied electric fieldE<−4 V/mm, where a negative value ofEcorresponds to a nearby object that is biased positive relative to the input surface, results in a high spatial resolution and a quantum detection efficiency that is approximately equal to the open area ratio of the MCP. An electric field −1<E<5 V/mm results in low spatial resolution, in which up to 32% of the measured signal appears as a localized noise that extends several millimeters from the point of ion impact, and a maximum quantum detection efficiency of approximately 0.87. Furthermore, a separate peak in the pulse‐height distribution arises from ions striking the web of the MCP detector and has a much lower pulse magnitude than that of ions striking channels. ForE≳5 V/mm, the spatial resolution increases, and the quantum detection efficiency slightly decreases from its maximum value with increasingE. The characteristics of each of these electric field configurations are analyzed in the context of the yield and transport of secondary electrons created at the web of the MCP detector, and the results can be scaled to other ions and energies according to the secondary electron yield of ions striking the web. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146562

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The application of the high B mode concept has allowed an effective upgrading of the superconducting electron cyclotron resonance (ECR) ion source SC‐ECRIS, which is now one of the best operating ECR ion sources in the world in terms of highly charged ion production. To increase the high charge state intensities and the total extracted current we tried to enlarge the plasma volume, but no clear evidence of volume effects was substantially achieved. We also tried to increase the magnetic field of the trap. The theory which led to these experiments is outlined in the following along with the results of tests using larger plasma volumes and tests with larger magnetic field. Even if the theoretical basis is not always well established, the beneficial effect of magnetic field enhancement on ECR source performances is confirmed. The capability of superconducting ECR ion sources to get higher results with respect to room temperature source by means of a higher and variable hexapolar field is underlined. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146563

出版商:AIP    

年代:1996

数据来源: AIP