摘要:

A computer‐controlled four‐detector photopolarimeter (FDP) has been constructed using four windowless planar‐diffused Si photodiodes, operational amplifiers, an analog‐to‐digital (A/D) converter, and a personal computer with peripherals. A nonplanar light path is selected with incidence angles at the first three detectors of ∼65° and with rotations of ∼45° between the successive planes of incidence. The last detector, which is coated for minimum reflectance, intercepts the beam at a small angle and the residual light it reflects is dumped. A 1‐mW He–Ne laser beam (&lgr;=632.8 nm) passes through the polarizing optics of an ellipsometer to provide the polarization states needed for calibration and testing. With an optimum set of calibration states, the instrument matrixAis determined. The FDP is subsequently tested and found to correctly measure the normalized Stokes parameters of a large number of states with an average absolute error of ∼0.01, which is attributed to imperfections in the calibration optics. This first prototype instrument has a precision of ∼0.2%.

ISSN:0034-6748    

DOI:10.1063/1.1139971

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A tunable diode laser infrared spectrometer has been constructed which can measureinsituvibrational spectra of liquids interacting with metal surfaces. The spectrometer uses a zinc selenide photoelastic modulator and commercially available diode lasers to make single‐beam, single‐pass measurements of molecular vibrations attributable to monolayer concentrations of molecules chemisorbed or physisorbed on metal surfaces. It also measures bulk spectra of liquids from a single reflection in an attenuated total reflection mode. With a suitable sample cell it would be possible to investigate liquids or gases at wide ranges of temperature, pressure,pH, etc.

ISSN:0034-6748    

DOI:10.1063/1.1139972

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

We analyze a ‘‘rim‐type’’ chopper. The pulse duration can be varied at a fixed pulse repetition rate by changing the chopper‐to‐beam offset distance. Overall performance is discussed in terms of the transmission function, pulse length, and velocity‐selection properties.

ISSN:0034-6748    

DOI:10.1063/1.1140253

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

We have developed and tested an inexpensive ion detector with dark‐count rates below 10−4s−1and excellent background rejection. Each 40‐keV ion that strikes a grazing‐incidence Al2O3conversion dynode ejects a few tens of secondary electrons, which enter separate pores of a microchannel plate and are independently multiplied to saturated pulse height. The pulses are summed to produce an output signal that is proportional to the number of secondary electrons. This permits pulse‐height discrimination against backgrounds of low‐energy ions, electrons, and photons. We have successfully tested the detector with C+, Na+, K+, Rb+, and Cs+at 5–40 keV, and with 36‐keV C−and CH−. It should detect ions and neutrals of all species, at energies above 5–10 keV, with good efficiency and excellent background discrimination. Counting efficiency and background discrimination improve with higher ion energy. The detector can be operated at pressures up to at least 2×10−7Torr and be exposed to air repeatedly without requiring reactivation. The maximum ion count rate is 3×106s−1in pulse‐counting mode and 6×109s−1in current‐integrating mode. Detection of 40‐keV ions at rates below 10−2s−1was required in development of a 10‐cm radius 40‐keV cyclotron dedicated to high‐sensitivity radioisotope dating by accelerator mass spectrometry (AMS). In the cyclotron, the detector suppresses to 6×10−4 s−1the background count rate from the presence of low‐energy ions, photons, and electrons.

ISSN:0034-6748    

DOI:10.1063/1.1139973

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Four types of composite torsion antennas for low‐frequency gravitational radiation have been developed and tested at low temperature. They exhibited high quality factors comparable with that of a single‐piece antenna. These experiments suggest a large‐scale composite antenna may be built and retain a high quality factor.

ISSN:0034-6748    

DOI:10.1063/1.1139996

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A novel technique to measure the magnetic field strength is demonstrated, which is based on blow‐off beam probing combined with Doppler‐tuned laser spectroscopy. The field strength is determined from the Zeeman splitting of the LiI resonance line (670.8 nm) with good time and spatial resolutions (&Dgr;t<100 &mgr;s, &Dgr;r<5 mm). The measurable field strength is less than 1 T with an accuracy of 10%.

ISSN:0034-6748    

DOI:10.1063/1.1139997

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Results of steady‐state discharge test of coaxial LaB6cathodes in a multicusp plasma generator are described. After a single‐unit test of a compact, 6.4‐mm‐diam coaxial LaB6cathode, a discharge test of two cathodes with one heater power supply was carried out with success. In addition, a new tapered coaxial cathode, which was designed to prevent overheating of LaB6due to ohmic heating by discharge current, was investigated. During steady‐state plasma source operation, a discharge current as high as 180 A was obtained with this tapered cathode.

ISSN:0034-6748    

DOI:10.1063/1.1139998

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A receiving system for a Thomson scattering experiment is described. This system includes a multichannel grating spectrometer designed for use with a high repetition rate Nd:YAG laser. Fiber‐optic coupling bundles are used at the input and output ends. High throughput is maintained with large‐diameter, lowf‐number grating and aspheric lenses. The detectors are high‐responsivity, temperature‐compensated avalanche photodiodes. Results of the calibration, including anti‐Stokes Raman scattering, are presented. The spectrometer is designed to operate in theTerange between 50 eV and 2 keV with a minimum electron density sensitivity of 1.6×1011cm−3.

ISSN:0034-6748    

DOI:10.1063/1.1139999

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A time‐of‐flight method for measuring electrostatic potentials in plasmas using a modulated electron beam has been developed. The beam is injected along the magnetic field in a cylindrical plasma geometry. The phase of the electron beam modulation is detected using a Rogowski loop which encircles the beam and plasma, and the phase information is in turn related to the electrostatic potential. Measurements in vacuum and in plasma have been performed.

ISSN:0034-6748    

DOI:10.1063/1.1140000

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

This paper discusses the use of a photoconductively switched radial transmission line transformer as a high‐gradient particle accelerator power system. In particular, a 1.8‐m‐radius radial line with a one‐way transit time of 10 ns was fabricated and the voltage attenuation/amplification of a radially traveling wave measured. These results are compared with numerical solutions to the radial‐wave equations using the method of characteristics. The line was operated as a step‐down transformer by driving the inner radius with a pulse generator and measuring open circuit voltage at its outer radius. The voltage attenuation of the transformer agrees fairly well with an approximate theory for short‐pulse propagation along the line (where pulse lengths are roughly one‐tenth the one‐way transit time of the line), and a more accurate computer solution using the method of characteristics has correctly predicted the voltage response of the line. These results imply that moderate voltage, short duration pulses (approximately 1 ns) can be amplified to very high voltages by uniformly driving the outside radius of this type of transmission line. The use of photoconductive switches to generate a radially converging, high‐power wave transient required for high‐gradient particle accelerators is suggested as an alternative to other methods because the switches can be synchronized to within several tens of picoseconds, and control of subsequent sections can be accomplished for relativistic systems.

ISSN:0034-6748    

DOI:10.1063/1.1140001

出版商:AIP    

年代:1988

数据来源: AIP