摘要:

Pulsed transverse electric (TE) glow discharges used to produce population inversions in gas lasers at 1–20 atm require high‐speed, high‐voltage, high‐current capacitor banks. In this article we first review and compare the circuits in common use to produce the required fast, self‐sustained glow discharges in CO2, excimer, and N2lasers. The parameters and circuit types given will be useful to future designers of pulsed gas lasers to design and to optimize any proposed circuit in order to yield any desired operating conditions and parameters. Then‐stage circuit types presented are capacitor‐transfer (C‐C),L‐Cinversion, Marx bank, and fourfoldL‐Cinversion, with their double‐sided counterparts, and also their transmission‐line counterparts, such as the Blumlein circuit. A one‐parameter differential equation is developed which describes the general seriesC‐L‐Rcircuit. Electrical pulses measured on various lasers are compared with the differential equation solutions for various bank impedances and load resistances. We then present the design and measurements of a new automatically preionized, double‐sided,L‐Cinversion circuit for an 800‐mJ, TE CO2laser, and compare it to previous systems. Methods to lengthen the discharge pulse, and some novel active mode locking techniques are discussed. We compare theL‐Cinversion circuit, the fourfoldL‐Cinversion circuit, the conventional Marx bank, and the ‘‘double Marx bank’’ for lasers and other applications, such as pulsed particle accelerators. Finally, we discuss capacitor bank interconnections, electro‐optic probe systems, and various triggering methods.

ISSN:0034-6748    

DOI:10.1063/1.1144131

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Time‐of‐flight spectra for Maxwell–Boltzman (MB) distributions of antiprotons initially held in an ion trap and detected after being launched through a 50‐cm‐long shielding drift tube have been calculated. The distributions used are of temperature 0.4–40 K, cubic length 0.003–3.0 cm, and number 10–100 particles. The mutual Coulomb repulsion of the particles causes a reduction in the number of late arrival particles expected from the MB velocity distribution. The Coulomb energy is not equally divided among the particles during the expansion. The energy is transferred preferentially to the outer particles so that the reduction in the number of slow particles is not necessarily large. The reduction factor is found to be greater than unity when the potential energy of the trapped ions is greater than ∼5% of the ions’ kinetic energy and is ∼2 for the launch parameters of the Los Alamos antiproton gravity experiment.  

ISSN:0034-6748    

DOI:10.1063/1.1144132

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A tapered undulator, in which the entrance and exit magnetic gaps are different, will show an increase in the energy width of the harmonics compared to the nontapered case. This increase can occur without substantial broadening in the collimation of the undulator radiation. We present the spectral properties measured for a tapered 3.3‐cm period prototype undulator of the Advanced Photon Source at the Cornell High Energy Synchrotron Source. The width of the on‐axis first harmonic at 6.9 keV increased from 0.32 to 0.66 keV for a gap tapering of 12%. Minimal angular broadening in the first harmonic x rays was detected and measurements of off‐axis radiation were also performed. The results are found to be in good agreement with model calculations.  

ISSN:0034-6748    

DOI:10.1063/1.1144133

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A methodology is presented in order to optically characterize large, absorbing irregularly shaped particles. Two experimental systems were developed and implemented: a particle nephelometer which measures angular scattering from a single electrodynamically levitated particle at &lgr;=514.5 nm, and an integrating sphere spectrometer which measures the spectral hemispherical reflectance of particulates in the wavelength range from 450 to 1959 nm. The particulates examined were spherical carbon particles and different oil shale particles. Measurements of phase function and cross polarization on individual particles indicate an increase in back scatter with increasing particle albedo. Criteria for particle discrimination are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1144134

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A far‐infrared rotating‐analyzer ellipsometer which uses a step‐tunable, optically pumped gas laser as its light source is described herein. As polarizers novel metal grids with 10 000:1 polarization contrast were used. The instrument determines the complex dielectric function in the spectral range between 10 and 150 cm−1. A cryostat allows both reflection and transmission measurements from 10 to 330 K. Measurements of the birefringence of crystalline quartz, of both the carrier density and the scattering frequency of doped semiconductors, and of the low energy excitations of high‐TCYBaCuO ceramics are presented herein.

ISSN:0034-6748    

DOI:10.1063/1.1144135

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

In order to enhance research in the field of low‐temperature photophysics or photochemistry, a convenient multiple‐purpose spectrophotometer system was constructed. This system enabled us to measure the emission (and/or its excitation) and absorption (even under steady‐state photolysis) spectra of liquid and solid samples at a temperature ranging from 10 up to 313 K. The spectral resolutions (or the peak separations) were estimated to be ∼0.10–0.31 and ∼1.0–7.3 nm for an emission and its excitation spectra, respectively, recorded at a slit width between 0.05 and 0.5 mm. For an absorption spectrum recorded at a slit width of 0.5 mm, the resolution was still better than that recorded by a commercial spectrophotometer with a bandwidth of 0.2 nm. By recording a number of emission spectra (normalized by the excitation‐light intensities at various excitation wavelengths), a contour mapping for the simultaneous intensity representation of the emission and its excitation spectra was also possible.

ISSN:0034-6748    

DOI:10.1063/1.1144136

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

In Fourier transform ion cyclotron resonance (ICR) spectrometry until noweitherpositiveornegative ions (including electrons) could be trapped, due to the trapping potential applied. In the present article, the theory of simultaneous trapping of positive and negative ions, and the experimental realization are presented. Trajectory calculations for the ions trapped with both charge polarities are described. The new ICR cell employs a new kind of trapping electrodes, constructed with layers of grids. The simultaneous storage is illustrated by experimentals with sulfur hexafluoride.

ISSN:0034-6748    

DOI:10.1063/1.1144137

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

An easily realized inelastic electron tunneling spectrometer (IETS) controlled by computer through an IEEE‐488 interface bus is described. Components and circuits of the system are described in detail in order to help newcomers to IETS build a research quality spectrometer on a relatively low budget. The system design is much simpler and easier to implement than others reported in the literature, and experimental results indicate that the spectrometer has comparable resolution and signal‐to‐noise ratio. Additionally, in‐house software routines offer the system considerable flexibility in spectral data manipulation, for example, background correction, numerical differentiation, and subtraction of one spectrum from another may be performed.

ISSN:0034-6748    

DOI:10.1063/1.1144138

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We have calibrated the displacement/voltage (A˚/V) response of our piezoelectric scanning tube (PZT‐5A) by imaging graphite at over 40 temperatures between 4 and 300 K. We have also calibrated the (A˚/V) response as a function of voltage up to 220 V at room temperature, imaging a gold‐plated diffraction grating. We find that the temperature dependence of the (A˚/V) response is linear to within 10% and is reduced by a factor of 5.5 on decreasing temperature from 300 to 4.2 K. The near linearity with temperature of the (A˚/V) response makes the PZT‐5A lead zirconate titanate composition a convenient choice for low temperature scanning tunneling microscope piezo tube elements.

ISSN:0034-6748    

DOI:10.1063/1.1144139

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

An improved and reliable method for making sharp scanning tunneling microscopy (STM) tips is described. It is based on the widely used drop‐off electrochemical etching procedure, here modified to improve the control of the tip shape. A second etching is applied not only to remove the oxide layer from the tip surface, but also to sharpen the STM tips further. A tip radius less than 20 nm can be obtained reproducibly. The quality of the produced tips was inspected with transmission electron microscopy, and micrographs of tips produced with different times of second etching are shown. To produce tips which are all without an oxide layer an electronic phase control unit is necessary. Even without this etch controller more than half the tips are oxide free, and then only standard laboratory equipment is used for the tip production.

ISSN:0034-6748    

DOI:10.1063/1.1144140

出版商:AIP    

年代:1993

数据来源: AIP