摘要:

The purpose of this article is to discuss techniques and present data related to the performance of optical probing of the thickness of thin transparent materials and of the dimensions of mechanical components to a few‐microns resolution. The experimental apparatus for high‐resolution optical probing is based on nonlinear autocorrelation of partially mode‐locked laser pulses. Using the presence of the coherent spike in the autocorrelation trace as a marker, a resolution of the order of a few microns is obtained independently of the length of the pulse. The experimental apparatus consists of a rhodamine 6G dye laser synchronously pumped by the second harmonic of a cw mode‐locked Nd:YAG laser. The picosecond pulse train is sent to an optical autocorrelator similar to that used to measure pulse duration. To show the precision and versatility of the technique, applications are presented to the measurement of the thickness of transparent materials (plastic and liquid films), and to the measurement of dimensions of mechanical components.

ISSN:0034-6748    

DOI:10.1063/1.1139718

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A microreflectometer system to detect micrometer‐sized pinholes in specularly reflecting films has been developed. A modified compact disk player serves as an autofocusing reflectometer, with a feedback‐stabilized source and a spot size on the order of 1 &mgr;m. Pinholes can be identified by the drop in signal where the reflective layer is missing. Total pinhole area in a scanned region can be determined most simply by selecting an appropriate threshold in the reflected signal (below which the presence of a pinhole is indicated), and counting the number of pixels on either side of the threshold. Additionally, changes in overall reflectance, such as those caused by the growth of a uniform oxide layer on a thin metal sample, can be detected independently of pinhole formation. This information will be of great use in studying the environmental degradation of metal and rare‐earth/transition‐metal (RE–TM) alloy films and the effectiveness of various protective overlayers.

ISSN:0034-6748    

DOI:10.1063/1.1139719

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

An ESR spectrometer operating at 250‐GHz frequency (1.22‐mm wavelength) and 9‐T magnetic field is described. The utilization of far‐infrared (FIR) technology greatly simplifies its design and performance. Good frequency and field stability are achieved by unique designs which also conveniently permit the magnetic field to be swept. The potential utility of FIR–ESR is illustrated with examples of spectra from polycrystalline and liquid samples. In the latter case the increased spectral sensitivity to motional dynamics is stressed. Several ways in which the FIR–ESR spectrometer may be improved are also discussed.

ISSN:0034-6748    

DOI:10.1063/1.1139720

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

An electron‐paramagnetic‐resonance (EPR) reference‐arm microwave bridge is described that incorporates a FET microwave amplifier and a balanced quadrature mixer. An automatic frequency control (AFC) circuit is described that employs 70‐kHz frequency modulation of the oscillator. AFC feedback is based on formation of the sum of squares of theIandQoutputs of the mixer usinganalogdevices. The resulting AFC circuit is independent of the phase angle &agr; of the reference‐arm microwave voltage with respect to the signal‐arm microwave voltage at the mixer. AnL‐band bridge is described that incorporates the circuit. Good AFC lock was obtained from 1 &mgr;W to 100 mW of incident power independent of &agr; using a loop‐gap resonator ofQ=500.

ISSN:0034-6748    

DOI:10.1063/1.1139721

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Design principles and initial results are presented for a magnetic bottle electron spectrometer of high collection efficiency (2&pgr; sr) and good energy resolution. The instrument duplicates the carefully shaped axially decreasing magnetic field configuration of Kruit and Read [J. Phys. E16, 313 (1983)], but replaces the high‐field electromagnet central to the Kruit–Read design with two simple pole pieces energized by permanent magnets. The use of permanent magnets requires modifications of the transition region (between the high‐field electron production zone and the low‐field drift tube analyzer) to avoid axial field reversals associated with fringing fields.

ISSN:0034-6748    

DOI:10.1063/1.1139722

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A system to determine the density and temperature of ground‐state hydrogen atoms in a hydrogen plasma by measurement of the absorption of Lyman‐beta or Lyman‐gamma radiation is described. The Lyman‐series radiation is generated by resonant four‐wave sum‐frequency mixing in mercury vapor. A wide range of hydrogen atom densities can be measured by employing these two transitions. A sample measurement on a H−ion‐source discharge is presented. Extensions to Lyman‐alpha and other vacuum‐ultraviolet wavelengths are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1139723

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Three designs for negative‐ion plasma sources are described. Two sources utilize metal hexafluorides such as SF6and WF6to scavenge electrons from electron‐ion plasmas and the third relies upon surface ionization of alkali halide salts on heated alumina and zirconia. SF6introduced into electron‐ion plasmas yielded negative‐ion plasma densities of 1010cm−3with low residual electron densities, (ne/ni∼0.01–0.05). On alumina, plasma densities of 5×109cm−3were obtained for CsCl, CsI, and KI and 109cm−3for KCl. On zirconia 1010cm−3densities were obtained for CsCl. For alkali halide sources, electron densities ofne/ni≲10−4have been achieved.

ISSN:0034-6748    

DOI:10.1063/1.1139671

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A mass spectrometer which can be used to measure relative ion concentrations in a multi‐ion component plasma has been designed for use in a strong (1–4‐kG) uniform magnetic field. The spectrometer features an acceleration region which accelerates thermal ions through a series of three tantalum electrodes at a 30° angle to theBfield, and a collection region in which ions are selectively collected, depending on the size of their gyroradii, by a cylindrical collector. Relative ion concentrations are determined from measurements of the collector current as a function of accelerating voltage. Results obtained using this instrument in aQ‐machine device operated with a two‐ion (Cs+/K+) component plasma are presented.

ISSN:0034-6748    

DOI:10.1063/1.1139672

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The absolute x‐ray response of 18 EG&G Ortec partially depleted silicon surface‐barrier diodes (SBDs) has been measured at 8 and 17.5 keV. In addition we have examined the x‐ray response of four Tennelec and two United Detector Technology partially depleted SBDs. The variation in response to 8 keV x rays, for which the optical depth is about 5, is comparatively slight (≲12%). The variation in response to 17.5‐keV x rays, for which the optical depth is only ∼0.7, is comparatively large (∼100%). These variations are mainly attributable to differences in the SBD physical thicknesses, and thus to differences in optical depth. At both 8 and 17.5 keV the diodes respond linearly to large variations in incident flux (over three orders of magnitude). This linearity, and the diode x‐ray response, in general, is insensitive to large changes in the detector bias voltage; thus the depletion depth, proportional to the square root of the bias voltage, does not play a critical role in determining the x‐ray sensitive depth.Itisimportanttoemphasizethatthisfindingiscontrarytothecommonlyheldbeliefthatthex‐raysensitivedepthisequivalenttothedepletiondepth. In addition, this result has a direct bearing on both SBD andp‐i‐ndetectors intended for fully depleted operation, but used in an underbiased mode such that they are actually partially depleted. We conclude that SBDs have attractive features for quantitatively measuring x radiation from high‐intensity sources for whichh&ngr;≳10 keV.

ISSN:0034-6748    

DOI:10.1063/1.1139673

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A very‐high‐sensitivity magnetometer is described in detail. The sensitivity of the apparatus is typically of the order of 10−9A cm2/(Hz)1/2, so that changes in magnetic moment of 10−10A cm2can be detected. The magnetic moment can be calculated by simulation of the measurement system. An example of a hysteresis loop is shown. The size of the sample is determined by electron microscopy. The physical limits of the measurement system are worked out and discussed.

ISSN:0034-6748    

DOI:10.1063/1.1139674

出版商:AIP    

年代:1988

数据来源: AIP