摘要:

Design, construction, methods of measurement, and uses of high‐resolution capacitive pressure gauges in low temperature applications are reviewed. Pressure gauges for use from 10−3to over 107Pa, with a resolution of as high as 1×10−8are described. Many uses that have been made of these gauges are mentioned with emphasis on3He melting pressure thermometry.

ISSN:0034-6748    

DOI:10.1063/1.1144184

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A feedback loop using an optoelectronic system has been tested successfully for the stabilization of the output energy at the fourth‐harmonic frequency of a Nd‐YAG laser (266 nm). The system presented includes an optical device to monitor the laser output energy at the nonconverted wavelengths and an electronic circuitry to optimize the laser output energy at the fourth‐harmonic frequency. This optimization is achieved by the real‐time correction of the frequency quadrupling laser crystal angle with respect to the input beam, using a stepping motor oscillating around the optimum crystal position. Results show that the present system provides a laser output energy stability better than ±15% for a long‐term operation at the fourth‐harmonic frequency, and keeps the locking even during the warming phase, immediately after the laser turning on. This system was designed for automatic LIDAR operations in field experiments, but its principle of operation can also be applied to any type of harmonic generator for either solid‐state or dye laser.

ISSN:0034-6748    

DOI:10.1063/1.1144185

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

An instrument, based on the principle of microscopic measurements using transient reflecting gratings, has been built for investigation of modified metallic surfaces. After holographic illumination of focused light pulses of short duration, dynamic processes are observed by detecting the reflecting diffraction of the synchronously delayed probe pulse, while the sample is two‐dimensionally scanned. Distribution imaging and relaxation time (or diffusivity) imaging are demonstrated for ion‐implanted silicon wafers.

ISSN:0034-6748    

DOI:10.1063/1.1144186

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A traditional Mach Zehnder interferometer has been fitted with a feedback loop that maintains a constant and known phase difference between the two optical beams. This stabilization is necessary so that signal averaging will not distort the signal. To increase sensitivity for small phase shifts and determine absolute phase shifts when large phase shifts are involved a dual beam technique, which uses circularly polarized monochromatic light, is implemented. In one arm of the interferometer a phase shift of 90° between the two polarization orientations is introduced via a quarter wave plate. Two photodiodes independently detect the polarized light beams that maintain a 90° phase difference. One of these signals provides the input for the stabilization while the other (with enhanced sensitivity) is used to monitor the density. Unambiguous phase shifts are calculated from the information contained in both signals. The interferometer is being used to monitor gas density changes resulting from vibrational to translational energy transfer.

ISSN:0034-6748    

DOI:10.1063/1.1144187

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A simple and inexpensive system is reported for a whispering‐gallery‐mode (WGM) laser using a dye‐doped solid small sphere. A WGM laser is pumped by a compact transversely excited atmospheric (TEA) UV N2laser. Experiments using the inexpensive system and some features in the WGM laser are demonstrated.

ISSN:0034-6748    

DOI:10.1063/1.1144188

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

An apparatus has been developed to measure the shape of the liquid‐liquid interface of a phase‐separated binary mixture after a temperature quench. The working principle of the apparatus is to measure the shape of the interface by using the reflection of a scanning light beam to find out the slope of the interface at various positions, and then the shape of the interface is obtained by a numerical integration. A real‐time display sensitive to the shape of the interface is also provided to facilitate alignment of the optics. Results from calibrations show that a vertical resolution of 1 &mgr;m over a horizontal distance of 5 cm can easily be attained.

ISSN:0034-6748    

DOI:10.1063/1.1144189

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

In most optical methods proposed for imaging an absorbing object embedded in a turbid medium, data are collected using a single source and detector scanned mechanically across the surface of the medium. In our setup, we exploiteddestructiveinterferenceof diffusive photon density waves originating from two sources to localize an absorbing (or fluorescent) body in a scattering medium. A frequency‐domain instrumentation is described that scans several laser‐beam spots across the surface of a turbid medium using 1D (or 2D) acousto‐optical deflectors. An additional acousto‐optic deflector is used to establish arbitrary phase shifts for the interfering photon‐density waves. A destructive interference pattern was created to laterally localize an absorbing (or fluorescent) body in the reflection and transmission modes. In some experiments the destructive interference pattern was altered by modulating the individual beam intensities to improve sensitivity and ameliorate surface texture problems. The experimental results were retrieved from a gated intensified CCD camera at 246 MHz modulation frequency. Results indicate that less than a 1 mm displacement of a small object embedded 10 mm in a medium with optical characteristics similar to bloodless skin tissue can be detected.

ISSN:0034-6748    

DOI:10.1063/1.1144190

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Ultrasensitive detection of molecular hydrogen is reported by using Doppler‐free (2+1) resonance‐enhanced multiphoton ionization through theE,F 1&Sgr;+gstate. By using an arrangement with two near‐transform‐limited counterpropagating laser beams, a single‐shot detection efficiency of 6.8×103molecules/cm3has been demonstrated. Frequency scans of the two‐photon transitions show that the detection efficiency is limited by ac Stark effects.

ISSN:0034-6748    

DOI:10.1063/1.1144191

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

An improved spectrometer design for photoelectron yield spectroscopy is described. Basis of the new spectrometer is a computer‐designed electron optics that images the emission spot into the electron multiplier and thereby improves the sensitivity for electrons emitted from the sample. The collection efficiency was experimentally determined to 98.3%. A background of stray electrons which limits the ultimate sensitivity of the method could be substantially reduced by minimizing multiple beam reflections and by coating critical surfaces with a high work function material such as platinum. As a result, photoyield spectra of Au with a dynamical range of ten orders of magnitude are routinely obtained.

ISSN:0034-6748    

DOI:10.1063/1.1144192

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A new Wien filter has been designed for electron spectroscopic imaging. The shape of the electrodes and the magnetic pole pieces of the filter has fourfold symmetry and therefore the Wien condition giving a straight optical axis is satisfied even in the fringing field region. The second‐order aberration coefficients of the filter are formulated in a simple form. The filter is applied to a spectroscopic low‐energy reflection electron microscope in a retarding condition. The optics of the image‐forming lens system is analyzed using the transfer matrix method. The achromatic focus is achieved when the distances of the objective plane and the imaginary image plane to the filter are equal. A condition for obtaining the image free from second‐order aberrations is found. The total magnification of the instrument is 3000–14000 times; energy resolution of 2 eV is attained for an initial beam divergence angle of 10 mrad.

ISSN:0034-6748    

DOI:10.1063/1.1144193

出版商:AIP    

年代:1993

数据来源: AIP