摘要:

A reflecting waxicon has been demonstrated to generate long, smooth, CO2laser induced breakdown plasmas in atmospheric pressure gases including nitrogen, argon, and air. A waxicon or compound axicon is a mirror consisting of two concentric cones which form aW‐shaped cross section. The protruding central cone of the waxicon also functions as an electrode for laser guided electrical discharges. In contrast to conventional mirrors, this waxicon design produces nearly uniform laser intensity in a fixed length of breakdown plasma. The length of the laser induced breakdown plasma has been measured as a function of incident laser power and agrees well with predictions of a ray tracing code.

ISSN:0034-6748    

DOI:10.1063/1.1137780

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

A novel optical velocimeter has been designed in order to measure with a high resolution electrophoretic mobility distributions of suspended particles. It uses a transmission grating on which the dark‐field image of the particles is focused. A spectral analysis of the transmitted time‐modulated light intensity allows the determination of the velocity spectrum. The principle, a description of the apparatus, and some results are given. The velocity resolution is significantly better than with the laser Doppler techniques for different reasons which are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1137781

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Saturated abosorption on a low‐pressure mixture of CO2and CH3OH inside a hot cell is used to demonstrate how the frequencies of molecular infrared transitions in near coincidence with a CO2laser emission can be obtained with sub‐Doppler resolution.

ISSN:0034-6748    

DOI:10.1063/1.1137782

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

A new design for a cylindrical spinner suitable for magic angle spinning nuclear magnetic resonance (NMR) is described. The rotor has a large sample volume (0.66 cm3) and is capable of spinning speeds from 500 Hz to 5 kHz at drive gas pressures below 50 lb/in.2. The rotor is completely supported by gas bearings. Axial positioning is provided by the rotor’s T shape, leaving the bottom surface available for a photoelectric tachometer. The coil is wrapped on a form machined into the outer surface of the stator, producing a high filling factor. Also described is an instrument which controls the spinning speed of such a rotor to ±0.6 Hz around a set speed in the range of 3–4 kHz. The rotor’s speed is determined by means of a photoelectric tachometer. The instrument then compares this measured speed to the desired value and adjusts the gas flow to the rotor to correct any difference.

ISSN:0034-6748    

DOI:10.1063/1.1137783

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

A NMR pickup coil cooled to low temperature generates virtually no noise. Advantage can be taken of this fact in the low megahertz range by proper design and, in particular, by taking the current noise sourcesinof the room‐temperature input circuitry carefully into account. A low‐noise rf line and a method to measure very smallin’s in the 10‐kHz–1‐MHz frequency range are described.

ISSN:0034-6748    

DOI:10.1063/1.1137784

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

A digital phase‐sensitive detector for a modified Bruker electron‐spin‐resonance (ESR) spectrometer, equipped with an Aspect 2000 minicomputer is described. Magnetic field modulation is derived from a clock in the computer, which makes it possible to perform the data acquisition fully synchronously with the modulation. The resulting high phase accuracy makes it possible to compress the data to a single modulation period before the Fourier transformation. Both the in‐phase and the phase‐quadrature signals (of the first or second harmonic) are recorded simultaneously. The system is so efficient that the data processing including the Fourier transformation is approximately 1000 times faster than a previously reported digital phase‐sensitive detector system for ESR [T. Watanabeetal., Appl. Spectrosc.34, 456 (1980)].

ISSN:0034-6748    

DOI:10.1063/1.1137785

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

In a vibrating sample magnetometer the signal contains a spurious component due to the ac magnetization induced in the sample as it vibrates in an imperfectly uniform dc magnetic field. In high‐conductivity and superconducting samples, the spurious signal may be larger than that due to the dc magnetization. A quantitative analysis is given, and measurements made in an uncompensated solenoid are compared with those made in a fourth‐order solenoid.

ISSN:0034-6748    

DOI:10.1063/1.1137786

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

A mass spectrometer consisting of an electric sector followed by a magnetic sector is described. The geometry is a cylindrically symmetric generalization of the Mattauch–Herzog spectrometer. With its large annular entrance aperture and a position‐sensitive detector the instrument provides a large geometric factor and 100% duty factor making it appropriate for spacecraft experiments.

ISSN:0034-6748    

DOI:10.1063/1.1137787

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

A scanning Auger microprobe (SAM) equipped with a cylindrical mirror analyzer and noncoaxial ion gun has been adapted for ion scattering spectrometry (ISS). An optimally designed movable entrance aperture limits the scattering angle, providing high mass resolution and good sensitivity. Much of the electronics of the original SAM is employed for ISS, and switching the mode of operation is easily accomplished. The critical part of the apparatus is the entrance aperture, and its design is discussed in detail.

ISSN:0034-6748    

DOI:10.1063/1.1137788

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Numerical calculations are used to determine the magnitude and directions of surface atomic displacements produced by imaging a tungsten specimen in a field ion microscope. These displacements are induced by surface forces resulting from the high electric field required for imaging in the instrument. The computations reveal that the maximum displacements occur in the brightly imaging regions of a tungsten emitter and can be as large as 0.1 nm. A color photographic technique is used to directly reveal the displacements in an actual experiment. The results of theexperiments corroborate those of the calculations.

ISSN:0034-6748    

DOI:10.1063/1.1137789

出版商:AIP    

年代:1984

数据来源: AIP