摘要:

Electron polarimeters based on Mott scattering are extensively used in atomic and molecular, solid state, nuclear, and high‐energy physics. This use stems from the increasing realization that much additional information concerning many physical processes can be obtained through spin‐dependent measurements. In this review we discuss the basic physics and application of Mott polarimetry. A number of different Mott polarimeter designs are described that illustrate the wide range of operating energies (10 eV–1 MeV) and geometries that can be used in such instruments. The calibration of Mott polarimeters is discussed together with the potential sources of systematic error that can arise and that can limit measurement accuracies. The aim is to present a comprehensive practical guide to Mott polarimetry and the capabilities of the technique.

ISSN:0034-6748    

DOI:10.1063/1.1143371

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The design, construction, and operation of a high‐resolution electron‐energy‐loss spectrometer featuring a position‐sensitive resistive anode detector and differential pumping are described. The position‐sensitive detector provides a 66‐fold increase in acquisition speed over a single‐channel spectrometer. The differential pumping provides pressure isolation of 105between the spectrometer elements, except the lenses, and the sample region. An optically isolated multicomputer‐based control and data acquisition system provides complete spectrometer control and automated sample cleaning and characterization. The spectrometer, together with a differentially pumped supersonic molecular beamline, permitsinsitumeasurements of the interaction of a wide range of gas molecules with solid surfaces.  

ISSN:0034-6748    

DOI:10.1063/1.1143320

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We report measurements of the ratio of the perpendicular velocity to the parallel velocity, &agr;=v⊥ /v∥, of a relativistic electron beam gyrating in a magnetic field by the use of (1) Cerenkov emission from a glass plate, detected by a gated microchannel plate image intensifier camera, and (2) electron‐beam‐induced radiation darkening pattern on the same glass plate. The measurements are based on a direct determination of the Larmor radius of an electron beam of known energy. Experiments were performed on a long‐pulse electron beam accelerator withe‐beam diode parameters:VD= 0.6–0.9 MV, pulse length=0.5–1 &mgr;s,ID= 1–10 kA. The experimental value of &agr; agrees with simulation results from particle trajectory codes as well as theoretical predictions from Busch’s theorem and adiabatic theory.

ISSN:0034-6748    

DOI:10.1063/1.1143321

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The combination of a custom‐made scanning tunneling microscope with a commercial molecular‐beam‐epitaxy (MBE) system for 3‐in. wafers is reported. The design of the microscope allows the exchange of the tip and piezo scanning unit in ultrahigh vacuum, thus offering the possibility to apply various local probe techniques with the same instrument. The tip can be cleaned by baking and by Ar+‐ion sputtering. Good thermal stability and stiffness of the microscope is obtained by a lever‐type design using two similar parallel piezo tubes for the scanner and for a mechanical contact close to the tip, respectively. A two‐stage spring vibration isolation with internal viscous damping is used to achieve good mechanical stability for atomic‐scale resolution without any further vibration isolation of the MBE system.

ISSN:0034-6748    

DOI:10.1063/1.1143322

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

This paper presents the calibration of piezoelectrically actuated capacitance micrometers for use as a transfer standard of nanometer level precision using x‐ray interferometry. Because of the interferometer’s extreme sensitivity to twisting moments, there is a pressing need for high‐quality transfer systems to widen its range of applicability. Two promising candidates for this are piezoelectric actuators controlled by internal capacitive sensors and parallel‐plate capacitive micrometry. Both are investigated to determine useful precision for the discrimination and traceability over the range 1–20 nm. It is shown that systems of high mechanical stability can readily be produced. They offer at the very worst traceable accuracy of a few tenths of a nanometer, with, in the case of the gauge, a wide bandwidth of greater than 1 kHz. It is argued that existing technologies can provide calibrators working at relatively rapid speeds with uncertainties better than around 20 pm over usefully large ranges, presently 15 &mgr;m.

ISSN:0034-6748    

DOI:10.1063/1.1143323

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We have developed a method for determining metal‐atom number‐density integrated over a line‐of‐sight (i.e., the column density) by measuring the optical depth in the wings of the pressure‐broadened resonance lines. This method is capable of monitoring the column densityinsituduring photoelectric absorption measurement of metal vapors in a synchrotron radiation beamline. The present method requires measuring the reduced absorption coefficients of the metal–metal and metal–buffer‐gas collisional quasimolecules &ggr;MMand &ggr;MGand the effective vapor lengthlbefore its use. We thus describe also the procedure for obtaining &ggr;MM, &ggr;MG, andlusing He‐buffered Yb vapor as a specific example.

ISSN:0034-6748    

DOI:10.1063/1.1143324

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We demonstrate that the fidelity of a hologram is often impaired by multiple beam interference during the recording process. We describe a simple and widely adaptable procedure for eliminating such impairment, and we give a quantitative measure of the gain in fidelity that may ensue in the case of object waves recorded on silver halide emulsion atf/6.3.

ISSN:0034-6748    

DOI:10.1063/1.1143325

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The polarization phase sensor (PPS) is an optical sensor capable of measuring absolute displacements between two segments of a spherical mirror. The sensing apparatus consists of a white light polarization interferometer which forms a set of interference fringes representative of the displacement between the two segments. A detector array senses these fringes and computer software performs an analysis. The result of these calculations is a measurement of the absolute misalignment between the two segments. The sensor, in its current configuration, is capable of measuring ±30 &mgr;rad of tilt between the two segments with an accuracy of 3.29 &mgr;rad and a precision of 2.27 &mgr;rad and ±2 &mgr;m of piston between the two segments with an accuracy of 0.00516 &mgr;m, and a precision of 0.031 &mgr;m. This paper will address the optical design and operating characteristics of this sensor. A conclusion will discuss alternate modes of operation and upgrades to the instrument which will increase piston capture range.

ISSN:0034-6748    

DOI:10.1063/1.1143326

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

An electronic technique is described whereby the heterodyne mixing frequency of a pulsed LIDAR transmitter is displayed on a color‐coded linear bar graph. The technique is of great utility for manually fine tuning the laser output frequency when the use of conventional frequency counters and spectrum analyzers is impractical in a rapidly firing system.

ISSN:0034-6748    

DOI:10.1063/1.1143327

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

This work describes a stroboscopic optical boxcar technique for the determination of fluorescence lifetimes which achieves performance comparable to techniques such as time‐correlated single photon counting or phase modulation. The stroboscopic technique is based on the use of a traveling wave injected into a delay line connecting the dynodes of a photomultiplier tube. The transient potential difference created between two adjacent dynodes results simultaneously in significant amplification and the generation of a ‘‘gate’’ for the amplification process. Accurate control of the timing between the flashing of the gated lamp and the computer controlled delayable triggering of the photomultiplier tube pulser allows the gate to be placed at any time position within the range of the digital delay generator. The intensity of the fluorescence emission can thus be measured as a function of time relative to the excitation flash yielding data which is very similar to that from time‐correlated single photon counting. Data analysis is done by iterative reconvolution in a procedure very similar to the analysis of time‐correlated single photon counting data. Fluorescence lifetimes from a few hundred picoseconds to hundreds of nanoseconds can be determined to an accuracy and precision of better than ±2%.

ISSN:0034-6748    

DOI:10.1063/1.1143328

出版商:AIP    

年代:1992

数据来源: AIP