摘要:

Measurements of spectral wavelengths in Bragg diffraction from crystals often require refractive index corrections to allow a detailed comparison of experiment with theory. These corrections are typically 100–300 ppm in the x‐ray regime, and simple estimates may sometimes be accurate to 5% or better. The inadequacies of these estimates are discussed. Even with a possibly improved index of refraction estimate, this correction is insufficient since additional systematics in the diffraction process occur at or above this level. For example, asymmetries of diffraction profiles with &pgr;‐polarized radiation or due to three‐beam diffraction can approach the magnitude of refractive index corrections for flat or curved crystals. The depth of penetration of the x‐ray field inside curved crystals, the shift of the mean angle to the diffracting planes, and lateral shifts around the crystal surface are rarely considered but can dominate over refractive index corrections, particularly for high‐order diffraction or medium‐energy x rays. Shifts and nonlinearities arise when diffracting surfaces lie off the Rowland circle, and exhibit strong and rapidly varying angular dependencies. Johann geometries with the source located on the Rowland circle should be avoided to minimize profile truncation shifts from crystal ranges or minimum grazing angles, and to avoid extreme scaling corrections. Other significant shifts are identified and illustrated, with functional relations provided to allow an estimation of related magnitudes. The central concerns of this paper are the effects on flat crystal diffraction and curved crystal diffraction in the Johann geometry, with a source and crystal of variable dimensions and location. Experiments often interpolate or extrapolate from calibration lines, so dependencies upon the diffracting angle are as important as the magnitude of the corrections. These dependencies are presented in formulas and graphs. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146428

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Perfect crystals in transmission (Laue) geometry can be used effectively for x‐ray monochromators, and moreover, perfect Laue crystals show an interesting focusing effect when the incident beam is white and divergent. This focusing is directly dependent on the incident beam divergence and on the diffraction profile width of the crystal. The aim of this work is to study whether this property can be used for focusing a synchrotron x‐ray beam, and to obtain quantitatively the dimensions of the resulting monochromatic beam. We have experimentally measured the size of an undulator beam after diffraction from a diamond crystal in Laue geometry, and we analyze and explain the results by comparison with ray‐tracing simulations. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146141

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The results of the measurements of spectral and angular distribution of the U5.0 (5 cm period) and U8.0 (8 cm period) Advanced Light Source (ALS) undulators are described. The spectra of on‐axis undulator radiation were measured for various values of the deflection parameterK. In particular, the highKcase was studied, representing the region between the undulator and wiggler limits. Good agreement in harmonic peak flux and width is found between the measurements and the computations that include the real magnetic field, the electron beam energy spread, and the electron beam emittance. The effect of the undulator taper on the spectral characteristics of the radiation was analyzed. At small taper (∼0.5% gap variation) significant reduction in peak brightness and flux of the fifth harmonic was observed with small effect on the fundamental. The near field effect in the undulator radiation was studied by measuring the off‐axis spectral and angular distributions of the radiation. The broadening and the fine structure in the distributions at large off‐axis angles were observed, resulting from the near field effect. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146142

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A 5 kHz high repetition rate excimer laser has been developed. An average laser power of 0.56 kW at 5 kHz operation, which remains stable for 1 s, is obtained. This duty time is limited only by overheating of the switching thyratrons. The 5 kHz operation is attained by some improvements to the gas conditions, the UV‐preionization scheme, and the gas flow speed in the discharge region. The gas is circulated at an effective flow velocity of 137 m/s by a newly developed two‐stage axial blower. The gas conditions are optimized experimentally to achieve 5 kHz operation. To obtain uniform preionization, the locations of pin electrodes for the preionization are determined on the basis of numerical results. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146143

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We report a new feedback system for reducing timing jitter between optical pulses from two synchronously pumped mode‐locked lasers (SPL1 and 2) pumped by common pulses from a mode‐locked laser. The beam from SPL1 is divided into two parts, and one of which is optically delayed from the other. Both of these parts are mixed with the beam from SPL2 to generate two sum‐frequency beams. The intensity difference between the two sum‐frequency beams serves as a measure of the relative timing of pulses from the two lasers. This intensity difference is used as an error signal for the feedback loop. Timing jitter between pulses from SPL1 and SPL2 having an autocorrelation function with a full‐width at half‐maximum of ≊3 ps was reduced from ≊7 ps (feedback off) to less than 3 ps (feedback on). ©1995 American Institute of Physics. 

ISSN:0034-6748    

DOI:10.1063/1.1146144

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The objective of the present study was the development of a new calibration standard for the laser‐Doppler perfusion monitors. The beat frequency spectrum obtained from a solution of latex spheres undergoing Brownian motion was compared to that obtained from a porous polyethylene material containing the same solution. The mixture of static and dynamic scattering events in the latter case was expected to produce a spectrum similar to that obtained in the real human tissue. The results obtained demonstrate clearly the difference between the signals recorded from the commonly used motility standard which are the result of multiple Doppler shifting and homodyne mixing, and those generated from our enhanced model which predominantly result from single Doppler shifting and heterodyne mixing. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146145

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A system for the automatic acquisition and recording of images from video input scenes to a volume holographic optical memory has been designed and constructed. This memory is intended for use as a template database for reference images for an optical correlator. The system has been tested and commissioned; initial results indicate that system parameters such as hologram reconstruction quality are of a sufficiently high standard for the application. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146146

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

This article describes a new double beam spectrophotometer specially conceived for optical absorption measurements on low‐absorbing microsamples. The available long‐working distance makes this apparatus attractive for use on samples placed in special environments such as heating stages, biological cells, and particularly hydrostatic pressure cells. Its performance has been tested in optical absorption measurements for different Mn2+and Cu2+complexes. We applied the instrument for investigating the electronic spectrum of Cu2+doped (CH3CH2NH3)2CdCl4crystals under hydrostatic pressure using a Sapphire anvil cell. A salient feature of this work is the enormousredshift(1400 cm−1) experienced by the first Cl−→Cu2+charge transfer band at 26 kbar. We briefly comment on the origin of this shift. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146147

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

An optical analyzer has been conceived to achieve outdoor pollution imagery. The experimental apparatus associates an interferometric correlator with a linear charge‐coupled device (CCD) image sensor and a data acquisition unit for PC‐compatible computers. This paper presents the principle of measurement and describes the optical head and the main parts of the acquisition unit. A laboratory experiment of SO2gas imagery is presented, proving the feasibility of our method; results and performance are reported. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146148

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We report the use of infrared spectroscopy to unambiguously identify the gaseous reaction products evolved during the course of a surface reaction under ultrahigh vacuum conditions. The apparatus consists of two independent, liquid‐nitrogen‐cooled samples; one is used to trap the gaseous products generated by reaction on the surface of interest. The trapped products are subsequently identified using surface infrared spectroscopy. We demonstrate the utility of this product trapping infrared reflection absorption spectroscopy technique, for the separation of isomers of butene, which are indistinguishable using conventional mass spectrometry, as well as the identification of radical species, such as ⋅CH3, which are important in diamond growth. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146149

出版商:AIP    

年代:1995

数据来源: AIP