摘要:

Operation of an UV preionized pulser sustainer TEA CO2laser with a discharge volume of 45 cc is described. The laser could provide 522 mJ optical pulses of 6 &mgr;s duration (full width at half‐ maximum) with 12% efficiency for a 1:1:6 (CO2:N2:He) gas mixture at one atmospheric pressure. To the best of our knowledge, this is the maximum energy per pulse reported so far for an all solid state switched TEA CO2laser with this efficiency. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145635

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A simple, computer‐controlled high‐speed peak detector for monitoring relative energies in experiments that involve pulsed lasers, is described. In many experiments the laser pulse energy is monitored by feeding the output from a photomultiplier to the 1 M&OHgr; input of an oscilloscope having a bandwidth of about 100 MHz. The computer‐controlled peak detector described in this paper can effectively replace the oscilloscope in such cases. There is, further, an additional advantage that the data can be processed shot by shot. High speed and long hold time are achieved by using two peak detectors in tandem. The first peak detector is capable of tracking fast pulses, but has a low hold time. The second peak detector is slower than the first but has a long hold time. The peak value is held for several minutes without appreciable decay, so that several channels can also be monitored one by one manually with an ordinary volt meter. Its versatility in measuring shot‐to‐shot energy variation of laser pulses, and in real‐time pulse selection are demonstrated. Saturation characteristics of a nitrogen laser pumped dye laser has also been studied with two such peak detectors operated simultaneously. ©1995 American Institute of Physics. 

ISSN:0034-6748    

DOI:10.1063/1.1145636

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A novel wide‐band Doppler LIDAR detection technique (up to GHz range), by using two sets of digitally selected reference frequencies, is developed. It combines the advantages of two well‐known approaches—the analog quadrature detection (low sampling frequency and data rate, highly dynamic range) and the direct digitizing (fully digital controlling and processing without coherent oscillator minimum analog stages, very easy tuning) at the same accuracies as the Doppler estimates. This technique may be applied in airborne and satellite Doppler LIDARs as well as in low‐cost ground‐based systems using CO2or solid‐state laser sources. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145637

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

An integrated instrumentation which combines in the same system static and dynamic laser light scattering and time‐resolved fluorescence spectroscopy is described. The two types of measurements can be performed simultaneously on the same sample contained in a thermostated cuvette. The light scattering allows measurements of molecular weights and hydrodynamic radii in the range of 20 A˚ to a few micrometers. The overall time resolution of fluorescence measurements is around 50 ps. The system provides the simultaneous acquisition of the fluorescence decay curve, of the time integrated emission spectrum, and of two time‐gated spectra. The light‐scattering technique gives information on the global structure of the aggregates, while fluorescence measurements are sensitive to the local interactions of a fluorescence probe with the surroundings. The contemporary use of these two complementary techniques can be quite valuable mostly for biological samples for which stability and reproducibility with time can sometimes be a problem. As an example, combined measurements of the dimension of dimyristoylphosphatidylcholine vesicles around their temperature transition and of fluorescence lifetimes of the diphenylhexatriene probe incorporated in the vesicles is shown. ©1995 American Institute of Physics. 

ISSN:0034-6748    

DOI:10.1063/1.1145638

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The detector signals from a total integrated scatter (TIS) instrument, which uses a focusing Coblentz sphere, have been evaluated. Models for the calculation of correct reflectance and transmittance values for both scattering and nonscattering samples are presented. In particular, the correction for multiple reflections between sample and detector, the detector efficiency versus angle of incidence, and the symmetry properties of the Coblentz sphere have been investigated. Experimental results are compared with results obtained with an integrating sphere using a model for the correction of sphere asymmetry. The results show that the transmittance and reflectance values obtained with the TIS instrument and the integrating sphere agree only when the presented correction factors are properly taken into account. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145639

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

An automated flame coherent forward‐scattering (CFS) spectrometer with a xenon high‐pressure lamp has been constructed for fast sequential multielement analysis. To improve detection limits an on‐axis multipass mirror system is used and, in addition, the light intensity is detected by the photon counting technique. The spectrometer is operated by a menu oriented program. Computer controlled functions, interfacing, data acquisition, and handling as well as analytical modes are described. Nonlinear analytical curves are used for evaluation and for calculating the detection limits and the analytical working range. The detection limits of the analytical system are compared with those of other CFS, AAS, and AES spectrometers. Even with a continuum light source, which allows fast sequential multielement capability, the detection limits are lower than those reported for flame CFS before. Analytical results obtained for drinking water samples are compared to measurements with flame AAS. ©1995 American Institute of Physics. 

ISSN:0034-6748    

DOI:10.1063/1.1145640

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We describe an experiment that couples a high‐resolution Fourier transform spectrometer (FTS) to a supersonic jet of radicals. A 1‐mm‐i.d. cylindrical SiC nozzle is resistively heated to 1500 K in order to decompose organic precursors and generate expansions of jet‐cooled radicals. We have used this apparatus to pyrolyze alkyl nitrites to make alkoxy and nitric oxide radicals. The residence time of radicals in this hot nozzle is roughly 20 &mgr;s RONO→&Dgr;RO+NO. We use the FTS to detect the IR absorption of the product NO (&ngr;0=1876.1 cm−1) at resolutions as fine as 0.005 cm−1FWHM. We observe the product NO from the pyrolysis of CH3CH2ONO to be rotationally cooled to roughly 50 K. The IR spectra indicate that the optical path length is about 3/4 cm and that the nitrites pyrolyze to produce approximately 1014NO radicals cm−3some 9 mm downstream from the nozzle. Our spectrometer is capable of detecting an absorption signal of 0.1% over a bandwidth of 100 cm−1at 0.005 cm−1resolution. Depending on the infrared cross section of the radical, this implies that we are able to monitor diatomic radical densities of roughly 5×1012cm−3(quantum state)−1. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145641

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The design and implementation of a pressure cell for the study of hydrothermal reactions byinsituenergy dispersive x‐ray diffraction is described. The cell permits the study of both the kinetics and mechanism of formation of a wide range of important solid‐state compounds such as zeolites and other microporous solids. Reactions can be studied over a wide range of temperature (5–230 °C) and autogenous pressure [0–400 psi (gauge)] conditions. The use of this apparatus is illustrated by a study on the synthesis of a microporous tin chalcogenide phase performed on Station 9.7 of the UK Synchrotron Radiation Source. ©1995 American Institute of Physics. 

ISSN:0034-6748    

DOI:10.1063/1.1146451

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The requirements on the radiation source, the monochromator/mirror, the diffractometer, and the crystal dispersive analyzer for an optimum instrumentation dedicated to high resolution resonant inelastic scattering experiments are formulated. The possibility for the application of dispersion compensation is stressed. A provisional instrumentation at the HARWI–Compton beamline is described and test measurements of the resonant inelastic scattering cross section of Cu for incident photon energies scanning across theKthreshold and for scattered photon energies near theK&agr;1line are reported. By means of model calculation the important role of correct absorption correction of resonant inelastic scattering data is emphasized. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145642

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A novel method of Fourier transform spectroscopy of the transient signals from wide, inhomogeneously broadened magnetic resonance spectra is described and analyzed. It has the advantages of high resolution, high sensitivity, and freedom from the distortions introduced by the finite amplitude of the pulsed rf magnetic field and the finite bandwidth of the receiving system. It consists of recording the transient signal at a series of magnetic fields, shifting the frequency of the transient by the corresponding field step for each point, and summing the corresponding Fourier transformed signals. Although the primary emphasis is on pulsed NMR, the analysis also applies to pulsed ESR. Criteria for the range and step interval of the magnetic field variation are discussed. The accuracy and sensitivity of the method are compared with earlier methods of spin echo spectroscopy. A description of the corresponding measurement of NQR, NMR, and ESR spectra obtained by stepping the frequency of the spectrometer is also presented. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145643

出版商:AIP    

年代:1995

数据来源: AIP