摘要:

Analog and digital technologies are presented for precise measurement of propagation delay of photons from source and detector placed on portions of the human body. The goal of the apparatus design is to quantify absorption(&mgr;a)and scattering(&mgr;s′)induced by biological pigments and biological structures, respectively. Body tissues are highly scattering with a mean distance between scatterers of less than a mm (at 700–850 nm). Significant absorption is mainly due to 5&percent;–10&percent; of the tissue volume occupied by blood. Measurement of&mgr;aand&mgr;s′is done by both time and frequency domain equipment. This article focuses upon frequency domain equipment because of its simplicity, reduced noise bandwidth, versatility, and the strong analogy to very high frequency/ultrahigh frequency communication devices, particularly those using phase modulation. Comparisons are made of homodyne and heterodyne systems together with evaluation of single and multiple side band systems, with particular emphasis on methods for multiplexed optical and radio frequencies by frequency encoding or time-sharing technologies. The applications of these phase modulation systems to quantitative brain and muscle blood oximetry, functional activity of the forebrain, and other important problems of medical science, are presented. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1149123

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A continuous-angle laser light scattering instrument has been developed that consists of an ellipsoidal mirror and a charge-coupled device detector. Continuous and simultaneous measurement for angular dependence of scattered intensity is achieved over the wide scattering angle with high angular resolution. Data acquisition by the instrument is quite rapid compared to conventional light scattering instruments and it takes less than 1 s in most cases. Characteristics of this instrument are evaluated and static light scattering data for linear polystyrene are presented. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1149124

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Most of the detectors commonly used for radiometric measurements have a more or less poor cosine response. By means of a reflective entrance optics in front of the detection system, we have reduced relative cosine errors below 5&percent; up to zenith angles of 75°. Cosine correction is performed by a roughened polytetrafluoroethylene (PTFE) plate which diffusely reflects parts of the incident radiation into a light guide with the detector at its end. It provides for a neglectible wavelength cosine error dependence and a significantly better radiant efficiency. Originally designed for irradiance measurements of solar global radiation and its photobiological effective irradiance, the entrance optics may also be used for determination of radiant flux from lamps by integrating the lamp irradiance over an enveloping surface as it is done in spectrogoniometric measurements. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1149125

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A procedure for making spatially resolved, Stokes vector image maps of polarized light is described. The imaging system consists of a circular polarizer and a charge coupled device (CCD) camera. A series of four images are captured and the polarization maps are computed and displayed using MATLAB software. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1149126

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Using a detailed ray-tracing code for capillary optics, interpretation is given for parallel bore hole and tapered capillary generated far-field images. These images can be used to indicate the presence of various types of surface imperfections (i.e., surface roughness or waviness) or shape distortions of the optical device. The capillary output patterns were recorded at the optical beam line of the European Synchrotron Radiation Facility by using a monochromatic, highly parallel incident synchrotron beam. Capillaries of various dimensions were studied, with inlet diameters in the range of 30–70 &mgr;m, outlet diameters of 22–42 &mgr;m, and capillary length values ranging from 10 to 23 cm. The far-field images were taken at a distance of 10–11 cm from the capillary exit using a high resolution charge coupled device camera. By comparisons of simulated and experimental capillary output patterns, the effects of surface roughness/waviness, as well as axial distortions are studied with respect to the angular distribution of the generated capillary beam. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1149127

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The University of New Mexico/Sandia National Laboratories small-angle scattering laboratory provides a wideq-range,3×10−4 Å−1<q<0.7 Å−1,for the structural analysis of materials on length scales from a few angstrom to ∼0.1 &mgr;m. The wideq-range is accomplished by combining data from a Bonse-Hart spectrometer(3×10−4 Å−1<q<3×10−2 Å−1)and a 5 m pinhole(3×10−3 Å−1<q<0.7 Å−1)instrument. Automation of the data acquisition systems along with a variety of sample environments and sample changers yields flexible, high throughput instruments. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1149128

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

In this article, the important physical parameters which affect the electron current and energy in electron cyclotron resonance x-ray source are discussed. The electron trajectory in an empty cylindrical cavity (TE111mode), magnetized with dc magnetic field is plotted for the electrons with and without the initial velocity. Magnetic field tapering effect on the electron acceleration and the maximum attainable energy of the electron is studied. The advantages of waveguide coupling over the coaxial coupling for exciting theTE111mode of the cavity are discussed. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1149129

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

In view of time correlated photon-counting experiments using wavelengths at the red end of the electromagnetic spectrum, we developed a simple electronic circuit for periodical gated quenching of silicon avalanche photodiodes. We compare the performance of this device with commercially available passive and active quenching modules and a reference photomultiplier. The detection system’s nonlinearities, i.e., dead time and afterpulsing, lead to direct and indirect distortions of photocount correlation functions. We characterize this nonlinear behavior by measuring intensity auto- and cross-correlation functions and supply nonlinearity parameters for each of the four detection systems. In addition, transfer functions are given which allow an estimate for the highest count rates accessible for each detection system. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1149130

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A new spectrometer for the coincidence study of(e,2e)single ionization, ande,(3-1)eor(e,3e)double ionization by electron impact is described. The system is based on two double toroidal analyzers for the ejected electrons and a cylindrical electrostatic analyzer for the scattered electrons. It allows angular and energy distributions of the ejected electrons to be measured over almost the totality of the collision plane, using dual two-dimensional position sensitive detectors. The design and operation of the spectrometer is described with a special emphasis on the imaging properties of the system. The performance (energy and angular resolutions,&ellip;) and the calibration of the spectrometer are discussed and sample results for(e,2e),e,(3-1)eand(e,3e)experiments on the rare gases are presented. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1149131

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Two modifications of the interdigital accelerating H structure forming the basis for upgrading both the main and prestripper sections of the Kharkov multicharged ion linac (MILAC) are described. Possible application of this type of structure to heavy ion accelerator is discussed. It is shown that the use of the interdigital H structure in this particular case has enabled three major problems to be solved, namely: (i) to increase the operating wavelength from 2.1 m of the previously used Alvarez structure up to 6.3 m, (ii) to double the acceleration rate, and (iii) to increase the shunt impedance by 2–4 times. New methods and designs are described for tuning the cavities at an operating frequency and transforming the sinusoidal field distribution, peculiar to the H mode, into the homogeneously distributed field along the structure axis, with varying period lengths. Characteristics of the MILAC main and prestripper sections are given. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1149132

出版商:AIP    

年代:1998

数据来源: AIP