T-ray computed tomography

We demonstrate a tomographic imaging modality that uses pulsed terahertz (THz) radiation to probe the optical properties of three-dimensional (3D) structures in the far-infrared. This THz-wave computed tomography (T-ray CT) system provides sectional images of objects in a manner analogous to conventional CT techniques such as x-ray CT. The transmitted amplitude and phase of broadband pulses of THz radiation are measured at multiple projection angles. The filtered backprojection algorithm is then used to reconstruct the target object, including both its 3D structure and its frequency-dependent far-infrared optical properties.     

Artifacts,assumptions, and ambiguity: Pitfalls in comparing experimental results to numerical simulations when studying electrical stimulation of the heart

Insidious experimental artifacts and invalid theoretical assumptions complicate the comparison of numerical predictions and observed data. Such difficulties are particularly troublesome when studying electrical stimulation of the heart. During unipolar stimulation of cardiac tissue, the artifacts include nonlinearity of membrane dyes, optical signals blocked by the stimulating electrode, averaging of optical signals with depth, lateral averaging of optical signals, limitations of the current source, and the use of excitation-contraction uncouplers. The assumptions involve electroporation, membrane models, electrode size, the perfusing bath, incorrect model parameters, the applicability of a continuum model, and tissue damage. Comparisons of theory and experiment during far-field stimulation are limited by many of these same factors, plus artifacts from plunge and epicardial recording electrodes and assumptions about the fiber angle at an insulating boundary. These pitfalls must be overcome in order to understand quantitatively how the heart responds to an electrical stimulus. (c) 2002 American Institute of Physics.     

From squeezed atom lasers to teleportation of massive articles

The development of the Raman atom laser promises to make available new techniques for accessing and manipulating the quantum statistical properties of Bose-Einstein condensates. In this work we show how, combined with the already existing methods for the manipulation of quantum states of light which are central to quantum optics, the Raman input-output coupling mechanisms potentially enable the production of quadrature squeezed and sub-Poissonian atomic beams, and entanglement between atomic and optical fields. We also propose a method of measuring the quantum statistics of the atomic beam by transferring them to an optical field. Finally, by combning these techniques, we propose a method of teleporting the atom laser beam from one trapped condensate to another.     

On the topological charge concentrated at a point

For SU(2) gauge fields over the 4-dimensional sphere with a finite number of points x₁, x₂, ..., and x_N removed, there are gauge transformations which modify the topological charge concentrated at x_j by adding n_j, where n₁, n₂, …, and n_N. are integers such that Σ^N_{j = 1}n_j = 0. However, the reduction modulo Z of the topological charge at a point is well defined, being given in terms of the secondary characteristic classes of Chern and Simons, except when the topological charge is indeterminate.     

Single axial mode pumping and external mirror operation of a pulsed spin-flip Raman laser at 10.6 μm

By the addition of an external cavity to a single axial mode, TEA CO₂ laser pumped, In Sb spin-flip Raman laser, a tenfold increase in first Stokes output and a twenty-five fold increase in second Stokes and anti-Stokes outputs has been observed.     

Amplification of picosecond dye laser pulses

Small signal and saturated gains of picosecond pulses in Rhodamine dye amplifiers have been measured. A 17 cm amplifier produces a maximum small signal gain of ≈20, and with three amplifiers in series, peak pulse powers of > 3 GW are obtained. Mode-locking of Rhodamine 6G in the spectral range 575–600 nm is improved by employing DQOCI as saturable absorber.     

The effects of site selected variables on human responses to traffic noise,part III: Community size by socio-economic status by traffic noise level

This paper reports the results of the third part of a field study of human responses to traffic noise. The influence of traffic noise level, community size, and socio-economic status were investigated in a controlled manner determined by subject selection procedures. Human responses were obtained from interviewer administered questionnaires, and were as spatially and temporally coincident with the noise measurements as possible. Noise measurements were obtained from several days of rapidly sampled digital recordings. Traffic noise level was the major predictor of the intensity of elicited responses. A number of other significant effects were observed largely related to community size. These were explained as due to parallel variations in the perceived necessity of vehicles, the annoyance with aircraft noise, and the logarithm of the vehicle flow rate. The results did demonstrate effects related to community size, and thus it is unwise to extrapolate the results of large city noise studies to small communities and rural areas.     

Megawatt VUV xenon laser employing coaxial electron-beam excitation

3 nsec laser pulses, of bandwidth 1.3 nm, are obtained from a 10 J, 600 keV coaxial diode electron-beam pumping arrangement. Uniform pumping, with a well defined cylindrical geometry, facilitates experimental investigation of the laser parameters. Gas heating limits the laser repetition rate. While mirror damage at present limits the peak power to ∽ 1 MW, higher powers seem available. The addition of helium results in a drastic reduction of peak molecular xenon fluorescence.     

Passive mode-locking of flashlamp pumped Rhodamine dye-lasers

A simple dye-laser system is described in which Rhodamine dyes are pumped by a co-axial linear air flashlamp in a cylindrical elliptical pumping reflector. Output pulses lasting up to 1.5sec and containing up to 250 mJ energy, have been successfully mode-locked to produce 100% modulated pulse trains. Employing a diffraction grating as cavity reflector to tune the laser frequency, in each case, for maximum absorption by the same Q-switching dye, successful mode-locking has been achieved with both Rhodamine B and Rhodamine 6G. Time resolved emission spectra have been recorded with an image tube streak camera and the effect of resonant reflectors has been studied.This work was described in a paper presented at the IEEE Conference on Laser Engineering and Applications, Washington, May 1969.