Biomedical subjects

Edward S Fry

Publications and source records attributed to Edward S Fry.

5 recordsLinked to original sources

PubMed2006

Integrating cavities: temporal response.

The temporal response of an integrating cavity is examined and compared with the results of a Monte Carlo analysis. An important parameter in the temporal response is the average distance d between successive reflections at the cavity wall; d was calculated for several specific cavity designs--spherical shell, cube, right circular cylinder, irregular tetrahedron, and prism; however, only the calculation for the spherical shell and the right circular cylinder will be presented. A completely general formulation of d for arbitrary cavity shapes is then derived, d =4V/S where V is the volume of the cavity, and S is the surface area of the cavity. Finally, we consider an arbitrary cavity shape for which each flat face is tangent to a single inscribed sphere of diameter D (a curved surface is considered to be an infinite number of flat surfaces). We will prove that for such a cavity d =2D/3, exactly the same as d for the inscribed sphere.

Journal Article↗

PubMed2006

Design and analysis of a flow-through integrating cavity absorption meter.

We present a design for a flow-through integrating cavity absorption meter. This instrument, in principle, is capable of measuring the spectral optical absorption coefficient of natural waters in situ independently of scattering effects. Monte Carlo simulations are used to determine the design parameters and evaluate instrument performance. We investigate both detector response and the distribution of radiant energy inside the instrument and present empirical equations describing these quantities as a function of the absorption coefficient. The effects of changing the instrument geometry are illustrated. Finally, we discuss the effects of scattering on the instrument performance and verify that they are negligible for natural waters.

Journal Article↗

PubMed2006

Narrow-linewidth, multi-Watt Yb-doped fiber amplifier at 1014.8 nm.

We report on an efficient, narrow linewidth, two-stage fiber amplifier at 1014.8 nm based on Yb-doped double-clad fibers. The fibers are cooled to liquid-nitrogen temperatures in order to suppress absorption at the operating wavelength. We achieved output powers of up to 5.0 W at a linewidth of less than 3 MHz by seeding the amplifier with the radiation from an external cavity diode laser.

Journal Article↗

PubMed2006

Directed spontaneous emission from an extended ensemble of N atoms: timing is everything.

A collection of static atoms is fixed in a crystal at a low temperature and prepared by a pulse of incident radiation of wave vector . The atoms are well described by an entangled Dicke-like state, in which each atom carries a characteristic phase factor exp(ik0.r(j)), where is the atomic position in the crystal. It is shown that a single photon absorbed by the N atoms will be followed by spontaneous emission in the same direction. Furthermore, phase matched emission is found when one photon is absorbed by N atoms followed by two-photon down-conversion.

Journal Article↗

PubMed2002

Photoacoustic tomography of biological tissues with high cross-section resolution: reconstruction and experiment.

A modified back-projection approach deduced from an exact reconstruction solution was applied to our photoacoustic tomography of the optical absorption in biological tissues. Pulses from a Ti:sapphire laser (4.7 ns FWHM at 789.2 nm) were employed to generate a distribution of photoacoustic sources in a sample. The sources were detected by a wide-band nonfocused ultrasonic transducer at different positions around the imaging cross section perpendicular to the axis of the laser irradiation. Reconstructed images of phantoms made from chicken breast tissue agreed well with the structures of the samples. The resolution in the imaging cross section was experimentally demonstrated to be better than 60 microm when a 10 MHz transducer (140% bandwidth at -60 dB) was employed, which was nearly diffraction limited by the detectable photoacoustic waves of the highest frequency.

Acoustics↗