Induction of lambda prophage near the site of focused UV laser radiation.

DNA damage from photon scatter or beam spread during UV excimer laser irradiation was investigated using the induction of bacteriophage lambda in E. coli BR339. Prophage induction in these cells leads to the production of beta-galactosidase which can be detected colorimetrically by the application of appropriate substrates. An agar surface overlayed with BR339 cells was placed at various distances from the focal point of a converging lens and exposed to either 193 or 248 nm laser radiation. Energy densities ranging from approximately 5 mJ/cm2 to 30 J/cm2 were used. Ablation with 193 nm laser radiation produced an 800 microns wide clear 'trench' surrounded by a 500 microns zone of cells in which lambda had been induced. Following ablation with 248 nm laser radiation, the zone of induction was several millimeters wide. Exposures to 193 nm radiation at 170 mJ/cm2/pulse produced visible ablation of the agar surface at 1.7 J/cm2. Lambda induction was observed surrounding cleared ablation areas. The presence of induction in this system suggests that both 248 and 193 nm excimer laser radiation delivered at high energy densities has sufficient spread or scatter to damage DNA in cells surrounding areas of ablation.

Infrared optical fibers for surgical applications.

The basic characteristics of fibers that are appropriate for surgical use in the infrared are reviewed. New fiber materials, such as sapphire, fluorozirconate and chalcogenide glasses, and polycrystalline fibers are discussed as well as their applicability for surgical procedures.

XeF waveguide laser.

Waveguide laser operation on the 351- and 353-nm transitions of the XeF rare-gas halide molecule has been demonstrated using a fast Blumlein circuit that operated at 2-20 Hz. Laser energy densities of ~8 mJ/liter have been observed from a 62.5-microl volume of flowing NF(3):Xe:He (1:4:150) gas mixture.

Lifetime and collisional quenching measurements of XeF*(B) by photolysis of XeF2.

By photolyzing XeF 2 using ArCl* 175-nm radiation, the spontaneous radiative lifetime of the XeF(B --> X) band has been measured to be 14.25 + 0.2 nsec. Also, the rates of two-body collisional deactivation of the XeF(B) state by Ne, Ar, and XeF 2 have been determined to be 7.7 X 10(-13) cm3 sec(-1), 4.9 X 10(-12) cm3 sec(-1), and 2.6 X 10(-10) cm3 sec(-1), respectively. A three-body quenching rate of 7.2 X 10(-32) cm6 sec(-1) was found for Ar. The large two- and three-body quenching rates of XeF* by Ar suggest that Ne may be preferable to Ar as a diluent in high-pressure XeF (350-nm) laser mixtures.

Infrared measurements of sapphire fibers for medical applications.

Infrared transmission losses as low as 8 dB/km at 1060 nm and damage a threshold above 1.3 kJ/cm(2) at 2940 nm have been measured for experimental single-crystal sapphire fibers.

Broadband flexible waveguides for free-electron laser radiation.

We refined flexible waveguides previously developed for CO(2) and Er:YAG laser radiation to transmit free-electron-laser (FEL) radiation. One can tune this laser over several segments of the radiation spectrum. This laser has a high peak power of as much as 10 MW with pulse energy of as much as 100 mJ. We made the waveguides of either Teflon or fused-silica tubes internally coated with metal and dielectric layers. We optimized the internal coatings specifications for transmission of various radiation wavelengths in the mid-IR range and enabled transmission of high-peak radiation. We performed experiments in three major FEL sites in the United States over a more than 1-year period when we measured and examined various characteristics of transmission. We used the analysis of these experiments as feedback to further improve these waveguides. The good preliminary results encourage us to invest more effort to further develop these waveguides until a suitable waveguide is obtained for this type of laser and make possible its introduction to the medical field where its characteristics can be exploited in surgical applications.

Attenuation measurement of infrared optical fibers by use of a hollow-taper-based coupling method.

An alternative method for attenuation measurement of infrared (IR) fibers is described. The method includes a simple technique for direct laser-to-fiber coupling with an uncoated glass hollow taper. The operating principle of the hollow taper is based on the grazing-incidence effect of light reflection. The hollow taper forms a smooth Gaussian-shaped profile of the output laser emission and provides the proper conditions for equilibrium-mode distribution of optical power within the test IR fibers. The experimental hollow-taper-based coupling method is used for measurement of attenuation and bending losses of various kinds of IR fiber, including solid-core (fluoride, chalcogenide, and germanium-doped) and hollow fibers.

Effect of coolant flow on the performance of round sapphire tips in a saline field.

Round sapphire and silica tips have been studied as surgical probes for focusing Nd:YAG laser radiation during various surgical indications. Since most of these data have been obtained with silica tips from Surgical Laser Technology, there are limited data on the physical performance of round sapphire tips. An investigation of round sapphire tip performance during tissue ablation was undertaken. Nd:YAG laser power was delivered in repetitive 2-sec exposures to a round sapphire tip placed on fresh skinned chicken breast. Total exposures of 1,000 J were performed at different saline perfusion rates. The tip's performance in terms of tissue perforation rate, blanched tissue area, tissue heating rate, and forward transmission was measured. Best tip performance occurred at the lowest cooling rates and was independent of the tip's forward transmission value. No physical deterioration of the tip's optical surface was observed. Round sapphire tip performance in a saline field is primarily determined by the tip's temperature.

Testing optimum viewing conditions for mammographic image displays.

The viewbox luminance and viewing room light level are important parameters in a medical film display, but these parameters have not had much attention. Spatial variations and too much room illumination can mask real signal or create the false perception of a signal. This presentation looks at how scotopic light sources and dark-adapted radiologists may identify more real diseases.