350 mJ electro-optically Q-switched 2.79†µm Cr:Er:YSGG MOPA.

We report on developing three flashlamp-pumped electro-optically Q-switched Cr:Er:YSGG lasers with the Q-switch based on a La3Ga5SiO14 crystal. The "short" laser cavity was optimized for high peak power applications. In this cavity, 300 mJ output energy in 15 ns pulses at a 3 Hz repetition rate was demonstrated with pump energy below 52 J. However, several applications, such as Fe:ZnSe pumping in a gain-switched regime, require longer (∼ 100 ns) pump pulse duration. We developed a 2.9 m long laser cavity that delivers 190 mJ of output energy in 85 ns pulses for these applications. We also demonstrated the Cr:Er:YSGG MOPA system producing 350 mJ output energy at 90 ns pulse duration and 47.5 J of pumping, corresponding to an amplification factor of 3.

High power single-mode delivery of mid-infrared sources through chalcogenide fiber.

Mechanically robust and low loss single-mode arsenic sulfide fibers are used to deliver high power mid-infrared sources. Anti-reflection coatings were deposited on the fiber facets, enabling 90% transmission through 20 cm length fibers. 10.3 W was transmitted through an anti-reflection coated fiber at 2053 nm, and uncoated fibers sustained 12 MW/cm2 intensities on the facet without failure. A Cr:ZnSe laser transmitted >1 W at 2520 nm, and a Fe:ZnSe laser transmitted 0.5 W at 4102 nm. These results indicate that by improving the anti-reflection coatings and using a high beam quality mid-infrared source, chalcogenide fibers can reliably deliver ≥10 W in a single mode, potentially out to 6.5 µm.

Crystalline Cr²âº:ZnSe/chalcogenide glass composites as active mid-IR materials.

We propose new transition metal (TM)-doped ZnSe/As2S3:As2Se3 composite materials for mid-IR fiber lasers. The composites are the suspension of crystalline micro- and nanosized TM²âº:ZnSe or TM²âº:ZnS powders in chalcogenide glasses with the refraction index matching. Mid-IR room-temperature lasing of Cr²âº:ZnSe/As2S3:As2Se3 microcomposite material is demonstrated at the 2.4 µm wavelength.

Mid-IR laser oscillation in Cr2+:ZnSe planar waveguide.

We demonstrate 2.6 µm mid-infrared lasing at room temperature in a planar waveguide structure. Planar waveguides were fabricated using pulsed laser deposition (PLD) by depositing chromium doped zinc selenide thin films on sapphire substrate (Cr2+:ZnSe/sapphire). Highly doped Cr2+:ZnSe/Sapphire thin film sample was also used to demonstrate passive Q-switching of Er:YAG laser operating at 1.645 µm.

Mid-infrared Cr2+:ZnSe random powder lasers.

We report simple methods of laser active Cr2+:ZnSe powder fabrication with average grain sizes of either approximately 10 or approximately 1 microm without crystal growth stage. Pure, uniformly mixed ZnSe and CrSe powders annealed at 1000 masculineC for 3 days in a sealed evacuated (approximately 10(-4) Torr) quartz ampoule exhibited middle-infrared laser action at room temperature under 1.56 microm excitation of D(2) Raman shifted radiation of Nd:YAG laser. The output-input characteristic clearly demonstrated the threshold-like behavior of the output signal with the threshold energy level of 0.5 and 3 mJ in 2.9 mm spot for 10 and 1 microm grain sizes, respectively.

Evanescent cavity ring-down spectroscopy (e-CRDS) of hemoglobin absorption at the silica-water interface.

The absorption of hemoglobin (Hb) from controlled urine samples was observed using the technique of evanescent cavity ring-down spectroscopy (e-CRDS). A room temperature, alexandrite laser pumped LiF:F2(+**) color-center pulsed laser was used to excite Hb at 425 nm. A minimum absorbance level of 2.57 x 10(-4) was achieved corresponding to a minimum detectable concentration of Hb in urine of 5.8 nM. These levels could have advantages in the diagnosis of hemoglobinurea. The formation of layers of Hb upon the silica surface allowed for an increased sensitivity for smaller concentrations of Hb than would be expected for only a free floating solution. The formation of the layers also suggested a higher binding constant of Hb to the silica surface than between other layers of Hb molecules. Future studies are underway to understand the effects of salinity on the observed absorption due to the competitive binding of Na+ to the surface. Absorption isotherm modeling will also be used to better understand the development of layers upon the surface.

Fluorescence assay for monitoring Zn-deficient superoxide dismutase in vitro.

A method has been developed for selective detection of the zinc-deficient form of Cu, Zn superoxide dismutase (SOD1) in vitro. Zinc-deficient SOD1 mutants have been implicated in the death of motor neurons leading in amyotrophic lateral sclerosis (ALS or Lou Gerhig's disease). Thus, this method may have applicability for detecting zinc-deficient SOD1 mutants in human ALS patients samples as well as in a transgenic mouse model of ALS and in cultured motor neurons. We determined previously that structural analogs of 1,10 phenanthroline, which react specifically with Cu(I), react with the active Cu(I) of SOD1 when zinc is absent, but not when zinc is also bound, as evidenced by the fact that the reaction is inhibited by pretreatment of the enzyme with zinc. We report herein that bathocuproine, or its water-soluble derivative bathocuproine disulfonate, react with zinc-deficient SOD1 to form a complex which fluoresces at 734 nm when excited at 482 nm. Fluorescent intensity is concentration dependent, thus we propose to use fluorescent confocal microscopy to measure intracellular levels of zinc-deficient SOD1 in situ.