Gary C. Tisone

Spectroscopic studies of diatomic noble gas halides. II. Analysis of bound‐free emission from XeBr, XeI, and KrF

The strong ultraviolet emission bands (’’Spectrum I’’) of XeBr, XeI, and KrF have been photographed following electron‐beam excitation of appropriate noble gas/halide mixtures at moderate to high pressures. These diffuse spectra are analyzed through trial‐and‐error theoretical simulations. The upper‐state vibrational frequencies are estimated to be 120±10, 112±8, and 310±20 cm−1 for XeBr, XeI, and KrF, respectively. The analysis also yields approximate shapes for the lower‐state potential curves in the Franck–Condon region. Lasing is observed in XeBr (2818 A) and KrF (2484, 2491 A) but not in XeI.

Spectroscopic studies of diatomic noble gas halides: Analysis of spontaneous and stimulated emission from XeCl

A XeCl emission band system with peak intensity near 3080 A is reported and analyzed. The vibrational analysis of this spectrum includes 24 violet‐degraded bands assigned to Xe35Cl and Xe37Cl, and yields (for Xe35Cl) ΔTe=32 405 cm−1, ωe′=195.2 cm−1, ωe″=26.3 cm−1, and De″=255 cm−1. The weakly bound 2Σ+ ground state of XeCl resembles a van der Waals state, whereas the excited state is the analog of the CsCl ground state. Approximate potential curves are derived for these XeCl states. Lasing is observed on the 0–1, 0–2, and 0–3 bands of this transition, with a peak output power of 1.5×104 W.

High power uv noble‐gas‐halide laserf

Using an axial electron‐beam excitation scheme to excite mixture of argon, krypton, and fluorine, 108 J of laser energy, corresponding to a peak power of 1.9×109 W, was obtained from KrF at 2484 A. In addition, ArF was observed to lase at 1933 A with a maximum energy output of 92 J, corresponding to a power of 1.7×109 W. The maximum energy for KrF was obtained with total gas pressures of 1400 Torr using 4 Torr of fluorine and partial pressures of krypton greater than 100 Torr. When the partial pressure of krypton was less than 100 Torr both ArF and KrF were observed to laser simultaneously.

Oscillator performance and energy extraction from a KrF laser pumped by a high-intensity relativistic electron beam

A laser cell with 21 of excitation volume was used to study the electron-beam pumped KrF laser system at excitation rates of 1.8- 7.0 MW/cm³. The system was optimized as an oscillator for various mixtures of Ar, Kr, and F<inf>2</inf>at total pressures of 1000 and 2500 torr. The resulting optimum conditions gave an intrinsic efficiency (laser energy out/electron-beam energy deposited) of 12 percent for the 1000 torr total pressure mixture with an output energy of 11 J/1. An efficiency of 10 percent with an output of 40 J/1 was obtained for the 2500 torr mixture. The system was then used as an amplifier to measure the extracted power as a function of input power for the two mixtures. The small-signal gain go, the nonsaturable absorption α, and the saturation intensity I<inf>s</inf>were determined for the two mixtures. Analysis of the data gave g<inf>0</inf>= 16-18 percent/cm,<tex>\alpha = 0.75-1.25</tex>percent/cm, and I<inf>s</inf>= 2 MW/cm²for the 1000 torr mixture and g<inf>0</inf>= 17-19 percent/cm,<tex>\alpha = 1.0-1.5</tex>percent/cm, and<tex>I_{s} = 9</tex>MW/cm²for the 2500 torr mix.

Laser‐controlled etching of chromium‐doped 〈100〉 GaAs

The photocontrolled etching of 〈100〉 Cr:GaAs in HNO3 is examined in the wavelength region of 334–514 nm with an Ar ion laser. The etching rate decreases with increasing wavelength and correlates with the optical absorption coefficient in the GaAs. The etching process is found to be photochemically and not thermally controlled. Etch rates for the UV are 30(μ/s)/(MW/cm2) for laser intensities between 3 and 80 kW/cm2.

Study of the XeCl laser pumped by a high-intensity electron beam

We present the results of a detailed experimental study of the XeCl laser pumped by a high-intensity electron beam. The laser system was optimized as an oscillator for mixtures of Xe and HCl with Ne, Ar, and Kr diluents. The peak intrinsic efficiency (laser energy out/electron-beam energy deposited) was near 4.5 percent for each of these diluents. Small-signal gain and background absorption were measured as a function of electron-beam deposition rate from 0.4 to 6 MW/ cm3. The ratio of small-signal gain to absorption was found to be constant over this range with a value of ∼5. Measurements of absorption in the presence of a large photon flux indicated that there was no appreciable saturable contribution to the absorption. Measurements of fluorescence from the B and C states indicate that collisional mixing between these states is very rapid. The formation efficiencies of the B and C states are estimated to be 0.15 and 0.05, respectively. A vibrational relaxation rate of between 1 and 1.5 \times 10^{-10} cm3. s-1was determined. The effect of this finite relaxation rate is to reduce the energy available to the stimulated process by a factor of 0.67-0.75. Estimates of the XeCl* deactivation rates by HCl and electrons were also obtained. A value of 1.7 \times 10^{-9} cm3. s-1was obtained for quenching by HCl, and a value of \sim 1 \times 10^{-7} cm3. s-1was estimated for electron deactivation.

Molecular-iodine laser

Abstract Molecular iodine has been observed to lase on eight vibrational bands of the 3460–3015 A band system. The laser was produced by electron-beam-pumping mixtures of a iodine-donor compound (HI, CF 3 I, or CH 3 I) and argon. The highest energy output obtained was 1.0 J in a 40 ns pulse, corresponding to an average power of 25 MW.

Studies of an 80‐J KrF oscillator at excitation rates of 2–7 MW/cm3

We have examined the performance of a 2‐liter KrF oscillator pumped by a high‐intensity electron beam. For input pump rates of 7 MW/cm3, up to 80 J of laser energy is extracted from the cavity in 50 ns with an efficiency (laser energy divided by deposited electron‐beam energy) of 11%. Values of the small‐signal‐gain length product g0L, the absorption length product αL, and the saturation intensity Is were determined to be 6–16, 0.3–0.6, and 1–10 MW/cm2, respectively.

A Refractive INdex Gradient (RING) diagnostic for transient discharges or expansions of vapor or plasmas

The refractive index gradient (RING) diagnostic described uses a fast, silicon, photodiode quadrant detector with a differential amplifier to temporally detect the refraction of a CW laser by transient discharges or expansions of vapor, gas, or plasma. The method is a local one-dimensional time-resolved, quantitative, species-discriminating (i.e., atoms or electrons) Schlieren technique. The diagnostic is easy to field, sensitive (the minimum deflection angles detectable are approximately=0.3 mu rad), and fast (risetime=11+or-1 ns). Circuit design, performance, and diagnostic theory are discussed. To illustrate the utility of this technique, examples of measurements on LEVIS (laser evaporation ion source), a laser-produced, active, lithium ion source, are given. Measured properties include vapor/plasma production thresholds, expansion velocities, and time-resolved gradient and density spatial profiles. Comparisons of the RING results with measurements using a Faraday cup and a double-floating Langmuir probe are presented. >

Ultraviolet fluorescence identification of protein, DNA, and bacteria

Recent food poisoning incidents have highlighted the need for inexpensive instrumentation that can detect food pathogens. Instrumentation that detects the relatively strong ultraviolet (UV) fluorescence signal from the aromatic protein amino acids in bacteria could provide a solution to the problem of real-time pathogen measurements. The capabilities of UV fluorescence measurements have, however, been largely ignored because of the difficulty in identifying pathogens in the presence of interfering backgrounds. Implementation of fluorescence measurements thus requires methodologies that can distinguish fluorescence features associated with pathogens from those associated with proteins, harmless bacteria, skin, blood, hair follicles, pesticide residue, etc. We describe multispectral UV fluorescence measurements that demonstrate the feasibility of detecting and identifying protein, DNA, and bacteria using a relatively simple UV imaging fluorometer and a unique multivariate analysis algorithm.