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Some laser techniques for chemical detection

Description: Spectroscopy provides a fast sensitive method for chemical analysis. Lasers are high intensity narrow bandwidth, collimated light sources in the infrared, visible, and ultraviolet spectral regions. Wavelength tunable lasers can be used for spectroscopic chemical identification by means of techniques such as opto-acoustic spectroscopy, thermal lensing, and fluorescence excitation. These methods all share the useful characteristic that their detection sensitivity to small quantities of chemicals improves with higher laser intensity. We have developed apparatuses to use these techniques for trace chemical identification and detection. In addition, a useful improvement to thermal lensing, which we designate thermal deflection spectroscopy, has been developed.
Date: January 1, 1980
Creator: Sander, R.K. & Buchwald, M.I.
Partner: UNT Libraries Government Documents Department

Resonantly enhanced vacuum-ultraviolet generation and multiphoton ionization in carbon monoxide gas

Description: Competition between three-photon resonantly enhanced vacuum ultraviolet third-harmonic generation and six-photon multiphoton ionization using the A state in gaseous carbon monoxide is observed. Excitation spectra of the third-harmonic emission exhibit increasing blue shifts and broadening with increasing pressure due to the phase matching requirements. Estimates for the efficiency and tunability show that third-harmonic generation in carbon monoxide molecules is a promising source for coherent vacuum ultraviolet light.
Date: January 1, 1982
Creator: Glownia, J.H. & Sander, R.K.
Partner: UNT Libraries Government Documents Department

Ignition dynamics of high explosives

Description: Mechanical insults of granular high explosives (HE) can result in localized areas of elevated temperature, or hot spots. The evolution of these hot spots is a central issue of HE science. Because of the complexity involved, it is worthwhile to study mechanical and reaction processes in isolation. Mechanical processes are isolated and studied using inert materials or weak insults where reaction may be minimal. Likewise, purely thermal processes can be considered to isolate HE reaction response. In this work the authors study the radiant ignition of various HEs of interest, including HMX (C{sub 4}H{sub 8}N{sub 8}O{sub 8}), PBX 9501 (95% HMX, 2.5% Estane, 2.5% BDNPA/BDNPF), RDX (C{sub 3}H{sub 6}N{sub 6}O{sub 6}), TATB (C{sub 6}H{sub 6}N{sub 6}O{sub 6}), and PBX 9502 (95% TATB, 5% Kel-F) and aged PBX 9502. Initial work has included unconfined samples at ambient pressure in air. Diagnostics have included photodiodes to record first light emission, high speed photography, microthermocouple and IR emission measurement to obtain surface temperature, IR emission of gases above the pellet, and a novel nonlinear optical technique to characterize the dynamic {beta}-{delta} solid phase transformation and the formation of a liquid layer. The authors find that ignition delays at various power levels is very similar for HMX and RDX; except that the minimum radiant flux needed for RDX ignition is higher. The addition of only 5% binder (PBX 9501) causes significantly longer ignition delays at lower heat fluxes compared with HMX alone. TATB and TATB-based explosives exhibit much longer ignition delays than HMX. In contrast to HMX, however, no measurable difference is observed in TATB by the addition of a binder (PBX 9502, aged or pristine).
Date: December 31, 1998
Creator: Ali, A.N.; Son, S.F.; Sander, R.K. & Asay, B.W.
Partner: UNT Libraries Government Documents Department

Use of multivariate regression for analysis of CO{sub 2} laser lidar data from long pathlengths in ambient atmosphere

Description: Until recently use of lasers for long path absorption measurements has relied on using differential absorption at two wavelengths to look for one species at a time in the atmosphere. With the advent of multi-line CO{sub 2} lasers it is now feasible to generate 30 to 40 lines in a rapid burst to look for spectra of all the chemical species that may be present. Measurements have been made under relatively constant meteorological conditions in a summertime desert environment with a multi-line tunable laser. Multivariate regression analysis of this data shows that the spectra can be accurately fit using a small number of spectral factors or eigenvectors of the time dependent spectral data matrix. The factors can be rationalized in terms of lidar system effects and atmospheric composition changes.
Date: August 1, 1997
Creator: Sander, R.K.; Quagliano, J.R. & Fry, H.
Partner: UNT Libraries Government Documents Department

Lifetime and quenching measurements of C/sub 2/H emission produced by vacuum ultraviolet photolysis of C/sub 2/H/sub 2/. [C/sub 2/H radicals]

Description: The state-of-the-art tunable vuv sources are used to produce excited C/sub 2/H photofragments (C/sub 2/H*) via the photolysis of acetylene molecules. The quenching rate constants of the C/sub 2/H emission by a number of species are determined. The collision-free fluorescence lifetimes are measured at different excitation wavelengths. The excitation energy threshold for producing the observed emission is determined. In addition, a correlation between the excitation energy and the emission wavelength is observed. 27 refs., 6 figs., 2 tabs.
Date: January 1, 1985
Creator: Tiee, J.J.; Sander, R.K.; Quick, C.R. Jr.; Romero, R.J. & Estler, R.
Partner: UNT Libraries Government Documents Department

Laser-based instrumentation for detection of chemical-warfare agents

Description: Several laser-based techniques are being developed for remote, point, and surface contamination detection of chemical warfare agents. These techniques include optoacoustic spectroscopy, laser-induced breakdown spectroscopy, and synchronous detection of laser-induced fluorescence. Detection limits in the part-per-million to part-per-billion regime have been demonstrated.
Date: January 1, 1981
Creator: Quigley, G.P.; Radziemski, L.J.; Sander, R.K. & Hartford, A. Jr.
Partner: UNT Libraries Government Documents Department

Vacuum ultraviolet photolysis of acetylene in the 110- to 135-nm region

Description: State-specific photofragmentation of acetylene in the 110- to 135-nm region has been studied using vuv laser and synchrotron sources. Investigations have been focused on learning the spectroscopic identity of the excited photoproducts by examining their time-resolved fluorescence. Results of the quenching of the excited photofragment emission and the emission polarization measurements are presented. An interpretation of these results in relating the observed photoproducts to the vuv photodissociation process is discussed. 13 refs., 3 figs., 1 tab.
Date: January 1, 1986
Creator: Tiee, J.J.; Sander, R.K.; Quick, C.R. & Estler, R.
Partner: UNT Libraries Government Documents Department

Resonant multiphoton ionization for the detection of technetium

Description: Experiments were carried out to determine optimum wavelengths for the selective ionization of technetium and to estimate the ultimate sensitivity obtainable for resonant ionization mass spectrometry detection of Tc in real samples. Results indicated that the 3099 and 3098 A lines may be analytically useful. The rate of ion production by laser excitation using pulsed lasers and techniques for volatilization of the sample are discussed. (MCG)
Date: January 1, 1983
Creator: Nogar, N.N.; Miller, C.M.; Downey, S.W. & Sander, R.K.
Partner: UNT Libraries Government Documents Department

Laser-based instrumentation for the detection of chemical agents

Description: Several laser-based techniques are being evaluated for the remote, point, and surface detection of chemical agents. Among the methods under investigation are optoacoustic spectroscopy, laser-induced breakdown spectroscopy (LIBS), and synchronous detection of laser-induced fluorescence (SDLIF). Optoacoustic detection has already been shown to be capable of extremely sensitive point detection. Its application to remote sensing of chemical agents is currently being evaluated. Atomic emission from the region of a laser-generated plasma has been used to identify the characteristic elements contained in nerve (P and F) and blister (S and Cl) agents. Employing this LIBS approach, detection of chemical agent simulants dispersed in air and adsorbed on a variety of surfaces has been achieved. Synchronous detection of laser-induced fluorescence provides an attractive alternative to conventional LIF, in that an artificial narrowing of the fluorescence emission is obtained. The application of this technique to chemical agent simulants has been successfully demonstrated. 19 figures.
Date: January 1, 1982
Creator: Hartford, A. Jr.; Sander, R.K.; Quigley, G.P.; Radziemski, L.J. & Cremers, D.A.
Partner: UNT Libraries Government Documents Department

Ignition dynamics of high explosives

Description: The laser ignition of the explosives HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, C{sub 4}H{sub 8}N{sub 8}O{sub 8}), {delta}-phase HMX, PBX 9501 (95% HMX, 2.5% Estane, 2.5% BDNPA/BDNPF), TATB (1,3,5-triamino-2,4,6-trinitrobenzene, C{sub 6}H{sub 6}N{sub 6}O{sub 6}), and PBX 9502 (95% TATB, 5% Kel-F) and aged PBX 9502 has been conducted with the intent to compare the relative sensitivities of those explosives and to investigate the effect of beam profile, binder addition, and porosity. It has been found that there was little difference between a gaussian beam and a top hat profile on the laser ignition of HMX. The authors observe that the addition of binder in the amounts present in PBX 9501 resulted in longer ignition delays than that of HMX. In contrast to HMX, the addition of binder to TATB in PBX 9502 shows no measurable effect. Porosity effects were considered by comparing the ignition of granular HMX and pressed HMX pellets. Porosity appears to increase ignition delay due to an increased effective absorption scale and increased convective heat loss. This porosity effect also resulted in longer ignition delays for {delta}-phase HMX than for {beta}-phase HMX. In order to simulate ignition in voids or cracks, the standard ignition experiment was modified to include a NaCl window placed at variable distances above the sample surface. When ignition experiments were performed at 29 W/cm{sup 2} and 38 W/cm{sup 2} a critical gap distance was observed of 6 {+-} 0.4 mm below which ignition was severely inhibited. This result underscores the importance of gas phase processes in ignition and illustrates that conditions can exist where simple ignition criteria such as surface temperature is inadequate.
Date: April 1, 1999
Creator: Ali, A.N.; Son, S.F.; Sander, R.K.; Asay, B.W. & Brewster, M.Q.
Partner: UNT Libraries Government Documents Department

Aging and PBX 9502

Description: Components made from PBX 9502, an insensitive high explosive formulated with triaminotrinitrobenzene (TATB) and Kel-F 800 binder, have been in service for nearly two decades. Since that time, samples have been destructively evaluated to determine if potential changes that might affect safety, reliability, or performance have occurred in the high explosive with time. Data from routine, historical testing is reported elsewhere. This paper focuses on specific tests conducted to evaluate the effects of natural aging on handling sensitivity (through the small-scale tests of Human Electrostatic Discharge, friction, and Drop Weight Impact), compressive strength, and thermal ignition. Also reported are the effects of a radiation environment on TATB. Small-scale sensitivity tests show no differences between aged and unaged material. Observed differences in compressive strength behavior are attributed to conditions of original material rather than aging effects. Thermal ignition by flame and laser methods showed no changes between aged and unaged material. Extreme levels of radiation are shown to have only minimal effects in explosive response tests. PBX 9502 is concluded, once again, to be a very stable material, aging gracefully.
Date: December 31, 1998
Creator: Skidmore, C.B.; Idar, D.J.; Buntain, G.A.; Son, S.F. & Sander, R.K.
Partner: UNT Libraries Government Documents Department

CO{sub 2} dial transmitter/receiver noise characterization and related correlated noise issues

Description: Our approach concerning the development of hard target return CO{sub 2} DIAL transmitter/receiver systems is two phased- (i) through analysis and experiment, develop a fundamental understanding of the transmitter/receiver physics specific to DIAL systems and (ii) apply these fundamentals in the development of optimal performance DIAL transmitter/receiver systems. We present our progress and results towards these objectives with the following topics addressed: A general overview of the DIAL transmitter/receiver system characterization effort with a focus on transceiver noise processes. The effects of correlated noise on DIAL performance, especially those effecting statistical convergence over long sample structures, is , introduced. And, preliminary measurements of a low-noise, ``white`` receiver prototype are presented.
Date: February 1, 1996
Creator: Cooke, B.; Schmitt, M.; Goeller, R.; Czuchlewski, S.; Fuller, K.; Olivas, N. et al.
Partner: UNT Libraries Government Documents Department

Bubble chamber spectroscopy for chemical analysis: A new concept

Description: A new technique for the detection of trace concentrations of molecules in solution has been developed. This system utilizes the amplification characteristics of a bubble chamber in which energy deposition from laser absorption is monitored. In the experimental set-up, a trace quantity of solute is introduced into liquid propane that is contained in a small (10 ml) stainless steel cell at 120 psi. The propane is superheated by sudden reduction of the cell pressure. Before wall nucleated boiling occurs, target solute molecules are energized by a laser pulse. Absorption of pump laser energy results in the formation of nucleation centers which develop into bubbles and which in turn are detected by CCD camera. Preliminary experiments with crystal violet used as a test absorber have demonstrated detection sensitivity of 10 parts per trillion (ppt).
Date: February 1, 1995
Creator: Atencio, J. H.; Luo, Xin; McCreary, E. I.; McCown, A. W. & Sander, R. K.
Partner: UNT Libraries Government Documents Department

Atmospheric effects on CO{sub 2} differential absorption lidar performance

Description: CO{sub 2} differential absorption lidar (DIAL) performance can be adversely affected by the ambient atmosphere between the laser transmitter and the target through a number of different processes. This work addresses two sources of atmospheric interference with multispectral CO{sub 2} DIAL measurements: effects due to beam propagation through atmospheric turbulence and extinction due to absorption by atmospheric gases. The authors compare measurements of the effective beam size after propagation to predictions from a beam propagation model that includes turbulence effects such as beam steering and beam spreading. They also compare the experimental measurements of atmospheric extinction to those predicted by both a standard atmospheric transmission model (FASCODE) and a chemometric analysis.
Date: May 1, 1996
Creator: Petrin, R.R.; Quagliano, J.R.; Nelson, D.H.; Schmitt, M.J.; Quick, C.R.; Sander, R.K. et al.
Partner: UNT Libraries Government Documents Department