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Smart active multiwave sensing with zero background amplitude modulated probes

Description: Recently, a new approach to multi-wavelength remote sensing has been proposed based on the generation and detection of spectral ``pickets`` synthesized from the frequency filtered bandwidth of a modelocked laser. Using linear array liquid crystal spatial light modulator (SLM) technology for spectral filtering permits real time grey scale control of individual picket amplitudes and phases, making it possible to independently modulate picket characteristics in the kHz to MHz regime. Due to the versatility of this approach, a whole suite of spectroscopies based on detection techniques that are similar to conventional sideband spectroscopies can be implemented. These techniques not only inherit the S/N advantages of their conventional counterparts, they can also be easily extended to simultaneous multi-wavelength operation using frequency multiplex techniques and configured for real time adaptive data acquisition. We report the laboratory demonstration and theoretical development of a new class of zero background AM modulated spectroscopic probes for differential absorption measurements. Preliminary detection sensitivities on the order of 10{sup {minus}6} can be inferred from our measurements. Application of this technique to realistic remote sensing scenarios, advantages over other modulation and direct detection approaches, as well as the present limitations and theoretical limits to detection sensitivity will be discussed.
Date: July 1, 1994
Creator: Ruggiero, A.J.; Young, R.A. & Jelsma, L.
Partner: UNT Libraries Government Documents Department

Enhancing the analytical performance of laser-induced breakdown spectroscopy

Description: This is the final report of a one-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). The objective of this work is to enhance the analytical capabilities of laser-induced breakdown spectroscopy (LIBS). LIBS is a method of elemental analysis in which powerful laser pulses are focused on a sample to form a microplasma. LIBS is perhaps the most versatile elemental analysis method, applicable to a variety of different real-world analysis problems. Therefore, it is important to enhance the capabilities of the method as much as possible. Accomplishments include: (1) demonstration of signal enhancements of 5--30 times from soils and metals using a double pulse method; (2) development of a model of the observed enhancement obtained using double pulses; (3) demonstration that the analytical performance achievable using low laser-pulse energies (10 and 25 mJ) can match that achievable using an energy of 100 mJ; and (4) demonstration that time-gated detection is not necessary with LIBS.
Date: December 31, 1998
Creator: Cremers, D.A.; Chinni, R.C.; Pichahchy, A.E. & Thornquist, H.K.
Partner: UNT Libraries Government Documents Department

Precision measurements of the hyperfine structure in the 23P state of 3He.

Description: The unusually large hyperfine structure splittings in the 23P state of the 3He isotope is measured using electro-optic techniques with high precision laser spectroscopy. Originally designed to probe the fine structure of the 4He atom, this experimental setup along with special modifications I implemented to resolve certain 3He related issues has made possible new high precision hyperfine structure measurements. Discussed are the details of the experimental setup and the modifications, including in depth information necessary to consider while performing these measurements. The results of these hyperfine structure measurements give an order of magnitude improvement in precision over the best previously reported values.
Date: May 2003
Creator: Smiciklas, Marc
Partner: UNT Libraries

Investigation of Tunable Diode Spectroscopy for Monitoring Gases in Geothermal Plants

Description: The results of an investigation directed at the development of instrument-tation for the real-time monitoring of gases, such as hydrogen sulfide (H2S) and chloride (HCl), in geothermal process streams is described. The geothermal power industry has an interest in the development of new low maintenance techniques since improved capabilities could lead to considerable cost savings through the optimization of various gas abatement processes. Tunable diode laser spectroscopy was identified as a candidate tech-nology for this application and a commercial instrument was specified and procured for testing. The measurement principle involved the use of solid state diode lasers and frequency modulation techniques. The gallium arsenide diode lasers employed emit light in the 0.7 to 2.0 micron region of the electromagnetic spectrum. This region contains the overtone and combination absorption bands of a number of species of industrial interest, including H2S and HCl. A particular device can be tuned over a small range to match the absorption line by changing its applied temperature and current. The diode current can also be sinusoidally modulated in frequency as it is tuned across the line. This modulation allows measurements to be conducted at frequencies where the laser intensity noise is minimal; and therefore, very high signal-to-noise measurements are possible. The feasibility of using this technology in various types of geothermal process streams has been explored. The results of laboratory and field studies are presented along with new advances in laser technology that could allow more sensitive and selective measurements to be performed.
Date: August 1, 2006
Creator: Partin, J. K.
Partner: UNT Libraries Government Documents Department

Vertical cavity surface-emitting laser scanning cytometer for high speed analysis of cells

Description: We have constructed a new semiconductor laser device that may be useful in high speed characterization of cell morphology for diagnosis of disease. This laser device has critical advantages over conventional cell fluorescence detection methods since it provides intense, monochromatic, low-divergence fight signals that are emitted from lasing modes confined by a cell. Further, the device integrates biological structures with semiconductor materials at the wafer level to reduce device size and simplify cell preparation. In this paper we discuss operational characteristics of the prototype cytometer and present preliminary data for blood cells and dielectric spheres.
Date: December 31, 1995
Creator: Gourley, P.L.; McDonald, A.E. & Gourley, M.F.
Partner: UNT Libraries Government Documents Department

Laser-induced reactions in a deep UV resist system: Studied with picosecond infrared spectroscopy

Description: One of the most technologically important uses of organic photochemistry is in the imaging industry where radiation-sensitive organic monomers and polymers are used in photoresists. A widely-used class of compounds for imaging applications are diazoketones; these compounds undergo a photoinduced Wolff rearrangement to form a ketene intermediate which subsequently hydrolyses to a base-soluble, carboxylic acid. Another use of organic molecules in polymer matrices is for dopant induced ablation of polymers. As part of a program to develop diagnostics for laser driven reactions in polymer matrices, we have investigated the photoinduced decomposition of 5-diazo-2,2-dimethyl-1,3-dioxane-4,6-dione (5-diazo Meldrum`s acid, DM) in a PMMA matrix using picosecond infrared spectroscopy. In particular, irradiation of DM with a 60 ps 266 nm laser pulse results in immediate bleaching of the diazo infrared band ({nu} = 2172 cm{sup -1}). Similarly, a new band appears within our instrument response at 2161 cm{sup -1} (FWHM = 29 cm{sup -1}) and is stable to greater than 6 ns.; we assign this band to the ketene photoproduct of the Wolff rearrangement. Using deconvolution techniques we estimate a limit for its rate of formation of {tau} < 20 ps. The linear dependence of the absorbance change with the pump power (266 nm) even above the threshold of ablation suggest that material ejection take place after 6ns.
Date: December 31, 1995
Creator: Lippert, T.; Koskelo, A. & Stoutland, P.O.
Partner: UNT Libraries Government Documents Department

Development of a hand-portable photoionization time-of-flight mass spectrometer

Description: ANL is currently developing a portable chemical sensor system based on laser desorption photoionization time-of-flight mass spectrometry. It will incorporate direct sampling, a cryocooler base sample adsorption and concentration, and direct surface multiphoton ionization. All components will be in a package 9 x 11 x 4 in., weighing 15-18 lbs. A sample spectrum is given for a NaCl sample.
Date: June 1996
Creator: Dieckman, S. L.; Bostrom, G. A.; Waterfield, L. G.; Jendrzejczyk, J. A. & Raptis, A. C.
Partner: UNT Libraries Government Documents Department

Optical properties of fluids in microfabricated channels

Description: Microfabricated channels are widely thought to be the key to realizing chemical analysis on a microscopic scale. Chemical and biological information in the microchannels is often probed with optical techniques such as fluorescence, Raman and absorption spectroscopy. However, the optical effects of a microchannel are not well characterized. For example, it is important to understand the optics of the channel in order to optimize optical coupling efficiency. The authors consider various designs for enhancing the sensitivity of fluorescence detection in a microchannel.
Date: March 1, 1997
Creator: French, T.; Gourley, P.L. & McDonald, A.E.
Partner: UNT Libraries Government Documents Department

Spectroscopic diagnostics on high-density, strongly-coupled ICF plasmas. Final report, February 1, 1995--November 30, 1995

Description: During the period February 1, 1995 to November 30, 1995, the authors have upgraded their equipment in anticipation of the restart of the Omega-Upgrade laser at the University of Rochester Laboratory for Laser Energetics/National Laser User Facility, and also have completed exploratory experiments on aluminum targets related to both continuum and line emissions near series limits where lines blend into the continuum. Descriptions of results of these experiments are presented in this report, including the description of a particular dielectronic satellite spectral line whose observation relative to other lines offers a convenient localized indicator of high density in aluminum plasma. 3 refs., 8 figs.
Date: February 1, 1996
Creator: Griem, H.R.; Elton, R.C. & Welch, B.L.
Partner: UNT Libraries Government Documents Department

Thomson scattering from inertial confinement fusion plasmas

Description: Thomson scattering has been developed at the Nova laser facility as a direct and accurate diagnostic to characterize inertial confinement fusion plasmas. Flat disks coated with thin multilayers of gold and beryllium were with one laser beam to produce a two ion species plasma with a controlled amount of both species. Thomson scattering spectra from these plasmas showed two ion acoustic waves belonging to gold and beryllium. The phase velocities of the ion acoustic waves are shown to be a sensitive function of the relative concentrations of the two ion species and are in good agreement with theoretical calculations. These open geometry experiments further show that an accurate measurement of the ion temperature can be derived from the relative damping of the two ion acoustic waves. Subsequent Thomson scattering measurements from methane-filled, ignition-relevant hohlraums apply the theory for two ion species plasmas to obtain the electron and ion temperatures with high accuracy. The experimental data provide a benchmark for two-dimensional hydrodynamic simulations using LASNEX, which is presently in use to predict the performance of future megajoule laser driven hohlraums of the National Ignition Facility (NIF). The data are consistent with modeling using significantly inhibited heat transport at the peak of the drive. Applied to NIF targets, this flux limitation has little effect on x- ray production. The spatial distribution of x-rays is slightly modified but optimal symmetry can be re-established by small changes in power balance or pointing. Furthermore, we find that stagnating plasma regions on the hohlraum axis are well described by the calculations. This result implies that stagnation in gas-filled hohlraums occurs too late to directly affect the capsule implosion in ignition experiments.
Date: July 8, 1997
Creator: Glenzer, S.H.; Back, C.A. & Suter, L.J.
Partner: UNT Libraries Government Documents Department

Adsorption on nanosurfaces: A detailed look at metal clusters using infrared spectroscopy

Description: A technique known as infrared photodissociation spectroscopy is being used at Argonne to probe the intimate details of how molecules and atoms adsorb onto metal clusters. Clusters of transition metal atoms, produced by laser vaporization of a metal target, are allowed to react with small molecules, producing cluster complexes whose properties mimic those of the small metal-containing particles that make up many industrial catalysts. A powerful infrared laser is used to excite the characteristic vibrations of the atoms or molecules adsorbed on the surfaces of the clusters, causing the complexes to fragment. The resulting photodissociation spectrum is capable of revealing whether the adsorbed molecules have undergone a chemical reaction after sticking to the cluster surface. This techniques has been used to show that methyl alcohol molecules readily adsorb to the surfaces of small iron clusters, but do not undergo further reaction once they are there. This behavior is fundamentally different from that observed on macroscopic iron surfaces, where methyl alcohol readily reacts to form smaller fragment species. It is anticipated that these experiments will contribute to the understanding of particle size effects and their influence on reaction mechanisms and pathways in heterogeneous catalysis systems.
Date: August 1, 1997
Creator: Knickelbein, M.B.
Partner: UNT Libraries Government Documents Department

Nonlinear optical microscopy for imaging thin films and surfaces

Description: We have used the inherent surface sensitivity of second harmonic generation to develop an instrument for nonlinear optical microscopy of surfaces and interfaces. We have demonstrated the use of several nonlinear optical responses for imaging thin films. The second harmonic response of a thin film of C{sub 60} has been used to image patterned films. Two photon absorption light induced fluorescence has been used to image patterned thin films of Rhodamine 6G. Applications of nonlinear optical microscopy include the imaging of charge injection and photoinduced charge transfer between layers in semiconductor heterojunction devices as well as across membranes in biological systems.
Date: March 1, 1995
Creator: Smilowitz, L.B.; McBranch, D.W. & Robinson, J.M.
Partner: UNT Libraries Government Documents Department

Use of a laser doppler vibrometer for high frequency accelerometer characterizations

Description: A laser doppler vibrometer (LDV) is being used for high frequency characterizations of accelerometers at Sandia National Laboratories (SNL). A LDV with high frequency (up to 1.5 MHz) and high velocity (10 M/s) capability was purchased from a commercial source and has been certified by the Primary Electrical Standards Department at SNL. The method used for this certification and the certification results are presented. Use of the LDV for characterization of accelerometers at high frequencies and of accelerometer sensitivity to cross-axis shocks on a Hopkinson bar apparatus is discussed.
Date: December 31, 1995
Creator: Bateman, V.I.; Hansche, B.D. & Solomon, O.M.
Partner: UNT Libraries Government Documents Department

Remote detection of trace effluents using Resonance Raman spectroscopy: Field results and evaluation

Description: Resonance Raman spectroscopy (RRS) possesses many characteristics that are important for detecting, identifying and monitoring chemical effluents. Raman scattering is a coherent, inelastic, two-photon scattering process where an exciting photon of energy h{nu} promotes a molecule to a virtual level and the subsequently emitted photon is shifted in frequency in accordance with the rotational-vibrational structure of the irradiated species, thereby providing a unique fingerprint of the molecule. Under resonance enhancement, the Raman scattering cross-sections have been observed to increase up to 6 orders of magnitude above the normal scattering cross-sections, thereby providing the practical basis for a remote chemical sensor. Some of the other advantages that a Raman sensor possesses are: (1) very high selectivity (chemical specific fingerprints), (2) independence of the spectral fingerprint on the excitation wavelength (ability to monitor in the solar blind region), (3) chemical mixture fingerprints are the sum of its individual components (no spectral cross-talk), (4) near independence of the Raman fingerprint to its physical state (very similar spectra for gas, liquid, solid or solutions), (5) no absolute calibration is necessary because all Raman signals observed from a given species can be compared with the Raman signal for N{sub 2}, whose concentration is known very accurately, and (6) insensitivity of the Raman signature to environmental conditions (no quenching, or interference from water vapor). In this presentation, the technology of resonance Raman spectroscopy as applied to the detection of narcotics production activities will be presented along with some recent experimental results.
Date: October 1, 1995
Creator: Sedlacek, A.J. & Chen, C.L.
Partner: UNT Libraries Government Documents Department

Towards measuring the charge radius of {sup 6}He and {sup 8}He.

Description: We report on the progress towards measuring the charge radius of {sup 6}He and {sup 8}He nuclei by performing laser spectroscopy on these helium atoms in a magneto optical trap (MOT). First tests to produce neutral {sup 6}He atoms via the {sup 12}C({sup 7}Li, {sup 6}He){sup 13}N reaction at the ATLAS accelerator have been successfully conducted. The MOT apparatus including the laser system and the discharge source to populate the metastable level are currently being set up.
Date: May 15, 2002
Creator: Mueller, P.; Wang, L.-B.; Bailey, K.; Drake, G. W. F.; Du, X.; Greens, J. et al.
Partner: UNT Libraries Government Documents Department

[Studies of autoionizing states relevant to dielectronic recombination. Final report]

Description: Laser spectroscopy experiments on autoionizing states of alkaline earth atoms allow the inverse process, dielectronic recombination, to be studied in great detail under controlled and variable conditions. The research is also relevant to problems in physical chemistry involving excited molecules, and it has helped to clarify the physical processes of zero kinetic energy electron spectroscopy and coherent control.
Date: October 15, 1999
Creator: Gallagher, Thomas P.
Partner: UNT Libraries Government Documents Department

Ultrafast scanning probe microscopy

Description: The authors have developed a general technique which combines the temporal resolution of ultrafast laser spectroscopy with the spatial resolution of scanned probe microscopy (SPM). Using this technique with scanning tunneling microscopy (STM), they have obtained simultaneous 2 ps time resolution and 50 {angstrom} spatial resolution. This improves the time resolution currently attainable with STM by nine orders of magnitude. The potential of this powerful technique for studying ultrafast dynamical phenomena on surfaces with atomic resolution is discussed.
Date: January 1, 1994
Creator: Botkin, D.; Weiss, S.; Ogletree, D. F.; Salmeron, M. & Chemla, D. S.
Partner: UNT Libraries Government Documents Department

Detecting Molecular Properties by Various Laser-Based Techniques

Description: Four different laser-based techniques were applied to study physical and chemical characteristics of biomolecules and dye molecules. These techniques are liole burning spectroscopy, single molecule spectroscopy, time-resolved coherent anti-Stokes Raman spectroscopy and laser-induced fluorescence microscopy. Results from hole burning and single molecule spectroscopy suggested that two antenna states (C708 & C714) of photosystem I from cyanobacterium Synechocystis PCC 6803 are connected by effective energy transfer and the corresponding energy transfer time is {approx}6 ps. In addition, results from hole burning spectroscopy indicated that the chlorophyll dimer of the C714 state has a large distribution of the dimer geometry. Direct observation of vibrational peaks and evolution of coumarin 153 in the electronic excited state was demonstrated by using the fs/ps CARS, a variation of time-resolved coherent anti-Stokes Raman spectroscopy. In three different solvents, methanol, acetonitrile, and butanol, a vibration peak related to the stretch of the carbonyl group exhibits different relaxation dynamics. Laser-induced fluorescence microscopy, along with the biomimetic containers-liposomes, allows the measurement of the enzymatic activity of individual alkaline phosphatase from bovine intestinal mucosa without potential interferences from glass surfaces. The result showed a wide distribution of the enzyme reactivity. Protein structural variation is one of the major reasons that are responsible for this highly heterogeneous behavior.
Date: August 3, 2007
Creator: Hsin, Tse-Ming
Partner: UNT Libraries Government Documents Department

Fast events in protein folding

Description: The primary objective of this work was to develop a molecular understanding of how proteins achieve their native three-dimensional (folded) structures. This requires the identification and characterization of intermediates in the protein folding process on all relevant timescales, from picoseconds to seconds. The short timescale events in protein folding have been entirely unknown. Prior to this work, state-of-the-art experimental approaches were limited to milliseconds or longer, when much of the folding process is already over. The gap between theory and experiment is enormous: current theoretical and computational methods cannot realistically model folding processes with lifetimes longer than one nanosecond. This unique approach to employ laser pump-probe techniques that combine novel methods of laser flash photolysis with time-resolved vibrational spectroscopic probes of protein transients. In this scheme, a short (picosecond to nanosecond) laser photolysis pulse was used to produce an instantaneous pH or temperature jump, thereby initiating a protein folding or unfolding reaction. Structure-specific, time-resolved vibrational probes were then used to identify and characterize protein folding intermediates.
Date: April 1, 1996
Creator: Woodruff, W.; Callender, R.; Causgrove, T.; Dyer, R. & Williams, S.
Partner: UNT Libraries Government Documents Department

Magnetic resonance and optical spectroscopic studies of carotenoids. Progress report, December 1, 1994--November 30, 1995

Description: The fundamental goals of this project are (1) to understand the role of a host matrix in the formation and decay mechanisms of carotenoid cation radical and dication and (2) to determine the special properties of carotenoids that enable them to serve as photoprotective agents in photosynthesis and as possible components in electron transfer processes. Results to date are discussed briefly. Work will continue as outlined in the original proposal with emphasis on using simultaneous electrochemistry EPR, and optical methods, variable temperature electrochemistry using microelectrodes and fast scans to examine the more unstable intermediates formed upon electrochemical oxidation of synthetically prepared carotenoids.
Date: June 1, 1995
Creator: Kispert, L.D.
Partner: UNT Libraries Government Documents Department

Laser induced fluorescence imaging of thermal damage in polymer matrix composites

Description: A simple, fluorescence-based imaging system was developed for identifying regions of thermal damage in polymer-matrix composites (PMCs). PMCs have important applications where low weight and high mechanical strength are needed. One concern in the aerospace industry is the tendency of some PMC materials to become irreversibly damaged when exposed to high temperatures. Traditional nondestructive evaluation (NDE) techniques are capable of detecting physical flaws, such as cracks and delaminations, but have not proven effective for detecting initial heat damage, which occurs on a molecular scale. Spectroscopic techniques such as laser-induced fluorescence provide an attractive means for detecting thermal damage on large, irregularly shaped surfaces. This paper describes instrumentation capable of rapidly detecting thermal damage in graphite/epoxy components.
Date: December 31, 1996
Creator: Wachter, E.A.; Fisher, W.G. & Meyer, K.E.
Partner: UNT Libraries Government Documents Department