The Regional Laser and Biotechnology Laboratories (RLBL) is a user facility available to visiting scientists. A variety of kinetic and spectroscopic measurements are made routinely. Apparatus for several physical studies is described, and representative results are presented. One important class of measurements is pump-probe, in which a sample is excited with a pulsed laser source, then probed, or examined, with a second light source. Another focus of the RLBL is providing reliable methods for biophysical measurements.

A technique has been developed which allows the determination of a two-photon absorption cross-section to be made relative to the Raman scattering cross-section in nitrogen. Spatial and temporal effects associated with the lasers are ratioed out to give a result in-dependent of laser parameters. The necessary theory to extract a cross-section from the measured ratio of a Coherent Anti-Stokes Raman Scattering (CARS) signal in N₂ to a four-wave mixing signal in NO has been developed. The technique has been demonstrated on the R22 S12(J" = 9 1/2) line in NO and a cross-section of (2.9 + 1.8) x 10-49 cm4-s was determined. This technique appears to be applicable to a number of other diatomic molecules.

Experiments will be described which illustrate how tunable dye lasers are used to determine the quantum state distributions of the free radicals that are produced in photochemical systems. Other experiments will be described to show how lasers can be used to accurately measure the effects of internal energy upon the rate of chemical reactions.

High resolution (10 MHz) stimulated Raman Q-branch spectra of molecules important in combustion are reported. In addition to the normal linear pressure broadening, line interference which leads to collisional narrowing is demonstrated. If proper account is not taken of this latter effect, large errors in the temperature and/or pressure as extracted from the spectral profile can result. The formalism which describes the spectrum and accounts for both line broadening and line interference effects is reviewed. The resulting ("relaxation") matrix equation (NxN for an N-line spectrum) can be reduced by means of a perturbation solution to a spectral distribution involving a line-broadening coefficient and a line-interference coefficient for each line. This approach is applied successfully for the spectra of N₂ and CO. Further, it is shown that for the simple diatomics the J-dependent line broadening/interference coefficients can be expressed in terms of simple scaling/fitting laws for the rates of rotationally inelastic collisions. The use of fitting laws leads to a simple parameterization of all the elements of the relaxation matrix and therefore allows a determination of the spectrum. This latter approach is applied to the analysis of the Q-branch spectrum of NO, for which the perturbation solution cannot be applied because of the nearly degenerate Q-branch lines arising from its two ground state electronic configurations. It is shown that collisional narrowing in the NO Q-branch spectrum is reproduced quite well by employing a fitting law model.

Rotational population measurements have been made on nitrogen neutrals and nitrogen ions in a pulsed supersonic expansion. The ions were produced by electron impact of the neutrals under conditions identical to those used for measurements of the neutrals. For nitrogen neutrals, two-photon laser induced fluorescence on the a--X transition was used to determine distributions, while single photon laser induced fluorescence on the well known B-X transition was used for the ions. This is the first example of the use of two-photon LIF for the detection and monitoring of N₂ in a supersonic beam. Our data on the ion is compared to data in the literature for both the X and B states as well as populations calculated from our neutral data using the dipole model and the dipole plus 9 quadrupole interactions model. Details of these comparisons will be discussed.

Resonance ionization mass spectrometry has been used to study the formation of atomic ions. A one-wavelength, two-photon ionization scheme was used that is potentially applicable to nearly 50 elements. Thermal vaporization from rhenium filament substrates is described, and the controlling physical processes are enumerated. The laser characteristics which affect ionization are also discussed. Results are presented for vanadium and iron.

The microscopic spatial distribution of biological compounds can be imaged using a coherent anti-Stokes Raman scattering (CARS) microscope. Spatial resolution of less than one micrometer has been achieved and excellent molecular discrimination using chemically similar molecular species has been obtained using digital image processing techniques.

A fiber optic device has been realized to perform in-situ spectroscopic measurements of physiological fluids, blood in particular. Based on the use of a single optical fiber, the device can be mounted on any kind of in-vivo catheter. Solid state light emitter, receptor, as well as fiber directional couplers, have been used throughout the design, to achieve good feasibility and handiness. A two wavelength technique has been adopted to monitor hemoglobine oxygen saturation.

The use of lasers as a means to generate populations of such transients as radicals, excited states and ions in the laboratory and as a probe of their concentration is discussed. The experimental arrangements for studies of the spectroscopy of radicals and ions, the excited state dynamics of radicals and reaction kinetics of these species are illustrated using examples from our laboratory and others. Specific results discussed include the reaction kinetics of the C₃ radical, spectroscopy and excited state dynamics of the cyclopentadienyl and NO₃ radicals and initial experiments on the dimethyldi-acetylene ion and the reaction system of C₄H/C₄H₂.

Multiphoton ionization of molecules can be observed easily in both premixed and diffusion flame environments. Recent experiments on NO, PO, and butadiene show that this method is very sensitive for trace species detection and is well suited for making profile measurements. Multiphoton ionization complements laser-induced fluorescence techniques and now appears to be the best prospect for extending optical diagnostic studies to additional polyatomic molecules.

Optical diagnostics in the area of high pressure propellant combustion require techniques which are effective in a highly turbulent, luminous, and sooting environments. Broadband, folded Coherent Anti-Stokes Raman Spectroscopy (CARS) shows particular promise in addressing these problem areas. The coherence and high intensity of the pulsed CARS signal make spatial and temporal rejection of interfering light possible. Sample volumes can be small and well defined when non-colinear beam geometrics are used. With pulsed and broad band lasers, the temperature and concentration of a flame species can be measured in a single shot, thus making the CARS technique suitable for the measurement of rapidly changing phenomena. This report describes our experimental setup for CARS measusrements and the progress we have made thus far in the application of CARS to double-base rocket propellant flames.

Resonance and near-resonance absorption of frequency-stabilized, grating-tuned CW CO laser radiation have been used to measure real time CO and NO production in several combustion and energetic molecule reaction systems studied in a shock tube. In the resonance absorption studies in which the CO product was probed, examples of the extraction of key rate constants in several decomposition and oxidation reactions will be discussed. The NO product, which exhibits strong near-resonance absorption of the CO laser radiation at high temperatures and pressures, was probed in the decomposition of highly energetic molecules such as methyl nitrite and nitromethane. Additionally, an example of the use of the CO laser for the probing of H₂O under high temperature and pressure conditions in shock waves will also be reviewed.

Atmospheric pressure flames stabilized on research burners have been probed with cw ion lasers to measure detailed temperature and species concentration profiles. Using high-throughput collection optics and multichannel spectroscopic detection, Raman spectra are obtained and converted to profiles of major species and temperature. Due to coincidences of electronic transitions with laser wavelengths, the key radical species C₂, CN, NCO, OH, and NH have also been profiled, using fluorescence spectroscopy. The experimental apparatus, observations, and analysis of typical data are discussed.

We have measured time-dependent absorption spectra following nanosecond laser photolysis of some nitrotoluenes in several solvents. In non polar media, rapid intra-molecular hydrogen atom transfer occurs in electronically excited 2,4-dinitrotoluene to yield the aci-quinoid isomer, which is observed as a broad transient absorption. In methanol and in acetonitrile the initial aci-form subsequently undergoes deprotonation with a first-order rate constant of ca. 2 x 105 s-1, to form the 2,4-dinitrobenzyl anion. The corresponding anion is also generated from 2,4,6-trinitrotoluene in methanol, but we have been unable to demonstrate that its production occurs via the aci-form.

Processes for the combustion and gasification of coal present challenging instrumenta-tion problems. The combination of high temperatures (2,000°-3,000°F), high pressure (100-1,000 psig), corrosive atmospheres, and erosive conditions create difficult sensor design and material problems. As advanced processes (e.g., entrained gasifiers) are pursued, sensors must fulfill additional performance requirements such as higher accuracy and faster response time in order to meet process safety and control needs. This paper is divided into two major sections. The first section provides background information on fossil energy processes. The second section describes a technique developed to enhance combustion spectroscopy by reducing the interference caused by blackbody radiation. This technique, named BLOC (Blackbody Observation and Cancellation), can reduce the effects of blackbody radiation by 20 dB or more. The two sections presented are: Section I -- Fossil energy background. Section II -- Combustion emission line spectroscopy.

Surface enhanced Raman scattering (SERS) spectra and intensities vs voltage dependences are influenced by the chemical parameters an experimentalist can select for the electrolytes in electrochemical cells with coinage metal (Ag, Cu, and Au) electrodes. Specific examples with different salts (e.g., 1 M KNO₂ and 1 M KSCN) in aqueous electrolytes are presented, particularly in terms of the influence of the solubility of Ag salts on the SERS character-istics. The influence of the electrolyte concentration, pH value, temperature, and solvent on the SERS characteristics is also reviewed.

Several laser-controlled thermal and photochemical processes at liquid/solid interfaces are described. These include etching of silicon dioxide and copper in a number of aqueous and organic solvents. Reactions range from simple, thermally-enhanced types to photo-chemically sensitized systems. Advantages and limitations of the liquid phase in surface processing are discussed.

Normal unenhanced Raman spectra (NURS) of CO and 02 adsorbed on Ni(111) have been recorded at residual gas pressure, as well as after an exposure of 105L CO. This is the very first observation of such spectra from low polarizability molecules adsorbed on poor Raman signal enhancers. Spectra have been recorded at -175°C as well as at room temperature. Ni-C and C-0 stretches of on-top and bridges species along with the 0-0 vibration of physisorbed oxygen are assigned.