Characterization of background reflectivity for MEDUSA

The DARPA MEDUSA program goal is to detect, locate, and identify electro-optical threats in the vicinity of a moving platform. Laser sensing will be employed to find these threats by looking for anomalous reflections from threat sensors. However, the reflectivity variability (clutter) in both natural and manmade backgrounds will inherently limit target detection levels. In parallel with advanced component development by several aerospace contractors, a study of this clutter limitation was initiated in the long-wave (LW) and midwave (MW) infrared spectral regions to properly drive system design parameters. The analysis of clutter and associated limits on detection has been a major component of LANL efforts in laser remote sensing for non-proliferation. LANL is now analyzing existing data and conducting additional selected measurements in both the LWIR (9 and 10.6 pm) and MWIR (4.6 pm) in support of the DARPA program to increase our understanding of these clutter limitations and, thereby aid in the design and development of the MEDUSA system. The status of the LANL effort will be discussed. A variety of different natural and manmade target types have been investigated. Target scenes range from relatively low clutter sites typical of a southwestern desert to higher clutter downtown urban sites. Images are created by conducting raster scans across a scene interest. These images are then analyzed using data clustering techniques (e g K-means) to identify regions within the scene that contain similar reflectivity profiles. Data will be presented illustrating the reflectivity variability among different samples of the same target type, Le. within the same cluster, and among different data clusters. In general, it is found that the variability of reflectivities among similar targets is well represented by a log-normal distribution. Furthermore, manmade target tend to have higher reflectivities and more variability than natural targets. The implications of this observation for MEDUSA systems designed to locate and identify threat sensors will be discussed. The implications for chemical sensing applications will also be addressed

Single photon excimer laser photodissociation of highly vibrationally excited polyatomic molecules

The ir + uv photodissociation of SF/sub 6/ has been performed using CO/sub 2/ and ArF lasers. The two-color photolysis significantly enhances the photodissociation process over ArF irradiation alone and is found to preserve the initial isotopic specificity of the ir excitation process

Multiphoton-induced fluorescence and ionization of B/sup 1/. sigma. /sup +/ carbon monoxide

The B/sup 1/..sigma../sup +/ state of carbon monoxide was created by a two-photon absorption of 230-nm laser radiation. The B/sup 1/..sigma../sup +/ state was identified by the positions of the 0-0 absorption band Q-branch and the vibrational bands of B/sup 1/..sigma../sup +/ ..-->.. A/sup 1/PI fluorescence occurring in the 525-nm region. Collision-induced b/sup 3/..sigma../sup +/ ..-->.. a/sup 3/PI emission in the 350-nm region was also observed. The lifetimes of both the B/sup 1/..sigma../sup +/ state and the b/sup 3/..sigma../sup +/ state were measured as well as the self-quenching rate constants and the B/sup 1/..sigma../sup +/ quenching rate by N/sub 2/. In addition to the two-photon-induced fluorescence of B/sup 1/..sigma../sup +/ carbon monoxide, a three-photon ionization was observed. Laser power-dependence studies indicated that ionization of the B/sup 1/..sigma../sup +/ state is readily saturated, implying that most B/sup 1/..sigma../sup +/ state CO is ionized rather than fluorescing. Measurement of the polarization ratio for circularly and linearly polarized excitation of fluorescence and ionization suggests that another three-photon process is occurring and occurs more efficiently for linear polarization

Intramolecular isotope effect in laser multiphoton dissociation of CH_2DCH_2Cl

The ratio r = [HCl]/[DCl], for the decomposition of ethyl 2d_1 chloride, CH_2DCH_2Cl, induced by intense CO_2 laser beams, has been measured under different experimental conditions. Changes in beam energy, beam geometry, rotational lines, irradiation time and pressure have no discernible effect on r. It is shown that a narrow distribution with an average excess energy of E+V = 15 ± 2 photons (35–46 kcal/mole) and RRKM theory are mutually consistent with the observed value of r = 2.6 ± 0.1. The implications of these results for the mechanism of multiphoton absorption are analyzed

Two-photon optically pumped molecular gas visible laser. [Ammonia]

Recent investigations of the multiphoton ionization (MPI) spectrum of gaseous ammonia have led to the discovery of a novel two-photon pumped molecular gas electronic transition laser. Resonant, two-photon electronic excitation of NH/sub 3/ in the near uv (approx. 305 nm) leads to the first observation of fluorescence from NH/sub 3/ excited states (B and C'), and, at higher pressures, to lasing action (approx. 570 nm) between numerous C' and A state vibronic levels. A frequency-doubled Nd:YAG pumped dye laser (a few mJ) is focused into a cell containing NH/sub 3/ (or ND/sub 3/). Stimulated emission is observed in the forward and backward direction at NH/sub 3/ pressures greater than approx. 200 torr, without external mirrors to provide feedback. Conversion coefficiencies (output NH/sub 3/ pulse energy/input pulse energy) as high as 2% have been observed

Ultraviolet Laser Photochemistry of Halogenated Methanes

The uv laser photochemistry of CF/sub 2/Br/sub 2/, CCl/sub 4/, CCl/sub 3/F, and CCl/sub 2/F/sub 2/ was studied. The emission spectra and dynamics of the halogenated alkyl radicals formed from the excimer laser photolysis of these compounds are reported. Possible mechanistic routes are also examined. Some results are given from studies on the kinetics of CCl, CCl/sub 2/, and CClF ground state radicals with various reactants

Multiphoton laser-induced-fluorescence studies of simple species

Recent studies have demonstrated multiple-photon excitation of atomic species. Bischel and coworkers have provided a detailed description of two-photon excitation fluorescence in the detection of atoms generated in a low pressure discharge and its possible application as a diagnostic tool in flame and plasmas. It is also believed that such techniques can be useful in detecting molecular transients which are difficult to detect otherwise as demonstrated in two-photon laser-induced fluorescence (LIF) detection of NO. In this paper, we discuss our recent two-photon LIF studies on I and Br atoms, which are produced via laser photolysis of molecular precursors. The two-photon LIF study of HS and DS radicals is presented as a test case for the detection of other important radical species such as C/sub 2/H and CH/sub 3/, which are currently being investigated in our laboratory. In addition, excitation of three-photon resonances of I/sub 2/, N/sub 2/, and H/sub 2/ is discussed

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

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

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]

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

Title: Target Characterization in 3D Using Infrared Lidar Target Characterization in 3D Using Infrared Lidar

ABSTRACT We report examples of the use of a scanning tunable CO 2 laser lidar system in the 9-11 µm region to construct images of vegetation and rocks at ranges of up to 5 km from the instrument. Range information is combined with horizontal and vertical distances to yield an image with three spatial dimensions simultaneous with the classification of target type. Object classification is made possible by the distinct spectral signatures of both natural and man-made objects. Several multivariate statistical methods are used to illustrate the degree of discrimination possible among the natural variability of objects in both spectral shape and amplitude