ABSTRACT
A thermal luminescence (TL) spectroscopy method for detecting organic impurities in water solution is presented. Infrared emissions by the dissolved organic matter are measurable, once a thermal gradient between it and the water medium is established, at those TL frequencies that are absorbed by the contaminant, following irradiation by a pulsed microwave beam. This detection window of opportunity closes as the liquid reaches thermal equilibrium at elevated temperatures and on collapse of the gradient. TL radiance liberated by a suspected contaminated water sample is scanned interferometrically about the maximum thermal gradient event, where N interferograms are acquired and grouped into contiguous sets of two, with N/2 interferogram elements per set. The coadded averages of these sets enhance the sensitivity of measurement to a small variance in emissivity and are Fourier transformed, and the adjacent spectra are subtracted. The difference spectrum is preprocessed with linear baseline, noise filtration, scaling, and parity operators to reveal a clear emissions band signature of the solute of dimethylmethylphosphonate to concentrations of parts per 10(3) and less. An artificial neural network facilitates detection of the contaminant by pattern recognition of the contaminant's infrared band signature.
ABSTRACT
Artificial neural network systems were built for detecting amino acids, sugars, and other solid organic matter by pattern recognition of their polarized light scattering signatures in the form of a Mueller matrix. Backward-error propagation and adaptive gradient descent methods perform network training. The product of the training is a weight matrix that, when applied as a filter, discerns the presence of the analytes on the basis of their cued susceptive Mueller matrix difference elements. This filter function can be implemented as a software or a hardware module to a future differential absorption Mueller matrix spectrometer.
ABSTRACT
A standoff method of detecting liquids on terrestrial and synthetic landscapes is presented. The interstitial liquid layers are identified through their unique molecular vibration modes in the 7.14-14.29-microm middle infrared (fingerprint) region of liberated thermal luminescence. Several seconds of 2.45-GHz beam exposure at 1.5 W cm(-1) is sufficient for detecting polydimethyl siloxane lightly wetting the soil through its fundamental Si-CH3 and Si-O-Si stretching modes in the fingerprint region. A detection window of thermal opportunity opens as the surface attains maximum thermal gradient following irradiation by the microwave beam. The contaminant is revealed inside this window by means of a simple difference-spectrum measurement. Our goal is to reduce the time needed for optimum detection of the contaminant's thermal spectrum to a subsecond exposure from a limited intensity beam.
ABSTRACT
The complete 16-element Mueller matrices for backscattering from amino acids, sugars, and other enantiomorphic compounds pressed into wafer form were measured at infrared wavelengths. For each compound a pair of CO(2) laser lines was selected from the 9.1-11.6-mum region such that one line excited an absorption band in the compound, whereas the other did not. It was observed that at least some of the matrix elements differed significantly depending on which of the two wavelengths was used in the measurement. We propose that a neural network pattern recognition system can be trained to detect the presence of specific compounds based on multiwavelength backscatter Mueller matrix measurements.
ABSTRACT
The optical design of a passive remote sensor, a panoramic spectroradiometer (PANSPEC), and its computer-simulated image performance are presented. PANSPEC monitors the surrounding infrared environment for chemical clouds, detecting a presence once absorption or emission spectra characteristic of the chemical species are resolved. PANSPEC broadcasts chemical presence and cloud heading when equipped with a laser transmitter that projects a polarized laser beam source with phase encryption back through the optical system into object space. Various merit functions were programmed and accessed during computer optimization runs for shaping and positioning of the instrument's semishell entrance window, collector, collimator, interferometer, and imager. The result is a balanced near-diffraction-limited circular image, 6.3 mm across with 10-line pairs/mm spatial resolution at 50% modulation, and an f/2.3 working speed.
ABSTRACT
We treat infrared patterns of absorption or emission by nerve and blister agent compounds (and simulants of this chemical group) as features for the training of neural networks to detect the compounds' liquid layers on the ground or their vapor plumes during evaporation by external heating. Training of a four-layer network architecture is composed of a backward-error-propagation algorithm and a gradient-descent paradigm. We conduct testing by feed-forwarding preprocessed spectra through the network in a scaled format consistent with the structure of the training-data-set representation. The bestperformance weight matrix (spectral filter) evolved from final network training and testing with software simulation trials is electronically transferred to a set of eight artificial intelligence integrated circuits (ICs') in specific modular form (splitting of weight matrices). This form makes full use of all input-output IC nodes. This neural network computer serves an important real-time detection function when it is integrated into pre- and postprocessing data-handling units of a tactical prototype thermoluminescence sensor now under development at the Edgewood Research, Development, and Engineering Center.
ABSTRACT
Computation of Mueller matrix elements by infrared scattering from randomly rough two-dimensional surfaces and results of a method for graphic display of the data are presented. A full wave electromagnetic scattering model first generates raw data elements of the 4 × 4 Mueller matrix F(θ, nλ, kλ, σs(2), ?h(2)?) in beam backscattering angle (θ) ranging from normal to oblique incidence, in refractive index of the beam scatterer (nλ - ikλ) spanning the 9 ≤ λ ≤ 12.5 µm midinfrared band, and in mean-squared slope ((σS(2)) and mean-squared height (?h(2)?) of the scattering surface. These data are next compressed into a graphics format file occupying considerably less computer storage space and mapped into color images of the Mueller elements as viewed on a high-resolution graphics terminal. The diagonal and two off-diagonal elements are animated in the λ-θ plane according to varitions in σs(2) and ?h(2)?. Predicted elements for polarized IR beam energies on vibrational resonance of the surface molecules, and particularly the off-diagonal elements, show subtle properties of the scatterer as viewed in the animation sequences.
ABSTRACT
An optical technique to identify the presence of chemical coatings over rough surfaces is described. It is based on the selective use of elements of the 4 x 4 Mueller matrix. The full-wave theory of electromagnetic scattering is used to predict six independent Mueller elements from randomly rough uncoated (dry) and coated (wet) surface materials as functions of the media complex dielectric coefficients, backscattering angle, and midinfrared wavelengths of laser-beam excitations that are polarization modulated. The set of independent elements at beam wavelengths and backscattering angles [M(mn) (lambda(i), lambda(i))] most sensitive to i optically thick contaminant coatings are statistically obtained from the full-wave database, and detection-parameter sets [lambda(i), lambda(i)] are inputs to another algorithm designed to identify the contaminant coating (when present and interacted by the irradiating beams). These algorithms facilitate the operation of a multi-CO(2) laser-ellipsometer facility now under development at the U.S. Army Chemical Research, Development, and Engineering Center for the remote detection of chemical or biological surface contaminants.
ABSTRACT
The strong mid-infrared bands of contaminant liquids wetting sand and soil can be remotely detected by 0.103-eV laser irradiation with beam intensity well below that which chars the terrain. Emissions from heated nonvolatile interstitial liquid layers and extinction of thermoluminescence by beam-generated vapors of volatile contaminants are spectrally distinct within the infrared contaminant fingerprint spectral region-as measured by a Michelson interferometer based FT-IR radiometer instrument. The contaminant's vibrational resonance intensities change proportionally in magnitude and sign in measured contiguous difference FFT spectra, within a specific beam-to-sample dwell period. The onset irradiation time and period for detecting these bands can differ according to amount and volatility of contaminant, beam intensity and its time of dwell necessary to produce sufficient thermoluminescence flux, and on the quantity of interferogram data acquisitions.
ABSTRACT
Reflectivity changes of Ge have been measured as a function of the intensity of the stronger of two optical beams having different frequencies, the frequency difference being produced through stimulated Rayleigh and Brillouin scattering. The observed nonlinear components of the weak beam reflectivity is smaller, and the diffracted beam generated by the surface grating arising from the interference of the incident beams is drastically reduced, compared to results with equal frequency input beams. The experimental results are compared with theoretical predictions, and, while limited qualitative agreement was obtained, substantial discrepancies remain which have not yet been explained.
ABSTRACT
The changes in the real and imaginary parts of the index of refraction of germanium have been measured at 6943 A as a function of incident power up to 5 MW/cm(2). The results indicate that for nanosecond pulses the primary cause of the change is heating with temperature changes of up to 350 degrees C. In addition, a diffraction grating formed on the surface by interference between the intense beam and a probing beam produces an additional effective change in reflectivity as well as a spatially separated diffracted beam. It is shown that, for a grating spacing of 20 mum, transverse diffusion effects cause no degradation in the effectiveness of the grating.
