Erik S. Roese

Differential absorption Mueller matrix spectroscopy and the infrared detection of crystalline organics

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.

Photopolarimetric lidar dual-beam switching device and Mueller matrix standoff detection method

We present an optomechanical switching device (OSD) for a photopolarimetric lidar system with differential-absorption Mueller matrix spectroscopy standoff detection method. An output train of alternate continuous-wave CO2 laser beams [...L1:L2...] is directed onto suspect chemical-biological (CB) aerosol plume or the land mass it contaminates (S) vis-à-vis the OSD, where L1 [L2] is tuned on [detuned off] a resonant molecular absorption moiety of CB analyte. Moreover, both incident beams and their backscattered radiances, from S, are polarization-modulated synchronously so as to produce gated temporal voltage waveforms called scattergrams recorded on focus at the receiver end of polarization lidar sensor system. All 16 elements of the Mueller matrix (Mij) of S are measured via digital or analog filtration of constituent frequency components in these running scattergram data streams (phase-sensitive detection). A collective set of normalized differential elements {ΔMi,j} (ratioed to element M11) that are susceptible to the analyte, probed on-then-off its molecular absorption band, form a unique detection domain that is scrutinized. Any mapping onto this domain in Mueller-space, from incoming sensor scattergram data sets preprocessed by algorithm and forwarded through a trained neural network pattern recognition system, cues a standoff detection event.

Thermal luminescence sensor for ground-path contamination detection

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 contaminants thermal spectrum to a subsecond exposure from a limited intensity beam.

Thermal luminescence water monitor

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 contaminants infrared band signature.

Surface contamination detection by means of near-infrared stimulation of thermal luminescence

A method for remotely detecting liquid chemical contamination on terrestrial surfaces is presented. Concurrent to irradiation by an absorbing near-infrared beam, the subject soil medium liberates radiance called thermal luminescence (TL) comprising middle-infrared energies (upsilon(mir)) that is scanned interferometrically in beam duration tau. Cyclic states of absorption and emission by the contaminant surrogate are rendered from a sequential differential-spectrum measurement [deltaS(upsilon(mir), tua)] of the scanned TL. Detection of chemical warfare agent simulant wetting soil is performed in this manner, for example, through pattern recognition of its unique, thermally dynamic, molecular vibration resonance bands on display in the deltaS(upsilon(mir), tau) metric.

Development of inkjet-deposited test standards for optical sensors

The US Army Research, Development and Engineering Command – Chem Bio center is leading an inter-agency working group, to expand chemical inkjet printing techniques, and to fabricate surface standards in a controlled, uniform and quantifiable fashion, for the evaluation of stand-off active and passive optical systems. A CommercialOff-the-Shelf (COTS) standard inkjet printer was redesigned to deposit precise amounts of chemicals and explosive material on defense relevant surfaces, allowing for the generation of calibration test standards. RDECOM-CB is currently utilizing the inkjet techniques to support an Army forensics detection program where inkjet samples are used for detection of trace energetic materials and illicit drugs of abuse within residual latent fingerprints, as well as leading a North Atlantic Treaty Organization (NATO) Task Group (TG) to develop and recommend to NATO a reference standard methodology (or methodologies) for fabricating quantifiable surface standards for the evaluation of stand-off active and passive optical systems. QA/QC were performed on printed materials to determine accuracy and precision. Raman imaging and the Image-J software package was used to calculate particle statistics such as size distribution, average particle size, and fill factor. The software algorithm finds individual particles and calculates their area from a brightfield image montage. An approximate diameter of each particle, and the total fractional area of the surface covered are also calculated. For qualitative analysis Raman Chemical Imaging is performed to confirm the chemical make-up of the deposited samples. For the quantitative analysis, printed samples were analyzed by either Ion Chromatography with Conductivity Detection (IC-CD) for potassium chlorate based explosives analysis or LC-MS/MS for RDX analysis. We will present the results of inkjet samples produced for the Army forensics program as well as NATO benchmark exercise that consisted of printing trace amounts of inkjet explosive samples and performing QA/QC procedures to determine accuracy, precision and mass transport efficiency.

Thermal luminescence spectroscopy chemical imaging sensor.

The authors present a pseudo-active chemical imaging sensor model embodying irradiative transient heating, temperature nonequilibrium thermal luminescence spectroscopy, differential hyperspectral imaging, and artificial neural network technologies integrated together. We elaborate on various optimizations, simulations, and animations of the integrated sensor design and apply it to the terrestrial chemical contamination problem, where the interstitial contaminant compounds of detection interest (analytes) comprise liquid chemical warfare agents, their various derivative condensed phase compounds, and other material of a life-threatening nature. The sensor must measure and process a dynamic pattern of absorptive-emissive middle infrared molecular signature spectra of subject analytes to perform its chemical imaging and standoff detection functions successfully.