To obtain a real-time noninvasive analysis of the content of the aqueous humor (AH) in the eye, a confocal dark-field ophthalmic probe was designed and optimized by ray-tracing software. The confocal technique allows Raman spectrometric sampling of the AH with suppressing signals from the surrounding tissues. Dark-field illumination prevents the excitation light to reach the vulnerable retinal tissue directly. In order to evaluate the optical performance and safety of this method, a functional prototyped eye contact probe has been designed and tested on ex vivo rabbit eyes.

A trace chemical detector is described that combines external-cavity quantum cascade lasers and a mercury cadmium telluride camera to capture hyperspectral images of the diffuse reflectance from a target surface in the long-wave infrared. The system is able to generate individual hypercubes in <0.1  s. When raster scanning the laser beam over the target surface, areal coverage rates of >60  cm²  /  s have been achieved. Results are presented for standoff distances ranging from 0.1 to 25 m. Hyperspectral images generated by the system are analyzed for spectral features that indicate the presence of trace surface contaminants. This approach has been found to be highly capable of detecting trace chemical residues on a wide variety of surfaces, and we present a collection of detection results to demonstrate the capabilities of this technology. Examples include the detection of 10  μg of saccharin powder on a wide range of substrates, 0.2  μg of an explosive residue on a computer keyboard, residual pharmaceuticals within a plastic baggie, and a contaminated fingerprint on cell phone case.

Gas chromatography (GC) is a staple analytical technique used to separate chemical mixtures (analytes) prior to identification with a hyphenated technique, such as mass spectrometry or Fourier transform infrared (IR) spectroscopy. Traditionally, analytes elute through the GC separation column where they are detected when they exit. We have developed a technique to perform in situ IR spectroscopy during the process of separating the analytes along the GC column. This is achieved by spin coating the stationary phase onto a germanium prism and actively probing the stationary phase in an attenuated total reflectance configuration with a quantum cascade laser.. The GC column is formed by pressing a molded epoxy lid, with grooves that form the tubular column, onto the stationary phase coated prism.

Since solids are only sometimes seen en masse in a pure bulk form, and for liquids other than water almost never, a capability to model reflectance spectra from analytes deposited on various substrates would be highly advantageous. If available, the real, n  (  ν  )  , and imaginary, k  (  ν  )  , components of the complex refractive index,   n∼    =  n  +  ik, can be used to simulate infrared spectra, accounting for reflection, refraction, and absorption phenomena as a function of wavelength. We focus on using the Pacific Northwest National Laboratory (PNNL) derived n  /  k vectors for solid and liquid analytes deposited as thin layers on different types of substrates including conductors, such as aluminum, and inorganic dielectrics, such as glass. The model is an adaptation of the Monte Carlo ray trace modeling program, TracePro, extended through the use of its macrolanguage. The model is tested using thin films of organic liquids including silicone oil and no. 2 diesel fuel, as well as organic solids such as caffeine and acetaminophen on aluminum and glass. The predicted spectra for the solid films were compared to experimental hemispherical reflectance data measured using a Fourier transform spectrometer with an integrating sphere. The thickness of the calculated layer is a parameter for predicting the (transflectance) spectra and is obtained using the areal density measured from gravimetric methods to generate the thin-layer samples. Comparison of the calculated spectra with experimental hemispherical reflectance data shows excellent agreement, indicating promise for the use of measured n  /  k data to synthesize reference spectral data. In particular, accounting for the inhomogeneity of the deposits greatly improved the match with experimental data. Finally, the theoretical modeling shows that for thicker layers (ca. 20 to 100  μm) of typical organics possessing moderately strong k values, the longwave infrared features are often saturated and better spectral contrast is obtained from the overtone/combination bands in the shortwave infrared.

We describe an optical bench design that efficiently projects broadband infrared energy from a supercontinuum (SC) source onto an extended target and collects the backscattered return. The optical system enables standoff spectral measurements of surfaces at up to 15 m away with a continuous spectral range from 3.6 to 11  μm. The goal of the optical system is to maximize energy transmission and capture under various fundamental and practical constraints imposed by the SC fiber laser source (broad spectrum, high divergence exiting the fiber), spectrometer (light collimation), detectors (étendue limits), and the overall system (size, weight, and cost). The design effort led to an all-reflective, off-axis configuration for both the transmitter and receiver, using custom-designed enhanced gold surfaces. We are able to successfully capture >90  %   of the source energy and transmit it with low loss to the remote target while maintaining a nearly diffraction-limited Gaussian beam. The receiver telescope matches the detector étendue while providing uniform (±2.5  %  ) off-axis signal collection over the target area to enable scanning of the SC laser spot.

The development of a field-portable fiber-laser based hyperspectral imaging system for standoff detection and identification of trace levels of explosives is presented. The prototype system combines a hybrid of frequency and time-resolved coherent anti-Stokes Raman scattering (CARS) spectroscopy techniques with spatial scanning for rapid detection of microscopic traces of explosives on liquid or solid surfaces. An all-fiber light source architecture enables generation of three CARS excitation beams from a compact, single-unit femtosecond fiber laser and a highly nonlinear optical fiber. The light backscattered from the target surface is collected by a spectrometer, and a high-resolution automated stage system allows for two-dimensional microscopic CARS imaging. We demonstrate trace explosive detection in <100  ms.