Infrared microspectroscopy using prism-based spectrographs and focal plane array detection.

Several prism-based spectrographs employing a mercury cadmium telluride (MCT) focal plane array detector have been interfaced to an infrared microscope. In the combined system, the area-defining aperture of the microscope also served as the entrance slit to the spectrograph. This investigation considered the fundamental limits of diffraction for both the spectrograph and microscope in order to determine both the spatial and spectral resolution of the system as a whole. Experimental results for spectral resolution, spectral range, and peak-to-peak noise have been presented. Finally, the dynamic capabilities of one spectrograph/microscope combination were investigated.

Rapid molecular imaging using attenuated total internal reflection planar array infrared spectroscopy for the analysis of counterfeit pharmaceutical tablets.

A planar array infrared (PA-IR) spectrograph containing an attenuated total internal reflection (ATR) accessory has been constructed in order to permit rapid analysis of poorly transmitting materials. The technique has been optimized to allow molecular spectroscopic information to be collected in roughly 2 seconds with a corresponding peak-to-peak noise value as low as 2.14 x 10(-4) absorbance units. Additionally, up to 150 spectra could be extracted from sample sizes as large as 6 mm where each spatial element measured 40 x 200 microm at the sample position. An application study for this technique entailed developing an embedding method that allows cross-sectioned pharmaceutical tablets to be brought into intimate contact with the internal reflection element (IRE) of the accessory. A supplemental investigation involved calculating the yield strength of multiple IRE materials in order to determine the maximum amount of pressure that can be applied to a sample without damaging the IRE. Finally, feasibility was demonstrated for using the instrument/accessory as a means to rapidly authenticate suspected counterfeit pharmaceutical tablets.

Infrared microspectroscopic imaging using a large radius germanium internal reflection element and a focal plane array detector.

Previously, we established the ability to collect infrared microspectroscopic images of large areas using a large radius hemisphere internal reflection element (IRE) with both a single point and a linear array detector. In this paper, preliminary work in applying this same method to a focal plane array (FPA) infrared imaging system is demonstrated. Mosaic tile imaging using a large radius germanium hemispherical IRE on a FPA Fourier transform infrared microscope imaging system can be used to image samples nearly 1.5 mm x 2 mm in size. A polymer film with a metal mask is imaged using this method for comparison to previous work. Images of hair and skin samples are presented, highlighting the complexity of this method. Comparisons are made between the linear array and FPA methods.

Prism-based infrared spectrographs using modern-day detectors.

A comparison of prism-based spectrographs to grating-based spectrographs is made when each of the systems is coupled to a modern-day liquid-nitrogen-cooled photovoltaic array detector. A comparison of the systems is also made using a room-temperature microbolometer array detector. Finally, infrared microspectroscopy of samples whose size is approximately 10 micrometers will be demonstrated using a prism spectrograph outfitted with both types of detectors. The results of the study show that prism-based spectrographs offer an economical alternative to grating-based systems when spectral coverage is more critical than spectral resolution. The results also demonstrate that spectra with good signal-to-noise ratios can be collected on any of the systems with a total integration time of 10 seconds or less.