Mid-infrared lasers made from IV-VI semiconductor materials are used by our group to assemble tunable laser spectrometers, which we have used to perform a variety of molecular absorption spectroscopy experiments [1-13]. Our group has made significant contributions to the TLS field by developing new applications in the area of non-invasive medical diagnostics (breath analysis) and by creating more user-friendly instrumentation. The picture at the upper right shows an early laboratory prototype instrument equipped with a closed-cycle cooling system for the laser/detector assembly, a 100 meter multi-pass gas sampling cell, associated electronics, and custom-written software. This TLS system along with additional TLS instruments designed and built by Ekips Technologies were used to perform the work documented in the references listed below. The plots to the right show measured laser emission spectra in the 1874-1877 cm-1 range for different laser injection currents, a second harmonic laser absorption spectrum for a gas sample containing nitric oxide (NO), and corresponding NO linestrengths from the Hitran database. TLS instruments exhibit excellent molecular selectivity (with multiple species and isotopic detection capabilities), fast response times (typically less than one second), and high sensitivity (less than 1 ppb minimum detection limits). Such features, for example, allow real-time measurement of specific biomarker molecules in exhaled breath. The figure below at right shows a second harmonic laser absorption spectrum in the 1912 cm-1 spectral range for an exhaled breath sample where unambiguous signals for exhaled NO (ppb range) and CO2 (% range) are clearly observed. The figures below show NO and CO2 concentration trends for real-time exhaled breath measurements. The first plot on the bottom left shows the initially high NO concentration from the upper airway, which is due to the high levels of NO in the nasal cavity, while the lower airway has a much lower NO concentration. Lower airway breath sample is confirmed by the end-tidal peak in the CO2 trend. It is well established that high levels of exhaled NO are associated with inflamed airway and that an inflamed airways is a chronic condition of untreated asthma. The second plot below on the left shows NO and CO2 trends for two asthmatic breath samples, one from a patient treated with inhaled corticosteroid anti-inflammatory therapy and the other from an untreated patient. The clear difference between lower airway NO concentrations, 8.9 ppb versus 52.9 ppb, shows the utility of TLS in evaluating lung health and monitoring therapy regimens. Visit the EkipsTechnologies website (www.breathmeter.com) for more information on the application of this TLS technology to non-invasive medical diagnostics.
