James D. Jeffers

Nitric oxide breath testing by tunable-diode laser absorption spectroscopy: application in monitoring respiratory inflammation

We used a high-resolution mid-IR tunable-laser absorption spectroscopy (TLAS) system with a single IV-VI laser operating near 5.2 microm to measure the level of exhaled nitric oxide (eNO) in human breath. A method of internal calibration using simultaneous eNO and exhaled CO2 measurements eliminated the need for system calibration with gas standards. The results observed from internally calibrating the instrument for eNO measurements were compared with measurements of eNO calibrated to gas standards and were found to be similar. Various parameters of the TLAS system for eNO breath testing were examined and include gas cell pressure, exhalation time, and ambient NO concentrations. A reduction in eNO from elevated concentrations (approximately 44 parts in 10(9)) to near-normal levels (<20 parts in 10(9)) from an asthmatic patient was observed after the patient had received treatment with an inhaled glucocorticoid anti-inflammatory medication. Such measurements can help in evaluating airway inflammation and in monitoring the effectiveness of anti-inflammatory therapies.

Measurement of acetaldehyde in exhaled breath using a laser absorption spectrometer

A high-resolution liquid-nitrogen-free mid-infrared tunable diode laser absorption spectroscopy (TDLAS) system was used to perform real-time measurement of acetaldehyde concentrations in human exhaled breath following ingestion of an alcoholic beverage. Acetaldehyde absorption features were measured near 5.79 mum (1727 cm(-1)) using a IV-VI semiconductor laser, a 100 m long path optical gas cell, and second- harmonic detection coupled with wavelength modulation. Acetaldehyde levels were measured with a minimum detection limit of 80 ppb for 5 s integration time. The variations in exhaled acetaldehyde levels over time were analyzed prior to and following ingestion of two different amounts of white wine. A method to calibrate acetaldehyde measurements internally using water vapor absorption lines was investigated to eliminate the need for system calibration with gas standards. The potential of a TDLAS system to be used as a noninvasive clinical tool for measurements of large volatile compounds with possible applications in cancer detection is demonstrated.

Cross-plane thermal conductivity of a PbSnSe/PbSe superlattice material

The cross-plane thermal conductivity of a PbSnSe/PbSe multi-period superlattice (SL) grown by molecular beam epitaxy is obtained from continuous wave photoluminescence (PL) measurements and finite element analysis (FEA). PL measurement and FEA for a structure consisting of a multiple quantum well light emitting layer on top of a PbSnSe/PbSe SL with three different periodicities of 2.4, 3.6, and 4.8 nm revealed a cross-plane lattice thermal conductivity of 0.8 W/mK. The 58% reduction relative to the 1.9 W/mK value for bulk PbSe is attributed to enhanced scattering and/or reflection of acoustic phonons within the short-period SL material.

New widely tunable mid-IR lasers and their use in molecular spectroscopy

Newly available mid-infrared lasers made from IV-VI compound semiconductors exhibit tuning ranges of over 200 cm-1. In addition to allowing detection of a variety of species with a single laser, such wide tunability enables detection of large molecules with broad absorption bands. This paper presents results from detailed measurements of IV-VI diode laser emission obtained using an automated Fourier transform infrared (FTIR) spectroscopic testing system. Single mode emission wavelengths were determined for different combinations of heatsink temperature and injection current. These data were then used to design and perform molecular spectroscopy experiments in which laser emission wavelength was modulated by either current or temperature tuning. Current tuning over narrow spectral regions (up to 3 cm-1) allowed detection of various small to medium sized molecules such as carbon disulfide, ammonium hydroxide, and benzene, but failed to detect larger molecules such as toluene. We show that temperature tuning a IV-VI laser over at least 50 cm-1, however, can enable detection of large molecules such as toluene and improve the detection sensitivity of medium sized molecules such as benzene. This new technique extends the use of mid-infrared laser spectroscopy to measurement of large molecules that do not have resolvable ro-vibrational structure.

Fourier transform spectrometer for high resolution characterization of mid-IR IV-VI diode lasers

A Fourier transform spectrometer was used to characterize the emissions of IV-VI semiconductor mid-IR lasers. A completely automated hardware and software system was used to generate and analyze emission spectra.