Patrick J. McCann

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.

IV–VI compound midinfrared high-reflectivity mirrors and vertical-cavity surface-emitting lasers grown by molecular-beam epitaxy

Midinfrared broadband high-reflectivity Pb1−xSrxSe/BaF2 distributed Bragg reflectors and vertical-cavity surface-emitting lasers (VCSELs) with PbSe as the active material were grown by molecular-beam epitaxy. Because of an extremely high index contrast, mirrors with only three quarter-wave layer pairs had reflectivities exceeding 99%. For pulsed optical pumping, a lead salt VCSEL emitting at the cavity wavelength of 4.5–4.6 μm operated nearly to room temperature (289 K).

Above-room-temperature continuous-wave mid-infrared photoluminescence from PbSe/PbSrSe quantum wells

Strong photoluminescence between 3 and 4 μm was observed at temperatures as high as 55 °C from PbSe/PbSrSe multiple-quantum-well structures grown on BaF2 (111) substrates by molecular-beam epitaxy. Fabry–Perot interference fringes dominated the spectra, indicating that the luminescence was primarily due to stimulated emission processes. Peak emission energies were determined by fitting Gaussian functions to the spectra, and they showed that emission energies at 25 °C decreased from 402 to 312 meV as quantum-well thickness increased from 40 to 200 A. The temperature tuning coefficient was also observed to decrease from 0.400 meV/K for a 200 A multiple-quantum-well sample to 0.313 meV/K for a 40 A multiple-quantum-well sample.

Simultaneous NO and CO(2) measurement in human breath with a single IV-VI mid-infrared laser.

A tunable diode laser absorption spectroscopy (TDLAS) system equipped with a IV-VI mid-IR laser operating near 5.2>mu;m was used to measure exhaled nitric oxide (eNO) and carbon dioxide (CO(2)) simultaneously in human breath over a single exhalation. Breath was sampled in real time, and eNO levels were measured from seven volunteers, two steroid-naive asthmatics and five nonasthmatics. Measured CO(2) levels were used as an internal standard to verify correct breath collection and calculate eNO values. Calculated eNO concentrations agreed well with reported values for asthmatic and nonasthmatic individuals.

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.

Carrier dynamics in self-organized quantum dots and their application to long-wavelength sources and detectors

Carrier dynamics in self-organized quantum dots have been studied using temperature-dependent differential transmission spectroscopy and room temperature high-frequency electrical impedance measurements on quantum dot lasers. These results suggest the existence of a long relaxation time (∼100 ps) for the excited state carriers at higher temperatures with the dominant scattering mechanism being electron hole scattering, The long relaxation time is exploited to realize far-infrared sources and detectors based on intersubband transitions in quantum dots. Quantum dot detectors with large detectivity (D * = (9-10)×10 9 cm Hz 1 2 /W) and responsivity (R = 100 mA/W) have been reported at T = 40 K. A unique unipolar intersubband quantum dot laser (13.3 μm) has also been reported at T = 283 K. using the long intersubband relaxation time and the short interband recombination time to achieve population inversion between the ground and the excited states.

Molecular beam epitaxy of InSb on Si substrates using fluoride buffer layers

The molecular beam epitaxy of InSb/Si structures was accomplished using group IIa fluoride buffer layers. InSb growth was initiated by opening the In and Sb shutters simultaneously at substrate temperatures between 300 °C and 400 °C, producing In-terminated InSb(111)-A surfaces on CaF2/Si(111) substrates. Reflection high-energy electron diffraction, electron channeling, and high resolution x-ray diffraction measurements indicated that the InSb layers were of good crystalline quality. Electron mobilities at room temperature were as high as 65 000 cm2/V s for an 8-μm-thick InSb layer grown on CaF2/Si(111). On CaF2/Si(001) substrates, the InSb layers grew in the (111) orientation with two domains 90° apart. These InSb layers and ones grown on BaF2/CaF2/Si(111) substrates exhibited inferior electrical and structural properties compared to structures grown on CaF2/Si(111) substrates.

Room-temperature far-infrared emission from a self-organized InGaAs/GaAs quantum-dot laser

Far-infrared spontaneous emission at 300 K and lower temperatures, due to intersubband transitions in self-organized In0.4Ga0.6As/GaAs quantum dots, has been characterized. Measurements were made with a multidot layer near-infrared (∼1 μm) interband laser. The far-infrared signal, centered at 12 μm, was enhanced after the interband transition reached threshold at 300 K. The results are explained in terms of the carrier dynamics in the dots.

Phase equilibria and liquid phase epitaxy growth of PbSnSeTe lattice matched to PbSe

The phase equilibria data necessary for growing solid compounds of Pb1−xsSnxsSe1−ys Teys lattice matched to PbSe from melts consisting of (Pb1−xLSnxL)1−z (Se1−yLTeyL)z are presented. Liquidus data for values of xL from 0% to 40% and yL from 0% to 40% for temperatures between 450 and 540 °C are also presented. The influence of tellurium on the liquidus temperature is shown to be negligible at least for yL less than 40%. A crossover in the liquid‐solid tie lines of tin, xs vs xL, for layers grown at 650 and 450 °C is observed at xL equal to 14%. The liquid‐solid tie‐line data for tellurium, ys vs yL, show a low segregation coefficient relative to selenium for yL less than 40%, thus explaining tellurium’s limited influence on the liquidus temperature. The lattice‐matching conditions for xL =5%, 10%, and 20% are yL =16.4%, 25%, and 33.5%, respectively. A significant lattice‐pulling effect is observed for the 5% tin case and is expected for the 10% and 20% tin cases. This effect, along with the low relative se...

Band gaps, effective masses and refractive indices of PbSrSe thin films: Key properties for mid-infrared optoelectronic device applications

Key properties of PbSrSe thin films grown by molecular beam epitaxy have been studied for mid-infrared optoelectronic device applications. Detailed knowledge of the material parameters for the device design is required. The material parameters considered are: temperature-dependent band gaps, composition (or band gap)-dependent effective masses, and energy-dependent refractive indices. The study has been carried out by a combination of temperature-dependent photoluminescence and absorption measurements with the theoretical models on PbSrSe thin films of Sr compositions of as high as 0.276. The derived empirical equations for band gaps, effective masses, and refractive indices have been employed successfully in PbSe/Pb0.934Sr0.066Se multiple quantum well mid-infrared laser systems, for studying the band offsets and subband behavior. We have shown that the derived material parameters clearly promise of being applied to other PbSrSe thin films and PbSe/PbSrSe heterostructure systems for their optoelectronic a...