Khosrow Namjou

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.

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.

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.

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.

The Breathmeter - A new laser device to analyze your health

It is widely believed that measurement of molecules in exhaled breath can provide a window into the metabolic state of the human body, detect the presence of cancer, monitor respiratory diseases, assess liver and kidney function, determine exposure to toxins, and possibly, even diagnose schizophrenia. Such conjectures are further supported by recent work performed by researchers at the Pine Street Foundation. Laser spectroscopic techniques, in particular, tunable laser absorption spectroscopy (TLAS), are candidate technologies for breath analysis applications. The paper presents the Breathmeter from Ekips Technologies. The Breathmeter is based on TLAS and consists of four primary components: 1) the laser source module, 2) sample gas cell, 3) optical detector, and 4) associated electronics hardware and software. The optical board layout of the breath meter system was shown. Its applications and future works were also discussed

Intersubband gain and stimulated emission in long-wavelength (/spl lambda/=13 /spl mu/m) intersubband In(Ga)As-GaAs quantum-dot electroluminescent devices

The dynamics of injected carriers and the conditions for intersubband gain and population inversion in In(Ga)As-GaAs self-organized quantum dots have been studied. Direct femtosecond pump-probe spectroscopy as a function of temperature and excitation density confirms earlier results and shows a long (>100 ps) electron relaxation time between the excited states and ground state in the dots. Intersubband gains as high as 170 cm/sup -1/ are calculated in the dots. Far-infrared spontaneous emission centered around 13 /spl mu/m is observed in edge-emitting light-emitting diodes. Stimulated emission, with a distinct threshold around 1.1 kA/cm/sup 2/ in the light-current characteristics, is observed in plasmon-enhanced waveguide devices. The intersubband threshold occurs after a threshold is observed for interband lasing (/spl sim/1 /spl mu/m) in the same device.

Evaluation of breath biomarkers and serum haptoglobin concentration for diagnosis of bovine respiratory disease in heifers newly arrived at a feedlot

OBJECTIVE To evaluate exhaled N(2)O (eN(2)O), exhaled CO (eCO), and serum haptoglobin concentrations as diagnostic criteria for bovine respiratory disease (BRD) and determine whether a combination of biomarkers would be useful for predicting health outcomes of heifer calves. ANIMALS 337 heifer calves newly arrived at a feedlot. PROCEDURES Body weights, serum haptoglobin concentrations, and rumen temperatures were determined. Calves (n = 183) were randomly selected for breath sampling. Variables were compared among calves that remained healthy and those requiring treatment. RESULTS Body weight at the time of first and second antimicrobial treatments did not differ from that at arrival, whereas body weight at the time of third antimicrobial treatment was lower. Temperature was lower at arrival, compared with that during antimicrobial treatment. Ratio of eN(2)O:eCO(2) was lowest at arrival, intermediate at the first and second antimicrobial treatments, and greatest at the third antimicrobial treatment. Ratio of eCO:eCO(2) was greater at times of antimicrobial treatment, compared with arrival. Concentration of serum haptoglobin was greatest at the time of the first antimicrobial treatment, lowest at the times of second and third treatments, and intermediate at arrival. Arrival ratios of eN(2)O: eCO(2) and eCO:eCO(2) and concentration of haptoglobin did not differ among heifers subsequently treated 1, 2, or 3 times. CONCLUSIONS AND CLINICAL RELEVANCE Although breath analysis was successfully implemented in a research feedlot, arrival rumen temperature, eN(2)O, eCO, and haptoglobin concentration were not accurate in predicting occurrence of BRD during a preconditioning program. However, these biomarkers might support the diagnosis of BRD.

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.

Breath testing with a mid-IR laser spectrometer

A mid-IR tunable diode laser absorption spectrometer (TDLAS) equipped with a multiple-pass gas cell was used to measure breath samples from a number of student volunteers at the University of Oklahoma. Test subjects included one to two pack-a-day cigarette smokers and non-smokers. The concentrations of four different molecules, N2O, 12CO2, 13CO2 and CO, were measured by each laser scan in the 2206.1 cm-1 to 2207 cm-1 spectral range. The average concentration of nitrous oxide (N2O) increased slightly for smokers versus non-smokers and was generally higher (12%) than the approximately 255 ppm concentration measured in ambient air. Carbon monoxide concentrations, however, were much higher in breath samples from cigarette smokers. Ambient concentrations of carbon monoxide, approximately 0.4 ppm, increased from approximately 1.0 ppm in non-smokers to levels over 13.4 ppm in smokers. These measurements provide clear evidence of the well-known effect that cigarette smoking has on replacing oxygen with carbon monoxide in human hemoglobin. Carbon dioxide concentrations of smokers were generally decreased by approximately 12%. Mid-IR laser measurements also provided 13CO2/12CO2 isotope ratio values, and smokers had a approximately 30% greater concentration of isotopic 13C in their breath. The possible mechanisms for 13CO2 isotopic increases are at present unknown. Overall, long-path TDL spectroscopy of exhalation products is a uniquely powerful tool. The TDL systems can be used for noninvasive diagnosis of a wide range of metabolisms and pathologies.