A thermophotovoltaic (TPV) device design based on multiple quantum well (MQW) materials composed of Pb0.81Sn0.19Se wells and Pb0.80Sr0.20Se barriers, which are nanostructured materials that can be gown on low-cost silicon, was modeled to predict electrical power generation densities. MQW materials with intersubband energy gaps of 343 meV and 450 meV in a dual junction configuration were studied. For a thermal radiator at a temperature of 1364ºC the short circuit current density was estimated to be 12.1 A/cm2 for each junction. Open circuit voltages for each junction ranged from 130 mV to 262 mV depending on bandgap and temperature. Power generation densities for this dual junction device increased from 2.7 W/cm2 to 3.4 W/cm2 as temperature decreased from 50ºC to 7ºC. Using a conservative value of $1/cm2 for the manufacturing of this silicon-based TPV device technology, the costs for this novel electrical power generation technology are projected to be less than $0.30/W.
A promising absorption spectroscopy application for mid-IR lasers is exhaled breath analysis where sensitive,
selective, and speedy measurement of small gas phase biomarker molecules can be used to diagnose disease and monitor
therapies. Many molecules such as nitric oxide, ethane, formaldehyde, acetaldehyde, acetone, carbonyl sulfide, and
carbon disulfide have been connected to diseases or conditions such as asthma, oxidative stress, breast cancer, lung
cancer, diabetes, organ transplant rejection, and schizophrenia. Measuring these and other, yet to be discovered,
biomarker molecules in exhaled breath with mid-IR lasers offers great potential for improving health care since such
tests are non-invasive, real-time, and do not require expensive consumables or chemical reagents. Motivated by these
potential benefits, mid-IR laser spectrometers equipped with presently available cryogenically-cooled IV-VI lasers
mounted in compact Stirling coolers have been developed for clinical research applications. This paper will begin with a
description of the development of mid-IR laser instruments and their use in the largest known exhaled breath clinical
study ever performed. It will then shift to a description of recent work on the development of new IV-VI semiconductor
quantum well materials and laser fabrication methods that offer the promise of low power consumption (i.e. efficient)
continuous wave emission at room temperature. Taken together, the demonstration of compelling clinical applications
with large market opportunities and the clear identification of a viable pathway to develop low cost mid-IR laser
instrumentation can create a renewed focus for future research and development efforts within the mid-IR materials and
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.
The properties of quantum dot intersubband light emitters and the unique carrier dynamics in the quantum dots that lead to the realization of these long wavelength devices are described. The favorable relaxation times can be exploited to realize far IR emission and detection based on intersubband transitions in the dots.
Carrier dynamics in self-assembled quantum dots, grown by molecular beam epitaxy, have been studied. The temperature dependence of the relaxation times, measured by room temperature high frequency impedance response of quantum dot lasers and by low temperature (T=4K) differential transmission spectroscopy. strongly suggests that electronhole scattering is the dominant scattering mechanism in quantum dots. The favorable relaxation times can be exploited to realize far infrared emission and detection based on intersubband transitions in the dots.
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.