Properties of fluoride microresonators for mid-IR applications.

We study crystalline fluoride microresonators for mid-infrared (mid-IR) applications. Whispering gallery mode resonators were fabricated with BaF2, CaF2, and MgF2 crystals. The quality factors were measured at wavelengths of 1.56 and 4.58 µm. The impacts of post-fabrication processing, impurities, and surface water are highlighted. The mid-IR optical losses due to multiphoton absorption are measured. It is found that MgF2 resonators have a room temperature Q-factor of 8.3×106 at a wavelength of 4.58 µm, limited by multiphoton absorption.

Design and performance of indium seals for size-constrained tunable laser spectrometers.

Indium seals have been used extensively in ultra-high vacuum and cryogenic applications. Typically, these seals use indium alongside or in place of other metal gaskets in stainless-steel vacuum flanges, with some custom applications for flanges sealing directly with glass (optics or tubes). Here, we present the design and performance of three pressed indium seals (99.99% In) between aluminum and 0.5 in. diameter sapphire optics and aluminum and gold coated Kovar semiconductor packages (TO-66 and TO-39). Test fixtures were designed to mimic those of future tunable diode laser spectrometers for Earth, planetary, and manned spaceflight environmental monitoring applications. Successful high-hermeticity seals [<10-10 atm cc/s (He)] were achieved for all seals formed with sufficient pressure applied to allow indium to flow between mating surfaces. The hermeticity of the seals was maintained after temperature cycling (-10 to +80 °C, 20 cycles), with the optical seals surviving extended duration tests (-55 to +85 °C, per MIL-STD-883). Semiconductor packages (TO-39) subjected to these extended tests saw a moderate increase in leak rate [∼5 × 10-9 atm cc/s (He)]; however, further testing showed that either the glass-metal package seals or the indium were affected (the sample size was too small to draw firm conclusions for future applications). Overall, these results suggest long-term survivability of indium seals for Kovar-aluminum and sapphire-aluminum interfaces [>10 years at 10-10 atm cc/s (He)], where the coefficient of thermal expansion differs by approximately four times.

Tunable laser spectroscopy for carbon dioxide capnography and water vapor sensing inside a breathing mask: application to pilot life support.

Tunable laser spectroscopy (TLS) near 2683 nm was used to measure carbon dioxide and water vapor inside a pilot mask during jet fighter flights. Measurement frequency was 100 Hz in order to capture breathing profiles and other gas flow dynamics. Analysis of the full inhalation and exhalation breathing cycle allowed precise monitoring of breathing performance and interaction of the pilot with the life-support system. Measurements revealed dynamic phenomena pertaining to mechanical gas flow and pilot respiration that may be used to understand gas delivery stresses imposed upon the pilot and pilot physiology during flight. Typically, such measurements are made with non-dispersive infrared instrumentation for only carbon dioxide with intrinsic challenges regarding time and optical resolution. The TLS approach is a major advance because the sensor is placed directly into the mask improving its time response and enabling use of water vapor measurements that are less impacted from memory effects. This article presents the implementation of TLS and shows highly time-resolved pilot breathing data for high-performance aircraft tests.

Mars laser hygrometer.

We have designed and built a miniature near-IR tunable diode laser (TDL) spectrometer for measuring in situ the water vapor mixing ratio either in the Martian atmosphere or thermally evolved from Martian soil or ice samples. The laser hygrometer uses a thermoelectrically cooled single-mode distributed-feedback TDL at 1.87 microm to scan over a selected vibration-rotation line of both H2O and CO2 near 5327.3 cm(-1). A working prototype that weighs only 230 g has been built and used to generate spectra whose analysis demonstrates precision sensitivities as fine as 1 part in 10(6) by volume in 1 s or 0.1 part in 10(6) in 10 s at Martian pressures and temperatures. Absolute uncertainties of approximately 5% are calculated.