Development of a laser heterodyne radiometer for regional methane leak detection.

We have developed and tested a laser heterodyne radiometer (LHR) for detecting methane leaks from upstream oil and gas infrastructure and landfills that uses the Sun as the signal light source, demonstrating here sensitivity sufficient to detect "super-emitter" leaks (>50/, 1166 slm). Tracking optics follow the Sun during its apparent daily transit across the sky, and the system collects direct absorption data and optionally the 1f and 2 wavelength modulation spectroscopy (WMS) signals. The direct absorption data are processed in real time using a retrieval algorithm with a 5 s update rate to reveal the methane concentration versus altitude for each measurement line of sight.

Development of a passive optical heterodyne radiometer for near and mid-infrared spectroscopy.

We have developed a novel laser heterodyne radiometer using a fiber-coupled distributed feedback laser as the local oscillator to perform spectroscopic measurements of small molecules in the near-infrared (NIR) spectral region. Here, we demonstrate measurement of HCN and in the lab and and in the atmospheric column. In addition, we demonstrate detection of a neutral iron, Fe(I), Fraunhofer line in the spectrum of the sun, at a vacuum wavelength of 1559.

Varied line-space grating for flat spectral response of coupling to single-mode fiber.

We use a planar linear grating with varied line-space grooves to introduce a tailored one-dimensional phase variation profile that results in an aberrated point-spread function at the focal plane. A design procedure for the period chirp map for such gratings is developed. As an example, we present theoretical and experimental results on a mechanically ruled, varied line-space echelle grating in single-mode fiber-coupled optical multiplexers in the wavelength region of 1545 nm.