Using Ge etalon in gas sensing project involving quantum cascade lasers

Jagadeeshwari (Esha) Manne, PhD student, University of Alberta Project: Infrared absorption spectroscopy with Quantum cascade laser. The advance of Quantum cascade (QC) lasers fabricated by band structure engineering offers an attractive new option for IR absorption spectroscopy. QC-DFB lasers are of particular interest to gas-sensing applications because they emit single frequency radiation which falls within the 3-15 um window, where the fundamental absorption bands of most of the molecules are located. Research Activities: QC laser characterization Exploring different strategies for trace gas detection and comparing the detection limits and sensitivity for open-path measurements.

I am a graduate student pursuing my doctoral studies at the University of Alberta. The Ge- etalon will be used for non-profit research here at the university. I am presently working on a gas sensing project involving Quantum cascade laser.

The mid-IR region is ideally suited for absorption spectroscopy since the fundamental vibrational transitions of a number of molecules lie here. Quantum cascade (QC) lasers  fabricated by band structure engineering offer an attractive new option for sensitive IR absorption spectroscopy. Distributed feed-back pulsed QC lasers are of particular interest for they allow the realization of a room temperature, compact IR source with relatively high output power. In particular, their combination with the pulsed-CRDS technique has the potential for high sensitivity trace gas analysis. The goal of our present work is to develop a technique for quantitative online analysis of trace constituents in exhaled breath.  We are using pulsed-CRDS technique in combination with a mid IR QC laser operating near 970 cm^-1 to measure ammonia levels in exhaled breath. An unlocked ring-down cavity was designed for these studies which can be operated at atmospheric or reduced pressure. We have already attained a detection limit of 25 ppb for ammonia. We are in a process of improving the system to get down to sub ppb levels with this technique.

The etalon will be used for characterization of the laser which would be an important step in choosing the right parameters for the laser for gas-sensing applications.

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