Application of Balanced Detection to Absorption Measurements of Trace Gases with Room-Temperature, Quasi-cw Quantum-Cascade Lasers

• Published in: Applied optics (2004) Vol. 40; no. 6; p. 812
• Main Authors: Sonnenfroh, D M, Rawlins, W T, Allen, M G, Gmachl, C, Capasso, F, Hutchinson, A L, Sivco, D L, Baillargeon, J N, Cho, A Y
• Format: Journal Article
• Language: English
• Published: United States 20.02.2001
• ISSN: 1559-128X
• DOI: 10.1364/AO.40.000812

Distributed-feedback quantum-cascade (QC) lasers are expected to form the heart of the next-generation mid-IR laser absorption spectrometers, especially as they are applied to measurements of trace gases in a variety of environments. The incorporation of room-temperature-operable, single-mode QC lasers should result in highly compact and rugged sensors for real-world applications. We report preliminary results on the performance of a laser absorption spectrometer that uses a QC laser operating at room temperature in a quasi-cw mode in conjunction with balanced ratiometric detection. We have demonstrated sensitivities for N(2)O [10 parts in 10(6) volume-mixing ratio for a 1-m path (ppmv-m)] and NO [520 parts in 10(9) volume-mixing ratio for a 1-m path (ppbv-m)] at 5.4 mum. System improvements are described that are expected to result in a 2 orders of magnitude increase in sensitivity.