Applications of quantum cascade lasers in chemical sensing

Distributed Feedback (DFB) QC lasers operate on inherently single frequency, but their tuning range is limited. We show that Continuous Wave (CW) QC DFB lasers, due to its high thermal load and relatively wide working temperature range, could tune over 10cm in a single current ramp pulse as short as 100μsec, thus giving more capability for this kind of robust QC lasers for chemical sensing. In this paper, we tested the tuning range by using this laser to measure the CO2 dissolved in water. Due to strong absorption in the MIR by water, direct spectroscopic measurement of CO2 in water has been limited to optical path lengths of only dozens of microns, and measurable concentration resolution of only 200mg/L. The high power and brightness of Quantum Cascade lasers could penetrate much deeper optical depths[1-3], i.e. 100s microns, and providing much higher averaging speed to achieve higher concentration resolution. We demonstrate that we could penetrate as deep as 800micron of water with our tunable EC QC laser built upon the amplifier above.