Distributed Feedback Quantum Cascade Lasers for Trace Gas Detection

This proposal concerns the fabrication and delivery of the Quantum Cascade (QC) semiconductor laser as a coherent light source operating in the mid-infrared region of the optical spectrum. This laser is unique as a semiconductor laser in that it utilizes only one carrier type, electrons, from recycled intersubband transitions to efficiently generate photons [1]. The photon emission energy itself is determined by the difference in subband energies. The QC laser is lightweight, compact, energy efficient and widely tunable by either temperature or current. The QC laser emission wavelength can span the entire 3.4 - 17 mm region employing the exact same semiconductor materials, growth and fabrication technologies by modification of QW layer thickness and periodicity [2]. The wavelength region between 4 - 12 mm is particularly important for high sensitivity detection of such compounds as NOx, N2O, CO, CO2, H2O and CH4. QC lasers are reliable, stable sources with intrinsic linewidths of a few MHz [3] and are capable of output powers useful for trace gas detection [4-7]. The QC laser is an ideal, cost effective source for extraterrestrial atmospheric and planetary sensing of biogenic compounds.