A compact, single-pass and low-power-consumption methane sensing system is presented and its sensitivity is investigated for a set of reference cells with pressures of 7.4, 74 and 740 Torr and the same methane concentration of 1351 ppm. A single-mode GaSb-based continuous-wave (CW) distributed feedback (DFB) tunable diode laser at 3270 nm and wavelength modulation spectroscopy were employed to collect 2f spectra in the ν3,R3 band of 12CH4. A modulated Voigt line profile model was used to fit the collected 2f spectra. The best detectivity of 4 ppbm is obtained for the highest pressure cell using an Allan-Werle variance analysis.
We report on the experimental measurement of active region lattice (TL) and electronic temperatures (Te) in terahertz quantum cascade devices based on the phonon-photon-phonon scheme, by means of microprobe band-to-band photoluminescence spectroscopy. Three mesa devices, differing for doping region and number of quantum wells composing the active region, have been investigated. With device on, under band alignment for lasing condition, we
measured a difference (Te - TL) ~ 40 K much smaller than the typical value (Te - TL ~ 100 K) reported for resonantphonon THz QCLs.