Fig. 2: Schematic representation of the hybrid dual-comb spectroscopy signal acquisition.
From: Quantum cascade laser based hybrid dual comb spectrometer
Two quantum cascade laser frequency comb (QCL-FC) modes N (red) and M (blue) spaced by (N-M)·fIBN are frequency tuned by driving current or heat sink temperature variations. This tuning corresponds to variations in the down-converted heterodyne beatnotes (HBN) signals, having amplitudes that are continuously monitored. Retrieval of the variations in the HBN amplitudes enables simultaneous reconstruction of molecular transitions that are spaced by (N-M)·fIBN in the THz frequency domain. RF: radio frequency; IQCL: QCL driving current; TQCL: QCL heat-sink temperature.
