Ultra-broadband external-cavity quantum cascade laser synchronization for mode-hop free tuning

The LASVEGAS (Laser Absorption Spectrometer for Volatile and Evolved GASes) instrument is a prototype ultrabroadband external-cavity (EC) quantum cascade laser (QCL) -based spectrometer under development for potential extraterrestrial mission, where simultaneous broad spectral coverage and fine resolution are highly desirable. This is accomplished with an array of EC-QCLs with unique spectral coverage, allowing efficient scaling of the spectral emission range over hundreds of cm^-1. To date, the tuning range of the instrument exceeds 600 cm^-1 within a span bounded approximately by 944 cm-1 and 1930 cm^-1. To access local mode hop free tuning, we leverage a simulation of the EC geometry in order to synchronize the parameters of the EC. While specific mode hop free scans are limited by the dynamic range of the laser drive current and are limited to the scale of 1.5 cm^-1, mode hop free sections of adjacent scans can be stitched together. The simulation is used to coordinate the position of the stages in the EC, controlling the EC “air” length and the grating angle.