Fast high-resolution spectroscopy of dynamic continuous-wave laser sources

Time-resolved, high-accuracy and high-resolution spectroscopy of rapidly tuned continuous-wave lasers is critical to realizing their full potential for sensing, but is not possible with conventional spectrometers. We demonstrate a coherent dual-comb-based spectrometer capable of measuring continuous-wave optical waveforms at time resolutions of 30 mu s and 320 mu s over terahertz bandwidths. Within each time interval, the spectrometer returns the laser frequency spectrum with kilohertz absolute accuracy and time-bandwidth limited precision. Unlike etalon-based techniques, each measurement is independently calibrated, which allows for discontinuous source tuning between measurements and the characterization of arbitrary continuous-wave waveforms. To demonstrate the broad applicability of the technique, we measure a laser during a nonlinear scan over 28 nm, a laser step-scanned over a 42-nm span containing several molecular absorption lines, a mechanically perturbed laser, and two lasers tuned simultaneously. Our approach should enable optimized waveforms for sensing applications including multispecies gas detection(1-3), coherent laser radar(4-6) and optical metrology(7-9).