Ultra-rapid broadband mid-infrared spectral tuning and sensing

Abstract: Tunable mid-infrared lasers are essential for optical sensing and imaging. Existing technologies, however, face challenges in simultaneously achieving broadband spectral tunability and ultra-rapid scan rates, limiting their utility in dynamic scenarios such as real-time characterization of multiple molecular absorption bands. Here, we present a high-speed approach for broadband wavelength sweeping in the mid-infrared region, leveraging spectral focusing via difference frequency generation between a chirped fiber laser and an asynchronous, frequency-modulated electro-optic comb. This method enables pulse-to-pulse spectral tuning at a speed of 5.6 THz/us with 380 elements. Applied to spectroscopic sensing, our technique achieves broad spectral coverage (2600-3780 cm-1) with moderate spectral resolution (8 cm-1) and rapid acquisition times (6.3 us). Notably, the controllable electro-optic comb facilitates high scan rates of up to 2 Mscans/s across the full spectral range (corresponding to a speed of 60 THz/us), with trade-offs in number of elements (~30) and spectral point spacing or resolution (33 cm-1). Nevertheless, these capabilities make our platform highly promising for applications such as flow cytometry, chemical reaction monitoring, and mid-IR ranging and imaging.