Ultra-rapid broadband mid-infrared spectral tuning and sensing

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. 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/μs with 380 elements. Applied to spectroscopic sensing, our technique achieves broad spectral coverage (2600 to 3780 cm−1) with moderate spectral resolution (8 cm−1) and rapid acquisition time (∼6.3 μs). 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/μs), 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-infrared ranging and imaging.