6.5-12 μm ultra-broadband long-wavelength infrared laser with superior temporal stability seeded by a single-wavelength quantum cascade laser

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Abstract
Ultra-broadband long-wavelength infrared (LWIR) lasers covering 8–15 μm wavelength range are uniquely valuable for spectroscopic applications in chemical sensing, environmental monitoring, and biomedical diagnostics, owing to their alignment with fundamental molecular vibrational fingerprints. To resolve multiple complex molecular signatures and probe transient chemical dynamics, broad spectral coverage and stable temporal characteristics are two essential requirements, which remain as significant technical challenges. Optical-optical modulation of continuous-wave (CW) quantum cascade lasers (QCLs) has recently been demonstrated for generating broadband stable mid-infrared radiation below 5 μm, however, its extension into the more critical LWIR region has not yet been realized. Here, we demonstrate a CW QCL seeded optical parametric amplifier (OPA) generating coherent ultra-broadband LWIR radiation spanning from 6.5 to 12 μm. A high temporal stability with a standard deviation of 1.2% is measured. At a pump energy of 4.5 μJ, the CW-seeded OPA achieves a LWIR peak-power gain of 7 orders. As a proof of concept, a multi-wavelength absorption spectroscopic measurement of polystyrene is demonstrated, employing the ultra-broadband LWIR laser. Our results showcase a simple and effective method in generating LWIR radiation with a broad spectral coverage, high peak-power gain and stable temporal characteristics for advanced spectroscopic applications.
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