Spectroscopy in the molecular fingerprint spectral region (6.7–20 µm) yields critical information on material structure for physical, chemical, and biological sciences. Despite decades of interest and effort, this portion of the electromagnetic spectrum remains challenging to cover with conventional laser technologies. In this paper, we present a simple and robust method for generating super-octave, optical frequency combs in the fingerprint region through intra-pulse difference frequency generation in an orientation-patterned gallium phosphide crystal. The attainable brightness from this tabletop source reaches the same level achievable by infrared synchrotron radiation with a bandwidth spanning from 4 to 12 µm. We demonstrate the utility of this unique coherent light source for high-precision, dual-frequency-comb spectroscopy of methanol and ethanol vapor. These results highlight the potential of laser frequency combs for a wide range of infrared molecular sensing applications from basic molecular spectroscopy to nanoscopic imaging.

中文翻译：

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明亮的宽带红外频率梳进行分子指纹识别

分子指纹光谱范围（6.7–20 µm）中的光谱学提供了有关物理，化学和生物科学材料结构的重要信息。尽管经过数十年的关注和努力，电磁波频谱的这一部分仍然难以用传统的激光技术覆盖。在本文中，我们提出了一种简单而稳健的方法，该方法可通过在取向图案化的磷化镓晶体中通过脉冲内差频生成在指纹区域生成超倍频程光频梳。从此台式光源获得的亮度达到了红外同步加速器辐射所能达到的相同水平，其带宽范围为4至12 µm。我们展示了这种独特的相干光源在高精度，甲醇和乙醇蒸气的双频梳状光谱。这些结果凸显了激光频率梳在从基本分子光谱到纳米成像的各种红外分子传感应用中的潜力。