Alcatel Thales III-V laboratory, 1, Avenue Augustin Fresnel, Campus Polytechnique, Palaiseau, France.
Opt Lett. 2010 Nov 1;35(21):3607-9. doi: 10.1364/OL.35.003607.
Optical-feedback cavity-enhanced absorption spectroscopy is demonstrated in the mid-IR by using a quantum cascade laser (emitting at 4.46 μm). The laser linewidth reduction and frequency locking by selective optical feedback from the resonant cavity field turns out to be particularly advantageous in this spectral range: It allows strong cavity transmission, which compensates for low light sensitivity, especially when using room-temperature detectors. We obtain a noise equivalent absorption coefficient of 3 × 10(-9)/cm for 1 s averaging of spectra composed by 100 independent points. At 4.46 μm, this yields a detection limit of 35 parts in 10(12) by volume for N(2)O at 50 mbar, corresponding to 4 × 10(7) molecules/cm(3), or still to 1 fmol in the sample volume.
利用量子级联激光器（发射波长为 4.46μm）在中红外波段演示了光反馈腔增强吸收光谱学。通过从共振腔场进行选择性光反馈，激光线宽减小和频率锁定在该光谱范围内特别有利：它允许强腔透过率，这补偿了低光灵敏度，特别是在使用室温探测器时。我们获得了 3×10(-9)/cm 的噪声等效吸收系数，用于由 100 个独立点组成的光谱的 1 s 平均。在 4.46μm 处，对于 50 毫巴的 N(2)O，这在 10(12)体积分数下产生了 35 部分的检测限，对应于 4×10(7)分子/cm(3)，或者在样品体积中仍然为 1 fmol。
