基于双共振光学参量振荡器的中红外连续滤波游标光谱
Mid-infrared continuous-filtering Vernier spectroscopy using a doubly resonant optical parametric oscillator
摘要：
我们提出了一个连续过滤游标光谱仪工作在3.15-3.4 $μ$ m的范围内，基于飞秒双共振光学参量振荡器，一个腔的精细度为340，光栅安装在振镜扫描器和两个光电二极管。该光谱仪允许在25 ms内以8 GHz分辨率采集一个跨越250 nm带宽的光谱，足以在大气压下解析分子线。主动锁定确保连续光谱的良好频率和强度稳定性，并实现连续信号采集和有效平均。使用法布里-珀罗标准具或电流计扫描器位置信号来校准相对频率标度。我们测量纯CH ${_4}$以及干燥和实验室空气的光谱，并通过模型光谱的多线拟合提取CH ${_4}$和H ${_2}$ O浓度。光谱仪的品质因数为1.7x10 ${^-}$ ${^9}$ cm ${^-}$ ${^1}$ Hz ${^-}$ ${^1}$ ${^/}$ ${^2}$/光谱元件，CH ${_4}$的最小可检测浓度为360 ppt Hz ${^-}$ ${^1}$ ${^/}$ ${^2}$，16 s后平均值降至90 ppt。
英文摘要：
We present a continuous-filtering Vernier spectrometer operating in the 3.15-3.4 $μ$m range, based on a femtosecond doubly resonant optical parametric oscillator, a cavity with a finesse of 340, a grating mounted on a galvo scanner and two photodiodes. The spectrometer allows acquisition of one spectrum spanning 250 nm of bandwidth in 25 ms with 8 GHz resolution, sufficient for resolving molecular lines at atmospheric pressure. An active lock ensures good frequency and intensity stability of the consecutive spectra and enables continuous signal acquisition and efficient averaging. The relative frequency scale is calibrated using a Fabry-Perot etalon or, alternatively, the galvo scanner position signal. We measure spectra of pure CH${_4}$ as well as dry and laboratory air and extract CH${_4}$ and H${_2}$O concentrations by multiline fitting of model spectra. The figure of merit of the spectrometer is 1.7x10${^-}$${^9}$ cm${^-}$${^1}$ Hz${^-}$${^1}$${^/}$${^2}$ per spectral element and the minimum detectable concentration of CH${_4}$ is 360 ppt Hz${^-}$${^1}$${^/}$${^2}$, averaging down to 90 ppt after 16 s.
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