Chen Bing, Sun Yu R, Zhou Ze-Yi, Chen Jian, Liu An-Wen, Hu Shui-Ming
Appl Opt. 2014 Nov 10;53(32):7716-23. doi: 10.1364/AO.53.007716.
A cavity ring-down spectrometer is built for trace gas detection using telecom distributed feedback (DFB) diode lasers. The longitudinal modes of the ring-down cavity are used as frequency markers without active-locking either the laser or the high-finesse cavity. A control scheme is applied to scan the DFB laser frequency, matching the cavity modes one by one in sequence and resulting in a correct index at each recorded spectral data point, which allows us to calibrate the spectrum with a relative frequency precision of 0.06 MHz. Besides the frequency precision of the spectrometer, a sensitivity (noise-equivalent absorption) of 4×10 cm Hz has also been demonstrated. A minimum detectable absorption coefficient of 5×10 cm has been obtained by averaging about 100 spectra recorded in 2 h. The quantitative accuracy is tested by measuring the CO concentrations in N samples prepared by the gravimetric method, and the relative deviation is less than 0.3%. The trace detection capability is demonstrated by detecting CO of ppbv-level concentrations in a high-purity nitrogen gas sample. Simple structure, high sensitivity, and good accuracy make the instrument very suitable for quantitative trace gas analysis.
搭建了一台用于痕量气体检测的光腔衰荡光谱仪，该光谱仪采用电信分布式反馈（DFB）二极管激光器。光腔衰荡腔的纵向模式用作频率标记，无需对激光器或高精细度腔进行主动锁定。应用一种控制方案来扫描DFB激光器的频率，依次逐个匹配腔模，并在每个记录的光谱数据点产生一个正确的索引，这使我们能够以0.06 MHz的相对频率精度校准光谱。除了光谱仪的频率精度外，还展示了4×10⁻⁹ cm⁻¹ Hz⁻¹/²的灵敏度（噪声等效吸收）。通过对2小时内记录的约100个光谱进行平均，获得了5×10⁻¹¹ cm⁻¹的最小可检测吸收系数。通过测量重量法制备的N₂样品中的CO浓度来测试定量准确性，相对偏差小于0.3%。通过检测高纯度氮气样品中ppbv级浓度的CO，证明了痕量检测能力。结构简单、灵敏度高和准确性好使得该仪器非常适合定量痕量气体分析。
