Ultrasensitive, self-calibrated cavity ring-down spectrometer for quantitative trace gas analysis.
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 4×10-11cm-1Hz-1/2has also been demonstrated. A minimum detectable absorption coefficient of 5×10-12cm-1has been obtained by averaging about 100 spectra recorded in 2  h. The quantitative accuracy is tested by measuring the CO2concentrations in N2samples prepared by the gravimetric method, and the relative deviation is less than 0.3%. The trace detection capability is demonstrated by detecting CO2of 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.
Bing
B
Chen
Yu R
YR
Sun
Ze-Yi
ZY
Zhou
Jian
J
Chen
An-Wen
AW
Liu
Shui-Ming
SM
Hu
D002138:Calibration; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005740:Gases / Q000032:analysis*; D008832:Microchemistry / Q000295:instrumentation*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013057:Spectrum Analysis / Q000295:instrumentation*; D020349:Surface Plasmon Resonance / Q000295:instrumentation*
D005740:Gases