V-cavity stabilized quantum cascade laser-based cavity ringdown spectroscopy for rapid detection of radiocarbon below natural abundance

Abstract

Mid-infrared laser absorption spectroscopy utilizing a high-finesse optical cavity enables high precision trace analysis of gas molecules. In particular, optical detection of radiocarbon (14C) based on cavity ringdown spectroscopy using a quantum cascade laser (QCL) is gaining attention as an alternative to accelerator mass spectrometry. This paper reports a compact-packaged narrow-linewidth QCL system utilizing resonant optical feedback from an external V-shaped cavity. Based on frequency noise analysis, the derived laser linewidth is 44 kHz for 100 μs integration time with the capability to perform seamless frequency scanning around 10 GHz. We installed this laser system within a table-top cavity ringdown spectrometer for 14CO2. A single-shot detection limit of 1.2 × 10−9 cm−1 Hz−1/2 leading to a detectable abundance evaluated from a noise analysis of 0.2 in fraction modern 14C for a 10-s averaging time was achieved. This capability of rapid analysis for 14CO2 is suitable for various applications requiring trace 14C analysis.

Development of 2.2 μm cavity ring-down spectrometer for tritiated water analysis

“…In our previous study, frequency stabilization of the DFB diode laser based on optical feedback has been developed for highly sensitive 14 C detection with CW-CRDS and a single detection limit of 1 × 10 −9 cm −1 Hz −1/2 and a reachable detection limit in 10 s measurement (acquisition rate of approximately 55 signals s −1 ) of 5 × 10 −11 cm −1 was demonstrated. 9,27) If systematic fluctuations can be controlled for 600 s with the acquisition rate of 10 2 signals s −1 , the required sensitivity can be achieved. In addition, since absorption line intensities in the 4 μm region are around one order of magnitude larger than those in the 2 μm region, further improvement in sensitivity could be expected by transitioning to that wavelength region.…”

“…4) Recently, a novel analytical method based on laser absorption spectroscopy has been developed for radioactive carbon-14, one of the radionuclides that emit low-energy β particles. [5][6][7][8][9] In this method, highly sensitive cavity-enhanced laser absorption spectroscopy, called cavity ring-down spectroscopy (CRDS), 10,11) is utilized, and quantitative and rapid determination of 14 C was demonstrated for biomedical applications and nuclear engineering. For tritium, optical spectroscopic data were obtained by several different techniques, such as laser absorption spectroscopy, Fourier transform infrared spectroscopy, and CRDS.…”

Spectroscopic detection of radiocarbon dioxide based on optical feedback linear cavity enhanced absorption spectroscopy

“…To alleviate this, measurement of 14 CO 2 spectra based on cavity ringdown spectroscopy (CRDS) is proposed. [20][21][22] CRDS is time-based measuring technique, which deduces the intracavity absorption from the variation of the ringdown time. 23 Consequently, CRDS is immune to the relative intensity noise and the fluctuation of the coupling coefficient.…”

“…However, in cavity‐based spectroscopy, the variation of the coupling coefficient of the laser to the cavity, caused by the frequency discrimination between the laser and the cavity, is the dominant noise, which seriously deteriorates the detection sensitivity. To alleviate this, measurement of 14 CO 2 spectra based on cavity ringdown spectroscopy (CRDS) is proposed 20–22 . CRDS is time‐based measuring technique, which deduces the intracavity absorption from the variation of the ringdown time 23 .…”