Cavity Ringdown Spectroscopy of PH2 Radical in 465-555 nm

Absorption spectra of jet-cooled PH2 radicals were recorded in the wavelength range of 465- 555 nm using cavity ringdown spectroscopy. The PH2 radicals were produced in a supersonic jet by pulsed direct current discharge of a mixture of PHa and SF6 in argon. Seven vibronic bands with fine rotational structures have been observed and assigned as 0 0^, 2 0^n, and 2 1^n （n=1- 3） bands of the A^2A1- X~ 2B1 electronic transition. Rotational assignments and rotational term values for each band were re-identified, and the molecular parameters including rotational constants, centrifugal distortion constants, and spin-rotation interaction constants were also improved with reasonably high precision. In addition, large perturbations observed in each quantum number of total angular momentum of the a axis level of the excited vibronic states were briefly discussed.

Determination of breath isoprene in 109 suspected lung cancer patients using cavity ringdown spectroscopy

Background:Lung cancer is one of the most common malignant tumors worldwide.Currently,effective screening methods for early lung cancer are still scarce.Breath analysis provides a promising method for the pre-screening or early screening of lung cancer.Isoprene is a potential and important breath biomarker of lung cancer.Material and Methods:To investigate the clinical value of isoprene for diagnosing lung cancer patients,a cavity ringdown spectroscopy(CRDS)based near-real time,sensitive analysis method of breath isoprene is developed in our lab.In this paper,92 breath samples from lung cancer patients,17 breath samples from patients with benign lesions,and 107 breath samples from healthy people were collected.Results:Research indicates that breath isoprene concentration is significantly higher in healthy individuals(221:3±122:2 ppbv)than in patients with lung cancer(112:0±36:6 ppbv)and benign lung lesions(127:9±41:2 ppbv).The result of Receiver Operating Characteristic(ROC)curve suggests that the concentration of isoprene is meaningful for the diagnosis of lung cancer(AUC=0:822,sensitivity=63:6%,specificity=90:2%,P<0:01).Conclusion:This study demonstrates that the CRDS breath isoprene analysis system can effectively analyze a large sample of human breath isoprene,and preliminarily confirms the use of breath isoprene as a biomarker for lung diseases.

Agile cavity ringdown spectroscopy enabled by moderate optical feedback to a quantum cascade laser

Cavity ringdown spectroscopy(CRDS),relying on measuring the decay time of photons inside a high-finesse optical cavity,offers an important analytical tool for chemistry,physics,environmental science,and biology.Through the reflection of a slight amount of phase-coherent light back to the laser source,the resonant optical feedback approach effectively couples the laser beam into the optical cavity and achieves a high signal-to-noise ratio.However,the need for active phaselocking mechanisms complicates the spectroscopic system,limiting its primarily laboratory-based use.Here,we report how passive optical feedback can be implemented in a quantum cascade laser(QCL) based CRDS system to address this issue.Without using any phase-locking loops,we reflect a moderate amount of light(–18.2 dB) to a continuous-wave QCL simply using a fixed flat mirror,narrowing the QCL linewidth from 1.2 MHz to 170 kHz and significantly increasing the laser-cavity coupling efficiency.To validate the method's feasibility and effectiveness,we measured the absorption line(P(18e),2207.62 cm^(−1)) of N_(2)O in a Fabry–Perot cavity with a high finesse of ~52000 and an inter-mirror distance of 33 cm.This agile approach paves the way for revolutionizing existing analytical tools by offering compact and high-fidelity mid-infrared CRDS systems.

Preliminary investigation into feasibility of dissolved methane measurement using cavity ringdown spectroscopy technique

For the exploration of gas hydrate resources by measuring the dissolved methane concentration in seawater, a continuous-wave cavity ringdown spectroscopy (CW-CRDS) experimental setup was constructed for trace methane detection. A current-modulation method, rather than a cavity-modulation method using an optical switch and a piezoelectric transducer, was employed to realize the cavity excitation and shutoff. Such a current-modulation method enabled the improvement of the experimental setup construction and stability, and the system size and stability are critical for a sensor to be deployed underwater. Ringdown data acquisition and processing were performed, followed by an evaluation of the experimental setup stability and sensitivity. The obtained results demonstrate that great errors are introduced when a large fitting window is selected if the analog-to-digital converter has an insufficient resolution. The ringdown spectrum of methane corresponding to the 2 nu(3) band R(4) branch was captured, and the methane concentration in lab air was determined to be 2.06 ppm. Further experiments for evaluating the quantitative ability of this CW-CRDS experimental setup are underway from which a high-sensitivity methane sensor that can be combined with a degassing system is expected.