Remote or standoff detection of greenhouse gases, air pollutants, and biological agents with innovative ultrafast laser technology attracts growing interests in recent years. Hybrid femtosecond/picosecond coherent Raman spectroscopy is considered as one of the most versatile techniques due to its great advantages in terms of detection sensitivity and chemical specificity. However, the simultaneous requirement for the femtosecond pump and the picosecond probe increases the complexity of optical system. Herein, we demonstrate that air lasing naturally created inside a filament can serve as an ideal light source to probe Raman coherence excited by the femtosecond pump, producing coherent Raman signal with molecular vibrational signatures. The combination of pulse self-compression effect and air lasing action during filamentation improves Raman excitation efficiency and greatly simplifies the experimental setup. The air-lasing-assisted Raman spectroscopy was applied to quantitatively detect greenhouse gases mixed in air, and it was found that the minimum detectable concentrations of CO2 and SF6 can reach 0.1% and 0.03%, respectively. The ingenious designs, especially the optimization of pump-seed delay and the choice of perpendicular polarization, ensure a high detection sensitivity and signal stability. Moreover, it is demonstrated that this method can be used for simultaneously measuring CO2 and SF6 gases and distinguishing 12CO2 and 13CO2. The developed scheme provides a new route for high-sensitivity standoff detection and combustion diagnosis.
Background: Preoperative assessment clinics have great benefits in reducing surgical cancellations, saving hospital resources and improving patient satisfaction. However, previous studies did not focus on patients with comorbidities. With advancements in medicine and aging population, the number of elderly patients with multiple comorbidities is increasing. This study was designed to assess the effectiveness of a preoperative assessment clinic for patients with multiple comorbidities.Methods: This prospective, observational study enrolled patients with multiple comorbidities from Nov 1, 2019 to Oct 31, 2020 in a tertiary teaching hospital in China. Patients either visited the preoperative assessment clinic before admission or received an anesthesia consultation after admission. The impact of clinic visits on operating room cancellations, length of hospital stay before surgery, length of hospital stay after surgery, major postoperative complications, incidence of postoperative intensive care unit (ICU) admission, readmission to any hospital within 30 days after surgeries and total in-hospital costs were analyzed.Results: A total of 326 eligible cases were included. Eighty-seven of 108 cases who visited the clinic before admission were scheduled for selective surgeries. In all, 218 patients received an anesthesia consultation after admission. The cancellation rate in the inpatient group was 7.80%, while no surgeries were cancelled in preclinic group (P=0.016). A preoperative assessment clinic visit statistically decreased the length of inhospital stays before surgery from 93.02 to 76.11 h (P=0.010). After propensity score matching, significant differences in operating room cancellations (0 vs. 6.48%; P=0.015) and length of stay before surgery (76.11 vs. 92.22 h; P=0.038) persisted between two groups. No significant differences between the two groups were found in terms of prognosis, including major postoperative complications, incidence of postoperative ICU admissions, and readmissions to any hospital within 30 days (P>0.05).Conclusions: Among patients with comorbidities undergoing major surgeries, a preoperative assessment clinic visit was more efficient than an anesthesia consultation after admission. These findings may provide impetus for the opening of preoperative assessment clinics for critical patients in China.
We develop a background-free single-beam coherent Raman scattering technique enabling the high-sensitivity detection of greenhouse gases. In this scheme, Raman coherence prepared by a femtosecond laser is interrogated by self-generated narrowband air lasing, thus allowing single-beam measurements without complex pulse shaping. The unique temporal and spectral characteristics of air lasing are beneficial for improving the signal-to-noise ratio and spectral resolution of Raman signals. With this method, SF6 gas present at a concentration of 0.38% was detected in an SF6–air mixture. This technique provides a simple and promising route for remote detection due to the low divergence of Raman signals and the availability of high-energy pump lasers, which may broaden the potential applications of air lasing.
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