講演情報
[17p-WL2_301-14]Measurement of High-Concentration Carbon Dioxide via Background-Free Mid-Infrared Absorption Spectroscopy
〇(P)Neil Irvin Cabello1, Shinta Ozawa1, Tetsuhiro Kudo1, Takao Fuji1 (1.Toyota Tech. Inst.)
キーワード：
ultrafast phenomenon、mid-infrared spectroscopy、nonlinear optics
Mid-infrared absorption (MIR) spectroscopy in tandem with the Lambert-Beer law is typically used to optically determine the concentration of gases. This is provided that the concentration is low enough that Lambert-Beer law is applicable and that the detector dynamic range is sufficient to resolve the absorption dip in the transmission spectrum. Thus, this becomes an issue at high concentrations where the absorption dip reaches the signal floor, making the determination of concentration by IR spectroscopy very difficult. In our previous study, we have demonstrated background-free MIR absorption spectroscopy by upconverting the free-induction decay (FID) signal via to visible range by four-wave difference frequency generation (FWDFG) of the time-resolved optically gated absorption pulses and the FID in a silicon membrane. We bypassed the dynamic range issue inherent in typical MIR absorption spectroscopy systems, as absorption signals are obtained as positive emission signals, instead of dips in a transmission spectrum.
Here, we measured the FID absorption signals from high-concentration CO2 gases, which would normally be impossible to scan in a conventional FTIR system. As a result, we were able to observe an increasing split distance between the P and the R branches as the CO2 concentration was increased, and the numerical simulation reproduced the experimental results well. This splitting appears to be an intrinsic feature of the background-free system, and the splitting energy shows a clear correlation with the CO2 concentration. It is therefore possible to determine the concentration of high-concentration gases, where Lambert-Beer’s law significantly deviates or fails. Detailed splitting mechanism due to the real part of the susceptibility will be discussed in the presentation.
Here, we measured the FID absorption signals from high-concentration CO2 gases, which would normally be impossible to scan in a conventional FTIR system. As a result, we were able to observe an increasing split distance between the P and the R branches as the CO2 concentration was increased, and the numerical simulation reproduced the experimental results well. This splitting appears to be an intrinsic feature of the background-free system, and the splitting energy shows a clear correlation with the CO2 concentration. It is therefore possible to determine the concentration of high-concentration gases, where Lambert-Beer’s law significantly deviates or fails. Detailed splitting mechanism due to the real part of the susceptibility will be discussed in the presentation.