NCTS (South)





SPEAKER 陳炫辰 - Umea University (UmU), Sweden

TITLEFrequency-Comb-Referenced Singly-Resonant OPO for Sub- Doppler Spectroscopy of H3+ Molecular Ions

ABSTRACTThe triatomic hydrogen molecular ion, H3+, which consists of three protons and two electrons, is regarded as the simplest polyatomic molecule. It is also thought to be the starting point from which the chemical processes in interstellar space and also in planetary atmosphere originate. Among all studies on H3+, high resolution spectroscopy not only gives us fundamental insight into its nature but also provides highly accurate information for theoretical calculations like determining the molecular structure, refining the potential energy surface (PES) and comparing with the results of vibrational band calculations. However, until now the uncertainty given by previous experimental measurements has been about 0.005 cm-1, and it is expected to be hard to achieve higher accuracy due to the limitation imposed by the Doppler-limited resolution. Recently, we are able to observe the sub-Doppler spectrum of H3+ in an extended negative glow discharge plasma using the nonlinear saturation spectroscopic technique. A very promising and reliable laser source, mid-IR optical parametric oscillator (OPO) that was referenced to GPS-disciplined optical frequency comb, enables us to achieve higher level of accuracy. In this talk, we present our results of frequency measurements of H3+. The accuracy of the absolute frequency measurements of H3+ R(1,0) in the ν2 fundamental band near 3.668 μm had been achieved within 10-5 cm-1. Also, the linewidth of the homogeneous line profile had been first investigated. With the systematical measurements of linewidth with different pressures and with different input powers, the pressure broadened coefficient was fitted carefully and the result showed a great progress compared with the classical Langenvin model.