High Precision Mid-IR Spectroscopy of 12 C 16 O 2 [10 0 1,02 0 1] I ← Band Near 2.7 µm Jow-Tsong Shy Department of Physics, National Tsing Hua University, Hsinchu, Taiwan

Motivation and Goal [10 0 1,02 0 1] I ← and [10 0 1,02 0 1] II ← bands near 2.7 µm are two important absorption bands in atmosphere Urban’s group has made heterodyne frequency measurements for 9 transitions with an accuracy of 600 kHz in Our goal is to provide more accurate measurements

Experimental Set-up

Experimental Scheme

Ti:sapphire Laser Side Fringe Locking to a Stable Cavity Frequency stability: 10 kHz; Frequency drift <100 kHz/hr

Offset Locking of Nd:YAG Laser U. Shunemann et al., Rev. Sci. Instrum. 70, 242 (1999)

Saturated 4.3 μm Fluorescence

Longitudinal Fluorescence Cell Used in frequency stabilization of CO 2 laser previously

Direct Detection vs. Fluorescence Detection Direct Detection Fluorescence Detection

Advantages of Saturated Fluorescence Detection Zero background Higher S/N No interference fringes

Second Harmonic Demodulated Spectrum P = 20 mTorr FWHM = 1.5 MHz

Urban’s Spectrum

Uncertainty OFC 5 kHz Iodine stabilized of Nd:YAG laser 10 kHz Nd:YAG laser offset locking 10kHz Ti:sapphire laser locking 10 kHz Fitting error 5 kHz Uncertainty 40 kHz

Observed Transitions – P lines

Observed Transitions – R lines 19 transitions measured to 40 kHz accuracy

Molecular Constants

Molecular Constants Comparison

Comparison between observed and calculated frequencies Standard deviation = 46 kHz

Summary 19 transitions have been measured to an accuracy of 40 kHz Accurate molecular constants of the [10 0 1,02 0 1] I vibrational level have been determined

Future Works Improve the collection efficiency of the longitudinal florescence cell (X 10) More measurements on [10 0 1,02 0 1] I ← band New measurements on [10 0 1,02 0 1] II ← band

Acknowledgement Chun-Chieh Liao Kuo-Yu Wu Yu-Hung Lien Che-Chung Chou $$ NSC & MOE of Taiwan DFG and OFC systems Carry out all measurements Molecular constants fitting