High Precision Mid-IR Spectroscopy of 12 C 16 O 2 : ← Band Near 4.3 µm Jow-Tsong Shy Department of Physics, National Tsing Hua University, Hsinchu, Taiwan

Motivation Carbon dioxide is a major product of combustion and an important greenhouse gas. New and refined molecular constants is of great importance to atmospheric chemistry, meteorology, and astrophysics ← , ← , and [10 0 1,02 0 1] I,II ← bands are the most important absorption bands from 2.5 to 5.0  m. No extensive heterodyne frequency measurements of the line center up to now.

Fundamental band and Hot 4.3 mm

Combinational 2.7 mm

No good laser sources Frequency measurement is difficult before OFC is invented

Goal Tunable DFG (difference frequency generation) source Saturation spectroscopy of CO 2 Absolute frequency measurements FA09: ← band FA10: [10 0 1,02 0 1] I ← band

Tunable DFG Source PPLN: periodically-poled lithium niobate

Tunable DFG Source (Iodine stabilization and OFC)

Experimental Set-up

Experimental Scheme

Iodine Stabilization of Nd:YAG Laser a10 hyperfine component of R(56) 0-32: (5) -15 ℃

Third Derivative Spectrum of CO 2 Fundamental Band Transition

Ti-Sapphire Stabilization

Optical Frequency Comb repetition frequency: ~ 1 GHz average power: 200 ~ 300 mW Spectral range: 500 ~ 1450 nm Overall stability: s (phase locked to a GPS disciplined Rb atomic clock)

Uncertainty OFC 5 kHz Iodine stabilized of Nd:YAG laser 10 kHz CO 2 stabilized Ti:sapphire laser 15 kHz Uncertainty 30 kHz

Accuracy Check: R(60) Mazzooti et al kHz Our result kHz  f = 21 kHz Pressure shift ? Mazzotti et al. Opt. lett. 30, 997 (2005) Our result

Experimental Results (1)

Experimental Results (2)

Experimental Results (3)

Experimental Results (4) Total 56 lines (32 R lines and 24 P lines) Accuracy 30 kHz

Comparison with HITRAN Data

Molecular Constants Fitting

Molecular Constants (1)

Molecular Constants (2)

Summary 56 fundamental band transitions have been measured to an accuracy of 30 kHz Accurate molecular constants of the ground vibrational level have been determined

Future Works Remeasure R(18) and R(40) transitions Measure high J transitions using a hot cell Measure hot band transitions

Thank you for your attention!