1. High Precision Mid-IR Spectroscopy of 12 C 16 O 2 : 00 0 1← 00 0 0 Band Near 4.3 µm Jow-Tsong Shy Department of Physics, National Tsing Hua University, Hsinchu, Taiwan

2. 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. 00 0 1← 00 0 0, 01 1 1← 01 1 0, and [10 0 1,02 0 1] I,II ← 00 0 0 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.

3. Fundamental band and Hot Band @ 4.3 mm

4. Combinational Bands @ 2.7 mm

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

6. Goal Tunable DFG (difference frequency generation) source Saturation spectroscopy of CO 2 Absolute frequency measurements FA09: 00 0 1← 00 0 0 band FA10: [10 0 1,02 0 1] I ← 00 0 0 band

7. Tunable DFG Source PPLN: periodically-poled lithium niobate

8. Tunable DFG Source (Iodine stabilization and OFC)

9. Experimental Set-up

10. Experimental Scheme

11. Iodine Stabilization of Nd:YAG Laser a10 hyperfine component of R(56) 0-32: 563 260 223 513 (5) kHz @ -15 ℃

12. Third Derivative Spectrum of CO 2 Fundamental Band Transition

13. Ti-Sapphire Stabilization

14. Optical Frequency Comb repetition frequency: ~ 1 GHz average power: 200 ~ 300 mW Spectral range: 500 ~ 1450 nm Overall stability: 10 -12 @ 1000 s (phase locked to a GPS disciplined Rb atomic clock)

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

16. Accuracy Check: R(60) Mazzooti et al. 71500327991.5 kHz Our result 71500327970.5 kHz  f = 21 kHz Pressure shift ? Mazzotti et al. Opt. lett. 30, 997 (2005) Our result

17. Experimental Results (1)

18. Experimental Results (2)

19. Experimental Results (3)

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

21. Comparison with HITRAN Data

22. Molecular Constants Fitting

23. Molecular Constants (1)

24. Molecular Constants (2)

27. 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

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

29. Thank you for your attention!