1. Precision Measurement of CO 2 Hotband Transition at 4.3  m Using a Hot Cell PEI-LING LUO, JYUN-YU TIAN, HSHAN-CHEN CHEN, Institute of Photonics Technologies, National Tsing Hua University, Hsinchu, Taiwan YU-HUNG LIEN, JOW-TSONG SHY, Department of Physics, National Tsing Hua University, Hsinchu, Taiwan June 21, 2011

2. Page  2 Many of ro-vibrational transitions of atmospheric molecules such as CO 2, CH 4 and N 2 O are in the mid-infrared spectral region. High- resolution and high sensitivity mid-IR absorption measurement techniques play an important role in the molecular spectroscopy. Motivation From WiKi 4.3 μm

3. Page  3 Introduction The CO 2 hotband 01 1 1← 01 1 0 P(30) line has been chosen due to it has a good compromise between a suitable transition line strength for saturated absorption spectroscopy and low absorption in air. Saturated Absorption Spectrum Lamb-dip Linewidth Absolute Frequency

4. Page  4 Objectives  To obtain the saturated absorption spectrum of the CO 2 hotband transition with the higher signal intensity  To measure and analyze the Lamb-dip linewidth precisely  To measure the absolute transition frequency accurately 01 1 1 01 1 0 00 0 0 4.3 um 667 cm −1 01 1 1 01 1 0 00 0 0 4.3 um Heating  Using a CO 2 hot cell  Using the relationship between the peak amplitude of the derivative signal and the modulation width. H.M. Fang, et al., Opt. Commun., 257, 76-83 (2006)  Using an optical frequency comb

5. Page  5 The saturated absorption spectrometer is based on the pump-probe scheme Lamb-dip spectroscopy Experimental setup DFG: 2.6 μm to 4.7 μm with few mW output power Lamb-dip

6. Page  6 Third-derivative saturated absorption spectrum DFG power @ 4.33 μm ~ 3 mW Modulation width ~ 2.5 MHz Gas pressure ~ 30 mTorr Gas temperature ~ 700 K S/N > 1000 at 1 Hz bandwidth

7. Page  7 The intensity variation of the 3 rd derivative saturated absorption signals versus CO 2 cell temperature and pressure The intensity of the 3 rd derivative saturated absorption signals versus the temperature of the CO 2 cell at fixed pressure 30 mTorr The intensity of the 3 rd derivative saturated absorption signals versus the gas pressure at fixed temperature 700 K

8. Page  8 Linewidth measurements by the 3 rd derivative signals H.M. Fang, et al., Opt. Commun., 257, 76-83 (2006) H 3 (W) max : the peak amplitude of the 3 rd derivative signals W: modulation width δL: Lorentzian FWHM δL = 3.071(42) MHz

9. Page  9 Linewidth measurements by the 2 nd derivative signals H 2 (W) max : the peak amplitude of the 2 nd derivative signals W: modulation width δL: Lorentzian FWHM δL = 2.964(72) MHz H.M. Fang, et al., Opt. Commun., 257, 76-83 (2006)

10. Page  10 Linewidth measurements by the 1 st derivative signals δL (Lorentzian FWHM ) = 2.91(24) MHz For enough small modulation width (W << ω 0 ), the Lorentzian linewidth (Lamp-dip FWHM) is the √ 3 times frequency width of the 1 st derivative peak to peak signal.

11. Page  11 Measurements 1 st  δL = 2.91(24) MHz 2 nd  δL = 2.964(72) MHz 3 rd  δL = 3.071(42) MHz constant fit  δL = 3.040(36) MHz Lamb-dip Linewidth analysis Calculations Pressure broadening ~ 104 kHz Transit-time broadening ~ 77 kHz Power broadening ~ 2.9 MHz Total broadening  3.081 MHz

12. Page  12 Absolute frequency measurements

13. Page  13 Absolute frequency measurements CO 2 01 1 1-01 1 0 P(30)Transition Center Frequency (MHz)Difference (MHz) This work69 267 228.761 (20)0 Ref. a69 267 227.764 (75)-0.997 Ref. b69 267 233 MHz with a 0.1 MHz error4.239 Ref. c69 267 232.493.729 Ref. a ： S. Borri et al., Opt. Express 16, 11637-11646 (2008) Ref. b ： HITRAN (http://cfa-www.harvard.edu/HITRAN ) Ref. c ： Charles E. Miller et al., J. Mol. Spectrosc. 228, 329-354 (2004) Difference = Ref. － This work

14. Page  14 Measurements of several nearby weak transitions 12 C 16 O 2 20 0 1-20 0 0 R(4) 16 O 12 C 18 O 01 1 1-01 1 0 P(12)f 16 O 12 C 18 O 01 1 1-01 1 0 P(12)e 12 C 16 O 2 03 3 1-03 3 0 Q(19) 12 C 16 O 2 01 1 1-01 1 0 P(30) From HITRAN The weak transitions are lower by two orders of line strength than hotband P(30) line.

15. Page  15 No.TransitionThis work a (MHz)HITRAN b (MHz)Difference a － b (MH) L1 12 C 16 O 2 20 0 1-20 0 0 R(4)69266995.409 (95)69266944.86250.547 L2 16 O 12 C 18 O 01 1 1-01 1 0 P(12)f69267025.884 (139)69266986.05339.831 L4 16 O 12 C 18 O 01 1 1-01 1 0 P(12)e69267481.268 (151)69267441.64839.620 L5 12 C 16 O 2 03 3 1-03 3 0 Q(19)69267536.410 (115)69267857.700- 321.290 Measurements of several nearby weak transitions

16. Page  16 Conclusions  The tunable CW DFG source covers the spectral range from 2.6 μm to 4.7 μm with output power of few mW.  The 3 rd derivative Lamb-dip signal of 12 C 16 O 2 hot band 01 1 1- 01 1 0 P(30) line with SNR > 1000 at 1 Hz bandwidth is obtained.  12 C 16 O 2 hot band 01 1 1-01 1 0 P(30) transition center frequency of 69,267,228.761(15) MHz and its linewidth of 3.040(36) MHz are accurately measured.  Several nearby weak transitions, such as 12 C 16 O 2 20 0 1-20 0 0 R(4), 16 O 12 C 18 O 01 1 1-01 1 0 P(12)f, 16 O 12 C 18 O 01 1 1-01 1 0 P(12)e, and 12 C 16 O 2 03 3 1-03 3 0 Q(19) are also observed and their absolute frequencies are measured too.

17. Page  17 Thanks For Your Attention!