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

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

Page  3 Introduction The CO 2 hotband ← 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

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 um 667 cm − 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, (2006)  Using an optical frequency comb

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

Page  6 Third-derivative saturated absorption spectrum DFG 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

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

Page  8 Linewidth measurements by the 3 rd derivative signals H.M. Fang, et al., Opt. Commun., 257, (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

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, (2006)

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.

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  MHz

Page  12 Absolute frequency measurements

Page  13 Absolute frequency measurements CO P(30)Transition Center Frequency (MHz)Difference (MHz) This work (20)0 Ref. a (75) Ref. b MHz with a 0.1 MHz error4.239 Ref. c Ref. a ： S. Borri et al., Opt. Express 16, (2008) Ref. b ： HITRAN ( ) Ref. c ： Charles E. Miller et al., J. Mol. Spectrosc. 228, (2004) Difference = Ref. － This work

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

Page  15 No.TransitionThis work a (MHz)HITRAN b (MHz)Difference a － b (MH) L1 12 C 16 O R(4) (95) L2 16 O 12 C 18 O P(12)f (139) L4 16 O 12 C 18 O P(12)e (151) L5 12 C 16 O Q(19) (115) Measurements of several nearby weak transitions

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 P(30) line with SNR > 1000 at 1 Hz bandwidth is obtained.  12 C 16 O 2 hot band P(30) transition center frequency of 69,267, (15) MHz and its linewidth of 3.040(36) MHz are accurately measured.  Several nearby weak transitions, such as 12 C 16 O R(4), 16 O 12 C 18 O P(12)f, 16 O 12 C 18 O P(12)e, and 12 C 16 O Q(19) are also observed and their absolute frequencies are measured too.

Page  17 Thanks For Your Attention!