1. MID-IR SATURATION SPECTROSCOPY OF HeH + MOLECULAR ION HSUAN-CHEN CHEN,CHUNG-YUN HSIAO Institute of Photonics Technologies, National Tsing Hua University, Taiwan JIN-LONG PENG Center of Measurement Standards, Industrial Technology Research Institute, Taiwan TAKAYOSHI AMANO Department of Physics and Astronomy and Department of Chemistry, University of Waterloo, Canada JOW-TSONG SHY Department of Physics, National Tsing Hua University, Taiwan *Mail Address : shy@phys.nthu.edu.tw 2011/ 6 / 21 – International Symposium of Molecular Spectroscopy

2. http://en.wikipedia.org/wiki/NGC_7027 It has been suggested that HeH + would be present in some areas of interstellar space. NGC 7027

3. AuthorsMeasured TransitionsUncertainty [1979] D.E. Tolliver, G. A. Kyrala and W.H. Wing Fundamental Band : P(12)-P(13) ν = 2-1 : P(9)-P(11) [1982] P. Bernath and T. AmanoFundamental Band : R(0)-R(4) and P(1)-P(4) [1987] D. J. Liu, W. C. Ho and T. OkaPure Rotation ν = 0 R(6) [1989] M.W. Crofton, R.S. Altman, N.N. Haese and T. Oka ν=1-2 R(1)-R(5), R(8), P(1) and its isotopes [1997] F. Matsushima, T. Oka and K. Takagi Low J pure rotation J=1 ← 0 and J=2 ← 1 [FIR] [1997] Z. Liu and P.B. DaviesQuasi-bound to quasi-bond and bond to quasi- bond Difficulties of experiments of HeH + : Low concentration of HeH + We plan to improve the accuracy of ro-vibrational transitions by 2 orders of magnitude using saturation spectroscopy.

4. > Light Source – CW Optical Parametric Oscillator ---- Enough power for saturation. > Extended Negative Glow Discharge Tube ---- Low pressure, high concentration of ion. > Optical Frequency Comb ---- Frequency ruler for precision measurement.

5. Increasing the signal of the saturation spectroscopy of molecular ion. Idler Wavelength :2.7 – 3.9 μm Average Power : > 300 mW @ 7 W pump Frequency Tuning : > 40 GHz (Mode-Hop-Free) Free-Running Stability : < 500 MHz @ 8 hours

6. Characteristics of negative glow region:  Largest glow intensity  Highest concentration of positive ions  Nearly field free  The region is relatively short n+n+ n-n-

7. － + Negative glow Region Positive column Flow mixture of He:H 2 = 98 : 2 (120 mtorr) Discharge Current : 16 mA Ethanol cooled at -70 o C Benefits of extended negative glow : Lower gas pressure (~100 mtorr) Narrower linewidth for precision measurement

8. B field (300 Gauss) － + Negative glow Region Positive column Flow mixture of He:H 2 = 98 : 2 (120 mtorr) Discharge Current : 16 mA Ethanol cooled at -70 o C Benefits of extended negative glow : Lower gas pressure (~100 mtorr) Narrower linewidth for precision measurement

9. B field (300 Gauss) － + Negative glow Region Flow mixture of He:H 2 = 98 : 2 (120 mtorr) Discharge Current : 16 mA Ethanol cooled at -70 o C Benefits of extended negative glow : Lower gas pressure (~100 mtorr) Narrower linewidth for precision measurement

10. Repetition Rate : 250 MHz Supercontiuum : 1030 ~ 2200 nm RF Reference : GPS-locked Rubidium clock Accuracy : < 10 -11 @ 1000 sec (~few kHz in the MIR region) 1.062 μm 1.4-1.8 μm2.7-3.9 μm

12. B Field Modulation - Concentration Modulation Linewidth (FWHM): 420 MHz (Temperature at -64 o C) Absorption : 0.0128 %

13. Frequency Modulation Method – Idler wave Modulation Frequency : 31 kHz Modulation Depth : 7.6 MHz Laser Intensity : ~ 10 kW/m 2

14. Linewidth = 7.07 +/- 0.45 MHz * Gas Pressure = 120 mtorr Fitting Function : Hui-Mei Fang et. al., Opt. Comm., 257, 1, 76-83(2006)

17. We thank to the National Science Council (NSC), Ministry of Education, Natural Science and Engineering Research Council of Canada ( NSERC ) and Industrial Technology Research Institute.

19. Mean S.T.D.

20. Zeeman Shift ~ 10 kHz Power Broadening can be ignored.

21. Motivation > The Importance of HeH + > Previous work Our Spectroscopic System > Light Source –CW Optical Parametric Oscillator > Extended Negative Glow Discharge Tube > Fiber-Based Optical Frequency Comb Experimental Arrangement and Result Summary and Future Work Acknowledgement