在本論文中，我們建立了一套偵測分子離子中紅外飽和吸收光譜的光譜系統，此系統包含產生分子離子的延伸負輝光放電管以及偵測光源：單頻、波長可調且可精確量測頻率的中紅外光光學參量振盪器 (Mid-IR Optical Parametric Oscillator)。我們使用一1064 nm Nd:YAG雷射作為PPLN OPO的pump光源，產生的近紅外signal光波長範圍為1450 nm ~ 1880 nm，中紅外idler光波長範圍為2.6 ~ 4.2 μm。鎖頻部份，我們將OPO的signal光穩頻在一fiber OFC上並將pump頻率offset鎖頻在另一碘穩頻的Nd:YAG雷射上，透過改變offset的頻率可以改變pump頻率，進而改變idler頻率。
在H3+的研究中，本實驗室曾利用飽和吸收光譜加上光頻梳量測H_3^+ 〖 ν〗_2基頻帶 (fundamental band) R(1,0)躍遷譜線的中心頻率，準確度為250 kHz。後來B. J. McCall 以雜訊壓抑腔增強光外差速度調制光譜法(NICE-OHVMS : Noise Immune Cavity Enhanced Optical Heterodyne Velocity Modulation Spectroscopy)，最近S. Schlemmer group也以冷離子井 (cold ion trap)配合OPO及fiber OFC (optical frequency comb)量測低溫 (10 K) H_3^+的吸收譜線，他們的譜線中心頻率的測量結果與我們有5 ~ 10 MHz的差距。這樣的差距可能是來自於idler光頻率調制的影響，所以我們將原本調制OPO idler光頻率的系統改為調制idler光強度的光譜量測系統。
最後我們嘗試以此改進的系統量測H3+ R(1,0)的飽和吸收光譜，得到譜線中心頻率為81,720,377.357 MHz，準確度為492 kHz，結果與B. J. McCall研究團隊相差67 kHz。未來我們將改善碘穩頻鎖頻及offset lock鎖頻的準確度和譜線訊躁比以得到更準確的譜線中心頻率。我們也將廣泛量測H3+、HeH+ 和HeD+的譜線。

1. Thomson, J.J., Rays of Positive Electricity. Philosophical Magazine, 1911. 21(122): p. 225-249.
2. Oka, T., Observation of the Infrared-Spectrum of H3+. Journal of the Optical Society of America, 1980. 70(12): p. 1577-1577.
3. Carney, G.D. and R.N. Porter, H3+ Ab-Initio Calculation of Vibration Spectrum. Journal of Chemical Physics, 1976. 65(9): p. 3547-3565.
4. Oka, T., et al., Hot and Diffuse Clouds Near the Galactic Center Probed by Metastable H3+. The Astrophysical Journal, 2005. 632(2): p. 882.
5. Drossart, P., et al., Detection of HJ on Jupiter. Nature, 1989. 340: p. 539.
6. Hogness, T. and E. Lunn, The Ionization of Hydrogen by Electron Impact as Interpreted by Positive Ray Analysis. Physical Review, 1925. 26(1): p. 44.
7. McKellar, A.R.W. and J.K.G. Watson, The Infrared Spectrum of H3+ Revealed. Journal of Molecular Spectroscopy, 1998. 191(1): p. 215-217.
8. Wu, K.Y., et al., Measurement of the ν2 Fundamental Band of H3+. Physical Review A, 2013. 88(3): p. 032507.
9. Chen, H.C., et al., High-Resolution Sub-Doppler Lamb Dips of the ν2 Fundamental Band of H3+. Physical Review Letters, 2012. 109(26): p. 263002.
10. Hodges, J.N., et al., High-precision and High-accuracy Rovibrational Spectroscopy of Molecular Ions. The Journal of Chemical Physics, 2013. 139(16): p. 139.
11. Asvany, O., J. Krieg, and S. Schlemmer, Frequency Comb Assisted Mid-infrared Spectroscopy of Cold Molecular Ions. Review of Scientific Instruments, 2012. 83(9): p. 093110.
12. Crofton, M.W., et al., Infrared Spectra of 4HeH+, 4HeD+, 3HeH+, and 3HeD+. The Journal of Chemical Physics, 1989. 91(10): p. 5882-5886.
13. Amano, T. and A. Maeda, Double-Modulation Submillimeter-Wave Spectroscopy of HOC+ in the ν2 Excited Vibrational State. Journal of molecular spectroscopy, 2000. 203(1): p. 140-144.
14. Robertsson, L., et al., International Comparison of 127I2-stabilized Frequency-doubled Nd: YAG Lasers between the BIPM, the NRLM and the BNM-INM, October 2000. Metrologia, 2001. 38(6): p. 567.
15. Cordiale, P., G. Galzerano, and H. Schnatz, International Comparison of Two Iodine-stabilized Frequency-doubled Nd: YAG Lasers at λ= 532 nm. Metrologia, 2000. 37(2): p. 177.
16. Hong, F.L., et al., Rotation Dependence of the Excited-state Electric Quadrupole Hyperfine Interaction by High-resolution Laser Spectroscopy of 127I2. JOSA B, 2001. 18(10): p. 1416-1422.
17. Hong, F.L., et al. Portable I2-stabilized Nd: YAG Laser for Wavelength Standards at 532 nm and 1064 nm. in SPIE's International Symposium on Optical Science, Engineering, and Instrumentation. 1998. International Society for Optics and Photonics.
18. Hall, J., et al., Optical Heterodyne Saturation Spectroscopy. Applied Physics Letters, 1981. 39(9): p. 680-682.
19. Shirley, J.H., Modulation Transfer Processes in Optical Heterodyne Saturation Spectroscopy. Optics Letters, 1982. 7(11): p. 537-539.
20. Jaatinen, E., D.J. Hopper, and J. Back, Residual Amplitude Modulation Mechanisms in Modulation Transfer Spectroscopy that Use Electro-optic Modulators. Measurement Science and Technology, 2009. 20(2): p. 025302.
21. Quinn, T., Practical Realization of the Definition of the Metre, including Recommended Radiations of Other Optical Frequency Standards (2001). Metrologia, 2003. 40(2): p. 103-133.
22. Gillespie, L.J. and L.H. Fraser, The Normal Vapor Pressure of Crystalline Iodine. Journal of the American Chemical Society, 1936. 58(11): p. 2260-2263.
23. Schünemann, U., et al., Simple Scheme for Tunable Frequency Offset Locking of Two Lasers. Review of Scientific Instruments, 1999. 70(1): p. 242-243.
24. Hodges, J.N., et al.New High Precision Linelist of H3+. in 69th International Symposium on Molecular Spectroscopy. 2014.
25. A. V. Smith, SNLO software, Sandia National Laboratories (2005) , available at http://www.sandia.gov/imrl/X1118/xxtal.htm.
26. H. M. Fang, Studies of Laser Stabilization Using Molecular Iodine, PhD .dissertation, National Chiao Tung University, 2004.
27. Smith, P.W. and R. Hänsch, Cross-Relaxation Effects in the Saturation of the 6328-Å Neon-Laser Line. Physical Review Letters, 1971. 26(13): p. 740-743.