Optical frequency comb (OFC) is a revolutionary tool for frequency measurement. It links Cesium clock and optical frequency with a single mode-locked laser. This direct link enables the OFC to work as an absolute frequency measurement tool itself.
We measured the absolute frequency of seventeen R-branch transitions of ν3 fundamental band of Nitrous Oxide (N2O) from J= 5 to J= 45 using an OFC. We investigated the saturation spectra of these transitions using a Periodically Poled Lithium Niobate (PPLN) Difference Frequency Generation (DFG) source. Refined molecular constants of N2O 0001 vibrational level are also obtained.
In addition, we have improved the performance of our OFC by replacing the old Spectra Physics pump laser (Millennia V) with a Coherent Verdi G5 laser. The average power and stability greatly improved and the warm-up time was reduced from few hours to less than 30 minutes.

[1] H. Schnatz, B. Lipphardt, J. Helmcke, F. Riehle, and G. Zinner, Phys. Rev. Lett. 76,
18 (1996).
[2] T. W. Hänsch, Passion for Precision, Nobel Lecture (2005). [www.nobelprize.org/nobel_prizes/physics/laureates/2005/hansch-lecture.htm]
[3] Orazio Svelto, Principles of Lasers, Kluwer Academic / Plenum Publishers, 4th
Edition (1998).
[4] B. E. A. Saleh, M. C. Teich, Fundamentals Of Photonics, Wiley-Interscience, 2nd
Edition (2007).
[5] J. C. Knight, et al., Opt. Soc. Am. B, 19, 753 (2002).
[6] J. P. Gordon, Opt. Lett. 11, 662 (1986).
[7] M. Bellini and T. W. Hänsch, Opt. Lett. 25, 1049 (2000).
[8] S. T. Cundiff, J. Phys. D: Appl. Phys. 35, R43 (2002).
[9] D. J. Jones, S.A. Diddams, J. K. Ranka, A. Stentz, R.S. Windeler, J.L. Hall, and S. T.
Cundiff, Science 288, 635 (2000).
[10] M. Zimmermann, Ch. Gohle, R. Holzwarth, Th. Udem, and T.W. Hänsch, Opt. Lett.
29, 310 (2004).
[11] GigaOptics GmbH, GigaJet20 Laser, GigaJet20 femtosecond oscillator data sheet.
[12] Menlo Systems GmbH, High Sensitivity Detector Unit APD210/310, APD210/310 data sheet.
[13] CIPM, Mise en pratique de la définition du mètre Iodine 532 nm (2003).
[14] M. Bryant, S. W. Reeve, W. A. Burns, J. Chem. Educ. 85, 121 (2008).
[15] R. A. Toth, J. Opt. Soc. Am. B, 4, 357 (1987)
[16] Chun-Chieh Liao, High Precision Mid-Infrared Spectroscopy of 12C16O2:
0001 ← 0000 Band near 4.3 μm and [1001,0201]I ← 0000 Band near 2.7 μm,
Ph.D. thesis, National Tsing Hua University (2007).
[17] R. A. Toth, J. Opt. Soc. Am. B, 3, 1263 (1986).