MC2.2 11:00 AM – 11:15 AM
Measurement of Acetylene-d Absorption Lines with a SelfReferenced Fiber Laser Frequency Comb Jie Jiang Dept. of Physics and Astronomy, University of British Columbia, Vancouver, BC, V6T 1Z1 Canada (604)-822-2754 (Voice) 604-822-5324 (Fax)
[email protected]
John Bernard and Alan Madej Institute of National Measurement Standards, National Research Council of Canada, Ottawa, ON, K1A 0R6 Canada (613)-993-9385 (Voice) 613-952-1394 (Fax)
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Sibyl Drissler and David J. Jones Dept. of Physics and Astronomy, University of British Columbia, Vancouver, BC, V6T 1Z1 Canada (604)-822-2754 (Voice) 604-822-5324 (Fax)
[email protected]
Andrzej Czajkowski Department of Physics, University of Ottawa, 150 Louis Pasteur, Ottawa, ON, K1N 6N5 Canada
By establishing a direct link between the SI Cs primary frequency standard and optical frequencies, femtosecond frequency combs (FFC) [1,2] have drastically reduced the difficulty of optical frequency metrology and have opened a new vista of applications where optical radiation can be measured and controlled at extreme accuracy. Motivated in part by the need for wavelength standards at telecommunications wavelengths, the extensive measurement of the acetylene (12C2H2 and 13C2H2) absorption transitions at 1.5 µm has recently been performed by three groups [3-7]. As an extension of our prior work, we have employed a self-referenced fiber laser frequency comb to create a reference atlas of transitions of another acetylene isotope (12C2HD) whose 2ν1 band covers the C-band telecom spectrum from 195 to 198 THz. In 2006, Doppler line limited measurements of transitions using this isotope were reported with uncertainties of 10 MHz [8]. Using the FFC together with a cavity-based 1.5-µm diode laser- saturation-absorption spectrometer [9], we have reduced this uncertainty to less than 2 kHz. Shown in Fig. 1, our FFC is based on a stretched-pulse erbium-doped fiber laser and is similar to the system first developed by Tauser et al [10]. The laser output is split into two branches. In each branch after an all-fiber pulse stretching, amplification and recompression, a pulse train (of 70-fs pulses) with an average power of 150 mW is injected into 25 cm of Highly Nonlinear Fiber (HNF) [11]. One branch is used to self-reference the FFC via a single arm f-to-2f interferometer [1] and is locked to a National Research Council of Canada (NRC) maser reference. Signal-to-noise ratios of the self-referenced beat of better than 35-dB in a 100 kHz bandwidth were obtained. A heterodyne measurement of the 12C2HDstabilized diode laser is performed with the second branch. Details of the saturation dip stabilized diode laser system are given elsewhere [6, 9]. Heterodyne beat signal-to-noise ratios between the diode laser and the comb system of 35 to 40 dB were obtained (100-kHz bandwidth) and were of sufficient stability and spectral purity to be directly counted using a NRC maser referenced frequency counter. Preliminary results of the frequency measurements for several lines across the band have been made and indicate that the saturated absorption resonances are of sufficient quality for metrological use. Studies of the shift of the line center frequency for the P(16) line of the 2ν1 band were performed as a function of cell pressure, intra-cavity power and applied modulation excursion and show reproducibilities at the kilohertz level even for variations in such parameters. In the present work, the operating parameters of 2.0 Pa pressure, 0.2 W intracavity saturation power, and 1.8 MHz peak-to-peak modulation excursion were typically employed. The reproducibility of the P(16) line over several days of measurements spanning over two weeks has been shown to be better than 0.5 kHz. A preliminary value for this transition at the specified operating conditions is f(P(16)) = 195 903 630 363.5 kHz ± 1 kHz. The stability of the stabilized laser was 5 × 10-12 at 1 s averages with the instability decreasing to 1 × 10-12 at 60 s averages. The self-referenced fiber laser comb provides a very reliable and straightforward system by which large numbers of reference frequencies can be measured. Work is currently directed toward the
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measurement of the 2 ν1 band reference lines and it anticipated that over 50 such transitions will be obtained having coverage extending from 195 THz to 198 THz with uncertainties of better than 2 kHz
References [1] D. J. Jones et al, Science 288, 635 (2000). [2] R. Holzwarth et al, Phys. Rev. Lett. 85 (11), 2264 (2000). [3] F.-L. Hong et al, Opt. Lett. 28, 2324 (2003). [4] C. S. Edwards et al, Appl. Phys. B 80, 977 (2005). [5] C. S. Edwards et al, J. of Mol. Spect. 234, 143 (2005). [6] A. A. Madej et al, J. Opt. Soc. Am. B 23, 741 (2006). [7] A. A. Madej et al, J. Opt. Soc. Am. B 23, 2200 (2006). [8] J.L. Hardwick et al, J. of Mol. Spect. 239, 208 (2006). [9] A. Czajkowski et al, Opt. Comm. 234, 259 (2004). [10] F. Tauser et al, Opt Exp. 11, 594 (2003). [11] T. Okuno et al, IEEE J. Sel. Top. in Quan. Elec. 5, 1385 (1999).
Figure 1.Femtosecond frequency comb based on a stretched-pulse fiber laser. A two branch configuration is employed. One branch is used for the self-referencing via a single-arm f-to-2f interferometer. Measurement of the acetylene-stabilized diode laser is performed with the second branch.
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