title: Precise frequency-difference measurement between the 1.66-mum transitions of methane.
abstract: We determined 66 frequency differences (FD's) between rovibrational lines of methane at the 1.66-mum region. Following the technique developed by Nakagawa et al.[Opt.Lett.20, 410 (1995)], we measured the FD's as the optical beat frequency between two external-cavity diode lasers locked at 1-MHz-wide saturated absorption dips of the methane lines. Even though the methane lines often overlap in Doppler-limited resolution, the spectrometer that we use resolves them and determines their FD's with better than 40-kHz precision. This fact demonstrates that the methane lines are promising candidates for frequency reference and that this technique has great potential for high-resolution molecular spectroscopy.
authors.forename: K
authors.initials: K
authors.lastname: Suzumura
authors.forename: C
authors.initials: C
authors.lastname: Ishibashi
authors.forename: H
authors.initials: H
authors.lastname: Sasada