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We performed an absolute frequency measurement of the ¹S0-³P0 transition in 87Sr with a fractional uncertainty of 1.2 x 10-15, which is less than one-third that of our previous measurement. A caesium fountain atomic clock was used as a transfer oscillator to reduce the uncertainty of the link between a strontium optical lattice clock and the SI second. The absolute value of the transition frequency is 429 228 004 229 873.56(49) Hz. [ABSTRACT FROM AUTHOR]

We propose simple schemes to phase-lock the carrier envelope offset frequency (fceo) referring to the repetition rate (frep) of an optical frequency comb. We demonstrate the locking of fceo such that fceo = (1/2)frep, (1/3)frep, and (2/3)frep. The Allan deviation and signal-to-noise ratio of the coherent δ-function peak for the in-loop beat signal are 5.3 × 10−17/τ and 80–85 dB·Hz, respectively, where τ is the averaging time of the frequency measurement. These new locking schemes simplify the sign and mode-number determination in frequency measurements. [ABSTRACT FROM AUTHOR]

We have carried out dual-comb spectroscopy and observed in a simultaneous acquisition a 140-THz-wide spectrum from 1.0 to 1.9 µm using two fiber-based frequency combs phase-locked to each other. This ultrabroad-wavelength bandwidth is realized by setting the difference between the repetition rates of the two combs to 7.6 Hz using the sub-Hz-linewidth fiber combs. The recorded spectrum contains five vibration-rotation bands of C2H2, CH4, and H2O at different wavelengths across the whole spectrum. The determined transition frequencies of C2H2 agree with those from the previous sub-Doppler resolution measurement of individual lines using CW lasers within 2 MHz. [ABSTRACT FROM AUTHOR]

We demonstrate that dual-comb spectroscopy, which allows one to record broadband spectra with high frequency accuracy in a relatively short time, provides a real advantage for the observation of pressure-broadening and pressure-shift effects. We illustrate this with the ν1+ν3 vibration band of 12C2H2. We observe transitions from P(26) to R(29), which extend over a 3.8 THz frequency range, at six pressures ranging up to 2654 Pa. Each observed absorption line profile is fitted to a Voigt function yielding pressure-broadening and pressure-shift coefficients for each rotation-vibration transition. The effectiveness of this technique is such that we are able to discern a clear dependence of the pressure-broadening coefficients on the nuclear spin state, i.e., on the ortho or para modification. This information, combined with the pressure-shift coefficients, can facilitate a detailed understanding of the mechanism of molecular collisions. [ABSTRACT FROM AUTHOR]