Frequency comb metrology with an optical parametric oscillator

Abstract

Abstract:We report on the first demonstration of absolute frequency comb metrology with an optical parametric oscillator (OPO) frequency comb. The synchronously-pumped OPO operated in the 1.5-µm spectral region and was referenced to an H-maser atomic clock. Using different techniques, we thoroughly characterized the frequency noise power spectral density (PSD) of the repetition rate f rep , of the carrier-envelope offset frequency f CEO , and of an optical comb line ν N . The comb mode optical linewidth at 1557 nm was determined to be ~70 kHz for an observation time of 1 s from the measured frequency noise PSD, and was limited by the stability of the microwave frequency standard available for the stabilization of the comb repetition rate. We achieved a tight lock of the carrier envelope offset frequency with only ~300 mrad residual integrated phase noise, which makes its contribution to the optical linewidth negligible. The OPO comb was used to measure the absolute optical frequency of a near-infrared laser whose second-harmonic component was locked to the F = 2→3 transition of the 87 Rb D2 line at 780 nm, leading to a measured transition frequency of ν Rb = 384,228,115,346 ± 16 kHz. We performed the same measurement with a commercial fiber-laser comb operating in the 1.5-µm region. Both the OPO comb and the commercial fiber comb achieved similar performance. The measurement accuracy was limited by interferometric noise in the fibered setup of the Rb-stabilized laser.

Singly and doubly resonant femtosecond optical parametric oscillators for precision spectroscopy from the near-to mid-infrared

“…This has recently been extended to longer wavelengths corresponding to the molecular fingerprint region by using an OPGaP OPO operating between 6 and 8 µm [7]. The resolution of the spectral measurement in DCS is generally limited to the mode spacing of the combs, often 100 MHz or higher, but the individual comb modes generated by a femtosecond OPO also have the potential to be used for spectroscopy, since their modal linewidths can be less than 100 kHz, and extend across a wide spectral range, making it possible to perform heterodyne measurements revealing the emission linewidth of an independent cw source [8].…”