Frequency comb metrology with an optical parametric oscillator
Read this new paper by K. Balskus et al. which reports on the first demonstration of absolute frequency comb metrology using an optical parametric oscillator (OPO). Absolute optical frequency metrology is widely done using a frequency comb where the repetition rate and the carrier envelope offset frequency is stabilised using an f-to-2f interferometer and locking electronics. In this paper the experiment fully characterises three key features: the frequency noise power spectral density (PSD) of the repetition rate, of the carrier-envelope offset frequency and of an optical comb line.
As the pump source for the OPO, a gigajet modelocked, Ti:Sapphire femtosecond oscillator was used, a Laser Quantum ultrafast laser capable of an average power of 1.45 W at high repetition rate, which was tightly locked by a Laser Quantum TL-1000 stabilisation unit.
Previously, fibre-based comb systems were used which are typically known to have relatively high-frequency noise compared to that of a Ti:Sapphire laser due to contributions from spontaneous emission. Commonly, larger feedback bandwidth is required for fibre-combs in order to compensate for this higher frequency noise. In contrast, femtosecond optical parametric oscillator frequency combs benefit from the extremely low-noise parametric gain process.
Moreover, OPOs are widely tunable, to easily reach the targeted metrology wavelength for an extended range of experiments.
Click here to read the paper in full to find out experimental and results details.