24 March 2017
- Photo of a Titanium-Sapphire based femtosecond laser cavity.
The optical clocks developed in the laboratory aim at realizing frequency standards made with ultra-stable laser referenced to extremely narrow atomic transitions. The oscillation frequencies of these standards are typically of several hundred Tera-Herz (optical frequencies from near-IR to UV). For such high frequencies, it is of course impossible to use directly the oscillating signal in a time measurement system since there is no electronic system which can go that fast. The traditional solution was based on extremely heavy and complex frequency chains which were historically developed at SYRTE, as well as a handful of other metrology laboratories in the world. Nowadays, we use self-referenced optical frequency combs based on pulsed lasers of ultra-short duration (femto-seconds). The invention and realization of these techniques awarded T. Hansch et J. Hall the Nobel prize in Physics in 2005.
For comparing two optical clocks working with different atoms and therefore at different wavelength, it is necessary tu use very high performance
optical frequency combs (like, for example, when comparing the Mercury optical clock and the Strontium optical clock at SYRTE). Likewise, to connect
the optical frequency standards with the primary frequency reference of the laboratory (based on micro-wave clocks), it is mandatory to have access
to extremely reliable optical frequency combs working at exceptionally high level of performances.
The research projects related to optical frequency combs in the laboratory have as a main goal to realize reliable systems with high enough performance
not to be a limitiation for optical frequency clocks activities. Wether it is for optics-optics comparissions or for optics-microwave, the comb system
should not add any uncertainty or instability in the measurement. In addition, we carry on research on the generation of ultra*low phase-noise microwave
signals with optical frequency cobs, in collaboration with the "Photonic oscillator" project of the "micro-wave frequencies" team.
Two technologies are currently developed: the combs based on Titanium-Sapphire femto-second lasers, and those based Erbium doped fiber based femtosecond
lasers. Both technologies are in constant improvement in term of performance and reliability.
Contact
Yann Le Coq
- Email: Yann Le Coq (at) obspm.fr
- Tel.: +33 (0) 1 40 51 21 01