An optical frequency comb is an ultra-short pulsed laser whose repitition rate is locked to the accuracy of an atomic clock, such as those based on the electronic transition frequencies of Rubidium and Caesium. This pulse train in the time domain is represented as a "comb" of frequencies in the Fourier domain. The stability of the wavelength and hence frequency of each "tooth" in the comb is then also referenced to the atomic clock, thus tying the three important standards of time, length and frequency.
In this project, we will use a commercial turn-key frequency comb, which spans the visible and infra-red spectrum, as an absolute frequency reference. The aim is to develop a stabilisation scheme for an auxilliary laser using this reference to make ultra-high resolution displacement measurements for instrumentation in gravitational wave physics.
In a different application, we aim to use heterodyne interferometry involving an auxilliary laser referenced to the frequency comb to facilitate ultra-precise lineshape measurements of molecular optical absorption transitions.
One exciting prospect is to distribute these frequency stablised optical sources across a building, or between remotely separated laboratories using optical fibres. It is known that a length of fibre can introduce random Doppler shifts to the laser frequency. We aim to design and implement a system to cancel these remote delivery noise sources using digital signal processing.