High repetition rate Ti:sapphire-based
femtosecond comb

Our high repetition rate Ti:sapphire-based femtosecond optical frequency comb is based on a Kerr-lens mode-locked Ti:sapphire laser which has a ring cavity design with a repetition rate of about 800 MHz. This uses mirrors with negative group velocity dispersion coatings to provide dispersion compensation.

This higher repetition rate system offers several advantages for optical frequency measurements. In particular:

• The higher power per comb mode gives improved signal-to-noise in the beat with an optical frequency standard
• The larger mode spacing makes it easier to establish the comb mode number in cases where the frequency being measured is not previously well known

The comb produced directly from the laser is broadened using microstructured fibre. The absolute position of all the comb modes in the resultant octave-spanning spectrum is then determined using a self-referencing arrangement very similar to that developed for our lower repetition rate Ti:sapphire-based comb.