Noise dynamics of a prism-based Cr:forsterite laser frequency comb

Mode-locked Cr:forsterite lasers are of significant interest as infrared frequency combs due to their ability to generate stable high repetition rate femtosecond pulses. However, self-referenced Cr:forsterite frequency combs tend to exhibit wide carrier-envelope offset frequency ($f_{0})$ linewidths. These large $f_{0}$ linewidths can be attributed to significant frequency noise across the comb's spectral bandwidth and result in broad comb teeth. We have stabilized a prism-based Cr:forsterite frequency comb and observed narrowing of the $f_{0}$ linewidth from $\sim $1 MHz down to $<$100 kHz when a knife edge is inserted into the intracavity beam as a spectral filter. This can also be further reduced after phase-locking the comb to a low-phase noise rf oscillator. Thus, the introduction of an intracavity knife edge significantly reduces the frequency noise of the system and enables more effective stabilization of the entire comb. A theoretical model has been used to investigate the noise dynamics of the phase-stabilized comb system. It includes: the pump laser power (P), the frequency dependence of the $f_{0}$ response to pump power changes ((d$f_{0}$/dP)($\nu ))$, and the frequency dependence of the femtosecond laser's relative intensity noise, RIN($\nu )$. Supported by AFOSR FA9950-05-1-0304 and NSF ECS-0449295