Prism-based Cr:forsterite laser frequency comb stabilization and carrier-envelope offset frequency linewidth narrowing.

Infrared frequency combs in the near IR, based on lasers such as Cr:forsterite, are important for frequency measurements in the telecommunications band. We have actively stabilized a self-referenced prism-based Cr:forsterite frequency comb using both prism and power control inside the cavity. We also report dramatic reduction in the linewidth of the carrier envelope offset frequency ($f_{0})$ by at least two orders of magnitude simply by inserting a knife edge into the laser cavity after the prisms. We have stabilized the laser when the $f_{0}$ beat width was both wide ($\sim $1.5 MHz) and narrow ($\sim $10 kHz) although the locking was less robust with the narrower beat note. We measured the fractional stability of the comb by counting the repetition frequency ($f_{r})$ and $f_{0}$. The fractional stability of the comb at 10 s was limited by the frequency counter resolution to $<$10$^{-12}$. An optical characterization of the stability is in progress. Furthermore, we will use this comb to characterize optical frequency references based on acetylene-filled hollow photonic band gap optical fibers.