title: Mid-infrared 333 MHz frequency comb continuously tunable from 1.95 to 4.0 μm.
abstract: We report a 333 MHz femtosecond optical parametric oscillator in which carrier-envelope offset stabilization was implemented by using a versatile locking technique that allowed the idler comb to be tuned continuously over the mid-infrared range from 1.95 to 4.0 μm. A specially designed multi-section, multi-grating, periodically poled KTP crystal provided simultaneously phase-matched parametric down-conversion and pump + idler sum-frequency generation, enabling strong heterodyne signals with the pump supercontinuum (employed for locking) to be obtained across the tuning range of the device. The idler comb offset was stabilized to a 10 MHz reference frequency with a cumulative phase noise from 1 Hz-64 kHz of <1.3  rad maintained across the entire operating range, and average idler output powers up to 50 mW.
authors.forename: Karolis
authors.initials: K
authors.lastname: Balskus
authors.forename: Zhaowei
authors.initials: Z
authors.lastname: Zhang
authors.forename: Richard A
authors.initials: RA
authors.lastname: McCracken
authors.forename: Derryck T
authors.initials: DT
authors.lastname: Reid