title: Frequency stabilization of quantum-cascade lasers by use of optical cavities.
abstract: We report a heterodyne beat with a linewidth of 5.6+/-0.6 Hz between two cavity-stabilized quantum-cascade lasers operating at 8.5 microm . We also present a technique for measuring this beat that avoids the need for extreme isolation of the optical cavities from the environment, that of employing a third servo loop with low bandwidth to force one cavity to track the slow drifts and low-frequency fluctuations of the other. Although it is not fully independent, this technique greatly facilitates heterodyne beat measurements for evaluating the performance of cavity-locked lasers above the bandwidth of the third loop.
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Taubman
authors.forename: Tanya L
authors.initials: TL
authors.lastname: Myers
authors.forename: Bret D
authors.initials: BD
authors.lastname: Cannon
authors.forename: Richard M
authors.initials: RM
authors.lastname: Williams
authors.forename: Federico
authors.initials: F
authors.lastname: Capasso
authors.forename: Claire
authors.initials: C
authors.lastname: Gmachl
authors.forename: Deborah L
authors.initials: DL
authors.lastname: Sivco
authors.forename: Alfred Y
authors.initials: AY
authors.lastname: Cho