title: Sub-kilohertz linewidth narrowing of a mid-infrared optical parametric oscillator idler frequency by direct cavity stabilization.
abstract: We stabilize the idler frequency of a singly resonant optical parametric oscillator directly to the resonance of a mid-infrared Fabry-Perot reference cavity. This is accomplished by the Pound-Drever-Hall locking scheme, controlling either the pump laser or the resonant signal frequency. A residual relative frequency noise power spectral density below 10(3)  Hz(2)/Hz is reached on average, with a Gaussian linewidth of 920 Hz over 100 ms, which reveals the potential for reaching spectral purity down to the hertz level by locking the optical parametric oscillator against a mid-infrared cavity with state-of-the-art superior performance.
authors.forename: I
authors.initials: I
authors.lastname: Ricciardi
authors.forename: S
authors.initials: S
authors.lastname: Mosca
authors.forename: M
authors.initials: M
authors.lastname: Parisi
authors.forename: P
authors.initials: P
authors.lastname: Maddaloni
authors.forename: L
authors.initials: L
authors.lastname: Santamaria
authors.forename: P
authors.initials: P
authors.lastname: De Natale
authors.forename: M
authors.initials: M
authors.lastname: De Rosa