title: Frequency-comb-referenced singly-resonant OPO for sub-Doppler spectroscopy.
abstract: We present a widely-tunable, singly-resonant optical parametric oscillator, emitting more than 1 W between 2.7 and 4.2 μm, which is phase locked to a self-referenced frequency comb. Both pump and signal frequencies are directly phase-locked to the frequency comb of a NIR-emitting fs mode-locked fibre laser, linked, in turn, to the caesium primary standard. We estimate for the idler frequency a fractional Allan deviation of ∼ 3 × 10⁻¹²τ⁻½ between 1 and 200 s. To test the spectroscopic performance of the OPO, we carried out saturation spectroscopy of several transitions belonging to the ν1 rovibrational band of CH₃I, resolving their electronic quadrupole hyperfine structure, estimating a linewidth better than 200 kHz FWHM for the idler, and determining the absolute frequency of the hyperfine components with a 50-kHz-uncertainty.
authors.affiliation: INO–CNR, Istituto Nazionale di Ottica, Sezione di Napoli, and LENS, European Laboratory for Nonlinear Spectroscopy, Via Campi Flegrei 34, I-80078 Pozzuoli (NA), Italy.
authors.forename: I
authors.initials: I
authors.lastname: Ricciardi
authors.forename: E
authors.initials: E
authors.lastname: De Tommasi
authors.forename: P
authors.initials: P
authors.lastname: Maddaloni
authors.forename: S
authors.initials: S
authors.lastname: Mosca
authors.forename: A
authors.initials: A
authors.lastname: Rocco
authors.forename: J-J
authors.initials: JJ
authors.lastname: Zondy
authors.forename: M
authors.initials: M
authors.lastname: De Rosa
authors.forename: P
authors.initials: P
authors.lastname: De Natale