title: Measurement of the intrinsic linewidth of terahertz quantum cascade lasers using a near-infrared frequency comb.
abstract: We report the measurement of the frequency noise power spectral density of a quantum cascade laser emitting at 2.5THz. The technique is based on heterodyning the laser emission frequency with a harmonic of the repetition rate of a near-infrared laser comb. This generates a beatnote in the radio frequency range that is demodulated using a tracking oscillator allowing measurement of the frequency noise. We find that the latter is strongly affected by the level of optical feedback, and obtain an intrinsic linewidth of ~230Hz, for an output power of 2mW.
authors.affiliation: Laboratoire Matériaux et Phénomènes Quantiques, Université Paris Diderot and CNRS, 10 rue A. Domontet L. Duquet, 75205 Paris, France.
authors.forename: M
authors.initials: M
authors.lastname: Ravaro
authors.forename: S
authors.initials: S
authors.lastname: Barbieri
authors.forename: G
authors.initials: G
authors.lastname: Santarelli
authors.forename: V
authors.initials: V
authors.lastname: Jagtap
authors.forename: C
authors.initials: C
authors.lastname: Manquest
authors.forename: C
authors.initials: C
authors.lastname: Sirtori
authors.forename: S P
authors.initials: SP
authors.lastname: Khanna
authors.forename: E H
authors.initials: EH
authors.lastname: Linfield