title: Phase seeding of a terahertz quantum cascade laser.
abstract: The amplification of spontaneous emission is used to initiate laser action. As the phase of spontaneous emission is random, the phase of the coherent laser emission (the carrier phase) will also be random each time laser action begins. This prevents phase-resolved detection of the laser field. Here, we demonstrate how the carrier phase can be fixed in a semiconductor laser: a quantum cascade laser (QCL). This is performed by injection seeding a QCL with coherent terahertz pulses, which forces laser action to start on a fixed phase. This permits the emitted laser field to be synchronously sampled with a femtosecond laser beam, and measured in the time domain. We observe the phase-resolved buildup of the laser field, which can give insights into the laser dynamics. In addition, as the electric field oscillations are directly measured in the time domain, QCLs can now be used as sources for time-domain spectroscopy.
authors.affiliation: Laboratoire Pierre Aigrain, Ecole Normale Supérieure, CNRS (UMR 8551), Université P. et M. Curie, Université D. Diderot, 75231 Paris Cedex 05, France.
authors.forename: Dimitri
authors.initials: D
authors.lastname: Oustinov
authors.forename: Nathan
authors.initials: N
authors.lastname: Jukam
authors.forename: Rakchanok
authors.initials: R
authors.lastname: Rungsawang
authors.forename: Julien
authors.initials: J
authors.lastname: Madéo
authors.forename: Stefano
authors.initials: S
authors.lastname: Barbieri
authors.forename: Pascal
authors.initials: P
authors.lastname: Filloux
authors.forename: Carlo
authors.initials: C
authors.lastname: Sirtori
authors.forename: Xavier
authors.initials: X
authors.lastname: Marcadet
authors.forename: Jérôme
authors.initials: J
authors.lastname: Tignon
authors.forename: Sukhdeep
authors.initials: S
authors.lastname: Dhillon