title: Phase locking of a 1.5 Terahertz quantum cascade laser and use as a local oscillator in a heterodyne HEB receiver.
abstract: We demonstrate for the first time the closure of an electronic phase lock loop for a continuous-wave quantum cascade laser (QCL) at 1.5 THz. The QCL is operated in a closed cycle cryo cooler. We achieved a frequency stability of better than 100 Hz, limited by the resolution bandwidth of the spectrum analyser. The PLL electronics make use of the intermediate frequency (IF) obtained from a hot electron bolometer (HEB) which is downconverted to a PLL IF of 125 MHz. The coarse selection of the longitudinal mode and the fine tuning is achieved via the bias voltage of the QCL. Within a QCL cavity mode, the free-running QCL shows frequency fluctuations of about 5 MHz, which the PLL circuit is able to control via the Stark-shift of the QCL gain material. Temperature dependent tuning is shown to be nonlinear, and of the order of -16 MHz/K. Additionally we have used the QCL as local oscillator (LO) to pump an HEB and perform, again for the first time at 1.5 THz, a heterodyne experiment, and obtain a receiver noise temperature of 1741 K.
authors.affiliation: European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile. drabanus@eso.org
authors.forename: D
authors.initials: D
authors.lastname: Rabanus
authors.forename: U U
authors.initials: UU
authors.lastname: Graf
authors.forename: M
authors.initials: M
authors.lastname: Philipp
authors.forename: O
authors.initials: O
authors.lastname: Ricken
authors.forename: J
authors.initials: J
authors.lastname: Stutzki
authors.forename: B
authors.initials: B
authors.lastname: Vowinkel
authors.forename: M C
authors.initials: MC
authors.lastname: Wiedner
authors.forename: C
authors.initials: C
authors.lastname: Walther
authors.forename: M
authors.initials: M
authors.lastname: Fischer
authors.forename: J
authors.initials: J
authors.lastname: Faist