Open AccessPhase locking of a 15 Terahertz quantum cascade laser and use as a local oscillator in a heterodyne HEB receiver
Author(s) -
D. Rabanus,
U. U. Graf,
Martin Philipp,
Oliver Ricken,
J. Stützki,
B. Vowinkel,
Martina C. Wiedner,
Christoph Walther,
M. Fischer,
Jérôme Faist
Publication year - 2009
Publication title -
optics express
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.394
H-Index - 271
ISSN - 1094-4087
DOI - 10.1364/oe.17.001159
Subject(s) - quantum cascade laser , optics , local oscillator , terahertz radiation , physics , superheterodyne receiver , phase locked loop , heterodyne (poetry) , phase noise , laser , cascade , optoelectronics , microwave , chemistry , chromatography , quantum mechanics , acoustics
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.