Towards the full frequency stabilization of quantum cascade laser frequency combs
Authors: Cappelli F., Campo G., Galli I., Consolino L., Giusfredi G., Cancio P., Borri S., Hinkov B., Mazzotti D., Bartalini S., Faist J., De Natale P.
Autors Affiliation: CNR-INO – Istituto Nazionale di Ottica, Largo Enrico Fermi 6, Firenze FI, 50125, Italy; LENS – European Laboratory for Non-Linear Spectroscopy, Via Nello Carrara 1, Sesto Fiorentino FI, 50019, Italy; Institute of Solid State Electronics, TU Wien, Floragasse 7, Vienna, 1040, Austria; Institute for Quantum Electronics, ETH Zurich, Zu¨rich, 8093, Switzerland
Abstract: Optical frequency combs (OFCs) generated by quantum cascade lasers (QCLs) have recently been proven in the mid infrared  and they have already been applied to spectroscopy in free-running operation . It is clear however that for more demanding applications such as high-resolution and accuracy spectroscopy and metrology the performance obtained in free-running operation is not enough, since a consistent amount of frequency noise is present. The first attempt of frequency stabilizing a quantum cascade laser comb (QCL-comb) against a metro-logical difference-frequency-generated comb through a single phase-locking chain using the laser bias current as actuator  gave a reduction of the single QCL-comb tooth linewidth from 500 kHz down to values ranging from 1 to 23 kHz in a 40-ms time scale. This is still a partial result since for a total stabilization and control a second actuator is needed. Here we propose the use of feedback from a controlled mirror as a second actuator. With two actuators (at least partially independent) it is possible to correct both for offset and spacing frequency fluctuations. © 2017 IEEE
Conference title: 2017 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference (CLEO/Europe-EQEC 2107)
KeyWords: Quantum cascade laser; Optical frequency comb