Simultaneous frequency locking and monitoring using a bi-directional THz quantum cascade laser
B Mirzaei (TU Delft - QN/Gao Lab)
N. Van v. Marrewijk (TU Delft - Tera-Hertz Sensing)
D Hayton (SRON–Netherlands Institute for Space Research)
Jian Gao (SRON–Netherlands Institute for Space Research, TU Delft - QN/Gao Lab)
Tsung Yu Kao (Massachusetts Institute of Technology)
Q Hu (Massachusetts Institute of Technology)
J. L. Reno (Sandia National Laboratories, New Mexico)
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Abstract
We have performed frequency locking of a dual, forward reverse emitting 3rd order distributed feedback quantum cascade laser (QCL) at 3.5 THz. By using both directions of THz emission in combination with two gas cells and two power detectors, we can for the first time perform frequency stabilization, while monitor the frequency locking quality independently. We also characterize how the use of a less sensitive pyroelectric detector can influence the quality of frequency locking, illustrating experimentally that the sensitivity of the detectors is crucial. Using both directions of THz radiation has a particular advantage for the application of a QCL as a local oscillator, where radiation from one side can be used for frequency/phase stabilization, leaving the other side to be fully utilized as a local oscillator to pump a mixer.