Frequency locking of single-mode 3.5-THz quantum cascade lasers using a gas cell

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Published Date

25-01-2012

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Source:

Applied Physics Letters, 100 (4), 2012

Faculty

Applied Sciences

Department

QN/Quantum Nanoscience

Abstract

We report frequency locking of two 3.5-THz third-order distributed feedback (DFB) quantum cascade lasers (QCLs) by using methanol molecular absorption lines, a proportional-integral-derivative controller, and a NbN bolometer. We show that the free-running linewidths of the QCLs are dependent on the electrical and temperature tuning coefficients. For both lasers, the frequency locking induces a similar linewidth reduction factor, whereby the narrowest locked linewidth is below 18?kHz with a Gaussian-like shape. The linewidth reduction factor and the ultimate linewidth correspond to the measured frequency noise power spectral density.