title: Quantum cascade laser-based mid-IR frequency metrology system with ultra-narrow linewidth and 1  ×  10⁻¹³-level frequency instability.
abstract: We demonstrate a powerful tool for high-resolution mid-IR spectroscopy and frequency metrology with quantum cascade lasers (QCLs). We have implemented frequency stabilization of a QCL to an ultra-low expansion (ULE) reference cavity, via upconversion to the near-IR spectral range, at a level of 1×10(-13). The absolute frequency of the QCL is measured relative to a hydrogen maser, with instability <1×10(-13) and inaccuracy 5×10(-13), using a frequency comb phase stabilized to an independent ultra-stable laser. The QCL linewidth is determined to be 60 Hz, dominated by fiber noise. Active suppression of fiber noise could result in sub-10 Hz linewidth.
authors.forename: Michael G
authors.initials: MG
authors.lastname: Hansen
authors.forename: Evangelos
authors.initials: E
authors.lastname: Magoulakis
authors.forename: Qun-Feng
authors.initials: QF
authors.lastname: Chen
authors.forename: Ingo
authors.initials: I
authors.lastname: Ernsting
authors.forename: Stephan
authors.initials: S
authors.lastname: Schiller