Abstract

The QCL comb was first unveiled in the mid-IR in 2014, proven a true comb by a technique called beatnote spectroscopy[1]. The temporal field profile of such a comb is of great interest, but unfortunately such a technique does not capture phase information. We already know the inherently short upper-state lifetime of QCLs inhibits transform limited pulses[2] as in conventional mode-locked laser combs, precluding more conventional techniques which rely on nonlinear photonics. From even early experimental evidence, the electric field is known in fact to be more FM like[1], and this is supported by numerical work [3].

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