Quantum cascade laser based hybrid dual comb spectrometer

Four-wave-mixing-based quantum cascade laser frequency combs (QCL-FC) are a powerful photonic tool, driving a recent revolution in major molecular fingerprint regions, i.e. mid- and far-infrared domains. Their compact and frequency-agile design, together with their high optical power and spectral purity, promise to deliver an all-in-one source for the most challenging spectroscopic applications. Here, we demonstrate a metrological-grade hybrid dual comb spectrometer, combining the advantages of a THz QCL-FC with the accuracy and absolute frequency referencing provided by a free-standing, optically-rectified THz frequency comb. A proof-of-principle application to methanol molecular transitions is presented. The multi-heterodyne molecular spectra retrieved provide state-of-the-art results in line-center determination, achieving the same precision as currently available molecular databases. The devised setup provides a solid platform for a new generation of THz spectrometers, paving the way to more refined and sophisticated systems exploiting full phase control of QCL-FCs, or Doppler-free spectroscopic schemes

Selective excitation of zone-folded phonon modes within one triplet in a semiconductor superlattice

The selective optical excitation of coherent zone-folded acoustic phonon modes in a semiconductor superlattice is demonstrated. By using a time-delayed control pulse, we show the modification of phonon amplitudes within a phonon triplet and demonstrate that the phase relation of phonon modes can be mapped over time delays of several tens of picoseconds. This method with high spectral resolution has the potential to tailor specific amplitudes of phonon modes that are otherwise only collectively excited