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In the early 1950s, Fermi, Pasta and Ulam (FPU) published a seminal report in which they numerically investigated the dynamics of a one-dimensional anharmonic chains of particles [1]. They argued that, owing to the nonlinear coupling, the system would irreversibly relax to a state of thermal equilibrium, in which the energy is equidistributed among all modes. Instead of such a thermalization process,...
Optical sidebands are generated by difference frequency mixing between a resonant bandgap near-infrared beam and a terahertz (THz) wave. This is realized within the cavity of a THz quantum cascade laser using resonantly enhanced non-linearities. Multiple order optical sidebands and conversion efficiencies up to 0.1% are shown.
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