Since the advent of the first laser, the spectral purity of these devices was assumed to be limited by the unavoidable presence of spontaneous emission, as elegantly expressed by the Schawlow-Townes formula.
Indeed, this limit does not apply to Quantum Cascade Lasers (QCLs), according to CNR-INO researchers that have directly measured the intrinsic linewidht of a QCL. They provided the first experimental confirmation of a new theory, that predicts the overcoming of this limit and the achievement of an exceptional intrinsic spectral purity.

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News by Bartalini Saverio