Laser Zap

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Schawlow - Townes Linewidth

The fundamental linewidth of a laser, which only acquires quantum noise, was already predicted by Schawlow and Townes even before the laser was experimentally demonstrated. The famous Schawlow-Townes equation is as follows: \[ \Delta \nu_{laser} = \dfrac{ \pi h \nu (\Delta \nu_c )^2 }{ P_{out}} \] with the photon energy \( h \nu \), the resonator bandwidth \( \Delta \nu_c \) (full width at half-maximum, FWHM), and the output power \( P_{out} \). Reference: RP Photonics