Excess spontaneous emission in non-Hermitian optical systems. II. Laser oscillators

Abstract

When the Petermann excess-spontaneous-emission factor described in the accompanying paper [Siegman, preceding paper, Phys. Rev. A 39, 1253 (1989)] is taken into account, we find that the quantum-noise fluctuations or Schawlow-Townes fluctuations in the output spectrum of a laser oscillator will be multiplied by this excess noise factor. The excess spontaneous emission in a laser oscillator cannot be canceled by adjoint-mode-excitation techniques as it can be in a laser amplifier. The resulting noise enhancement can be very sizable (100 to 1000 times or more) in gain-guided laser oscillators, and especially in laser oscillators using geometrically unstable cavities with moderate to high magnifications and Fresnel numbers.