Photons diffusing through a scattering gain medium: threshold and intensity fluctuations
Gain g: -Intensity: -Phase: below thresholdStep: 0
Random lasers (Letokhov 1968, Lawandy et al 1994): in a disordered medium with gain, photons undergo
random walks between scatterers. If gain exceeds loss per mean-free-path, stimulated emission amplifies
light despite no cavity. Above threshold, intensity spikes with large fluctuations — a signature of
random lasing distinct from conventional lasers. The threshold condition: g·l_gain ≥ 1.