Measurements of Operation Parameters and Nonlinearity of A Nd3+-Doped Fibre Laser by Relaxation Oscillations

The optical nonlinearity, saturation of the lower laser level, and spontaneous emission modify the relaxation oscillations in a Nd3+-doped fibre laser. A novel four-level rate-equation model correctly describes the modified laser dynamics and allows the determination of the second-order susceptibility of the fibre, lifetimes of upper and lower laser levels, cavity loss, and the number of oscillating modes by monitoring relaxation oscillations. Measurements on five different Nd3+-doped fibres are reported.