Substructure of high-power stimulated emission pulses from a fiber laser

It is demonstrated experimentally that an individual spike in a regular series of intensity pulsations from a glass-fiber laser having a core doped with neodymium ions, consists of a train of short pulses having a duration of 2–8 nsec and a period of $\sim15$ nsec. The spectrum of stimulated emission from a fiber laser with a total half-width $\Delta\lambda\lesssim$ 1.8–5.6 nm, governed by the pump energy, takes the form of discrete narrow lines with the half-width $\Delta\lambda\leq$ 0.075–0.3 $\mathring{A}$. This character of the stimulated emission is attributed to the self-mode-locking in a fiber laser due to the effect, at the emission wavelength of $\lambda$ = 1.06 $\mu$, of short-lived color centers which are produced in the glass by the ultraviolet part of the pump radiation spectrum.