The time characteristics and spectral composition of the emission were determined for a fiber laser with a core doped with 6 wt.% Nd2O3. The study was carried out at the stimulated emission threshold as well as below and above it. In the subthreshold stage the emission spectrum of the active glass fiber narrowed to a width less than 100 A and the pulse duration decreased. At the threshold pumping energy the stimulated emission was quasicontinuous (pulse duration Δτ = 75–200 μsec) and the half-width of the spectrum was Δλ<0.017 A. All the known time and spectral characteristics of the stimulated emission from solids were exhibited in a simple manner by the investigated glass-fiber laser.

Threshold, time, and spectral characteristics of 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 ~15 nsec. The spectrum of stimulated emission from a fiber laser with a total half-width Δλ 1.8–5.6 nm, governed by the pump energy, takes the form of discrete narrow lines with the half-width Δλ ≤ 0.075–0.3 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 λ=1.06μ, of short-lived color centers which are produced in the glass by the ultraviolet part of the pump radiation spectrum.

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

It was found experimentally that stimulated emission from a fiber laser made of neodymium-doped phosphate glass could operate in quasi-cw and structured spike regimes, depending on the content of cerium oxide in the glass. The total half-width of the emission spectrum of such a fiber laser did not exceed 1.0--1.2 nm when the pump energy exceeded the threshold by a factor of 4.5. The time dependence of the intensity of stimulated radiation was influenced mainly by the presence or otherwise of short-lived color centers absorbing at the laser emission wavelength lambda = 1.06 ..mu.., which were created in glass by the ultraviolet part of the pump radiation.

V. V. Mumladze

Papers

Threshold, time, and spectral characteristics of a fiber laser

Stimulated radiation of Nd3+ and Yb3+ in glass filaments at 300 and 77°K

The properties of active glass fiber in an amplification regime