Abstract

Rare-earth-doped fibers exploiting the three-level transitions in Er³⁺, Nd³⁺, and Pr³⁺ are used for applications including lasers and optical amplifiers. For both applications it is important to know how the process of the transient buildup of the emission depends on the population inversion dynamics. Here we describe the properties of the relaxation oscillations ω_relax in an Er-fiber laser and in a Nd-fiber laser for the three-level ⁴F_3/2 — ⁴I_9/2 transition in comparison with the four-level ⁴F_3/2 – ⁴I_11/2 transition. The linear cavity containing a piece of Nd(Er)-doped fiber as a gain medium was defined by a dichroic flat mirror and reflection grating in a Littrow configuration. The pump from a Ti:sapphire laser operating at 810 nm (980 nm) was coupled into the fiber through a dichroic mirror. A 1:10 plate beamsplitter was used as output coupler. A chopper placed in the collimated pump beam was used to observe the transient evolution of the laser.

© 1994 IEEE