Pulsing mechanism based on power adiabatic evolution of pump in Tm-doped fiber laser

Abstract

We prove an alternative pulsing mechanism based on the power adiabatic evolution of a pump in a Tm-doped fiber laser. A pulsed laser technique, unlike Q-switching and gain switching, is explored under the equilibrium between the stimulated emission and absorption. After the laser reaches a continuous wave (CW) steady state, the temporal fluctuation of pump power is called power adiabatic evolution if it does not break the balance between the stimulated emission and the absorption. Under pump power adiabatic evolution the population densities in the upper and lower laser levels get clamped to their steady-state values, and the temporal shape of the output laser is identical to that of the pump. Based on the power adiabatic evolution of the pump a laser pulse can therefore be generated by a pulsed pump which is added to a CW pump. Moreover, the temporal profile, duration and peak power of the laser pulse can all be precisely controlled. The power adiabatic evolution of the pump can be achieved in the two pumping schemes of the Tm-doped fiber laser, provided that the duration of the pump pulse is broader than a certain value. The study on the pulsing mechanism highlights an alternative pulsed technique possessing several advantages over Q-switching and gain switching.