Novel diode-pumping schemes for near-IR rare-earth lasers

Abstract

Solid-state lasers are being considered for an increasing number of applications in which the laser radiation would be directed over inhabited regions. Eyesafe lasers such as the Raman shifted Nd 1.06 µm or the Er 1.5 µm have therefore received much attention recently. In this talk we will consider two interesting alternatives to such eyesafe laser systems. Both of these systems utilize thulium as the active laser ion in which the lower laser level is an excited state. The Tm3+ 3H4 3F4 transition at 1.5µm, however, is normally self-terminating due to the long lower level lifetime (-10 ms) relative to the upper level lifetime (-1 ms). As a result CW laser emission can only be obtained by depopulating the 3F4 level. This has been done in two systems: 1) a Tm, Ho:YLF crystal in which energy is transferred from the Tm ion to the Ho ion, which is then lased at 2 µm and 2) a Tm, Tb:YLF crystal in which a cross-relaxation process between the Tm and Tb ions depopulates the Tm 3F4 level without requiring a cascade laser process. These four level CW lasing schemes can also provide tunable CW operation and may provide other advantages over three level eyesafe laser systems.