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 Tm^{3+ 3}H₄ 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.

© 1990 Optical Society of America