Laser emission at 413 and 730 nm in upconversion-pumped YLiF₄:Nd³⁺

The authors report laser transitions of the neodymium ion at 413.0 and 729.5 nm, using upconversion pumping of YLiF4+ at low temperature. The upconversion pumping mechanisms shows some unusual nonlinearities, which are explained by a rate equation model that includes contributions from cross relaxation. The laser behavior is substantially different from that in LaF3+, highlighting the strong dependence of the operation of upconversion lasers on the host crystal.