High power 2μm Tm 3+-doped fibre lasers

Using Tm ³⁺-doped double-clad silica fibre we have produced high power, high efficiency 2μm lasers. To date we have achieved a 59% slope efficiency relative to launched pump power using single end pumping and double passing the pump light. By pumping the fibre laser from both ends, we achieved up to 118W peak output power with 54% slope efficiency relative to launched power at 25% duty cycle. The quantum efficiency of this laser was 120% relative to launched pump power, which we attribute to a cross-relaxation process in Tm ³⁺ ( ³H ₄, ³H ₆→ ³F ₄, ³F ₄). We have also demonstrated fixed wavelength operation of the laser near 1.9μm by using fibre Bragg gratings.