Efficient upconversion-pumped continuous wave Er3+:LiLuF4 lasers

Abstract

We report on detailed spectroscopic investigations and efficient visible upconversion laser operation of Er3+:LiLuF4. This material allows for efficient resonant excited-state-absorption (ESA) pumping at 974nm. Under spectroscopic conditions without external feedback, ESA at the laser wavelength of 552nm prevails stimulated emission. Under lasing conditions in a resonant cavity, the high intracavity photon density bleaches the ESA at 552nm, allowing for efficient cw laser operation.We obtained the highest output power of any room-temperature crystalline upconversion laser. The laser achieves a cw output power of 774mW at a slope efficiency of 19% with respect to the incident pump power delivered by an optically-pumped semiconductor laser. The absorption efficiency of the pump radiation is estimated to be below 50%.To exploit the high confinement in waveguides for this laser, we employed femtosecond-laser pulses to inscribe a cladding of parallel tracks of modified material into Er3+:LiLuF4 crystals. The core material allows for low-loss waveguiding at pump and laser wavelengths. Under Ti:sapphire pumping at 974nm, the first crystalline upconversion waveguide laser has been realized. We obtained waveguide-laser operation with up to 10mW of output power at 553nm.