04 Mar 2004
Researchers detail the first femtosecond oscillator based on an ytterbium (Yb)-doped sesquioxide crystal.
A passively modelocked Yb:Sc2O3 laser has given as much as 0.8 W of power in the picosecond range with a pump efficiency as high as 47%. And, with dispersion compensation, pulses as short as 230 fs at an average power of 0.54 W were obtained at 1044 nm. (Optics Letters 29 391)
“We believe this value [47%] represents the highest reported optical-to-optical pump efficiency with respect to the absorbed power of any modelocked laser, including those based on the thin-disk concept,” say the authors from Germany’s Max-Born Institute; the Institute for Laser Physics in Hamburg and the Ferdinand-Braun Institute in Berlin in their paper.
The team modelocked the Yb-doped laser using a semiconductor saturable-absorber mirror (SESAM) placed in a z-shaped resonator. Both a Ti:sapphire and diode lasers were used as pump sources.
“For all arrangements investigated, the modelocked operation showed no tendencies toward passive Q-switching and was stable for hours in the diode-pumped configuration,” the authors report.
Yb-doped materials are of interest because they have small quantum defects, which reduce the thermal load, and the absence of excited-state absorption, upconversion, cross relaxation and concentration quenching. Combining these properties with sesquioxides brings additional benefits of a better thermal conductivity and a larger splitting of the ground state than tungstates or YAG lasers. This makes them good for highly efficient ultrashort-pulse laser sources.