Sesquioxide source emits fs pulses

23 Jul 2004

Scientists in Hamburg and Berlin make a modelocked Yb:Lu₂O₃ laser.

A German team claims to have made the first femtosecond laser based on a Yb-doped sesquioxide (Lu₂O₃) crystal. The passively modelocked source emits pulses as short as 220fs with an average power of 266 mW at 1033.5 nm (Optics Express 12 14).

It was constructed by researchers from the Max Born Institut in Berlin and the Institut für Laser Physik,at the University of Hamburg. They say that because Yb:Lu₂O₃ offers a higher thermal conductivity and broader emission band than Yb:YAG it is an attractive alternative for creating an efficient source of high-power, short pulses at 1µm.

Their Z-design modelocked laser contains a series of fold mirrors, an uncooled Yb:Lu₂O₃ crystal and a semiconductor saturable absorber mirror which causes passive modelocking. The Yb:Lu₂O₃ crystal was pumped by a Ti:Sapphire laser emitting up to 2 W at 976 nm.

In this configuration the laser operated in the picosecond regime, generating a train of pulses as short as 1.16 ps with a pump efficiency of 32% and a slope efficiency of 42%.

However, by placing a set of dispersion compensating prisms into the cavity the team was able to create a modelocked train of femtosecond pulses (220 fs) with an average power of 266 mW.

It believes that output powers in the watt range could be achieved by using crystals with less impurities and higher pump powers.

Author
Oliver Graydon is editor of Optics.org and Opto & Laser Europe magazine.