11 Apr 2003
Researchers build a modelocked thin disk laser that emits the highest average power reported to date.
A Swiss German collaboration claims to have built a mode-locked laser that emits femtosecond pulses with the highest average power reported to date. The thin-disk Yb:YAG laser built by a team from the Swiss Federal Institute of Technology (ETH) in Zürich and TRUMPF-Laser in Schramberg, Germany generates a stream of 810 fs pulses with an average power of 60 W (Optics Letters 28 367)
The design makes use of a thin-disk laser head developed by TRUMPF and ETH's expertise in semiconductor saturable absorber mirror (SESAM) technology.
At the heart of the laser is a 100 micron thick Yb:YAG disk. One face of the disk is coated for high reflectivity at both the pump and laser wavelength (940 nm and 1030 nm respectively) while the other side is anti-reflection coated for both wavelengths. The disk was pumped with up to 370 W of 940 nm light from diode bars.
The 1030 nm light from the laser head is then passed through a series of 11 dispersive mirrors to a semiconductor saturable absorber mirror (SESAM) which induces passive mode-locking. The laser pulses then travel back through the cavity, passing the disk for a second time before exiting through an output coupler.
At a pulse repetition rate of 34.3 MHz, the laser emits pulses with an energy of 1.75 microJ and a peak power of 1.9 MW. The team says that it could improve the performance of the laser by optimizing the disperse mirrors, the current versions suffer from slight thermal lensing, and redesigning the cavity so that the pulses pass through the disk four times before exiting the laser. The latter redesign would help reduce thermal distortions by reducing the intracavity power by a factor of two.
Oliver Graydon is editor of Optics.org and Opto & Laser Europe magazine.