External cavities promise cheap high-power sources

17 Jun 2002

Researchers in Switzerland and the UK have demonstrated what they believe to be the first passively mode-locked surface-emitting semiconductor laser.

Ursula Keller from the ETH Institute in Zurich and Anne Tropper of Southampton University presented their results to the Advanced Solid-State Lasers (ASSL) 2000 meeting in Davos, Switzerland, on 13 -16 February.

They used a 2 W high-brightness diode laser as a pump source, and a semiconductor saturable absorber mirror (SESAM) as the mode locker. The laser generated two stable, mode-locked output beams with 11 mW each of average power, a 26 ps pulse duration and a repetition rate of 4.4 GHz.

In contrast with edge-emitting semiconductor lasers, vertical external cavity surface-emitting lasers (VECSELs) allow a scaling up of the mode area to generate a high average power and high pulse energies. At the same time the external cavity enforces a diffraction-limited output.

The team expects to see a substantial increase of output power with improved cooling systems, better VECSEL designs and a higher pump power. Ursula Keller believes that this concept will lead to compact, reliable, cost-effective and efficient pulsed laser sources with high average power in a diffraction-limited beam, subpicosecond pulse durations and multigigahertz repetition rates.

PH

Keller and Tropper's novel design for a VECSEL laser cavity breaks new ground.