Thin-disk ultrashort-pulse laser oscillator delivers 350 W average power

Ultrafast laser sources are at the heart of an ever-​expanding range of fundamental scientific studies and industrial applications, from high-​field-physics experiments with attosecond temporal resolution to micrometer-​precision machining of materials. To push the envelope even further, repetition rates of several megahertz and average output powers of hundreds of watts are required.

A particularly compelling route to realizing such high-​power laser pulses is to generate them directly by scaling up the power output from laser oscillators, rather than relying on multi-stage amplifier systems. The latter approach adds a high degree of complexity, whereas the former leads to robust and potentially cost-​effective devices.

Researchers led by Ursula Keller at ETH Zurich's Institute of Quantum Electronics have now taken the power-​scaling approach to a new level. They present a source that combines the simplicity and high repetition rates of oscillators with record-​high average output power from this type of laser.¹

The ETH team worked with a Yb:YAG thin-​disk laser oscillator in which the gain material is about 100 μm thick. This geometry affords a relatively large surface area, which in turn helps cooling. Still, thermal effects remained a major bottleneck, and since 2012 the record output power had stood at 275 W.

Reducing thermal effects

Combining several advances in thin-​disk laser technology developed in the Keller group, PhD student Francesco Saltarelli, senior research scientist Christopher Phillips, and colleagues achieved an average output power of 350 W, a pulse duration of 940 fs, andan energy of 39 μJ at a 8.88 MHz rate—values that are of immediate interest for applications both in science and industry.

A key aspect of the work is that the researchers found a way to enable several passes of the pump beam through the gain medium without inflicting detrimental thermal effects, and so could reduce the stress on the relevant components. The ability to control effects due to heating opened the gate to go beyond the 275 W level and to set the new benchmark. The approach now developed can be taken even further though, and output powers beyond 500 W seem realistic. With further improvements, the ETH researchers estimate that the kilowatt level could be approached.

Source: https://scitechdaily.com/milestone-in-ultrashort-pulse-laser-oscillators-paves-way-to-even-more-powerful-lasers/

REFERENCE:

1. F. Saltarelli et al., Optics Express, Vol. 27, Issue 22, pp. 31465-31474 (2019); doi: 10.1364/OE.27.031465