New benchmark set for ultrafast thin-disk laser oscillator technology

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A commercial thin-​disk head. The disk is surrounded by monolithic prisms that route the pump beam between reflections. Credit: TRUMPF GmbH + Co. KG

Researchers at ETH Zürich's Institute of Quantum Electronics have demonstrated a sub-​picosecond thin-​disk laser oscillator delivering 350​W average output power, which they say sets a new benchmark for this type of laser.

Ultrafast lasers are at the heart of an ever-​expanding range of fundamental scientific studies and industrial applications, from high-​field-physics experiments to laser micromachining. In order to advance such applications further — for example by increasing micromachining throughput — megahertz repetition rates and multi-hundred-Watt average output powers are required.

In Optics Express, the ETH researchers reported that rather than using multi-​stage amplifier systems to achieve such higher average powers, they instead scaled up the power output from a laser oscillator. They explained that this approach is not only less complex, but could also lead to robust and potentially cost-​effective devices.

The team worked with a thin-​disk laser oscillator, where the gain medium — the material in which the quantum processes leading to lasing take place — is shaped as a disk, typically around 100μm-thin. While this geometry affords a relatively large surface area, which in turn helps cooling, thermal effects have previously remained a major bottleneck for this technology. As a result, the record output power achievable using thin-​disk laser oscillators has been limited to 275W since 2012.

Now, however, the ETH researchers have been able to break this limit by combining several advances in thin-​disk laser technology, which has enabled them to achieve several passes of the pump beam through the gain medium without inflicting detrimental thermal effects — reducing the stress on the relevant components. As a result, they were able to achieve an average output power of 350W, with pulses 940fs long and each carrying an energy of 39μJ, at a repition rate of 8.88MHz.

Such values are of immediate interest in both scientific and industrial applications, according to the researchers, who going forward intend to take the developed approach even further, with intentions to reach output powers exceeding 500W. With additional improvements, they even estimate that the kilowatt level could come into sight.

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