Green FS Laser Achieves Record Power

The first-ever laser to generate an average power of 280 W at a 515-nm wavelength with perfect beam quality now is ready to operate at the touch of a button. The turnkey laser is based on a Yb:Innoslab amplifier with frequency doubling. Fraunhofer ILT said no other laser system has ever offered more output with diffraction-limited beam quality in the visible spectral range.

As part of the Korona cooperation project, which aims to produce coherent radiation with wavelengths in the extreme-ultraviolet region below 100 nm, research scientists from the Fraunhofer Institute for Laser Technology ILT installed a femtosecond laser at the Max Planck Institute of Quantum Optics MPQ.

The 100-nm wavelength range can be opened up by generating high harmonics of femtosecond radiation. Scaling up the average power creates the potential for new applications in this wavelength range. What’s more, Innoslab lasers are commercially available. The company EdgeWave GmbH, a spinoff from Fraunhofer ILT, has been marketing pulsed solid-state lasers based on the Innoslab platform for scientific and industrial use for about 10 years. The company Amphos GmbH, another Fraunhofer ILT spinoff, develops and sells Yb:Innoslab lasers in the power range from 100 to 1000 W.

This femtosecond laser system with 280 W at 515 nm was installed at the MPQ in Garching. (Image: Fraunhofer Institute for Laser Technology ILT)

Average output power of several hundred watts with diffraction-limited beam quality has been demonstrated using ytterbium-doped laser media at 1-µm wavelength in fiber, Innoslab and thin-disk geometry. The Fraunhofer ILT scientists hold the record with their Yb:Innoslab amplifier, generating an output power of 1.1 kW.

If they are to be widely used, these beam sources must be reliable and easy to operate. The scientists from Fraunhofer ILT have installed a laser system at the MPQ that delivers an average power of 280 W at a 515-nm wavelength and an almost diffraction-limited beam quality of M² < 1.4 using near-industrial construction and user interface. It works by amplifying the radiation from a commercial femtosecond laser with 3-W output power in a Yb:Innoslab amplifier to 470 W at a pulse duration of 700 fs and then doubling its frequency in a nonlinear crystal. As a result, the scientists at the MPQ have an average power at their disposal that is one magnitude higher than that generated by commercially available systems.

Ultrashort-pulse lasers have manifold applications in materials processing. It is widely recognized that they offer higher-precision ablation than lasers with longer pulses. The femtosecond laser can process materials such as glass that are otherwise transparent for light with the laser wavelength. This ability is based on the process of multiphoton absorption that occurs at high peak intensities. Frequency conversion from the infrared to the green spectral range doubles the photon energy. As a result, fewer photons are needed for absorption, making it more effective.

Another application of green laser radiation is the processing of copper and other materials that absorb radiation particularly well in this spectral range. Scaling up the average power permits a higher throughput and renders industrial use economically viable, as the costs per watt are significantly reduced.

The Yb:Innoslab amplifier will be presented May 23 to 26 at Laser World of Photonics 2011 in Munich.

For more information, visit: www.ilt.fraunhofer.de