Ti:Sapphire Illuminating World’s Ultrafast Lasers
February 18, 2019
The Extreme Light Infrastructure (ELI) is one of Europe’s crowning scientific achievements. It’s a four-location array of some of the world’s most intense lasers, brought together for research into a range of fascinating applications. These lasers are so powerful that laws of light-matter interaction change fundamentally. Particles charged under the influence of laser light unlock secrets for everything from physics and materials research to life sciences.
Playing a key role in the development of ELI was HEM Ti:Sapphire from GT Advanced Technologies. ‘HEM’ stands for Heat Exchanger Method, which is a proprietary GTAT process that enables the production of superior crystalline structures in sizes of up to 280mm in diameter. Here, a seed crystal is centered at the bottom of a crucible and surrounded by broken pieces of sapphire called ‘crackle.’ The crackle is highly pure, which ensures high optical transmission in the crystals. After being grown in a directional solidification process, the resulting sapphire boule is then precisely cooled to minimize stress. “The HEM process allows us to achieve sapphire crystalline quality and size well beyond what is obtainable elsewhere,” explained GTAT Vice President Kurt Schmid. “The furnace design is very elegant and efficient, which is why we can offer large-form-factor, defect-free sapphire that other manufacturers cannot produce.”
Ultrafast lasers like ELI need a trio of attributes in their sapphire. “They want to confirm that it meets their high-level spec, is optically perfect, and is polished to ultra-smooth surfaces,” said Schmid. For these applications, GTAT is producing laser optics in both 200mm and 220mm sizes. “There is excellent homogeneity created by the HEM process, no bubbles, and very high Figures of Merit,” he noted. “We also use advanced laser polishing and high-damage coatings on our sapphire optics to create angstrom-level roughness with low sub-surface damage levels which translate to high laser damage thresholds,” said Schmid.
GTAT’s Ti:Sapphire has a very wide emission range from 660nm to 1180nm and high power-density pumping capabilities meant for these leading-edge applications. “We are the first ones considered when the need is for a Ti:saph based ultra-fast laser,” said Schmid. And what other areas of use exist for these lasers? “We see the need across radiotherapy, proton therapy, accelerator physics, nuclear physics, far field physics, infrared spectroscopy, and material characterization,” said Schmid. “It’s an exciting place to be, helping to enable systems that push our learning forward.”
“Our work at GTAT isn’t limited to making the sapphire,” said Schmid. “We’re at the forefront of working with universities and our esteemed national laboratories to develop new crystal designs that will allow them to do even more with ultrafast lasers than they can now.” In addition to its ongoing work as a research partner, GTAT is invested in laser damage threshold testing. “High Intensity Lasers are harnessing and focusing some of the most powerful man-made energy, and the ELI initiative in Europe exists to push that science forward,” said Schmid.