FEATURE OPTICAL COATINGS
g
such as high laser fluence applications like materials processing and areas demanding the processing of smaller runs of optics more quickly. ‘We definitely see advances in these two
areas propagating elsewhere, potentially into the space arena. For instance, when we develop a coating for a 355nm YAG
“The lessons learned in the development of optimised manufacturing techniques as required for space- qualified optics will find their way into terrestrial products”
harmonic in the UV, such a coating is immediately applicable to the UV spectrum coming from the sun and other stars for either analysis or protection from solarisation. So tricks we pick up for a high volume arena like laser optics, will have utility in other markets,’ he commented.
An optical stabilising reference cavity within a vacuum chamber
Towards a coating-free future? While many organisations around the world devote their time to the development of next-generation optical coatings, some are now focusing their attention on a future that might do away with the need for coatings altogether. One such organisation is the University of Rochester, where a team of scientists has created an interesting new technique that visualises ‘the complete evolution of micro- and nanoscale structural formation on a material’s surface’ – which
could eventually pave the way for future ‘coating-free’ space telescopes. Over the past few years, a research team led by Chunlei Guo, professor of optics and physics at the university, has developed a range of laser processing technologies capable of equipping regular metal surfaces with special properties, such as the ability to attract or repel water or absorb a large amount of light – all without any type of chemical coating. These special surface
effects come from a range tiny micro- and nano-structures that the team create on the metal surfaces, as Guo explained. ‘To understand how these tiny structures were formed, we set out to develop an imaging technique that allows us to resolve the complete evolution of micro- and nanoscale structural formation, both during and after the application of a laser pulse,’ he said. To resolve the surface evolution, the team begins by using a stronger laser pulse to induce the surface morphological change, followed by another pulse that acts like a camera flash to illuminate the changing dynamics.
This imaging pulse occurs at a later time
– somewhere between one quadrillionth of a second to a few hundred billionths of a second later – providing the researchers with a ‘movie frame’ at each time delay. By piecing all these frames together, Guo said he and his team can collect a complete movie of what happens on the metal surface and how these structures are formed in real time. ‘Currently, space-based instruments mostly focus on spatial, rather than temporal, resolution. But I think the temporal capacity can come into play in the future. At that point, the basic principle of our technique will apply,’ he said. ‘We have plans for further commercial
A schematic of the CMS crystalline mirror coatings 28 Electro Optics May 2017
developments for our functionalised surfaces. Moving forward, making our process more efficient and controllable is very important and the imaging technique will be crucial in these developments,’ he added. EO
@electrooptics |
www.electrooptics.com
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