FEATURE OPTICAL COATINGS
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the fact that the lens will not be exposed to the vacuum of outer space means that there have not yet been any ‘out of the norm’ requests for coatings specifically adapted to the conditions seen in Earth orbit. ‘Much of what we sell that goes into outer space is still contained in some sort of environment control structure. As such, we have not really developed anything recently specifically for space,’ Bagwell commented. ‘However, once you go very broadband,
or want to view say, solar flares, the design space gets very dicey. Material selection, deposition parameters, and heat build-up all become rigid design restrictions that must be accounted for,’ he added.
Crystalline Coatings Elsewhere, Austria and US-based company Crystalline Mirror Solutions (CMS) manufactures high-performance optical sub-assemblies, such as low-noise reflectors for precision interferometry, using a novel crystalline coating technique. In terms of space-based systems, the firm also supplies end mirrors for ultra-stable optical reference cavities used in the construction of narrow-linewidth (sub-Hz) laser systems. As co-founder Garrett Cole explained, such high-end laser systems are ‘key elements’ in precision optical metrology – enabling record performance in atomic clocks, stable microwave generation, and laser ranging. Cole described CMS’s substrate-
transferred crystalline coating technique as a ‘radically new approach’ for realising high-performance optical interference coatings, allowing the integration of single-crystal multi-layers with a wide variety of relevant optical substrate materials possessing arbitrary, including curved, geometries. As part of a consortium
Chunlei Guo, professor of optics and physics at the University at Rochester
of a near-infrared ‘optical local oscillator’ – or OLO – with millihertz linewidth while working within the stringent packaging constraints of a satellite platform. ‘[Another] of the major focuses of
“We think there is a particular application within
led by Airbus and funded by the European Space Agency (ESA), the company is currently working on the first implementation of crystalline coatings – or semiconductor super-mirrors, as it calls the final optical components – in a space- relevant application. As part of this project, the CMS team will coat super-polished fused silica substrates with an ultrahigh- reflectivity multilayer stack. A pair of these coated optics will then be assembled into an optical cavity, which will ultimately be employed as an optical reference for a cavity-stabilised laser system. According to Cole, the ultimate goal of this effort is to supply a robust and high-performance optical reference cavity for the construction
26 Electro Optics May 2017
this effort is to further enhance the technological readiness level of our coatings and pursue space qualification of the final optics. This includes rigorous tests of the mechanical stability, radiation hardness, environmental stability and lifetime of our semiconductor super-mirrors,’ he said.
health care, specifically the monitoring of a patient’s breath whilst under anaesthetic”
Trickle down
Looking ahead, MPO’s Kessler believes that the development of new optical coating technology will continue at a rapid pace – and predicts it is ‘almost a given’ that technologies developed for space and similar applications will eventually trickle down to
other markets. In fact, according to Pindard, Artemis Optical is already making similar products for commercial and industrial applications, noting that band-pass filters can be used for observing and monitoring ‘any number of colours, gases or moisture’. ‘Our products are currently in use
alongside industrial and food production lines to ensure that levels of particular fats and chemicals are within the acceptable limits for product acceptance,’ Pindard said. ‘Generally speaking, the tolerances of the manufacture of parts required for the
space sector are more stringent than those in commercial applications. Being able to meet those requirements has pushed the envelope of our process capabilities and places us in a strong position to be able to offer a higher performing coating to these other markets. We think that there is a particular application within health care, specifically the monitoring of a patient’s breath whilst under anaesthetic,’ he added. Although CMS’s current core customers
are academic and scientific end users at universities and national laboratories, Cole also reported an ‘uptick in demand’ from industrial customers in similar market areas such as optical metrology for time and frequency standards, laser ranging, and microwave source development. The company is also actively expanding the ‘application space of its novel coatings by targeting additional industrial sectors such as trace gas detection via optical ringdown and high-power laser machining systems. ‘Our goal is that the space qualification of
our low-noise mid-IR optics will enable us to also pursue space-relevant applications for our mid-IR and high thermal conductivity, or high power, optics,’ he said. ‘Moreover, the lessons learned in the development of optimised manufacturing techniques as required for constructing space-qualified optics will certainly find their way into terrestrial products,’ he added.
Edmund Optics’ Bagwell pointed out
that market segments other than space are currently driving the coatings work at Edmund Optics – particularly in fields
@electrooptics |
www.electrooptics.com g
J. Adam Fenster at University of Rochester
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