FRONTIERS PHOTONICS


ENVIRONMENT/ENERGY


ENVIRONMENT/ ENERGY


ASTRONOMY


Advances in optics fabrication push space exploration further


A Cranfield University team developed new tools and machinery to make the mirrors on the James Webb Space Telescope


S


ome 30 years and $10bn in the making, the James Webb Space Telescope (JWST) generated big


expectations before it was launched in December 2021. But its discoveries since have exceeded the ambitions of even the scientists who helped create it. Among a long list of breakthroughs, the


telescope has already uncovered the earliest galaxies, formed just after the Big Bang, obtained the clearest images to date of stars being born, and has detected signs of hazy skies, clouds, and water vapour on an exoplanet. These early successes would not have been possible without the research and innovation that went into the numerous optics and photonics components that make up the space telescope. One such example is a team at Cranfield


University, in Bedfordshire, England, who developed and manufactured the complex mirrors within James Webb’s mid-infrared instrument (MIRI) using an ultra- precision CNC machine tool designed and manufactured at Cranfield. Making these sophisticated components involved five years of development and the invention of completely new instruments and processes. MIRI is the only mid-infrared instrument


in Webb’s instrument suite and it contains more than half of the mirror surfaces that exist within the whole telescope. Thanks to state-of-the-art instrument design and components, MIRI can deliver mid-infrared images and spectra with an unprecedented combination of sharpness and sensitivity. The team at Cranfield University


Precision Engineering Centre was awarded a contract from the UK’s Astronomy Technology Centre to manufacture the image slicers and re-imager mirrors that sit inside four separate integral field units (IFUs) within MIRI’s medium-resolution


James Webb’s mid-infrared view of the Pillars of Creation. MIRI’s mid-infrared data will help researchers determine exactly how much dust is in this region – and what it’s made of


spectrograph. These IFU mirror arrays perform a specific light-handling task that creates so-called ‘data cubes’, which enable astronomers to examine, for example, the atmospheres of Earth-like planets located around distant stars. The Cranfield team manufactured 12 components overall, each containing a set of tiny mirrors – totalling 132 mirror surfaces produced overall. The critical


aspect was ensuring the aluminium mirrors were cut sharply to minimise the effect of stray light, explained Prof Paul Shore, who led the project in the early 2000s: “You’re collecting a lot of light from a great big telescope, and then you’re focusing down onto a tiny mirror. Some of the image slicers had 24 mirrors over 16mm. So if there are any deadband regions between those mirrors, it represents a fairly big


6 Photonics Frontiers 2023


SCIENCE: Nasa, ESA, CSA, STScI IMAGE PROCESSING: Joseph DePasquale (STScI), Alyssa Pagan (STScI)


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