To really understand what makes the solar wind tick, heliophysicists must analyze the minuscule features on the sun‘s surface that help speed up the star’s charged particles out through the solar system. And to perform that task with higher precision, they need higher ways of seeing in ultraviolet.
Enter a technology called the photon sieve: a form of lens that helps subtly bend ultraviolet light toward a camera. To be clear, a photon sieve isn’t any strange lens; it’s a cutting-edge work of engineering only possible with the latest techniques. Sun-facing spacecraft later this decade are expected to enter Earth‘s orbit with photon sieves of their arsenal.
A photon sieve looks like a honeycomb, its hexagonal structure supporting a skinny membrane of silicon or niobium. The membrane is thin indeed: NASA engineers have developed sieves as thin as 100 nanometers, which is about the width of a human hair. The thinner the sieve, the more light it may well transmit.
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NASA’s sieves are also pockmarked with concentric circles of tiny holes. The biggest is at a sieve’s center, with every following ring going outward getting smaller, with their holes decreasing in size as well At their smallest, the perforations will be as tiny as 20 micrometers across. That is concerning the size of a bacterium. “It is a sheer physical challenge to construct sieves with such precision,” Doug Rabin, a heliophysicist at NASA’s Goddard Space Flight Center, said in a statement.
This setup allows a sieve to act like a lens, refracting the ultraviolet light passing through and bending it in order that a camera behind it may well see more detail.
Photon sieves are engineered to see in extreme ultraviolet (EUV), which has shorter wavelengths and better energy than other varieties of ultraviolet light. Today’s sun observatories, corresponding to the Solar Dynamics Observatory (SDO), already watch our star’s EUV light. But a future observatory with a photon sieve could resolve the advantageous details in EUV with 10 to 50 times more precision than SDO can manage today.
A 250-micrometer-thick-membraned sieve will go up on the Virtual Super Optics Reconfigurable Swarm (VISORS), for example, expected to launch in 2024. One other sieve is planned to suit into the Multi-slit Solar Explorer (MUSE), presently scheduled for 2027.