James Webb and AMWritten by Alinor
The James Webb Space Telescope gives humanity an opportunity to gaze deeper upon the star-scattered abyss of the night.
Our collective response towards these ancient clouds of incomprehensible size ranges from cosmic dread to awesome inspiration. In some strange mix of irony and obviousness, the only reason the James Webb telescope is able to image the far and large is because of recent advances in our understanding of the close and small. Much like extragalactic astronomy, nanotechnology operates on an unfathomable scale; we'll run through several of the nanotechs that make the magic happen.
All four of the telescope's measurement instruments detect infrared light from celestial bodies billions of light years away. The combination of the Mid-Infrared Instrument (MIRI), Near-Infrared Camera (NIRCam), Near-Infrared Spectrograph (NIRSpec), and Near-Infrared Imager and Slitless Spectrograph/Fine Guidance Sensor (NIRISS/FGS) is why we can now peer into what was once invisible. The “Mid-” and “Near-” refer not to the distance from Earth (at least not directly), but the wavelengths of infrared light. James Webb uses arsenic doped silicon (Si:As) detectors for the mid-infrared range, whereas mercury-cadmium-telluride (HgCdTe) is used for the near-infrared detectors. Doped silicon may be familiar to some readers as useful in the arena of nanoelectronics, but as explored by Jon Geist in 1989, arsenic can also be used as the adulterant for photosensitivity. The goal is to make the doped semiconductor sensitive enough to register low energy mid-infrared wavelengths, but not so sensitive as to allow pure chance to trigger a “detection”. HgCdTe is used for a similar reason - except that it allows for extraordinary flexibility as to what it can detect by us changing the ratio of mercury to cadmium. HgCdTe is a relatively new material that’s historically been pushed aside due to the difficulty of consistent manufacturing; recent strides in nanotechnology (molecular beam epitaxy and liquid phase epitaxy) now makes the production of homogeneous HgCdTe not only a possibility, but a business opportunity, as proven by companies like Teledyne. In our societal quest to uphold Moore’s law, advanced materials such as HgCdTe could be the solution to the novel problems we constantly encounter.
NIRSpec can analyze the composition of stars and nebulas from light through spectroscopy. While astronomical spectroscopy has long been known - since the 1800s, delving into what makes up exoplanets billions of lightyears away was impossible without the use of cutting-edge materials. In order to tackle the cosmic equivalent of light pollution, NIRSpec needs to be able to block unwanted light with incredible precision, and be resistant to mechanical fatigue. Enter microshutters - tiny, shuttered windows the size of a couple strands of human hair. Clustered stars’ composition can be measured in short succession, thanks to the successful implementation of nanomachines. On the surface, the idea is trivial. There’s an arm, and it opens or closes windows depending on the signal. Alas, the 13-page 2007 paper by M. J. Li, T. Adachi, et al. suggests it may not be so simple after all. The nano machinery must withstand the temperatures, radiation, time, and weight. They also need to completely block out the light while still being able to open and close relatively easily. Imagine trying to open and close a door, sealed to completely block the airgap. Luckily, scientific advances in a variety of thin-film-deposition techniques lets the microshutters do their job to a degree of perfection. With regards to its applications on the ground - Harvey Moseley, the Microshutter Principal Investigator, comments: "The microshutters are a remarkable engineering feat that will have applications both in space and on the ground, even outside of astronomy in biotechnology, medicine and communications."
The third example among many that showcases the use of nanotech on the James Webb Space Telescope is the engineering behind the mirrors. Or perhaps more accurately, their positioning. The mirror lattice acts as a funnel for the light to be collected at the detectors. Unlike normal funnels, however, the positioning of the mirrors among all spatial degrees of freedom needs to be precisely controlled on the scale of nanometers. Enter the nano-actuators designed for the JWST. While these machines exist on a scale we can visually see, its true magic lies in that it manages to successfully position the mirrors to nanoscopic precision. Similarly to the microshutters, the fundamental mechanics of the nano-actuators is not particularly new. And similarly again, the ingenuity of the technology lies in the scaling towards incredibly fine resolutions. Successful development of the nanoactuator has been ascribed to two inventions patented around the year 2000. Furthermore, in a mechanical device which commands such precision, performance testing is absolutely paramount. Microscopy techniques familiar to many in the nanotech industry such as interferometry were relied upon extensively in making sure that the actuator fell within the success criteria. The infinitesimal positional deviation needed by the telescope echoes down here on Earth too, in the development of both consumer and enterprise electronics.
History has proven that the leaps and bounds in the field of astronomy affects every-day life today. Conversely, the reverse is also true. New breakthroughs within the realm of solid state physics, computational chemistry, and quantum electronics quickly translate towards humanity’s progress on the interstellar front. Technological creativity and interdisciplinary collaboration opens doors previously thought to be locked, and nowhere is this more obvious than in the emerging world of nanotechnology and novel materials at large.
For extra reading regarding the telescope:
G.H. Rieke, “Infrared Detector Arrays for Astronomy”, Annual Review of Astronomy and Astrophysics 2007 45:1, 77-115
Jon Geist, "Infrared absorption cross section of arsenic in silicon in the impurity band region of concentration," Appl. Opt. 28, 1193-1199 (1989)
M. J. Li, T. Adachi, C. A. Allen, S. R. Babu, S. Bajikar, M. A. Beamesderfer, R. Bradley, N. P. Costen, Kevin Denis, A. J. Ewin, D. Franz, L. Hess, R. Hu, K. Jackson, M. D. Jhabvala, D. Kelly, T. King, G. Kletetschka, A. S. Kutyrev, B. A. Lynch, S. E. Meyer, T. Miller, S. H. Moseley, V. Mikula, B. Mott, L. Oh, J. T. Pontius, D. A. Rapchun, C. Ray, S. Schwinger, P. K. Shu, R. Silverberg, W. W. Smith, S. Snodgrass, D. Sohl, L. Sparr, R. Steptoe-Jackson, R. J. Thate, F. Wang, L. Wang, Y. Zheng, C. Zincke, "Microshutter array system for James Webb Space Telescope," Proc. SPIE 6687, UV/Optical/IR Space Telescopes: Innovative Technologies and Concepts III, 668709 (20 September 2007)
Warden, R.M. (2012). Cryogenic Nano-Actuator for JWST.
For introductory reading regarding scientific concepts: