Interferometry: Cooler Than You Think
By John Oncea, Editor
Interferometry is a technique often applied in astronomy that allows us to pick up details that even the largest telescopes today cannot resolve. It has been used to measure the speed of light in different directions and create the first-ever image of a black hole. So, what’s next?
What is the common bond between these three seemingly disparate facts?
- The first cosmic event observed in both gravitational waves and light — gravitational waves produced by colliding neutron stars — was made by LIGO Caltech with the use of the U.S.-based Laser Interferometer Gravitational-Wave Observatory (LIGO); the Europe-based Virgo detector; and some 70 ground- and space-based observatories.
- Since 2008, how many days have been 24 hours long (to the 10,000th of a second)? According to Twitter user @Rainmaker1973, one. There has been one 24-hour day in the past 14 years.
- After three-and-a-half years of planning, Apple was given a patent for a Smart Ring device. According to Smart Ring News, “The patent description describes a comprehensive vision of a product that allows the wearer to interface other devices and services more efficiently, safely, and discreetly — compared to today's touch-based User Interfaces.”
Smart Ring also notes, “According to Apple’s Smart Ring patent description, the ring device with a display, touch-sensitive surface, and multiple sensors will provide faster and more efficient methods and interfaces to control external devices — thus increasing the effectiveness, efficiency, and user satisfaction.”
Well, truth be told there is probably more than one commonality here but give yourself a point if you guessed interferometers, a tool used in many fields of science and engineering.
Oh, and before you go, interferometer (the tool) and interferometry (the technique) are used interchangeably in this article. So, just a heads up.
Interferometry 101 (Or Move On To The Next Section If You Already Know What This Is)
LIGO Caltech explains, “Interferometers are investigative tools (that) work by merging two or more sources of light to create an interference pattern, which can be measured and analyzed; hence 'Interfere-o-meter', or interferometer. The interference patterns generated by interferometers contain information about the object or phenomenon being studied. They are often used to make very small measurements that are not achievable any other way. This is why they are so powerful for detecting gravitational waves — LIGO's interferometers are designed to measure a distance 1/10,000th the width of a proton!”
There are, according to Explain That Stuff, several different types of interferometers, each based roughly on the principle. The six common types are the Michelson, Fabry-Perot, Fizeau, Mach-Zehnder, Sagnac, and Twyman-Green interferometers and most of the “modern interferometers use laser light because it's more regular and precise than ordinary light and produces coherent beams (in which all the light waves travel in phase). The pioneers of interferometry didn't have access to lasers (which weren't developed until the mid-20th century) so they had to use beams of light passed through slits and lenses instead.”
But you probably already knew that. So, let’s move on to some of the innovative ways interferometers are being used today.
There’s Gold In Them There Interferometers
Market Study Report expects the interferometry market to reach $843.6 million by 2028, up from the $619.9 million it was worth last year. That’s a significant amount of dollars being spent on this tool. But why is that money being spent?
One reason is for directly detecting and characterizing the bulk of exoplanets from the ground, a subject The Keck Institute for Space Studies (KISS) discussed in its workshop Exploring Exoplanets with Interferometry. The Keck workshop specifically focused on new concepts for interferometric observations for exoplanet research including:
- How new micro-thruster technologies and innovative, new low-cost spacecraft might enable separated spacecraft concepts such as the new Large Interferometer for Exoplanets (LIFE) mission now under study by ESA
- How novel materials may allow the use of integrated optics for interferometric recombination in the MIR
- How low-noise, high QE MIR detector technologies can be further advanced
- How near-term high dynamic range interferometric efforts on ground-based telescopes can demonstrate new technologies relevant to space-based missions
- How interferometric astrometry on separated spacecraft might take advantage of new technological approaches to achieve the <0.1 micro-arcsec precision needed to detect and characterize the masses and orbits of Earth analogs otherwise not detectable via the RV technique.
Another reason to get excited about interferometers is the prevention of traffic jams in space. The Johns Hopkins University Applied Physics Laboratory reports experts are predicting traffic in cislunar space (the space below the Moon and above geosynchronous Earth orbit) is going to get much busier creating a need for additional situational awareness capabilities to prevent space traffic jams.
“Easier access to space, enabled by the increase in commercial launch capabilities, has opened new possibilities for both countries and companies to use this region and the lunar surface for a variety of purposes, ranging from placing military assets and conducting science to mining resources and manufacturing in space,” notes Johns Hopkins.
Playing a key role in keeping space traffic safely moving is … interferometry. “This summer, Erin Fowler, an APL aerospace engineer, led a project to evaluate the use of very long baseline interferometry (VLBI) to track spacecraft in cislunar space,” writes Johns Hopkins. “Often used in radio astronomy, VLBI is a technique to observe phenomena in greater resolution than would be possible with even the largest single telescope.
“In VLBI, multiple telescopes collect a radio signal. The time difference between the arrival of the signal at the telescopes is then used to calculate their distance from one another. This allows the observations of the same signal made by many telescopes to be combined. The resulting observation mimics that of a telescope with a size equal to the maximum separation between telescopes. The farther the telescopes are from each other, the higher the resolution of the observation.”
Long story short: “Fowler’s team conducted a simulation study to determine whether it would be valuable to use VLBI to enhance spacecraft tracking capabilities in cislunar space. Using a simulation of entirely ground-based telescopes, the team found that it would be a helpful solution for space domain awareness. But when a space-based telescope was added to the simulated ground-based assets, the team noticed an exciting improvement in tracking ability.”
One final example of interferometry’s value ─ this from Robotics & Automation News ─ focuses on how precision Beryllium mirror manufacturer Cambridge Technology uses interferometry hardware and software solutions to streamline its manufacturing processes and add efficiencies, as well as time and cost-savings across the company. “Technological advances over recent years have elevated metrology from being a ‘necessary evil’ in manufacturing scenarios to enabling technologies, allowing the measurement of previously impossible part characteristics and therefore driving innovation across numerous industry sectors,” writes Robotics & Automation News.
Cambridge Technology had already been using laser interferometry to measure the surface form of almost every precision beryllium mirror it produces. But, its original laser interferometry solution was prone to environmental vibrations and second measurement data was stored as individual text files (or text reports) which meant that it was extremely difficult to analyze.
The company chose to upgrade its laser interferometers and, as a result, has realized “cost savings by removing bottlenecks in production and quality control, and in turn, has provided better utilization of staff resources and an overall improvement in manufacturing efficiencies.”