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Space is perhaps no longer ‘the final frontier’, but as an operating environment for optical components it remains in many ways the ultimate test of the technology’s reliability, resilience, and precision – far more so, typically, than with terrestrial applications.
The reason we know this is that our own products have successfully delivered excellent results on missions for agencies such as ESA, JAXA and NASA including Mars Perseverance, Mars 2020 Rover, Hyabusa 2, Trace Gas Orbiter (TGO), and LISA Pathfinder, with ExoMars Rover due to launch in September 2022.
It stands to reason that if they can deliver in space and meet the demands of the most exacting requirements of all, then they are also capable of delivering excellence in terrestrial applications too.
So, what exactly are these technologies, what are they used for, and what are the differentiating features that enable them to deliver the benefits that such demanding and high-profile space missions cannot do without?
Let us start with the most fundamental requirement of all: the ability to filter white light into specific narrow-bands tuned precisely to the correct wavelength. When placed in front of a detector they can be used to accomplish a number of critical spectroscopy objectives, including mineral analysis of asteroid rocks (Hyabusa 2), detection of methane gas in the Earth’s atmosphere (ExoMars TGO), bio sample analysis (ExoMars Rover), including the search for evidence of extra-terrestrial life (Mars 2020 Rover).
The demands placed by these missions are significant. Speed of tuning is often a key factor since it increases the number of data points that can be accessed in a given time.
Instruments with moving parts in space are enemies of reliability and thus contributors to component failure, so the ideal tuning solution will be solid-state – no moving parts.
Sensitivity is, equally, a key criterion. Imaging spectrometers must be sensitive enough to successfully gather sufficient light for exceptionally accurate operation in the depths of space where light levels may be at a premium. In addition, the instrument components must be ruggedized and resistant to vibration, radiation and of course temperature fluctuations in some of the most demanding of operating environments.
Accuracy and sensitivity, reliability and robustness, speed and responsiveness – a challenging combination of vital ingredients for an optical filter that must deliver not only in this world, but beyond.
The solution of choice for most space agencies is acousto-optic tunable filter (AOTF) based spectroscopy. G&H have been commissioned to design, engineer and build AOTFs for multiple missions. Each has been custom developed.
An AOTF rapidly and dynamically selects a specific wavelength, potentially from the UV/VIS through to mid-IR with the correct combination of devices. As the applied frequency of the electronic drive is varied, the transmitted wavelength changes, ‘tuning’ the wavelength of the transmitted beam to the detector.
Our AOTFs respond distinctively to all the challenges of operating in a space environment, which enables them to meet and exceed requirements in industrial settings too.
They deliver accurate tuning of light in timescales of tens of microseconds or less which gives the potential to deliver real-time spectral imaging. They have no moving parts, and are fully controllable electronically, via appropriate software designed for this purpose.
Critically, G&H meets the manufacturing challenges of large-aperture filters, thanks to their ability to grow the vital tellurium dioxide (TeO2) acousto-optic substrate at unsurpassed scale at its facility in Cleveland, US, thus maintaining and guaranteeing integrity of supply.
At the same time, there are laser applications in space that are beyond spectroscopy, one of which is the ability to measure, with extreme accuracy the movement of objects in a gravitational field.
The LISA Pathfinder mission, for example, is helping to pave the way for future missions by testing gravitational wave detection, using lasers to control and measure, from satellites, two test masses in a near-perfect gravitational free-fall.
The acousto-optic frequency shifters (AOFSs) engineered for this mission encode the lasers, enabling the satellites to navigate with the unprecedented precision required for this manoeuvre.
Space exploration is a highly complex and specialist field, requiring components that are reliable, accurate, hard-wearing, and that meet extensive operational and legislative requirements, including stringent accreditations.
Needless to say, engineering of this kind also requires the highest possible caliber of expertise, total and minute focus on client requirements, and a formidable track-record of success. This is precisely why G&H’s acousto-optic technologies are so well placed to deliver unrivalled benefit to terrestrial sectors, too.
From forensics, to archaeology, aerospace and defense, to industrial and telecommunications applications, the spectroscopy, measurement and analysis that stable, acousto-optic devices deliver, can enable photonics to change the world – not just model it.
Tried and tested in the unforgiving environment of orbit, the ability of AOTF and AOFS components (amongst other AO devices) to deliver outperformance in earthbound applications is, now more than ever before, without question.