It’s an age-old astronomical truth: To resolve smaller and smaller physical details of distant celestial objects, scientists need larger and larger light-collecting mirrors. This challenge is not easily overcome given the high cost and impracticality of building and — in the case of space observatories — launching large-aperture telescopes.
However, a team of scientists and engineers at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, has begun testing a potentially more affordable alternative called the photon sieve. This new-fangled telescope optic could give scientists the resolution they need to see finer details still invisible with current observing tools – a jump in resolution that could help answer a 50-year-old question about the physical processes heating the sun’s million-degree corona.
Although potentially useful at all wavelengths, the team specifically is developing the photon sieve for studies of the sun in the ultraviolet, the wavelengths needed to disentangle the coronal heating mystery. With support from Goddard’s Research and Development program, the team has fabricated three sieves and now plans to begin testing to see if it can withstand the rigors of operating in space — milestones achieved in less than a year. “This is already a success,” said Doug Rabin, who is leading the R&D initiative.
Variant of Fresnel Zone Plate
The optic is a variant of something called a Fresnel zone plate. Rather than focusing light as most telescopes do through refraction or reflection, Fresnel plates cause light to diffract — a phenomenon that happens when light travels through a thin opening and then spreads out. This causes the light waves on the other side to reinforce or cancel each other out in precise patterns.
Fresnel plates consist of a tightly spaced set of rings, alternatingly transparent or opaque. Light travels through the spaces between the opaque zones, which are precisely spaced so that the diffracted light overlaps and focuses at a specific point, creating an image that can be recorded by a solid-state sensor.
The photon sieve operates largely the same. However, the sieve is dotted with millions of holes precisely placed on silicon in a circular pattern that takes the place of conventional Fresnel zones.
The team wants to build a photon sieve at least three feet, or one meter, in diameter — a size they think could achieve up to 100 times better angular resolution in the ultraviolet than NASA’s high-resolution space telescope, the Solar Dynamics Observatory.
“For more than 50 years, the central unanswered question in solar coronal science has been to understand how energy transported from below is able to heat the corona,” Rabin said. “Current instruments have spatial resolutions about 100 times larger than the features that must be observed to understand this process.”
Rabin believes his team is well along the way in building an optic that can help answer the question.
Millions of Holes
In just a few months’ time, his team built three devices measuring three inches wide — five times larger than the initial 17-millimeter optic developed four years ago under a previous R&D-funded effort. Each device contains 16 million holes whose sizes and locations were determined by team member Adrian Daw. Another team member, Kevin Denis, then etched the holes in a silicon wafer to Daw’s exacting specifications using a fabrication technique called photolithography.
Team members Anne-Marie Novo-Gradac and John O’Neill have acquired optical images with the new photon sieves, while Tom Widmyer and Greg Woytko have prepared them for vibration testing to make sure they can survive harsh g-forces encountered during launch.
“This testing is to prove that the photon sieve will work as well as theory predicts,” Rabin said. Although the team has already accomplished nearly all the goals it set forth when work began late last year, Rabin believes the team can enlarge the optics by a factor of two before the end of the fiscal year.
But the work likely won’t end there. In the nearer term, Rabin believes his team can mature the technology for a potential sounding-rocket demonstration. In the longer term, he and team member Joe Davila envision the optic flying on a two-spacecraft formation-flying CubeSat-type mission designed specifically to study the sun’s corona.
“The scientific payoff is a feasible and cost-effective means of achieving the resolution necessary to answer a key problem in solar physics,” he said.
The “Industry 4.0” concept, first introduced by the German government, has recently extended the scope of compact high-power laser applications to, for instance, laser manufacturing, vehicle engine development, or thruster systems for space exploration.
However, integration of a controllable Q-switch into compact solid-state lasers has been challenging because of the mechanisms of EO and AO effects. In addition, previous Q-switches needed a large-sized power supply, which prevented downscaling of the entire system.
Now, researchers at Toyohashi University of Technology, Iowa State University, and the Institute for Molecular Science have developed a magneto-optic (MO) Q-switched laser for the first time, using a 190-micron-thick magnetic garnet film with labyrinth-shaped magnetic domains. They used custom-made coil and circuits to generate the pulsed magnetic field to be applied to the magnetic garnet, and successfully generated optical output with a pulse width of tens of nanoseconds. This is the first demonstration ever of a Q-switched laser driven by magnetic domain motions, and also the first evidence of the possibility of an integrated Q-switched laser. “The device was two orders of magnitude smaller than other reported controllable Q-switches,” commented Associate Professor Taira.
“Ultimately, you could artificially control the rain and lightning over a large expanse with such ideas.”
The adage “Everyone complains about the weather but nobody does anything about it,” may one day be obsolete if researchers at the University of Central Florida’s College of Optics & Photonics and the University of Arizona further develop a new technique to aim a high-energy laser beam into clouds to make it rain or trigger lightning.
The solution? Surround the beam with a second beam to act as an energy reservoir, sustaining the central beam to greater distances than previously possible. The secondary “dress” beam refuels and helps prevent the dissipation of the high-intensity primary beam, which on its own would break down quickly. A report on the project, “Externally refueled optical filaments,” was recently published in Nature Photonics.
Water condensation and lightning activity in clouds are linked to large amounts of static charged particles. Stimulating those particles with the right kind of laser holds the key to possibly one day summoning a shower when and where it is needed.
Lasers can already travel great distances but “when a laser beam becomes intense enough, it behaves differently than usual – it collapses inward on itself,” said Matthew Mills, a graduate student in the Center for Research and Education in Optics and Lasers (CREOL). “The collapse becomes so intense that electrons in the air’s oxygen and nitrogen are ripped off creating plasma – basically a soup of electrons.”
At that point, the plasma immediately tries to spread the beam back out, causing a struggle between the spreading and collapsing of an ultra-short laser pulse. This struggle is called filamentation, and creates a filament or “light string” that only propagates for a while until the properties of air make the beam disperse.
“Because a filament creates excited electrons in its wake as it moves, it artificially seeds the conditions necessary for rain and lightning to occur,” Mills said. Other researchers have caused “electrical events” in clouds, but not lightning strikes.
But how do you get close enough to direct the beam into the cloud without being blasted to smithereens by lightning?
“What would be nice is to have a sneaky way which allows us to produce an arbitrary long ‘filament extension cable.’ It turns out that if you wrap a large, low intensity, doughnut-like ‘dress’ beam around the filament and slowly move it inward, you can provide this arbitrary extension,” Mills said. “Since we have control over the length of a filament with our method, one could seed the conditions needed for a rainstorm from afar. Ultimately, you could artificially control the rain and lightning over a large expanse with such ideas.”
So far, Mills and fellow graduate student Ali Miri have been able to extend the pulse from 10 inches to about 7 feet. And they’re working to extend the filament even farther.
“This work could ultimately lead to ultra-long optically induced filaments or plasma channels that are otherwise impossible to establish under normal conditions,” said professor Demetrios Christodoulides, who is working with the graduate students on the project.
“In principle such dressed filaments could propagate for more than 50 meters or so, thus enabling a number of applications. This family of optical filaments may one day be used to selectively guide microwave signals along very long plasma channels, perhaps for hundreds of meters.”
Other possible uses of this technique could be used in long-distance sensors and spectrometers to identify chemical makeup. Development of the technology was supported by a $7.5 million grant from the Department of Defense.
Numerous other promising avenues exist for the fibre-top cantilever, such as minimally invasive surgery
Scientist Davide Iannuzzi and his team have developed a method to place novel miniaturised mechanical devices on the tips of optical fibres. The technology has many applications, such as providing a new generation of small, super sensitive sensors for research, medical, and industrial applications.
The team received support from the European Research Council (ERC) in the form of two grants. The first EU-funded project was called FTMEMS (‘Fibre-top micro-machined devices: ideas on the tip of a fibre’) and he secured the second one, called FTBATCH (‘Small, but many: scalability to volume production in fibre-top technology’), to demonstrate that the technology could be scaled up to market competitively.
Iannuzzi likens the round end of the optical fibre to a swimming pool and the ‘fibre-top cantilever’ to a diving board. Inspiration for the idea came to Iannuzzi, Iannuzzi, who is based at the Vrije Universiteit Amsterdam, while he was conducting experiments in fundamental physics. The usual approach of shining a laser beam onto a cantilever was unwieldy and was not always accurate.
“Commercial instruments were causing spurious effects,” recalls Iannuzzi. “After some searching around it struck me – why not fabricate the cantilever onto the end of an optical fibre?”
This innovative idea possesses a number of clear advantages. By combining the mechanical reliability of micro-electro mechanical systems (MEMS) with the precision of optical fibre interferometers, it is highly sensitive. In addition, its all-optical sensing and portable size means it can function in extreme conditions and be controlled remotely.
Without the backing of the ERC, Iannuzzi would have had a much harder time proving the commercial worthiness of his innovative ideas. ERC support helped the researcher to scale up the production processes and analyse the market potential of different applications.
One of the most promising uses of this technological breakthrough is as ultra-versatile, super-sensitive sensors. For example, fibre-top cantilevers can be used, without the need for bulky and expensive equipment, for atomic-force microscopy (AFM) to record, ‘like the stylus of a record player’, the surface of an object with a nano-scale resolution.
Numerous other promising avenues exist for the fibre-top cantilever, such as minimally invasive surgery. With all this potential at stake, Iannuzzi discovered that being in the lab was not enough and decided to take his idea to market.
Drawing on the Italian tradition of design excellence and small-scale innovation and the Dutch acumen for transforming ideas into profitable products, Iannuzzi established, in 2011, a start-up called Optics11.
“The company is going very well,” Iannuzzi says with evident pleasure. “We have three employees and we’re about to hire a fourth, on top of the two founders. We’re expanding our range of applications.”
In fact, the firm is pursuing a customer-driven approach to its patented technology. Through interactions with scientists and researchers in various fields, says Iannuzzi, Optics11 is able to identify exciting new ideas for applications.
In addition to benefiting society and provide the basis for new business and jobs, this also has a benevolent feedback effect. “This helps the academic perspective as well, by generating ideas for new research avenues. For example, after talking to neuroscientists, we are now exploring ways to apply the technology in the neurosciences,” he says
Given the well-documented difficulty Europe experiences in translating research into innovation, fellow scientists may wonder how Iannuzzi finds combining a lab coat with a business suit, so to speak. “I find being an entrepreneur very interesting and very exciting. It’s very stimulating,” he enthuses.
What advice would this scientist-entrepreneur give other researchers wishing to take the leap into business?
“It requires a change of mindset. You have to know that this is not your field, so you have to be open to learning and getting the right help and advice,” he says. And this is exactly what Iannuzzi has done, seeking assistance from his university’s technology transfer office and teaming up with a professional entrepreneur to run the firm.
Iannuzzi has also become an unofficial adviser and mentor to fellow scientists at his university, helping them to consider the best way to bring their ideas to market.
While acknowledging the importance of innovation and commercialisation, Iannuzzi cautions against the dangers of overemphasising this aspect. “It is important that we give scientists the opportunity to try academic entrepreneurship,” he says. “However, it is wrong if everything is focused on that. Blue sky research is also necessary. ”
“I don’t want to live in a world without philosophers,” he concludes.