Defence, Features, Laser cutting

UniSA and UoA scientists demonstrate method to upscale fibre laser technology

Researchers from the University of South Australia, the University of Adelaide and Yale University have been collaborating their research.

American and Australian researchers from the University of South Australia (UniSA), the University of Adelaide (UoA) and Yale University have been collaborating their research to unlock the potential of contemporary fibre lasers.

Fibre lasers use an optical fibre cable made of silica glass to guide light. The resulting laser beam is more precise than with other types of lasers because it is inherently less ‘lumpy’ allowing it to propagate straighter and remain focused.

Throughout their research, the team of scientists have demonstrated that the use of multimode optical fibre can be used to scale up the power of fibre lasers by three-to-nine times without deteriorating the beam quality so that it can focus on distant targets.

These findings were recently published and UoA research associate and PhD recipient, Dr Ori Henderson-Sapir, said that he wants to see his contribution positively impact society.

“Our research launches Australia into a world-leading position to develop the next generation of high-power fibre lasers, not only for defence applications, but to aid new scientific discoveries,” he said.

The breakthrough is a product of both innovation and collaboration, as the project was a multi-national effort between Australia and US.

Co-first author, Dr Linh Nguyen, a researcher at UniSA’s Future Industries Institute said, “It is a very closely collaborative project. Both the Australian and American universities received funding from the US Airforce Office of Scientific Research (AFOSR) to jointly pursue this project.”

“Many of us have had technically intense meetings every week to discuss the results and progress over the entire years of the project. My colleague Dr. Stephen Warren-Smith and I will visit Yale early next year to continue the relationship,” Nguyen continued.

The project has progressed far since it first began, but Nguyen emphasised that there is still work left to be done.

“It took us roughly two and a half years to demonstrate the proof-of-concept. But this research, and its relevant work, is still ongoing,” he explained.

High-power lasers in defence

For some time, defence forces around the world have been pursuing the use of laser technology for defence applications.

“The defence industry has always pursued the use of lasers for decades. But only until recently only had real success thanks to using single-mode high power fibre lasers which provide high power and good beam quality,” said Nguyen.

To effectively utilise lasers as a countermeasure, the laser must be powerful without any beam quality deterioration.

“The beam quality is an important factor in defence applications. To shoot down or dazzle the control of something far away, the laser beam needs to be well confined during propagation through the atmosphere, so that the intensity is maintained,” explained Nguyen.

“If you have a laser that is powerful, but that power was spread out over a very large area as it propagates to the target, then it cannot damage the target but instead will coat it like a warm blanket.”

There are several advantages to using lasers as countermeasures.

A laser beam does not require any tracking – unlike conventional ballistics weapons – as the beam can travel at the speed of light.

Lasers also produce no sound, and they are mostly invisible to the naked eye. Without detection equipment, they remain silent and deadly.

Finally, lasers are cheap to use. They don’t require ammunition, but only power instead. Currently, militaries are utilising lasers as a cheap countermeasure to drones.

“High-power fibre lasers are vital in manufacturing and defence, and becoming more so with the proliferation of cheap, unmanned aerial vehicles in modern battlefields,” Nguyen explained.

“A swarm of cheap drones can quickly drain the missile resource, leaving military assets and vehicles with depleted firing power for more combat-critical missions. High-power fibre lasers, with their extremely low-cost-per-shot and speed of light action, are the only feasible defence solution in the long run.

“This is known as asymmetric advantage: a cheaper approach can defeat a more expensive, high-tech system by playing the large number,” Nguyen said.

Most countries using laser technology as a countermeasure are using single-mode lasers, which come with their own limitations.

“Many countries are pursuing research and development in laser weapons and most, if not all, are following the use of single-mode high power fibre lasers,” said Nguyen.

“To get over the power limit, they combine many of such lasers together using a so-called ‘spectral beam combining’.”

This method involves combining lasers of different wavelengths to produce a powerful beam, but this upscaling method is inherently limited.

“The more contaminated the laser colour, the smaller number of them can be combined,” Nguyen explained.

Currently, the US Navy has deployed the AN/SEQ-3 Laser Weapon System or XN-1 LaWS.

The laser utilises a solid-state laser array and is primarily used for targeting asymmetric threats like drones.

Henderson-Sapir believes that their breakthrough could be used to create even more effective systems in the future.

“It could be used for shooting down drones, rockets, or even mortars,” he said.

While systems haven’t been developed yet using their new design, the team is confident that it won’t be long before militaries around the world are utilising scaled-up multimode fibre laser technology.

“Fibre lasers have already been extensively field-tested and ship-deployed for defence applications, particularly in the US,” said Nguyen.

“Our technology is more at the fundamental level that will enable the next generation of high-power fibre lasers, with unpreceded level of power. Such power level could open new possibilities in defence strategy that is currently unavailable.”

“Personally, I think we are about three to five years away from achieving record power level from high power fibre lasers using this technique, and likely a few more years of engineering work to make it feasible for actual deployment on ships, large military vehicles or airplanes.”

The science

The word ‘laser’ is an acronym for ‘light amplification by stimulated emission of radiation’.

In laymen’s terms, a laser is a device that triggers atoms or molecules to emit light of specific wavelengths, which is then enhanced or amplified.

Depending on the colour, light will have a wavelength of varying peaks. In the visible spectrum, violet, for example, has the shortest wavelength peak, whereas red has the longest.

Lasers, however, are not alike to naturally occurring light, as laser wavelengths are aligned with similar wavelength peaks, since they rarely occur naturally; scientists must make lasers themselves.

“Lasers are built with three major elements. One is the energising source, second is the gain medium, and third is the resonator,” said Henderson-Sapir.

For example, a gain medium could be a crystal rod, doped glass, semi-conductor device or a gas-filled tube.

“By building a resonator around the gain medium, it can cause the material which was excited to emit photons,” said Henderson-Sapir.

Photons are light particles that make up the focused laser beam.

“Because of the resonator, there is a preference for those photons to be amplified in the direction of the mirrors, and eventually emitted through a partially transmissive mirror” Henderson-Sapir continued to explain.

What sets fibre lasers apart from a more basic sold-state laser is the optical fibre and the use of laser diodes to energise the fibre laser.

Laser diodes are semiconductor devices that can emit a beam of high intensity light.

The optical fibre is a small, but flexible glass, which is used as the gain medium.

Unlike solid-state lasers, fibre lasers utilise optical fibres doped with rare-earth elements such as erbium or ytterbium.

When using a laser diode and optical fibre in laser manufacturing, the beam itself becomes less sensitive to environmental effects.

“The tiny piece of glass, which is very robust, can be bent or pointed wherever where you want,” Henderson-Sapir said.

But a major engineering challenge when creating powerful fibre lasers, specifically for defence and manufacturing applications, is generating a focused and powerful beam without deterioration.

“Our colleagues at Yale University have been working on a different wavelength and method of laser. We’re working on pulsed lasers at 1.51 microns and Yale is working on continuous beams at 1.0,” said Henderson-Sapir.

“We already have results, and we’re going to conferences about implementing the same method in a system where we are amplifying the signal.”

“We’re currently at the state of the art and Yale University has surpassed the state of the art,” Henderson-Sapir explained.

Manufacturing applications

Henderson-Sapir expects that this technology will be used in the manufacturing sector long before it is used in defence.

“I think that manufacturing applications are going to come online faster than defence, in my opinion on this particular laser design, because it is much more amenable for really solving problems that the manufacturing industry has,” he said.

“To get a system that’s robust in the field that can also handle being used on a tank in a battlefield is a totally different kettle of fish compared to sitting in a locked cabinet on a relatively clean production floor,” Henderson-Sapir explained.

Henderson-Sapir elaborated that scaled-up lasers could be used in metal works, particularly in cutting steel and welding. A high-powered laser can be used to cut very thick materials, and at a distance. This ultimately ensures that the laser machine will remain effective and undamaged overtime.

“Nowadays, when you want to weld large chunks of metal, it becomes difficult and the only way to do it is to use high power lasers or acetylene torches,” Henderson-Sapir said.

“But potentially this will allow you to go to thicker materials or weld dissimilar materials better because, for example, welding dissimilar materials is a serious problem and difficult to do.

“Laser welding is a good way of doing it, but sometimes you need more power than what is available.”

Remote sensing applications

Infrared fibre lasers have potential to be useful in remote sensing and medical applications.

Remote sensing in lasers refers to laser technology that can collect information from a distance about an object, environment, or surface.

“We’re talking about applications which are related to greenhouse sensing, being able to monitor and quantify their levels, being able to monitor and quantify, for example, how much methane is being emitted by feedlots,” said Henderson-Sapir.

High-powered fibre laser technology will also have immediate applications in monitoring wind patterns.

Monitoring wind patterns with lasers can be beneficial for maintaining and optimising wind farms.

“Wind has, because it’s moving air, an effect on the return wavelength of the laser,” said Henderson-Sapir.

“By comparing the colour of the laser that we sent, to the return echo of the wind, you can tell the speed of the wind, and by counting the time it took for the return to come back, you can observe differences.”

Subsequently, engineers and scientists could determine the speed of a wind field before it reaches a wind turbine.

In-turn, wind turbine blades can be adjusted to ensure that it is rotating in the best direction.

The blades can also be angled to catch the most optimal amount of wind.

“All of these things can be done to get the maximum power out of expected wind patterns,” Henderson-Sapir explained.

While the possibility of technological innovation is exciting, the full potential of these multimode fibre lasers will not be apparent until later in the future.

The team will soon be reporting their findings at the 2024 CLEO Conference and Exhibition later this year.

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