Intense Lasers: Seeing the light

_{This article was written by Dr Stuart Clark and published in the Innovations magazine #5}.

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“Lasers are still a relatively young technology,” says Christophe Simon-Boisson, chief scientist for laser at Thales. “There’s still plenty of room for improvement, specifically in two areas: power and efficiency.”

 
Thales has been researching and building lasers for 30 years. In 2012, it developed and delivered the Berkeley Lab Laser Accelerator (BELLA) system in the Lawrence Berkeley National Laboratory in California. During the night of 20 July 2012, BELLA became the first laser to deliver a petawatt of power – the equivalent of one million billion watts. It was achieved by delivering all of the energy into a pulse that lasted for just a femtosecond (one millionth of a billionth of a second).
 
Leaping beyond this, the European research programme Extreme Light Infrastructure for Nuclear Physics (ELI-NP) has contracted Thales to provide two 10-petawatt lasers. These will underpin a new European laboratory in Bucharest, Romania, which has been launched to perform unprecedented scientific research. In one project, this exceptionally powerful laser will be used to investigate the nuclei of atoms to better understand how the chemical elements are formed inside stars.
 
According to Simon-Boisson, one of the ultimate scientific goals for this technology is to produce a laser with sufficient power to create a tiny spot of focused energy similar to that which encompassed the universe at the time of the Big Bang. This is many years away but, if it could be achieved, it would allow scientists to investigate the possible creation of matter out of a vacuum – the process that is thought to have happened during the formation of the universe.
 
But this isn’t all about scientific research and theory, of course – extreme lasers also offer practical applications far outside the lab. Simon-Boisson draws an analogy with the car industry:

For example, in the manufacture of silicon-based electronic components, sand is heated to become glass or amorphous silicon, then heated again until it transforms into a crystalline form that can be used for electronics. This is known as “silicon annealing” and traditionally is done in a furnace but the movement of the hot air makes the process difficult to control. By using pulsed lasers – which deliver pulses that last for a nanosecond (a billionth of a second) – manufacturers could heat and transform the glass quickly, precisely and efficiently.
 
Another process that would be rendered easier and more precise is “peening”, where a metal sheet is strengthened by subjecting it to repeated shocks. This can be done with a hammer – but by firing a laser at a thin sheet of water running over the metal surface, the instantaneous expansion of the water into vapour acts like a mechanical blow, achieving the same results with far greater efficiency.
 
The faster pulsing femtosecond lasers have applications in the medical world as well, for procedures such as cauterising tissue, skin resurfacing to remove scars or tattoos, and to shrink or destroy tumours and polyps. All of these applications could benefit from more precisely controllable lasers, which would allow surgeons to more accurately perform procedures.
 
The generation of X-rays for medical imaging could benefit greatly. At present, they are produced using mini-particle accelerators like old fashioned television vacuum tubes. An intense laser could replace this bulky, fragile technology and be simpler to maintain, minimising life-cycle costs for the equipment.
 
Another natural role for lasers is to produce the isotopes. There are hundreds of applications for radio isotopes – for example, some are used by doctors for scintigraphy, where a small dose of a mildly radioactive substance is introduced in a patient’s blood stream to identify everything from blockages to internal bleeding. A high intensity laser accelerating electron particles into atomic nuclei could be more efficient and cheaper to maintain in the long run than the existing particle accelerators used for the process.
 
More efficient and intense lasers could allow for the highly precise targeting of tumours in cancer patients, generating the particles needed for proton therapies. These treatments use highly focused beams of protons to target tumours while minimising any damage to nearby healthy tissue. Currently, generating protons requires a synchrotron particle accelerator, which is large and expensive. This means that, despite the therapy being well understood, only 41 centres in the world offer the treatment. Laser-accelerated protons would considerable reduce the size and cost of the necessary machinery.

In addition to the civilian applications, there is currently a widespread interest in developing military applications for these more powerful lasers.

Defensive systems do not use pulsed lasers but rely on the continuous delivery of laser light to a target. In summer 2013, for example, declassified documents from the UK government revealed that a laser system was deployed on British ships during the Falklands war. The aim of the weapon was quite simple – to dazzle Argentine pilots who were attempting low-level bombing runs – but the technology involved had to be consistent and accurate in order to work.
 
In the years since, the power that can be delivered by lasers has increased to the point where they could be used to take down aircraft or destroy targets from a distance. The chief benefit from a laser system over standard projectile weaponry is that there are essentially no consumables; bulky shells do not need to be carried. Instead, as long as the laser has a power supply, it can continue to fire. This means that the “cost per shot” is lower than conventional weaponry.
 
The US Navy is already testing a laser weapon system called LaWS, while in the UK, the Royal Navy is exploring a laser-based directed-energy weapon (DEW) and hopes to have something in theatre before 2020.
 
The UK Government is also investing in lasers with “disruptive capability” – new technologies that have the potential to disrupt adversaries. They state that it is “high risk/high return areas of research that can deliver potentially game-changing advances”. Lasers could form a part of that although the exact role that they would play is classified for now.

 
Despite their potential, none of these groundbreaking applications will happen overnight, whether in the military or the medical profession. Simon-Boisson estimates that it will take 15-20 years or more for lasers to become efficient and advanced enough for their long-term potential to be realised.