Nations are in a competition these days to see who can build the most powerful laser. In 2015, Japan achieved 2 Petawatts or PW, that is 2 million billion watts. In 2016, China got their own petalaser, weighing in at 5.3 PW. In March of 2019, Romania’s Extreme Light Infrastructure for Nuclear Physics (ELI-NP) project reached 10 PW.
By comparison, the most powerful consumer laser you can buy anywhere in the world, the Spyder 3 Arctic, is about 3.5 watts (according to their website). Your typical laser pointer is measured in milliwatts. You can build more powerful lasers yourself as you can see in this insane 100 Watt laser video from YouTuber styropyro, but lasers can be extremely dangerous not only because they can blind, burn, or cut you (they are used to cut metal after all) but also generate so much heat that they would be a significant fire hazard without proper cooling.
Petawatt lasers are extremely powerful but generally don’t use as much energy as you would think. A watt is a measure of energy over time and these lasers typically generate bursts of high power light lasting only a trillionth of a second. The first one was developed at Lawrence Livermore National Lab, home of the National Ignition Facility (which incidentally I nearly ended up working on but turned down the job [with some regret] to go to Georgia Tech).
Ultrapowerful lasers have been following a Moore’s law style curve similar to that of computers for the last 40 years. Indeed, ever since they were invented in the 1960s at HRL Laboratories (one of my former employers), lasers have seen incredible uses in industry and military applications. Yet, the potential from ultrapowerful lasers is even greater because it could be a pathway to the holy grail of energy generation: nuclear fusion.
There are plans in the works in Russia, China, and elsewhere to build lasers in excess of 100 PW which is where the science really starts getting interesting. We could see antimatter created from vacuum, for example.
Some articles suggest that the laser rips apart empty space. That is hardly what is going on. Rather, the energy is so intense and concentrated that it vastly increases the probability of matter production from electric fields or photons splitting into particles.
(Side note for physics nerds: Antimatter production from vacuum and an electric field is the Sauter-Schwinger effect. Photons from light can also produce matter-antimater pairs in a phenomenon called Breit-Wheeler pair production or electron-positron photoproduction.)
The key metric for how powerful a laser is when it comes to fusion or any other interesting physical phenomenon is its intensity in watts per square centimeter. See this graph for what happens at each intensity.
The planned 100 PW laser in Shanghai will be able to achieve about 10 to the 23rd power Watts per square centimeter in 15 femtosecond bursts. That is about how long it takes light to travel half the length of a human blood cell.
While we can see all kinds of interesting effects at these levels, one fascinating possibility is that we could observe the effects of light actually interacting electrodynamically with itself. This is something that, in case you didn’t know, does not normally happen. Light interacts with matter all the time, but it is essentially invisible to other light. This could create an effect as if light is bending through vacuum.
It turns out that the intensity required to observe these effects is about 1 million times more than the Shanghai laser would provide (which would be a Zettawatt laser), but we have a trick so that we could observe those effects now using relativity.
The critical intensity to observe light-light interaction is about 4.6 times 10 to the power 29. But the laser intensity is one of those quantities that changes depending on your state of motion (velocity) relative to it. This comes from Einstein’s theory of special relativity.
The trick is simply to fire a beam of electrons at close to the speed of light at the laser. Because of relativity, you can boost the apparent intensity in the reference frame of the electrons by a million times by firing them at 99.99995% the speed of light (minimum). You can do this using the laser itself in a process called laser-wakefield or plasma acceleration.
The current record for electron acceleration is held by Lawrence Berkeley National Lab which achieved 4.25 GeV electrons which is equivalent to 99.999999277% the speed of light or more than enough to achieve these effects.
Another trick is called Compton backscattering in which electrons are used to amplify photons of light. This can also boost the intensity using relativistic effects from the electrons. The record there is held by the Japanese facility The Laser Electron Photon (LEP) experiment at 2.9 GeV.
Besides producing matter from vacuum, at these intensities light behaves nonlinearly because of Quantum Electrodynamics (QED). In nonlinear QED, Maxwell’s equations that govern electrodynamics are modified to add additional terms that involve the electric and magnetic fields interacting with themselves and each other. This can effectively cause light to bend in empty space as it scatters off of virtual pairs of electrons and positrons. Nonlinear QED could be one way of exploring deeper aspects of quantum field theory than a particle accelerator can achieve. (For example, it could find discrepancies in quantum field theory itself by looking at very high order nonlinearities in the theory as well as strong-field regions where perturbative approaches break down.) Here is a chart of the kind of science we could achieve.
One of the unfortunate aspects of this race if you are an American is that the United States is losing the race. China, Russia, Japan, and Europe are all ahead of us despite our having started the race twenty years ago. The United States, instead, has put its money into lower power, higher energy lasers such as the National Ignition Facility, in an attempt to study nuclear fusion, and effectively do atomic testing without needing an atom bomb by creating similar conditions. The time has come for the USA to rethink its energy research strategy or let other nations take the helm in developing these technologies.
Right now the most powerful planned laser in the US is the ZEUS project at U Michigan, looking to achieve 3 PW. Given that these lasers could have huge economic as well as scientific value in creating new sources of energy as well as medical uses and new understanding of the quantum universe, the $16 million seems small compared to the nearly $1 billion that the EU is spending on their 10 PW project. A 2018 National Academies of Science report found that the US needed to update its strategic planning for ultra-high power lasers to be more competitive.
Ultimately there is a balance between research dollars in the US, but when it comes to big science the US has frequently been content to sit on the sidelines and let other nations take the glory. (I’m old enough to remember the huge disappointment when the Texas supercollider program was cancelled.) After all science is borderless, right? Why take on the cost when other nations will do the work and you get the benefit? But at the same time, these facilities are marching to the orders of other nations with different priorities than our own. American business and science could have a far more powerful relationship if we put more resources into these lasers and similar large efforts. And, in the end, Americans don’t like losing at anything, do we?