Scientists want to rip the Universe apart. At least that is what a Daily Mail headline might read. Lasers can now reach power in the petawatt range. And, when you focus a laser beam that powerful, nothing survives: all matter is shredded, leaving only electrons and nuclei.
But laser physicists havent stopped there. Under good experimental conditions, the very fabric of space and time are torn asunder, testing quantum electrodynamics to destruction. And a new mirror may be all we need to get there.
On average, the amount of power used by humans is about 18 terawatts. A petawatt is 1,000 times larger than a terawatt. The baddest laser on the planet (currently) produces somewhere between 5 and 10 petawatts, and there are plans on the drawing board to reach 100 petawatts in the near future. The trick is that the power is not available all the time. Each of these lasers produces somewhere between 5-5000 J of energy for a very very short time (between a picosecond—10-12s—and a few femtoseconds—10-15s). During that instant, however, the power flow is immense.
Numbers beyond 42
The numbers get even more mind blowing when you consider that all of that energy is focused, such that the intensities reach something like 1022W/cm2. To put this in perspective, you start creating a plasma when intensities hit 1012W/cm2. Once intensities get above 1025W/cm2, if the light hits just a single electron, there's enough energy to start a cascade of electron-positron production out of the vacuum. If the laser intensity hits 1029W/cm2, not even that single electron is required—the light will rip virtual electrons out of the vacuum, generating real charges from the apparent nothingness of empty space.
But getting to 1025W/cm2 is tough. The issue is one of material. Or, rather it's the lack of a material that can survive long enough to focus the laser light. This is where plasma mirrors come in.
Plasma mirrors were all the rage a few years ago when petawatt lasers were all fresh and new. The idea is actually very simple. A plasma is a gas of conducting particles, with its electrons being very light and easy to move around. When light hits the plasma, the electrons are accelerated back and forth, following the lights electric field. In doing so, the electrons absorb and re-emit the light in the opposite direction. In other words, the light reflects from the plasma, just like it does from a chrome bumper.
A plasma is basically already as destroyed as a material can be, so the laser beam cannot damage the plasma.
It was initially thought that plasma mirrors could not act as a good focusing element, though. Essentially, it is impossible to get the shape right. But 24 hours of supercomputer time has shown that a plasma mirror might be the right way to go. New developments in model code allowed researchers to simulate a full 3D laser pulse impacting on a surface. Researcher Henri Vincenti from France has taken advantage of these computational developments to adapt this code to open up new ways to increase the intensity of some very bright lasers.
Vibrating into focus
In his model, the surface was placed at an angle to a laser beam. A laser beam has an intensity profile that is highest in the center and fades off to the outside. Combine the intensity profile with the angle of the surface, and the plasma generated by a laser pulse forms a relatively smooth elliptical shape. This means that the light reflected from the plasma will focus to a well-defined point.
That is nice, but what follows is even better. As the light intensity gets really high, the collective motion of the electrons starts to look a bit like the motion of the woofer Read More – Source
