At intensities around 1024 Watts per square centimeter the field should be strong enough to start to break the mutual attraction between some of the electron-positron pairs. This is basically breaking the quantum vacuum of space.
New research proposes the collision between an electron beam with energy in the tens of GeV and a laser pulse of intensity 1024 Watts per square centimeter at, crucially, normal incidence is a viable platform for studying the breakdown of perturbative strong-field QED. Experimental exploration of nonperturbative quantum electrodynamics (QED) is challenging as large electromagnetic fields comparable to the critical field of QED Ecr = 1.3 × 1018 Vm−1 are required. Ever-increasing laser intensities make it possible to probe fields that are effectively supercritical, i.e., have magnitude greater than Ecr. This is achieved using the Lorentz boost when ultrarelativistic electrons collide with an intense laser pulse.
The Quantum Electrodynamic Vacuum or QED vacuum is the field-theoretic vacuum of quantum electrodynamics. It is the lowest energy state (the ground state) of the electromagnetic field when the fields are quantized.
To approach 100 PW, one option is to combine several such pulses—four 30-PW pulses in the case of the SEL and a dozen 15-PW pulses at the XCELS. But precisely overlapping pulses just tens of femtoseconds long will be “very, very difficult,” says LLNL laser physicist Constantin Haefner. They could be thrown off course by even the smallest vibration or change in temperature, he argues. The OPAL, in contrast, will attempt to generate 75 PW using a single beam.
Mourou envisions a different route to 100 PW: adding a second round of pulse compression. He proposes using thin plastic films to broaden the spectrum of 10-PW laser pulses, then squeezing the pulses to as little as a couple of femtoseconds to boost their power to about 100 PW.
Once the laser builders summon the power, another challenge will loom: bringing the beams to a singularly tight focus. Many scientists care more about intensity—the power per unit area—than the total number of petawatts. Achieve a sharper focus, and the intensity goes up. If a 100-PW pulse can be focused to a spot measuring just 3 micrometers across, as Li is planning for the SEL, the intensity in that tiny area will be an astonishing 1024 watts per square centimeter (W/cm2)—some 25 orders of magnitude, or 10 trillion trillion times, more intense than the sunlight striking Earth.
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