Texans Build World’s Most Powerful Laser. Sort of.

More than a petawatt, but of course it’s pulsed, not continuous. Joules of energy in femtosecond-ish long pulses will yield a petawatt pulse, and it hasn’t earned its title quite yet, but it’s expected to.

The pulse compression, which they do with gratings, can also be done with prisms and chirped mirrors. Pulses tend to disperse, because the speed of light in a medium varies with wavelength, so the blue and red end of the pulse travel at slightly different speeds (normal dispersion will have the blue light going just a little slower than red light). The grating method uses grating pairs in place of mirrors, tilted so the blue end of the pulse travels a shorter distance so it can catch up to the red end; a similar arrangement can be done with pairs of prisms. Chirped mirrors have different reflective layers that allow the red end of the pulse to penetrate further before reflecting. Because this laser is going for high power in addition to short pulse length, they actually stretch the pulse out with gratings in the opposite orientation, before amplifying it (to limit the peak power in the gain medium) and then compressing.