A weak laser pulse—about 1 billionth of a joule—is created, split, and carried on optical fibers to 48 preamplifiers that increase the pulse’s energy by a factor of 10 billion, to a few joules. The 48 beams are then split into four beams each for injection into the 192 main laser amplifier beamlines.
Each beam zooms through two systems of large glass amplifiers, first through the power amplifier and then into the main amplifier. In the main amplifier, a special optical switch traps the light, forcing it to travel back and forth four times, while special deformable mirrors and other devices ensure the beams are high quality, uniform, and smooth.
From the main amplifier, the beam makes a final pass through the power amplifier. By now, the beams’ total energy has grown from 1 billionth of a joule to 4 million joules—all in a few millionths of a second.
The 192 beams proceed to two ten-story switchyards on either side of the target chamber where they are split into quads of 2×2 arrays. Just before entering the target chamber, each quad passes through a final optics assembly, where the pulses are converted from infrared to ultraviolet light and focused onto the target.
For ignition experiments, the target consists of a tiny metal can called a hohlraum containing a capsule of frozen fusion fuel. Laser beams entering the top and bottom holes of the hohlraum strike its inside walls, creating x rays that compress the fuel capsule to extreme temperatures and densities.
NIF’s 192 laser beams travel about 1,500 meters from their birth to their destination at the center of the spherical target chamber. Yet the journey from start to finish takes only about 5 microseconds.