with a low-power flash of 1053-nanometer (nm) infrared light generated in an ytterbium-doped optical fiber laser termed Master Oscillator. Its light is split and directed into 48 Preamplifier Modules (PAMs). Each PAM conducts a two-stage amplification process via xenon flash lamps. The first stage is a regenerative amplifier in which the pulse circulates 30 to 60 times, increasing its energy from nanojoules to tens of millijoules. The second stage sends the light four times through a circuit containing a neodymium glass amplifier similar to (but much smaller than) the ones used in the main beamlines, boosting the millijoules to about 6 joules. According to LLNL, designing the PAMs was one of the major challenges. Subsequent improvements allowed them to surpass their initial design goals. The main amplification takes place in a series of glass amplifiers located at one end of the beamlines. Before firing, the amplifiers are first optically pumped by a total of 7,680 flash lamps. The lamps are powered by a capacitor bank that stores 400 MJ (110 kWh). When the wavefront passes through them, the amplifiers release some of the energy stored in them into the beam. The beams are sent through the main amplifier four times, using an optical switch located in a mirrored cavity. These amplifiers boost the original 6 J to a nominal 4 MJ. Given the time scale of a few nanoseconds, the peak UV power delivered to the target reaches 500 TW. Near the center of each beamline, and taking up the majority of the total length, are spatial filters. These consist of long tubes with small telescopes at the end that focus the beam to a tiny point in the center of the tube, where a mask cuts off any stray light outside the focal point. The filters ensure that the beam image is extremely uniform. Spatial filters were a major step forward. They were introduced in the Cyclops laser, an earlier LLNL experiment. The end-to-end length of the path the laser beam travels, including switches, is about . The various optical elements in the beamlines are generally packaged into Line Replaceable Units (LRUs), standardized boxes about the size of a vending machine that can be dropped out of the beamline for replacement from below. After amplification is complete the light is switched back into the beamline, where it runs to the far end of the building to the target chamber.