Major laser facilities are so large that they cannot be shown in a single picture. A simplified schematic is shown in Fig. 10.42. A weak pulse of the right spatial and temporal profiles is generated in an oscillator at the left. The same pulse is sent into each laser chain. Each identical chain consists of increasingly large amplifiers to raise the power of the beams. At the right-hand side, the beams enter a switch yard consisting of mirrors to bring the beams into the target chamber (the white sphere) at the desired angles. The beams have a finite length, since light travels at 1 feet (30 cm) per second, so a 1-ns pulse is only a foot long. Each beam path has to have the same length for the beams arrive at the same time. In between the amplifiers are

optical units to reject the reflected light and to maintain the same time variation, spatial profile, and smoothness that the beams started with. The light is divided into multiple beams not only to illuminate the target uniformly, but also to avoid over­heating the glass in each beam.

The NIF laser has 192 beams divided into 48 groups of four each. The neo­dymium in the doped glass is driven into an excited state by a pulse of light from flash lamps. Originally, the lamps were like the electronic flashes in cameras. Recent conversion to solid-state units like LED flashlights have greatly reduced the complexity and cost. It takes 400 MJ of capacitors to store the energy for the lamps. An excited amplifier lases when it is tickled by the light from the previous stage. The total length of each light path is 300 m, the length of three football fields for either kind of football. Nd-glass lasers produce infrared light with 1.06 pm wave­length. This is upshifted to 3w with single crystals of potassium dihydrogen phos­phate. The 3w light has a wavelength of 351 nm, which is in the ultraviolent, so different optical materials have to be used. Figure 10.43 shows individual beam tubes in the earlier Nova laser. Figure 10.44 shows the NIF laser bay before it was all covered up. The optical elements in each beam tube have to be held in exact alignment and kept completely dust free. In NIF, the optical equipment between each amplifier stage is preassembled in refrigerator-size boxes so that spares can be slipped into place from below if one element fails.

Nd-glass lasers were developed also at the Institute for Laser Engineering in Osaka, Japan, under the leadership of Prof. Chiyoe Yamanaka. Other important participants in the development of glass lasers were Academicians N. G. Basov and A. M. Prokhorov in competing groups at the Lebedev Institute in Moscow; Kip Siegel, who founded KMS Fusion in Michigan; Moshe Lubin, who founded the Laboratory for Laser Energetics in Rochester, New York; the group at the Rutherford-Appleton Laboratory in England; and Edouard Fabre’s laboratory

at the Ecole Polytechnique in Palaiseau, France, which led to the Laser Megajoule being constructed in Bordeaux.