Preamplifiers at NIF. (Credit: © LLNL / www.llnl.gov)

A device that increases the energy of the laser beam. By passing the laser beam through a series of amplifiers, a very significant increase in its energy can be achieved. For example, the laser required for laser-driven fusion research at NIF is amplified from 1 billionth of a joule to several million joules. The core of the amplifiers is an optical gain medium illuminated by flashlamps, which cause the excitation of electrons in the medium. The passage of the laser beam through the medium causes de-excitation, which releases a wave of photons of the same wavelength as the laser beam, thereby amplifying it.