Shiva Laser - Description

Description

Shiva incorporated many of the advancements achieved on the earlier Cyclops and Argus lasers, notably the use of amplifiers made of Nd:glass slabs set at the brewster angle and the use of long vacuum spatial filters to "clean" the resulting laser beams. These features have remained a part of every ICF laser since, which leads to long "beamlines". In the case of Shiva, the beamlines were about 30 m long.

Prior to "firing", the laser glass of the Shiva was "pumped" with light from a series of Xenon flash lamps fed power from a large capacitor bank. Some of this light is absorbed by the neodymium atoms in the glass, raising them to an excited state and leading to a population inversion which readies the lasing medium for amplification of a laser beam. A small amount of laser light, generated externally, was then fed into the beamlines, passing through the glass and becoming amplified through the process of stimulated emission. This is not a particularly efficient process, only a small amount of the energy stored in the glass is dumped into the beam (about 20%) and the "pumping" wastes a considerable amount of power by generating light that the neodymium cannot absorb. In total, around ~1% of the electricity used to feed the lamps ends up amplifying the beam on most Nd:glass lasers.

After each amplifier module there was a spatial filter which was used to smooth and "clean" the beam of any nonuniformity or power anisotropy which had accumulated due to nonlinear effects of intense light passage through air and glass. The spatial filter is held under vacuum in order to eliminate the creation of plasma at the focus (pinhole).

After the light had passed through the final amplifier and spatial filter it was then used for experiments in the target chamber, lying at one end of the apparatus. Shiva's 20 beamlines delivered a ~.5 to 1 nanosecond pulse of 10.2 kJ of infrared light at 1062 nm wavelength, or smaller peak powers over longer times (3 kJ for 3 ns).

By today's standards, Shiva was fairly inexpensive. The entire device, including test equipment and buildings, cost about $25 million when it was completed in 1977 (~81 million 2005 dollars).