The Megajoule Laser
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The laser line
The twenty-two laser lines at the LMJ are located on either side of the experimental chamber in the four laser halls.
Twenty-two laser lines are installed in the four halls. © CEA
Each laser line consists of eight virtually identical laser beamlines.
A laser line is composed of three elements:
A laser line. © CEA
The laser source delivers the initial light pulse that will be amplified in the line. Its role is to generate the initial beam and give it its spatio-temporal shape and frequency (color of light). Laser beams are generally circular in shape. However, in the case of the LMJ, the laser beam will be square in order to optimize the structures' small form factor. Measuring 40 × 40 mm upon exiting the source, the beam increases in size to 400 × 400 mm in the amplifier section. It has little energy (of the order of one joule) and lasts a few billionths of a second.
The LMJ laser source comprises:
The initial pulse emitted by the laser source is greatly amplified in the LMJ (by a factor of approx. 20,000) in order to obtain the energy required for each experiment. This amplification is performed by the amplifier section, which is also referred to as the amplifier chain.
Each laser beam acquires its energy by passing through the amplifier four times. This principle has the advantage of extracting the maximum amount of energy from the amplifiers and significantly reducing the size of the laser halls.Simply put, the amplifier blocks consist of:
Dust on the surface of optical components can lead to laser-induced damage. As in the microelectronics industry, it is necessary to maintain a clean environment that is assessed in terms of the number of particles greater than 5 microns per cubic foot (per 28,317 cubic centimeter) of air.
The amplified laser beams are carried to the experimental chamber. Each beam is oriented by a set of six successive mirrors to switch them from a parallel configuration (in the laser halls) to a configuration in which they are distributed all around the test chamber.
Before entering the experimental chamber, each beam passes through a frequency conversion and focusing system.
In the frequency conversion and focusing system:
For more information:
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