The Laser Mégajoule (LMJ) facility has about 40 large optics per beam. For 22 bundles with 8 beams per bundle, it will contain about 7.000 optical components. First experiments are scheduled at the end of 2014. LMJ components are now being delivered. Therefore, a set of acceptance criteria is needed when the optical components are exceeding the specifications. This set of rules is critical even for a small non-conformance ratio. This paper emphasizes the methodology applied to check or re-evaluate the wavefront requirements of LMJ large optics. First we remind how LMJ large component optical specifications are expressed and we describe their corresponding impacts on the laser chain. Depending on the location of the component in the laser chain, we explain the criteria on the laser performance considered in our impact analyses. Then, we give a review of the studied propagation issues. The performance analyses are mainly based on numerical simulations with Miró propagation simulation software. Analytical representations for the wavefront allow to study the propagation downstream local surface or bulk defects and also the propagation of a residual periodic aberration along the laser chain. Generation of random phase maps is also used a lot to study the propagation of component wavefront/surface errors, either with uniform distribution and controlled rms value on specific spatial bands, or following a specific wavefront/surface Power Spectral Distribution (PSD).
KEYWORDS: Diagnostics, Near field, Optical amplifiers, Plasma, Mirrors, Frequency conversion, Calibration, Picosecond phenomena, Space operations, Fusion energy
The Laser Integration Line (LIL) was first designed as a prototype to validate the concepts and the laser architecture of
the Laser MegaJoule (LMJ). The LIL facility is a 4-beam laser representing a quad structure of the LMJ. A set of test
campaigns were conducted to safely ramp up laser performance. The main goal was to measure quad-specific features
such as beam synchronization and focal spot (size, smoothing contrast ratio or irradiation nonuniformity) versus the LMJ
requirements. Following the laser commissioning, the LIL has become a major instrument dedicated to the achievement
of plasma physics experiments for the French Simulation Program and was also opened to the academic scientific
community. One of the attributes of the LIL facility is to be very flexible to accommodate the requests of plasma
physicists during campaigns. The LIL is constantly evolving to best meet the needs of target physicists. Changes made or
planned are either to improve the quality of laser beams, or to increase the LIL Energy-Power operating space. To
optimize preparation and design of shot campaigns, the LIL performance status has been elaborated. It gives information
about the characteristics of the laser in terms of near field and far field, defines the steps to maintain performance,
explains how the facility responds to the request, details settings (smoothing, shaping of the focal spot, energy, temporal
pulse shaping, beam pointing) and gives the limits in energy and power. In this paper, an overview of the LIL
performance is presented.
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