High-Energy Laser Facilities

The ability to temporally shape the pulse of a laser beam is of critical importance to run optimal and reliable experiment on large high-power lasers infrastructures like LULI2000 (France) or the STFC Laser Facility (UK), but also for the most intense laser sources such as LLNL-NIF in the US and CEA-LMJ in France.

The ModBox-FrontEnd is challenging the state of the art of temporal pulse shaping performance. It is able to generate laser pulses with any kind of temporal shape, with a capability to correct the pulse characteristics even at high repetition rate. And compared with a simple modulation solution, an integrated ModBox solution offers unique performance in terms of contrast and stability.

The ModBox Front-End is based on Exail’s unique know-how in designing and manufacturing LiNbO₃ modulation solutions. The company has built up a strong experience in such systems and successfully installed them in many research facilities all over the world, and in industrial companies. Customers have selected the ModBox FE for the stability, reproducibility and quality of the impulsions generated, but also for its reliability over a period of several months. Exail know-how in the modelization of complex electro-optic system in the RF domain enables advanced correction capability (see experimental curve below). With this feature, ModBox users can easily perform pulse shaping with a high level of fidelity.

Exail masters all three key components needed for optical pulse shaping application: the Electro-Optical Modulator (EOM) based on lithium niobate technology, the high speed and high voltage linear driver for EOM modulators and the modulator bias control (MBC) board. The ModBox-FrontEnd integrates screened and selected components that are controlled by a dedicated software interface for intuitive (and gradual) control to provide reliable and stable operation. Today, each ModBox can be customized to the customer’s needs, thanks to our standardized building blocks.

Megajoule class laser facilities such as National Ignition Facility (LLNL NIF, US) or CEA Laser MegaJoule (France) carry out extremely complex laser-matter interaction experiments with an incredibly high level of homogeneous compression, by accurately synchronizing hundreds of laser beams on a millimeter size target. These experiments induce electromagnetic perturbations and radiation constraints consisting of a pulse mixing X-rays, 14 MeV neutrons and gamma-rays. Within the experimental hall of the facilities, all the equipment (laser and plasma diagnostics, control command links, …) are exposed to these radiations.

Optical fiber technology presents several advantages for integration in these facilities, such as their robustness and their immunity to most of the electromagnetic perturbations. Exail develops accurate optical fibers for diagnostics in radiation-rich environments. They are specialized state-of-the-art measuring instruments able to collect data from the experiment in real-time, in particular related to the temporal shaping of the laser beams.

In a decade, Exail has become the sole supplier of radiation resistant diagnostics optical fibers, enabling the LLNL NIF and the CEA LMJ to reach new limits such as fusion ignition or thermonuclear gain fusion. Indeed, Exail rad-hard fibers guarantee the quality and accuracy of the data collected at any point of the facility, up to the experiment chamber where radiation levels are extreme. Experiments were mostly conducted “blindly” before the use of Exail diagnostic fibers, due to the poor information that could be recovered from the target.

Such highly specific optical fibers for diagnostics in high-energy laser facilities are now available in the portfolio of Exail, produced at the Lannion site. They are multimode optical fibers, with “graded-index refractive-index profiles” used to reduce the dispersion impact on measurement quality. In classic step-index multimode optical fibers, the signal is propagated through different optical modes that travel at different speeds. Thus, the temporal information of a given signal is not preserved through propagation. This is of the utmost importance when the light is carrying diagnostics data related to a thermonuclear reaction you want to monitor. Fortunately, Graded-Index MultiMode (MMGI) optical fiber ensures that each mode injected into the fiber reaches the diagnostic sensor at the other end at the exact same time.

Exail graded-index multimode (MMGI) fibers exist with various core size and NA. Standard versions have a Ge-doped core surrounded by a silica cladding, radiation resistant MMGI (rad-MMGI) fibers are also available and have a Fluorinated core. The doping composition of the core, the cladding diameter and coatings can be tailored.

Exail manufactures optical fibers that are designed to resist radiation, but also for operation in extreme temperatures thanks to different coatings available (read page dedicated to this application).