CONTROLLING lightning with lasers LARGE SCIENTIFIC PROJECT
Figure 2. Photography of the laser developed by Trumpf scientific for the LLR project.( Copyright LLR project).
Achieving an energy of one joule per pulse proved more difficult than expected, due to the strong thermal effects that occur at high power. In the end, including 5 amplification stages, the laser still achieved a record energy of 720 mJ at 1060 nm. After two years of development, the first tests with the laser were carried out at the former Orsay Linear accelerator laboratory in France, to characterize and optimize the filaments produced at 150 m using an enlarging telescope. Stopped for almost a year by the COVID pandemic, the project then resumed in 2021 for the final experiment, where the laser and its transport and focusing device were installed at the top of Mount Saentis. and the tower, the lightning that strikes the tower develops into ascending lightning precursors that start at the top of the tower. Known as upward leader, these discharges are therefore easily intercepted by the laser. This configuration is similar to that used in the pioneering experiment by Uchida et al. in the 90s. The first challenge was to build the world ' s most powerful high-average high-peak power ultrafast laser, with the aim of delivering laser
pulses with an energy of 1 Joule, a duration < 1 ps at a repetition rate of 1 kHz. Trumpf ' s laser prototype is 1.5 meters wide, 8 meters long and weighs over 3 tons( see Figure 2). Its 5-block design means it can be transported by a cable car to the summit of Saentis, which is not accessible by car. The first two years of the project were devoted to the development of the laser by Trumpf, and to the study of lightning events at the Mont Saentis in the absence of laser.
The lightning experiment
Supervised by the University of Geneva, this 4-month installation on the top of Mount Saentis proved to be particularly complex. On the one hand, the laser had to be installed in an air-conditioned environment with filtered air, because at high average power, dust in the amplifiers can easily damage the entire chain. It
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