Nom de l'entreprise / du laboratoire: Laboratoire d'Optique Appliquée, ENSTA, Ecole polytechnique, CNRS

When an intense femtosecond laser pulse propagates in air, it gives rise to filamentation, a spectacular process in which the beam contracts spatially to form a thin channel of light in which the intensity is maintained at ~1013 W/cm2. Filamentation is accompanied by the formation of a long column of short-lived plasma generated in the wake of the laser pulse. This column is capable of guiding lightning [1] and producing secondary radiation from THz [2] to UV [3], which can be used for remote sensing applications in the atmosphere [4].
 
The recent development of laser technologies based on amplification in Yb:YAG crystals has made it possible to significantly increase the power of femtosecond lasers [5]. This type of very promising laser source was used by our team for the first demonstration of lightning guidance by laser filamentation [1], but the significant thermal effects that appear at this power are still poorly understood and very few studies of filaments have been carried out at this wavelength.
 
This internship will focus on the detailed characterization of the plasma produced in air by a 200 mJ, 800 fs laser pulse at 1.03 µm and 515 nm. We will also evaluate the effect of the laser repetition rate on the filamentation and characterize the different radiation produce by the filament at 1.03 µm.
 
Candidates should have a basic knowledge of optics or plasma physics, a good level of English and solid academic references.
This internship will be remunerated and may lead to an extension into a Ph.D thesis.

Publications by the team related to the subject
[1] Laser-guided lightning, Nature Photonics 17, 231 (2023)
[2] White-Light Filaments for Atmospheric Analysis, Science 301, 61 (2003)
[3] Conical Forward THz Emission from Femtosecond-Laser-Beam Filamentation in Air, Phys. Rev. Lett. 98, 235002 (2007)
[4] Lasing of ambient air with microjoule pulse energy pumped by a multi terawatt IR femtosecond laser, Opt. Lett. 39,1725 (2014)
[5] Ultrafast thin-disk multipass amplifier with 720 mJ operating at kilohertz repetition rate for applications in atmospheric research, Optics Express 28, 30164 (2020)