Light in the extreme ultraviolet (XUV) is a universal probe of mater, may it be in diluted or condensed phase: photons associated with this spectral range carry energy of 10 to 100 eV, sufficient to directly ionize atoms, molecules or solids. Large scale instruments such as synchrotrons or the lately developed free electron lasers (FEL) work in this spectral range and are used to both study fundamental light matter interaction and develop diagnosis tools. However these instruments do not offer the temporal resolution require to study light matter interactions at their ultimate timescales, which is in the attosecond range (1as = 10-18s). An alternative is offered by the recent development of XUV sources based on high order harmonic generation (HHG). They are based on the extremely nonlinear interaction of a femtosecond intense laser beam with a gas target. Our laboratory has pioneered the development, control and design of these sources providing XUV attosecond pulses.



During this PhD project, we will develop specific setups to allow these attosecond pulse to carry angular momenta, may it be spin, orbital or generalized angular momenta. This will open new applications roads through the observations of currently ignored spectroscopic signatures. However, we will set the focus on the fundamental aspects of light-matter interaction in the highly nonlinear regime with angular momenta involved, in particular on beams with unusual topologies such as Möbius strips.

The student will acquire practical knowledge about lasers, in particular femtosecond lasers, and hands on spectrometric techniques of charged particles. He/she will also study strong field physical processes which form the basis for high harmonic generation. He/she will become an expert in attosecond physics. The acquisition of analysis skills, computer controlled experiments skills will be encouraged although not required.



Detailed subject at the web page: http://iramis.cea.fr/LIDYL/Pisp/thierry.ruchon/

High order laser harmonic generation in crystals is a new promising source of ultrashort coherent radiation in the extreme ultraviolet spectral domain (50-150 nm). The aim of this PhD work is to use the recent progress of the nano-manufacturing technologies in order to shape the emitting face of the non linear medium to manipulate the spatio-temporal properties of the radiation. Transposing the methods developed for linear meta-optics in the visible range to the strong field interaction regime, the student will extend their control abilities to a very large spectral bandwidth, in order to generate attosecond pulses shaped on demand.

Nowadays, femtosecond lasers are the most intense light sources available on Earth, with a power that can reach that of the solar radiation over an area as large as Australia and that can be focused down to focal spots having the diameter of a human hair. These extreme radiation sources are a valuable tool for the study exotic states of matter, but also as a "driver" of secondary sources of compact and ultra-short particles or light.



Despite these remarkable properties, femtosecond lasers still lack the intensity required to explore new fundamental regimes where the laser-matter or laser-quantum vacuum interaction becomes dominated by strong-field Quantum ElectroDynamic (QED) effects. These QED regimes are found for example around some astrophysical objects such as black holes and neutron stars. Moreover, femtosecond lasers typically have a wavelength of ~ 1 micrometer, but some potential technological applications (e.g., photolithography) require much smaller wavelengths, of the order of ten nanometers.



In order to manipulate the properties of femtosecond lasers and overcome these barriers, we are studying optical devices called "relativistic plasma mirrors", which can convert a laser pulse into X-UV radiation, while considerably boosting its intensity by Doppler effect.



This multi-disciplinary thesis project concerns the optimization of the “plasma mirror” physical system in order to improve the properties of the boosted laser beams and to enable the use of these boosted lasers for the above mentioned applications.



The activity will rely on Particle-In-Cell numerical simulations with the open-source code “WarpX“ on the latest exascale class supercomputers to determine the optimal parameters for the generation of boosted beams. An auxiliary code development activity is foreseen to support the simulation campaigns. The simulations will be essential to guide experiments that will be performed on our 100 TW laser facility, UHI100, with controlled temporal contrast, which is essential for the realization of this type of experiments, and then on PW-class lasers (e.g. Apollon at École Polytechnique or other international facilities).



The PhD student will have the opportunity to be part of a dynamic team with strong national and international collaborations. He/she will also acquire the necessary skills to participate in laser-plasma interaction experiments in international facilities. Finally, he/she will acquire the required skills to contribute to the development of a complex software written in modern C++ and designed to run efficiently on the most powerful supercomputers in the world. The development activity will be carried out in collaboration with the team led by Dr. J.-L. Vay at LBNL (US).



Bibliography:

> A.Myers et al. “Porting WarpX to GPU-accelerated platforms” Parallel Computing, 108, 102833, 2021

> L.Fedeli et al. “Probing Strong-Field QED with Doppler-Boosted Petawatt-Class Lasers” Phys. Rev. Lett. 127, 114801, 2020

> H.Vincenti “Achieving Extreme Light Intensities using Optically Curved Relativistic Plasma Mirrors” Phys. Rev. Lett. 123, 105001, 2019

> H Vincenti et a. “Optical properties of relativistic plasma mirrors” Nat. Comm. 5 : 3403, 2014

Summary :

The student will use attosecond laser techniques to study ultrafast dynamics of molecules in liquid and gas phase. Inner level attosecond photoionization will be used to study in real time: scattering/rearrangement/transfer electron dynamics, as well as solvation effects.



Detailed summary :

In recent years, the generation of sub-femtosecond pulses, known as attoseconds (1 as=10-18 s), has made spectacular progress. These ultrashort pulses open new perspectives for the exploration of matter on a timescale that was previously inaccessible. Their generation is based on the strong non-linear interaction of short (~20 femtoseconds) and intense infrared (IR) laser pulses with atomic or molecular gases. This produces high order harmonics of the fundamental frequency, over a wide spectral range (160-10 nm) covering the extreme ultraviolet (XUV). This high-energy radiation is able to ionize molecules by removing inner-layer electrons. In the time domain, this coherent radiation appears as pulses of ~100 attoseconds duration [1].



With these attosecond pulses, it becomes possible to study the fastest dynamics in matter, those associated with electrons, which naturally occur on this timescale. Attosecond spectroscopy thus allows the study of fundamental processes such as photoionization and addresses questions such as : How long does it take to pull an electron out of an atom or molecule? How does the electron cloud rearrange? These questions have become hot topics in the scientific community but have so far been studied in isolated systems, in the gas phase [2,3]. Advanced sampling technologies now allow us to study these electronic dynamics in a solvated medium where the behavior of electrons on these attosecond timescales is unknown. What energy or electron transfers take place in 10-18 second? Can we measure electron scattering effects in a liquid? These questions are a new challenge for our field on the experimental and theoretical level.



The objective of this thesis is first to implement attosecond techniques established in gas phase to the liquid phase. Two complementary detections will be used, photoelectron detection and transient absorption. By combining the information obtained by each technique, we will be able to measure the scattering of the photoelectron after its creation but also the fate of the ionized molecule: rearrangements/electron transfers, solvation effects.



The experimental work will include the development and the implementation of a beamline, installed on the FAB100 laser of the ATTOLab Excellence Equipment, allowing: i) the generation of attosecond radiation; ii) its characterization by quantum interferometry; iii) its use in photoionization and absorption spectroscopy. Theoretical aspects will also be developed. The student will be trained in ultrafast optics, atomic and molecular physics, quantum chemistry, and will acquire a broad mastery of XUV and charged particle spectroscopy techniques. Knowledge in optics, nonlinear optics, atomic and molecular physics is a prerequisite.

The thesis work could lead to experimental campaigns in French and associated European laboratories (Hamburg-DESY).



References :

[1] Y. Mairesse, et al., Science 302, 1540 (2003)

[2] V. Gruson, et al., Science 354, 734 (2016)

[3] A. Autuori, et al., Science Advances 8, eabl7594 (2022)