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Univ. Paris-Saclay

Sujet de stage / Master 2 Internship

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13 nm high order harmonic generation for nanometer scale resolution lensless imaging

Contact: BOUTU Willem, , willem.boutu@cea.fr, +33 1 69 08 51 63
Possibility of continuation in PhD: Non
Deadline for application:07/05/2021

Full description:
Coherent diffractive imaging (CDI) is a lensless imaging technique that uses spatial coherence and Fourier optics to remove the traditionallyused objectiveoptics in order to reach wavelength limited spatial resolution in X-ray microscopy. First developed for synchrotron facilities, its implementation onlaser based short wavelengthsources has allowedfor the rise of nanoscale femtosecond imaging. For more than 10 years the CEA-LIDYL has developed new CDI techniqueson laboratory sources, such as Fourier Transform Holography with Extended Reference [1], Stereo 3D imaging [2], or single shot CDI for time resolved experiments [3,4].

Those small scale sources arebased on anultra nonlinearphenomenon called high order harmonic generation (HHG), discovered at CEA-Saclay 30 years ago [5}. When focusing a femtosecond infrared laser beam on a gas jet, one can generate ultrashort (femtosecond to attosecond) coherent radiation in the extremeultraviolet domain.This process is now well understood, and is currently undergoing a rapid democratization for ultrafast spectroscopy experiments. However, the low photon flux is a strong limitation for many applications.

At CEA-LIDYL we recently acquired a high repetition rate femtosecond laser and developed a new technology for high flux HHG source, based on a long capillary geometry. The aim of the internshipis to implement this new apparatus on the laser in the group new laboratory. After optimization and characterization of the harmonic emission, the fellow will use the λ=13nm radiation to perform a first CDI experiment, with the aim of demonstrating nanometer scale spatial resolution on a large size solid-state sample using an imaging technique called ptychography [6]. This first demonstration is a first step towards the development of a new beamline dedicated to lithographymask inspection, a vital toolfor microelectronics industry. These developments will take placein the framework of a new jointlaboratory with Orsay SME Imagine Optic, which is aiming at proposing new metrology tools at short wavelengths.

1. Gauthier et al., Single-shot Femtosecond X-Ray Holography Using Extended References, PRL 105, 093901 (2010)
2. Duarte et al., Computed stereo lensless X-ray imaging, Nat. Photonics 13, 449 (2019)
3. Ravasio et al., Single-Shot Diffractive Imaging with a Table-Top Femtosecond Soft X-Ray Laser-Harmonics Source, PRL 103, 028104 (2008)
4. Boutu et al., Impact of noise in holography with extended references in the low signal regime, Opt. Express 24, 6318 (2016)
5. Ferray et al., Multiple-harmonic conversion of 1064 nm radiation in rare gases, J. Phys. B 21, L31 (1988)
6. Thibault et al., High-Resolution Scanning X-ray Diffraction Microscopy, Science 321, 379 (2008).
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