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Harmoniques cohérentes du Laser à Electrons Libres générées à partir d'harmoniques produites dans les gaz sur le prototype de l'accélérateur SCSS

Abstract : Today, single-pass Free Electron Lasers (FELs) allow the structure of matter to be studied in the femtosecond domain. Yet, even if the produced radiation, the so-called Self Amplified Spontaneous Emission (SASE) is highly bright, the longitudinal coherence is partial; the spectral and temporal profiles are composed of a series of peaks, called “spikes”, and present important statistical fluctuations. We demonstrate here the strong and coherent amplification of the 5th harmonic of a Ti: Sa laser (800 nm, 10 Hz, 100 fs) generated in a gas cell, i.e. 160 nm, and seeded in a FEL. This spectacular phenomenon is associated to the generation of intense and coherent Non Linear Harmonics (NLH) at 54 nm and 32 nm. The experiment has been carried out on the SCSS (SPring-8 Compact SASE Source, Japan) Prototype Accelerator. This facility is mainly based on a thermionic cathode electron gun, a LINAC and an in-vacuum undulator (2 sections of 4.5 m length), in which the external harmonic source is overlapped transversally, spectrally and temporally with the electron beam (150 MeV, 10 Hz, 1 ps). With only one undulator section, the 160 nm seeded emission achieves three orders of magnitude higher intensity than the unseeded one, and presents a quasi perfect Gaussian shape in the spectral distribution. Moreover, the FEL saturation length is twice smaller. In view of the low seed level required, such amplification associated to NLH schemes would allow the generation of fully coherent soft X-ray radiations down to the “water window”.
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https://tel.archives-ouvertes.fr/tel-00267686
Contributor : Guillaume Lambert <>
Submitted on : Friday, March 28, 2008 - 10:12:35 AM
Last modification on : Thursday, February 1, 2018 - 1:38:02 AM
Long-term archiving on: : Thursday, May 20, 2010 - 10:37:46 PM

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  • HAL Id : tel-00267686, version 1

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Guillaume Lambert. Harmoniques cohérentes du Laser à Electrons Libres générées à partir d'harmoniques produites dans les gaz sur le prototype de l'accélérateur SCSS. Physique Atomique [physics.atom-ph]. Université Paris Sud - Paris XI, 2008. Français. ⟨tel-00267686⟩

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