Seeding SPARC facility with Harmonic Generation in gases: Preliminary tests of the Harmonic Generation in gas chamber

A coherent short wavelength source can be realized with a Free Electron Laser using High Gain Harmonic Generation configuration. The injection of an external light source in the first part of an undulator results in a coherent light emission in its second part. The SPARC FEL (Frascati, Italy) can be configured to test such schemes. We propose to use the High Order Harmonic Generation (HOHG) in gases process as the seed. HOHG produces a coherent XUV source by focusing an intense laser pulse into a gas medium. This beam, composed of odd harmonics of the fundamental laser, is then shaped using a telescope of two spherical mirrors, allowing the focusing at a given position, in the SPARC undulator. Appropriate tuning of the undulator gaps will amplify either 3rd or 5th harmonic seeded or non-linear harmonics of those wavelengths, allowing the perspective of producing VUV coherent radiation. The vacuum chambers for harmonic generation and shaping have been realized and tested at the CEA (Saclay, France). We present these tests.