The COXINEL line has been designed at Synchrotron SOLEIL for electron beam manipulation in view of a seeded free electron laser using Laser plasma acceleration (LPA). After first studies on electron beam transport and undulator radiation in the spontaneous emission regime using LPA from Laboratoire d’Optique Appliquée (Ecole Polytechnique, France), the line has been moved to the HZDR, Dresden, Germany, for high quality LPA electrons driven by the DRACO laser. We report here on the demonstration of a seeded FEL at 275 nm driven by the HZDR LPA.

We report the first lasing of a seeded FEL fully driven by a laser plasma accelerator. The experiment was performed at HZDR (Germany), coupling the high quality electron beams of the HZDR laser plasma accelerator with the versatile COXINEL beam manipulation line. Using an external seed at 270 nm, the FEL signal was observed at 275 nm. We explain how this slight red-shift confirms previous predictions [1], show the precise control over the FEL wavelength and give evidence of the longitudinal coherence of the emitted pulses. All experimental results are strongly supported by analytic modeling and Genesis numerical simulations. Our results substantiate the continuous progress of LPA technology to enable FEL operation and finally bring temporal coherence to those compact promising sources. [1] M Labat et al 2020 New J. Phys. 22 013051.