High Field Plasmonics by Luca Fedeli

Author:Luca Fedeli
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

Target name

Resonance angle

Groove spacing

F

–

–

G15

1.35

G30

2

G45

3.41

The thickness of all the targets was 10 m, while the peak-to-valley depth of the gratings was 0.25 m ()

4.2.2 Experimental Results

The experimental activity consisted in testing all the targets listed in Table 4.2 with various angles of incidence of the laser pulse, alternating between the two diagnostics available for electron detection. The outcome of the experimental activity is presented hereunder, starting with the results for the spatial distribution of the electron emission.

Spatial Distribution of Electron Emission

The electron emission from the front face of the target changes dramatically when gratings are used instead of flat foils. Figure 4.6 shows the spatial distribution of the electrons, as collected by the Lanex screen for two selected shots, respectively on a simple flat target and on a grating target at resonance. The emission from the flat foil is rather diffused, with a hole in correspondence of the specular reflection of the pulse. The signal reaches its maximum in a region around this hole. The ponderomotive force exerted by the reflected pulse on the electrons may be responsible for this feature. Instead, for a grating target irradiated at resonance, the emission is strongly localised at (close to the target tangent), with an intensity times larger than what observed for flat foil at the same angle. The angular aperture of this collimated electron bunch is .

Fig. 4.6The figure reproduces an acquisition with the Lanex screen for a simple flat target (top) and for grating target (bottom). Both targets were irradiated at pulse incidence. The Lanex screen was wrapped with an Al foil, in order to filter out electrons with energy MeV. The parabolic dashed lines in the pictures give the local angle corresponding to the position on the screen

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