Spatial characterization of 0.5 MeV proton beam, driven by 12 fs, 35 mJ, 1019 W/cm2 intense laser-foil interaction is presented. The accelerated proton beam has been applied to obtain a high-resolution, point-projection static radiograph of a fine mesh using a CR-39 plate. The reconstruction of mesh edge blurring and particle ray tracing suggests that these protons have an effective source size (FWHM) of just 3.3 ± 0.3 µm. Furthermore, the spatial distribution of the proton beam recorded on the CR-39 showed that the divergence of these particles is less than 5-degree (FWHM). The low divergence and small source size of the proton beam resulted in an ultralow transverse emittance of 0.00032 π-mm-mrad, which is several orders of magnitude smaller than that of a conventional accelerator beam.

The calibration of an ion detection system was carried out for protons and carbon ions from a few tens of keV up to about 1 MeV energies. A Thomson spectrometer deflecting the particle beam accelerated from a laser plasma creates the ion spectra on a phosphor screen behind a micro-channel plate (MCP), which are recorded by a camera. During calibration, the ion spectra simultaneously hit the slotted CR-39 track detector installed in front of the MCP and, passing through the adjacent CR-39 stripes, the MCP. The calibration provides the ratio of the interpolated values between two consecutive stripes of the camera signal and the total number of particles recorded on the corresponding stripe of CR-39. The efficiency of proton detection by CR-39 was also measured in a conventional accelerator beam and found to drop by 20% below 100 keV.

Spatial characterization of proton beam, driven by 12fs, 35mJ, 1019 W/cm2 intense laser-foil interaction is presented. Measurement shows low divergence (3.8-degree), small source size (< 4.5 µm) and 0.00038 π-mm-mrad normalized emittance of proton beam.