Energy spectrum of ions generated by femtosecond laser and plasmas interaction at the back-side of target

In the ultra-short and ultra-intense laser interaction with 7 μm Cu target, we use CR39 and Thomson spectrometer to detect the energy spectrum of protons and carbon ions at the normal direction of target back. Protons, C 4+, C 3+, C 2+ and C 1+ ions have been observed experimentally. In addition, the results show that the ions are emitted along the target rear-side normal direction and the ions were cut-off at a certain energy. What is more, the yield of proton is much higher than the one of carbon ions, and the ratio of the maximum cut-off energy of the C 4+, C 3+, C 2+ and C 1+ ions is about 4: 3: 2: 1.