Study of X-ray emission enhancement via a high-contrast femtosecond laser interacting with a solid foil

We observed the increase of the conversion efficiency from laser energy to Kα x-ray energy (ηK) produced by a 60 fs frequency doubled high-contrast laser pulse focused on a Cu foil, compared to the case of the fundamental laser pulse. ηK shows a strong dependence on the nonlinearly modified rising edge of the laser pulse. It reaches a maximum for a 100 fs negatively modified pulse. The hot electron efficient heating leads to the enhancement of ηK. This demonstrates that high-contrast lasers are an effective tool for optimizing ηK, via increasing the hot electrons by vacuum heating.