Enhancement of ion generation in femtosecond ultraintense laser-foil interactions by defocusing

Xu, M. H. and Li, Y. T. and Carroll, D. C. and Foster, P. S. and Hawkes, S. and Kar, S. and Liu, F. and Markey, K. and McKenna, P. and Streeter, M. J. V. and Spindloe, C. and Sheng, Z. M. and Wahlstrom, C. -G. and Zepf, M. and Zheng, J. and Zhang, J. and Neely, D. (2012) Enhancement of ion generation in femtosecond ultraintense laser-foil interactions by defocusing. Applied Physics Letters, 100 (8). -. 084101. ISSN 0003-6951 (https://doi.org/10.1063/1.3688027)

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Abstract

A simple method to enhance ion generation with femtosecond ultraintense lasers is demonstrated experimentally by defocusing laser beams on target surface. When the laser is optimally defocused, we find that the population of medium and low energy protons from ultra-thin foils is increased significantly while the proton cutoff energy is almost unchanged. In this way, the total proton yield can be enhanced by more than 1 order, even though the peak laser intensity drops. The depression of the amplified spontaneous emission (ASE) effect and the population increase of moderate-energy electrons are believed to be the main reasons for the effective enhancement.