Laser-to-proton energy transfer efficiency in laser-plasma interactions

It is shown that the energy of protons accelerated in laser-matter interaction experiments may be significantly increased through the process of splitting the incoming laser pulse into multiple interaction stages of equal intensity. From a thermodynamic point of view, the splitting procedure can be viewed as an effective way of increasing the efficiency of energy transfer from the laser light to protons, which peaks for processes having the least amount of entropy gain. It is predicted that it should be possible to achieve $\apprge 100$ increase in the energy efficiency in a six-stage laser proton accelerator compared to a single laser-target interaction scheme.