Generating High Efficiency Terahertz Radiation From Relativistic Nano-Bunches in the Interaction of Ultrarelativistic Lasers With Thin Solid Targets

The interaction of femtosecond laser pulses with thin solid targets is one of the most efficient methods to obtain terahertz (THz) radiation. In the specific conditions, the electron of plasma surface distribution became so localized and nano-bunches are formed which causes coherent synchrotron emission (CSE). In this mechanism which occurs when the relativistic laser is obliquely incident on plasma, the plasma electrons gather in a very dense and thin layer of nanometer width. The electrons of nano-bunch can emit intense coherent emissions in different ranges of electromagnetic radiation. In this study, producing high-efficiency THz radiating from relativistic nano-bunches is discussed. The effect of plasma and nano-bunch parameters, the mobility of ions, the initial thermal velocity of electrons, and the speed of electrons are investigated. According to the results, the direct relation between the width of the nano-bunch and the efficiency is seen. The nonlinear relation between the initial thermal velocity of electrons and the THz yield is seen. In the desirable conditions, a high THz yield of up to 37% is obtained from nano-bunches with the initial thermal velocities as 0.3 of light speed.