Subrelativistic infrared and terahertz pulses from petawatt class laser interaction with complex nanodimensional targets

Abstract

Generating high-field infrared and terahertz radiation during interaction of a super-intense laser pulse with a complex nanodimensional target consisting of nanowires or nanofoils is studied. During interaction, dense bunches of electrons are extracted out of the target and accelerated in the laser field, generating intense electromagnetic radiation. Depending on the duration and shape of the laser pulse, three interaction modes can be realized. In the first mode, the laser pulse is smooth, and the electrons are only partially displaced from the target. In this case, a unipolar radiation pulse is generated with duration of about that of the laser pulse. In the second mode, the laser pulse is nonadiabatic with the amplitude of the first half-cycle about the maximum pulse amplitude. Here, most of the electrons are extracted from the target at the beginning of interaction, and unipolar and bipolar pulses with duration of dozens of laser periods can be generated. Changing the target geometry allows one to control the period and number of oscillations in the generated radiation. Finally, in the intermediate mode of short laser pulses with an insufficiently steep front, oscillations of the formed electron bunches may occur in the Coulomb field of ions, leading to radiation with a frequency several times lower than that of the laser. Using numerical simulation, the characteristics of infrared and terahertz radiation in three interaction modes are found. It is shown that the amplitude of generated radiation can reach subrelativistic values, and the intensity conversion efficiency can be about one percent. The advantages of using complex nanowire targets are elucidated. Such targets allow to generate a train of terahertz and infrared pulses with controlled delay between them.