ИСТИНА

Engineering ultrashort pulses from infrared and terahertz bands is considered. During superintense laser pulse interaction with nanostructured target, dense high-charge bunches of electrons are forced out of the target and accelerated in the laser field, generating intense electromagnetic radiation. Three interaction modes can be realized. In the first mode, the laser pulse is smooth so the electrons are partially displaced from the target. Here, characteristics of the low-frequency part of the generated radiation are determined by the laser and target parameters. In the second mode, the laser pulse has large amplitude and steep front, then, most of the electrons are displaced from the target at the beginning of interaction. In this mode, unipolar and bipolar pulses with duration of tens of laser periods can be generated. Changing the target geometry allows one to control the duration of the period and the number of the periods in the generated radiation. Finally, in the intermediate mode (short laser pulses with insufficiently steep front) electron bunches can oscillate in the field of ions, producing radiation with lower frequency than the laser one. Using numerical simulations, characteristics of generated pulses are found. Choosing appropriate nanostructure of the target, the shape of the generated pulse can be engineered and a train of such pulses with controlled delay between them can be produced. It is shown that in modern laser installations, the radiation amplitude can reach subrelativistic values, and the conversion efficiency can be about one percent. The study was supported by RFBR project 19-52-45035-Ind-a.