Study of two color THz generation with sub-and terawatt laser filament at low pressure gas

THz generation under two-color four-photon interaction of femtosecond TiSa laser radiation in a low-pressure nitrogen at sub-and terawatt power levels has been studied. Method for characterizing the parameters of a femtosecond filament formed in a low-pressure gas based on the average ablation rate and X-ray output from a solid-state target interacting with the filament was developed. In sub-terawatt laser power it was found that under the condition P/Pcr=const, the pressure decrease and the energy increase within 10 times correspond to enhance in the average ablation rate by 2 times and an increase in the fluence and intensity by about 3 times. Under terawatt laser power, energy density in the filament is about 15 J/cm2, the intensity is 2.5*1014W/cm2, and the THz signal reaches a maximum at a nitrogen pressure of 10 mbar (this corresponds to the 3Pcr regime) and is of the order of 1300 nJ.