Excitation-wavelength-dependent terahertz wave modulation via preformed air plasma

摘要

We report excitation-wavelength-dependent terahertz wave modulation via a preformed air plasma created by a synchronized 800-nm laser pulse traveling orthogonal to the pump pulses. With a preformed plasma, both the modulation depth of the terahertz energy and the change in terahertz wave polarization increase with the increasing excitation-laser wavelength. The results are well explained by the photocurrent model with a wavelength-dependent ionization rate. We also experimentally detect the refractive index of the two-color field changed by the preformed air plasma. These results improve our understanding of the theoretical mechanism and expand the practical applications of terahertz wave generation and modulation. Published by AIP Publishing.