Wavelength Scaling of Terahertz Wave Absorption via Preformed Air Plasma

Two-color laser mixing in gases can result in the emission of broadband, single-cycle terahertz (THz) pulses. In this study, we find that THz wave absorption is observed when the THz wave and preplasma beam are focused on the same point, and that the wavelength of the preplasma beam can influence the absorption. The experimental results reveal that the THz wave absorption becomes less pronounced with increasing preplasma wavelength. We found that the absorption decreased sharply at a wavelength of 1400 nm, which may be related to the preplasma density, and the preplasma fluorescence profiles were measured using a charge-coupled device arrangement to prove our conjecture. In addition, the full-width at half-maximum of the frequency of the THz wave becomes broadened during absorption. The experimental results agree well with our presented model.