Terahertz dependence on the laser phase and wavelength in two-color circularly polarized laser fields

Two-color circularly polarized laser fields with the same helicity (CP-S) are an appealing type of driving field that is essential for generating strong terahertz (THz) radiation. In this work, we theoretically investigate how the phase delay between two components in a CP-S field and their wavelength affect THz radiation yield with a photocurrent model. Simulations show that, as the laser wavelength increases, the THz yield becomes more and more phase dependent, which is maximized when the relative phase is 0 and minimized when the relative phase is π . Such a phase dependence is completely different from the commonly used two-color linearly polarized laser pulse with parallel polarizations (LP-P). In addition, in the CP-S field, the THz radiation energy may exhibit a wavelength scaling λ α ( λ is the fundamental wavelength) with a bigger exponent than in the LP-P field at longer wavelengths. Our findings have important implications for the generation of powerful THz radiation via femtosecond laser interaction with gasses.