Generation and modulation of fully circularly polarized ultrabroadband THz radiation using two-color gas plasma techniques

We present a single-arm method for generating circularly polarized THz radiation via two-color plasma, achieving a record ellipticity of 0.99. By optimizing the tilting and rotation angles of the BBO crystal, its position, and the chirp applied to the fundamental harmonic wave, we extend circular polarization up to 30 THz, which remains robust above 8 THz. Elaborating on this finding, we introduce two ultrafast THz modulators capable of dynamically controlling polarization, ellipticity, and energy of plasma-driven THz pulses. The first device, based on a Pockels cell, adjusts the polarization axis of the fundamental harmonic wave, while the second, using an acousto-optic beam deflector, finely tunes its incidence angle on the BBO crystal. These modulators enable rapid and precise manipulation of THz fields, paving the way for advancements in spectroscopy, adaptive sensing, and ultrafast photonic technologies.