Tunable Circularly Polarized Terahertz Radiation from Magnetized Gas Plasma

It is shown, by simulation and theory, that circularly or elliptically polarized terahertz radiation can be generated when a static magnetic (B) field is imposed on a gas target along the propagation direction of a two-color laser driver. The radiation frequency is determined by $\sqrt{{\omega }_p^2+{\omega }_c^2\mathrm{/}4}+{\omega }_c\mathrm{/}2$, where ${\omega }_p$ is the plasma frequency and ${\omega }_c$ is the electron cyclotron frequency. With the increase of the B field, the radiation changes from a single-cycle broadband waveform to a continuous narrow-band emission. In high-B-field cases, the radiation strength is proportional to ${\omega }_p^2\mathrm{/}{\omega }_c$. The B field provides a tunability in the radiation frequency, spectrum width, and field strength.