High intensity, monochromatic THz emission from obliquely colliding laser pulses in a plasma

Terahertz emission from plasmas driven by short-duration laser pulses appears mostly as a wideband, burst of a few cycles, as the emission mechanism is determined by the generation of transient current of comparable duration with the driving pulses. In that case, control of the emission spectra is relatively difficult compared to other mechanisms that use oscillating currents. Previously we proposed a novel mechanism of generating terahertz emission using a plasma dipole oscillation (PDO) [1-3], that is generated by collision of two detuned, short laser pulses. As the emission utilizes the plasma oscillation, the spectrum is narrow and frequency is readily controllable. Here, we discuss several new aspects of PDO-based emission: increased efficiency by obliquely colliding, long laser pulses, control of high harmonics generation by driving pulse shape, and mixture of dipole and quadrupole emission with different polarizations in a magnetized condition. We discuss how those features of PDO can be relevant to astrophysical radio bursts and plasma diagnostics as well as strong light sources in the terahertz band.