Interaction of colliding laser pulses with gas plasma for broadband coherent terahertz wave generation

Colliding of two counter-propagating laser pulses is a widely used approach to create a laser field or intensity surge.We experimentally demonstrate broadband coherent terahertz(THz)radiation generation through the interaction of colliding laser pulses with gas plasma.The THz radiation has a dipole-like emission pattern perpendicular to the laser propagation direction with a detected peak electric field 1 order of magnitude higher than that by single pulse excitation.As a proof-of-concept demonstration,it provides a deep insight into the physical picture of laser–plasma interaction,exploits an important option to the promising plasma-based THz source,and may find more applications in THz nonlinear near-field imaging and spectroscopy.