It is found that there is an upper-limit critical power for self-guided propagation of intense lasers in plasma in addition to the well-known lower-limit critical power set by the relativistic effect.Above this upper-limit critical power,the laser pulse experiences defocusing due to expulsion of local plasma electrons by the transverse ponderomotive force.Associated with the upper-limit power,a lower-limit critical plasma density is also found for a given laser spot size,below which self-focusing does not occur for any laser power.Both the upper-limit power and the lower-limit density are derived theoretically and verified by two-dimensional particle-in-cell simulations.The present study provides new guidance for experimental designs,where self-guided propagation of lasers is essential.
Terahertz (THz) radiation has attracted much attention due to its wide potential applications. Though radiation can be generated with various ways, it is still a big challenge to obtain strong tabletop sources. Plasma, with the advantage of no damage limit, is a promising medium to generate strong THz radiation. This review reports recent advances on strong THz radiation generation from low-density gases and high-density solid targets at different laser intensities.
