Strong, tunable terahertz emission by two-color picosecond laser irradiation

It is shown by particle-in-cell simulations that powerful terahertz (THz) radiation can be generated by picosecond (ps) laser pulses below 1014W/cm2 via a two-color laser scheme. At such laser intensities, increasing the laser duration can result in significant enhancement in THz intensities. From 0.03 ps to 0.9 ps the enhancement climbs to nearly 40× before saturating until 2 ps. This demonstrates that low intensity, readily available ps laser technology could be utilized for driving powerful THz sources. By contrast, for laser intensities high enough to completely ionize the gas medium, it is found that the THz emission decreases with increasing pulse duration: optimal conversion is found for few-femtosecond drivers.