Study of backward terahertz radiation from intense picosecond laser-solid interactions using a multichannel calorimeter system

A multichannel calorimeter system is designed and constructed which is capable of delivering single-shot and broad-band spectral measurement of terahertz (THz) radiation generated in intense laser-plasma interactions. The generation mechanism of backward THz radiation (BTR) is studied by using the multichannel calorimeter system in an intense picosecond laser-solid interaction experiment. The dependence of the BTR energy and spectrum on laser energy, target thickness and pre-plasma scale length is obtained. These results indicate that coherent transition radiation is responsible for the low-frequency component (<![CDATA[${ 1 THz) of BTR. It is also observed that a large-scale pre-plasma primarily enhances the high-frequency component (}$]]> 3 THz) of BTR.