Fig. 1. Schematic layout of eight-channel THz calorimeter system.

Fig. 2. Linear response of the detector to energy of near-infrared and THz wavelengths.

Fig. 3. (a) Experimental setup of THz radiation spectrum measurement in ultra-intense laser–plasma interaction experiment. (b) Spectral sensitivity of the multichannel calorimeter system.

Fig. 4. (a) The measured BTR energy from a $5~\unicode[STIX]{x03BC}\text{m}$ copper target as a function of the pump laser energy. (b) The measured BTR spectrum with driven laser energy on target varying from 14 J to 54 J from a $5~\unicode[STIX]{x03BC}\text{m}$ copper target.

Fig. 5. (a) The measured BTR energy as a function of copper foil target thickness. (b) The measured BTR spectrum with copper foil target thickness varying from $1~\unicode[STIX]{x03BC}\text{m}$ to $100~\unicode[STIX]{x03BC}\text{m}$.

Fig. 6. (a) The measured BTR energy from a $100~\unicode[STIX]{x03BC}\text{m}$ copper target as a function of delay between pre-pulse and main pulse. (b) The measured BTR spectrum from a $100~\unicode[STIX]{x03BC}\text{m}$ copper target with different delays between pre-pulse and main pulse, no pre-pulse, 400 ps and 1000 ps, respectively.