Transition radiation from rear surface of solid targets irradiated by ultraintense laser pulse

The spatial pattern and spectrum of transition radiation have been measured at the normal direction from the rear surfaces of targets, employing an optical CCD camera and an OMA optical multichannel spectrometer on the 100 TW femtosecond laser facility.The spatial pattern presents a cirque shape, and the region of optical radiation has larger radiation angle and optical intensity distribution. The spectrum of transition radiation presents a sharp peak in the vicinity of 800 nm, which is the laser basic harmonic. That is the result of the coherent transition radiation generated by microbunches of hot electron beams produced in transport. The main acceleration of hot electrons comes from resonance absorption．