Measurement of transition radiation in femtosecond laser-solid target interaction

For rearching the acceleration mechanism of hot electron, the integrated image pattern and spectrum of optical transition radiation (OTR) were measured at the normal direction from the rear side of targets employing optical CCD camera and OMA optical multi-channel spectrometer. The experiment was carried out on the 100 TW laser. The measured integrated image pattern presents a ring-shape of about 225 μm in diameter. In the near edge of the ring-shape there is a bright localized signal, which indicates a filament effect exists during hot electron transportation. The spectrum presents a series of nonperiodic sharp peaks between 300～500 nm, which is attributed to the coherent transition radiation (CTR) of hot electron generated by v×B acceleration mechanism near 400 nm(2ω0).