Experimental study of optical emission from the rear surface in ultrashort ultra-intense laser interaction with solid targets

Optical emission generated by hot electrons passing through solid targets is measured from the rear surface of a metallic foil. The integrated image taken by CCD camera shows that the optical emission forms a ring, on the edge of the ring there is a bright localized signal, which is the optical transition radiation ( OTR). The optical emission spectrum shows a series of sharp nonperiodic peaks between 300-500nm, obviously near 400nm(2 omega). The sharp peaks are ascribed to the coherent transition radiation (CTR) of hot electron-beam microbunching generated by v x B acceleration mechanism. The OTR intensity decreases with the increase of the target thickness.