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 CC D camera shows that the optical emission forms a ring, on the edge of the ring t here is a bright localized signal, which is the optical transition radiation (OT R). The optical emission spectrum shows a series of sharp nonperiodic peaks bet ween 300—500nm,obviously near 400nm(2ω). The sharp peaks are ascribed to the c oherent transition radiation (CTR) of hot electron-beam microbunching generated by v×B acceleration mechanism. The OTR intensity decreases with the increase of the target thickness.