The relaxation oscillation of the amplified spontaneous radiation pulses emitted from a single-mirror Cu/CuBr laser has been observed for the first time and the experimental characteristics of the relexation oscillation were obtained. In addition, the spatial and temporal distributions of the light pulse intensity of the amplified spontaneous radiation were also measured and found to be oomparativel yuniform. The spatial coherence of the amplified spontaneous radiation was found to be better than that of the laser with the same lasant.