In an optically pumped semiconductor disc laser, which is always with a multiple layer active region and a large spot size, the spontaneous emission of quantum wells will be trapped by the waveguide caused by the multiple layer, travel a long excited distance relative to the surface-emitting mode and be subsequently amplified. Here we demonstrate a new mechanism for the amplified spontaneous emission (ASE): the etalon effect of the sub-cavity formed by the bottom distributed Bragg reflector and the top airsemiconductor interface. The spectral characteristics of this ASE including its temperature dependence, pump power dependence and observing angle dependence are experimentally studied, and the results are in good agreement with the theoretical model.
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