Decrease in Spontaneous Emission at the Onset of Lasing in Semiconductors

It has been shown experimentally that spontaneous emission in semiconductors decreases at the onset of lasing. This has been observed qualitatively by a visual method in CdS and GaAs lasing in a total internal-reflection cavity under electron-beam pumping. More quantitative observations have been made on CdSe and CdS optically pumped by a HeNe laser and Argon laser, respectively. The decrease in spontaneous emission occurs across the entire spectrum. It seems reasonable to believe that this decrease also occurs in Fabry-Perot cavities. No explanation for the new phenomenon has been found and it seems to be inconsistent with earlier published theory suggesting that the spontaneous emission should saturate after lasing sets in.