Experimental observation on anomalous emission in Mg vapor

When the 3s3p ¹P level of an Mg atom is resonantly excited by a laser, an anomalous emission with a wavelength of 5184 Å can be observed, which corresponds to the transition for 3s4s ³S to 3s3p ³P ₂. According to the temporal behavior of this emission and its intensity dependence on atom density, it is believed that the experiment seems to show the transition from a spontaneous process to a cooperative process. The population inversion between 3s4s ³S and 3s3p ³P ₂ is created by inelastic collisions of the lower excited 3s3p ¹P atoms.