1ST-ORDER PHASE-TRANSITION IN A LASER THRESHOLD

A mechanism for achieving a first-order phase transition in the threshold characteristics of a laser is discussed, and data demonstrating the effect are presented. It is suggested that a first-order phase transition can be realized through the design of a laser active region if the gain medium is localized to a spatial region with longitudinal dimensions much less than the wavelength of the resulting laser light. Evidence of the first-order phase transition is presented in the spontaneous emission characteristics of a microcavity semiconductor laser, which shows a decrease in the separation energy of the quasi-Fermi levels at threshold, along with hysteresis in the light versus current characteristics.