Abstract

As the volume of a microlaser approaches a cubic wavelength in the material and the resonator is constructed so that a large fraction β of the spontaneous emission from the gain region is emitted into the lasing mode, the threshold for lasing, as measured by a sharp increase in the light emitted from the lasing mode as a function of pump power, begins to vanish. At β = 1 the laser appears to be thresholdless because the input/output light curve is a straight line with no threshold kink.¹ However, it has been argued² that in this limit there are still properties of the cavity light output that distinguish a threshold when there is of the order of one photon in the cavity averaged over time. One good in dicator of the threshold phenomena is the level of amplitude fluctuations in the light output. There are large amplitude fluctuations in a low-β laser near threshold that indicate a transition to the coherent state of the light field. Theoretical models³ show that in some cases these amplitude fluctuations nearly disappear in the limit of β, resulting in a very nearly thresholdless laser. We address this question of thresholdless lasing by studying a series of microdisk lasers⁴ for which β varies between 0.04 and 0.2. Similar studies⁵ have been made by using vertical-cavity lasers with a lower β value.

© 1995 Optical Society of America