  Measured and calculated results are presented on the emission properties of a
new class of emitters operating in the cavity quantum electrodynamics regime.
The structures are based on high-finesse GaAs/AlAs micropillar cavities, each
with an active medium consisting of a layer of InGaAs quantum dots and
distinguishing feature of having substantial fraction of spontaneous emission
channeled into one cavity mode (high-beta factor). This paper shows that the
usual criterion for lasing with a conventional (low-beta factor) cavity, a
sharp nonlinearity in an input-output curve accompanied by noticeable linewidth
narrowing, has to be reinforced by the equal-time second-order photon
autocorrelation function for confirming lasing. It will also show that the
equal-time second-order photon autocorrelation function is useful for
recognizing superradiance, a manifestation of the correlations possible in
high- microcavities operating with quantum dots. In terms of consolidating the
collected data and identifying the physics underlying laser action, both theory
and experiment suggest a sole dependence on intracavity photon number. Evidence
for this comes from all our measured and calculated data on emission coherence
and fluctuation, for devices ranging from LEDs and cavity-enhanced LEDs to
lasers, lying on the same two curves: one for linewidth narrowing versus
intracavity photon number and the other for g(2)(0) versus intracavity photon
number.
