The lasing behavior of solution-based colloidal quantum dots within an open microcavity is reported. The small size and wide tunability of the cavity provide single mode lasing over a wavelength range in excess of 25 nm. By extracting the lasing threshold and differential gain for the fundamental cavity mode over this spectral range, gain spectroscopy of the quantum dot solution is demonstrated. This new approach could help in the optimization of laser gain media and provides a way of constructing miniature laser arrays for on-chip integration.
