The optical losses in dry-etched monolithic microresonators have been studi
ed as a function of their lateral dimensions. Cylindrical microresonators w
ith various radii have been etched from a planar GaAlAs/GaAs microcavity wi
th a very high quality factor (Q congruent to 11 700). Measurements of the
resonance linewidth, using Ti-sapphire laser spectroscopy allowed to study
the degradation of the Q factor at small radii. The Q factor is four times
smaller in 1.1 mu m radius microresonators, compared to the unprocessed cav
ity. This degradation is attributed to optical scattering from sidewalls, w
hose efficiency is shown to scale with the guided mode intensity at the mic
roresonator edge. (C) 1999 American Institute of Physics. [S0003-6951(99)01
007-4].