We have grown a very high finesse microcavity using distributed Bragg
reflectors of AlxGa1-xAs and AlAs. The measured Fabry-Perot mode has a
linewidth of 0.84 angstrom at 930 nm. This implies a finesse in exces
s of 5500 and an effective (mirror corrected) finesse greater than 145
0. Comparison with theoretical calculations for such a structure shows
that (i) the growth rates are stable to 0.25% over 14 h and (ii) the
internal losses are less than 1 cm-1. (C) 1994 American Institute of P
hysics.