Ultrahigh finesse microcavity with distributed Bragg reflectors

We have grown a very high finesse microcavity using distributed Bragg reflectors of AlxGa1−xAs and AlAs. The measured Fabry–Pérot mode has a linewidth of 0.84 Å at 930 nm. This implies a finesse in excess of 5500 and an effective (mirror corrected) finesse greater than 1450. 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.