Ultra-high-finesse IV–VI microcavities for the midinfrared

IV–VI semiconductor-based midinfrared microcavities with very high-quality factors were grown by molecular-beam epitaxy. The structures consist of PbTe/EuTe Bragg mirrors with three to five layer pairs rendering reflectivities in excess of 99.7%. The PbTe resonator layer between the reflectors has an optical length of λ/2, which yields a first-order cavity. The transmission spectra of the microcavities show a very narrow Lorentzian-shaped Fabry–Perot resonance at 1877 cm−1 (λ=5.32 μm) with a full width at half maximum of 0.63 cm−1 78 μeV. This corresponds to an ultrahigh effective cavity finesse of 1700.