High-finesse mid infrared microcavities based on lead salts

Microcavities for the mid-infrared range with very high quality factors were fabricated by molecular beam epitaxial growth of IV–VI semiconductor layers. The samples consist of PbTe/EuTe and Pb0.95Eu0.05Te/EuTe Bragg mirrors with three to five layer pairs rendering reflectivities well above 99%. The transmission spectrum of a View the MathML source cavity shows three Lorentzian shaped Fabry–Perot resonances in the mirror stop band, whereas a PbTe λ/2 microcavity exhibits one narrow resonance maximum at View the MathML source (View the MathML source) with a full-width at half-maximum of View the MathML source. This corresponds to a very high effective cavity finesse of 1100, which is to the best of our knowledge the highest value for the mid infrared spectral region.