Patent ID: 7777886

Claim:
An optical subsystem for cavity-enhanced spectroscopy, the optical subsystem comprising: a source of optical radiation providing a first beam of optical radiation; a strong focusing element disposed to receive the first beam of optical radiation and to provide a second beam of optical radiation; an optical resonator receiving the second beam, wherein the optical resonator has a lowest order mode and also has one or more higher order modes distinct from the lowest order mode; a weak focusing element disposed on a path of the second beam between the strong focusing element and the optical resonator, wherein a magnitude of an optical power of the weak focusing element is substantially smaller than a magnitude of an optical power of the strong focusing element, and wherein the combination of the strong focusing element and the weak focusing element provides an exact or approximate mode match between the second beam and the lowest order mode of the optical resonator; a translation plate disposed on the path of the second beam between the strong focusing element and the optical resonator; wherein positions and angles of the weak focusing element and translation plate are fixed during assembly of the optical subsystem to minimize or approximately minimize excitation of the higher order modes of the optical resonator by the second beam while coupling the second beam to the lowest order mode.