We are exploring air wavelength references useful for interferometry. Femtosecond comb frequency measurements determine mode wavelengths of a stable optical cavity in vacuum, and subsequently a tunable laser is locked to the modes in air.
and Hollberg, L.
Wavelength References for Optical Interferometry, Proc. 2005 Conf. Lasers and Electro-Optics, Baltimore, MD, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=30063
(Accessed June 10, 2023)