Doppler-free two-photon spectroscopy

Doppler-free two-photon spectroscopy

[däp·lər ‚frē ¦tü ¦fō‚tän spek′träs·kə·pē]
(spectroscopy)
A version of Doppler free spectroscopy in which the wavelength of a transition induced by the simultaneous absorption of two photons is measured by placing a sample in the path of a laser beam reflected on itself, so that the Doppler shifts of the incident and reflected beams cancel.
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