Definition of etalon in English:

etalon

noun

Physics
  • A device consisting of two reflecting glass plates, employed for measuring small differences in the wavelength of light using the interference it produces.

    • ‘The change in resonance frequency of the etalon measures the change in optical-path length.’
    • ‘We specialize in very large aperture etalons with diameters up to 150 mm.’
    • ‘Our products range from simple condenser lenses to precision etalons.’

Origin

Early 20th century: from French étalon, literally standard of measurement.

Pronunciation:

etalon

/ˈɛtəlɒn/