front surface geometry

in luminescence
A system where excitation and observation are from the same face of the sample (\(\alpha\ \angle\ 90^{\,\unicode{x26ac}}\), \(\beta\ \angle\ 180^{\,\unicode{x26ac}}\) where \(\alpha \) = @A00346@ of incidence of the exciting beam on the plane surface of the sample, and \(\beta \) = @A00346@ between the exciting direction and observation direction.)
PAC, 1984, 56, 231. (Nomenclature, symbols, units and their usage in spectrochemical analysis-Part VI: molecular luminescence spectroscopy) on page 244 [Terms] [Paper]