A system where excitation and observation are from the same face of the sample (α ∠ 90°, β ∠ 180° where α = angle of incidence of the exciting beam on the plane surface of the sample, and β = angle between the exciting direction and observation direction.)
Source:
PAC, 1984, 56, 231. 'Nomenclature, symbols, units and their usage in spectrochemical analysis-Part VI: molecular luminescence spectroscopy' on page 244 (https://doi.org/10.1351/pac198456020231)