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.)