Abstract
The observability of the quantum oscillation (Shubnikov-de Haas oscillation) in optical absorption and microwave absorption in metals or semimetals in the normal skin effect region is investigated for typical cases of relative directions of magnetic field and wave propagation. The unobservably small or observable but small quantum oscillation in most existing experimental results is reasonably understood from this study, while the existence of greatly enhanced quantum oscillation in both longitudinal and transverse magnetoreflections at the plasma reflection edge is predicted. Further it is also predicted that this purely quantum oscillation at the plasma edge should appear in Faraday rotation and Voigt phase shift with great amplitude.