Enhancement of the reflectivity of a Ge crystal under irradiation with giant-pulse ruby laser light (a few MW) has been studied by using a He-Ne gas laser as the probe light. Instantaneous values of n and k of the complex index of refraction (n=n(1+ik) have been obtained separately by means of measuring the Stokes' parameters of the reflected probe light. The relative amplitude reflection coefficient, tan ψ=(ρ_p/ρ_s)^½, and the relative phase difference, δ=δ_p-δ_s, have been studied experimentally in relation to the angle of incidence of the probe light. All the experimental results have been explained fairly well on the basis of the theory proposed by the authors.