Nonlinear effects in thermal fixing of photorefractive holograms: harmonics and combinationalgratings - Limeres J; Carrascosa M; de la Cera EG; deMiguel-Sanz EM; Arizmendi L (Photorefractive Effects, Materials, And Devices 2001 (Osa Trends In Optics And Photonics Series), 2001)