Stationary self-confined beams at 633 nm in Bi₁₂SiO₂₀ crystals

Self-confinement of light beams at the wavelength of 633 nm is presented for the first time in B12SiO20 (BSO) photorefractive crystals. The 633 nm wavelength is slightly absorbed in BSO, not enough for efficient photorefractive nonlinearity. However, superposing on the 633 nm beam a second beam at 514.5 nm, two-step absorption processes can generate a hot free-carrier population in the conduction band. If a bias voltage is applied, the conducting electric field, responsible for the current flowing inside the crystal, is spatially modulated according to the red-beam profile and a spatial modulation of the material dielectric constant occurs. Efficient self-trapping is demonstrated both from the theoretical and experimental points of view.