Collinear Bragg diffraction in photorefractive Bi(12)SiO(20)

We demonstrate the possibility of collinear Bragg diffraction in photorefractive Bi(12)SiO(20) (BSO) crystals of two incident writing and readout beams of different wavelengths. Two grating wave vectors K(1) and K(2) are created by interference of independent and collinear beams at wavelengths lambda(1) and lambda(2). In the photorefractive medium the nonlinearities of the photoinduced space-charge field generate the new grating wave vectors K(NL) = mK(1) +/- nK(2). Bragg diffraction is thus achieved at a readout wavelength lambda(R) such as 1/lambda(R) = (m/lambda(l)) +/- (n/lambda(2)). The proposed method permits quasi-nondestructive readout of a phase-volume grating in BSO at lambda(R) = 840 nm (semiconductor laser) while recording is done by interference of two incident and collinear beams at lambda(1) = 632.8 (He-Ne laser) and lambda(2) = 514.5 (Ar laser).