Saturation effects in photorefractive lithium niobate

The saturated photorefractive phenomenon is investigated in lithium niobate. Time fluctuations associated with the process having a characteristic duration of a few seconds are produced with focused laser beams at power densities of a few hundred watts/cm2. Below the turbulence limit, the time variations of the refractive index can be fitted to an exponential cosine autocorrelation function.A new method is described which makes it easy to study the static, optically induced, refractive index inhomogeneities as a function of temperature. Activation energy values of 0.98 ± 0.02, 0.22 ± 0.01 and 0.36 ± 0.01 eV. are obtained by this method and agree with data found in the literature for the unsaturated regime.A Data Acquisition System is used to record the temporal changes in the refractive index on magnetic tape. As the temperature is slowly varied from 27°C to 70°C, the corresponding power spectra show the evolution of a pronounced envelope.