We show that the group velocities of light pulses can be decelerated dramatically by the use of a dispersive phase-coupling effect through a wave mixing process.We have observed experimentally such a phase-coupling-induced ultraslow light propagation with a group velocity as low as 0.05m/s in a photorefractive Bi12SiO20 crystal at room temperature. Moreover, the ultraslow light is amplified in the Bi12SiO20 crystal because of the unidirectional energy transfer from a coupling beam to the ultraslow light. This technique to produce ultraslow light propagation is valid for all nonlinear wave mixing processes with a dispersive phase-coupling effect.

become as high as 36% and 3.1cm-1, respectively, below 120K. The results of holographic recording experiments are compared with measurements of the dielectric susceptance, electric conductivity, and absorption of acoustic waves to establish a relationship between the change in photorefraction and the temperature dependence of the dielectric and ultrasonic behavior. Iron doping of α-LiIO3 enhances the photorefraction considerably.

The photorefractive effect is investigated in nominally pure a-LiIO3 crystals within the 333-514.5 nmspectral range. In the temperature range of 180 K-240 K, i.e., the temperature range of the superionic phasetransition, a dramatic decrease of the diffraction efficiency by a factor 100 is observed. This can be explainedby the formation of an ionic complementary grating having an activation energy for thermal erasure of 0.3260.03 eV. Thermal fixing can be achieved by holographic recording at temperatures below about 180 K,developing the complementary grating at room temperatures, and finally recovering the complementary gratingbelow 180 K. In contrast to the assumptions made for the thermal fixing process in other crystals, e.g.,LiNbO3, the mobile ionic species in a-LiIO3 are mainly lithium ions.

We investigate UV photorefraction in Mg-doped LiNbO3 crystals. Strong UV photorefraction is achieved inhighly Mg-doped LiNbO3 crystals with high two-wave mixing gain, fast response, and low noise. It is alsodemonstrated experimentally that so-called damage-resistant dopants such as Mg are damage resistant only inthe visible and that they will enhance photorefraction in the UV.

We investigated the light-induced backward scattering in doubly doped lithium niobate crystals andobserved an intensity threshold effect. It will be shown that scattering microregions are locallyrecorded in the sample by holographic interaction due to the existence of the threshold effect.Experimental results of multilayer recording point out that this property could be used forhigh-density multilayer-like bit data optical storage while keeping high signal-to-noiseratio.