Self-diffraction of frequency-modulated light in the Bi$_{12}$TiO$_{20}$ crystal

The self-diffraction of frequency-modulated light in the photorefractive Bi$_{12}$TiO$_{20}$ crystal was studied experimentally. To observe the effect, the crystal was illuminated by two light beams with the relative frequency shift $\Delta f(t)$. In the experiments, linear frequency modulation was used: $\Delta f(t)=At$. As a result of the light self-diffraction on a hologram moving with a constant acceleration, the power of the light beams at the crystal output changed in the form of a chirp pulse. It was found that the pulse appears at the instant of stopping the interference pattern, and its duration is determined by the rate of frequency change $A$ and the hologram recording time $\tau_{sc}$.