Theory of beam coupling and pulse shaping of mode-locked laser pulses in a photorefractive crystal

We describe how optical beams from a mode-locked laser will couple in a photorefractive crystal. We show that the two-beam-coupling gain coefficient is proportional to the square of the electric field correlation of the incoming light pulses. Consequently we show that two-beam-coupling experiments can measure the average coherence length of mode-locked laser pulses. We also describe how the temporal envelopes of the mode-locked optical pulses distort as they couple and propagate through the photorefractive crystal, and we give examples of how pulses can be shaped by using photorefractive coupling.