R. M. Pierce

Measuring photorefractive trap density without the electro-optic effect.

Two optical beams can couple in a photorefractive crystal without using the electro-optic effect. Beam coupling is due to a spatially modulated absorption caused by the rearrangement of trapped charges. We use these gratings to determine the effective photorefractive trap density for several barium titanate crystals.

Measurement of the photorefractive phase shift.

We present a method to separate the effects of trap gratings and electro-optic gratings in BaTiO(3) crystals, and we determine the true spatial shift between the electro-optic grating and the optical intensity pattern. At small beam-crossing angles this spatial shift is strongly affected by a photogalvanic current in the crystal.

Measuring the coherence length of mode‐locked laser pulses in real time

We demonstrate a new technique for displaying the electric field autocorrelation function of a laser pulse in real time, using two‐beam coupling in a photorefractive crystal. This technique does not require phasematching, is simple to align, and can be used over the entire visible and near‐infrared regions of the spectrum, even with weak laser beams.

Photorefractive coupling between orthogonally polarized light beams in barium titanate.

In certain crystals, photorefractive two-beam coupling is predicted for orthogonally polarized optical beams. The prediction follows from the phenomenological tensor form of the photogalvanic current. We demonstrate this coupling by measuring the complex beam-coupling coefficient in barium titanate and show that the photogalvanic current correctly predicts the form for the coefficient as a function of the beam crossing angle.