New optical probe of GHz polarization dynamics in ferroelectric thin films

We describe a method for measuring the response of ferroelectric thin films to microwave-frequency electric fields. A mode-locked Ti:sapphire laser is used to generate a microwave drive signal that is phase locked to an optic al probe pulse. The induced polarization change in the ferroelectric film i s measured stroboscopically via the electro-optic effect. Images are acquir ed by scanning the laser beam across the sample in a confocal geometry. Tim e resolution is achieved by changing the delay between the electrical pump and the optical probe. Initial results show large local phase shifts in the ferroelectric response of closely separated (1 mu m) regions of a Ba0.5Sr0 .5TiO3 thin film. This new experimental technique may help to understand th e physical mechanisms of dielectric loss in these materials. (C) 1999 Ameri can Institute of Physics. [S0034-6748(99)00809-6].