  We demonstrate dynamic and arbitrary multisite two-photon excitation in three
dimensions using the holographic projection method. Rapid response (fourth
dimension) is achieved through high-speed noniterative calculation of the
hologram using a video graphics accelerator board. We verify that the projected
asymmetric spot configurations have sufficient spatiotemporal photon density
for localized two-photon excitation. This system is a significant advance and
can be applied to time-resolved photolysis of caged compounds in biological
cells and complex neuronal networks, nonlinear microfabrication and volume
holographic optical storage.
