  We demonstrate fluorescence imaging by two-photon excitation without scanning
in biological specimens as previously described by Hwang and co-workers, but
with an increased field size and with framing rates of up to 100 Hz. During
recordings of synaptically-driven Ca$^{2+}$ events in primary rat neurone
cultures loaded with the fluorescent Ca$^{2+}$ indicator Fluo-4 AM, we have
observed greatly reduced photo-bleaching in comparison with single-photon
excitation. This method, which requires no costly additions to the microscope,
promises to be useful for work where high time-resolution is required.
