Instead of galvanometric mirrors, the AODscope (Karthala System) employs a pair of AODs to deflect and shape the excitation beams. Mechanical movements being absent, the AODs can switch between different excitation points in much shorter times than mechanical mirrors (twenty microseconds). Microscopes based on this technology are called random access multiphoton microscopes (RAMP) [1], because they can scan spatially non-connected ROIs. The AODscope at the INT has two sets of AOD pairs, which thus constitute two independent excitation paths.

One path (3D) employs a 50 kHz tunable femtosecond laser source (Mango, Amplitude), which allows to target neurons within a 3D volume at a rate of up to 25 kHz per neuron. This method, called three-dimensional Custom Access Serial Holography (3D-CASH) [2], is ideal for high-speed 3D recording of calcium signals in awake animals, as the excitation modality eliminates motion artefacts and corrects for the neuropil fluorescence.

The other excitation path (2D) uses an 80 MHz laser (Coherent Discovery) and is suitable for fast 2D imaging (at a speed comparable to that of resonant scanners) and for targeting excitation points or small volumes (axial extension of few tens of micrometers) on the focal plane. A custom random-access modality called ULoVE (Ultrafast Local Volume Excitation) works particularly well for in-vivo recording of GeVIs [3], enabling researchers to perform direct optical measurement of changes in the membrane potential of the GeVIs-expressing cells.

[1] Duemani Reddy, Gaddum, et al. "Three-dimensional random access multiphoton microscopy for functional imaging of neuronal activity." Nature neuroscience 11.6 (2008): 713-720.

[2] Akemann, Walther, et al. "Fast optical recording of neuronal activity by three-dimensional custom-access serial holography." Nature Methods 19.1 (2022): 100-110.

[3] Liu, Zhuohe, et al. "Sustained deep-tissue voltage recording using a fast indicator evolved for two-photon microscopy." Cell 185.18 (2022): 3408-3425.