EODs for kHz imaging

J. Schneider et al., and S. Hell recently published a paper on STED microscopy, using EODs (electro-optical deflectors) to scan 512 x 512 pixels at frame rates of 1000 Hz. Compared to AODs, EODs offer the costumer-friendly advantage of not dispersing the the spectral components of the laser beam. Their main weakness is a small deflection angle. In her thesis from 2012, Jale Schneider gives an overview of manufacturers of EODs:

Company deflection angle per kV [mrad] aperture [mm] capacity [pF]
Conoptics Inc. USA 7.8 2.5 180
NTT Photonics Laboratories, Japan 150 0.5 1000-2000
Leysop Ltd., GB 1.5 3 50
Leysop Ltd., GB 3 2 50
Leysop Ltd., GB 5 1 50
Quantum Technologies, USA 3.5 3 100
AdvR Inc., USA 24 < 0.8 < 100

For resonant scanning, the aperture is ~ 5 mm, the deflection angle 90-260 mrad (depending on resonant frequency).

The capacity of the crystal displayed in the table comes into play indirectly, with a smaller capacitance demanding less from the high-voltage driver system of the EOD. In the appendix of her thesis, Jale Schneider also gives an overview of commercial high-voltage driver systems, although for her work she custom-built one.

Maybe at some point, this will become interesting for voltage imaging in dendrites. Assume one could drive the Conoptics EOD with 5 kV, and let’s further assume a 60x objective (focal length of ca. 3 mm) and a scan lens/tube lens system with magnification 3x. Then one has a 7.5 mm diameter beam on the back focal plane, and a FOV in the sample of ca. (3 mm)/3*tan(5*0.0078 rad) = 40 μm. Such a system would be an alternative to the AOD-based approach, which was, for instance, used by Arthur Konnerth’s lab for kHz calcium imaging of dendritic spines (250 × 80 pixels, field of view = 28 × 9 μm, 40x objective).

[Update] It seems that this estimation is only approximately correct. As described in the thesis cited above, the Conoptics EOD can use the 2.5 mm aperture only for a non-deflected beam. It seems that even for a +- 7.2 mrad deflection, the maximum unclipped beam diameter is only 1.5 mm.

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