The transport of intensity (TIE) technique allows for label-free quantitative phase imaging by acquiring two or more images from different focal planes. However, current TIE systems can be limited in speed or accuracy by methods used for the control and selection of the focal planes. Here, we introduce a novel microscope that combines an acousto-optic liquid lens (TAG lens) with illumination engineering to achieve precise electronic defocus control, indistinguishable from traditional mechanical defocusing, at microsecond timescales. Such high speed enables phase-imaging of dynamic events, including an evaporating droplet or a moving microorganism, at diffraction-limited resolution and rates of up to 150 Hz.
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