An optical device includes an electro-optical layer and conductive electrodes disposed over opposing first and second side of the electro-optical layer. Control circuitry is configured to apply at least first control voltage waveforms and second control voltage waveforms between the conductive electrodes so as to generate respective first and second phase modulation profiles in the electro-optical layer, which cause rays of optical radiation that are incident on the device to converge or diverge with respective first and second focal powers, and to change from the first focal power to the second focal power by concurrently applying overshoot control voltages to each of a plurality of the conductive electrodes for different, respective transition periods, followed by application of the second control voltage waveforms.