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Opaque lens

Normally (a) a wavefront in a laser beam would scatter in all directions as it passes through an opaque sample, producing a speckled pattern of light on a screen. But in Mosk and Vellekoop’s technique (b) the wavefront is split into segments, and the phase each of these is altered to pre-empt the scattering so that they all arrive at a single point in-phase.

The trick is to know how the “complex amplitude” of each segment’s field will be affected as it passes through the sample. Without altering any, these amplitudes - the thick arrows in (c) - will all add randomly so that much of the total field cancels-out. But by even altering the phase of just one segment - the short dashed arrow - this destructive effect can be reduced (d). (Credit: Ivo Vellekoop and Allard Mosk)