Speckle reduction

Speckle reduction apparatus includes a radiation path and a mask arranged within the radiation path. The mask includes an array of electrically controllable cells configured to form a pattern on the mask that varies with time. The speckle reduction mask includes a first linear array including first parallel lines arranged to change the phase of incident radiation, and a second linear array including second parallel lines arranged to change the phase of incident radiation and further arranged such that cells are formed at the intersections of the first parallel lines and the second parallel lines. The speckle reduction mask includes a N1×N2 array of cells, A, formed according to: ATA= δk,l, where AT is the transpose of A, is a real and positive constant, dk,l is Kronecker delta and N1≠N2.