The present invention relates to an optical scanner (300) for providing a deviation of electromagnetic radiation wherein the deviation varies in time, the optical scanner comprising at least a first Risley pair (100i) having a first pair of optical elements (105a, 105b) and a second Risley pair (100ii) having a second pair of optical elements (105c, 105d), wherein the optical elements (100a, 100b) in the first Risley pair are arranged to counter-rotate at a first rotation rate; and the optical elements (100c, 100d) of the second Risley pair are arranged to counter-rotate at a second rotation rate in a manner so that a desired time dependency of the deviation of the radiation is obtained.
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