| CPC G02B 7/1821 (2013.01) [G01M 1/36 (2013.01); G02B 26/0816 (2013.01)] | 20 Claims |

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1. A method of balancing a mirror unit for a laser deflection device, wherein the mirror unit comprises:
a mirror for deflecting a laser beam, wherein the mirror extends in a mirror plane parallel to a first direction and to a second direction perpendicular to the first direction;
a rotor for rotating the mirror around a rotation axis parallel to the first direction; and
a mirror holder holding the mirror to the rotor; and
wherein the method comprises modifying a mass distribution of the mirror unit in said mirror plane or in a balance plane containing said rotation axis, by arranging one or more balancing weights on the mirror unit, wherein a centre of mass of the one or more balancing weights is arranged in said mirror plane or in said balance plane;
wherein modifying a mass distribution of the mirror unit in said mirror plane or in said balance plane by arranging the one or more balancing weights on the mirror unit comprises:
deflecting a laser beam with the mirror on a laser beam position sensor, wherein the laser beam position sensor registers a position of the deflected laser beam on the laser beam position sensor as a position signal, rotating the mirror unit around the rotation axis, thereby causing a translation of the position signal in a first sensing direction corresponding to said rotation; and
measuring a deviation of the position signal in a second sensing direction perpendicular to the first sensing direction; and
configuring the one or more balancing weights such as to reduce or eliminate the measured deviation of the position signal in the second sensing direction.
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