In order to position a laser beam in " two dimensions ", it is possible either to rotate one mirror along two axes-used mainly for slow scanning systems-or to reflect the laser beam onto two closely spaced mirrors that are mounted on orthogonal axes.
22.
Why is the solid angle element d ( omega ) equal to dl * dm / sqrt ( 1-l ^ 2-m ^ 2 ), where l and m are direction cosines with respect to two orthogonal axes ?-- talk ) 03 : 57, 18 May 2010 ( UTC)
