This video explains the laser beam deflection principle of Leica Microsystems‘ laser microdissection systems (Leica LMD). The laser, the beam expander, motorized attenuator, motorized iris diaphragm for limiting the aperture for cutting and the scan unit are situated in the instrument’s special incident light axis. The scan unit consists of two prism wedges whose thickness and wedge angle are chosen so that the laser beam, after passing through the two prism wedges, is directed precisely through the center of the back focal plane of the objective.
The two prism wedges can be rotated independently of each other round the laser axis by motor control, so that it is possible to set any angle of entry into the objective and therefore reach various points of the sample with the laser. Due to this telecentric imaging of the collimated laser beam through the center of the back focal plane, the focused beam always hits the surface of the sample perpendicularly.