Brother HL-5340D Service Manual page 51

(2) Exposure
The laser beam radiated from a laser diode inside the laser unit is concentrated into a
constant width by a slit in the CO lens cell and then reflected by a polygon mirror rotating at
high speed. The evenly charged exposure drum is irradiated with reflected light and exposed.
Surface potential is lowered by such exposure and a printed image is formed.
Laser diode CO lens
Polygon mirror
Laser unit
Exposure drum
Fig. 2-16
2-18 Confidential