A laser scanning microscope is a special light microscope which uses a focused laser beam to scan a sample. The scanning of the laser across the sample is done by driving the laser in the x and y directions.  The image is composed in software by combining the measured light points.

The microscope is build from two DVD pick-up heads. The laser of the DVD head is used to illuminate the sample at a tiny spot, focused with the DVD head’s own focusing mechanism.

The resolution of the image is defined by the number of measurements taken in x direction and the number of lines in y. The maximum resolution is limited by the numerical aperture of the system’s objective lens and the wavelength of the laser as in conventional optical microscopes. In fluorescence observations, the resolution is often limited by the strength of the signal. More sensitive photo-detectors or increasing the intensity of the illuminating laser can compensate.

See the article here for details with schematics here.