The working principle is rather simple, really:

The key enabler for this project is the combination of cheap molded acrylic aspheres and cheap low-to-medium power 405nm laser diodes. These lenses have the optimal shape to collimate the laser emission from a miniature semiconductor laser inside the diode housing. They really do great things for that special case but they still work ok when not focused to infinity but rather at 25 to 50 mm. In this finite conjugate setup, the laser spot is focused along an arc as the laser diode and lens are moved relative to each other which makes the spot blurry as you move it farther to the left or right. While this may produce sub-100µm spots one can still do better by doing a few microns of refocusing, doing the initial focusing along the way.