How does beam shaping (collimation) of a laser diode work?

A bare laser diode emits a strongly divergent, elliptical beam – the bare diode does not produce a usable spot but rather a fanned-out cone. For practical use the beam must be collimated – reshaped into a parallel, directed beam. Standard solution: a collimator lens directly in front of the diode, mounted in an M9 × 0.5 housing (brass or aluminium). A single-lens optic turns the divergent beam into an approximately parallel beam. On high-quality collimators (e.g. our Colli-LA) we use an aspheric glass lens with AR coating, 5 mm aperture, focal length approx. 4 mm. For especially round beam profiles, correction optics can be added behind the collimator.