This https://www.gentec-eo.com/blog/spot-size-of-laser-beam article states that laser beam width changes along the length of the ray (the function stated doesn’t look like it could be a constant 1)
Is it impossible to create optics that completely parallelize laser light? If not, why so?
You can’t have a perfectly parallel beam. There are two equivalent ways to see this.
The uncertainty principle: the photons making up the beam have to have some spread (uncertainty) in their transverse momentum because they’re confined in position to a certain beam width.
Diffraction: by creating a beam of a certain width, you must have a certain amount of diffraction that causes the beam to diverge.
Fundamentally, these are the same. They come from the wave nature of light.
