Can someone explain how beam divergence works?

[Mr. Q]

I don't understand why it's so hard to make parallel beams for laser pointers. If you can refract light any way you want, couldn't you adapt a lens' surface according to its input to point every incoming photon straight out?

 

[Cyparagon]

No. The short answer is quantum physics (specifically the principles of diffraction) prohibits this.

Here's the longer answer

 

[LaserMicroscope]

No. The short answer is quantum physics (specifically the principles of diffraction) prohibits this.

Here's the longer answer

Gaahhhhh darn it Cyparagon, you had to go and link to the VERY document I was going to reference while writing out an over-long explanation. I really need to get better at beating you to posts when I’ve had a bourbon and I’m feeling wordy.

 

[LaserMicroscope]

Though I did get the reaction image first. Small victories.

cheers