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# Lowest possible divergence

#### solar00

##### New member
Just curious, but what is the lowest possible divergence that can be archieved today (and in theory)
I know perfect divergence (which is actually no divergence at all)isn't possible due to limitations by the laws of physics.

#### pseudonomen137

##### New member
Its actually dependent on the beam diameter. Theoretically, with an infinitely large beam diameter you could have no divergence. The smaller you make the beam though, or the less coherent, or the longer wavelength, the more it diverges.

#### laserterd

##### New member
well the pulsars divergance is in the negatives right? so negative infinity would be the lowest i think... which isnt really possible yet. negative divergance means it gets small first, then gets bigger. i think on the pulsar the focul point is like 18 feet or something.

#### pseudonomen137

##### New member
laserterd said:
well the pulsars divergance is in the negatives right? so negative infinity would be the lowest i think... which isnt really possible yet. negative divergance means it gets small first, then gets bigger. i think on the pulsar the focul point is like 18 feet or something.
Negative and positive divergence are the exact same thing. If you look at a diverging beam and trace it the other way, its a converging beam. In either case, the rate of divergence will end up the same (if it converges at a certain rate, past the focal point it will diverge at that rate). So whether you're approaching it from a number you're calling negative or positive, the lowest divergence to strive for is 0mRad - nothing at the infinites.

#### solar00

##### New member
Shouldn't it be possible to create a beam with.. say a diameter of 1mm with a divergence of 0,01mrad for example or even lower.(through air)
Can something like this be done with a wavelength between 400 and 700nm.
Or is there some (simplified) way to calculate this?

I mean calculating the minimum divergence just by filling in a few variables (diameter, wavelength, density and refraction index of the medium the beam passes through)

L

#### likewhat

##### Guest
Far field divergence has a simple form for a gaussian beam

Divergence (defined as half angle) = wavelength/Pi/minimum spot size (e^-2 radius)