Question about collimator lens.

[reginak]

Well I know that beam expanders are avaiable, but I searched the forum to try to understand why no collimator lens and found nothing. Is there a lens to reduce the beam size while sacrifing the divergence?

Thanks

 

[anselm]

Green DPSS usually have a beam expander (an expanding lens + plus a collimating one)
after the crystals. If you can remove that, like for example with the modules from DX pens,
you get a super thin, terribly divergent (3metres- dot size of hand) beam,
which comes out of the crystal directly.

You might be able to do what you intend by replacing the collimator lens
you have for a different (smaller?, shorter?) one. What you need exactly
i'll let someone answer who knows.

 

[steve001]

Well I know that beam expanders are avaiable, but I searched the forum to try to understand why no collimator lens and found nothing. Is there a lens to reduce the beam size while sacrifing the divergence?

Thanks

What do you mean by sacrificing ?

 

[anselm]

What do you mean by sacrificing ?

The smaller the beam diameter, the worse the divergence.
Guess that's what she meant...

 

[Limecat]

What do you mean by sacrificing ?

Well I know that beam expanders are avaiable, but I searched the forum to try to understand why no collimator lens and found nothing. Is there a lens to reduce the beam size while sacrifing the divergence?

Thanks

The smaller the beam diameter, the worse the divergence.
Guess that's what she meant...

Well you guys are in luck. confining the beam makes the divergence angle greater by virtue of physics. No extra lenses required.

 

[goninanbl00d]

You could always use a beam expander in reverse. You'd get a needle-thin beam with terrible divergence.

Limecat, it doesn't depend so much on beam diameter, but rather the M2 factor. The M2 factor is what determines how much the beam can be focused to for a given divergence.

Encyclopedia of Laser Physics and Technology - M2 factor, laser beam, quality factor, beam divergence, caustic, ISO Standard 11146

In other words, you get to a point where lasers with poor M2 factor simply can't be collimated any further.

 

[Limecat]

You could always use a beam expander in reverse. You'd get a needle-thin beam with terrible divergence.

Limecat, it doesn't depend so much on beam diameter, but rather the M2 factor. The M2 factor is what determines how much the beam can be focused to for a given divergence.

Encyclopedia of Laser Physics and Technology - M2 factor, laser beam, quality factor, beam divergence, caustic, ISO Standard 11146

In other words, you get to a point where lasers with poor M2 factor simply can't be collimated any further.

That's right, which means that the divergence can be no better than the regular divergence angle: lambda / ( pi * w_0). So again, a short wavelength and a small waist (which is related to the spot size) would give you the best divergence.