Lens diameters

[Tech_Marco]

In my opinion, I think the beam expander should be installed right after a laser tube. Not only reduce stress on the reflection mirrors, it also improve collimation. I believe power may be improved as well because wider travelling beam. However, the focus angle will be sharper than without the beam expander. Therefore, a longer focus lens should be used if one is planning to do cutting but not for engraving.

Marco

[Techgraphix]

In my opinion, I think the beam expander should be installed right after a laser tube.

You're right, but in my case I had trouble aligning it properly. A mount similar to the mirrormounts would be better but I didn't had any room to place it right in front of the tube.. When I had to build another laser I would spare some space for that..
And the divergence of my laserbeam is almost zero ... 5mm near the tube and the same 5mm in the right down corner..

I don't understand how a beamexpander could make a divergence from the laserbeam into a straight beam as the lenses have a fixed focuspoint...

Kees

[DonL]

In my opinion, I think the beam expander should be installed right after a laser tube.

You're right, but in my case I had trouble aligning it properly. A mount similar to the mirrormounts would be better but I didn't had any room to place it right in front of the tube.. When I had to build another laser I would spare some space for that..
And the divergence of my laserbeam is almost zero ... 5mm near the tube and the same 5mm in the right down corner..

I don't understand how a beamexpander could make a divergence from the laserbeam into a straight beam as the lenses have a fixed focuspoint...

Kees

From what I understand, the lense at the end of the laser tube is not a focal lense but a columator lense that is ment to shape the beam, depending on the quality of the tube, it could have a low or high divergence.
The beam expander expands the beam and reshapes it to a low divergence. Because of the laws of optics, a larger beam entering the focal lense creates a smaller focal point with more intensity

With high divergence, the focal point is smaller and power is higher at the far end away from the laser tube where with low divergence the focal point is more uniform across all of the X/Y axis

Here is a rough diagram to illustrate - Correct me if I am wrong, I am no expert. A normal beam with low divergence (High Quality Tube) would have a more uniform beam like the illustration with the expander only the beam would not be bigger so the focal point would be like the first illustration at the home position all across the X-Y area.

So a Beam Expander can be used to shape and expand the beam for a higher power and smaller final focal point in low quality tubes giving you a uniform beam across the X-Y and for high quality tubes it just makes the beam larger for a smaller focal point with more concentrated power since the beam was already fairly uniform across the X-Y

Added Bonus - The expanded beam is less intense until it is focused so it is easier on the mirrors and focusing lens coatings

[Techgraphix]

In this article you can find what I mean..
http://www.newport.com/Focusing-and-Col ... ntent.aspx

In figure 7 you can see a black line entering the first lens straight and exit the second lens straight too..
But the blue line is entering the first line somewhat diverging and as you can see it is still diverging when it exits the second lens, which mean that a BeamExpander does make your beam wider but doesn't make a diverging beam straight.

Kees

[DonL]

In this article you can find what I mean..
http://www.newport.com/Focusing-and-Col ... ntent.aspx

In figure 7 you can see a black line entering the first lens straight and exit the second lens straight too..
But the blue line is entering the first line somewhat diverging and as you can see it is still diverging when it exits the second lens, which mean that a BeamExpander does make your beam wider but doesn't make a diverging beam straight.

Kees

I did read the article and yes and no... It does not eliminate divergence but it does reduce it
and I quote

"The divergence angle of the resulting expanded beam

θ3 = y2/f2 = θ1|−f1|/f2

is reduced from the original divergence by a factor that is equal to the ratio of the focal lengths |-f1|/f2. So, to expand a laser beam by a factor of five we would select two lenses whose focal lengths differ by a factor of five, and the divergence angle of the expanded beam would be 1/5th the original divergence angle."

So in this example if your beam divergence was 10% from the X-Y 0.0 to X-Y max so 5mm to 5.5mm with the above beam expanded the divergence would .1mm rather than .5mm so you are correct, the beam still diverges but not as much