Galilean beam expander and spherical aberration

In summary, the conversation discusses the best way to arrange plano-convex and plano-concave lenses for a Galilean beam expander/contraction to reduce spherical aberration. The general rule is to "split the powers" and have the curved face facing the collimated beam and the flat face facing the diverging/converging beam. However, the Melles Griot catalogue shows a different arrangement, which is actually incorrect for the negative lens. According to the correct arrangement shown in a link provided by mgb_phy, the spherical aberration is reduced significantly. The conversation concludes with the reminder to never have the flat face facing a collimated beam.
  • #1
Shaddyab
19
0
Sorry for posting this post in two different place, I could not decide where is the best place to post it.

I am trying to build a Galilean beam expander/contraction using a plano-convex and plano-convace lenses. My question is how should I arrange them to reduce the spherical aberration?
Should the two plano surfaces face each other (http://www.mellesgriot.com/glossary/imagesDir/Gallilean.gif" ), the two curvatures surfaces facing one another, or some different way.

I need to know that both for a beam expander and beam contraction.

Thank you
 
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  • #2
General rule is 'split the powers' = minimise the amount of curvature at each face.
That is the curved face should face the colimated beam and the flat face - the diverging/converging beam.
 
  • #3
Thank you for your answer.

What is confusing me is that according to this document from Melles Griot
http://www.mellesgriot.com/pdf/CatalogX/X_01_27-28.pdf"
they should be aligned in a different way ( see figure 1.32 )

So what way reduces the spherical aberration better?

Thanks
 
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  • #4
I think their catalogue is just showing a diagram, this one has more detail
http://www.edmundoptics.com/TechSupport/DisplayArticle.cfm?articleid=270
 
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  • #5
mgb_phys said:
I think their catalogue is just showing a diagram, this one has more detail
http://www.edmundoptics.com/TechSupport/DisplayArticle.cfm?articleid=270

I do not think it is only a diagram, they are driving an example.
 
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  • #6
Shaddyab said:
Thank you for your answer.

What is confusing me is that according to this document from Melles Griot
http://www.mellesgriot.com/pdf/CatalogX/X_01_27-28.pdf"
they should be aligned in a different way ( see figure 1.32 )

So what way reduces the spherical aberration better?

Thanks

Surpisingly, they are showing it wrong for the negative lens. Note in Fig. 1.31, that arrangement has worse aberration than the other way around (1.069 vs. 0.272)

mgb_phy's link to Edmund has the correct figure at the top of the web page.

The way I remember it is: never have the flat face facing a collimated beam.
 
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1. What is a Galilean beam expander?

A Galilean beam expander is an optical device that is used to increase the size of a laser beam without affecting its divergence. It consists of a negative lens and a positive lens placed in close proximity to each other, with the negative lens in front of the positive lens. This configuration allows the beam to expand while maintaining its collimation, making it useful for applications such as laser cutting and laser surgery.

2. How does a Galilean beam expander work?

The negative lens in a Galilean beam expander diverges the incoming beam, while the positive lens converges it. This results in the beam expanding without changing its divergence angle. The amount of expansion can be adjusted by changing the spacing between the lenses or by using lenses with different focal lengths.

3. What is spherical aberration and how does it affect a Galilean beam expander?

Spherical aberration is a common optical aberration that occurs when light rays passing through the edges of a lens do not converge at the same point as light rays passing through the center of the lens. In a Galilean beam expander, this can cause distortion and blurring of the expanded beam. To minimize spherical aberration, high-quality lenses with precise curvatures are used in the construction of the beam expander.

4. What are the advantages of using a Galilean beam expander?

The main advantage of a Galilean beam expander is its ability to expand a laser beam without changing its divergence angle. This makes it useful for applications where a larger beam size is needed without compromising the beam quality. Additionally, the compact size of the device makes it easy to integrate into existing optical setups.

5. What are some common applications of Galilean beam expanders?

Galilean beam expanders are commonly used in laser systems for cutting, welding, and drilling materials. They are also used in medical applications such as laser eye surgery and dermatology procedures. Other applications include laser marking, micromachining, and lithography.

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