Expander lenses question

[Hemlock_Mike]

I can't remember how to calculate magnification of a beam expander. There is a formula which uses the FL of the two lenses. Anyone remember?

Mike

 

[steve001]

Division is what you need to do

 

[Hemlock_Mike]

Steve ----
Then if I have a -25mm into a +125mm (assuming I use absloute values) I have 5X !! Correct?

Also, Using a plano-convex as my input lens should still work, just make the expander longer..........

Mike

 

[steve001]

Steve ----
Then if I have a -25mm into a +125mm (assuming I use absloute values) I have 5X !!  Correct?

Also, Using a plano-convex as my input lens should still work, just make the expander longer..........

Mike

Correct. Beam expanders come in two types, Galilean and Keplerian. The first uses consists of a negative then positive lens the other one two positive lenses
What order are you placing the lenses with respect to the laser output ?
What diameter is the 125 mm lens ?

 

[Hemlock_Mike]

Steve, I've built BE's before, I just forgot the formula... I thought there was more to it. I usually draw it on graph paper before I build.

Right now I have a 1.5" Dia x 5" FL objective lens. I need a ~.75" x ~18 mm +/- for the input.

Mike

 

[steve001]

Have you tried Edmund Optics or there other subsidiary Anchor Optics for generally experimental lenses.
Even though there are companies selling singlets none that I'm aware sell them already AR coated as Edmund Optics does, that's the reason I point folks to them

http://www.lightmachinery.com/optical-calculations.php

direct page link to Thin Lens Gaussian Beam  Program
http://www.lightmachinery.com/gausbeam.php

I just used the program and assuming certain values using a -25mm EFL lens and a 125 mm EFL lens you should have a beam diameter of 5mm exiting the positive lens with a Rayleigh Length of 20853.190mm or  68.415978 feet. Adding a second negative lens will increase the Rayleigh Length from 20853.190mm to 86723.545 or 284.526066 feet. Beam diameter will be 10.2mm. The beam will have a divergence of .12 mrd in both cases. You could used a -12.5mm EFL lens and get nearly the same values.
As I said these figures are just guesses based upon what I think your set is like.