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ArcticMyst Security by Avery

Low divergence optics

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I'm thinking about making a low divergence add on for my Aries (the same principles can be used for other lasers)

http://www.mellesgriot.com/products/optics/fo_4.htm

Basically, I would get a "cap"  1.5" in diameter and add an achromatic or plano convex lens to it (flatter side toward the beam source).  Hopefully it will make the divergence better.  I've just purchased about $100 worth of lenses and mounts from Sunex (http://www.optics-online.com/) and I'll keep you all up to date.

The biggest problem will be centering the mount on my laser so the axis of the beam is parallel to the axis of the lens.
 

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steve, if you have a machined shop in your area I'd speak with them to see if they can machine parts that screw in to your laser.
you don't need an achromatic lens, a plano-convex will work nicely. Then new lens should have a focal length a least 10mm longer than the one presently on the laser so you notice a real difference in beam divergence. Look down a few posts for light machinery optical calculators I posted a link to an applet for calculating beam divergence based upon the focal lengths of the lenses used. I have done what you want to do. I replaced both lenses with new ones both are AR coated Vis0 from Edmund Opticals. They will send you a free catalog. One lens has a focal length of -6mm and the other a focal length of 48mm. Spot size at 351 feet is about 3.5-4cm
 
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What I'm trying to do is keep the Aries "stock" and make an "add-on" that I can place a laser mount on.  I have already purchased the lenses and mounts.  Now we just have to wait for them to arrive.

thanks for the link and ideas!!!
 
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This is the set of optics I ordered.  I think I should have enough lenses to improve the beam.
I will make a post again once I have the parts and everything assembled and tested.

Item         Description                                                                   Cost $

CMT830    Lens holder, M8x0.5, 5.6, centered                                   6.00  
PXP005     Plano-convex lens precision grade BK7 D= 8 EFL= 10        14.25  
CMT746A  Lens holder, M8x0.35, centered **ideal for DSL746**        6.00  
PXP015     Plano-convex lens precision grade BK7 D= 8 EFL= 18        14.25
ACH008-016    Achromatic doubet lens, D=8, EFL=16                        27.50
PXP009    Plano-convex lens precision grade BK7 D= 8 EFL= 15         14.25  
 
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stevetexas said:
This is the set of optics I ordered.  I think I should have enough lenses to improve the beam.
I will make a post again once I have the parts and everything assembled and tested.

Item         Description                                                                   Cost $

CMT830    Lens holder, M8x0.5, 5.6, centered                                   6.00  
PXP005     Plano-convex lens precision grade BK7 D= 8 EFL= 10        14.25  
CMT746A  Lens holder, M8x0.35, centered **ideal for DSL746**        6.00  
PXP015     Plano-convex lens precision grade BK7 D= 8 EFL= 18        14.25
ACH008-016    Achromatic doubet lens, D=8, EFL=16                        27.50
PXP009    Plano-convex lens precision grade BK7 D= 8 EFL= 15         14.25  

If your goal is to improve divergence, you'll need to increase the beam diameter. By adding on lenses, you will NOT simply improve the beam (otherwise the manufacturer would have already done that with the high end). What you can do it trade off min diameter with divergence.

The way you do this is by "upcollimating the beam". The general ideal is that you diverge the beam to make it larger, and then recollimate it so you have a larger spot, but in return you get better divergence when properly aligned.

The problem I see with the list you have is that there are no diverging/concave/negative focus lenses. You can work around this by using a regular positive focus one as it will diverge after the focus, but that means you'll have to place the re-collimating lens much further away. For instance, using a positive converging lens at +15mm focus instead of a negative diverging at -15mm would increase the length of your add on by a little over an inch.. if that matters to you.

After that though, you just need to use a stronger lens for divergence and a weaker one for converging. As a rough estimate, take the absolute value of the converging lens' focal divided by the diverging lens' focal and that is about how many times your divergence will be improved, and how much larger your minimum spot size will be.

Good luck! And out of curiosity, how are you planning on attaching the setup to your laser?
 
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To mount it (reversibly) I'll be using 1.5" copper end cap with 6 set-screws (3 in front, 3 in back) to hold it in position and align it over the head of the Aries.  I'll drill out a hole in the cap for the beam, and epoxy the mount at the front.  

The set screws will allow percise alignment of the axis of the mount with the axis of the beam since there is some space between the cap and the head of the Aries.
 
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stevetexas said:
This is the set of optics I ordered. I think I should have enough lenses to improve the beam.
I will make a post again once I have the parts and everything assembled and tested.

Item Description Cost $

CMT830 Lens holder, M8x0.5, 5.6, centered 6.00
PXP005 Plano-convex lens precision grade BK7 D= 8 EFL= 10 14.25
CMT746A Lens holder, M8x0.35, centered **ideal for DSL746** 6.00
PXP015 Plano-convex lens precision grade BK7 D= 8 EFL= 18 14.25
ACH008-016 Achromatic doubet lens, D=8, EFL=16 27.50
PXP009 Plano-convex lens precision grade BK7 D= 8 EFL= 15 14.25

I've got some bad news for you. None of the lens you've bought will greatly improve your beam divergence. If you swap out the old lenses for new there will be no improvement and it could actually be worst.
The expander lens always has to have a noticeably shorter focal length than the collimating lens. To keep the working distance between lenses short the expander lens must be a negative focal length. I think typically the collimating lens in these tpyes of laser is anywhere from 15-18mm EFL. You can before hand determine by using the applet I mention previously what your new beam divergence will be if you input the beam diameter and beam divergence as per specs.into the first two boxes in the gaussian beam applet then input the focal lengths of the lenses into the other appropriate boxes. Distances between lenses must be taken into account.
 
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I don't intend to open the laser - I will add on optics in the beam path. I'll epoxy the lens holder in the beam path at the front of the cap...
 

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This is just a prototype but it works for its purpose - I'll be making another one that is a little nicer
 

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See - the cap is removeable - no need to mess with the internal optics
 

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even if it doesn't work to narrow the beam, I will still be able to add filters, lenses and diffraction gratings just to modify the beam... ;)
 
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Stevetexas, did you read my post about upcollimation? Any single lens will just ruin your beam specs by bringing it to a close focus. With the diverging/converging combo you can make a beam expander to lower divergence. You probably want a diverging lens too though as getting by with two convergings is just a bit of a waste of space.
 
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pseudonomen137 said:
Stevetexas, did you read my post about upcollimation? Any single lens will just ruin your beam specs by bringing it to a close focus. With the diverging/converging combo you can make a beam expander to lower divergence. You probably want a diverging lens too though as getting by with two convergings is just a bit of a waste of space.

Pseudo - yes, I did read it and am looking for a suitable optic now - thanks for the input!!!
 




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