Sanwu beam expander lens question

[Ramsey_innovations]

Hey i just got a Sanwu 3x be and I'm wondering if the input lens (objective lens of a beam expander) is in backwards. I tried searching for any info here first but came up with nothing. Anyway, the flat surface on the input side lens is facing the diode. All the diagrams I've seen on beam expanders show either a convex or concave surface facing the diode, depending on weather it's a Keplerian or Galilean. See Edmund optics... https://www.edmundoptics.com/knowledge-center/application-notes/lasers/beam-expanders/
The beam expander works fine but I'm concerned about back reflections. Can anyone with one of these Sanwu's check their's and see if it's the same please? Any help or advice would be greatly appreciated, thanks!

 

[RedCowboy]

I have several and they are all like that, also that little lens is AR coated, I wouldn't worry about it......... mine have been working just fine for many many house or use.

 

[Ramsey_innovations]

I have several and they are all like that, also that little lens is AR coated, I wouldn't worry about it......... mine have been working just fine for many many house or use.

Ok, that's a relief. Thanks Red, I really appreciate the info. I wasn't liking the idea of having to take it apart to flip the lens over.

 

[steve001]

Hey i just got a Sanwu 3x be and I'm wondering if the input lens (objective lens of a beam expander) is in backwards. I tried searching for any info here first but came up with nothing. Anyway, the flat surface on the input side lens is facing the diode. All the diagrams I've seen on beam expanders show either a convex or concave surface facing the diode, depending on weather it's a Keplerian or Galilean. See Edmund optics... https://www.edmundoptics.com/knowledge-center/application-notes/lasers/beam-expanders/
The beam expander works fine but I'm concerned about back reflections. Can anyone with one of these Sanwu's check their's and see if it's the same please? Any help or advice would be greatly appreciated, thanks!

There is a reason why lenses are placed with certain surfaces facing the diode. Those reasons are not critical for hobbyists. But if you want to know pop Edmund an email. Something that you might want to do is swap out the negative focal length lens with a lens that has a shorter focal length. If that is problematic then adding another negative lens might be a solution. The end result is a higher power beam expander. I suggest (quessing) either a 6 or 9 mm diameter plano-concave. Edmund has them already AR coated.
How to measure the focal length of a negative lens.

 

[Ramsey_innovations]

There is a reason why lenses are placed with certain surfaces facing the diode. Those reasons are not critical for hobbyists. But if you want to know pop Edmund an email. Something that you might want to do is swap out the negative focal length lens with a lens that has a shorter focal length. If that is problematic then adding another negative lens might be a solution. The end result is a higher power beam expander. I suggest (quessing) either a 6 or 9 mm diameter plano-concave. Edmund has them already AR coated.
How to measure the focal length of a negative lens.

Thank you for the reply Steve. I was thinking about doing just that if i had to open it up anyway. My concern with that though is that the image lens probably isn't large enough diameter to go any higher in magnification. As it is, the beam is close to, if not exceeding 80% of the image lens' diameter. Correct me if I'm wrong but using a shorter focal length objective lens would diverge the light faster resulting in a situation where clipping would occur prior to the image lens. I'm using a g8 lens from DTR for pre-expander collimation. Perhaps swapping that out for one of my old g2's might help in that situation but I'm not completely sure. I will say though that the resulting beam and spot after adding the expander are surprisingly clean with very little scatter/splash, I'm happy with that. It did however require some shimming between the beam expander body and the adapter to correct alignment. I didn't check it with my mitutoyo test indicator, but i suspect that either the adapter has some axial runout from the front face to the back face or the lenses aren't aligned well....and the threads are indeed quite sloppy. It's pretty cheap looking.... Does anyone here make better quality adapters? I believe the threading is M11x0.5 to M9x0.5 but I'd have to check to be sure.

 

[steve001]

Thank you for the reply Steve. I was thinking about doing just that if i had to open it up anyway. My concern with that though is that the image lens probably isn't large enough diameter to go any higher in magnification. As it is, the beam is close to, if not exceeding 80% of the image lens' diameter. Correct me if I'm wrong but using a shorter focal length objective lens would diverge the light faster resulting in a situation where clipping would occur prior to the image lens. I'm using a g8 lens from DTR for pre-expander collimation. Perhaps swapping that out for one of my old g2's might help in that situation but I'm not completely sure. I will say though that the resulting beam and spot after adding the expander are surprisingly clean with very little scatter/splash, I'm happy with that. It did however require some shimming between the beam expander body and the adapter to correct alignment. I didn't check it with my mitutoyo test indicator, but i suspect that either the adapter has some axial runout from the front face to the back face or the lenses aren't aligned well....and the threads are indeed quite sloppy. It's pretty cheap looking.... Does anyone here make better quality adapters? I believe the threading is M11x0.5 to M9x0.5 but I'd have to check to be sure.

I don't no nothing about adapters. But I do know that a lens that is curved as I suspect those G lenses are are much more difficult to align than a lens with one flat side. Something else to experiment first with educational grade lenses. If that beam expander comes apart to remove the collimating lens swap it out for a longer focal length lens. You need extension tube wide enough to fit over the beam expander and to that mount the lens on the end. Another option would be to remove the negative lens and use a single postive lens set at the lenses focal length from the diode will collimate the beam. The reason typically two lenses are used is for creating a short working distance between lenses keeping a beam expander compact as possible.

 

[RedCowboy]

The Sanwu 3.3xBE has a 25mm output so as your beam from your nubm44 with a 3E or G8 is about 6mm wide then expanded 3.3x means it hits your 25mm output lens @ 19.8mm wide........if you doubled the input lens to make a 6.6xBE then you would be trying to fit a 40mm expanded beam through a 25mm output lens which means you would have to use a shorter FL primary such as a DTR G2 to reduce the dia. of your beam at the expense of divergence so what you gain on one end you lose on the other........now if you were only using the BE for Gaussian dpss 532nm beams 3mm wide then you could double your power by changing your input lens and it will fit your output lens.

I have made expedient beam expanders and slide focus arrangements from aluminum tube, PVC and even rolled up card stock, I like 30# Black card stock but beware of keeping your diodes window clean if using a big sliding lens without a primary in your module.

 

[Ramsey_innovations]

The Sanwu 3.3xBE has a 25mm output so as your beam from your nubm44 with a 3E or G8 is about 6mm wide then expanded 3.3x means it hits your 25mm output lens @ 19.8mm wide........if you doubled the input lens to make a 6.6xBE then you would be trying to fit a 40mm expanded beam through a 25mm output lens which means you would have to use a shorter FL primary such as a DTR G2 to reduce the dia. of your beam at the expense of divergence so what you gain on one end you lose on the other........now if you were only using the BE for Gaussian dpss 532nm beams 3mm wide then you could double your power by changing your input lens and it will fit your output lens.

I have made expedient beam expanders and slide focus arrangements from aluminum tube, PVC and even rolled up card stock, I like 30# Black card stock but beware of keeping your diodes window clean if using a big sliding lens without a primary in your module.

That's pretty much what i figured. Thanks again Red!
Years ago, when i had a cnc lathe i made a sliding style BE for a 532nm tec stabilized Labby i had. It's much too large for this build though. I recently went through my laser optics and diode collection.... I have horded tons of stuff I've since forgotten about, mostly from a NASA/military contractor surplus store (skycraft) in central FL. Tons of lenses, diodes, pbs cubes, dichros, mirrors etc... I don't even want to think about how much $$$$$ I spent. I could have done something custom with the cnc router/mill i have now but for only $60 for this BE i figured it wasn't worth the effort at this point.

 

[RedCowboy]

I also have amassed a ton of stuff, some of it I will never use, some is buried under other forgotten stuff, searching my house would be a nightmare.

The problem with slide focus is fine tuning, threaded is so much nicer but for cheap you make do with what you have or can easily acquire........I do enjoy the Melles Griot, Linos and other professional units I have scored at a fraction of their original cost, but ordering a 1000.00 part for a project is tough for me to justify so slip, slide and swear will do until I find my range and adapt an adjuster.

---edit---
Oh, the 3xBE threads are oddball, something like 10.4mm @ 0.5 pitch, Rich/Lifetime17 had a tap custom made and can likely make you an adapter.

 

[Ramsey_innovations]

I also have amassed a ton of stuff, some of it I will never use, some is buried under other forgotten stuff, searching my house would be a nightmare.

The problem with slide focus is fine tuning, threaded is so much nicer but for cheap you make do with what you have or can easily acquire........I do enjoy the Melles Griot, Linos and other professional units I have scored at a fraction of their original cost, but ordering a 1000.00 part for a project is tough for me to justify so slip, slide and swear will do until I find my range and adapt an adjuster.

---edit---
Oh, the 3xBE threads are oddball, something like 10.4mm @ 0.5 pitch, Rich/Lifetime17 had a tap custom made and can likely make you an adapter.

10.4mm...oh geez it figures it would be something odd. Thanks for the info, I'll pm him tomorrow.