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PBS beam combining two NUBM38s

Junkers

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What are the typical power limitations when it comes to combining beams using PBS cubes? I see them advertised commonly with power ratings of 5W or 8W but am not sure if that is per incident beam or overall. I suspect that if multiple beams were incident upon a cube (as we commonly see with knife edging sets) the issue becomes keeping the cube cool so that the film does not break down. Being glass, thermal conductance is not favourable.

I do not want to use the likes of a NUBM31-34T as the larger area calls for a larger lens and in turn a longer FL. I would like to super impose two NUBM38s.

For contexts sake:
 



gazer101

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I don't know the answer but I don't think you need to worry at your power levels.
What I do know is that mirrors are currently far more laser-resistant than lenses, so one could try expanding some beams with a mirror expander, so there is a hole in the middle before putting them into the PBS (expect much more spaced out than usual due to the expanded beam) to reduce the power density and then reshrink them using another mirror expander:
1615879746718.png
 
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Junkers

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I'm assuming each input would need to pass through a focal lens before entering an expander. That seems like quite an elaborate setup for an XY gantry. I'd really like to stick with a PBS cube if it is possible.
 
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kecked

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those are not single diodes so you can almost combine two beams with each cube. It would be a lot of work. I’d just knife edge pairs then knife that. Then maybe pbs that but you better get your polarization right. First thing I’d try for cutting is just a lens. If the spot size can get tight enough it won’t matter. There is a guy on PL that does this with fibers. VDX
 
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Junkers

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I was thinking of using a single PBS cube as each string of 7 diodes is 2mm apart. I would need a 20mm+ cube though, AR coated and designated as high power, those don't come cheap. e.g.


I've found some cheaper ones in China but they have lower transmission efficiency (Tp 90%).

I have been playing around with some prisms and believe I can bring the beams together that way but it doesn't seem elegant. It's also relatively lossy and doesn't help balance out the polarity of the beam incident on the substrate.

Knife edging might be an option. What type of mirrors are best suited to this wavelength?
 

kecked

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Good quality broadband first surface mirrors should be fine. If it heats up up it on a heatsink. I doubt it will.
if the mirror is even 95%. That is only around 5W wasted on 100W.

I wonder if a single mirror on a slight angle could not knife edge a complete row. If the angle was just right it might work. Than pbs two rows each them knife that result into a telescope. Pretty much what Arctos did back in the day. You might be able to 3d print the mirror mounts as one piece that fits over the device and even the right angles off the end into the cubes. Well even hold the cubes. If I think of it you could make one piece to do the entire job just glue in the mirrors on one end and use a screw to adjust the angle. Yea I like this.
 

Light superglue

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To my understanding transmision efficiency of 90% should not mean that all 10% of light are absorbed by the cube, most of it can also be reflected into the holder. Of course this has to be tried but if it would be the case, I was thinking to make a water cooled PBS mount.

I saw such things in ebay:
 

RedCowboy

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I'm sure everyone knows this but I will mention it anyway, clean optics make a big difference.
BTW, OPT has a high quality coating but I don't see any 25mm+ cubes listed.
 

Light superglue

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Yes, why sellers specialised on maximun 5-10W laser engravers would sell 25mm cubes? Neither OP, nor lasertack and stanwax have those. Only ebay, ali or expensive certified multispecialists like Thorlabs have them but at >300usd + tax.
But even here they do not list any designed to work at 455nm (maybe just because of a special coating for each WL?):

And specs given for these cubes I think are for single beams, that is why with MDPs like NUBM31-38 I need to "DYODD" with transmission/reflexion and "calorimetry" tests.
 

Junkers

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At the moment I'm in two minds. I've ordered some cylindrical concave/convex lenses to reshape the NUBM38 output and increase its power density. I'm not sure how detrimental they'll be in terms of divergence but we shall soon see.

If you succeed with your efforts Light superglue then I'll probably follow suit. I'm very tempted to buy a cube regardless.
 

kecked

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PBS the two arrays but then knife edge the resulting beams. Don’t forget to use a waveplate when combining so the combined beams profile stays the same. Interested to see your result.
 

Light superglue

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There still stays one question: where can we get the waveplates of this size? And one will need two if one wants to combine four packs.

OPT only sells squares 10x10mm (maybe we can use two or four side by side?)
Stanwax only 15mm rounds
Yes, Thorlabs has 1" rounds but they are pretty pricey:

Do you have any experience of using WP with thick beam packs?
 

RedCowboy

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I have only worked with the OPT brand rotator and only when combining 2 beams, however I found some 1 inch rounds at Newport.

Actually looking at that again they seem to have omitted 445nm from their lineup, but I know there are fiber coupled 445 KE arrays being made for industry, you would think more peripheral products would also be available, maybe a company who deals in these products could direct us to a source ?......Ok probably not, but you never know and I expect we could have some made but at what cost IDK.

 
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kecked

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Nope only used them for single beam combining. Yea almost sounds like you need to fiber launch every diode and then combine. Not worth it. Might as well get your own chips and align an$ bond them yourself. What a pain.

Biggest WP I got was 1” and I got them from a guy named bridge on pl years ago. Can a single lens focus the array down to a spot ?
 

Junkers

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Nope only used them for single beam combining. Yea almost sounds like you need to fiber launch every diode and then combine. Not worth it. Might as well get your own chips and align an$ bond them yourself. What a pain.

Biggest WP I got was 1” and I got them from a guy named bridge on pl years ago. Can a single lens focus the array down to a spot ?
Yes, a single lens can focus them down to a spot. I've managed to sinter SS316L down to a track width of 0.2mm which is beyond what I expected.

Why do you suggest knife edging and a WP? The beam is already combined and given I'm trying to melt metal, I've read circular polarization is optimal. I had thought about using a rhomb but have a way to go yet before it becomes a priority.
 

kecked

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I had thought that the best way to get max power in the spot. The WP was because someone asked about combining two arrays. This allows you to overlay the two arrays in a pbs cube without having the beams in an x. Think I cross posted.
 




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