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Thorlabs Mounted Prism Pairs

Valiant

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Does anyone have experience with Thorlabs Mounted Anamorphic Prism Pairs?
(Can't post links yet, www. thorlabs. com/ newgrouppage9.cfm?objectgroup_id=149)

Looking at the PS875-A in particular for diversion correction on a 2 watt 520nm direct diode laser and a G8 collimator.
(www. thorlabs. com/ thorproduct.cfm?partnumber=PS875-A)

They appear to be an ideal fit for this task; the specs look good and they are ideally sized for handheld applications.

5412_PS875-A_SGL.JPG
 



RedCowboy

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Looks like a really nice bit of kit, however it's likely expensive and if you don't have the ability to machine and thread an adapter then why not just set a prism pair up yourself, also you can arrange them in different configurations to change the ratio.

What are you trying to do ? Do you want to circularize the beam in the near field or reduce the divergence ? I prefer to use cylindrical lenses.
 

Valiant

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Fair points all around.

As for price, I just grabbed this model for $110 on eBay today (there's others for sale there as well, from $185-200) which isn't too bad for lab/med/mil grade optics. I purchased a Thorlabs LT230P-B on eBay for $78 and the quality of the included collimator lens blows the DTR-G-8 out of the water; the ~$100 mark for high performance optics seems a sweet spot.

I looked into setting up a prism pair myself, but I'm really attracted to the form factor and size of these optics. 25mm is an ideal size, and I haven't found any readily available loose anamorphic prism pairs even twice that size (that aren't from expensive optics companies, anyway).

With this prism pair and the above collimation tube I'll be able to fit everything into a 30mm package housed in aluminum rod stock, even accounting for the prism pair's offset input. I haven't seen any pointers on lpf yet with that level of beam correction at that size, though admittedly I've only lurked here 4 months.

As for what I'm trying to accomplish, the primary goal is to correct the elliptical beam profile post collimation into a more cohesive 'dot' profile in order to achieve higher energy density (J/cm2) which then will be manipulated by successive interchangeable optics (e.g. beam expander, achromatic doublet, polarized filter) based on use case.

Laser Assembly.png
 
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RedCowboy

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As long as your beam enters the prism pair at the correct angle and doesn't get clipped, are you building your own nugm04 based unit ?

I posted about these little 12mm round corrected modules the other day but as for multi mode greens they only list the NDG7475 and not the nugm04 however they do have other optics.

 

Valiant

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Those Sparrow modules look fantastic! I wonder if they'd sell one without the diode, optics repositionable. Has anyone asked?

I actually switched gears with the project above a few days ago. Instead of using another NDG7475, I picked up a 450nm NUBM47-A1 which needs beam correction much more.
 

RedCowboy

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Yea, you want a 6X c-lens pair or 6.25, I usually use a large heat sink for my module with an optics shelf.
 

Valiant

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Yea, you want a 6X c-lens pair or 6.25, I usually use a large heat sink for my module with an optics shelf.
Do you have a recommended vendor or product for the lens pair and/or shelf? What do you use?
 

RedCowboy

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I make my own housings or have them made and my optics have been from group buys and vendors who are no longer in business, however you can get some from many places such as https://www.live-lasersystems.net/d/optics.html Click ( products ), then ( optics ) and you want 6.25 for the nubm44

Or go here https://optlasers.com/ and use the ( categories ) tab, click ( accessories and optics ) and then select ( cylindrical lenses ) and make sure to get 6X for 400-700nm which denotes the AR coating for low loss.
 

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Valiant

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Once I have the optics figured out, I'm machining the housing from 30mm 2024-T351 Aluminum rod stock. I don't have a lathe yet, but I do have a drill press and thankfully my plans so far have all been able to implement cylindrical subtractions.

I'll contact Live LaserSystems this weekend and ask if they would pretty please sell me one of those 12mm sparrow shelf + diode receiver units with the 1:6.25 pair you recommended. They look like a small enough vendor to not mind customized orders like that. Here's hoping!

Your pointer looks nice. What's the duty cycle with a sink that size? Also is that one of the X3 expanders?
 

RedCowboy

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My runtime is good, however without active cooling you can feel warmth after several minutes, but I usually don't lase all that long, still 5 min. continuous is no problem, also as we love to overdrive these laser diodes it's good to have a heavy sink or active cooling to keep the power fade away, which should prolong the lifespan, which is no doubt shortened from the 20K hour factory rating, which I expect is mean time to half brightness rather than mean time to failure because over time these laser diodes experience a progressive drop in output, it's slow however I expect overheating is a factor because when over driven output slowly declines as heat builds up then rebounds when cooled down, still the cooler you keep your diode while lasing, the slower the power drop and if you keep it properly cooled you won't see much if any drop, but most hobbyist don't care about a long duty cycle, not in a hand held portable type form factor.

If you have a drill press you can get some inexpensive end mills and a slide vice, this will allow you to do some milling but get a good quality slide vice.

Alignment is important, you want your beam to enter your beam expander nice and square, yes mine is a sanwu 3.3X

p.s. When using a sanwu 3.3XBE on a nubm44 with 6X pair I found the primary lens ( G2 ) needed to be a Sanwu G2 rather than DTR's G2 because of the slight focal length difference and the fit through the cheap and easy 3.3XBE is tight, I haven't used the 6.25 from Live or OPTS 6X yet so I don't know how much they differ but mine are 6X
 
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RedCowboy

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I forgot to mention you can also use one of the MM diodes with added FAC fiber from China, you only need to use a wide enough lens to catch the expanding beam and focus it to point at distance, they actually do pretty well but it's a good idea to put a dust window at the end of your module to protect the diodes can window, also can be used for hobby cnc with standard M9x0.5 barreled lenses.

 
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