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Anyone here collecting parts for, or working on a DPSS project?

Alaskan

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I'm wanting to compare notes with other hobbyists who are interested in DPSS technology, is anyone here planning, or working on a DPSS project? If you are, even if this thread is found much later, please add to it, I want to compare notes.

Chris
 



RedCowboy

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Been interested in diode pumped Nd:YAG but haven't built anything yet.
 

Alaskan

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Well, as I've been told before by experienced laser professionals in the past, it ain't as simple as some odd crystal found on ebay and shooting 1064 nm into it. I can hardly get any green at all using my 1064 nm 1.5 watt output pointer, without using the correct lens to properly focus into the material, the power density isn't high enough and that is only part of the problem.

I wish there was a YT video on SHG which gives a lot of practical optical advice for SHG, maybe there is, I will keep looking. The best I've found so far is one produced by Tech Ingredience. That said, there are lots of videos to be found about DPSS, good stuff, but I haven't found my DPSS SHG guru to follow yet.
 
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RedCowboy

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My 1st thought is maybe try pumping a smaller crystal and is your crystal mirrored on the ends, HR and OC mirrors ........well are you side pumping or end pumping.....I have taken apart the dpss 532nm lasers and put them back together and the alignment matters, I move the crystal set in the little fixture around until I get output, it can be picky and I suspect parts need to be within a range.

You should get some output even without mirrors shouldn't you ?

I'm sure there's plenty to learn and plenty to burn up while learning.

Have you read this yet ? I expect you have but here it is again. https://www.repairfaq.org/sam/lasercds.htm
 
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Gianakakis

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My 1st thought is maybe try pumping a smaller crystal and is your crystal mirrored on the ends, HR and OC mirrors ........well are you side pumping or end pumping.....I have taken apart the dpss 532nm lasers and put them back together and the alignment matters, I move the crystal set in the little fixture around until I get output, it can be picky and I suspect parts need to be within a range.

You should get some output even without mirrors shouldn't you ?

I'm sure there's plenty to learn and plenty to burn up while learning.

Have you read this yet ? I expect you have but here it is again. https://www.repairfaq.org/sam/lasercds.htm
Yea you will get output without the mirrors but they are pretty much needed for good results @Alaskan I suggest taking apart an eBay green pointer, getting the monolithic crystalline assembly out that contains the Nd:YaG and KTP pre-coated and then getting an 808nm diode with a g2 at least 300mw in power and focusing that into the crystal. Also as Red cowboy mentioned alignment is critical in getting good results, so If you don't get good results fiddle around with the rotation of the monolithic crystalline assembly.
 

Alaskan

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Thanks, that's it then, put the crystal in a cavity with mirrors. If I do not rotate the crystal to the correct angle I get nothing at all, so I have been rotating.
 

Alaskan

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Looking for 532 nm SHG cavities with mirrors, I have found some from YAG lasers which are separate from the YAG, but $$$.
 

ultimatekaiser

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Fun but expensive project. And yes they would be very expensive because they have to be absolutely rigid and precise.

You should get some output even without mirrors shouldn't you?
It depends on the gain of the medium involved. This is referred to as single pass gain, And generally the answer to it is no. But there are some instances where you definitely can get at least a little bit.

I do recognize that a YouTube video on this would be very helpful but unfortunately that involves so many topics that you would never be able to cover them all in a single video. There’s a lot of very complex physics involved. :)

If you’re making a Fabry Perot linear cavity, that would be fairly easy to start with, and aligning it would be not be too dissimilar to a helium neon laser with some extra components and rules.
 
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RedCowboy

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brianpe

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I am working on building one but it is very slow going. There's a lot I don't know...and the parts are quite expensive so I haven't run out and bought a ton of things to experiment with.

I started with a Spectra Physics ZLM I bought off eBay with the idea of converting it to 532. But I soon realized that there is a lot of beam folding in that cavity and I would have to replace all 10 mirrors and fit in a KTP with heater. And I wouldn't be surprised if one or more of the end mirrors is spherical.

I've now decided I will try to re-use the crystal and build something on an optical breadboard using all new materials so I have flexibility and room. Once that works I can look at machining something smaller. I've been reading a lot and there are a TON of variables and buying random parts off eBay doesn't give you the flexibility you need. My ultimate goal is something that looks like this:

Resonator Diagram.png

There are a lot of things I've learned:

Pumping

  • I plan to use Conherent FAPs. They're somewhat plentiful on eBay. No idea what a new one costs.
  • If you use FAPs, you really need to use Coherent's fibers or use fibers that are AR coated. I had some custom built from Thor Labs that weren't AR coated and destroyed both the fiber and a FAP. I have a new fiber coming from Coherent but it's taking months and the cost was over $300, so I'm constantly looking on eBay for them (1m Coherent fiber jumper part # 1005923).
  • I've built my own power supply for them that can be controlled by a microntroller. I'm working on V2 of that because V1 is a little too noisy and I worry about the FAP facets. I should be able to test V2 by the end of next week. The power supply runs on LiPos -- eventually I want this to be "luggable".

Resonator

  • You can't just throw a bunch of mirrors together. Each stage of the resonator (mirror, Vandiate, KTP, etc) needs to have an ABCD matrix calculated and altogether this determines if the cavity will be stable or not.
  • You can do the math for this in Excel, but there is an open source package called reZonator that takes all the work out of it.
  • Parallel only mirrors are very hard to align and not stable given the thermal lensing that will occur on the Vandinate. reZonator calculated that a 500mm concave end mirror would work for the above design.
  • I've never aligned a cavity before so I'm going to start very simple with just the vandinate and two mirrors to see if I can get an infrared beam, and then work up from there using an optical breadboard so I can move stuff around.
Alternative to building an end pumped cavity

  • If you search eBay for "laser marking pump module" you'll get a bunch of Nd:YAG modules. These are laser rods with integrated pump diodes. You just add mirrors, power, and a water pump. This could be a lot cheaper (and fewer things to engineer and go wrong) than using fiber coupling into a crystal. They're not cheap ($1500 for new Chinese ones), but 2 FAPS + fibers + collimating optics + crystal + TEC is going to cost more. I haven't gone there because I want this thing to be battery powered and the voltage requirements of these modules makes that harder.
  • To do this optimally you also need to temperature regulate the water to ensure the pump diodes sit around 808nm. These use YAG rods, not Vandinate, so they're robust but more picky about the pump wavelength.

Second Harmonic Generation
  • I've designed a mount for KTP that can fit a small cartridge heater, but I still need to learn a lot about what I need here. I'm going to buy a new KTP crystal from Eksma Optics to weed out odd angles and cuts I might get off eBay.
  • I've been reading Solid State Laser Engineering, and while I haven't done any math like that in over 25 years, there is a lot of value in that book. One thing I'm looking at now is proper phase matching of the KTP -- it's the difference between green and nothing, and even things like how long the KTP crystal is can have a huge effect.
  • I've looked at the two ovens /crystals above on eBay. Maybe they could work? But I couldn't find enough data to justify a purchase.

Sources

  • Right now I'm sourcing everything as new instead of buying used, so I can look at spec sheets and make sure I'm getting the right stuff. Of course I haven't really bought that much yet; I may course correct if this starts getting crazy expensive.
  • I've selected Edmund Optics for mirrors -- they have output couplers and curved mirrors and their tech support has been very helpful.
  • I'm going to use Eksma Optics for KTP and other crystals. They are a little cheaper than other places and have a good selection I can buy off the web.
  • Newport has the cheapest mirror and optics mounts I've found, and they have optical breadboards that are double density so you can pack things in tighter.
  • I don't have a machine shop, but I've been taking parts I custom designed in Fusion 360 and seeing what they would cost to machine through 3D Hubs -- they can do aluminum and stainless and their prices aren't terrible considering the cost of all this other stuff.

Right now I haven't even been able to get the Spectra Physics ZLM head to lase, so that's my first goal. I've bought a refocusable fiber collimator from Edmund Optics that will allow me to replace one of the FC fiber connections on the ZLM, and I hope that combined with my updated power supply will allow me to get some 1064 light out of it. I'd really like to get that to work before I rip the crystal out of it.
 

Alaskan

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Nice work, I need to copy your post to a Word doc. as a reference. I've been looking into using the same parts too, have more than one of those lasers. First, I'd like to produce 1064 nm, as you are working towards. I need an optics board too, I will look into the double density boards too, didn't know they offered those. Good work exploring the options on getting things machined and Fusion 360, another thing I need to check out.

What I've come to confirm is intracavity SHG is the only way to go for us at these power levels, well, at least for myself. Intracavity makes it far more involved to get something working, but supports the high gain needed.
 

brianpe

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Nice work, I need to copy your post to a Word doc. as a reference. I've been looking into using the same parts too, have more than one of those lasers. First, I'd like to produce 1064 nm, as you are working towards. I need an optics board too, I will look into the double density boards too, didn't know they offered those. Good work exploring the options on getting things machined and Fusion 360, another thing I need to check out.

What I've come to confirm is intracavity SHG is the only way to go for us at these power levels, well, at least for myself. Intracavity makes it far more involved to get something working, but supports the high gain needed.
I'm starting to think the harmonic separator is the way to go. This is basically a mirror that only reflects 532 so you can keep the 532 in the KTP section of the resonator. This opens up your options a bit as every mirror in the resonator doesn't need to be both 1064 and 532. And yes, everything I've seen shows that unless your are pulsing at very high power levels SHG has to be in cavity. The process needs a huge amount of incoming radiation to the KTP.
 

Arcygenical

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I got a nice 3mm LBO from ebay for 34$ so... APPARENTLY you can pump it with dual IR wavelengths and sum into the yellows and a few other optics (and a KTP I think) to hit that yellow I want.

Wow, that was one heck of an edit. Texting and walking is not my forte.

I'll find the paper for you. It's... Not very fleshed out - but, I couldn't pass up a mounted LBO for 34$.

Just ignore most of what I've said. The IR pumps are out of my price range. But still, LBO.
 
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kecked

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Get it to lase at 1154nm. That doubled is yellow. It’s possible. Find the optics.....good luck.

id like to hear more about 477nm pumping and what source makes 477nm. The yellow lbo I found is driven by 561nm. Don’t forget the rather temp sensitive oven for the crystals. I’ve never tried to make dpss but I have driven a ktp and bbo with a ps dye laser and getting the orientation right to make even a tiny amount of uv was hard.
 




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