Notes on do-it-yourself DPSS from parts available online

[goninanbl00d]

In this thread, I've scraped together information regarding these kits at the request of Prototype. This thread is also intended to help those attempting to build their own DPSS system from scratch.

If you simply want to build a green laser, this guide may be more useful:

http://laserpointerforums.com/f51/build-guide-comprehensive-guide-your-first-build-53972.html

However, if you want to build a DPSS laser from scratch, then this is for you. As of yet this is not a complete guide, however, I do plan on expanding it. It's a handy reference if you want to buy parts (such as crystals) online.

Firstly, quite a few people have asked about the kits offered on eBay by aerodynamics2006. He offers two different types of kits, one for building a 'laser pointer' and the other for a lab laser.

http://cgi.ebay.com.au/BIG-GREEN-LA...381?pt=LH_DefaultDomain_0&hash=item27b5e48acd

The parts for the laser 'pointer' is often the first thing brought up at the mention of a DIY DPSS system. This kit supplies a driver, driver and diode mount, independant Nd:YVO4 and KTP crystals, output coupler/expanding lens (one optic serving two roles) and a final expanding lens.

This kit is nothing more than a 25mm green laser module which has been disassembled. The driver holder is the exact same form factor as other 25mm modules sold by various stores online. As a result, this kit assembles into a 25mm green module, which is a drop-in fit for many of the larger 'torch' and RPL-style hosts available online.

Unlike the 12mm modules, these 25mm modules loosely conform to a form factor, all featuring a switch and LED in the same position. They have formed a de facto standard for high-powered Chinese portables.

The module takes a C-Mount diode- this is screwed directly to the base, and connected through the baseplate. The crystals are then aligned in the holder, and glued down with epoxy once in alignment.

Perhaps the most important thing to note here is the independant crystal set- the Nd:YVO4 and KTP are both heatsinked and seperated. Not only does this mean you can use the crystals in other projects, it also means that the crystals can handle much higher powers than possible with a simple bonded set.

Note the seperate KTP and Nd:YVO4

This also has the advantage of being able to temperature-control the Nd:YVO4 and KTP independantly, which is extremely important if you're intending to build a high-stability lab-style laser.

Independant crystal sets with an independant output coupler also handle heat better- they do not suffer from thermal lensing and distortion as badly, as the components are allowed to warm up at their own pace. This also reduces thermal-related stress which is a leading cause of death with cheap bonded crystal sets.

Although there are high-performance bonded crystal sets available, they are generally less stable due to thermal stresses, and often have shorter lives.

The seller also has individual mounted components available, and mounting blocks for Nd:YVO4 and KTP crystals. You can get larger crystals from eBay seller snoctony or from O-Like. Both sellers sell coated crystals with the appropriate HR and HT coatings required for operation, with an external HR being redundant in most cases.

Plano-convex OC mirrors are available from quite a few eBay sellers for a reasonable proce. Regardless, a collimating lens will be required after the OC, as the beam from the crystals will be highly divergent.(not as bad as an uncollimated diode beam, but on the order of 15-20mRad.

Going back to what aerodynamics2006 offers, he also sells a high-current driver, larger crystal sets and a TEC-cooled C-Mount diode jig.

Perhaps it comes as no surprise that these components are also parted from a complete laser- this time a lab unit sold by Trilights, reviewed by a few members here, and known to be overspec. The TriLights cooling system is below:

Although not apparant at first, the diode jig is exactly the same as the one found in the Trilights lab units.

eBay on top, TriLights on the bottom. Thanks to LPF member dnar for the photos.

The internals of the high-current driver are also identical. The driver parted out is from the Trilights 200-500mW series, and as a result has beefier internals:

eBay on the left, TriLights on the right. Thanks to LPF member dnar for the photos.

In most cases this seller has simply disassembled complete lasers, and is selling the parts off as kits or spare parts.

The seller also has C-Mount 808nm diodes, however, none have been tested and their suitability for pumping DPSS systems is unknown. They look to be brand new, and it is highly unlikely they are pulled from either the modules or the lab systems.

Not all 808nm diodes are suitable for pumping either. Although Nd:YVO4 has a broad adsorption spectrum(when comapred to Nd:YAG), the pump diode's wavelength is still required to be within 2-3nm of 808nm.

The problem with cheap diodes (especially the 300mW 808s that are all over eBay) is that they are usually off-spec, sometimes as much as 20nm. Although the power output may seem to be fine, being off by 20nm simply means you'll get little to no green output. That's also why you can't get a cheap pointer and replace the pump diode with somethng a little more powerful, other reason being that crystal set (or even coating) damage is almost inevitable.

 

[millirad]

^ Very nice info indeed! Keep up the good work.

 

[JLSE]

Nice write up :beer:

I remember that seller when I started into DPSS, he had some interesting
parts. I bought a 9mm 808 from him, but later started buying from
snoctony.

That seller also had received neg- feedback for parting out cheap
DX type modules and selling them as new 'better quality' pieces.

Seems he is still parting out lasers which is something that any of us
could easily do..

The only thing I don't like about the crystals being separate is the
alignment process..

I have had to work with these in 473nm, and the alignment is
super tricky.

When you have a visible output to work with, alignment and setting
the pieces in place is relatively simple.

The problem I have found with getting the 1064nm output is painstaking.
Though it behaves like a raw 532nm output, there is no visual reference.

Using a power meter on the 1064nm output can be misleading. Example,
you start off and get say 200mW of 1064, while you continue to probe for
a higher output, all of a sudden the 1064 drops, and the 808 bleeds through.
You can easily begin to measure the 808 output while there is reduced 1064...

If anything it just takes a long time. The rigs that ive tried with 473 are
also not bonded sets. I find you have to constantly go back and forth
between the 2 crystals and try to fine tune the 473 output that way.


Id like to how companies like CNI assemble their DPSS systems. Or at least
the order of things and how they go back to correct.

If you don't mind some additional pics.. Here's a trick
the boys over at CNI use in their 473's to 'correct' splash.
I now refer to this as the 'popcan' method.

I found a piece of tin which really looks like a cut pop (soda) can,
with a small hole. Its purpose is to 'clip' all the splash surrounding the
beam.

In the pics below, you can see the 1064 output, the splash that the
piece of tin was used for, and one of the 473 that I realigned putting
out 100mW / 80mW stable.

There is also a pic of a side by side with a 445 labby.

 

[goninanbl00d]

Thanks. This guide will be seeing quite a few improvements and additions as I get more time to work on (and through) it.

The seller hasn't changed one bit, actually.

He still has the cheap crappy bonded sets for sale $16AUD shipped though. Not worth it- quite a few of us have had them die from thermal-related stress or the coatings burning off.

He's selling the cavity kit for almost $300. At that price you could buy a complete 250mW module, with properly aligned cavity optics.

Mind you, these crystals probably would have suffered some form of damage during disassembly. The Chinese are known to love their epoxy.

You're better off buying a complete module, rather than wasting your time aligning something that decides to shit out high-order modes depending on how much the seller groped it back home.

Having said that though, DIY DPSS is still fun, but rather costly- and we haven't mentioned 473nm yet. I'd really love to buy some cheap crystals and some diodes, and start experimenting, but it seems my budget says otherwise.

It's certainly a fun learning experience though, and can be a very rewarding one at that.

Aligning two sets of crystals certainly wouldn't be easy- I'd expect there to be a lot of trial and error involved, especially if it's your first time.

But I suppose it does get easier with a bit of practice. Two-piece 473 would be worse, especially around 5W or so of 808nm.

What I really want to do, though, is, once I get standing-wave cavities perfected, to start experimenting with other cavity designs, possibly building a ring laser too. That probably won't happen any time soon, though. Either that, or a large DPSS with a YAG rod and some big diode bars.

There's been one question that's been itching in the back of my head, though. How do you keep KTP dry, and stop it turning to mush?

You can only keep it in a dry atmosphere for so long :/

 

[Benm]

Interesting to see that these kits are just disassembled modules - wouldn't make much sense to buy them though, unless they are somehow cheaper than the complete module.

As for keeping crystals dry: For KTP this isn't much of an issue, but the BBO crystals used to creating 473nm are hygroscopic and may require measures to keep moisture out.

 

[JLSE]

There's been one question that's been itching in the back of my head, though. How do you keep KTP dry, and stop it turning to mush?

You can only keep it in a dry atmosphere for so long :/

As mentioned below, I keep them packed with desiccant, and when employed in
a system, I assemble in a dry room, then seal them with o rings or silicone.

I dont think extreme measure is as needed like Benm said, unless your dealing
with BBO..

As for keeping crystals dry: For KTP this isn't much of an issue, but the BBO crystals used to creating 473nm are hygroscopic and may require measures to keep moisture out.

This is what ive heard... I keep mine in a sealed container inside another sealed container
with a few oz's of desiccant packs in each..

The only thing I dont store in a super dry environment are canned LD's.
Anything not protected or sealed gets the 'royal' treatment.

Hell of a way to lose invested money by not properly storing your
parts...

The great thing with living in Canada, is the only real humidity we see
is in the summer months. The rest of the year is pretty dry, and the level
of moisture is manageable. Still does not hurt to take proper
precautions.

 

[goninanbl00d]

As mentioned below, I keep them packed with desiccant, and when employed in
a system, I assemble in a dry room, then seal them with o rings or silicone.

I dont think extreme measure is as needed like Benm said, unless your dealing
with BBO..






This is what ive heard... I keep mine in a sealed container inside another sealed container
with a few oz's of desiccant packs in each..

The only thing I dont store in a super dry environment are canned LD's.
Anything not protected or sealed gets the 'royal' treatment.

Hell of a way to lose invested money by not properly storing your
parts...

The great thing with living in Canada, is the only real humidity we see
is in the summer months. The rest of the year is pretty dry, and the level
of moisture is manageable. Still does not hurt to take proper
precautions.

Ah, OK, thanks. :beer:

I already keep my crystal sets in dessicant, so it should be fine.

 

[JLSE]

Ah, OK, thanks. :beer:

I already keep my crystal sets in dessicant, so it should be fine.

On the topic of moisture, the CNI labbys ive been playing with
are not only sealed up, but in the front hidden behind
the faceplate is a filler hole. I'm guessing a nitrogen fill
after assembly?

I haven't gutted any of their 532's only 473.. I wonder
if this is something they do only for the BBO?

I have to get some more labby's from CNI in 532.
There is no better way to learn than to get your
hands in there and see how its done.

 

[goninanbl00d]

Yes, that is the case-532s are gas-filled too.

I remember someone here filling their CNI 532nm with argon, after they broke the seal.

Although the original filling gas would be nitrogen, argon is also inert and would be equally effective, if not more.