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KTP Crystal Size vs 1064nm Power Input.

Alaskan

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I'm interested in finding info on how large KTP crystals typically are in DPSS lasers for high output power levels of green. Does anyone know how large KTP crystals normally are in the China DPSS lasers for 10 watts of green CW output?

I found this info on Sam's Laser FAQ which gives me a great amount of info, but doesn't tell me the sizes we might find in commercial DPSS lasers at various rated output levels such as 5, 10, 25 and 50 watts. However, it appears a hydrothermal grown 3x3x7mm KTP crystal can do a whole lot of CW power input, far more than I'd be working with to produce 10 watts of green:



On another subject, has anyone here ever heard of directly pumping a KTP crystal with a 1064nm laser diode like this one? Curious how well that might work out.

http://www.ebay.com/itm/1064nm-3W-100-m-Aperture-C-Mount-Laser-Diode-/262694273052
 
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diachi

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Sizes used are going to vary, there will be a minimum, but sizes will vary above that. Selections will vary based on cavity design, power, cost and availability. More power will require a wider and higher crystal to accommodate a larger input beam so that the power density can be kept below the damage threshold. For CW lasers length is less of a concern and mostly affects conversion efficiency, up to a point. Standard lengths are 5mm and 7mm.


You might get some green by CW pumping a KTP crystal with a 1064nm diode but it's not going to be practical and I doubt you'd get very far. The low power will result in low conversion efficiency, the nature of a diodes MM output will definitely not help. There's a reason KTP is used in an intra-cavity configuration for CW lasers, it needs the higher powers present inside the cavity to become at all efficient. You could operate with a decent efficiency in an extra-cavity configuration if you are using a pulsed source (i.e. flash lamp pumped or Q-switched) for 1064nm as that will provide the high powers necessary for good efficiency.

Someone correct me if I'm wrong?
 

H2Oxide

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It depends largely on the intracavity beam. For example, if laser A and B are equal in power, but laser A has an input intensity of 200MW/cm^2 and a divergence of 10mrad, while laser B has an input intensity of 100MW/cm^2 and a divergence of 5mrad, then laser A will benefit most from a crystal around 5-6mm long, and laser B will use a crystal 7-8mm long. If the crystals were swapped, the conversion efficiency would drop drastically for both lasers.
 

Alaskan

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Oh lord, it's a power density computation, that complicates things. I have some ideas on the back burner and a few different crystals to choose from, so will work something out. Maybe by pure seat of my pants experimentation to see what happens but very time intensive to do that, having to make mounts for each size and temperature control them. I have some 3x3x3, 3x3x5, 3x4x20, 7x7x7x, 9x9x5mm crystals to experiment with. Although after watching LPF member Planters YT Tech Ingredients video on his 532nm project, unless the diode has a fiber output coupling to help homogenize the beam profile so it doesn't have hot corners which can physically distort the crystal surfaces, our C-Mount rectangular output 808nm diodes don't work as well for high power DPSS: https://www.youtube.com/watch?v=Pp9hliLJjg4

I've been told this KTP will work when driven with a diode or a pulsed ND:YAG. I have a 15 watt output large 400×1um emitter FAC corrected C-Mount diode I was thinking of trying with it, perhaps one of my FAP laser modules would be a better choice. Has anyone used a diode like that or a FAP laser module with large crystals like this before? If so, I'd like to see what the results were. I have not found a suitable flat vanadate crystal for high power pumping with 808nm yet, still looking for one on ebay, but non-linear crystals are far more common to find, the thicker YVO4 crystals non-existant when I look.



Here is a message I received from a friend about the above crystals:

They go to big pulsed scientific lasers made by continuum. They replaced the KDP doubler modules as KTP is much more efficient in making green, but they still use the KD*P or RDA for the THG units. They had a major engineering flaw, that if the beam hit the side internally the shock wave from the air being super-heated at the mount would make them crack. The fix is easy enough though, just glue them in the mounts with something optically translucent with a similar index to KTP, cheap clear RTV silicone glue will do. They like a bigger diameter high energy beam and are strictly pulsed duty crystals, they will shatter even at the 100W average q-switched level, but on the other hand you can do multi-gigawatt peak pulses with them on a triggered single shot or few Hz basis. I had a few of these a while back for a pulsed holography project i never completed.-customer cancelled it...
This is off topic for the thread, but wow, these new crystals can be flashed to lase with far less power than ND:YAG. Wish I could get my hands on one cheap, not an ebay item for years to come, if ever:



Yikes! Not hobbyist priced, I thought it might be expensive, but not that expensive.
 
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H2Oxide

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Yeah, doing it through brute force experimentation is going to be a costly project, though not completely impossible. If you want to take that route then all I can say is good luck. :p

The key is to find the perfect ratio between the drive and dephasing. If the crystal is too short, there won't be enough drive to get any reasonable efficiency. If the crystal is too long, dephasing will start to take over since it's a linear function, compared to drive which is a quadratic function.

There is an optimal crystal size for every cavity, though I'd recommend building your cavity to accommodate cheaper crystals, rather than build a custom cavity and end up needing custom crystals(!).

EDIT: regarding Nd:KGW, it looks like "KGW" is KGd(WO4)2. This makes me wonder if it would be possible to get a water-soluble analog such as KAl(SO4)2 (alum [yes the spice]) to lase if doped correctly. Then it wouldn't be too hard to grow at home, especially if the hydrates were capable of lasing. Just a thought. :can:
 
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Alaskan

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Well, I have a few to experiment with using a small eye YAG, ought to be interesting to play with them and see how they react, the YAG's don't put out much power, just a few mJ, so ought to be fine with any of the KTP crystals I have. The reason I am interested in the ND:KGW crystal is to reduce the size of the power supply battery needed to either flash, or side pump the crystal for portable operation. The water soluble idea is far beyond my ability to track anything about that, but you have me wanting to learn more.
 

H2Oxide

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Search Sam's made fan's. Pretty sure there is a page on home grown crystals using alum. Pretty sure the efficiency was low but it worked. I had forgotten about it until I saw this thread. I may see if I can find it when I have a keyboard in front of me.
Alum crystals are a 3rd grade science project. Super easy to grow, and with minimal equipment you can make nearly optical quality crystals. I'd love to see someone try to grow laser crystals out of it, but I haven't seen any reference to anything even remotely similar online.

However, people have grown KDP crystals at home. KDP isn't a gain medium, but it is a reasonably good NLO crystal. Maybe it'd be worth buying a pound of the raw material and trying it out Alaskan :whistle:.

Frequency Doubling with a KDP crystal

Homegrown KDP crystal and successful SHG attempt
 

Alaskan

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Growing crystals would be interesting, I spent a couple years researching the growth of crystals from a couple of organic sources and was very successful at doing so. Produced some of the highest purity organic compounds ever produced outside of a regular laboratory.
 
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H2Oxide

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I spent a couple years researching the growth of crystals from a couple of organic sources and was very successful at doing so. Produced some of the highest purity organic compounds ever done outside of a regular laboratory.
That doesn't sound suspicious at all. :whistle:
 

Alaskan

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I answered what it was in this thread earlier, the project was done as a extra credit project in organic chem class. Although completely legal also controversial, so I removed the post. Better to keep some things private, but this was near 20 years ago anyway.

Edit: I found a nice 808nm laser to push some power through my big SHG crystals. I have a 14mm long vanadate rod which can take the power from this big guy too.... :) I see some real green power in my future. Far field is a dot.

YVO4 rod:



I am still looking for a flat piece of YVO4/Vanadate 5mm to 8mm or larger on a side which is 4 to 6mm or thicker, if anyone sees one for a good price, please let me know.

More about the big 100W 808nm laser here (photo below): http://www.componentexchangeillinoi...nt-100WATT-808NM-water-cooled-laser-diode.php

 
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paul1598419

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Sorry, Alaskan. Just poking at your funny bone. The 100 Watt 808nm laser array looks amazing. I look forward to seeing how this progresses.
 

Alaskan

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I don't know what it is, had a blank look on my face and mind, now I need to google it.

Edit: I should have known as much as that stuff is in the news and that over the counter stuff used to make it. I am rather liberal viewed on drug law, but meth, not on that one.

I need some help with this 100/60 watt 808nm laser, the output is rectangular, but reading what someone selling one wrote, he said in the far field the output becomes a point which makes it suitable for pumping a vanadate to then SHG for green. I am getting conflicting information which makes me think that is non-sense, that I would be better off using a FAP laser output. Anyone?
 
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diachi

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I don't know what it is, had a blank look on my face and mind, now I need to google it.

Edit: I should have known as much as that stuff is in the news and that over the counter stuff used to make it. I am rather liberal viewed on drug law, but meth, not on that one.

I need some help with this 100/60 watt 808nm laser, the output is rectangular, but reading what someone selling one wrote, he said in the far field the output becomes a point which makes it suitable for pumping a vanadate to then SHG for green. I am getting conflicting information which makes me think that is non-sense, that I would be better off using a FAP laser output. Anyone?

You'll be better/easier using the FAP output for end pumping Vanadate, the beam quality is much better. Even if this bar is a point in the far field (how far?), it's still not going to be a nice homogeneous beam. I mean it'll work, but you'll get better results with the FAP.
 

Alaskan

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I'm thinking the same thing now, thanks for confirming. I read somewhere on line these beasts were used in newspaper printing.
 




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