Modelling the Laserscope resonator

[Laserman532]

Hmm, the beam waist/spot size in the KTP will be smaller (1.2mm instead of 1.6mm)... which means more green and maybe burned KTP .

Could you give any more detail about this? I don't understand why it matters whether "OC" or "RAM" is HT532, as long as they are both HR1064.

Let me ask you this..if the sam or ram didn't reflect any green would you have an output? It is ok to ask questions and I am not the authority on this design, but the facts are.........it has been pretty well figured out IMHO. The reason why I am saying that is because..........I havent seen anything better or newer.

Steve R. is much more up on the physics as to why's & why nots, may be he will chime in

You can have a very small spot size in the KTP, even a focused spot......as long as you do not exceed the damage threashold of the material I think I read 1MW /cm2 is the limit for KTP, may be wrong but I think that is what I remember

[weartronics]

Let me ask you this..if the sam or ram didn't reflect any green would you have an output?

Well not from the "OC", but I would expect an output from the SAM or RAM. I think this is what Piotr is talking about, taking the output from the RAM instead of the OC.

Of course, if the SAM was HT532 (and the others were all HR532), then you would get less 532 output than using the RAM or the OC, because any 532 generated in the opposite direction would have to go through every component in the resonator twice more before it could escape.

However, except for the resultant beam shape, I don't see any difference between using the "OC" or the "RAM" as the OC. In fact, if the "RAM" was 50/50 for 532 and the "OC" was HT532, I would expect to get approximately equally powered beams out of each one!

I thought only the 1064nm has to resonate, any 532nm can be released as soon as it is generated. Maybe I badly misunderstand the physics of this...

[mixedgas]

[quote=Laserman532;84266]Let me ask you this..if the sam or ram didn't reflect any green would you have an output? It is ok to ask questions and I

Steve R doesn't know jack about green yag systems above 7 watts.

I've watched Dick Anderson align KTP532s from scratch, I've watched him and others walk them. I've walked two beat up old ones. But I've never played with the cavity dimensions. I've went through the frustration of trying to get them into a tight fiber for a client, However nobody has ever let me play with one at 60 watts, way too expensive if I were to make a mistake.

When I was a young lad and walked up to Mr B at a ilda conference, he was rather tight lipped, so I concentrated on Are Gones. I wouldn't blame him, for not answering my questions, that was back when he wore Armani and drove a Porsche. He probably had a ND with laserscope too.

My personal green thing needs a small single phase lamp supply before I can play. Its a V resonator, Biophysic medical unit, rated for 3 watts, capable of say 7.

I could tell you a lot about lower power stuff, but not much on the big boys.

Yes, it does help somewhat if you have stable green passing through your crystal, but most people design the cavity with either a IR brewster plate or a IR 1/4 wave plate for stability of the green using spinning polarization etc. Laserscope is just different from what I know.

When I have a PSU, perhaps I could play around and answer your questions.

I mean there are issues with walkoff, which is the green beam coming off at a angle to the IR depending on the type of phase matching etc, which is why a older Melles has two beams etc.

Until then, try to find papers by a guy named Baer and a Guy named V. Magni.

Magni worked out how to make yags with argon quality beams.

Other then methods for producing 3-5 watts of yellow, I havent read yag papers for years. Not since I tried to aquire the parts 12 years ago to convert a trimedyne 1000 to green, and could only afford Chinese optics at 250$ a optic, which had coatings that burned, literally.

I'm 575 miles away from where my archives are, so by the time I can help you, you guys will have it solved. BTW, I'm 10 feet away from a model 850 right now. I've done shows using KTP532 and LEE Laser Systems and I've repaired the psu side of SP Merlins, but I have not played around with the cavities.

Steve

[Laserman532]

i am really LOLing actually my first time ROFLLING...Mr B? Armni? Porsche? thats funny. (I assume you are talking about me and it was a ferarri) Steve, I have always been "fairly" open with my knowledge or lack thereof... If I was tight lipped it was because I had secrets and relationships and a few ND's along the way as well. But I dont remember myself like that

Lets see. If the SAM mirror was 532HT and the OC and RAM were 532HR...wouldnt any green light that was generated propagate back towards the q-sw and rod and then have to propagate back through the q sw and the rod again?????????????? hhhhhhmmmmmmmmmmm i wonder if this would be a good thing I hope my drawing works out below.

sam------ktp------ram
-
-
oc------------rod----q sw---hr

[Laserman532]

Well not from the "OC", but I would expect an output from the SAM or RAM. I think this is what Piotr is talking about, taking the output from the RAM instead of the OC.

Of course, if the SAM was HT532 (and the others were all HR532), then you would get less 532 output than using the RAM or the OC, because any 532 generated in the opposite direction would have to go through every component in the resonator twice more before it could escape.

However, except for the resultant beam shape, I don't see any difference between using the "OC" or the "RAM" as the OC. In fact, if the "RAM" was 50/50 for 532 and the "OC" was HT532, I would expect to get approximately equally powered beams out of each one!

I thought only the 1064nm has to resonate, any 532nm can be released as soon as it is generated. Maybe I badly misunderstand the physics of this...

Ok now i sort of see where you are going with this concept...If the Ram were 532HT green would exit there and the beam would have better properties. But when taking into account the physics of critical phase matching and the requirement to make a stable resonator (as I understand it) one would only get doubling in one direction and you might not get the high power as you would get with the current archeticture. I'm sorry I just dont know because I never tried to change perfection I never questioned Dirk Kuizengua as to "why" it was always "how much for how little"

It seems that Piotr is in the best position to answer these lingering questions using his experimental apparatous.

[mixedgas]

Ferrari, Porsche,Armani, JC Penny, whatever.
I figured you had a ND or Two.

Steve

[laseralex]

I am not seeing a beam waist in the KTP, and I am not seeing the expected 2.5X magnification from the end face of the Nd:YAG rod to the KTP. Kuizenga says the 4.0mm diameter rod should image to 1.6mm diameter in the KTP. PSST only models TEM00, but at least I expected the ratio to be the same.

I just ran your model, and when I used the measurement tool I found that the beam width is approximately 2.5 times greater at the face of the YAG rod compared to the location of the KTP. At the race of the YAG rod (position = 179mm) I get 1.1076mm and at the center of the KTP (position =949mm) I get 0.4282. Plugging those into my calculator, I get 1.1076/0.4282=2.58. You are right that the software is only plotting the 1/e^2 of the TEM00 so it won't calculate based on the full 4mm aperture of the rod.

I think the issue is your expectation that the beam would be focused in the KTP. It is certainly reduced compared to the size in the rod (by that 2.5:1 factor), but it definitely isn't focused -- remember, the KTP is placed at the image plane of the relay, not at a focal point. I'm sure that was done intentionally, to reduce power density in the KTP thereby decreasing the likelihood of gray tracking.

-Alex

[weartronics]

Hi Alex,

Thanks for trying out the model, and welcome to PL!

You're right, I assumed that the KTP is at a focal point and this is wrong. It makes more sense that it is at an image plane like you described.

Now I understand this model, and I think it is correct. Piotr may be interested to change this model to use the RAM as the OC now.

Best regards,

weartronics

[laseralex]

Thanks for trying out the model, and welcome to PL!

Thanks -- I'm glad to be here. I've been lurking for a while but figured it was time to jump in.
...

Now I understand this model, and I think it is correct. Piotr may be interested to change this model to use the RAM as the OC now.

...

In typical situation the 532nm output beam emerges through OC optic (50cm cc). My observations are that if RAM optic was allowed to pass 532nm then the green beam would be available for further manipulation closer to i's origin (i.e. KTP) thus having better initial specs, than the beam we get from OC optic.

As a coincidence I do have a mirror HR@1.06/AR@532nm 15cm r.o.c. I would consider to put in place of RAM optic for evaluation in my hybrid KTP / Greenlight setup.

I think this experiment would result in disappointment. While it is true that the beam will be smaller it is perfectly offset by the larger divergence of the beam, which you should be able to see clearly from the Psst! model.

The diameter*divergence product of Piotr's laser is basically fixed by the limiting aperture of the YAG rod, the length of the cavity, and the ROC of the RAM; the latter two are also related, as you can see if you play around with the Psst! simulation. Changing those figures could yield a better beam quality that what he has right now, but that would come at the cost of lower output power (unless of course the current cavity isn't optimized.)

-Alex

[Junktronix]

Nice setup Piotr! I have several of the 7x125mm pump chambers here and I think at least one reflector set and some flow plates just in case you do blow it up

Thanks Pat!
For quite a time I ws working with Lasersonics pump chamber with 3x100mm rod and gold elliptic reflectors, but the results were not too good.
Now I switched to Greenlight YAG pump chamber with 7x125mm rod and huge 6kW lamp. My current single phase setup is limiting me to 25A to the lamp, giving ca 20W 532nm, q-sw. I'm considering modifying my PS to go up to 50A to the lamp to see what's waiting there for me Big Bang I bet

Outcoupling through RAM should just improve just beam quality, not power, due to smaller initial diameter at exit, thats all I guess. *What if* optic relay was set to 3.3 factor (from 2.5) is another uncertainity.

Piotr.K