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Old 05-25-2015, 06:03 PM #1
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Default What determines output of a Nd:YAG Lasers

I need help in understanding Nd:YAG Laser Modules. Basically, how is the output power determined with Nd:YAG technology?

CO2 Technology
I fully understand CO2 laser system. In short, the power is mainly determined by the distance between the two mirrors and the length of the CO2 tube. While there are several other factors to consider, the longer the tube, the high power the laser.

Nd:YAG Rod Technology
I understand from pictures and simple drawings that a Nd:YAG rod that has been doped is excited by either a flash tube or a diode laser (I like the diode laser method), and that there are two special mirrors for 1064 nm wave length. One mirror is totally reflective; the other is 80% reflective. What I do not understand is what determined the output power of a Nd:YAG rod laser. I have conducted weeks of research on the internet, and either I missed it, or I cannot find my answer. Where do I find the answer to “How is the output power determined with Nd:YAG technology?”

Thanks for your help.
Mike


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Old 05-25-2015, 07:54 PM #2
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Default Re: What determines output of a Nd:YAG Lasers

Quote:
Originally Posted by mikefalkner View Post
I need help in understanding Nd:YAG Laser Modules. Basically, how is the output power determined with Nd:YAG technology?

CO2 Technology
I fully understand CO2 laser system. In short, the power is mainly determined by the distance between the two mirrors and the length of the CO2 tube. While there are several other factors to consider, the longer the tube, the high power the laser.

Nd:YAG Rod Technology
I understand from pictures and simple drawings that a Nd:YAG rod that has been doped is excited by either a flash tube or a diode laser (I like the diode laser method), and that there are two special mirrors for 1064 nm wave length. One mirror is totally reflective; the other is 80% reflective. What I do not understand is what determined the output power of a Nd:YAG rod laser. I have conducted weeks of research on the internet, and either I missed it, or I cannot find my answer. Where do I find the answer to “How is the output power determined with Nd:YAG technology?”

Thanks for your help.
Mike
It is actually determined by real world measurement of output.

Thoery and imagined Ideal Nd:YAG can be used to conceptualize how and why it happens---google and find hundreds of articles and papers on same

Maybe this will help.
Neodymium ions in various types of ionic crystals, and also in glasses, act as a laser gain medium, typically emitting 1064 nm light from a particular atomic transition in the neodymium ion, after being "pumped" into excitation from an external source

Like other lasing mediums, the output power from a YAG, ruby, or similar solid state rod will rise according to pump energy - but only up to the point where the active lasing medium is saturated (i.e. all the dopant ions are raised to the upper state). Beyond this point, no amount of extra pump energy will make any difference beyond generating unwanted waste heat. Also, a low-% doped crystal will reach this state more quickly, and will have a longer fluorescence period because the laser 'chain reaction' is inhibited by a reduced population of contributing ions - something like sticking carbon rods in a nuclear reactor to slow it down.

See: Encyclopedia of Laser Physics and Technology - YAG lasers, Nd:YAG laser, Yb:YAG, yttrium aluminum garnet and Encyclopedia of Laser Physics and Technology - lasers, principle of operation, resonator, cavity, laser beam, stimulated emission

Sam's is a good source of a lot of information about lasers and points to where additional information is located see: Sam's Laser FAQ - Preface, Introduction, What is a Laser?, Safety

There are thousands of aticles and research papers explaining in greater detail the physics which are complicated --just google

Last edited by Encap; 05-25-2015 at 07:59 PM.
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Old 05-25-2015, 08:01 PM #3
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Default Re: What determines output of a Nd:YAG Lasers

Encap - That is a huge step in the right direction for me. The simple explanation that the output power is limited to the lesser of either the exciting power or the ability of the Nd:YAD rod is the first step for me. Thanks so much. Now I need to get a better understand the technical aspects and details. With this very basic understand, you have pointed me in the right direction. Many thanks.

Mike
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Old 05-25-2015, 09:00 PM #4
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Default Re: What determines output of a Nd:YAG Lasers

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Originally Posted by mikefalkner View Post
Encap - That is a huge step in the right direction for me. The simple explanation that the output power is limited to the lesser of either the exciting power or the ability of the Nd:YAD rod is the first step for me. Thanks so much. Now I need to get a better understand the technical aspects and details. With this very basic understand, you have pointed me in the right direction. Many thanks.

Mike
Yes in part and very simply you have it right in a marco way. Thermal effects--thermal focusing and stress induced birefringence of CW pumped rod creates stability limitations---play a substancial role in Nd:Yag lasers also.

Am not sure what aspects if any you are looking to understand--so can not comment more. Keep in mind each crystal is different in many ways so....the conceptual stuff is for an Idealized imaginary laser --real world results vary for a lot of reasons. What happens is only understood to a certain extent but good enough to be useful in development of practical and functional lasers obviously.
.
That you can make an Nd:YAG laser is due to the ability of Nd ion's energy level jumping possibiliy and the ability to make them jump + organize the resulting output. YAG is a good host material because Yttrium ions in YAG can be replaced with Nd in the crystal due to similar size and structure ---is a very complicated thing in real life. Many factors go into determining output possibilities of any given proposed system.

Though the pages of simplified explaination here: Laser : Fundamentals - The Nd*:YAG laser gives a good macro scale understanding og Nd:YAG

With Output formula Laser : Fundamentals - Output power formula

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Old 11-08-2016, 03:03 PM #5
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Default Re: What determines output of a Nd:YAG Lasers

Well folks, I'm going to necro on this one, I know, not accepted much of the time here but it is either that, where I can hopefully add more information on the same thread, if I get answers, or.... start a whole new thread. I think it is better to keep questions about the same thing (especially since this is a very inactive subject) in one thread than to splatter questions about the same thing (kinda) over several threads in the forum, over time.

Here is the deal, I have been searching the net trying to get a rule of thumb understanding of ND YAG cavities, and I still don't have what I am looking for. I did find this document (link below), which tells me a lot about different kinds of cavities including some formulas to help determine some things, but I am just looking for a rule of thumb here. OK, here is the question, why are some YAG cavities long and others short? I see in the article I have linked to that the modes can change, depending upon the cavity length, but I have a SSY1 with a very short cavity, another Lumenis eye laser YAG which also has a short cavity of just a few inches and I don't think they are putting out strange complex modes in a surgical eye laser, then I see these big YAG's like Continuum made and they are fairly long, probably 16 or more inches long, why?

The reason I am asking is this, I have a NOS dental YAG which is capable of up to 300mJ out and want to make a cavity for it, but not a long one. Can someone tell me more about why some are so short because that is what I want to do too. Encap, if you see this post I could sure use your help.

I found this article, now seeing there is far more to a cavity than I thought:

http://www.uobabylon.edu.iq/eprints/...14877_1775.pdf

Regarding the original question the thread was started for, I would have thought the answer he might have also been looking for was in regard to how many Joules of energy the flash lamp is putting into the rod. I know there are other factors, as mentioned, but the amount of power dumped into the flash lamp(s) is a biggie too. Of course, the rod doping, its diameter, length (with matching flash lamp length) and cavity wall reflectivity all play into it and probably a lot more I am still yet to learn... well, no doubt.

Edit: The second link you provided talked about the flash lamp or pump energy

Edit, back to add this video

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Last edited by Alaskan; 11-09-2016 at 06:22 PM. Reason: I edited to fix a typo and then came back and added more later.
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