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How does Nd:YAG rod length affect laser output?

Joined
Jan 27, 2019
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I searched online but couldn't find any information at all. Likewise in the forum, but the search function broke Nd and YAG into separate tokens and so it became too small and too common to search for.
In case it makes a difference, I'm assuming that the rod is being pumped with 820nm light.

How does Nd:YAG rod length affect laser output?
Does a longer rod enable faster excitation?
Does it affect the wavelength?
Does it affect output power?
It seems to me that there should be some change.

Thanks!

PS: I'm not actually a physicist, so go easy on me please.
 





Joined
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I would suggest browsing Sam's Laser FAQ. https://www.repairfaq.org/sam/lasercds.htm#cdstoc
I don't know with certainty that you will find what you're looking for but it's a good place to start and information sources are cited.
If you have access to academic journals, through a university VPN, for example, you can also do a google scholar search and find literature that has more information than you will need.
 
Joined
Jan 27, 2019
Messages
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Google your questions there are thousands of results.
Nobody is going to write a dissertation on Nd:YAG lasers on LPF.
In the meantime see
When I said I already did, I really do mean it (Gah! I can't post links... Gah 2x, you have a link so I can't quote you!) Ok, a picure then...
tmp.png

I searched the wikipedia article, but didn't see anything about rod length or rod dimensions.
Now I don't expect a dissertation, I expect a link or two to the answer.
 
Joined
Jan 27, 2019
Messages
35
Points
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I would suggest browsing Sam's Laser FAQ.
I don't know with certainty that you will find what you're looking for but it's a good place to start and information sources are cited.
If you have access to academic journals, through a university VPN, for example, you can also do a google scholar search and find literature that has more information than you will need.
That was a good place to start. But only for 532nm crystal laser pumping. There's nothing there on length, dimensions, or size for Nd:YAG rods.
I don't have access to a university.
 

atomd

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Nd3+ is 4 level system so unexcited molecules don't reabsorb pump light.
Excitation speed is mostly dependent on your pump shape as lifetime of Nd3+ is ~250ns.
Shape of the rod doesn't really matter but it defines resonator shape and efficiency / power is defined mostly by how well you overlap pump and resonator mode.
 
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Nd3+ is 4 level system so unexcited molecules don't reabsorb pump light.
Excitation speed is mostly dependent on your pump shape as lifetime of Nd3+ is ~250ns.
Shape of the rod doesn't really matter but it defines resonator shape and efficiency / power is defined mostly by how well you overlap pump and resonator mode.
So the only real improvement that an increase in rod length brings is a larger area to cool?
 

atomd

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or if your pump has big mode it can improve power. How are you planning to pump it?
 
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or if your pump has big mode it can improve power. How are you planning to pump it?
I was thinking of using Xenon flash tubes in a double ellipse configuration. There are several such tubes on ebay, like this one.
Granted, Krypton would be more efficient, but those tubes cost 2x or more than the xenon tubes.
 

atomd

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Ok then longer rod than tube makes no sense and just complicates alignment. (except if you want Q switching then longer rod may help a bit with thermal lensing).
 
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Ok then longer rod than tube makes no sense and just complicates alignment. (except if you want Q switching then longer rod may help a bit with thermal lensing).
Thanks, that answers my question.
But I am curious, what is "big mode" pumping? I tried googling it, but I'm not getting anything useful.
 

atomd

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Thanks, that answers my question.
But I am curious, what is "big mode" pumping? I tried googling it, but I'm not getting anything useful.
So the problem really comes from diode pumped lasers. If you have single mode laser you can focus it and way you want and you want cavity mode (that is where the light is in laser resonator) to overlap as well as possible with pump mode (where pumping laser hits the crystal).

With your flashlight pumping you're more or a less pumping entire rod with external pumped mode than internal so you're forced to use plane-plane resonator (or one that's close to it) to extract as much power as possible (and have resonator mode fill ~entire crystal).

When we do laser pumped lasers in lab we often use hemispherical or confocal laser resonator and getting modes to overlap as much as possible is a big thing. ND3+ is 4 level system so unpumped regions don't hurt much but in 3 level laser systems (like dye lasers I work on) just a tiny bit of unpumped resonator can hurt performance a ton.
 

atomd

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To be fair 50W 808nm laser diode array pop on ebay ~100$ so it's worth looking into instead of flashlight. Sure it's a bit more expensive but 10khz rep rate instead of few hz is just so much better on eyes
 
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Please don't hijack the thread.
That being said, maybe you wanted to ask me in particular? I think this is what you are looking for: https://www.ebay.com/itm/292286131264
Sorry -- I asked because flash tubes were mentioned in above posts. I saw those tubes you mention and they are arc lamps.
High pressure lamps blow up if flashed. (lucky I was wearing glasses) !!!!!! Thanks for looking.
 




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