What kind of rod is it?

[Alaskan]

This subject has enough to it to keep us studying for many years, specialists on top of their areas.

 

[styropyro]

You are right, forgot it's the other way around for doping, less for CW rods. I had even chimed into to another thread once pointing out CW rods are lower doped, how could I turn that around! Only reason I was interested in this rod is it has mirrors deposited on the ends for HR and OC. I would flash lamp drive this, already have the HV power supply and flash lamps I need, just need a mount and reflector cavity, to get it to produce the best power output.

The deposited HR/OC mirrors are very nice, now you don't have to mess with alignment. Those rods are hard to find IIRC.

Even if you don't know the doping concentration, Nd:YAG is forgiving somewhat because it is a 4 level laser system, so an underpumped portion of the rod won't absorb its own output. Now you could always do a calculation at 1% doping to get a ballpark estimate on input energy and power needed. Keep in mind though that the lifetime is 230 μs, which is less than 1/10 that of ruby, so you really need to blast it to get it to lase. If your flashlamp pulse is longer than the lifetime, you'll want it to be very intense. Luckily once you cross the inversion threshold, the rod will output a train of pulses until the lamp can no longer supply enough pumping power to keep the rod inverted.

I've got a newer edition in hardcover. It is an excellent text with a fair amount of math too. I have been reading it since I got it some months ago. It is also a great reference if you need to look something up quickly, but only after you are familiar with it.

I'll have to check out the newer edition, mine is the one from 1976. The math is nice if you want to learn the theory of what's happening at the atomic level, but it requires some knowledge of differential equations to make sense of it. Luckily for those without that math knowledge, the book is still filled with design parameters and other construction considerations that are hard to find via Google.

 

[Alaskan]

The seller reported he was able to get it to lase by simply wrapping the rod and flash lamp together using aluminium foil, and was able to put some nice burn marks on plastic, he doesn't have specifications other than the mirrors were found to be within 8 arc seconds parallel. I normally am not interested in rods without being able to use a q-switch of some kind with them, but being how simple this should be to get working due to having integral mirrors, it caught my attention. Price is 120 USD with a guarantee there is nothing wrong with the rod and is in perfect condition. By the color, I'm guessing somewhere around 1 percent doping, but that isn't something I can really know that way. However, being made for flash lamp pumping, it's diameter and length, I bet I'm close with that guess.

On the book, I can have my wife forward it to me later, I don't want to send it there now as my going to Qatar is not 100 percent, waiting on USAF approval.

 

[diachi]

I think most of us initially think the doping would be higher for a flash lamp pumped rod

It is, Styro just explained it earlier in the thread. :thinking:

 

[Alaskan]

Yea, what both of you said, it was an error in thinking at the moment, let's hope not due to old age.

 

[ultimatekaiser]

do a moh's hardness test. you can very lightly scratch the (non optical) side at one end a bit with something hard enough to scratch glass. YAG is hard like sapphire and fairly hard to damage so if it's a yag rod, then you'll know quickly as it wont scratch easily. glass is soft and doesn't dump heat very well either. yag is much more thermally efficient. that's the only easy way I can suggest to tell them apart easily.

you could also do a refractive test on them too. as they'd have different indices of refraction.

 

[paul1598419]

If I remember correctly, a piece of quartz is hard enough to scratch glass, but not hard enough to scratch ruby or sapphire.

 

[ultimatekaiser]

I believe you are correct. IIRC quartz is a 7, most borosilicate glass is about 5.5 (depending on the type) and yag is 8.5 i think.

 

[paul1598419]

If a YAG is the same hardness as a sapphire, it is a 9. Quartz is a 7, I think. I used to know these of the top of my head. I am sure Ruby and Sapphire are a 9, though.

 

[ultimatekaiser]

If a YAG is the same hardness as a sapphire, it is a 9. Quartz is a 7, I think. I used to know these of the top of my head. I am sure Ruby and Sapphire are a 9, though.

Alot of places round it up to 9. it's actually 8.5 according to most spec sheets I found. I looked them all up and verified they're all correct. though ultimately it doesn't matter as quartz still gives the desired effect. as would a razorblade most likely.

 

[LSRFAQ]

Density Grasshopper, Density.
Measure the Density, not the hardness!

It is almost certainly YAG, as ND: Glass has only really ever had one specific use in the last two decades in the laser industry. ND:Glass is used for it's wide gain bandwidth compared to ND:YAG.

ND:Glass is used for modest sized intermediate amplifiers in certain systems used in Energy research, and none of those systems would use a tiny mirrored rod.
Even though ND:Glass is easy to make compared to ND:YAG, it is a pain in the ass to set up in a working system. The reason why the lasting bandwidth matters is due to a unique issue in the ultrafast time domain and is far beyond the scope of this thread. I've used it once in my lifetime and I have no desire to fiddle with it unless there are spare rods laying around that are certified and tested. The Thermal conductivity is really bad, think several minutes between shots and it may need prefiring to condition it.
Nough said.

Steve

 

[paul1598419]

That is my understanding too, Steve. There have been Nd:Glass rods 2 meters long and 7.5 cm in diameter. They have been used in fusion reactions, but the thermal conductivity is so bad that the amount of energy you can pump into it is limited as well as the cool down time being much longer than other Nd media. Silica and phosphate glasses seem to be preferred when using glass. Another property I have found is the fluorescent linewidth on neodymium in glass is quite insensitive to temperature such that there is little change in performance over a temperature range of -100*C to 100*C.

 

[LSRFAQ]

I've installed ND:GLASS amplifiers. I know it quite well. The giveaway is it will lase around 1054 instead of 1064. It has, depending on mix, 30 to 50 nm of gain bandwidth which is the real reason it is used in big amplifiers. Due to thermal shock, and the low thermal conductivity of Phosphate Glass, what I installed was rated at 1 shot every five minutes.

So the odds of that rod being glass are nil. Non-zero, but very, very, low.

Alaskan, with the integral mirrors that rod will probably exhibit spiking, which is making a long train of self limited self q-switched pulses, once you pass a certain pump threshold. If you shape the current to the flash lamp with a series inductor, you can collapse that down into a smooth pulse with just a few leading spikes. This will make it more useful. You select the inductor to make the lamp current pulse have a very straight leading edge, an exponential decay, and about 270 microsecond pulse width. An extreme inductor will convert it into a long pulse laser if you have enough capacitance.

Steve

 

[RedCowboy]

Pretty purple glass, and just look at all the flash lamps, I can see them through the glass on the other side too.

 

[paul1598419]

So the odds of that rod being glass are nil. Non-zero, but very, very, low.


Steve

I agree with everything you said until I got to this line. What rod are you talking about. I have no idea. The information I have came from "Solid-State Laser Engineering", by Walter Koechner. I have a late edition hardcover copy.

 

[Encap]

I agree with everything you said until I got to this line. What rod are you talking about. I have no idea. The information I have came from "Solid-State Laser Engineering", by Walter Koechner. I have a late edition hardcover copy.

LSRFAQ is talking about the rod Alaskan asked the question about as to whether it is ND:YAG or ND:Glass in the OP when he asked "Guys, can someone give me an opinion of what you think this is? I'm being told it is a ND YAG by the seller and someone else who saw the photo that it is ND Glass, probably Russian manufacture." and LSRFAQ's reasoning behind the statement "So the odds of that rod being glass are nil. Non-zero, but very, very, low."---see the question in the OP .
Is what the entire thread has been concerned with and attempting to provide an answer to, primarily.
At least that is my take.