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Pumping a Ruby Rod

Mosc007

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I bought a Ruby Rod off Ebay some time ago. It does look like it might be ok. Ends are highly polished and its looks very clean looking inside it. No marks or colorations etc. It looks very pure.

Usualy these are pumped with Flash tubes. Getting flash tubes these days is rather difficult. At least getting ones that are usefull for pumping a Ruby Rod.

I have been thinking about pumping it with about 30 x 10 Watt LED's. I should be able to pump at least 600 Watts by using a Pulse at double the LED's rating.

My problem is what is the best Wavelength to Pump the Ruby Rod. 10 Watt LED's can be purchased in many different Wavelength.


Any suggestions as to the best wavelength to pump a Ruby Rod ?
 

Alaskan

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Pump with 550 nm green or 400 nm blue

Google: Ruby laser absorption bands.
 
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Mosc007

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Pump with 550 nm green or 400 nm blue

[urhttp://www.gc11.ac.in/wp-content/uploads/2017/02/Optics-IV-Assignment-of-Rahul-on-Ruby-Laser.pptx

Thanks. I have read a bit about the pumping frequency. Green at 550 nm but the documents don't say what wavelength the Blue should be.

Would you think only using 550 nm would be ok or maybe use both ?
 
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Mosc007

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Guess it's time to play and see what works. The LED's are not worth a great deal. Might order both and see what works best.
 

Alaskan

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Just found more info, you can get twice the pump efficiency at 550 nm compared to 400 nm blue.
 

Mosc007

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Just found more info, you can get twice the pump efficiency at 550 nm compared to 400 nm blue.

That's interesting. I was looking at the absorption graph and Blue is much higher than Green. It's easy to get Blue leds at 400 nm but Green is at best 520-530. Just a bit low.

I guess absorption is not the same as pumping wavelength.
 

vortish

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If you really want information on pumping a ruby rod or neodymium phosphate doped glass you really should ask UltimateKaiser! He understands the principles behind it I think better than just about any one on the forum! You really should pump it with a flash lamp if your looking to get a red beam out of it. It takes a lot of juice to get just a few microwatts out of those rods.

I did find some articles online on pumping ruby rods.
http://www.ece.umd.edu/~davis/C8.pdf

Its a little out of my league but I am interested in this as well. here is the wiki about laser pumping. https://en.wikipedia.org/wiki/Laser_pumping
it really is some fascinating reading.
 
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Mosc007

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I have read quite a bit in a few months after getting the Ruby Rod. The maths is way out of my league.

There doesnt seem to be a simple answer :)

I might just order some high power 405nm 10 watt LED's and see what happens. Violet is double the price of Green. But 550nm LED's are not easily available. I will aim for about a 600 Watt pulse at 405nm and hopefully something will happen. It will be pretty easy to drive the LED's with a pulser.

I have read about the CW Ruby Rod laser but it seems like it never made it into a commercial product.
 

WizardG

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I have read quite a bit in a few months after getting the Ruby Rod. The maths is way out of my league.

There doesnt seem to be a simple answer :)

I might just order some high power 405nm 10 watt LED's and see what happens. Violet is double the price of Green. But 550nm LED's are not easily available. I will aim for about a 600 Watt pulse at 405nm and hopefully something will happen. It will be pretty easy to drive the LED's with a pulser.

I have read about the CW Ruby Rod laser but it seems like it never made it into a commercial product.
Do you mean 600 watts peak power to the LEDs? I fear you may be a bit disappointed. A flashlamp used to pump a ruby rod will discharge hundreds or even thousands of joules of energy in a tiny fraction of a second giving peak pump power in the megawatts.
 

Alaskan

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I believe he must have meant peak LED power, might as well be considered pulsed CW, or just CW. May get some number of mw out of that rod if the light can be concentrated uniformly across the whole rod.
 
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styropyro

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Unless your ruby is tiny, you won't be able to pump it enough to lase with just 600W of LEDs. Maybe I'll go through the math to explain why...but there is a reason rubies are typically flashlamp pumped. You need a TON of energy in a very short amount of time (~0.003s) to make it lase. Also it doesn't matter if you were to use 550nm or 405nm...if you have sufficient energy from either it will lase.

Edit: The book "solid state laser engineering" by Koechner is a GREAT resource if you are looking to build a ruby laser. I learned so much from that book, and eventually used it to build my own ruby laser.
 
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Alaskan

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I'm not too hopeful a ruby rod can be driven hard enough with LED diodes to get a result, but I would like to see it happen, perhaps give up on the idea of a rod meant for flash lamp pumping and use a smaller length.

The first individual to discuss the possibility of a doped synth ruby being able to produce coherent light had eventually considered it impossible, due to how much energy it takes along with the size of a rod, believing it couldn't be driven hard enough to lase. However, one of the individuals who was at his lecture, Theodore Maiman, wanted to give it a try and came up with an idea to pump the rod more efficiently using a helical flash lamp coil inside a reflecting cavity... Obviously, it worked :)
 
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styropyro

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ughhh...now I'm just procrastinating... :D



A quick calculation shows that to reach total inversion in the rod, (doped 0.05% by mass Cr3+ and pumping with 400nm at 100% efficiency) you need 3854W of INPUT for every cubic centimeter of ruby rod. You need to be at half that to reach the threshold of lasing, but once it starts lasing you need to pump in even more energy to make up for that lost by the crystal.

So...you probably won't be doing that with LEDs. :eek: There's a reason those lamps for pumping ruby rods are operating in the megawatts when firing!!
 

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