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FrozenGate by Avery

Diode pump a ruby laser?

Markus Unread

Markus Unread

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Instead of flashlamp pumping a ruby rod laser, what about diode pumping? Does anyone know what pump frequency a 694.3 nm ruby rod likes best?
 





Technically you can use the 445nm diodes to pump it, but there's a problem, heat. I know of only one CW use of ruby laser rods, a very small piece was pumped by a 5W argon and even that barely produced any power out, the ruby rod was cooled with LN2. In theory you could align a couple XJ-A140 arrays with the knife-edge assemblies and go to town, so long as you don't mind your ruby rod shattering from thermal expansion.


Edit: It's also a Three-Level lasing medium. And the first CW attempt was using mercury arc lamps.

"A CW-pumped ruby laser, which used a rod 2 mm in diameter and 50 mm in length, generated an output of 1.3 watts at an input of 2.9 kW. Only a small part of the crystal's cross-section was excited by the filament arc, and lasing action occurred only in the small volume of 6 x 10-3 cm3. Using this value, the lamp input power per unit volume of active material required to obtain threshold is approximately 230 kW/cm3. The main reason for the poor efficiency was the low absorption of useful pump light by the small lasing volume."
Click to expand...

Read more here: http://www.repairfaq.org/sam/laserssl.htm#sslcwr
 
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I had no trouble loading the data sheet:

http://www.klastech.com/download/ipjmqq

Klastech uses resonance to build up a high enough 532 nm field from a green dpss to pump a tec cooled, tiny, ruby crystal and get cw. IE Fox Smith Interferometer. Consider thet 514 is on the edge of the ruby pump band, and 532 is in the middle, so much more conversion, and no need for the Ln2.

SAM and I are updating the Ruby chapter.

Steve
 
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I think ruby runs as a relaxation oscillator. The lower laser level is ground. In a basic flashlamp pumped system, a single pulse contains many sub-pulses: tiny pulses within a pulse. In theory it could oscillate continuously, but the rod would overheat due to the amount of energy needed from a broad band source.

I've pondered the possibility of transvers pumping a ruby. It could be pumped by a dye laser, and the dye laser beam could be focused to a line on the surface of the ruby. The pumping technique would be identical to how dye lasers are pumped using nitrogen lasers. However, a normal laser ruby would not work. It would require a ruby with high enough chromium content to absorb the dye laser beam at the surface - the same way R6G must be heavily concentrated in order to absorb all of the pump beam at it's surface. The main problem is that I do not know if such a ruby could be made to lase at all, let alone generate the common 694nm wavelength. Chromium might no longer be fluorescent enough, once heavily concentrated. Another problem is the fact that ruby is a 3 level laser. With the lower laser level being ground, over 50% of the chromium atoms must be excited before any laser activity is even possible. I believe that is part of the reason why the threshold of ruby is so horribly high. Once heavily concentrated, it might be correspondingly harder to reach threshold given the greater number of chromium atoms: ruby absorbs it's own output if unpumped! So what might be required, is some kind of balancing act: a balance between energy density via extinction depth of the pump beam, and percentage of chromium concentration. Again - not sure how chromium concentration affects lasing, if all other factors remain unchanged.

I'm just curious. I wouldn't be trying to do anything practical with such a setup. However, the peak power of a pulsed dye laser is higher than that of any CW laser I've encountered. So pumping with a pulsed dye laser might not be that difficult (just for a fun experiment) compared to doing the same using a diode laser based pump.

Jarrod
 
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Interesting article, thanks for sharing. I think we can let you off on the necroposting.
It's surprisingly not difficult to do. The paper is so concise that it technically could be replicated.
I have a ruby rod and a bdr-209, might have to think about getting some optics. The only thing is my rod is much longer, so would need longer focal length lenses and mirrors. This would sacrifice conversion efficiency though.

Edit: Here is my rod fluorescing under the 405, 520 and 532nm.

405nm: End pumped and side pumped.

ruby 405 resized.jpgruby 405 (2) resized.jpg

520nm:

ruby 520 resized.jpgruby 520 (2) resized.jpg

532nm:

ruby 532 resized.jpgruby 532 (2) resized.jpg
 
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A longer focal length will reduce the pump intensity, you might not reach the threshold.
 
Pump threshold for 405nm was 200mW. Increasing the focal length by two will reduce the intensity by four. So a 800mW+ BDR-209 should still meet the lasing threshold theoretically. Just edited my last post with some pics.
My rod is 180mm long, with a doped section length 120mm. I can therefore just get away with using 100mm FL optics. I would need 800mW+ of 405nm, or 1.6W of 445nm. Both are achievable. So I may look into this a bit more.

Edit: It appears that the conversion efficiency goes down to ~1.2% at FL 100mm compared to ~3% at FL 50mm. Meaning if pumped by my 850mW, I could see ~10mW. Not a lot of power, but would make for a very special laser.
 
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At all locations inside your ruby rod where the pump intensity is not above the threshold, self absorption of the 694 nm will occur. You may calculate the Rayleigh range for a 100 mm lens, this gives you an idea how long the well pumped length will be. I fear, the rod is by far too long. Ideal are 5 mm (although we are saying 8.5 mm in the paper).
 
Yep, this is what I thought could be a problem with a longer rod, as there is a lot of absorption. Still I have most of the necessary parts to hand. It's just the specialised optics I don't have. I'm just interested to see whether or not it is possible to even get a fraction of a mW out of it.
I recommend you introduce yourself on here, you sound like you've got some good knowledge already.
 
EBEOS said:
My name is Walter Luhs. I am the owner and creator of all laser kits on https://luhs.de.
I am holding a degree as engineer, physicist and PHD in physics (Photonics) since 1983.
Click to expand...
That would explain your expertise. Nice to meet you Walter. :) I’ve wondered about your kits for a while. That Pr:YLF also interested me. I recommend you introduce yourself in the welcome section of the forum. I’m sure you will fit in well here. (y)
 
Welcome, Walter. We do have several laser professionals here, so you will fit in nicely. I have not checked out any of your articles before today, but I plan on doing so soon. :cool:
 
CurtisOliver said:
Interesting article, thanks for sharing. I think we can let you off on the necroposting.
It's surprisingly not difficult to do. The paper is so concise that it technically could be replicated.
I have a ruby rod and a bdr-209, might have to think about getting some optics.
Click to expand...

But that rod is not lasing there. It does produce a red dot, but i'm sure it's not monochromatic, it's just fluorescing.

This is perhaps similar to a laser diode running below it's lasing threshold current: in produces light like an LED or something similar, but not monochromatic or collimated. If you'd put an optical cavity around that rod that would allow lasing using a flash lamp as the pump, i'm quite sure it would not lase using any of the setups you displayed.

Nice photo's none the less!
 
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