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Ruby and 445nm

suiraM

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I'm considering testing whether the 445nm diodes can pump a ruby for pulsed operation, much the same as in using a flashlamp, but with only this narrow band (which I read to be in the mid of one of the pumping bands). If it works, I may decide to see if LBO or BBO doubling works as well.

However, I'm wondering whether anyone has tried it (in which case duplicating the test is less attractive), and whether anyone knows a good source for a small ruby rod? The ones in most listings are positively huge, and the one I already have is definitely too large for a test.

Ideally, I would prefer a thin disc, coated or not.

The same trick should work for Ti:S with reduced efficiency, but I've been unable to find any sources that don't charge exhorbitant sums for even the smallest sample quantities. Anyone looking to part with one can PM me, of course. ;)

Anyway, any good sources for small ruby rods or discs, or any advice on the attempt?
 





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Ruby is a 3 level laser. It's possible to make it CW (I've seen it somehwere), but it's very hard. Any region not pumped is absorbing, so you'd need the right size of crystal with the right doping and match the pump beam to the mode diameter.
 
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Interesting idea there, I have always had an affinity with ruby as a laseing medium. I understand your wanting to do this with a small piece, but I have heard that cooling a ruby medium can be difficult. And please correct me if I'm wrong, but didn't the first CW ruby laser need liquid nitrogen for cooling? And if memory serves this was with a tiny 3mm long rod. :thinking:
 
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3mm wide, maybe. The surplus rangefinders didn't have any active cooling, but it was single-shot operation like with most ruby lasers.
 
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^^^The one I was remembering was CW pumped by some type of arc lamp, and did indeed use a cryogenic gas for cooling, I think this was sometime in the early 60s, the first successful attempt on CW for ruby. Anyone remember this?

Edit, I found it in the laser faq. They used a mercury vapor lamp, pumping a 1 inch x 0.0079 dia rod. But could only maintain an 110HZ repetition rate. And it's output was only 2 watts!!
 
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benmwv

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What exactly is the pump wavelength(s) of a ruby laser?
 

suiraM

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405nm is fine by me, but are you sure?

The graph I saw indicated higher absorption at 450nm than at 400nm, by far.
 
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405nm and 400nm are close together (unless you ment 445nm). Can you post a link to the graph? I've looked up graphs too, I found one listing the transmitted light instead of absorbtion through a ruby rod, which might cause confusion.
 

suiraM

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Yeah, 405nm is significantly better absorbed. But 445nm seems to be close to 532nm in this regard, and the actual brightness per wall plug watt should be a lot higher, or am I failing to get something important here?

The curve I had seen is not on hand anymore, sorry to say.

Of course, I could try to compare the 405nm and 445nm ones, since the absorption may just be enough to make up for the difference in sheer output. Either way, it will take lots of power, as I've been unable to find one shorter than 3" so far.

Incidentally, there's one on eBay now if someone is looking for a flashlamp sized one.
 
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Absorption at 445nm will be half of what it would be at 532nm, and a quarter of what it would be at 405nm. The power of the input beam scales roughly same way, a 500mW 405nm is comprable to a 2000mW 445nm.
As it's a level 3 laser a higher doping would not only mean a higher absorption, but also that a stronger pump is needed. A lower doping hardly absorbes the pump light. This sort of goes both ways, but to know that exactly I'd have to look up the equations.

As you need to pump the complete crystal a tiny crystal would be needed, or the pumping requirements would be insane. Something in the size of 1mm thick I'd guess, this would make end pumping possible which is much more efficient. Making the cavity resonant to the pump wavelength is mentioned and would be effective, but would require a single mode pump in order to couple to the cavity. This would add the difficulty of keeping a cavity in resonance, but this project won't be simple anyway.
 
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It raises me so many questions...making a laser like this, kind of out of the blue is insane! or do u have experience in that field?? What would be your q-switching method? and do u have the necessary mirrors? this projects looks so huge! (to the ones that dont know, curious fact...ruby laser is a bit like the Ti:Sa...but in this case its Cr:Sa...cromium doped saphire! :D )
 




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