Lambda Physics

[VDX]

... what could be pretty interesting to "reactivate" -- DIY-disk-lasers ... here cheap or DIY-AR-coatings would be of much help too

Viktor

[LambdaPhysics]

Do you have any idea how the "raw" disc can be produced (or procured)?
I could make the HR + AR coatings... The AR will be, indeed, cheaper but the HR will cost at least EUR25/pcs + the condition to have a minimum of 20 discs for a batch...

[VDX]

... for an easier approach you can source a ruby-disk or cylinder ... another way could be "UV-fluorescent" glass or plastic tiles ... have some, which emit green by illuminating with 450nm ... or "orange" plastic sheets and rubys, "activated" by 405nm.

[LambdaPhysics]

I am not specialized in lasers, so all this is quite fascinating to me. The little I knew about thin-disk lasers was mostly about how precise everything must be to actually achieve lasing. I honestly did not know that lasing could be obtained with something other than Yb:YAG – so this is really interesting to learn.
What would be the ideal dimensions for such a disk, and what level of surface quality is required before applying the optical coatings?

[VDX]

... AFAIK the planarity and surface quality of the "disk" is not so essential, as the resonator-mirrors

[buffo]

Victor, are you saying that the end faces of the lasing medium do not need to be ground to be optically flat and parallel? This seems incredible to me, as I know the early ruby lasers had extremely tight specs for the rod ends. Based on what I've read, the end faces needed to be parallel within 10 seconds of arc, and the faces themselves needed to be smooth ground so that they were flat within one-quarter of the wavelength of sodium light. (So no more than 147 nm difference between the highest and lowest point on the face.) Can you explain why this does not apply to thin disc lasers?

Full disclosure here: I'm not claiming to an expert. In fact, I have zero practical experience with ruby lasers; I've never tried to polish a bare ruby boule into a working rod, nor do I own an optical bench, or test flats, or any of the lapidary tools needed. I'm just quoting the specs that I vividly remember reading in a book many years ago. (A book that I liked so much that I later bought a copy, despite it being out of print, so I could have a copy sitting above my desk to double-check the quote above before I posted .) That book is John M. Carroll's "The Story of the Laser", and in Chapter IV he explains the construction of a ruby laser in detail, from boule, to resonator, to the flashlamp power supply, and finally the trigger supply.

Regardless, I'm very curious how a thin-disc laser could get around these demanding edge-face requirements.?.

Adam

[VDX]

... here the English link for "disc-laser" - https://en.wikipedia.org/wiki/Disk_laser

I don't know for sure, which specs the surfaces need - some laser-rods even have "slanted" ends to avoid destructive interferencies.

In the Wikipedia-link the back side of the disc is coated as back resonance miror ... in my 20W-Type from around 2005 the disk was placed inbetween a resonance cavity and "pumped" with a 60W IR-Laserdiode ...

[buffo]

... here the English link for "disc-laser" - https://en.wikipedia.org/wiki/Disk_laser

Yeah, that's the arrangement I had in mind. But I don't see anything in the article that talks about the surface of the disc... Still, given that the lasing medium is also the mirror, would that not imply that the surface quality is crucially important?

some laser-rods even have "slanted" ends to avoid destructive interferences

Indeed; the Nova laser at the National Ignition Facility used elliptical discs placed on the diagonal (I think at the Brewster's angle, in fact) inside each cylindrical pumping cavity with the flashlamps positioned around the circumference of the cavity.

However, those discs were still ground to be exceptionally flat and their faces were parallel to each other.

In the Wikipedia-link the back side of the disc is coated as back resonance miror

I don't see that in the article.?. The article talks about the active mirror concept, but I don't see any mention of an optical reflective coating on the surfaces of the lasing medium.

It was my understanding that the polished face of the disc *is* the mirror, just as the cleaved ends of a laser diode serves as the cavity mirrors - no external coatings required.

in my 20W-Type from around 2005 the disk was placed inbetween a resonance cavity and "pumped" with a 60W IR-Laserdiode ...

OK, so this was a disc with external mirrors, meaning the lasing medium was not connected to a heatsink at the bottom as in a traditional disc laser. This sounds similar to the amplifier arrangement from the Nova laser at the NIF I mentioned above.

In your laser, how flat were the faces of the disc?

Adam

[VDX]

... with my disc-laser then I was only using it some weeks, then the developer borrowed it for an exhibition and damaged it at transport back ... no further infos for it

The mirror coating was mentioned in the German version:

Diese Scheibe ist auf ihrer Rückseite mit einer hochreflektierenden Beschichtung bedampft und dient gleichzeitig als Resonatorspiegel.
(This disc is coated with a highly reflective coating on its reverse side and also serves as a resonator mirror.)