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Thread: ... will ruby spheres work for a DIY-laser?

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    Default ... will ruby spheres work for a DIY-laser?

    ... got a 16mm Ruby sphere and tested it on a 405nm-LED with 500mW optical output (the LED can emit up to 9Watts, but will need water cooling then).

    Here a video, showing the LED alone and with the Ruby sphere at max. 500mW output of 405nm - https://vimeo.com/285334438


    And some images:

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    For the human eye the glow stay red and will get only more intensive ... the camera is saturated at some hundred Milliwatts from the LED!


    Could be pretty interesting at max. 9Watts from the LED ... or with 3 of this 9Watt-LED's arranged around the "Äquator" of the sphere and two concave mirrors (one semi-transparent) on the "poles" focussing into the center of the sphere ...

    Viktor

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    I doubt it will lase but let use know if it does. You need mirrors to make it work. Calculate the threshold of the ruby I doubt you are anywhere near the threshold.

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    CW ruby has only ever worked in two cases, liquid nitrogen cooled and pumped by a CW Argon Ion Laser running at 514.5..
    At room temperature pumped by direct injection to the upper state via diode laser. The later was on the market for a while at a few tens of mW and withdrawn.

    Steve
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    ... so you think, 405nm won't be the right wavelength for pumping?

    Was thinking about placing concave mirrors, focussing on the sphere center, above the "poles" -- or silver-coating the poles - one 100% reflective, the other only around 90%, so the light could escape.

    27 Watts optical energy, injected around the "equator" into the sphere, should be enough to give some reaction ... if this works ...

    Viktor

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    ... has someone experience with pumping Fluoresceine?

    Have enough of it as powder or concentrated solution - here some of the (red) solution in the jar and two droplets of it in the left tube:

    Click image for larger version. 

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    And here some "illumination" tests with 405nm (min, max. at 500mW, same with camera adjusting brightness):

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    Viktor

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    Cool

    Quote Originally Posted by VDX View Post
    ... so you think, 405nm won't be the right wavelength for pumping?
    The visible absorbance peak for Ruby is in the blue-green spectrum. 405 nm is pretty far from that peak, so I strongly suspect you won't be able to get a population inversion, although you might still be able to get some fluorescence out of it.

    Was thinking about placing concave mirrors, focussing on the sphere center, above the "poles" -- or silver-coating the poles - one 100% reflective, the other only around 90%, so the light could escape.
    Those mirrors need to be super-precise. With a horizontal (rod) resonator and flat (planar) mirrors, they need to be ground flat within 1/4 the wavelength of sodium light. (So within 147 nm!) With a confocal cavity you do gain a bit of wiggle room with regard to mirror shape, but it's still going to be damned hard. Then too, you will need another lens to correct the beam coming out of that hemispherical output coupler...

    If you have access to a shop to grind your own mirrors, then you've got a shot. But if you need to order them custom, I'd think twice before spending the $$$ because you don't have a lot of gain medium available in the first place. As for pumping, I'd use 520 nm green diodes instead of 405.

    Finally, as Steve mentioned, Ruby normally operates in pulsed mode. To get CW operation you either need LN2 cooling or stupid-high pump levels.

    Adam
    Last edited by buffo; 08-17-2018 at 18:07.

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    ... what's with the idea to silver-coat the "poles" instead of using external concave mirrors?

    The manufacturer claims "super perfect spherical surface" ... but I doubt, the diameter fits the lambda/4 condition ...

    Viktor

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    How expensive is the ruby sphere? (How upset would you be if you ruined it?)

    If it's something you don't mind losing, then go ahead and try silvering the poles. (Assuming you have the ability to do so affordably.) Silver isn't the best option (dielectric coatings are more efficient), but it's better than nothing. Of course, even if you do get it to lase, you'll have to install optics above the north pole (output coupler) to collimate the beam.

    I agree that the surface of the sphere isn't going to be ideal. However, with a pair of hemispherical mirrors you'll have a confocal cavity, which means you might still be OK. As for the pumping, you can try the 405 nm pump since you already have it, but I think you'll get much better response from 520 nm direct-injection green instead.

    Honestly, I don't have a lot of faith that this will work, but assuming that you're just using parts you already have lying around (and assuming you don't mind messing up the ruby sphere), it's a fun idea - and if it does work it would be quite impressive.

    Adam

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    Some of the first Russian lasers were very large coated spheres filled with dyes. ... It depends on your definition of lasing. Spectral narrowing of the broad fluorescence to a single line with Coherence could be loosely considered lasing, but in this day and age people want to see a beam. Macro spheres make damn lousy resonators unless you mask the resonant coatings to just the ends. microspheres or tiny droplets are another story.
    ~
    Anyways one of the pump bands for Ruby upper stated is around 514-540... I can't guarantee you'll get any where close enough with 445..
    The company that briefly marketed a CW ruby placed TEC cooled micro crystal in a slave cavity of a 532 DPSS and thus did intracavity pumping at a beam waist in the cavity to achieve the huge pump field required.

    Steve
    Last edited by mixedgas; 08-20-2018 at 06:12.
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    ... the 16mm ruby spheres costs around 100 Euros, so not this expensive -- but it's more like "tinkering around", so not totally focused on forcing it to lase.

    Have too some Nd:YAG-rods already in a resonator setup from a flash-lamp pumped laser, where I was thinking about trying to end-pump the rod (instead of side-pumping with the flash-lamps) with 808nm diodes.

    Another option would be something sensitive to 975nm -- have different pig-tailed 975nm-diodes lying around with emitting powers of 5, 9, 25 and 30 Watts ... and combination possibilities for up to some Kilowatts of summed up CW power.

    But too -- not really focussed on laser-buildups ... have enough fiber-lasers (CW or pulsed) and other laser types for "material processing" in my basement

    Viktor

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