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Thread: When Carbon Dioxide Attacks

  1. #11
    mixedgas's Avatar
    mixedgas is offline Creaky Old Award Winning Bastard Technologist
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    When I get done setting them up to make PPE I'll get back to you.

    M2 Was the new HR. Not a great HR, but still an HR. What would normally go out to the workpiece was reflected back into the system.

    There was no magic energy gain, you still had the same amount of DC running into the plasma tubes. The tubes only have a little storage, you can Q-switch Co2, but that is not what was going on here. What did happen is, at 10 microns, the phase of the wave matters, so all of the wavetrains from the lasers lined up exactly in phase at that melted mirror mount. That is what is so damn amazing about this.

    OK, take a classical church bell. It is a very high "Q" or quality factor at one note.
    If you take a tiny radio speaker and set it the right spot at the right frequency, but with a small air gap between the bell and the speaker, after a few seconds the bell can store energy from the speaker and be heard to ring faintly. If you give it a few more seconds, the bell can get quite loud. Its actually quite possible if the phase of the wave in air is right, to "charge up" the bell to have more energy flowing inside at resonance then the speaker is putting out, and after some time the bell has enough energy stored that when you turn off the speaker it keeps ringing and starts to decay slowly. Hit the bell gently with the striker at exactly the right time and it might change resonant modes and dump everything stored in the bell in a short ring.

    You can do this in optics by having a really high "Q" three or four mirror cavity that is actively tuned by a servo to exactly match the cavity length to the pump laser wavelength and store energy in the cavity. One mirror is partially transparent at the pump wavelength. The others are all really high quality reflectors with low scatter.

    'Bow Tie" frequency doubler should bring up a picture.

    So some how, some way, the damn CO2 stored up circulating energy and something melted, and it was not just in one pulse either. That thing probably took five minutes to melt. I'm not saying anything amazing happened and the process was probably quite chaotic. But definitely multiple reflections happened at exactly the right phase to sum and store up some energy. 220 watts might have became 600 or 800 or so circulating power outside the plasma tubes. Till something let go and the mirror mount flexed enough to stop it.

    You see this every day in your HENE. A large HENE might have 100 watts of circulating laser power in the cavity, but we can only let out 0.05% percent or the laser emission dies.



    Sam has a page explaining that in the FAQ.

    Its all about the circulating power. Whatever the circulating power got to be in the M2 cavity arm was, it was a very large quantity of energy.
    The key to understanding when it quit was when the cheap Gold on Silicon mirror let go and burned up. I'll switch the system to moly or copper mirrors when I can.

    As for the three mirror mess, crude analogy:

    Think about it this way. You have three theoretical bells tuned to the same note. The only thing you can change is the spacing of the two outer bells relative to the inner bell. One of the outer bells is the input bell and is pumped gently. If you get the spacing (Phase) and Q of the bells, just right, the inner bell just transfers energy from the two outer bells back and forth and stores almost no energy on its own because of the phasing. You could argue that the middle bell is not there....

    I'll shoot a picture of a three mirror linear Hene soon. I actually have a few of them.

    ITFFMBT, is right...


    Zinc Selenide melts at 1550'C. So something got really, really hot.

    I don't understand it all, I just have to make it work.

    Steve
    Last edited by mixedgas; 04-14-2020 at 08:00.
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  2. #12
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    ... hmmm sounds interesting enough, to store it in the back of my head ... maybe a methode to "chirp" a setup of a fiberlaser (1070nm) or 200W-diode (975nm) ... "nearly" perpendicular injected beam inbetween two long mirror stripes, so it "zick-zack" hundredfold along the stripes ... and then bend one of the mirrors to find a "sweet spot" ?!?

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  3. #13
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    Quote Originally Posted by mixedgas View Post
    The key to understanding when it quit was when the cheap Gold on Silicon mirror let go and burned up. I'll switch the system to moly or copper mirrors when I can.


    Got it. If the mirror at M2 had been of similar quality to a true output coupler mirror, it would not have failed, and the only issue would be when the tech returned at the end of the run and noticed that nothing had actually been cut...

    Adam

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