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Thread: The Really Big Dye

  1. #21
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    If you really did want to get more energy I would suggest going to a MOPA configuration. As long as your windows are not blowing out yet you should be able to convert your current cell into a 1 or 2 amplifier(you probably have a gain >10 pass already if the cell looks like what I envision it does) and build a second smaller cell to use as the oscillator.

  2. #22
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    @Kecked
    That drawing is for their spatial filter. If they used a pinhole like a normal person it would explode, but by using 2 perpendicular slits like shown in the drawing you can spread the energy out.

  3. #23
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    The only other way I see is medium flow to take the inverted away
    The pulsed output occurs over 20usec, every few seconds. The medium does not move appreciably during each pulse other than to expand due to heating (thermal lensing). The dye is replaced many times between pulses.

    Why does a smaller cell work better? Would seem to work worse. I know very little about these lasers but they have fascinated me since I was a kid reading SciAm.
    This is because the dye is energy starved. The conversion efficiency of laser pumped dyes can reach 60% while lamp pumped lasers rarely exceed 1.5%. The flash lamps produce way more than 2.5% of their output, squarely in the absorption band of the dye. It is the achievable pump intensity with lasers that makes up a significant fraction of the differential. If the pump chamber is good (mine is excellent) and couples the lamp into the cell then the smaller the cell, the higher the cross sectional intensity in the cell. The limit is that the coupling efficiency is inversely proportional to the surface area of the cell vs the area of the reflective surface of the chamber.

    Are you going use it for a projector?
    Oh, my god, not unless we are at war!

    If you really did want to get more energy I would suggest going to a MOPA configuration.
    The current triggering method that I am using has too much jitter to permit that unless I configured the oscillator to be pumped by the same electrical pulse. I did consider this when I was using spark gap triggering, but the energy output might not be better. I base this on the fact that as I used output couplers of gradually increasing reflectivity ( I have a lot of mirrors), the output decreased. I don't think I am failing to extract the amplified energy effectively due to insufficient feed back or a lack of intra-cavity intensity. A MOPA is also supposed to improve beam quality, but here, I also question the fact that even a single mode signal will suffer from the distorting effects within the amplifier. ASE does not seem to be occurring as the output ceases when the mirrors are removed. In any case, the cell windows are the only optical elements that I have not damaged at some point. Knock on wood.

  4. #24
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    What sort of output coupler percentages are you using? I suppose it makes sense the gain would be modest given that your in-band pump fluence is relatively low compared to a laser pumped design, and the gain spectrum bandwidth is so large in the common dyes.
    Not sure if it was obvious to everyone, but my motivation for suggesting the MOPA was to help you avoid blowing up your cavity mirrors (in a single pass configuration you don't need any mirrors, and even in a multipass configuration the mirrors see at worst the output intensity without any enhancement from the cavity). But if your gain-per-pass is low you won't get great efficiency without a ton of passes and it looses its appeal.

  5. #25
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    I'm using 20% reflectance.

  6. #26
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    OK, the first video is up. There will be 3-4 to follow in short order for those interested in doing something along these lines. Hope you enjoy it.

    https://www.youtube.com/watch?v=vNby-VcR5FI

  7. #27
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    Quote Originally Posted by danielbriggs View Post
    Oh my god👊🙀. 25%. You could pop a car tire at a mile

  8. #28
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    What I don't mention is that I am supplying the lamp with 25% of the maximum INPUT power.

    Click image for larger version. 

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    In figure 5, this corresponds to approximately 125 J into the ablating wall lamp discussed in this paper. The OUTPUT is far from linear.

  9. #29
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    Impressive result! One of the highest energy hobby lasers I have seen, let alone a visible dye laser... Can you ionize air? With your short pulse duration and moderate beam quality it seems possible.

    Looking forward to the followup videos

  10. #30
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    Peter,

    I knew you would ask the one question that is my current, burning question. I am close. I am very close. When I post the video that goes into the optical design, you will see that I have incorporated some beam enhancing elements that make a very big improvement in beam quality and I think there is still some room for improvement. It is this and not the high energy that is the core of what makes this laser unusual.

    I may need an aspheric focusing lens to get to the necessary intensity. Also, the beam has some structure and this may be further improved with a pair of axicons. I already have these from Eskma. Note the hot spot in the burn pattern. If I can reapportion a greater fraction of the output into this mode(s), I'm sure I'll make it.

    Has this ever been done before with a lamp pumped dye.

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