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Thread: NUBM44 blue- New Video

  1. #121
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    Quote Originally Posted by jors View Post
    Correct vertical axis with a pair of prisms in inverse relation 1.65:1, so you shrink 8mm tall to 4,8mm tall, this is: 8/1.65x=4,8mm
    Now expand horiz axis until 4,8mm with cyls as usual.
    Can I rescale the vertical axis from 8mm to about 4.8mm with a pair of flipped cylindrical lenses instead of prisms? Just want to be sure I understand the theory. You are thinking of decreasing the vertical beam size and increasing the vertical divergence with another set of optics?

  2. #122
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    Curiously when the colours come from the same Laser tube (eg.Krypton- Blue/Red) this does not occur.
    This says a lot. And, I don't doubt your descriptions, but there must be an explanation. This is why good science trumps even good politics. The explanation needs to be found, not a consensus of opinions.

    Occasionally, I lightly fog the shop, this is a great method for aligning beams on the table, in a projector and for the spacing of lenses. This even works for IR when viewing the beams with a camera. This should not be overdone or done with oil based fog and the fog should be dumped outside ASAP to keep the residue down.

    It is clear that multi-colored beams can be aligned better or worse. However, there are still a lot of potential sources that might allow the components to be seen in even a well aligned output.

    The lasers are often multimode and the intensity across the beam, even from an ion may not be the same for each color.

    Also, Raleigh scattering increases as wavelength decreases and so a beam that appears bluish near the laser will be loosing its blue intensity to scatter as the beam travels down field. Even though the scattering will favor blue visibility there will be a point where the blue component has lost enough energy that the beam begins to appear reddish. This is a significant effect and I see this all the time even with beams that travel only a few tens of meters.

    It is possible that what is seen is primarily the scattered light that surrounds even a TEM00 beam. If the laser sources are not spatially filtered then this scattered light from optical components and from whispering modes generated within the laser itself (an interesting process I have been working with and I'll discuss later) can be significant. When the light is generated in the same tube these modes will tend to correspond for all the colors.

  3. #123
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    One of the reasons I am trying to get so much extra power is I plan to use a spatial filter on the combined result that clips so much of the beam that even when the beam moves due to expansion the core is still fully mixed. If I get 5W raw I expect to see 500mw of absolutely ion quality on the wall. The color halos drive me insane. If it was not so hot noisy and required 20 amps I'd get a whitelight ar/kr and call it a day. But then I'd complain about the residual dot and tail from the blanking servo.

  4. #124
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    If you plan to spatially filter all the colors at once then use an achromatic lens pair so that the different colors come to approx the same focal point between them. The chromatic aberration will also be less if you max the FL of this lens pair as well. Your losses do not have to be anywhere near this large, but if you are willing to loose a lot of power then under drive the diodes. Many mutli-modes will become single mode just above threshold and in any case the divergence improves when you do not drive them hard. The higher order modes have higher losses and higher divergence and as the gain (power) drops they will not lase.

  5. #125
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    Planters, how much power output have you seen from a multi-mode LD which will operate in single mode just above threshold? Can you tell me which diodes have behaved this way? Perhaps you haven't tested yourself but have the knowledge of this phenomena? Curious because I am interested in single mode laser pointers, maybe I can get more power out of a single mode LD designed to be single mode, that would be expected, but I had to ask.
    Glowing green eyes is a camera photoflash reflection.

  6. #126
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    It has been some time and the output was quite small. I am almost certain that you would be safer staying with the single mode diode. This property illustrates that the multimode beam quality progressively decreases with power.

  7. #127
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    Since Jordi seems to have nailed down the main questions posed in the thread I think we can go of topic a bit ....again!

    @ "The lasers are often multimode and the intensity across the beam, even from an ion may not be the same for each color."

    When colours are produced by two different laser tubes this has always been the reason I suspected to be the cause.
    The cases I described are all using multimode optics and the wave fronts look a but like the Alps so I assumed that different peaks caught different particles in the air .

    @ " "whispering modes generated within the laser itself (an interesting process I have been working with and I'll discuss later) "

    I am all ears on this one !

    Cheers

  8. #128
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    I am all ears on this one !
    This property is interesting. Nano lasers that are being developed for photonic applications where the lasers will operate within the electronic environment of computers, first for interconnects and later for processing, use this property. The laser cavity is formed by total internal reflection within nano dots or nano rings. The Q can easily exceed 1x 10^6. In macroscopic lasers like YAG rods and dye laser flow tubes these random ray paths can spiral around the interface between the laser medium and its interface with the outside environment. These modes produce very divergent outputs and as the spiral tightens, it will become less likely to produce any output and just acts to deplete the excited state. This is why a laser rod is fabricated with a rough grind on its outer circumference and why I have seen such an improvement in dye laser performance by grinding the ID of the flow tubes.

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