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Thread: Combining diodes...

  1. #1
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    Default Combining diodes...

    An interesting read...

    http://teradiode.com/technology/

  2. #2
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    Quote Originally Posted by laserdj View Post
    An interesting read...

    http://teradiode.com/technology/
    Totally agree !

    Thanks for the link.


    Cheers

  3. #3
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    I had considered this concept early on in designing a large array of diodes. It's pretty simple and might work with the AlGaAs diodes by tunning with temperature. A long linear array with aggressive cooling at one end only and a diffraction grating (transmissive or reflective your preference) might work. The wavelength shift with temperature in these diodes is pretty linear and so some temperature variation would probably only lead the combined output to shift rather than the individual beams to separate. Alternatively, a number of individual temperature regulated modules could be set up on a commen base and aimed at slightly different, but adjustable angles at a common grating where their convergent angles are neutralized. I might try this.

  4. #4
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    Holy crap.. This is REALLY IMPORTANT info for combiners... I had wondered about destructive interference being an issue for beam combining, but didnt realise just how significant an effect on output efficiency this could have...

    Apparently the beam power wavelength spectra must not overlap at all for optimal beam combining power. Not sure whether temp control of 445nm diodes will be able to shift the power spectrum of each diode so that they dont overlap. It might be necessary to use a VBG in front of them to clean up the beam. For a dual diode arrangement, just changing the linear polarization so that each diode is 90 degrees rotated, would be enough to effectively power combine without too much extra optics.

    I wonder if the 445nm diode design is really a single emitter, or actually more similar to the 808nm bar lasers. If it is, then an external VBG could perhaps be used to substantially improve the output power.

    Found these refs:


    http://www.pd-ld.com/wp-content/uplo...rightness1.pdf

    http://www.ll.mit.edu/news/Fan_LaserBeamCombining.pdf



    Cheers,

    Pete

  5. #5
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    Thanks for the references, I'm reading through them now. Not to worry though. I believe that the most successful of these techniques for producing a laser stack or an array of individual diodes that span a narrow range of wavelengths allow a superposition of the individual beams like wavelength multiplexing ( as is done in telecommunications to increase the bandwidth capability of a single fiber). When the laser cavities operate separately there is no destructive interference or significant interaction between the individual colors in the combined beam. The first step will be to test a few different wavelength combiners such as a prism, a reflective and a transmissive diffraction grating and scan a single diode such as the LOC-815 red through a practical temperature range. Then, after determining the angular deviation with temperature and the losses with each combiner then attempt to stabilize two diodes, if necessary incorporate knife edging ( to minimize the required angular and hence temperature offset ) and combine these two beams. Even with stable input power to each diode a closed loop TEC controler for each diode probably will be required and long term stability of the beams in the far field can be looked at. This is very doable. Any suggestions on a source for cheep,stable easy to work with closed loop TEC controllers? If this works I'm going to need a lot.

  6. #6
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    Wow

    Thanks for the links interesting reading


    cheers

    Andy

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    Regarding a practical application of these concepts, I have not made much progress to date as several other projects are competing for my time. As I looked into the individual components the most challenging will probably be locating a cost effective closed loop TEC controller ( I haven't found one yet). More encouraging, is that Edmond Optics markets reflective gratings with minimum 80% diffraction efficiency in the 600-650nm band. A deal breaker that needs to be evaluated early on is whether the individual diode's band width is small enough not to allow the grating to cause significant spread of the individual beams.

  8. #8
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    @Planters
    " A deal breaker that needs to be evaluated early on is whether the individual diode's band width is small enough not to allow the grating to cause significant spread of the individual beams."

    Fraid you have identified big problem here ! ....... I get the feeling that the grating might well have to be designed using holography to match bandwidths concerned and just "getting lucky" might well not hack it !.

    Also the wave shift in a given diode using just temperature, might well also be accompanied by a change in effective bandwidth with a different a harmonic distribution for any given colour ! This would imply the need to work "backwards" so as to speak to make the right grating !

    All this is pure conjecture of course, , so I eagerly await any results you obtain empirically!

    As far as closed loop TECs with interrelatable control I would suggest you talk to "Solarfire" or examen his posts on http://www.photonlexicon.com/forums/...-driver-thread!

    Thanks a million for all your posts... your straight forward hands on "build it and see " approach is a lifeline to someone like me as far as learning is concerned !

    Cheers

    PS. It occurred to me that you might be able to find "cone washers" or "O" rings just the right size to make your "Optima" locking ring trick, somewhat more manageable, when it comes to focusing "very multiple" barrels with wonky threads.

  9. #9
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    I will follow up on the TEC/Solarfire connection. Thanks!
    I agree that the empirical route is best here. After an interesting discussion with B. Benner at SELEM, we both were laughing at the concept of "good enough". Other factors that you may ignore or erroneously minimize often are significant enough to overwhelm a detail that you are struggling with.
    On the optima front, despite the hassle of the second ring retainer I really appreciate the elimination of any organics in the locking mechanism (read plastic flow).
    What is distracting me for the time being is a project down a completely new (non-diode path). I'm looking into a dye laser with very high beam quality and otherwise unobtainable colors such as yellow and orange as a complement to the proven diode systems. I'll post as this develops.

  10. #10
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    I understand the itch ... and am following the thread with interest !

    I am probably the only idiot in the world crazy enough to run a dyelaser setup (with a huge Argon) sitting in split sewage tube half full of concrete with lead sheeting over the other half (raised by pulleys for access) in a front line disco for three entire seasons ...... just cos I wanted ORANGE ! (read... free running R6G)
    Dark blue/lemon/orange is a whole different "key" in visual terms.

    Never noticed any beam quality problems though !

    Learned to be careful with bass heavy sound systems, which cause chronic arthritis in dyelasers... LOL
    Also learned (empirically) that colours from different resonator sources do NOT mix.. until moved.
    Strange sight (in that era) blue beam and red beam superimposed with no trace of magenta mix in the smoke.

    However given that you already have your cryogenic ultrajetski setup, have you thought about applying the same shrinkage idea to expensive 637nm diodes to get to orange/yellow ?

    I realised later (post-post) that cone washers would be a tad "wide" but does neoprene suffer from "plastic flow) ?

    Cheers

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