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Thread: Waveguide destructive interference?

  1. #1

    Default Waveguide destructive interference?

    All the patents I have read on waveguide CO2 lasers show the mirrors not being parallel to each other. - Shouldn't putting one pair of parallel mirrors at nλ λ and another pair of parallel mirrors at nλ mean that only the nλ pair causes light amplification, as the other pair interferes destructively?

  2. #2
    mixedgas's Avatar
    mixedgas is offline Creaky Old Award Winning Bastard Technologist
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    Quote Originally Posted by ganzuul View Post
    All the patents I have read on waveguide CO2 lasers show the mirrors not being parallel to each other. - Shouldn't putting one pair of parallel mirrors at nλ λ and another pair of parallel mirrors at nλ mean that only the nλ pair causes light amplification, as the other pair interferes destructively?
    Allow a field service engineer to make a educated guess as to what you are missing, please, in theory you are correct.

    I do not have a good mathematical model for you. However I can tell you from operational practice that you should not assume the longitudinal mode patterns are stationary. In a physical laser, multiple events such as plasma striations, variations in RF standing waves, and thermal effects in the gas and resonator cause the mode pattern to move constantly from variations in gain and index of refraction. I'd also imagine the mirror angle results in a series of traveling waves. True standing waves or single modes are thus rare, and one has to consider a integrated, aggregate, or average mode. One can be very sure that in most cases one should not assume the surface of the waveguide is optically perfect. Thus tilting the mirrors may be more advantageous to maximizing gain in the mode volume. In fact I would think correcting astigmatism would also be the reason for tilt.

    I build, operate, and repair gas and solid state lasers, however I do not usually design them. The above is my best guess to an answer to your puzzle based on what I see. I do not study complex polynomials. My area of study is not resonator physics, but I have spent much of my life adjusting them. However, in the systems I work on, we avoid any tilt.

    I would suggest A.E. Siegman's books on resonators. Dr. Silfvast's book is also good, and perhaps he is still at CREOL where he can answer your question formally. You may also try Dr Sam Goldwasser, PM me and I can connect you to him.

    For CO2 waveguide lasers, one would also look for works by Antony DeMaria

    A fast search shows: Carbon dioxide waveguide lasers with folds and tilted mirrors, C. A. Hill, P. E. Jackson, and D. R. Hall, Applied Optics > Volume 29 > Issue 15 > Page 2240

    Good Luck with your quest...


    Steve
    Last edited by mixedgas; 06-10-2014 at 17:31.
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  3. #3

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    Interesting that Siegman mentions Maxwell in the preface. I was just yesterday getting into his On Physical Lines of Force. If Siegman makes his subject as approachable as Maxwell does then this is going to be a great read.

    I think I have a simple method for making the standing waves a lot less rare, but it might be foolish of me to speak about it quite so freely right now... I'll have to refine my design before I do, and with good luck I'll pick up these inquiries again. Thank you most kindly for pointing me in the right direction.

    I've spent quite a few days reading repairfaq.org! - Just two months ago I had no idea what 'mode locking' was, or how 'q-switching' worked. I started my quest with an idea on how to demonstrate the basic function of a 'holographic' projector R2D2-style, but this is at least just as interesting. It has been a long time since I last had such an appetite for knowledge. =)
    Last edited by ganzuul; 06-11-2014 at 01:26.

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    Default Good to hear...

    Quote Originally Posted by ganzuul View Post
    Interesting that Siegman mentions Maxwell in the preface. I was just yesterday getting into his On Physical Lines of Force. If Siegman makes his subject as approachable as Maxwell does then this is going to be a great read.

    I think I have a simple method for making the standing waves a lot less rare, but it might be foolish of me to speak about it quite so freely right now... I'll have to refine my design before I do, and with good luck I'll pick up these inquiries again. Thank you most kindly for pointing me in the right direction.

    I've spent quite a few days reading repairfaq.org! - Just two months ago I had no idea what 'mode locking' was, or how 'q-switching' worked. I started my quest with an idea on how to demonstrate the basic function of a 'holographic' projector R2D2-style, but this is at least just as interesting. It has been a long time since I last had such an appetite for knowledge. =)
    Sam would love to hear that; you should send him a message. Best, Phil
    Phil Bergeron( AKA 142laser)

  5. #5

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    I sent him a wall of text using the feedback form on the RepairFAQ site... I'm PMing you both since I've gone done entered this into the Hackaday space race prize competition and there's a deadline. =)

  6. #6

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    He's very quick to reply. I'm glad. =)

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