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  1. #1
    Farsang's Avatar
    Farsang Guest

    Default Commercial Telescope for high Power Beam


    We have a fiber with a 300 Watts output at 900 nm, we'd like to
    collimate this output and generate a spot of about 5 Cm dia. at 1 Km
    away. Are there commercial telescopes that we could modify its
    input optics (to couple in the fiber output) to achieve this and can
    they handle 300 Watts light power?

    I was thinking of a reflective Newtonian Telescope with its eyepiece
    replaced by an imaging optics that images the fiber's core onto the
    focal plane of the telescope primary mirror. This imaging optics
    would have an appropriate ouput numerical aperture to create a
    collimated beam of 5 Cm dia. coming out of the the telescope primary
    mirror. Is this feasible and can the telescope optics handle 300
    watts ( the primary mirror probably has an enhanced aluminum coating)?

    Alternatively we could collimate the fiber output and send it into a
    Galilean beam expander (refractive type) but our preference is a
    commercial telescope (preferably with a tracking capability) that
    could with some modification give us this 5 Cm output beam.

    thanks for your comments and suggestions.

  2. #2
    Richard J Kinch's Avatar
    Richard J Kinch Guest

    Default Commercial Telescope for high Power Beam

    Farsang writes:

    Impossible to say without details on the "fiber".

    Consider that focusing a laser to 5 cm at 1 km can be pretty challenging.

  3. #3
    Roger Hamlett's Avatar
    Roger Hamlett Guest

    Default Commercial Telescope for high Power Beam

    "Farsang" <> wrote in message
    There is much more to this than you think...
    The actual 'collimation', is _easy_. 5cm, at 1km, is 'only' 12arc seconds.
    However the big problem will be the 'seeing'. If you look through a good
    rifle site at a target this sort of distance away, on a good day, it'll be
    quite easy to see, and stable. However on most days, the actual target,
    will be jumping around in the view, as heated air in the path between,
    makes it's effects felt. Expert shots, use the image processing in their
    brain, to average the target position, and look for the stable
    Commercial systems to achieve this sort of spot size, and accuracy, use
    adaptive targetting. I was involved in a system some years ago, that put
    10KW, into a slightly smaller spot size. The main beam, was accompanied by
    two reference beams, that 'scanned' a small distance up/down, and across
    respectively, and these carried a phase modulated signal, reflecting their
    scan 'position'. At the receive end, a detector picked up how far off the
    system was aiming, and sent a control signal back, to adjust the aim of
    the source. The whole system detected and adjusted it's aim, at over 1KHz.
    At times, the aim was moving several arc minutes from the initial point
    (there was a 'shutdown', on the beam, if the system could not correct fast
    enough to keep it inside the target). We also had to have reflection
    detection at the source, to shutdown the beam, when it went misty, since
    otherwise backscatter was dangeroous...
    At night, after the air has cooled, or in the very early morning, what you
    have in mind will work, but at midday, in most climates, the movement will
    be massive. Commercial versions of several scopes have been used for this
    type of work (open tube RC's in particular), but normally with optics at
    the receiver, that will accept quite large beam shifts.

    Best Wishes

  4. #4
    Jamie's Avatar
    Jamie Guest

    Default Commercial Telescope for high Power Beam

    With 300 watts at the distal end, the fiber must undoubtedly be
    multimode. In oder to get a 5 cm spot at 1km the output divergence
    must be less than 50 micro-radians, ignoring atmospherics such as
    turbulence. Given a multimode fiber that is 50/125, you will need a
    collimator with an effective focal length of 1m (quite reasonable for
    a commercial telescope primary element) and an aperture of at least 40
    to 50 cm to pass the output cone of the fiber, assumed to have an
    numerical aperture of 0.2 to 0.22, without loss. A commercial
    telescope with an aperture of 16 to 20 inches is quite rare.

    You may be able to buy an off-axis parabola (OAP) from SORL (Space
    Optics Research Labs at
    but their catalog listing only goes to 8 inches at 1m focal length. I
    would contact SORL and some other OEM reflective optics vendors for
    capabilities and, if appropriate, quotes.

    With an OAP, all you need is the fiber mount (I am assuming a bulkhead
    mating connector), the OAP and mount and a platform to support both of
    these with the proper geometry.

    It is also important that you don't light this contraption up anywhere
    that is not a closed range as the potentials for human injury and even
    fire hazards are too great. If you point this into the sky anywhere
    that is not consider closed and monitored air space and without the
    proper clearances, chances are you won't be caught, but if you are,
    the penalties would be dire.

    James Carter

    On May 24, 2:22 am, Farsang <> wrote:

  5. #5
    Farsang's Avatar
    Farsang Guest

    Default Commercial Telescope for high Power Beam

    On May 24, 6:08 am, Jamie <> wrote:

    Hi James:

    1- If most of the commercial telescopes primary element focal length
    is 1m, we don't necessarliy need an 40 - 50 cm aperture dia to fit in
    0.22 NA of the fiber. We could reduce this input NA by imaging the
    fiber output with some magification, say 3, this gives 0.22/3 = 0.73
    for input NA into the telescope primary.

    Taking your 1m focal length example for the primar, in order to get a
    collimated beam of 5 Cmm we need an input NA of about 0.025 (= 2.5Cm/
    100 Cm). To achieve this we need to image the fiber output by a
    magnification of
    8.8 ( = 0.22/0.025 ), this probably could be done with two lenses with
    focal ratio (f2/f1) of 8.8. This is what I meant by modifying input
    optics of a commercial telescope, in case of a Newtonian telescope
    (with a primary of 1m focal length) we replace its eyepeice with this
    imaging optics. This is in theory, the question was if this is
    practical with commercial telescopes and if such telescopes are
    available and can handle 300 W light power.

    2- You are right the fiber is a mutimode fiber ( with a core dia = 500
    um ).

    3- The experiment will be conducted in a closed enviroment for a
    shorter distance (i.e < 1Km) to check the feasibilty.


  6. #6
    Jamie's Avatar
    Jamie Guest

    Default Commercial Telescope for high Power Beam

    Sorry but you can't magically reduce the fiber's cone angle with a
    lens without increasing the apparent size of the of the fiber tip.
    This is due to a little 'gotcha' called the Lagrange Invariant. It's a
    fundamental aspect of first order optics and can ultimately be traced
    to the conservation of energy and thermodynamics. The more esoteric
    'optics' explanation would be conservation of radiance.

    Basically if you reduce the fiber's exit cone angle by a factor of X
    with a lens system, the image of the fiber tip will increase in size
    (magnification) by the same factor X. Then the angular divergence of
    the light from the collimator (that's essentially imaging the fiber
    tip to infinity) increases by X as well.

    If your fiber tip core is 500 um, then the system that I described
    must be scaled by 10x. That's a tall order even for custom optics and
    a generous budget.

    Good luck in your endeavors.

    James Carter

  7. #7's Avatar Guest

    Default Commercial Telescope for high Power Beam

    I happen to have a 20X SORL Beam expander for sale on Ebay.

    Item number: 140120742585



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