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Thread: Several questions at once

  1. #1
    Join Date
    Sep 2006
    Location
    OH, USA
    Posts
    114

    Default Several questions at once

    Hey there, long time no chat for me.

    I'm coming up with a project that requires me to separate a green laser beam into several weaker but equal powered beams. Here's the restrictions:

    1. The module must be small, and around 75-125mw 532nm. .75" body diameter or less, and if required, a powersupply of that same size. I easily find lab lasers for that power, but modules are not as easy to come by, at least for the right price. 100&#37; duty cycle is important, which knocks out any handheld lasers of that size and power. Beam quality is not, however, since the beam will be terminated in <12 inches. Also, $400 for a 75mw module is not an option.

    2. I must split the one beam into several balanced parallel beams. I've done this with regular microscope slides (figuring out angles based on an index of refraction), and I know that doing so is really poor since the the slides aren't meant for this type of work. I need to make about 6-8 beams go parallel to eachother, using various angles and/or materials to make these near-parallel beams. Think like how a laser harp looks, except without the scanning power that those normally have. I had a diffraction lens i ordered online from a DVD player that allowed me to do 3 parallel beams (which I could split up with mirrors) but I'd have to get another one since I need at least 6 beams, and I don't even know where to start anymore.

    I know, strange requirements, but I have a neat little project in the works, and would just like a second opinion on things before I put it together. Sorry I'm being a bit vague, but I don't want to give up the secret before I start developing. Any help would be appreciated!

    -Colin

  2. #2
    Join Date
    Oct 2006
    Location
    Central Florida
    Posts
    7,067

    Thumbs up

    Good luck man! I have used the scope slides before and it can be a pain but seems to work well. Are you sure they will split the beam equally? The space requierments seem a little tight also. Maybe you could get two 50mW modules and make twins with 3 beams a piece. Will this be mounted in a tube?
    Love, peace, and grease,

    allthat... aka: aaron@pangolin

  3. #3
    Join Date
    Jan 2006
    Location
    Charleston, SC
    Posts
    2,147,488,500

    Cool

    I think your best bet would be to use a diffraction grating (a line grating) to get a fan of beams and then use a single mirror for each beam to get them all parallel to each other.

    If you need them to all be the same power level, you could place neutral density filters in line with the zero-order and first order beams to knock down their intensity to match the second order beams.

    Why the restriction on size? If it could be slightly wider you'd be all set. (Use a table-top module.)

    Alternately, you could use 6 individual laser pointers with a common power supply. (Keep the driver board intact, but replace the batteries with a regulated power supply with a soft-start circuit.) You *can* run pointer modules continuously so long as you keep them cool. A good sized heat sink ought to do it. (Say, a cylinder of aluminum or brass roughly .5 inches in diameter that is drilled to accept the diode module.)

    What is the minimum acceptable power level per beam? If a little variation is allowed, then you might be able to go with the diffraction grating alone and skip the neutral density filters.

    Adam

  4. #4
    Join Date
    Jul 2007
    Location
    Melbourne, Australia
    Posts
    70

    Default

    How about using beamsplitters at different splitting rates? I've seen them for sale on eBay. Such as this one link. With that one you could make 10 beams if you could find the rest of the beamsplitters with proper ratio (eg: 1/9, 1/8, 1/7, etc until you ended up with the same optical power output on all beams). But then I guess it would be extremely hard to find ready made beamsplitters in these value as a complete set. Unless they're custom made.

    PS: keep in mind that using this many beamsplitters would cause quite a bit of loss down the chain. They add up in the end.

  5. #5
    Join Date
    Sep 2006
    Location
    OH, USA
    Posts
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    Default

    Well, another problem is the size of the splitter; I don't have the space required to allow a regular linear diffraction grating to expand the beams to a point of being able to work with them. Plus, I'd feel like I would need quite a nice laser, as making everything appear as bright as a 3rd-order beam seems like I would need to boost up those 3rd-order beams alot.

    The lasers themselves have to be small just because of the project, and they can't be uncomfortably heavy or bulky either like most table-top lasers. The final split beams can be any power 15mw or greater; though if I found an economical and practical solution that allowed me to go higher up I'd jump on it. Anything past 2mw will work for the technical side of my project, but I would prefer them brighter as I plan to be able to view the beams in a fog or haze. Visually it's important that all beams at least *appear* to be the same power, so a little room is available for variation, but not much.

    Using separate diodes would definitely work, particularly with the space problem, but the only problem is the money to purchase 6 to 8 15-30mw modules.

    Perhaps buying 2 50mw modules and using the 3-beam diffraction lens mentioned would work too, and I might be looking into pricing for that. Of course, if I decide I need 8 beams, that might be a problem, but would work for 6. Hmm.

    I apologize for the vagueness; I know it makes it harder to help, but I just want to make sure the project doesn't fully come out just yet.

    *VaThInK- posted near the same time. Yes, with the space issues, actual beam splitters would work assuming i had a powerful enough laser. That's definitely something ill look into.
    Last edited by BoomDog; 09-01-2007 at 11:36.

  6. #6
    Join Date
    Jul 2007
    Location
    Melbourne, Australia
    Posts
    70

    Default

    With 100mW laser you could get roughly around 10mW each if divided by 10 beams. Just a little bit less than the 15mW you required. But could be higher if you only require 6 beams. However the cash that you're going to spend on the beamsplitter cubes or plates would be quite prohibitive. I dunno though. Depends on your budget too.

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