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Thread: Dichroic Filter problems... (Bandpass)

  1. #1
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    Default Dichroic Filter problems... (Bandpass)

    Hi all.

    Bought a set of Dichro filters from David at Lasershowparts.
    The problem I am having is with the one that is supposed to (Pass Green and Blue, Reflect Red)...
    It Reflects Red fine, Passes Green fine, but does not Pass all of the Blue. It only passes like 30% of the Blue and Reflects the the other 70%...
    The other optic that came in the set works fine (Pass Red and Green, Reflects Blue) This one works fine and is the one mounted right in front of my green laser, adding blue first. The one with the issue is mounted next in the lineup in order to add the red before the galvo's. I can add the red, but the blue is blocked at that second dichro position...

    It seems to me that the bandpass is too short and cutting my blue in half (or more).

    My blue diode id 445nm. Anyone else seen this problem? Perhaps it would not be a problem if I had a 473 diode... But I planned this projector with 445.

    Also I realize I can simply swap the locations of the two dichro units, and add my red first, then the blue after, and the problem would be solved since the problem dichro would then never even see blue light, however I have machined my base plate for the current setup, and it was too much work to start changing positions. I need to figure out how to get a dichro that will work... adding the blue first and then the red, in that order...

    Any ideas or feedback would be appreciated. Also a source for where I can get a dichro that will work properly for my application.

    Thanks

    Robert

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    P.S. I just found this site which shows the specific bandpass info in Graph Form for a set of Chinese Dichro's.
    This perfectly explains the issue I am seeing. If all of the Chinese Dichro sets are like this, then you have to merge the Red First, (as they show it here) so the first Dichro never even sees blue light. Based on the Graph it looks like my estimate of pass 30% and Reflect 70% was pretty close...

    http://www.telectronic.hu/laser/laserdichro.htm


    Comments?
    Robert

  3. #3
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    I dont think laserwave sells the dichro you are looking for. But your setup is the best because red is the most expensive color so you want red closest to your galvo. I have the correct dichro but they are very high quality and expensive (50 euro)

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    the photo at the top of the www.teltronic.hu website is from one stop laser shop (http://www.onestoplasershop.com). they sell high quality dichros and mounts. just ask for their "high efficiency dichros".
    suppose you're thinkin' about a plate o' shrimp. Suddenly someone'll say, like, plate, or shrimp, or plate o' shrimp out of the blue, no explanation. No point in lookin' for one, either. It's all part of a cosmic unconciousness.

  5. #5
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    I have a couple dichroics in stock that are 1" square and will reflect red {628nm-671nm} and pass >96% blue {442-473nm} and >78% 532nm @ 45 deg AOI. They are $20 each shipped priority mail ....CONUS only !!
    You are the only one that can make your dreams come true....and the only one that can stop them...A.M. Dietrich

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    had the same issue and dilemma, this is why i didn't go for red close to the mirror even if it is the most expensive one.
    because of the 445 specs i putt in blue first, then added red and then added green.
    This was alo recommended by a laser optics specialist at a dutch research institute.
    works great for me, i also have the high end dichro's from onestoplasershop and they are the best i have seen so far.
    Michel

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    Quote Originally Posted by michelrietveld View Post
    works great for me, i also have the high end dichro's from onestoplasershop and they are the best i have seen so far.
    Michel
    And how many have you seen?

    Do you have measurement data from these dichros, so i can add them to the list of dichroics i have tested?

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    good point, not as much as others i can imagine, lets see:
    1) dichro's salvaged from chinese projector
    2) laserwave dichro's
    3) dichro's hobbybob uses
    4) one stop lasershop HE version

    What measurements are you looking for, i can measure beam strength before and after the dichro so i guess i can calculate the loss percentage, is this what you like to see?

    @Hobbybob, which version dichro's are you using? I know you were very enthousiastic about the ones i currently use ;-) after we measured the loss which was only 2 percent or so.

    Michel

  9. #9
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    Update:

    Thanks to all that replied to this thread.
    I ended up ordering a set from Edmund Optics.
    25mm Diameter 45 Deg. Red Dichroic Filter
    Stock No. NT47-266
    and
    25mm Diameter 45 Deg. Blue Dichroic Filter
    Stock No. NT47-267

    These work very well even with the 445nm Blue...

    Regards,

    Robert

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    can you verify the 98% reflect and 90% transmit on this one? it looks a bit lossy...

    the GB Dichro from stanwax looks better spec and is cheaper R>98% T>93% - suitable for 473nm & 445nm

    and the more expensive (still cheaper than edmund) dichros from ct lasers have better specs Reflectance in all wavelengths is >98%. Typically, >99%. Transmittance is >95%. Typically 97% https://www.ctlasers.com/purchases/p...products_id=98
    "its called character briggs..."

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