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Thread: Dichroic mirror issue,no effective at 45°

  1. #1
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    Default Dichroic mirror issue,no effective at 45°

    I have a problem.
    Someone should help me or explain to me why is my stanwax RGB2 rectangular (pass green reflect red+445nm blue) dichroic isn't effective @ 45°?
    The transmitted 532nm light has huge loss at this angle but when i turn the dichro about 10-15°the loss is less.

    And here comes the funny part...
    This issue is when i use my home built DPSS green.

    But.
    When i use a CNI laser(MGL-H-532 1W) the loss is on 45°is very little.
    And when i turn the dichro,the loss will again huge.
    What is this?
    Some photo to illustrate my words.
    You can see the reflections on different angles.
    The output laser power hasn't been increase or decrease.
    Click image for larger version. 

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  2. #2
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    Default

    it may be a polarization issue.

    Quote Originally Posted by epyn View Post
    I have a problem.
    Someone should help me or explain to me why is my stanwax RGB2 rectangular (pass green reflect red+445nm blue) dichroic isn't effective @ 45°?
    The transmitted 532nm light has huge loss at this angle but when i turn the dichro about 10-15°the loss is less.

    And here comes the funny part...
    This issue is when i use my home built DPSS green.

    But.
    When i use a CNI laser(MGL-H-532 1W) the loss is on 45°is very little.
    And when i turn the dichro,the loss will again huge.
    What is this?
    Some photo to illustrate my words.
    You can see the reflections on different angles.
    The output laser power hasn't been increase or decrease.
    Click image for larger version. 

Name:	DSCN0171.JPG 
Views:	11 
Size:	2.34 MB 
ID:	42444Click image for larger version. 

Name:	DSCN0172.JPG 
Views:	9 
Size:	2.02 MB 
ID:	42445Click image for larger version. 

Name:	DSCN0162.JPG 
Views:	7 
Size:	2.19 MB 
ID:	42446Click image for larger version. 

Name:	DSCN0163.JPG 
Views:	8 
Size:	2.33 MB 
ID:	42447Click image for larger version. 

Name:	DSCN0166.JPG 
Views:	8 
Size:	2.03 MB 
ID:	42448Click image for larger version. 

Name:	DSCN0167.JPG 
Views:	4 
Size:	2.14 MB 
ID:	42449
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    my best guess is...it has to do with the purity of polarization of the lasers - home built laser has poor purity - the CNI has very good purity - you can try to rotate the laser or use a polarization rotator to reach optimum transmission through dichroic. hope that makes sense to you AKA extinction ratio (the ratio of the polarizations from horiz to vert)
    Last edited by Laserman532; 03-05-2014 at 08:27.
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    Mmm are you sure a dichroic mirror is sensible to polarisation ? Me no, but it´s always time to learn

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    Quote Originally Posted by kl79 View Post
    Mmm are you sure a dichroic mirror is sensible to polarisation ? Me no, but it´s always time to learn
    you can demonstrate this phenom with a polarized laser and a microscope slide by fixing the slide and rotating the laser and measure the reflectance...of course it has been 40 years since i did this experiment but maybe things have changed He can study extinction ratios of polarized lasers for a better understanding.

    after re reading your post...with a pure dichroic (which these are probably not) you would be correct, but it is not a perfect optic...if it were perfect...i would agree..
    Last edited by Laserman532; 03-05-2014 at 08:47.
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  6. #6
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    i had to use a green wave plate from dave to resolve the same problem,as it was easier to do than mess around trying to rotate the dichro
    When God said “Let there be light” he surely must have meant perfectly coherent light.

  7. #7
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    After collecting some tech infos my guess was also the polarization sensitivity...Thanks.

    what if I'll use a focusing lens for the 808nm diode,just like in my CNI?
    I have one for 808nm AR.
    (i have to turn my diode mount ,because the vanadate and the diode are in the same mount the emitter is almost touches the crystal)

    Click image for larger version. 

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  8. #8
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    Quote Originally Posted by badger1666 View Post
    i had to use a green wave plate from dave to resolve the same problem,as it was easier to do than mess around trying to rotate the dichro
    You also used the same dichroics or You had also have unwanted losses?
    1/2 Waveplate will solves my problem?
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  9. #9
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    Great, another future issue to contemplate.

    Is this just for DPSS lasers?
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  10. #10
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    Hi epyn -

    Quote Originally Posted by epyn View Post
    1/2 Waveplate will solves my problem?
    It should (at the least..) help make it 'better'.. Curing this will-depend, as-posted by others, on the inherent pol-quality of your diy Green (..Huge props on diy'ing it, btw! Nice lil' 'L-fold' design.. A 1/2~ in a 'rotatable-mount', ie: something like this: http://www.photonlexicon.com/forums/...chmentid=30092 ..but, even simpler, is-fine.. that will allow you to 'tune' the pol-opimization for the dichro you are using. A 'quickie test' will be, indeed, to 'rotate your dichro', on the V-axis.. (not 'angle of incidence', (your 45˚, there..) but rotate it, vertically, keeping the same 'AOI'..) you should see the 'loss' from reflection get better / worse, w/ that same AOI..

    ..Another thing you can do is get a better dichro that is not so pol-sensitive.. 'OSLS', here in the US, carry some; Others may be able to recommend EU-side suppliers of such..

    Hope this helps..
    j
    ....and armed only with his trusty 21 Zorgawatt KTiOPO4...

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