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Thread: Two green polarized beam combining-maximize the brightness

  1. #1
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    Question Two green polarized beam combining-maximize the brightness

    Hello all,

    greetings from China.

    Recently I was asking one of my friend to do a tailor-made work for me. I wanted him to combine 2 green lasers (both polarized) into one beam so we could obtain almost double power(result will be 3 watts around). I want him to try combine the 2 flash light first then collimate later, so hopefully we don't need to bother with re-alignment in future by adjusting mechanics.

    We both know how to combine 2 beams with different polarization.

    But question keep bothering me is how much brightness boost can we expect by doing this?

    Does the combining influence the coherency somehow? If what I heard was correct coherency do influence the brightness(human eye).

    and, Is the beam polarization ratio related with perceptive brightness?

    I had experience of combining 2x5watts 532nm into 10watts, I felt there was just little(15-20%) brightness boost....But at that moment both beams was quite tight so I don't know my eye was kind of saturated or what....

    A single 10watts laser (not conbined) looks more brighter than a combined one, at least this is what I feel, or just my brain doesn't want to believe what I have seen?.

    Please advise...

    Sean
    Last edited by sean; 11-16-2010 at 23:28.

  2. #2
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    Power does not equal brightness, so you will not get double the brightness for a doubling of power.

    I've heard figures in the region of 4:1 (you need 4 times more power to double the brightness) but can't verify that. The power density (beam tightness) seems to affect how bright you perceive things more.

  3. #3
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    I know that power does not equal to brightness. and I wasn't trying to get double brightness by combining 2 beams.

    Let me simplify the question:

    single 10 watts beam with polarization ratio 100:1 compared with a 10 watts beam come from 2x5watts green combined which has ratio of 50:50, which one is brighter? assuming that both beam have same profile

    I did not compare them one next to each other. And also my main questions are in my first post. Does coherency and polarization ratio influence brightness or NOT...

  4. #4
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    A single 10watts laser (not conbined) looks more brighter than a combined one
    What are the respective resultant beam properties? This may go some way to answering your queries.

    Also, take a read of the recent threads about beam combining with PBS cubes and polarization - again, these may answer the queries you have

    http://www.photonlexicon.com/forums/...nd-power-gains....

    http://www.photonlexicon.com/forums/...?highlight=pbs

  5. #5
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    Quote Originally Posted by norty303 View Post
    Power does not equal brightness, so you will not get double the brightness for a doubling of power.

    I've heard figures in the region of 4:1 (you need 4 times more power to double the brightness) but can't verify that. The power density (beam tightness) seems to affect how bright you perceive things more.
    This is correct. Square law. 4 x power = 2 x perceived illumination.

    It's the same with audio. If you have a 100W amp, 400W will be twice as loud (assuming the speakers are rated to take it).

    For audio power into a speaker load, power in Watts (RMS) =
    Code:
             Vrms˛
      Wrms = -----
               R
    Square law.
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  6. #6
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    If you have a 100W amp, 400W will be twice as loud
    Nope, it takes 10x the input power to double the perceived loudness in decibels (+10db), disregarding other aspects such as power compression and other 'non-perfect' practical elements

    http://www.sengpielaudio.com/calculator-levelchange.htm

  7. #7
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    Quote Originally Posted by norty303 View Post
    Nope, it takes 10x the input power to double the perceived loudness in decibels (+10db), disregarding other aspects such as power compression and other 'non-perfect' practical elements

    http://www.sengpielaudio.com/calculator-levelchange.htm
    +10dB loudness is not 10 x power however. Likewise, 10xpower is not +10dB.

    +3dB power is 2 x power.
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  8. #8
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    +10dB loudness is not 10 x power however. Likewise, 10xpower is not +10dB
    Um, yes it is....

    Assuming a speaker of sensitivity 100db@1w/1m

    1W = 100db
    2W = 103db
    4W = 106db
    8W = 109db
    10W = 110db (or thereabouts, you do the exact math)

    Seeing as we're talking about 'perceived brightness' the fair comparison is with perceived loudness, not electrical power or any other function

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    Quote Originally Posted by norty303 View Post
    Seeing as we're talking about 'perceived brightness' the fair comparison is with perceived loudness, not electrical power or any other function
    I'll give you that!

    I guess our eyes and ears are fairly non-linear devices...
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  10. #10
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    OK maybe I have made it too complex

    a: 2 x 5w 532 3mm 1mrad, theoretically we can make 10 watts with 3mm 1mrad(polarization ratio 1:1)

    b: 1 x 10w 532 3mm 1mrad(polarization ratio 100:1)

    Now which one is brighter? Assuming human eye will distinguish the different brightness if there is any

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