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Thread: How to use PBS and Beam correction in a multi-diode high power 445nm laser projector?

  1. #1
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    Post How to use PBS and Beam correction in a multi-diode high power 445nm laser projector?

    Hello everyone

    I'm Dimitris from Greece and this is the first time i write. First I want to express my admiration and congratulations for the high level of all members of the forum. I love lasers, my first one was a JB-Twin Effect which i modified from 40mw-532nm/80mW-650nm to 600mw-445nm/300mW-635nm, then i made an RGB 20Kpps with 150mw-532nm/1000mw-445nm/300mW-635nm all with ready Chinese Modules and now i want to build a higher power single color (445nm) or RGB about 10W with good beam quality for outdoor use . I plan to use seperate laser modules (like these made from DTR) and not Chinese this time. I read about PBS and beam correction but i have some questions:

    1. PBS is to combine 2 beams of different polarisation in one. Does this means to rotate the one diode 90* ?
    2. Can i put 4-5 same diodes (ex. 445nm/1.6W Osram) and PBS in a serial way to combine all in a single beam and how many ?
    3. Can the last PBS or the dichros handle the increased power without cooling ?
    4. The beam correction with anamorphic prisms must be made for every beam before every PBS or for the final combined beam ?
    5. Same type diodes can be connected in series in one driver or every diode must have its own driver ?
    6. For better beam visibility at large distances (ex. 1-5Km) what is better higher power or thinner low divergence beams ?
    7. I've seen PBS for 635nm and 445nm diodes. Can i use PBS for 520nm diodes and what type ?

    Each answer is welcome and appreciated - i'm really a novice in lasers although i make audio electronic sircuits for a long time.
    Thanks for your time and patience and wish you the best.

    Dimitris Dimitropulos GREECE.

    Below are some photos of me and my home-made projector.
    Attached Thumbnails Attached Thumbnails Snap_2013.03.12 03.06.50_001.png  

    P2210036.JPG  

    PC080005.JPG  

    Last edited by ddimitris; 04-11-2014 at 15:13.

  2. #2
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    Hi Dimitris and wellcome aboard. Thanks for the pictures!

    Quote Originally Posted by ddimitris View Post
    1. PBS is to combine 2 beams of different polarisation in one. Does this means to rotate the one diode 90* ?
    This generally means that one diode has to be rotated 90 degrees (but this generates a + pattern of beams, which is not desirable. The use of a waveplate is recommended, this is a little glass thingy that changes polarisation by rotating it without the need to rotate the beam i.e. http://shop.stanwaxlaser.co.uk/wavep...risms-45-c.asp or the group buy stuff that dave at lasershowparts.com has available

    Quote Originally Posted by ddimitris View Post
    2. Can i put 4-5 same diodes (ex. 445nm/1.6W Osram) and PBS in a serial way to combine all in a single beam and how many ?
    well, how many you can combine depends on the size of your scanner mirrors. You can combine 4 fairly easily and fit on 5mm scanner mirrors, or you can do 16 like more experienced people here. Or, you can use the 9mm 445 diodes that can do 3watts each and get the job done with one or two diodes.

    Quote Originally Posted by ddimitris View Post
    3. Can the last PBS or the dichros handle the increased power without cooling ?
    yes they can. read through this thread, it has various good bits at various pages http://www.photonlexicon.com/forums/...ight=waveplate

    Quote Originally Posted by ddimitris View Post
    4. The beam correction with anamorphic prisms must be made for every beam before every PBS or for the final combined beam ?
    This is a bit unclear to me. How many PBS do you expect to use? Hate to spoil the fun, but you can only use one. If you add another it will just cancel half of your beams out (polarisation issues). So, assuming you use one pbs, you can place the anamorphic prism pair after the pbs. It also depends on how you stack the beams, so again, this question is a bit vague.

    Quote Originally Posted by ddimitris View Post
    5. Same type diodes can be connected in series in one driver or every diode must have its own driver ?
    you can connect diodes in series, or by using approrpriate resistors you can connect them in parallel. Ohm's law aplies. Most people prefer to keep things seperate and have a driver for each diode. This makes things safer for the diodes, as you risk loosing all diodes if you have one go open circuit in a multiple configuration

    Quote Originally Posted by ddimitris View Post
    6. For better beam visibility at large distances (ex. 1-5Km) what is better higher power or thinner low divergence beams ?
    I would say low divergence beams, but what would you be doing at that distance anyway? Check this out, too http://www.photonlexicon.com/forums/...ight=waveplate

    Quote Originally Posted by ddimitris View Post
    7. I've seen PBS for 635nm and 445nm diodes. Can i use PBS for 520nm diodes and what type ?
    any PBS would work. the 635 or 445 etc refer mainly to the antireflective coatings to minimise loses. so you can use a 445 pbs with 635 diodes, but the losses will be higher (i.e. closer to 10% instead of 2%). There are also broadband coated PBS that work with 400 - 700nm beams. Again dave will still have some of the broadband (BBAR PBS) left


    don't think i have answered your questions, this is just a small intro to get the discussion going
    Your post will receive more suitable answers if you provide more details, or even a quick and dirty sketch up of what you plan to build.

    A 10 w rgb is no small deal, building it and keeping it aligned will not be too easy

    In any case it is nice to see a fellow greek here, up to now it is you, me, a guy in chalkida and then the nearest neighbours are in malta and italy. makes it kind of difficult to arrange a laser meet
    Last edited by LaNeK779; 04-11-2014 at 15:52.
    "its called character briggs..."

  3. #3
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    Thank you LaNeK779.

    I've got it now. I thought i could put 4-5 PBS in one line and 4-5 diodes and increase the power but i didn't knew the polarisation issues. The projector i want to build is for a friend who owns a cafe-bar-restaurant near a lake and the projection over the lake will draw attention of the public. Sometimes it maybe used for a light show only for over-head projection (is it safe to project that power of laser beams on to people even if it fast scans with wide angle ???)

    Now i think to use two 1.6-3W/445nm Osram or M140 or Nichia diodes with one PBS and beam correction, two 0.7W/638nm Oclaro diodes and beam correction, and for green two 120mW/520nm Osram with one PBS or a 0.5-1W/532nm/DPSS Chinese module. As for drivers i don't know any convenient.
    The scanner i have is a TE-Lighting 20kpps controlled by the DMX-512 input and Freestyler freeware as i need only simple aerial beams.
    Please can you suggest a low cost combination with adequate quality (diode/module/lens/PBS/driver etc) ??

    Yours Dimitris D.

  4. #4
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    have you considered using conventional lights like a searchlight, or big spotlights to attract attention? lasers is not the only alternative for doing the job. Plus, 10watts if consisting mainly of blue will not get you so far in terms of visibility. get as much green as you can afford and then build around that. The problem these days, still, is getting enough red.

    the combination of 10w and crowds will make many people here stir uncomfortably in their seats (and not unjustified, too). There is some math involved to calculate the safe MPE (max permissible expposure) search around the forum and you' ll get tons of info. it generally has to do with beam diameter, beam divergence, audience distance, scanner speed and some other things. No limitations for overhead beams, as long as no audience members can get in the beam path. Keep in mind that 10w is a fire hazard too. You can light a cigarette with half that, and you will burn holes in things with even less


    just a few resources to keep your mind busy (i'm in a hurry today, i'll get back to you)

    our top notch guy for buying laser diodes, great service, cheapest prices https://sites.google.com/site/dtrlpf/home/diodes (member DTR )

    a very good source for brass parts, dichros, diode drivers, lens barrels etc http://lasershowparts.com/store/inde...ewCat&catId=84 (member dave )

    another great shop and a very helpfull guy, check out the downlaod section of the site. usefull info! http://shop.stanwaxlaser.co.uk/ (member stanwax )

    some harder to find specialties here, too http://www.lasertack.com/en/ (member lasertack )

    this guy also has a lot in terms of diode drivers http://www.photonlexicon.com/forums/...-smart-driver-) (member Bbe )
    "its called character briggs..."

  5. #5
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    For maximum visibility just but the biggest 532nm module you can afford
    Frikkin Lasers
    http://www.frikkinlasers.co.uk

    You are using Bonetti's defense against me, ah?

    I thought it fitting, considering the rocky terrain.

  6. #6
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    Hi again

    Sorry for my late response. I'm not all the time online because of other works. Also forgive my bad English. I read and understand easily even technical terms but it's a little hard to write what i'm thinking with correct spelling and syntax without using Google Translator occasionally.

    I believe that you are both very right. I sould go for a big 532nm module. After all as a beginner i will not manage easily align PBS, polarization lens, dichros etc. in a multi module projector. It was very hard to aling my simple RGB projector.

    What's the diference between 1W-Dpss-532nm and 1W-520nm-Direct Diode OSRAM ? What is better ?
    I found some 2W-Dpss-532nm modules at the price of 1W-520nm-Direct Diode OSRAM Module. What would you prefer ?

    All the resources that you inticate i've been watching them for a time but i didn't know they are members of the forum. They are all very good.

    And finally let me know if i get it correctly:

    The PBS let the first beam pass because of the same polarization of the beam and the PBS inner diagonial film while reflect the second 90 degrees rotated and produces a final beam like cross "+". The final beam has orizontal and vertical polarization and if it enters a second PBS the one beam will be reflected ??? This is why multi-beams designs are arranged in line array like Arctos ???
    If the second beam is not rotated a polarization lens is needed before the PBS ??? The first beam needs polarization lens or not ???

    For beam corection i saw cylindrical lens and anamorphic prisms. Which is better or easier to use ???

    Thank's Dimitris D.

    (ps: LaNeK779 i've send a private message in Greeks but i'm not sure if you got it)

  7. #7
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    I got the PM, just had a busy weekend and (again) I've got to go now. Sorry for not responding, a proper PM will be sent within this week


    a few quick notes... on alignment stanwax site has this superb guide http://www.stanwax.plus.com/lw/rgb%20alignment%20lw.pdf

    532nm and 520nm in terms of visibility are very close, depends a bit if ambient light is more or less (photopic vision curve versus scotopic vision curve http://www.lrc.rpi.edu/programs/Futu...ightgraph2.gif ).

    The point with the 520nm is that it is still too expensive and you have to find a mount, a lens, a driver and generally build the thing yourself. At the moment, I would go for the 2w dpss. just get a decent brand like cni or laserwave. Avoid ebay, contact a reputable shop like the ones i already mentioned, or www.goldenstarlaser.com

    You are correct about the + pattern and the "ärctos" layout. You are again correct about the first beam NOT needing a waveplate and the second beam NEEDING one if the diode is not rotated.

    The main difference of cylinder lenses and anamorphic prism pairs is that the cylinders are a fixed magnification ratio (i.e. a -25 and a 100 FL that give a magnification of 4:1), while the anamorphics depending on the angle between them can have magnification of 2:1 up to 6:1 (so easier to find exactly what you need for your lens - diode combo). The drawback of anamporphics is that the higher the magnification you choose, the higher the losses, because the angle that light hits the glass becomes more extreme and you get higher % of reflections. See this (click tab "specifications" for how it works) http://www.edmundoptics.com/optics/p...ism-pairs/2429
    "its called character briggs..."

  8. #8
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    Thank's, thank's and thank's again. I'll check the links you stated and come back again.

    Dimitris D.

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