Results 1 to 6 of 6

Thread: High losses on prisms

  1. #1
    Join Date
    Apr 2011
    Location
    Canada
    Posts
    80

    Unhappy High losses on prisms

    Hey everyone,

    I recently got a Power Meter and I measured my 445nm laser output with and without prisms. I have the prisms set up at 56.775 deg just like in zoof's templates.

    At 485mW, it put out 405mW. 83.5% transmission.
    At 500mW, it put out 420mW. 84.0% transmission.
    At 470mW, it put out 400mW. 85.1% transmission.

    Not good I got these prisms from Stanwax, and from what I've seen on the forum the lowest recorded loss was 2.5%, and the highest at 8.3%. Does anyone know why I am getting such a high loss?

    The laser in question is the one in the middle in these pictures:
    http://i.imgur.com/BHEsS.jpg
    http://i.imgur.com/Eah31.jpg

    Any help or advice is appreciated!

  2. #2
    Join Date
    Jan 2006
    Location
    Switzerland
    Posts
    129

    Default

    Did you check of what kind of glass they are made? Most often prisms are made of SF-11 because of the higher index of refraction (the compression ratio is the square of this). However SF-11 has high losses at 445nm, actually in the order what you measured. Low loss in the order of 2-3% can be achieved by prisms made of of BK-7, but unless this is specifically asked from the manufacturer, you may get SF-11 by default.

  3. #3
    Join Date
    Apr 2011
    Location
    Canada
    Posts
    80

    Default

    Well, I got them from stanwax and it specifically says they are for 445nm + it says it's BK7 glass in the description, so I would hope they aren't SF-11. http://shop.stanwaxlaser.co.uk/anamo...pair-311-p.asp

    Would these prisms from Dave be better?
    http://www.ebay.com/itm/Anamorphic-p...#ht_500wt_1413

    Edit: I fiddled with the position of the module, and I got the transmission up to 89% consistently. Still pretty low though.
    Last edited by ARGLaser; 05-12-2012 at 14:00.

  4. #4
    Join Date
    Jul 2007
    Location
    west sussex uk
    Posts
    2,280

    Default

    These losses are normal at those angles
    The quoted specs for the prisms would be at
    0deg .the larger the angle the bigger the loss but
    Better divergence
    When God said “Let there be light” he surely must have meant perfectly coherent light.

  5. #5
    Join Date
    Jan 2009
    Location
    Germany
    Posts
    241

    Default

    Actually the angle of 56.775 is the Brewster angle of BK7. When used at Brewsterangle an uncoated Prism pair (these look uncoated from the pictures) is expected to give ~8% loss which corresponds to the reflection losses of two surfaces hit at zero degrees. The other two surfaces have no losses provided polarization is right (p-polarization with regard to the incident plane of the surface).
    If the losses are higher and the glas has no absorption which is the case for BK7, there must be somthing wrong with the polarization of the incident light. Problably the used diode has a bad degree of polarization or it is not at the correct rotational orientation.

    Andreas

  6. #6
    Join Date
    May 2007
    Location
    1 hr from everything in SoCal
    Posts
    2,753

    Default

    Which diode are you using? 89% is not too bad considering that most 445's can throw out 1W without breaking a sweat. The newer 445s that are out have been abused up to 2.6W. How much power are you needing? If it is just a matter of effenciency, I can understand, but if your power requirements are affected too greatly by the losses, maybe a more powerful diode?
    If you're the smartest person in the room, then you're in the wrong room.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •