Page 2 of 4 FirstFirst 1234 LastLast
Results 11 to 20 of 31

Thread: Back reflection killing maXYZ module?

  1. #11
    Join Date
    Mar 2006
    Posts
    2,478

    Default

    Quote Originally Posted by Pitts View Post
    I was about to ask, given that I have one of Chucks dual Maxys whether or not one gains any added "protection" via the cube,mirror and dichro.
    This has been a good wake up call for me to be careful as well.

    Is this back reflection problem as bad with DPSS lasers ??

    During setup, when "stuff ups" are more likely to occur does running the laser at very low output offer any degree of protection ??

    Cheers

    Ray
    NZ
    [/COLOR]
    Anything that can return light will cause it, the path is perfectly reciprocal unless you use an optical isolator (expensive, and lossy), but you can at least avoid the cube and other parts reflecting by setting stuff at slight angles.

    Temporary use at low power during setup will help a LOT. Best keep it right down though, 10 mW, (30 max). That's safer for eyes too.

    DPSS lasers are pretty much immune because the various coatings and crystals form a strong barrier to the output light getting back to do harm. It might be possible to destabilise the cavity enough to notice a flicker, but no more than that.

  2. #12
    Join Date
    Feb 2005
    Location
    Switzerland
    Posts
    1,410

    Default

    Quote Originally Posted by lucerne View Post
    Sure, I know that. Ok, you could have missunderstand me. There are diodes with a few watts red
    But you said it already: They have big (too big!) emitters, so you want be able to get a nice beam out of them

    Marconis moduls looks nice, but I think, he uses normal 5.6mm or 9mm-diodes with 40-60um-emitter. In this case, there are no diodes over 150mW!
    So I think, he overdrive them a lot! Sometimes it works, sometimes not, like your problem now...
    Hello my compatriot

    I don't know if he overdrive them, but for sure he take care to reach the maximum lifetime. He makes a lot of burn-in tests to find the ideal power to run the diode each times he try a new one... Now they are rated at 225mW.
    With my module I can reach something like >510mW after the beamsplitter cube on my dual module, this is overdriving the diode (but I did that just for testing purpose).

    Seb

  3. #13
    Join Date
    Feb 2005
    Location
    Switzerland
    Posts
    1,410

    Default

    Arg, I just tryed to use an old maXYZ 5.6mm diode to make a high power red laser pointer, I did a lot of tests to find a solution to focus it right, but suddenly the diode died
    And nothing about back reflection, it died when I held it and had nothing in front of it... Now it emits a ridiculous amount of red light but still draw full current, and get hot after seconds.

    I think it is the excessive heat which destroyed it, it hasn't big heatsink when I was testing...

  4. #14
    Join Date
    Jul 2005
    Location
    Tampa Florida
    Posts
    502

    Default one solution...

    Here is a solution to the back reflection problem. Buy an optical isolator for the diode laser to protect it. As long as the laser is polarized this is possible. One problem...the optical isolator will cost several diode modules. So the best solution is to use less than maximum power especially when doing initial projector alignments to keep the back reflections slightly off axis. It is true that back reflection can kill a diode 'instantly".
    Phil Bergeron( AKA 142laser)

  5. #15
    Join Date
    Jan 2006
    Location
    Charleston, SC
    Posts
    2,147,489,446

    Default

    Quote Originally Posted by Pitts
    Is this back reflection problem as bad with DPSS lasers ?? During setup, when "stuff ups" are more likely to occur does running the laser at very low output offer any degree of protection ?
    Hi Ray!

    DPSS lasers are not nearly as suceptible to this sort of damage. Remember that the reflected light is going to be a multiple of the original diode frequency. So in a green laser, for example, when the reflected light enters the KTP/Vanadate crystals the coatings will be all wrong for the 532 nm light going back towards the diode. The optics, too, will be focused for IR and not for visible light. Finally, the pump diode normally isn't running anywhere near it's maximum possible limit, so you have some headroom there. (This partly answers your other question too: Yes, operating at low power levels reduces the risk of facet damage due to back reflection.)

    Bottom line: I don't personally know anyone that has killed a DPSS green laser through back-reflection. But I know 3 or 4 people that have killed direct-injection red diodes via back-reflection. (Including myself!)

    As far as running lower power during setup, that is *absolutely* a good idea, and not just to prevent back-reflection. It's easier to align things when the power levels are lower.

    After I built my optical table I connected all the blanking leads for the lasers together to a variable voltage bench power supply. Then I dragged the whole mess out onto my back porch at night and did the alignment. (Alignment is tricky, but if you have a really long throw it's easier to see where you're off.) I dialed it in up close using the adjustments on the individual laser tables, and then used the dichro mounts to tweak the far-field alignment. (Far field ended up being about 100 ft away from the projector.) At night you can see the spot 100 ft away even with the power turned way down, yet with the low power it's also easy to look at the dichro and make sure the beams are intersecting at the right point.

    Adam

    EDIT: D'oh! Just noticed there was a page two in this thread. Looks like the Doctor answered your question quite nicely. Sorry for the dupe.
    Last edited by buffo; 08-21-2007 at 11:05.

  6. #16
    Join Date
    Jun 2007
    Location
    northern maine.
    Posts
    329

    Default

    Quote Originally Posted by The_Doctor View Post
    DPSS lasers are pretty much immune because the various coatings and crystals form a strong barrier to the output light getting back to do harm. It might be possible to destabilise the cavity enough to notice a flicker, but no more than that.
    i hope not to drag the thread too far off topic, but i find this interesting because i had some flicker in the cni 532 i used.
    i did have some shiny aluminum surfaces showing in the optics area ,so i blackened them and the flicker went away.

  7. #17
    Join Date
    Oct 2005
    Location
    Melbourne, Australia
    Posts
    678

    Default

    hmm what about back reflection off an output window.

    I regularly see light thats reflect off our projector output window, hittng the galvo mirrors in turn and eventually end up on the lasers...

    its very random, ie laser has to be at the perfect angle... maybe the solution here is to tilt the output window so its not facing perfectly back at the scanners ?
    Now proudly stocking and offering the best deals on laser-wave

    www.lasershowparts.com
    http://stores.ebay.com.au/Lasershow-Parts

  8. #18
    Join Date
    May 2007
    Location
    Trieste, Italy
    Posts
    10

    Default

    Quote Originally Posted by aijii View Post
    hmm what about back reflection off an output window.

    I regularly see light thats reflect off our projector output window, hittng the galvo mirrors in turn and eventually end up on the lasers...

    its very random, ie laser has to be at the perfect angle... maybe the solution here is to tilt the output window so its not facing perfectly back at the scanners ?
    the same is with pol cubes... even if they are ar-coated a small amount of light will return back to the diode. You should be careful, setting the cube not exactly perpendicular to the beam. Pol cubes reflection is much worse than window reflection, because the beam is fixed so if the cube is perpendicular to the beam the diode will receive back reflections as long as it is powered! (i'm quite worried about that because i have 2 maxyz's red diodes with pol cube)

    if you are worried about back reflections from the output window, you have to tilt the window more than half of the maximum scanning angle, otherwise you will only change the point from where the beam will be reflected back. I think the easyest solution is to mark that point with a permanent black marker, that absorb the light

  9. #19
    Join Date
    Nov 2005
    Posts
    84

    Default

    I have killed 4 (yes, four) of them with back-reflection, so far.

    I've stopped worrying about it. They have been infinitely nice about replacing the diodes for very cheap.

  10. #20
    Join Date
    Jan 2006
    Location
    Charleston, SC
    Posts
    2,147,489,446

    Default

    Quote Originally Posted by eyceage View Post
    I have killed 4 (yes, four) of them with back-reflection, so far.
    Oh man... I think I'd be in tears after that. I recently managed to kill another one of my DVD diodes, but I think that was from static electricity, not back-reflection. (I've been careful to the point of paranoia ever since.) But back-reflection is always on my mind.

    Adam

Posting Permissions

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