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Thread: 240mW e-bay Lasers

  1. #11
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    Default Definitely Pumped

    $40 for a 200mW output laser?
    Junk. You cant even make IEC spec diode for that price.
    AVOID.
    Regards
    Calligula

  2. #12
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    It appears some sellers are quoting mW "power dissipation in pump laser diode" rather than "Desired wavelength optical power out" There is a big difference between these 2 figures. I saw one post "uses genuine 1W laser diode for long life" - the operating current was 300mA - A 1W diode is hardly thresholding at that.

  3. #13
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    Quote Originally Posted by uk-laser View Post
    I saw one post "uses genuine 1W laser diode for long life" - the operating current was 300mA - A 1W diode is hardly thresholding at that.
    Believe it or not, I fell into this kind of trap twice when I know nothing about lasers. In my case the seller stated that it uses 1.5W pump diode and requires 600mA during operation to produce 150mW of green light. Guess what, they hardly can popped a black balloon and I paid around $150 each . I don't have any meters at the time so I don't know what was the actual output of those POS (I would guess less than 50mW). What's worse, the first one died within a week and the second one only managed to last a week further than the first. I have learned my lesson when I built my first homemade 200mW green module from scratch. I used 2W pump diode running at 2.5A to achieve this. I could've got better conversion efficiency but I can only afford a crap and cheap crystal . I hope these kind of sellers who took advantage from "innocent" buyers got what they deserve.

    By the way, I don't get it why a lot of people keep on saying that a cheap DPSS laser pointers could produce more proportion of IR than the green light itself? I've never experienced this phenomenon before. My homemade unfiltered 200mW green module is only producing roughly around 25mW of not well collimated IR. I'm not an expert in any way on this and maybe my crystal is actually better than I thought. From what I've heard, most of the IR gets converted to either green light or heat. Leaving only a fraction of IR escapes through crystal. So I don't think it's possible to get a scenario where a green laser pointer produces 50mW of green and 200mW of IR. Could any expert please correct me if I'm wrong ?

    Cheers.

  4. #14
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    Cool Re: leaking IR from DPSS lasers

    Quote Originally Posted by VaThInK View Post
    By the way, I don't get it why a lot of people keep on saying that a cheap DPSS laser pointers could produce more proportion of IR than the green light itself?
    Cheap laser pointers typically have lousy optical coatings and often do not have an IR filter on the output. Consider this: According to Sams Laser FAQ, the record for DPSS efficiency is an output of 280 mw of green for 1 watt of pump at 808nm. So even in the best case, you've got a considerable amount of 808 nm IR that can escape the cavity if your optical coatings leak. Then, given that the frequency doubling process is only 40-60% efficient, you've got 500 to 600 mw of 1064 nm IR in the cavity as well, and some of this can also leak out. Remember that this is the BEST CASE with a $20,000 laser that has super high efficiency.

    Home made DPSS lasers often need 1.4 watts of pump at 808 nm to get 100 mw of green out. (Again, from the FAQ) That means you've got the potential to loose several hundred mw of 808 nm IR plus at least a couple hundred mw of 1064 nm IR through the output of the laser if your optical coatings aren't up to snuff (which they often aren't, since home-built lasers are built on a budget). That's what the IR filter is supposed to block. If you omit that filter, then *ANY* losses from the intra-cavity optics (either 808 nm or 1064 nm, or both!) will end up in the output beam.
    My homemade unfiltered 200mW green module is only producing roughly around 25mW of not well collimated IR.
    It's hard to collimate IR in the first place, so that's normal. But what those numbers are telling you is that 1) you have a good set of crystals that have decent, low loss optical coatings, and 2) your IR filter is probably a tad weak, since you're still loosing some IR out the business end of your laser. For a home-built 200 mw laser you shouldn't have more than 8 to 10 mw of IR in the output, if that much. (For comparison, I've got a 100 mw Lasever DPSS green that has less than .5 mw of IR in the output.)
    From what I've heard, most of the IR gets converted to either green light or heat.
    The efficiency of converting the 808nm pump energy to 1064 output from the vanadate crystal is around 30%. The rest should be trapped by the optical coatings in the cavity, where it will eventually be absorbed and converted to heat. (Trapping it in the cavity also boosts the conversion efficiency to 1064 nm.) However, if your coatings suck, then some of that waste 808 nm pump energy (up to 70% of it, theoretically) can leak out. Likewise, nearly half of the 1064 nm IR is lost during the frequency doubling stage in the KTP crystal. If the coatings trap it in the cavity like they're supposed to, then it, too, will eventually be absorbed and converted to heat or will contribute to increasing the conversion efficiency to 532 nm. But here too, if the coatings leak, you can have 1064 nm IR in your output beam.
    So I don't think it's possible to get a scenario where a green laser pointer produces 50mW of green and 200mW of IR.
    It's not only possible, it happens quite often when manufacturers use *cheap* crystals and then omit the IR filter at the business end of the laser. It's not uncommon to find a DPSS green laser that outputs 3 to 5 times it's rated optical output in IR. Of course, those same manufactures often include this leaking IR in the total power output rating of the laser, which is deceptive at best. In the specific case of a pointer that should be eye-safe, selling it without the IR filter in place makes it eye-UNSAFE, and that's why several people have spoken out about the practice in this thread.

    And just for the record, the leaking IR from a DPSS laser *does* pass through the cornea and *will* be focused on the retina - both the 808 nm and the 1064 nm IR. But since the human eye doesn't respond to IR, there will be no blink reflex. This makes leaking IR especially dangerous. (See this section of the laser FAQ for details...)

    More information about leaking IR from DPSS lasers can be found in this thread (near the end of the thread). Also check out this thread, it's got some good safety tips for DPSS laser users...

    Adam
    Last edited by buffo; 08-27-2007 at 16:16.

  5. #15
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    Ahh, thanks Adam for clarifying that out. Hopefully I'm never going to get a laser with that kind of conversion efficiency. That sucks . Maybe that was the case with the first two laser pointers I had. Great explanations Adam .

    Cheers,


    Victor.

  6. #16
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    Quote Originally Posted by Buffo View Post
    According to Sams Laser FAQ, the record for DPSS efficiency is an output of 280 mw of green for 1 watt of pump at 808nm. So even in the best case, you've got a considerable amount of 808 nm IR that can escape the cavity if your optical coatings leak. Then, given that the frequency doubling process is only 40-60% efficient, you've got 500 to 600 mw of 1064 nm IR in the cavity as well, and some of this can also leak out. Remember that this is the BEST CASE with a $20,000 laser that has super high efficiency.
    Adam
    My old Fengyuan (and relatively cheap) 532nm laser had a decent output of 260 - 280mW with a 1W pump diode running at 950mA
    And this was not IR, I added another IR filter before the power meter and the readings was almost as high...

    Seb

  7. #17
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    Quote Originally Posted by VaThInK View Post
    By the way, I don't get it why a lot of people keep on saying that a cheap DPSS laser pointers could produce more proportion of IR than the green light itself? I've never experienced this phenomenon before.
    I've got a LambdaPro 100 mW laser that puts out about 85 mW of green, but measures around 400 mW on a thermopile sensor. I discovered the actual values by testing with an IR filter borrowed from another laser. The IR was in a narrow beam, so it would have been the 1064 nm IR not the 808 nm pump light.

  8. #18
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    Quote Originally Posted by Buffo View Post
    It's hard to collimate IR in the first place
    It has to be done. KTP needs such a high energy to be efficient that it depends on a huge energy density in IR, and the only way to get it is to have the mirrors well aligned for multiple reflections. Divergence is limited by modes and by ratio of length to width even in a single mode cavity, as well as the wavelength itself, but in any laser capable of putting out useful amounts of green, it will never be bad.

  9. #19
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    Cool

    Quote Originally Posted by sbk View Post
    My old Fengyuan (and relatively cheap) 532nm laser had a decent output of 260 - 280mW with a 1W pump diode running at 950mA
    There isn't a date on that entry in the laser FAQ, so it's possible that they've improved the optical coatings since the article was added to the FAQ. But it also sounds abnormally high based on other DPSS lasers I've seen. I'm thinking you ended up with the pick of the litter with that laser. (Probably should have kept it!) Those are world-class numbers you're quoting; right on the limits of the efficiency curve...

    Adam

  10. #20
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    Yes it was very efficient, but I sold it a few times ago... (here's the ad on this forum : http://www.photonlexicon.com/forums/...ad.php?t=2251).
    But it was only TTL and had a quite big divergeance...

    The substitute (a Lasever) is not as much efficient, but has analogue blanking and very good divergeance

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