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532nm 50mw laser. Not 50mw of 532nm light. Is that normal?

The Purple Death

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Hello,
I bought this 532nm green laser:
It's rated for 532nm at 50mW. When I tested it with this LPM:
I can indeed get 50mW at 2.2v, in fact, I can probably get 100mW if I pushed it. But here's my problem, if I place this lovely UV/IR cutoff glass between the LPM and the laser then I only get 32mW of power.
I'm including the falloff graph here for your convenience.
The falloff graph indicates that 85% of the 532nm light will get through but even then the total 532nm light output is limited to 36.8mW, not 50mW.
I tried boosting the voltage, and thus the overall output of the laser, but the amount of 532nm light drops off. Likewise with lowering the voltage.
Yes, it did come with a driver, but the driver has all it's contacts unlabeled (what connects to where?), and so I'm driving it from a buck converter.

The question is this, are 532nm lasers mW value supposed to be counted with respect to total energy output, or strictly the 532nm light output (+- the typical few nm due to living in an imperfect world)?

Thanks
 

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Spoomples

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The power rating should just count the green, but cheap 532nm lasers tend to leak a lot of IR and have questionably accurate ratings. I hear that 30-80mw of green light is a common range for them. That particular LPM seems sketchy too, so the readings should be taken with a grain of salt.
 

paul1598419

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Well, these laser typically output ~20% IR. If your filter only passes 85% of the visible light you have lost 17.5 mW right there from a 50 mW total power DPSS laser. So, you might see a loss that only leaves you with 32.5 mW. I have some IR filters for these kinds of lasers that pass 95% of the visible light. Yours seems quite poor.
 

Encap

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What has been said above^^^

What do you expect from a $6.98 DPSS laser -- about the price of a good cup of coffee--- a toy quality LPM and the wrong type of UV/IR filter meant for a camera, a 650nm UV/IR Cut filter?

Try with a 808nm and 1064nm filter meant for a 532nm laser----look on ebay for "532nm laser IR filter" -- they are about $5.
Typically they say:
"You can get pure 532nm green laser when you add it.
Glass Lens!
Specially for Laser Power Meters!
Total light Transmissivity for 532nm laser >97.5
Total light Transmissivity for 808nm laser <2%
Total light Transmissivity for 1064nm laser <2%"
 
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The Purple Death

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Thanks, that answers my question quite well.
But if I can ask a related one, why does the amount of 532nm light increase only to a certain point and then though the amount of 808nm light increases, the amount of 532nm light decreases?
This only happens after the diode reaches room temperature, before that it can go up quite a bit more. I thought it might be the batteries, so I changed them to no avail.
 

paul1598419

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You are talking about a laser module that cost you $7.00. These are mass produced in China and the quality control is near nonexistent. Just buy a new one and be done with it.
 

Alaskan

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Those pointers are using critical angle cut KTP crystals, therefore they work at room temperature well enough, but they have an optimum temperature, when you run it in a cool environment the efficiency will be lower, when run too long they exceed the sweet spot temperature and are too warm and then loose efficiency on that end of the optimum temperature envelope. When hot, the crystal can also warp slightly, so the focus into the crystal can change some, IR will travel into and through the crystals differently when that happens with varied output results.
 

303mod109

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Thanks, that answers my question quite well.
But if I can ask a related one, why does the amount of 532nm light increase only to a certain point and then though the amount of 808nm light increases, the amount of 532nm light decreases?
This only happens after the diode reaches room temperature, before that it can go up quite a bit more. I thought it might be the batteries, so I changed them to no avail.
I would be VERY careful with those cheap dpss lasers. They put out unacceptable amounts of infared. I tested a green 303 with a infared pass filter and it wasn't looking good. Buy glasses to protect against infared and the wavelength of the laser.
 

diachi

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Those pointers are using critical angle cut KTP crystals, therefore they work at room temperature well enough, but they have an optimum temperature, when you run it in a cool environment the efficiency will be lower, when run too long they exceed the sweet spot temperature and are too warm and then loose efficiency on that end of the optimum temperature envelope. When hot, the crystal can also warp slightly, so the focus into the crystal can change some, IR will travel into and through the crystals differently when that happens with varied output results.
Too much pump power saturates the gain crystal too, so you'll reach a point where 532/1064nm output levels off eventually.
 

paul1598419

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Too much pump power saturates the gain crystal too, so you'll reach a point where 532/1064nm output levels off eventually.
That is true, however all the cheap 301 and 303 style pointers I have tested, and there have been many of these, leak up to 20% IR. That is small in comparison to the visible light. It is silly to fear the IR component and believe the visible component is somehow safer because you can see it. They both travel the same path, but the IR component diverges more quickly making it safer at a distance than the visible light, which is always far more powerful in the case of these cheap pointers.
 




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