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Why is my green laser putting out red light?

goninanbl00d

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So, this question's been asked one too many times, and most of the time the forum search function doesn't work properly either, and these answers get lost. I'm going to try and get a sticky for this thread too, if that isn't too much to ask for.

Why is my green laser only putting out red light?

You've just bought a new laser pointer from some site, and you've just opened it up, and put the batteries in. You press the button, and instead of seeing a green beam, you see a faint red dot. What's happening?

NEVER look into the laser at the dim red light- you run the risk of sustaining permanent, instantaneous retinal burns


To understand why this is happening, first you need to understand how a green laser pointer works.



As you can see, it's not a straightforward process, as is the case with red and violet laser pointers.

In a green laser pointer, 808nm laser radiation from a pump diode is used to generate 1064nm light in the gain medium (in this case, the YAG or YVO4). This 1064nm light is then doubled by the KTP to from 532nm light. There's no colour filters involved, it's a laser-pumped laser.

To achieve even a low-power output requires large amounts of 808nm IR pump radiation. For example, the pump diodes found in a 50mW green laser pointer will often average around 300mW IR output.

The human eye isn't very sensitive to 808nm IR- and it's barely visible. It takes several watts of 808nm to achieve visual parity with 1mW of 650nm. As a result, what is mistaken as a dim red light is easily capable of causing instantaneous eye damage.

Although this diagram shows an IR filter (which would cut out all of the infrared from the green beam), most cheap pointers and modules lack this IR filter.

The most common causes of this type of pointer failure are either driver/pump diode failure, or crystal set failure. In most cases, these are not user-serviceable, and the best option would be to return the defective pointer to the store for a refund or exchange.
 
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csshih

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good job indeed! hopefully this post will make some more careful with their cheap greenies.
 

qumefox

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It's also worth mentioning that this particular diagram is showing a relatively high end green pointer. Usually <$10 greens have neither a lens to focus the IR pre-crystals, or an IR filter.. Which is where the danger comes from. On IR filtered pens, you wouldn't even get the IR leakage.
 

AJ_Dual

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I would think the most common cause of this is weak almost dead batteries causing the 808nm diode to still lase, or maybe just LED, and it's below the threshold of the NdYVO4, or the KPT to produce 1048nm, then 532nm.

I've viewed the red light indirectly out the end of one of my lower powered greens, but could never view the spot on the wall or on paper using a camcorder, or digital cameras.

That's not to say it isn't some other kind of failure, and isn't a very dangerous amount of IR. MUCH better safe than sorry.

Spare eyes haven't been invented yet.
 

qumefox

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If this is in response to borg's question.. reread it carefully. heh.

I would think the most common cause of this is weak almost dead batteries causing the 808nm diode to still lase, or maybe just LED, and it's below the threshold of the NdYVO4, or the KPT to produce 1048nm, then 532nm.

I've viewed the red light indirectly out the end of one of my lower powered greens, but could never view the spot on the wall or on paper using a camcorder, or digital cameras.

That's not to say it isn't some other kind of failure, and isn't a very dangerous amount of IR. MUCH better safe than sorry.

Spare eyes haven't been invented yet.
 

laserlands

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This picture make complicated things easy. very nice stuff for beginners.
Thanks
 

AJ_Dual

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If this is in response to borg's question.. reread it carefully. heh.
LOL, no.

Just the OP. Low battery (and a driver that does not cut off after a certain point) is IMO the most common cause.

In borg's case, I'd say it's just colorblindness. :D
 




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