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How Much Extra Power Output does AR Coating Give?

gazer101

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So far all of my lenses (that I can tell) are uncoated, and I'm curious as to how much extra power coated ones could realistically grant (applied to a G2 single element glass lens).

If it's a meaningful increase, I might consider buying the coated ones for a bit more
 



CurtisOliver

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For a single pass the gain of AR coatings are negligible. Percentage transmittance will depend on quality of coating, lens material and input wavelength. Where AR coatings become essential is when you are either:
  1. Designing systems for maximum efficiency.
  2. The laser system has many optical components therefore will need to limit optical losses.
  3. Or in situations where back reflection needs to be limited.
I always prefer using AR coated optics as I am a efficiency freak and try to limit backreflections.
 

gazer101

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In my case I don't really need efficiency, but if [x many layers of] AR coating increases transmittance by even as little as 5% I'll consider it
 

CurtisOliver

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Sounds like a reasonable expectation. Can't remember BK7's optical transmittance offhand. But AR coatings can yield T=>99% at high quality. Assuming BK7 is T=~95% then ~4% gain.

Edit: Looks like BK7 is T=90-92%.

Coatings will normally provide a graph showing peak transmission at your wavelength.
 

gazer101

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I see this graph:
1612043761448.png

But I'd need to know the usual reflectance of a glass G2 lens (at 850nm) in order to assess how much extra power it would give

It seems that an ideal AR coating at 850nm will have a reflectance of only 0.25%

EDIT:
If this graph is true, at most there would be 5% reflectance in uncoated glass (but I'll assume that 0.5% of that is absorbed and not reflected), meaning that AR coating would only provide up to a 4.25% transmittance increase (44 mW increase for a usually 1W laser):
1612044695861.png

If somebody could fact check this, I think getting AR coating might be worthwhile after all. Every last drop of power counts!
 

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CurtisOliver

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For that we need to know what optical glass they are made out of. I know G2’s will not have T=99.75% specs so you are onto a winner with VIS-NIR AR coatings.
 

Encap

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If you don't have an LPM. Purchase a Laserbee LPM and get an AR coated version of the same lens you have or have one NIR coated to compare to the non-coated lens and find out in the real world. Is the only way you are going to know about any particular laser, lens, glass, or coating/coatings combinations as mentioned by CurtisOliver in post #2.
There are way to many hypotheticals and variables that need to be defined precisely to say anything other than "possible slight increase in output".

You can't trust some of the Chinese AR coatings or lenses to be high quality, these are just cheap pointer lenses.
According to DTR the only real G-2 lenses come from Will @ laser66. Everything else is just using his name to get sales. His bare lens element even in bulk are still $20. The rest are just China G-2's that took the name as the G-2 had great name recognition instead of making their own name for their product"
G-series lenses are just glass lenses with very short focal lengths and AR-coatings. There's nothing magical about them. They transmit more power only because the short focal length captures more of the output from the emitters, and that they don't have multiple lenses that cause extra per-lens losses. Capturing more of the emitter output means the G-series lenses have uglier beam-spots, as they capture all the beam artifacts present from the emitter as well.

I seriously doubt there are any NIR AR coated G2 lenses optimized for 850nm or any NIR transmissive glass "G2" lenses for a 1W 850nm laser diode output anyway. No demand/no market for them. No 1W 850nm pointers are offered by anyone and only a few low cost $30 to $60 1W 850nm lab style modules for night vision people.

PS "Unlike visible materials (such as N-BK7) that work well throughout the entire visible spectrum, IR materials are often limited to a small band within the IR spectrum, especially when anti-reflection coatings are applied." From overview: https://www.edmundoptics.com/knowle...e-correct-material-for-infrared-applications/
 
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gazer101

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I have an LPM and have ordered some cheap Chinese AR lenses, I will be surprised if there is any increase in transmittance (since they are so cheap) but otherwise I already get ~95% transmittance out of my current lenses (tested it) so there isn't too much room for improvement

In my case I'm not willing to spend $20 on a lens since the laser itself (with a non-coated G2) only costs $80
 




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