# Photons per sec at 100 percent power

Wild question When running at 100% power how many photons/sec is the GF laser pushing out?

It’s relative.

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Sorry I mean for the 40 watt. Either that or I don’t know what you mean by relative. Both myself and the laser are moving zero miles per hour relative to each other. 10600 nm photons I mean.

Photon energy, frequency and flux - Example

Perhaps my question should be:

What peak wattage does the GF push out?

Sorry, it was a poor special relativity joke.

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Well, I can’t say what the peak power is, since the forge uses a custom tube. I don’t know if the peak powers change with design.

But at 40W, and 10,600nm, you would have 2.13*10^37 photons per second.

(Wattage times wavelength, divided by plank times speed of light)

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I’ll defer to @jacobturner as my swag is within an order or two of magnitude of his.
I came up with 1.36*10^20 but I see a mistake I made in not considering the wavelength. I’d just extrapolated from someone else’s Calc at 500 nm.

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Well, we were off by enough I checked my work. I accidentally hit divide instead of multiply when putting 3.8*10^8 in my calculator for speed of light.

With that snafu fixed, the actual answer would be: 2.13*10^21

Which gets the order of magnitude shift correct to align with your 500nm calculation (roughly 20 times)

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Hot dang! I got it It was a relativity joke

This forum has the greatest people! I love that you were ok with my question and helped me with it!

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Right now I feel like Joey from Friends, when the other 5 friends speak intelligently about complex topics, and he just sits there and tries to correctly guess if he should nod or shake his head…

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Just be glad it’s not “Big Bang Theory”

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Ha, then I’d have to be Penny…you’re right!

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Imagine what Team Glowforge could do in product placement in Big Bang. I think Abby could use one on NCIS. Then we would start reading Glowforge fanfic.

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oh gawds. don’t make me have to get my “X considers themselves less nerdy than Y” poster. It ends with fanfic writers who make furry versions of themselves the hero of the story with a hilarious amount of other nonsense.

…okay…i really just look for excuses to find the picture of that tree flowchart. …now which 1tb HDD did I put that on?!

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The ROUGH numbers I got were:
.5 cm diameter beam at 40 W --> 203.72 W/cm2
.02032 cm (.008") diameter beam at 40 W --> 123,345 W/cm2

I made the focal point the width of the smallest kerf. This could be smaller:

.0127 cm (.005") diameter beam at 40 W --> 316,000 W/cm2

One more point:

A word about spot size (size of the focused beam)

There are fundamental laws of physics (bottle necks) that limit the size to which a beam of light (laser or otherwise) can be focused to. In our application, the first bottle neck says; even if all your tools (lasers and lenses) were perfect you can not focus a beam to a size smaller than its wavelength. The wavelength of CO2 laser is 10 micron (0.01 mm), therefore this is the smallest diameter of the circle it can be focused to.

We will explain these bottle necks in a little more detail later on but if you prefer not to read anymore, here it is:
If we remove the perfect assumption (the lens is not perfect and the laser is not perfect) then you would be doing amazingly good if your lens and laser are good enough to give you a spot size of 100 micron diameter ( 0.1 mm ). You will be doing excellent if you get 200 micron ( 0.2 mm ) and very good if you get 300 micron ( 0.3 mm ).

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Cool, so Glowforge gets an “Excellent” rating on the beam focusing from that quote

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yup

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