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 Laser Pointers Man, if I only had a nickel for every photon I shot out of my laser....

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04-22-2011, 09:18 PM #1
 Class 2 Laser Join Date: Mar 2011 Location: Charleston, SC Posts: 372 Rep Power: 72
Ibuprofen200mg
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Man, if I only had a nickel for every photon I shot out of my laser....

Ok, so you're shining your pointer around photons everywhere, but if you were bored enough (as I am), you just might care to know approximately how many photons you are blasting out per second? Sounds kind of cool anyway.

Well to do this you need some simple algebra, and a couple of facts about your laser pointer, it's wavelength and power output. Now of course an exact answer here is ridiculous because the laser output and wavelength are just close approximations and the constants being used in calculation are rounded off. Oh, and a scientific calculator might help too.

For my example I will use my ~380mw 405 nm from O-like.

The first thing we need to know is how much energy each photon in a beam of 405nm light has. The power of the pointer here does not matter.

the energy of each photon is given by E = (hc/λ)

where h= Planck's constant = 6.626*10 ^(-34) J*s

c= speed of light = roughly 3.0*10^(8) (m/s)

and λ= wavelength of light in meters, so 405 nm = 405*10^(-9) m, or in proper scientific notation 4.05*10^(-7)m

units should cancel and leave you with Joules, so the energy per photon of a 405 nm light source is

E= [(6.626*10 ^(-34) J*s)(3.0*10^(8) (m/s))]/4.05*10^(-7) =

4.908*10^(-19) Joules

OK, so now how to get the photons per second as promised.......well your laser output is generally in mW and each mW is a (1/1000) of a Watt so just take you mW power and divide by a thousand. In my case 380mW/1000 =
0.380 W

now remember that 1 Watt = J*s ! so if we know how many joules per second of energy is coming from the laser and we then know the energy of each photon, all we have to do is simply divide the output of the laser in Watts (J*s) by the energy per photon (J) to find out how many photons per second we are emitting.

in my case:

(0.380)J*s/ 4.908*10^(-19)J = 7.742*10^(17) OR roughly 774 Quadrillion photons per second!!!!!

Last edited by Ibuprofen200mg; 04-22-2011 at 09:22 PM.

04-22-2011, 09:25 PM #2
 Class 3R Laser Join Date: Dec 2010 Location: USA Cali Posts: 1,195 Rep Power: 54
Krogith
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Re: Man, if I only had a nickel for every photon I shot out of my laser....

You Need Another Hobby It Seems.....
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--Some Pictures--

Click This Link!!! 50 mW Laser does Eye damage from his friend waving it in his face...
Above >5mW you can damage Your Eyes with a Reflection in 1/100th of a second. It Doesn't Matter How Dim it "Looks"! It is still dangerous!
Above >100 mW you can burn your retina off any glossy surface just Reflecting The Beam off to your Eye!It's More Than Just a Mirror that you need to be Careful Of!!
And remember There is Never A Perfectly Diffused Surface, Do You want to Risk it?!

04-22-2011, 09:33 PM #3
 Class 2 Laser Join Date: Nov 2010 Location: Somewhere In The Mediterranean Posts: 479 Rep Power: 1374
snoutke
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Re: Man, if I only had a nickel for every photon I shot out of my laser....

OK.

And what should I do with this information?

04-22-2011, 09:59 PM #4
 Class 3R Laser Join Date: Dec 2010 Location: USA Cali Posts: 1,195 Rep Power: 54
Krogith
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Re: Man, if I only had a nickel for every photon I shot out of my laser....

^^ "Pew Pew" ^^
__________________
--Some Pictures--

Click This Link!!! 50 mW Laser does Eye damage from his friend waving it in his face...
Above >5mW you can damage Your Eyes with a Reflection in 1/100th of a second. It Doesn't Matter How Dim it "Looks"! It is still dangerous!
Above >100 mW you can burn your retina off any glossy surface just Reflecting The Beam off to your Eye!It's More Than Just a Mirror that you need to be Careful Of!!
And remember There is Never A Perfectly Diffused Surface, Do You want to Risk it?!

04-22-2011, 10:38 PM #5
 Class 2 Laser Join Date: Mar 2011 Location: Charleston, SC Posts: 372 Rep Power: 72
Ibuprofen200mg
Class 2 Laser

Join Date: Mar 2011
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Rep Power: 72
Re: Man, if I only had a nickel for every photon I shot out of my laser....

I'm not sure what use this information has other than novelty, and what use is a high-powered laser pointer anyway other than novelty? Sometimes you do things just to do them.

04-22-2011, 10:42 PM #6
 Class 3B Laser Join Date: Jun 2009 Posts: 2,712 Rep Power: 3309
Prototype
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Re: Man, if I only had a nickel for every photon I shot out of my laser....

Neat, never thought about it like that. +1 For creativity.
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Quote:
 Originally Posted by MoonShad0w No, bird, do not bite my F7 key off

04-23-2011, 01:12 AM #7
 Class 4 Laser Join Date: Sep 2007 Location: Wisconsin Posts: 9,315 Rep Power: 403710
Cyparagon
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Re: Man, if I only had a nickel for every photon I shot out of my laser....

I did that once (was equally bored). A formula I came up with is

Photons per second = (P*λ*10^17)/19.86

Where P is the power in watts, and λ is wavelength in nanometers.
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A problem well stated is a problem half solved.

04-23-2011, 02:04 AM #8
 Class 2 Laser Join Date: Mar 2011 Location: Charleston, SC Posts: 372 Rep Power: 72
Ibuprofen200mg
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Join Date: Mar 2011
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Re: Man, if I only had a nickel for every photon I shot out of my laser....

Yep, gives you the same number, I just showed the units and whatnot so people didn't think I was doing the ever so frowned upon "magic math" that I was accused of in high school.

Last edited by Ibuprofen200mg; 04-23-2011 at 02:05 AM.

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