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07-19-2011, 05:41 PM #1
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xanatos
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W/cm^2 to Joules conversion?

I need to convert some laser power specs. For the sake of convenience, let's say I have a 1 Watt 445nm laser irradiating exactly 1 square centimeter.

Question 1: Does this represent, properly, 1W/cm^2 ?

Question 2: if Q1 is correct, how would I convert that to joules per cm^2?

If Q1 is incorrect in assumption, how do I figure irradiance per cm^2 based on my measured output power in mW?

Much appreciated! Thanks,

Dave

07-19-2011, 05:56 PM #2
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Trevor
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Re: W/cm^2 to Joules conversion?

Q1 is correct.

Watts per centimeter squared means joules per second per centimeter squared.

Joules represent energy, watts represent watts per second. Watts times seconds gives you joules.

-Trevor
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07-19-2011, 06:00 PM #3
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Xtrm2Rick
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Re: W/cm^2 to Joules conversion?

correct me if im wrong but iirc it was something like this:

1 joule = 1W/s... or was it the other way around

aw im to slow... nicely explained Trevor

Last edited by Xtrm2Rick; 07-19-2011 at 06:05 PM.

07-19-2011, 06:06 PM #4
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Trevor
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Re: W/cm^2 to Joules conversion?

Yeah, power is energy over time - power is watts and energy is joules.

Some people refer to a joule as a "watt-second" though, referring to 1W*1s.

-Trevor
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```23:10 <ARG>    nothing has blown up yet :)
23:10 <Trevor> that is a distressingly low standard for success```

07-19-2011, 09:14 PM #5
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xanatos
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Perfect... I thought time factored in there somewhere. Thanks very much!

07-19-2011, 09:26 PM #6
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DrSid
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Re: W/cm^2 to Joules conversion?

Well not trying to be rude, but wikipedia has great articles on physics. You should try it .. or google, generally it will point right there.
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07-22-2011, 04:09 AM #7
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Mo13
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Re: W/cm^2 to Joules conversion?

Quote:
 Originally Posted by Trevor Q1 is correct. Watts per centimeter squared means joules per second per centimeter squared. Joules represent energy, watts represent watts per second. Watts times seconds gives you joules. -Trevor
He means watts represents joules per second. That's just a typo.

Quote:
 Originally Posted by Xtrm2Rick correct me if im wrong but iirc it was something like this: 1 joule = 1W/s... or was it the other way around
Quote:
 Originally Posted by Trevor Yeah, power is energy over time - power is watts and energy is joules. -Trevor
Actually no, it's the other way around, as in: 1W = 1J/s, but everything he said after that is absolutely correct!

I kinda feel like a jerk for correcting you guys, but I'd hate to see a project fail over something so silly.

BTW, I LOVE the title to this thread. (I know, I'm a total geek.)
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Last edited by Mo13; 07-22-2011 at 04:10 AM.

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