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# W/cm^2 to Joules conversion?

#### xanatos

##### Member
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

#### Trevor

##### Well-known member
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

#### Xtrm2Rick

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

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

aw im to slow... nicely explained Trevor

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#### Trevor

##### Well-known member
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

#### xanatos

##### Member
Perfect... I thought time factored in there somewhere. Thanks very much!

#### DrSid

##### New member
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.

#### Mo13

##### New member
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.

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

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

BTW, I LOVE the title to this thread. (I know, I'm a total geek.)

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