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# What is 1500mJ in mW

#### Midknight

##### New member
I was looking up some information on laser tattoo removal machines. And their output is measured in mJ. My guess is than it is the same as 1.5Watts. But I wouldn't be asking if I wasn't sure.

#### FrothyChimp

##### New member
The only thing you can figure out is average power as a rating in mJ means the laser is pulsed. To do this you also need to know the repetition rate. By the way 1.5J is quite a bit of energy for a small laser.

#### Spoz

##### New member
Watts is joules per second. You know joules, so you also need to know the seconds to be able to convert it.

Once you find out how many seconds the pulse is (likely to be measured in nanoseconds, in which case multiply by 10^-9), then:

1.5/s = Watts

As an example, take that 532nm laser that has a 4000mJ pulse for 50 milliseconds.

4000mJ = 4.0J
50ms = 0.05s

Watts = 4/0.05 = 80 Watts

#### Midknight

##### New member
Okay cool. That's a lot of power for a tattoo removal machine! How dose that not put a whole in your shin???

#### Cyparagon

##### Well-known member
How many gallons have the same weight as 3 yards?

But srsly, to your question - It's not focused and not readily absorbed by the skin.

#### SuicideKing

##### New member
Tatoos are mostly black and green ink. -Primary absorbers of red and infrared energy. Human skin does not absorb IR that well, so it's the tattoos that receive the real damage; carbonizing the inert pigments, so they can be processed out by the body.

Same process that lets you pop a red balloon inside a clear balloon with a green laser.