How powerful is an Nd:YAG laser for tattoo and PMU removal?

The power of lasers is usually expressed in mJ (millijoules), in other words thousandths of a joule.

The joule is a fairly abstract unit of energy in physics. What matters for us is to think of a joule as a certain amount of heat, of energy. So, 1 J = 0.2388 calories and, conversely, 1 calorie = 4.186 J.

I think everyone here knows the word calorie, but I will try to explain what it is from the point of view of physics.

1 calorie is the amount of energy needed to heat 1 gram of water by 1 degree Celsius. In general, this is a very small amount of energy, but let's look at it from the point of view of laser physics and do the maths:

On average, laser power is stated as 1,000 mJ, sometimes 1,600 mJ or even 2,000 mJ (though I wouldn't celebrate that: in reality the power is much lower). 1,000 mJ = 1 joule.

Pulse power = pulse energy ÷ pulse duration. What interests us here is the peak power the laser produces, roughly speaking, the peak power of the pulse. To make the calculation easier, let's divide 1 J by 1 nanosecond. We get 1 gigawatt. But that is hard to picture in real life.

Can you describe how much 1 gigawatt is? If not, read on!

Let's use our imagination :)

1 GW = 10% of the power of a rocket's engines. Can you imagine holding 1/10 of a space shuttle in your hands?!

1 GW = 50% of the power of the Hoover Dam hydroelectric plant (USA). Same question: you are holding half of a huge hydroelectric power station in your hands. Did you realise that?

1 GW = 10 fighter jet engines! I think no more questions are needed :)

And my favourite example, again from everyday life.

A clothes iron has a power of about 2,500 W. Just try to guess how many irons you would need to switch on for their combined power to equal an Nd:YAG laser. Have you guessed?

Here is the answer: 400,000!