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can output a maximum power of some level (maybe 1000W or 3500W, or something similar).
2. The second ‘power’ refers to the laser’s actual optical power output – the stuff that hits the skin!! This is NOT the same as the laser’s electrical power (see below). This is the power that is actually important. It tells us how quickly the energy or fluence may be supplied to the skin surface. A 1000W laser can deliver 1000 Joules of energy per second, whereas a 5000W can deliver five times that rate.
Device electrical power
A percentage of the laser’s electrical power is used to ‘drive’ the diode lasers (perhaps between 50 and 80%). So, the unit might have a power rating of 5000 Watts, but only between 2500 and 4000W is actually used to ‘fire up’ the laser. (The rest is used to pump the water, run the screen etc...
A percentage of this electrical power is converted into laser (light) power. This is the “output” power – it is NOT the same as the “electrical” power of the device! Now, lasers are never 100% efficient so not all of this power will be converted into the laser power. It depends how good the diodes are, but this might be between 75 and 90% (or thereabouts).
So, a 5000W (electrical power) device might deliver an optical power (to the skin) of around 2500W – this is the power we should be interested in. This is what actually hits the skin surface.
As a consequence, higher powered lasers deliver more energy/fluence in same pulsewidth than lower power lasers
For a pulsewidth of 20 milliseconds in three different lasers:
Laser Output Power (Optical)
1000
2500
5000
Maximum Fluence (J/cm2)
20
50 100
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