Page 59 - Lasers and IPLs in Medical/Aesthetic Applications v1.2
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Chapter 1 – Fundamentals of Medical/Aesthetic Lasers and IPLs v1.2
● The power density of the IPL system is calculated by dividing 20 J/cm2 by 10 ms yielding 2,000 W/cm2. However, the laser’s power density is 5 J/cm2 divided by 10 ns. A nanosecond is 1 billionth of a second so the peak power density of this laser will be 500,000,000 W/cm2 in each pulse.
● So, you can see that this laser can produce a power density which is 250,000 times that of the IPL system! If you were to draw a graph and show the maximum power density of the IPL as a 1 cm high point, then the laser would need a point 2.5 km high on the same graph (see above)!!
● Given that we now know that power density determines the outcome of any treatment you can see how knowing the fluence is not enough – you MUST know the power density.
 Why ‘Power Density’ is the Most Important Parameter in Clinical Treatments
    Power Density
Energy Spot size area
Pulse duration
 All three have an effect on the physical reaction!
Another wee technical note – power density is known as ‘intensity’ or, more correctly, ‘irradiance‘ in physics!
Spot Size
● Spot size is pretty obvious! The spot size is the area over which the light energy is deposited on the skin surface.
● It is an area and is measured in mm2 or cm2. ________________________________________________________________________ 58
Chapter 1 LEVEL A Fundamentals of Lasers/IPLs
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