Page 11 - Blog Posts v1

nm, in many systems). Incidentally, when the power spectrum is averaged across the 600 - 1200nm output, IPLs output an 'equivalent' wavelength of 820nm! This is useful for comparative calculations...
From the graph above we can see that these wavelengths are also absorbed by melanin. If we set the output energy of an IPL correctly, we will achieve precisely the same conditions as we did above with the lasers.
Given that we’re simply trying to heat up the follicles, the total amount of energy we deliver to them will determine how hot they become. If we deliver the appropriate energy in each device, over the same time, then they will all generate the same temperature in the follicles.
Pulsewidth
But it’s not that simple! It never is...
For the systems above to generate the same temperatures in the hair, they would all have to deliver their energy in the same time - the pulsewidth (or pulse length or pulse duration).
And this is where the confusion appears to set in. If we fire some energy at some hair in a particular pulsewidth, then the temperature will rise to some level. If we fire the same energy at the same hair in half that time, then the maximum temperature - in the hair - will he higher.
Why? Because of heat conduction during the pulse. These pulsewidths are typically in the millisecond range. These times are sufficiently long for a significant amount of heat to ‘escape’ from the target, while the pulse is still active. In other words, some of the heat is lost into the surrounding tissues which means that the hair cannot become as hot (while the adjacent tissues become hotter too!)
So a 10J pulse of energy from an alexandrite laser in a 5 ms pulse, will not generate the same temperature as a 30J pulse from a YAG laser in a 20ms pulse - simply because the yag pulsewidth will mean that more heat escapes while the pulse is firing. The hair treated by the alexandrite system will be hotter.
And this is why this topic is so tricky.
Different systems deliver their energies in vastly different pulsewidths. Diode lasers can easily use pulses more than 100ms long to deliver higher energies. IPLs systems typically use up to 50 or perhaps 100ms to deliver their energy. Alexandrite and YAG laser are usually shorter than both diodes and IPLs.
Another consideration is that the temperature of the hair is not the critical issue. We’re trying to denature (cook) the germ cells during the anagen phase. This requires that their temperature is raised for a certain length of time.
Mike’s Blog Posts 11