Page 180 - Chapter 3 - An Introduction to Laser/IPL Hair Removal
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Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
Comparison between lasers and IPLs – Results from clinical studies
An interesting comparative study was carried out by Bouzari et.al. in 2004. They looked at the long-pulsed Nd:YAG, alexandrite and diode lasers in various skin types.
Device
Fluence (J/cm2)
Pulsewidth (ms)
Spot diameter (mm)
Rep rate (Hz)
Power Density (Watt/cm2)
Power Density (W/cm2)
Mean hair reduction
Mean
Nd:YAG
40 to 55
25 to 32
6 to 8
1
1250 - 2200
1661
42%
Alex
15 to 25
10 to 20
8 to 10
1
750 - 2500
1659
66%
Diode
25 to 40
10 to 30
9
1
833 - 4000
1660
47%
The above data taken from -
Table 43 – Comparison of hair removal lasers
So, the above data shows a range from 750 W/cm2 to 4000 W/cm2 for the lasers while IPLs typically use around up to 3000 W/cm2.
Their ‘hair reduction’ measurements indicate alex, diode and Nd:YAG, in that order, but overall the alex and diodes appeared to be ‘better’ – they claim!! However, they made a mistake in this study - the absorption coefficients of melanin, at each wavelength, were not considered. We know from Table 13, that these are approximately 50 cm-1, 164 cm-1 and 129 cm-1 for the Nd:YAG, Alex and diode lasers, respectively.
This tells us that we need to deliver energy/power in the same proportions if we want to achieve similar results. The table above shows that the mean power densities delivered were roughly the same, for each device – at around 1660 Watts/cm2. To account for the lower absorption coefficient at 1064nm, they should have used a higher fluence. This would deposit more energy into the hair follicles and generated better results.
The curious finding is their % success with their diode laser – it appears quite low. For the power densities they were using, the success rate should have been comparable with the alexandrite laser. Their result of only 47% call into question the actual power delivered by their laser. ________________________________________________________________________ 180
Chapter 3 Laser/IPL Hair Removal
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