What are picolasers (picosecond lasers) ?
Employing the selective photothermolysis theory, the narrow pulse width “quality switch” lasers were developed to treat pigmentary disorders and tattoos because melanin and tattoo inks have a very short thermal relaxation time.
How do the “older generation” lasers work ?
Previously nanosecond (one billionth of a second) pulse duration Q-switched lasers (QSL) cause rapid expansion, fragmentation of melanin/tattoo pigment particles and this photoacoustic effect, together with its inherent photothermal effects lead to the destruction of the melanosomes and tattoo particles.
Hence for decades the nanosecond pigment including the QS ruby, Alexandrite and Nd: YAG lasers have been the laser for choice for treating pigmentary lesions and tattoos.
What is the problem with older generation lasers ?
However, these nanosecond lasers treatment sometimes do not achieve complete clearance of pigmentary lesions in particular tattoo inks.
In addition the post inflammatory hyperpigmentation (PIH) following Q-Switched lasers, especially from the 532nm wavelengths is not uncommon in darker skin types. This is probably due to a combination of the photoacoustic and photothermal effects of the lasers.
Efforts have been made over the last decade to develop pigment lasers with even shorter pulse width so as to cause minimal photothermal effects. Hence the picosecond (one trillionth of a second) lasers were introduced recently with the hope to improve treatment outcome, shorten treatment session, reduce the complications and widen the scope of applications
How do picosecond lasers work ?
Picosecond lasers with pulse width around 100 times shorter than nanosecond lasers appear to have many benefits in targeting the smaller particles. The peak tensile stress induced by shorter pulses is substantially higher than that produced by Q-Switched lasers.
Melanin and tattoo particles have and estimated thermal relaxation time of 40 to 1000 picoseconds. The shorter picosecond pulse duration takes advantage of photomechanical impact/stress instead of heat to shatter ink into the smallest of particles.
Because the particles are so small, they are more easily absorbed and eliminated through the body’s natural processes.
This means that with each treatment, the pigment will lighten and clear faster compared to nanosecond lasers.
Treating Tattoos
Lower fluence (energy/cm2) is required compared to Q-Switched nanosecond lasers and hence fewer treatments with significantly better clearance of stubborn greens and blues, that is previously treated hard to clear recalcitrant tattoos.
Picolasers on the market (as of 2015)
The first picosecond pigment laser is the 750 picosecond Alexandrite laser (755nm) called Picosure. The 750ps, pulse widthe is 7 times shorter than the Revlite 5ns pulse width and 70 times shorter than the QS Alexandrite laser with 50ns pulse width.
Subsequently 2 other picosecond lasers were introduced but both are Nd: YAG lasers with dual wavelength (50 and 750 picoseconds respectively)
More picosecond lasers will be introduced soon.
What is the evidence ? (at time of publication)
Tattoos and Pigment: so far several reports on the efficacy of the picosecond lasers for tattoos removal has been impressive, but the treatment outcome of other pigmentary disorders has also been anectodaly reported to be good. We await more reports
Acne Scars, Skin rejuvenation: there are as of now very few reports on their effectiveness. The outcome remains to be seen.
Goh Cl. Picosecond lasers. NSC Update in Dermatology and Venereology 2015 – Singapore
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