▶ Previous Artlcle : #18-3. Picosecond Laser
Given that the speed at which the acoustic shock wave passes through the tissue is the same as the speed through water (1,500 m/sec), when the diameter of the melanosome is 1 μm, the value from the formula is 333X10-12, or 333 picoseconds. Which means the SRT of a melanosome whose diameter is 1μs is 333 picoseconds.
Thus, only the picosecond laser whose pulse duration is 300 picoseconds or less among the currently available picosecond lasers can secure stress confinement during the laser irradiation.
The picosecond laser with stress confinement can treat pigmented lesions with effective energy and less side effects because it does not transmit acoustic shock waves out of the melanosomes.
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A nanosecond laser with thermal confinement based on the TRT reduces the thermal damage to the tissues surrounding the target chromophore to treat the legions with minimal side effects, while a picosecond laser with stress confinement based on the SRT reduces damage to the surrounding tissues caused by acoustic shock waves to minimize side effects.
Therefore, when compared to a nanosecond laser, a picosecond laser induces less damage and side effects to the surrounding tissues, a shorter recovery period, and markedly higher peak power to increase treatment effects.
More Effective Treatment with LIOB
Laser induced optical breakdown (LIOB) is a concept that makes a picosecond laser more effective on skin regeneration when compared to other lasers.
For the LIOB to form vacuoles in the epidermis or dermis, a high-intensity laser beam should be irradiated to the tissue.
Because the current picosecond lasers are insufficient in power density, however, fractional handpieces of micro lens array (MLA) or diffractive optical element (DOE) are used to increase the power density by more than 10 times to induce the LIOB.
Figure 4. Stress relaxation time of melanosome.
-To be continued
