Dependence of laser‐induced optical breakdown on skin type during 1064 nm picosecond laser treatment

Abstract

The current study aims to evaluate the dependence of laser-induced optical breakdown (LIOB) on skin types by using 1064 nm picosecond laser with microlens arrays (MLA) and diffractive optical elements (DOE). Both black and white skin tissues were examined to comparatively assess the LIOB effects in the skin in terms of laser-induced vacuolization.The black skin irradiated at 3.0 J/cm 2 demonstrated that MLA yielded a deeper distribution (180-400 μm) of laserinduced vacuoles with a size of 67 μm, compared to DOE (180-280 μm; 40 μm in size). However, the white skin presented that MLA created larger vacuoles (134 μm in size) in a smaller number at deeper distributions (125-700 μm) than MLA with the black skin. DOE generated no laser-induced vacuolization in the white skin. The white skin tissue with inherent higher scattering could be responsible for deeper vacuolization after the picosecond laser treatment. Further investigations are expected to determine the optimal treatment conditions for various skin types. K E Y W O R D Sdiffractive optical elements, fitzpatrick skin type, laser-induced optical breakdown, microlens arrays, picosecond laser skin treatment

Photoaging and Sequential Function Reversal with Cellular-Resolution Optical Coherence Tomography in a Nude Mice Model

“…In contrast, more UVA was absorbed in the dermis, and the size of the LIOB was smaller than that after UVB irradiation. Our study showed that the presence of melanin and hemoglobin is not a prerequisite for LIOB formation [24,29]. To create a breakdown, the irradiance threshold is a function of both medium characteristics, including the ionization energy and impurity level, and laser beam characteristics (wavelength/pulse width/spot size).…”

“…The thermal initiation pathway assisted by chromophores results in a lower irradiance threshold, which lowers the irradiance threshold by 20 times [27], whereas ubiquitous water lowers the irradiance threshold by 10-100 times [27,28]. Therefore, transparent and weakly absorbing tissues such as the cornea mainly rely on the multiphoton-initiated optical breakdown, whereas highly absorbing tissues such as dark skin require a much lower energy threshold [24,29]. The irradiance energy for nude mouse skin in our study was 0.00306667 × 10 13 W/cm 2 , which was approximately 362 times lower than that via the multiphoton absorption process (10 13 W/cm 2 ).…”

Morphologic and molecular biologic analyses of the skin rejuvenation effect of the fractional 1064‐nm picosecond laser: An animal study

“…The authors proposed that epidermal repair may lead to improvements in scars by regenerating the dermal matrix in human skin. Recent studies have also reported that light‐colored skin had a higher threshold for LIOB formation 31,32 . It was proposed that increased scattering of the laser in lighter skin with low melanin content could contribute to a limited formation of LIOB 31 .…”

In Vivo Identification of Skin Photodamage Induced by Fractional CO2 and Picosecond Nd:YAG Lasers with Optical Coherence Tomography

“…Picosecond lasers can cause laserinduced optical breakdown (LIOB) via multiphoton ionization, simultaneously resulting in high pressure and high temperature in the skin [9,10]. Such high pressure and temperature are usually combined with plasma expansion to further induce vacuolization beneath the skin surface, decomposing tiny pigments [11,12]. Therefore, the pressure wave can propagate from a shallow skin depth into the dermis, further triggering the tissue recovery.…”

“…Moreover, the existence and size of vacuoles are unpredictable. The induced photodamage, including photothermal and photoacoustic effects, is related to the optical properties of the skin, laser wavelength, incident photon energy, spot size of the treatment laser, focusing depth, and melanin [11,17]. The photodamage in clinical applications is unpredictable and varies between individuals.…”