Laser-induced optical breakdown effects of micro-lens arrays and diffractive optical elements on ex vivo porcine skin after 1064 nm picosecond laser irradiation

Efficacy and safety of a novel 785 nm picosecond neodymium-doped yttrium aluminum garnet laser for the treatment of facial benign pigmented lesions in Asian skin: a pilot study

BACKGROUND AND OBJECTIVES

Benign pigmented lesions and a general uneven tone in people with skin of color are growing issues that have been presented to dermatologists. To the best of our knowledge, this is the first controlled study to examine the efficacy and safety of using the newly introduced 785 nm neodymium-doped yttrium aluminum garnet (Nd:YAG) picosecond laser to treat facial benign pigmented lesions in Asian patients with diffractive lens array.

MATERIALS AND METHODS

A 785 nm Nd:YAG picosecond laser was used to treat 15 healthy female volunteers older than 18 years who had Fitzpatrick skin types II-IV and facial benign pigmented lesions. Each volunteer received five weekly treatments in dual modes. The clinical improvement was assessed by independent investigators and by objectively measuring the melanin index.

RESULTS

After the treatment, the melanin and erythema indices decreased, and the pigmented lesions showed clinical improvements. No serious adverse effects were observed during the study period.

CONCLUSIONS

A 785 nm Nd:YAG picosecond laser may be safe and effective in treating facial benign pigmented lesions in Asian skin.

Effect of fractional picosecond laser therapy using a diffractive optical lens on histological tissue reaction

BACKGROUND AND OBJECTIVES

Fractional ablative resurfacing techniques are preferred treatments for facial rejuvenation of aged skin. This study was performed to investigate the cutaneous effects of using a fractional picosecond laser at 1064 nm with a diffractive lens.

METHODS

The penetration depth according to the location of the handpiece tip was evaluated using an acrylic panel. Laser induced optical breakdown (LIOB) and cutaneous damage were observed after hematoxylin and eosin staining in guinea pigs. Collagen formation was evaluated using Victoria staining, Masson's trichrome (MT) staining, and immunohistochemical staining for collagen type III.

RESULTS

The penetration depth for LEVEL 1 was 499.98-935.23 μm (average: 668.75 ± 182.84 μm); the LIOB cavity area was 1664.17 ± 650.52 μm2. The penetration depth of LEVEL 2 was 257.12-287.38 μm (average: 269.77 ± 14.55 μm) with an LIOB cavity area of 1335.85 ± 214.41 μm2. At LEVEL 3, that was 36.17-53.69 μm (average: 52.15 ± 20.81 μm) and the LIOB cavity area was 1312.67 ± 1069.12 μm2. No epidermal tissue damage was observed and collagen formation was observed from day 14 under all conditions.

CONCLUSION

Diffractive optical element (DOE) lens arranged laser treatment system controlled the position of LIOB occurrence and an irradiating area.

Diffractive micro-lens array (DLA) for uniform and selective picosecond laser treatment

Picosecond Nd:YAG lasers using diffractive optical elements (DOE) and micro-lens arrays (MLA) have widely been used in dermatology for the treatment of pigmented lesions and skin rejuvenation. This study designed and developed a new optical element of diffractive micro-lens array (DLA) by combing the features of DOE and MLA in order to achieve uniform and selective laser treatment. Both optical simulation and beam profile measurement demonstrated that DLA created a square macro-beam consisting of multiple micro-beams in a uniform distribution. Histological analysis confirmed that the DLA-assisted laser treatment generated micro-injuries at various skin depths from the epidermal layer to the deep dermal layer (up to 1200 µm) by adjusting the focal depths while DOE showed shallow penetration depths and MLA created non-uniform micro-injury zones. The DLA-assisted picosecond Nd:YAG laser irradiation can provide a potential benefit for pigment removal and skin rejuvenation via uniform and selective laser treatment.

Characterization of picosecond laser-induced optical breakdown using harmonic generation microscopy

BACKGROUND AND OBJECTIVES

By creating microinjuries usually confined to the epidermis, a fractional picosecond 1064-nm Nd:YAG laser that delivers an array of highly focused beamlets can be effectively used for facial rejuvenation or resurfacing. However, the mechanism of dermal remodeling underlying this nonablative treatment remains unclear.

METHODS

Five participants having skin phototype III-IV were recruited for intervention using a fractional picosecond 1064-nm Nd:YAG laser system equipped with a holographic diffractive beam-splitting optic. The laser-induced histopathological changes on human skin were examined in vivo using a harmonic generation microscopy (HGM), visualizing second harmonic generation (SHG), and third harmonic generation (THG) contrasts dichromatically. SHG refers for collagen distribution, while THG represents for epidermal components in the HGM signal.

RESULTS

Histological hematoxylin and eosin staining and in vivo HGM imaging studies revealed the presence of epidermal vacuoles below the stratum granulosum along with keratinocyte degeneration or cytolysis. In addition to the epidermal vacuoles, HGM imaging exclusively demonstrated laser-induced shock wave propagation arranged as a THG-bright concentric pattern in the epidermis and loss of SHG signals in the papillary dermis immediately beneath the epidermal vacuoles.

CONCLUSIONS

Alongside generating epidermal vacuoles, the fractional picosecond 1064-nm Nd:YAG laser induced collagen changes. These collagen changes may lead to dermal remodeling and neocollagenesis underlying the fractional picosecond laser treatment.

A Randomized, Prospective, Split-Face Pilot Study to Evaluate the Safety and Efficacy of 532-nm and 1,064-nm Picosecond-Domain Neodymium:Yttrium-Aluminum-Garnet Lasers Using a Diffractive Optical Element for Non-Ablative Skin Rejuvenation: Clinical and Histological Evaluation

BACKGROUND

The advent of fractionated picosecond (ps) lasers has provided an opportunity to explore new ways of creating microinjuries in the skin to induce skin rejuvenation.

OBJECTIVE

To compare the efficacy and safety of diffractive optical element (DOE)-assisted ps neodymium: yttrium-aluminum-garnet (Nd:YAG) lasers with 532-nm and 1,064-nm wavelengths (532-nm and 1,064-nm Nd:YAG P-DOE) using a novel fractional handpiece for the treatment of photoaged skin.

METHODS

An ex vivo guinea pig skin experiment was performed by evaluating the histology of the skin after 532-nm Nd:YAG P-DOE irradiation. A randomized, prospective, split-face study was performed on eight subjects with 532-nm and 1,064-nm Nd:YAG P-DOE.

RESULTS

Based on the histological evaluation using ex vivo guinea pig skin, a reasonable safety profile and the potential to generate effective skin rejuvenation was observed using the 532-nm Nd:YAG P-DOE. Results demonstrated that both 532- and 1,064-nm Nd:YAG P-DOE were similarly effective in improving skin texture and skin pores; however, 532-nm Nd:YAG P-DOE was more effective in treating dyspigmentation.

CONCLUSION

At a preliminary level, this study revealed that 532-nm and 1,064-nm ps Nd:YAG lasers using DOE fractional technology may improve photoaged skin. In conclusion, 532-nm Nd:YAG P-DOE may be especially beneficial for skin with epidermal pigmentary lesions.

The comparison of the efficacy and safety of fractional 1064 nm Nd:YAG picosecond laser and nonablative fractional 1565 nm laser in the treatment of enlarged pores: A prospective split-face study

BACKGROUND AND OBJECTIVES

To compare the efficacy and safety of fractional 1064 nm Nd:YAG picosecond laser and nonablative fractional 1565 nm laser in the treatment of enlarged pores.

STUDY DESIGN/MATERIALS AND METHODS

Twenty patients received five monthly treatments at months 0, 1, 2, 3, and 4 and were followed up at months 5, 6, and 7. All patients were treated by fractional 1064 nm Nd:YAG picosecond laser (FxPico) on the left face, and nonablative fractional 1565 nm laser (ResurFx) on the right face as a control.

RESULTS

For the 19 patients who completed the study, both sides demonstrated significant improvement on pore counts (p < 0.01), while there was no significant difference between the two sides 3 months after the final treatment (p = 0.092). Excellence rate on the FxPico side (57.9%) was significantly better than the ResurFx side (36.8%) (p < 0.05). Sebum secretion and porphyrin value significantly decreased on both sides after five treatments and there was a higher reduction of sebum level on the ResurFx side. There was no difference between the two therapies in terms of overall satisfaction. Pain of treatment for the ResurFx side (average VAS 4.45 ± 1.60) is significantly higher than that for the FxPico side (average visual analog scale [VAS] 1.48 ± 1.36) (p < 0.001). Erythema, edema, and petechiae were common adverse effects and were mild to moderate. There was significantly higher incidence of hyperpigmentation for the ResurFx side (52.6%) compared with that for the FxPico side (5.3%) (p < 0.001).

CONCLUSION

Fractional 1064 nm Nd:YAG picosecond laser and nonablative fractional 1565 nm laser both are effective, efficient, and safe treatment regimens for enlarged pores, while fractional 1064 nm Nd:YAG picosecond laser has better clinical response with less treatment pain, shorter recovery period and much lower induction of hyperpigmentation.

Treatment of facial pigmented disorders with a 785-nm picosecond Ti:sapphire laser in Asians: A report of three cases

Since the advent of the theory of selective photothermolysis, the importance of targeting the chromophore and minimizing the surrounding damage has been extensively discussed. Picosecond-domain laser (ps-laser) treatment with a wide range of wavelengths is an emerging option for various pigmented lesions; however, no definitive treatment choice has been confirmed. The authors aimed to investigate the efficacy and safety of a ps-laser with a 785-nm wavelength for the treatment of facial pigmented lesions in Asians. Three Korean patients with facial pigmented lesions were recruited for the study. A 785-nm ps-laser with a fractionated and an unfractionated handpiece was utilized to administer the treatment. The clinical outcome was evaluated by a clinician by comparing pre- and post-treatment photographs. All patients exhibited a significant improvement in pigmented lesions including freckles, lentigines, and melasma, after three to four sessions of treatment. No adverse events, including post-inflammatory hyperpigmentation or hypopigmentation were observed. In conclusion, this novel 785-nm Ti:sapphire ps-laser may be an effective and safe modality for treating pigmented lesions in skin of color.

Biomechanical Sensing Using Gas Bubbles Oscillations in Liquids and Adjacent Technologies: Theory and Practical Applications

Gas bubbles present in liquids underpin many natural phenomena and human-developed technologies that improve the quality of life. Since all living organisms are predominantly made of water, they may also contain bubbles-introduced both naturally and artificially-that can serve as biomechanical sensors operating in hard-to-reach places inside a living body and emitting signals that can be detected by common equipment used in ultrasound and photoacoustic imaging procedures. This kind of biosensor is the focus of the present article, where we critically review the emergent sensing technologies based on acoustically driven oscillations of bubbles in liquids and bodily fluids. This review is intended for a broad biosensing community and transdisciplinary researchers translating novel ideas from theory to experiment and then to practice. To this end, all discussions in this review are written in a language that is accessible to non-experts in specific fields of acoustics, fluid dynamics and acousto-optics.

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

Although nude mice are an ideal photoaging research model, skin biopsies result in inflammation and are rarely performed at baseline. Meanwhile, studies on antiphotoaging antioxidants or rejuvenation techniques often neglect the spontaneous reversal capacity. Full-field optical coherence tomography (FFOCT) can acquire cellular details noninvasively. This study aimed to establish a photoaging and sequential function reversal nude mice model assisted by an in vivo cellular resolution FFOCT system. We investigated whether a picosecond alexandrite laser (PAL) with a diffractive lens array (DLA) accelerated the reversal. In the sequential noninvasive assessment using FFOCT, a spectrophotometer, and DermaLab Combo®, the photodamage percentage recovery plot demonstrated the spontaneous recovery capacity of the affected skin by UVB-induced transepidermal water loss and UVA-induced epidermis thickening. A PAL with DLA not only accelerated skin barrier regeneration with epidermal polarity, but also increased dermal neocollagenesis, whereas the nonlasered group still had >60% collagen intensity loss and 40% erythema from photodamage. Our study demonstrated that FFOCT images accurately resemble the living tissue. The photoaging and sequential function reversal model provides a reference to assess the spontaneous recovery capacity of nude mice from photodamage. This model can be utilized to evaluate the sequential noninvasive photodamage and reversal effects after other interventions.

Holographic point source for digital lensless holographic microscopy

A holographic point source (HPS) developed for digital lensless holographic microscopy (HPS-DLHM) is presented. The HPS is an off-axis phase transmission hologram of an experimental micrometer pinhole recorded on a photopolymer holographic film. An amplitude division interferometer, adjusted to operate at maximum diffraction efficiency, has been employed to record the hologram. The results of HPS-DLHM have been contrasted with the results obtained via conventional DLHM, and the two techniques were found to give similar measurements. Compared with conventional pinhole-based DLHM illumination, our cost-effective proposal provides increased mechanical stability, the possibility of wider spherical illumination cones, and shorter reconstruction distances. These superior features pave the way to applying this quantitative phase imaging (QPI) technique in biomedical and telemedicine applications. The imaging capabilities of our HPS-DLHM proposal have been tested by using an intricate sample of a honeybee leg, a low-absorption sample of epithelial cheek cells, a 1951 USAF test target, and smeared human erythrocytes.

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

Fractional laser treatment is commonly used for dermatological applications, enabling effective induction of collagen regeneration and significantly reducing recovery time. However, it is challenging to observe laser-induced photodamage beneath the tissue surface in vivo, making the non-invasive evaluation of treatment outcomes difficult. For in vivo real-time study of the photodamage induced by fractional pulsed CO₂ and Nd:YAG lasers commonly utilized for clinical therapy, a portable spectral-domain optical coherence tomography (SD-OCT) system was implemented for clinical studies. The photodamage caused by two lasers, including photothermal and photoacoustic effects, was investigated using OCT, together with the correlation between photodamage and exposure energy. Additionally, to investigate the change in the optical properties of tissue due to photodamage, the attenuation coefficients and damaged areas of normal skin and laser-treated skin were estimated for comparison. Finally, the recovery of the exposed skin with both lasers was also compared using OCT. The results show that OCT can be a potential solution for in vivo investigation of laser-induced tissue damage and quantitative evaluation.

Freeform beam splitting system design for generating an array of identical sub-beams

Laser beam splitting by freeform optics is promising but less studied. Instead of directly forming a target spot array, we propose to first convert the input beam into a closely connected Gaussian sub-beam array. All the Gaussian sub-beams have the same optical field distributions which thus can produce identical discrete spots on the target plane. Such a design concept is very beneficial to ensure the consistency for laser processing. Importantly, the introduction of an intermediate Gaussian sub-beam array can reduce diffraction effects when the size of each Gaussian sub-beam is sufficiently larger than that of the corresponding sub-area within the input beam. The desired transformation can be achieved by two typical systems. The first system consists of two plano-freeform lenses. The second system is composed of a plano-freeform lens and a lens with an entrance freeform surface and an exit surface of freeform lens array. The two freeform beam splitting systems can be determined based on appropriate ray mappings among the input, intermediate and target irradiance distributions and a subsequent double-surface construction. Geometrical and physical simulations verify the effectivenesses of the two beam splitting systems.

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

The current study aims to evaluate the dependence of laser-induced optical breakdown (LIOB) on skin types by using 1064 nm picosecond laser with micro-lens 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/cm² demonstrated that MLA yielded a deeper distribution (180-400 μm) of laser-induced 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.

Quantitative assessment of the long-term efficacy and safety of a 1064-nm picosecond laser with fractionated microlens array in the treatment of enlarged pores in Asians: A case-control study

Background

Enlarged facial pores are one of the common skin signs of photoaging that patients seek treatment for. However, objective data and long‐term assessment on the efficacy and safety of therapeutic procedures for this condition are limited.

Objective

To objectively evaluate the efficacy and safety of a 1064‐nm picosecond laser with microlens array (MLA) for pore tightening.

Methods

Twenty‐five patients with enlarged pores received three treatments with a 1064‐nm picosecond laser coupled with MLA at 4‐week intervals. Patients were evaluated using objective (measurement of pore volume using three‐dimensional photography) and subjective (clinical evaluation by two blinded dermatologists) assessments at baseline and at the 1‐, 3‐, and 6‐month follow‐ups. Adverse effects were also recorded during each visit.

Results

After three treatments, there was a significant reduction of pore size from baseline (p < 0.001). The improvement in pore size appearance significantly continued from the 1‐month to the 6‐month follow‐up visits (p = 0.013). The total average pore size was 1.15652 ± 0.614322 and 0.8087 ± 0.50515 at baseline and at 6 months after the final treatment, respectively, resulting in an average of 30% reduction in pore size. No cases of dyspigmentation, textural alteration, or scarring were documented.

Conclusion

Fractional 1064‐nm picosecond laser appears to be effective and safe for reducing pore size in Asians with minimal transient side effects.