Laser-induced Optical Breakdown Research Articles

Optimization of the Spot Spacings for Reducing Roughness in Laser-Induced Optical Breakdown Processes for Corneal Laser Vision Correction

The aim of this work is to implement an algorithm that simulates a simplified cutting surface based on laser-induced optical breakdown (LIOB). The algorithm includes the definition of a possible positioning of the laser pulses and calculation of the roughness for different parameter settings (including LIOB threshold, pulse energies, and spot spacings) as the difference between simulated and ideal target cut (local differences within the cut, i.e., the waviness of the simulated cut vs. the homogeneity of the ideal target cut). Furthermore, optimizations of specific variables, such as spot distance (along the pathway), track distance (between lines/tracks), and pulse energy, are performed. The simulations suggest that lower pulse energies (well above the LIOB threshold) combined with asymmetric spacings (spot-to-track distance ratio >> 1) may be effective to lower the roughness of laser cuts generated by LIOB processes. The importance of lowering pulse energies (well above the threshold) emphasizes the need for the LIOB threshold to remain low (as low as possible). Reducing roughness by decreasing spacings (thus, increasing dose for same pulse energies) may have negative implications in visual recovery (risk for overdose). In all cases, the roughness is multiple times larger (rougher) than equivalent simulations for ablative procedures.

Angular Patterns of Nonlinear Emission in Dye Water Droplets Stimulated by a Femtosecond Laser Pulse for LiDAR Applications

Femtosecond laser-induced fluorescence (FLIF) and femtosecond laser-induced optical breakdown spectroscopy (FIBS) are important tools for remote diagnostics of atmospheric aerosols using LiDAR (Light Identification Detection and Ranging) technology. They are based on light emission excitation in disperse media via multiphoton nonlinear processes in aerosol particles induced by high-power optical pulses. To date, the main challenge restraining the large-scale application of FLIF and FIBS in atmospheric studies is the lack of a valued theory of the stimulated light emission in liquid microparticles with a sufficiently broad range of sizes. In this paper, we fill this gap and present a theoretical model of dye water droplet emission under high intensity laser exposure that adequately simulates the processes of multiphoton excited fluorescence and optical breakdown plasma emission in microparticles and gives quantitative estimates of the angular and power characteristics of nonlinear emission. The model is based on the numerical solution to the inhomogeneous Helmholtz equations for stimulating (primary) and nonlinear (secondary) waves provided by the random nature of molecule emission in particles. We show that droplet fluorescence stimulated by multiphoton absorption generally becomes more intense with increasing particle size. Moreover, far-field plasma emission from liquid particles demonstrates a larger angular diversity when changing the droplet radius in comparison with multiphoton excited fluorescence, which is mainly due to the excitation of the internal optical field resonances in spherical particles.

Application of Picosecond Laser in Dermatology

ABSTRACT Background: Lasers are one of the most important treatment modalities in dermatology. Lasers interact with chromophores through several mechanisms that depend on fluence and pulse durations. Early lasers worked by photothermal interaction with pulse durations of 1 microsecond to 1 second. A picosecond laser is developed to confine photothermal effects and produce photomechanical effects and plasma induction. Purpose: To understand the mechanism of action and application of picosecond lasers for dermatological disorders. Review: Non-fractional picosecond lasers work by photomechanical interaction. Photomechanical interaction happens when pulse duration is less than inertial confinement time, causing fractures of chromophores with lower energy, or “cold ablation”. Fractional picosecond lasers work by laser-induced optical breakdown (LIOB). In LIOB, accelerated seed electrons cause an electron avalanche that produce a collection of free electrons called plasma, which ablates tissues. LIOB in the skin is always followed by photodisruption. In LIOB, vacuoles and debris were eliminated transdermally and dermal collagen and elastin increased. Picosecond laser may be applied in disorders requiring destruction of chromophores and for collagen and elastin disorders. It is currently the first-line treatment for tattoo removal (Nevus of Ota and Acquired Bilateral Nevus of Ota-like macules, or ABNOM). It has good efficacy and safety for solar lentigines, freckles, and cafe-au-lait macules (CALM). It is an additional treatment for moderate to severe melasma and hypertrophic scars, in combination with other treatments. The fractional picosecond laser showed moderate improvement and low risk of postinflammatory hyperpigmentation (PIH) for atrophic acne scars and produced improvement in striae alba.

Picosecond lasers in dermatology

The picosecond laser is one of the latest laser systems in dermatology and was originally developed to optimize tattoo removal. Advances in this technology has expanded the use of the picosecond laser to numerous other indications. This article provides an overview of the technical background as well as the indications of the picosecond laser in dermatological laser medicine and elucidates the possibilities and limits of this laser system. The article is based on areview of the current literature as well as experience from clinical practice in auniversity laser department. The picosecond laser enables aparticularly gentle and effective treatment due to ultra-short pulses and the principle of laser-induced optical breakdown. Compared to Q‑switched lasers, the picosecond laser has fewer side effects and is associated with lower pain intensity and shorter downtime. In addition to the removal of tattoos and pigmentary disorders, it is also used in the treatment of scars and rejuvenation. The picosecond laser has awide range of indications in dermatological laser medicine. The current data indicate that the laser is an effective method with few side effects. Further prospective studies have to be conducted to assess the efficacy, tolerability and patient satisfaction in an evidence-based manner.

MP35-10 MECHANISMS OF FIBER-TIP DEGRADATION DURING LASER LITHOTRIPSY

You have accessJournal of UrologyCME1 Apr 2023MP35-10 MECHANISMS OF FIBER-TIP DEGRADATION DURING LASER LITHOTRIPSY Yuri Pishchalnikov, William Behnke-Parks, and Marshall Stoller Yuri PishchalnikovYuri Pishchalnikov More articles by this author , William Behnke-ParksWilliam Behnke-Parks More articles by this author , and Marshall StollerMarshall Stoller More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000003269.10AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: Ureteroscopic lithotripsy breaks urinary stones using laser pulses delivered to the stone via optical fibers. Degradation of fibers reduces the efficacy of lithotripsy and varies with fiber diameter, stone composition, laser pulse energy and duration. The goal of this work was to reveal the physical mechanisms of fiber-tip damage (burnback) in water and air. METHODS: The dynamics of fiber-tip damage was studied using a high-speed camera Shimadzu HPV-X2 at a frame rate up to two million frames per second. The camera was mounted to a microscope focused on the 242-µm glass-core-diameter fiber positioned in direct contact with a target—typically, a glass slide coated with a 25±5 µm layer of hydroxyapatite (Himed, NY). Selected experiments were conducted with BegoStones and whole surgically retrieved urinary stones. Damaged fibers were cleaved to start each series of 20 pulses with flat fiber tips. Laser pulses were produced using a Lumenis VersaPulse holmium:YAG laser. Temporal profiles of infrared laser pulses and flashes of visible light were resolved using photodetectors. Cross-sectional profiles of laser-beam energy were assessed using Zap-It paper. Microscope images were used to measure the burnback length of the fiber. RESULTS: Burnback of optical fibers was associated with flashes of light (sparks) observed both in water and in air. Sparks in air could crack and fragment the fiber during single laser pulse. Twenty pulses in air produced the burnback length of 0.37 mm at 1.0 J (95% CI: 0.11–0.64 mm) and 0.14 mm at 0.6 J (95% CI: 0.10–0.18 mm), smaller than that at 1.0 J (p=0.010). In water, the fibers were damaged by sparks during the laser pulse and after the pulse during the collapse of laser-induced cavitation bubbles. Contribution of cavitation varied from insignificant to most dramatic, breaking a 1.1-mm length of the fiber in a single laser pulse. Cavitation without sparks showed no burnback with only minor damage of cladding (500 pulses, 1.0 J). Sparks were associated with an increased absorption of laser energy and were observed at laser energies typically >0.5 J and only with certain target materials near the fiber tip. Cross-sections of laser beams were larger with fibers damaged in air than that in water (p=0.007) and both were larger than that with undamaged fibers (p<0.005). CONCLUSIONS: These results suggest that the burnback degradation of optical fibers is associated mainly with laser-induced heating, ionization, and optical breakdown of target material. A better understanding of the mechanisms of fiber-tip damage will aid in development of future improvements to minimize degradation of optical fibers. Source of Funding: Research reported in this publication was supported by the National Institute of Diabetes and Digestive and Kidney Diseases of the National Institutes of Health under Award Number R43DK129104. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health © 2023 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 209Issue Supplement 4April 2023Page: e473 Advertisement Copyright & Permissions© 2023 by American Urological Association Education and Research, Inc.MetricsAuthor Information Yuri Pishchalnikov More articles by this author William Behnke-Parks More articles by this author Marshall Stoller More articles by this author Expand All Advertisement PDF downloadLoading ...

Microlesion healing dynamics in in vivo porcine skin after treatment with 1064 nm picosecond-domain Nd:YAG laser.

The fractionated picosecond laser produces microscopic lesions in the epidermis and dermis due to laser-induced optical breakdown (LIOB). There have been multiple histological reports, but the present literature lacks detailed in vivo studies after treatment with high-power laser systems. Our study aimed to characterize the healing patterns of microlesions induced with 150 ps duration 1064 nm MLA-type picosecond laser. The induced picosecond laser-tissue reactions with pulse energy of 50-250 mJ and different treatment modes were observed in in vivo porcine skin model over 10 days after the laser procedure. A macroscopic evaluation was combined with microscopic histological analysis to observe the healing dynamics of laser-induced microlesions. Superficial, intraepidermal cavitation bubbles were induced using microbeam fluence of 4-20 J/cm2 . Skin irritation scores positively correlated with pulse energy and dose. Our findings demonstrate that dose and pulse energy had a direct impact on epidermal thickness and lesions healing dynamics.

Diatomic Line Strengths for Fitting Selected Molecular Transitions of AlO, C2, CN, OH, N2+, NO, and TiO, Spectra

This work communicates line-strength data and associated scripts for the computation and spectroscopic fitting of selected transitions of diatomic molecules. The scripts for data analysis are designed for inclusion in various software packages or program languages. Selected results demonstrate the applicability of the program for data analysis in laser-induced optical breakdown spectroscopy primarily at the University of Tennessee Space Institute, Center for Laser Applications. Representative spectra are calculated and referenced to measured data records. Comparisons of experiment data with predictions from other tabulated diatomic molecular databases confirm the accuracy of the communicated line-strength data.

Effect of Laser-Induced Optical Breakdown on the Structure of Bsa Molecules in Aqueous Solutions: An Optical Study.

The influence of laser radiation of a typical surgical laser on the physicochemical properties of the Bovine Serum Albumin (BSA) protein was studied. It was established that the physicochemical characteristics of optical breakdown weakly depend on the concentration of protein molecules. At the same time, the patterns observed for an aqueous solution of BSA irradiated with a laser for different time periods were extremely similar to the classical ones. It was established that after exposure to laser radiation, the optical density of protein solutions increases. At the same time, the intensity of BSA fluorescence due to aromatic amino acid residues decreases insignificantly after exposure to laser radiation. In this case, the position of the excitation and emission maximum does not change, and the shape of the fluorescence spot on 3D maps also does not change significantly. On the Raman spectrum after exposure to laser radiation, a significant decrease in 1570 cm−1 was observed, which indicates the degradation of α-helices and, as a result, partial denaturation of BSA molecules. Partial denaturation did not significantly change the total area of protein molecules, since the refractive index of solutions did not change significantly. However, in BSA solutions, after exposure to laser radiation, the viscosity increased, and the pseudoplasticity of aqueous solutions decreased. In this case, there was no massive damage to the polypeptide chain; on the contrary, when exposed to optical breakdown, intense aggregation was observed, while aggregates with a size of 400 nm or more appeared in the solution. Thus, under the action of optical breakdown induced by laser radiation in a BSA solution, the processes of partial denaturation and aggregation prevail, aromatic amino acid residues are damaged to a lesser extent, and fragmentation of protein molecules is not observed.

Controlling bubble generation by femtosecond laser-induced filamentation

Femtosecond laser-induced optical breakdown in liquids results in filamentation, which involves the formation and collapse of bubbles. In the present work, we elucidate spatio-temporal evolution, interaction, and dynamics of the filamentation-induced bubbles in a liquid pool as a function of a broad spectrum of laser pulse energies (∼1 to 800 µJ), liquid media (water, ethanol, and glycerol), and the number of laser pulses. Filament attributes such as length and diameter have been demarcated and accurately measured by employing multiple laser pulses and were observed to have a logarithmic dependence on laser energy, irrespective of the medium. The size distribution of persisting microbubbles is controlled by varying the pulse energy and the number of pulses. Our experimental results reveal that introducing consecutive pulses leads to strong interaction and coalescence of the pulsating bubbles via Bjerknes force due to laser-induced acoustic field generation. The successive pulses also influence the population density and size distribution of the micro-bubbles. We also explore the size, shape, and agglomeration of bubbles near the focal region by controlling the laser energy for different liquids. The insights from this work on filamentation-induced bubble dynamics can be of importance in diverse applications such as surface cleaning, fluid mixing and emulsification, and biomedical engineering.

Review of Lasers and Energy-Based Devices for Skin Rejuvenation and Scar Treatment With Histologic Correlations.

Lasers and energy-based devices (EBD) are popular treatments for skin rejuvenation and resurfacing. Achieving desired outcomes and avoiding complications require understanding the effects of these devices at a histologic level. Currently, no comprehensive review summarizing the histologic effects of laser and energy-based treatments exists. To describe how lasers and EBD alter skin histology and improve the overall understanding of these devices. A PubMed search was conducted for studies with histologic analysis of fractional picosecond laser, fractional radiofrequency microneedling, nonablative lasers, and ablative lasers. Fractional picosecond lasers induce intraepidermal and/or dermal vacuoles from laser-induced optical breakdown. Fractional radiofrequency microneedling delivers thermal energy to the dermis while sparing the epidermis, making it safer for patients with darker skin phototypes. Fractional nonablative lasers induce conical zones of coagulation of the epidermis and upper dermis. Ablative lasers vaporize the stratum corneum down to the dermis. Traditional ablative lasers cause diffuse vaporization while fractional ablative lasers generate columns of tissue ablation. Lasers and EBD are effective for skin resurfacing and rejuvenation and have different mechanisms with disparate targets in the skin. Safe and effective use of devices requires understanding the histologic laser-tissue interaction.

In vivo characterization of the threshold of laser-induced optical breakdown (LIOB) of a fractional 1064nm Nd:YAG picosecond laser by optical coherence tomography: A step forward to precision laser therapy.

Clinical endpoints serve as an important guide to physicians during laser treatment. However, there are no reliable clinical endpoints for the fractional picosecond laser-induced optical breakdown (LIOB) whose threshold is dependent on the irradiance of the laser and epidermal melanin content of the skin treated. To determine the LIOB threshold in vivo of a 1064nm fractional picosecond laser for different skin colors. A cellular-level resolution optical coherence tomography (OCT) has successfully demonstrated that the in vivo morphological change of LIOB in the epidermis by a fractional picosecond laser. By measuring the melanin content in the area of the skin to treat using a skin imaging device, the physician would therefore be able to determine the threshold of LIOB visually under OCT for the skin of that particular melanin content. The pilot study has demonstrated that OCT may serve as a non-invasive modality to determine the thresholds of LIOB by a fractional picosecond laser. And the established correlation between melanin content and LIOB threshold in this pilot study may further guide physicians, that is, physicians may be able to predict the threshold of LIOB, without having to see the clinical endpoints, by simple measurement of melanin content of the skin to treat preoperatively.

Analytical optimization of the laser induced refractive index change (LIRIC) process: maximizing LIRIC without reaching the damage threshold

Abstract A method to determine the optimum laser parameters for maximizing laser induced refractive index change (LIRIC) while avoiding exceeding the damage threshold for different materials with high water content (in particular, polymers such as hydrogels or the human cornea) is proposed. The model is based upon two previous independent models for LIRIC and for laser induced optical breakdown (LIOB) threshold combined in a simple manner. This work provides qualitative and quantitative estimates for the parameters leading to a maximum LIRIC effect below the threshold of LIOB.

Astigmatism and spherical aberrations as main causes for degradation of ultrafast laser-induced cavitation in water

The generation of cavitation bubbles in water by focused laser pulses has been thoroughly studied, particularly due to the wide range of applications in biomedical fields, in particular for ophthalmic laser surgery. The presence of optical aberrations in any optical system deteriorates the precision of light focusing and may reduce the laser interaction efficiency in transparent media. In this paper, we analyze the influence of several controlled optical geometrical aberrations in the formation and dynamics of cavitation bubbles in water caused by laser-induced optical breakdown using femtosecond laser pulses. The maximum cavitation bubble diameter reduces with increasing aberrations, showing a drop of the energy coupling efficiency, ultimately leading to the absence of cavitation bubble. The study reveals that the secondary astigmatism and spherical aberrations degrade more rapidly the beam concentration than the other aberrations studied here (namely astigmatism first and second, coma, spherical and trefoil). The cavitation energy threshold becomes equally increased. This observation relates very well to numerical simulations evaluating the laser fluence at and around the focusing plane in the presence of aberrations. These results open the door to more controlled ultrafast laser assisted surgeries and processing in transparent media.

Thermal effects mediating the flow induced by laser-induced optical breakdown

Laser-induced optical breakdown is a nonintrusive, versatile means of depositing energy in a gas, though the laser-generated flow can be complex, and its coupling with the plasma dynamics is not fully understood. By comparing nonequilibrium-plasma, equilibrium-chemistry, and frozen-gas models, our simulations show that rapid heat release by electron recombination enhances the supersonic expansion of the plasma. The resulting shock wave leaves behind a vortical flow whose strength is suppressed by the high thermal conductivity of free electrons. These results indicate that, while thermal nonequilibrium is weak, chemical nonequilibrium is needed to accurately predict post-breakdown flow.

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 3.0J/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.

Recent Research and Development Status of Relaxed Optics and Laser Technology: A Review

It is shown that for laser technologies it was necessary to create a new branch of physics: Relaxed Optics (synthesis of methods of the physical optics, quantum electronics, physical chemistry, physics of irreversible phenomena in unitary system). It is allowed to explain complex chain processes of interaction light and matter. Possible applications of Relaxed Optical methods for the modeling of the laser-induced processes phenomena, including laser implantation (surface and subsurface processes), laser-induced optical breakdown (volume processes) and laser annealing of radiation and other defects in solid, are discussed. Perspectives of using these methods for the creation of new laser technologies, including creation new types of optoelectronic devices (heterostructures, diffraction lattices, etc.), resolution the problems of metallurgy, material science, painting, architecture and a building, are analyzed.

Hypersonic Imaging and Emission Spectroscopy of Hydrogen and Cyanide Following Laser-Induced Optical Breakdown

This work communicates the connection of measured shadowgraphs from optically induced air breakdown with emission spectroscopy in selected gas mixtures. Laser-induced optical breakdown is generated using 850 and 170 mJ, 6 ns pulses at a wavelength of 1064 nm, the shadowgraphs are recorded using time-delayed 5 ns pulses at a wavelength of 532 nm and a digital camera, and emission spectra are recorded for typically a dozen of discrete time-delays from optical breakdown by employing an intensified charge-coupled device. The symmetry of the breakdown event can be viewed as close-to spherical symmetry for time-delays of several 100 ns. Spectroscopic analysis explores well-above hypersonic expansion dynamics using primarily the diatomic molecule cyanide and atomic hydrogen emission spectroscopy. Analysis of the air breakdown and selected gas breakdown events permits the use of Abel inversion for inference of the expanding species distribution. Typically, species are prevalent at higher density near the hypersonically expanding shockwave, measured by tracing cyanide and a specific carbon atomic line. Overall, recorded air breakdown shadowgraphs are indicative of laser-plasma expansion in selected gas mixtures, and optical spectroscopy delivers analytical insight into plasma expansion phenomena.

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

The current study aims to investigate the effects of micro-lens arrays (MLA) and diffractive optical elements (DOE) on skin tissue via intra-dermal laser-induced optical breakdown (LIOB) after irradiation of 1064-nm picosecond laser light at high energy settings. Irradiation with MLA and DOE was tested on dimming paper, tissue-mimicking phantom, and dark pigmented porcine skin to quantitatively compare distributions of micro-beams, micro-bubbles, and laser-induced vacuoles in the skin. DOE yielded more uniform distributions of the micro-beams on the paper and laser-induced micro-bubbles in the phantom, compared to MLA. The ex vivo skin test confirmed that the DOE-assisted irradiation accompanied more homogeneous generation of the micro-beams on the tissue surface (deviation of ≤ 3%) and a high density of small laser-induced vacuoles (∼78 µm) in the dermis than the MLA-assisted irradiation (deviation of ∼26% and ∼163 µm). The DOE-assisted picosecond laser irradiation may help to achieve deep and uniformly-generated vacuolization under the basal membrane after intra-dermal LIOB for effective fractional skin treatment.

Laser processing of dielectrics using spatiotemporally tuned ultrashort pulses

The authors report on the theoretical and experimental studies of laser-induced optical breakdown on the surface of fused silica to elucidate the influence of time delay and spatial separation between two ultrashort pulses on the position and size of the modification. Carriers involved in the damage formation including free electrons in the conduction band and self-trapped excitons (STEs) are investigated. The relationship between damage morphology and time delay shows that the seeding carriers (free electrons and STEs) generated from the first pulse are found to play a significant role for the second pulse—which is temporally and spatially separated from the first pulse—in creating the critical electron density needed for an optical breakdown. Consequently, processing outcomes, such as accuracy (position of the hole) and resolution (size of the hole), depend on the interplay of various laser-induced physics that can be tailored for specific goals. As a demonstration, laser lithography with resolution below the diffraction limit is achieved by exploiting multipulse induced physics. This work is a step toward repeatable laser processing of dielectrics beyond the diffraction limit and provides insights into ultrafast laser-matter interaction under the condition of an extremely high pulse repetition rate.

Photoaging Reversibility in Asian Patients With Melasma Treated Using Picosecond Lasers With a Diffractive Lens Array: A 1-Year Prospective Observational Cohort Study.

Picosecond lasers appear to be effective and safe in treating pigmentation and photoaging disorders through laser-induced optical breakdown. To analyze the feasibility of photorejuvenation using picosecond lasers with diffractive lens array (DLA) in patients with melasma. Ten Asian (N = 10) women with melasma and Fitzpatrick skin Type IV were enrolled and treated using 755-nm picosecond alexandrite lasers with DLA. All individuals were assessed before treatment, and at 12, 20 weeks, and 1 year by post-hoc test on melasma area and severity index (MASI) and with VISIA Complexion Analysis System using percentile rank for measurement. The median participant age was 46.5 years. The average MASI continually and significantly (p < .05) decreased until the 1-year follow-up, with the photoaging characteristics, such as wrinkles and red areas improving simultaneously (p < .05). Spots, texture, pores, ultraviolet (UV) spots, brown spots, and porphyrins exhibited alleviation, but this improvement relapsed by the 1-year follow-up. No postinflammatory hyperpigmentation or hypopigmentation occurred. In patients with melasma, picosecond laser treatment with DLA may alleviate pigmentation disorder and the related photoaging characteristics (e.g., wrinkled skin and increased vascularity), and the effects may be maintained for a long time. Nevertheless, post-treatment clinical visits every 3 to 6 months are recommended.