The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Alfred Vogel - One of the best experts on this subject based on the ideXlab platform.
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synergistic effect of picosecond Optical and nanosecond electrical pulses on dielectric Breakdown in aqueous solutions
Photonics Research, 2021Co-Authors: Zachary Coker, Alfred Vogel, Gary D Noojin, Xiaoxuan Liang, Allen Kiester, Joel N Bixler, Bennett L Ibey, Vladislav V YakovlevAbstract:The combined effect of short (picosecond) Optical and (nanosecond) electrical pulses on dielectric Breakdown is investigated both theoretically and experimentally. It was demonstrated that nanosecond electrical pulses (nsEPs), being applied simultaneously with picosecond Optical pulses, reduce the threshold for Optical Breakdown. Experimental results are discussed with respect to an extended model for opto-electrical-induced Breakdown. The newly unveiled effect is expected to play a significant role in spatially confined electroporation and further advances in laser-ablation-based processes while also allowing for measurements of ambipolar diffusion constants.
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femtosecond laser induced nanocavitation in water implications for Optical Breakdown threshold and cell surgery
Physical Review Letters, 2008Co-Authors: Alfred Vogel, Norbert Linz, Sebastian Freidank, Guenther PaltaufAbstract:We determined the bubble radius ${R}_{\mathrm{max}}$ for femtosecond Optical Breakdown in water at 347, 520, and 1040 nm with an unprecedented accuracy ($\ifmmode\pm\else\textpm\fi{}10\text{ }\text{ }\mathrm{nm}$). At threshold, ${R}_{\mathrm{max}}$ was smaller than the diffraction-limited focus radius and ranged from 190 nm to 320 nm. The increase of ${R}_{\mathrm{max}}$ with laser energy ${E}_{L}$ is slowest at 347 nm, providing optimum control of cell surgery. Experimental results agree with a model of bubble formation in heated and thermoelastically stretched liquids. Theory predicts a threshold temperature ${T}_{\mathrm{th}}\ensuremath{\approx}168\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. For $Tg300\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, a phase explosion sets in, and ${R}_{\mathrm{max}}$ increases rapidly with ${E}_{L}$.
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stress wave emission and cavitation bubble dynamics by nanosecond Optical Breakdown in a tissue phantom
Journal of Fluid Mechanics, 2006Co-Authors: Emilalexandru Brujan, Alfred VogelAbstract:Stress wave emission and cavitation bubble dynamics after Optical Breakdown in water and a tissue phantom with Nd : YAG laser pulses of 6 ns duration were investigated both experimentally and numerically to obtain a better understanding of the physical mechanisms involved in plasma-mediated laser surgery. Experimental tools were high-speed photography with 50000 frames s -1 , and acoustic measurements. The tissue phantom consisted of a transparent polyacrylamide (PAA) gel, the elastic properties of which can be controlled by modifying the water content. Breakdown in water produced a purely compressive stress wave. By contrast, in stiff PAA samples and for sufficiently large pulse energies, the compression wave was followed by an intense tensile wave, similar to the behaviour previously observed in cornea. The elastic/plastic response of the medium led to a significant decrease of the maximum size of the cavitation bubble and to a shortening of its oscillation period which was found to be related to the generation of the tensile stress wave upon Breakdown. For increasing elastic modulus of the PAA, both the amplitudes of the bubble oscillation and of the stress wave emitted during bubble collapse decreased until the bubble oscillation was so strongly damped that no collapse stress wave was emitted. Numerical simulations were performed using a spherical model of bubble dynamics which includes the compressibility and elastic/plastic behaviour of the medium, viscosity, density and surface tension. The calculations revealed that consideration of the elastic/plastic behaviour of the medium surrounding the bubble is essential to describe the experimentally observed bipolar shape of the stress wave emitted upon Optical Breakdown. Water is a poor tissue model because the shape of the emitted stress waves and the bubble dynamics differ strongly for both materials. The mechanical properties of PAA were also found to be quite different from those of tissues. Experimental and numerical results provided evidence that the dynamic mechanical properties relevant for Optical Breakdown in PAA and tissue differ by as much as two orders of magnitude from the static values. The discovery of a tensile stress wave after Optical Breakdown in tissue-like media is of great importance for the assessment of collateral damage in laser surgery because biological tissues are much more susceptible to tensile stress than to compressive stress.
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mechanisms of femtosecond laser nanosurgery of cells and tissues
Applied Physics B, 2005Co-Authors: Alfred Vogel, Joachim Noack, G Huttman, Guenther PaltaufAbstract:We review recent advances in laser cell surgery, and investigate the working mechanisms of femtosecond laser nanoprocessing in biomaterials with oscillator pulses of 80-MHz repetition rate and with amplified pulses of 1-kHz repetition rate. Plasma formation in water, the evolution of the temperature distribution, thermoelastic stress generation, and stress-induced bubble formation are numerically simulated for NA=1.3, and the outcome is compared to experimental results. Mechanisms and the spatial resolution of femtosecond laser surgery are then compared to the features of continuous-wave (cw) microbeams. We find that free electrons are produced in a fairly large irradiance range below the Optical Breakdown threshold, with a deterministic relationship between free-electron density and irradiance. This provides a large ‘tuning range’ for the creation of spatially extremely confined chemical, thermal, and mechanical effects via free-electron generation. Dissection at 80-MHz repetition rate is performed in the low-density plasma regime at pulse energies well below the Optical Breakdown threshold and only slightly higher than used for nonlinear imaging. It is mediated by free-electron-induced chemical decomposition (bond breaking) in conjunction with multiphoton-induced chemistry, and hardly related to heating or thermoelastic stresses. When the energy is raised, accumulative heating occurs and long-lasting bubbles are produced by tissue dissociation into volatile fragments, which is usually unwanted. By contrast, dissection at 1-kHz repetition rate is performed using more than 10-fold larger pulse energies and relies on thermoelastically induced formation of minute transient cavities with lifetimes <100 ns. Both modes of femtosecond laser nanoprocessing can achieve a 2–3 fold better precision than cell surgery using cw irradiation, and enable manipulation at arbitrary locations.
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role of laser induced plasma formation in pulsed cellular microsurgery and micromanipulation
Physical Review Letters, 2002Co-Authors: Vasan Venugopalan, Arnold Guerra, Kester Nahen, Alfred VogelAbstract:We investigate experimentally the physical processes underlying pulsed cellular microsurgery and micromanipulation using nanosecond 532- and 1064-nm laser pulses focused at high numerical aperture. We find that the laser parameters employed for many microirradiation techniques are congruent with those leading to Optical Breakdown in water. We determine the size and shape of the laser-induced plasma, pressure of the emitted shock wave, and size and energy of the cavitation bubble formed by the expanding plasma. We discuss implications of the results for biophysical microirradiation procedures.
Babu Varghese - One of the best experts on this subject based on the ideXlab platform.
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Efficacy of minimally invasive nonthermal laser-induced Optical Breakdown technology for skin rejuvenation
Lasers in Medical Science, 2013Co-Authors: L Habbema, Robbert Van Hal, Rieko Verhagen, Babu VargheseAbstract:We demonstrate the efficacy of a novel minimally invasive nonthermal skin rejuvenation technique for wrinkle and fine-line reduction based on laser-induced Optical Breakdown. The Optical Breakdown caused by tightly focused near-infrared laser pulses creates a grid of intradermal lesions without affecting the epidermis, leading to skin rejuvenation. The pilot in vivo efficacy test performed on five subjects successfully demonstrates wrinkle and fine-line reduction, and improvement of other skin features without pain or any other unpleasant sensations or any social downtime associated with the treatment. The efficacy is evaluated objectively and subjectively by assessing the improvement of wrinkles and/or fine lines or skin texture after the treatment. The treatment is safe without side effects or social downtime, and all test subjects reported that the treatment is "perceptible but not painful." Four out of the five subjects who participated in this pilot study were assessed to have "minor" to "significant" improvements of wrinkles and fine lines by the professional panels. The results of this clinical study are expected to bring a paradigm shift in the present laser- and light-based skin rejuvenation methods by introducing a safe treatment procedure without damaging the epidermis, with no or little social downtime and with an efficacy that might be comparable to ablative techniques.
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minimally invasive non thermal laser technology using laser induced Optical Breakdown for skin rejuvenation
Journal of Biophotonics, 2012Co-Authors: L Habbema, Rieko Verhagen, Robbert Adrianus Maria Van Hal, Yan Liu, Babu VargheseAbstract:We describe a novel, minimally invasive laser technology for skin rejuvenation by creating isolated microscopic lesions within tissue below the epidermis using laser induced Optical Breakdown. Using an in-house built prototype device, tightly focused near-infrared laser pulses are used to create Optical Breakdown in the dermis while leaving the epidermis intact, resulting in lesions due to cavitation and plasma explosion. This stimulates a healing response and consequently skin remodelling, resulting in skin rejuvenation effects. Analysis of ex-vivo and in-vivo treated human skin samples successfully demonstrated the safety and effectiveness of the microscopic lesion creation inside the dermis. Treatments led to mild side effects that can be controlled by small optimizations of the Optical skin contact and treatment depth within the skin. The histological results from a limited panel test performed on five test volunteers show evidence of microscopic lesion creation and new collagen formation at the sites of the Optical Breakdown. This potentially introduces a safe, breakthrough treatment procedure for skin rejuvenation without damaging the epidermis with no or little social down-time and with efficacy comparable to conventional fractional ablative techniques. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
L Habbema - One of the best experts on this subject based on the ideXlab platform.
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Efficacy of minimally invasive nonthermal laser-induced Optical Breakdown technology for skin rejuvenation
Lasers in Medical Science, 2013Co-Authors: L Habbema, Robbert Van Hal, Rieko Verhagen, Babu VargheseAbstract:We demonstrate the efficacy of a novel minimally invasive nonthermal skin rejuvenation technique for wrinkle and fine-line reduction based on laser-induced Optical Breakdown. The Optical Breakdown caused by tightly focused near-infrared laser pulses creates a grid of intradermal lesions without affecting the epidermis, leading to skin rejuvenation. The pilot in vivo efficacy test performed on five subjects successfully demonstrates wrinkle and fine-line reduction, and improvement of other skin features without pain or any other unpleasant sensations or any social downtime associated with the treatment. The efficacy is evaluated objectively and subjectively by assessing the improvement of wrinkles and/or fine lines or skin texture after the treatment. The treatment is safe without side effects or social downtime, and all test subjects reported that the treatment is "perceptible but not painful." Four out of the five subjects who participated in this pilot study were assessed to have "minor" to "significant" improvements of wrinkles and fine lines by the professional panels. The results of this clinical study are expected to bring a paradigm shift in the present laser- and light-based skin rejuvenation methods by introducing a safe treatment procedure without damaging the epidermis, with no or little social downtime and with an efficacy that might be comparable to ablative techniques.
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minimally invasive non thermal laser technology using laser induced Optical Breakdown for skin rejuvenation
Journal of Biophotonics, 2012Co-Authors: L Habbema, Rieko Verhagen, Robbert Adrianus Maria Van Hal, Yan Liu, Babu VargheseAbstract:We describe a novel, minimally invasive laser technology for skin rejuvenation by creating isolated microscopic lesions within tissue below the epidermis using laser induced Optical Breakdown. Using an in-house built prototype device, tightly focused near-infrared laser pulses are used to create Optical Breakdown in the dermis while leaving the epidermis intact, resulting in lesions due to cavitation and plasma explosion. This stimulates a healing response and consequently skin remodelling, resulting in skin rejuvenation effects. Analysis of ex-vivo and in-vivo treated human skin samples successfully demonstrated the safety and effectiveness of the microscopic lesion creation inside the dermis. Treatments led to mild side effects that can be controlled by small optimizations of the Optical skin contact and treatment depth within the skin. The histological results from a limited panel test performed on five test volunteers show evidence of microscopic lesion creation and new collagen formation at the sites of the Optical Breakdown. This potentially introduces a safe, breakthrough treatment procedure for skin rejuvenation without damaging the epidermis with no or little social down-time and with efficacy comparable to conventional fractional ablative techniques. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Rieko Verhagen - One of the best experts on this subject based on the ideXlab platform.
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Efficacy of minimally invasive nonthermal laser-induced Optical Breakdown technology for skin rejuvenation
Lasers in Medical Science, 2013Co-Authors: L Habbema, Robbert Van Hal, Rieko Verhagen, Babu VargheseAbstract:We demonstrate the efficacy of a novel minimally invasive nonthermal skin rejuvenation technique for wrinkle and fine-line reduction based on laser-induced Optical Breakdown. The Optical Breakdown caused by tightly focused near-infrared laser pulses creates a grid of intradermal lesions without affecting the epidermis, leading to skin rejuvenation. The pilot in vivo efficacy test performed on five subjects successfully demonstrates wrinkle and fine-line reduction, and improvement of other skin features without pain or any other unpleasant sensations or any social downtime associated with the treatment. The efficacy is evaluated objectively and subjectively by assessing the improvement of wrinkles and/or fine lines or skin texture after the treatment. The treatment is safe without side effects or social downtime, and all test subjects reported that the treatment is "perceptible but not painful." Four out of the five subjects who participated in this pilot study were assessed to have "minor" to "significant" improvements of wrinkles and fine lines by the professional panels. The results of this clinical study are expected to bring a paradigm shift in the present laser- and light-based skin rejuvenation methods by introducing a safe treatment procedure without damaging the epidermis, with no or little social downtime and with an efficacy that might be comparable to ablative techniques.
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minimally invasive non thermal laser technology using laser induced Optical Breakdown for skin rejuvenation
Journal of Biophotonics, 2012Co-Authors: L Habbema, Rieko Verhagen, Robbert Adrianus Maria Van Hal, Yan Liu, Babu VargheseAbstract:We describe a novel, minimally invasive laser technology for skin rejuvenation by creating isolated microscopic lesions within tissue below the epidermis using laser induced Optical Breakdown. Using an in-house built prototype device, tightly focused near-infrared laser pulses are used to create Optical Breakdown in the dermis while leaving the epidermis intact, resulting in lesions due to cavitation and plasma explosion. This stimulates a healing response and consequently skin remodelling, resulting in skin rejuvenation effects. Analysis of ex-vivo and in-vivo treated human skin samples successfully demonstrated the safety and effectiveness of the microscopic lesion creation inside the dermis. Treatments led to mild side effects that can be controlled by small optimizations of the Optical skin contact and treatment depth within the skin. The histological results from a limited panel test performed on five test volunteers show evidence of microscopic lesion creation and new collagen formation at the sites of the Optical Breakdown. This potentially introduces a safe, breakthrough treatment procedure for skin rejuvenation without damaging the epidermis with no or little social down-time and with efficacy comparable to conventional fractional ablative techniques. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Matthew Odonnell - One of the best experts on this subject based on the ideXlab platform.
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enhanced Optical Breakdown in kb cells labeled with folate targeted silver dendrimer composite nanodevices
Nanomedicine: Nanotechnology Biology and Medicine, 2011Co-Authors: Christine Tse, Matthew Odonnell, M J Zohdy, Wojciech G Lesniak, Lajos P BaloghAbstract:Abstract Enhanced Optical Breakdown of KB tumor cells folate-targeted with silver-dendrimer composite nanodevices (CNDs) is described. CNDs [(Ag 0 ) 25 -PAMAM_E5.(NH 2 ) 42 (NGly) 74 (NFA) 2.7 ] were fabricated by reactive encapsulation, using a biocompatible template of dendrimer–folic acid (FA) conjugates. Preferential uptake of the folate-targeted CNDs (of various treatment concentrations and surface functionality) by KB cells was visualized with confocal microscopy and transmission electron microscopy. Intracellular laser-induced Optical Breakdown threshold and dynamics were detected and characterized by high-frequency ultrasonic monitoring of resulting transient bubble events. When irradiated with a near-infrared, femtosecond laser, the CND-targeted KB cells acted as well-confined activators of laser energy, enhancing nonlinear energy absorption, exhibiting a significant reduction in Breakdown threshold and thus selectively promoting intracellular laser-induced Optical Breakdown. From the Clinical Editor This study presents a novel method to selectively destroy cancer cells by combining biochemical targeting with topical laser irradiation. A human epidermoid cancer cell line was targeted with folated silver-dendrimer composite nanodevices and the labeled cancer cells were subsequently destroyed by the microbubbles generated due the enhanced energy uptake of the silver nanoparticles from the laser irradiation, as compared to unlabeled cells.
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acoustic estimation of thermal distribution in the vicinity of femtosecond laser induced Optical Breakdown
IEEE Transactions on Biomedical Engineering, 2006Co-Authors: M J Zohdy, Christine Tse, Matthew OdonnellAbstract:Laser-induced Optical Breakdown (LIOB), or photodisruption, can generate individual microbubbles in tissues for biomedical applications. We have previously developed a co-localized high-frequency ultrasound system to detect and characterize these laser-induced microbubbles. Because ultrasound speed varies with temperature, this system can also be used to directly estimate thermal effects in the vicinity of photodisruption. In this study, individual bubbles (sizes 60-100 mum) were created at the bottom of a water tank using a 793-nm, 100-fs Ti:Sapphire laser pulsed at 250 kHz. During and after Breakdown, pulse-echoes from the tank bottom in the region surrounding a bubble were recorded with a single-element 85-MHz ultrasonic transducer, and temperature-dependent pulse-echo displacements were calculated using phase-sensitive correlation tracking. These displacements were then fit to a finite-element heat transfer model to estimate the effective thermal distribution. Estimates were calculated for laser exposure times ranging from 6.25 to 312.5 ms (1600 to 78 000 laser pulses), at 1.5 and 4 J/cm2 fluences. Results suggest a minimal temperature increase (<1deg C) within 100 mum of a bubble created with <1600 laser pulses at 1.5 J/cm2 fluence. This implies that LIOB can be controlled to be thermally noninvasive in the bubble vicinity
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acoustic characterization of microbubble dynamics in laser induced Optical Breakdown
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, 2003Co-Authors: S M Milas, Stanislav Emelianov, Theodore B Norris, Kyle W Hollman, Matthew OdonnellAbstract:A real-time acoustic technique to characterize microbubbles produced by laser-induced Optical Breakdown (LIOB) in water was developed. Femtosecond laser pulses are focused just inside the surface of a small liquid tank. A tightly focused, high frequency, single-element ultrasonic transducer is positioned so its focus coincides axially and laterally with this laser focus. When Optical Breakdown occurs, a bubble forms and a pressure wave is emitted (i.e., acoustic emission). In addition to this acoustic signal, the microbubble is actively probed with pulse-echo measurements from the same transducer. After the bubble forms, received pulse-echo signals have an extra pulse, describing the bubble location and providing a measure of axial bubble size. Wavefield plots of successive recordings illustrate the generation, growth, and collapse of cavitation bubbles due to Optical Breakdown. These same plots also can be used to quantify LIOB thresholds.
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acoustic detection of microbubble formation induced by enhanced Optical Breakdown of silver dendrimer nanocomposites
Applied Physics Letters, 2003Co-Authors: S M Milas, Stanislav Emelianov, Theodore B Norris, Kyle W Hollman, Lajos P Balogh, James R Baker, Matthew OdonnellAbstract:We utilize a real-time acoustic technique, based on pulse-echo measurements to detect formation of microbubbles in an aqueous solution of a silver/dendrimer nanocomposite (DNC). Wave-field plots of successive recordings illustrate the generation and behavior of bubbles created by the Optical Breakdown process. A significant threshold reduction is achieved with DNC particles compared to its host dendrimer, enabling a diverse field of low-threshold Breakdown applications.
