Ablation Speed Research Articles

How do we assess the efficacy of Ho:YAG low-power laser lithotripsy for the treatment of upper tract urinary stones? Introducing the Joules/mm3 and laser activity concepts.

To estimate the total energy needed to ablate 1mm3 of stone volume (Joules/mm3) during flexible ureteroscopic lithotripsy using a low-power Ho:YAG laser device, as a proxy of lithotripsy efficacy. We selected 30 patients submitted to flexible ureteroscopy for renal stones whose volume was bigger than 500mm3. A 35W Ho:YAG laser (Dornier Medilas H Solvo 35, Germany) was used for every procedure with a 272µm laser fiber. We recorded laser parameters, the total energy delivered by the laser fiber, the time from the first laser pulse until the last one (lithotripsy time), and the active laser time as provided by the machine. We then estimated J/mm3 values and determinants, along with ablation speed (mm3/s), and laser activity (ratio between laser active time and lithotripsy time). Median (IQR) stone volume and stone density were respectively 1599 (630-3502) mm3 and 1040 (753-1275) Hounsfield units (HU). In terms of laser parameters, median (IQR) energy and frequency were 0.6 (0.4-0.8) J and 15 (15-18) Hz. Median (IQR) total delivered energy and lithotripsy time were 37,050 (13,375-57,680) J and 68 (36-88) min, respectively. Median (IQR) J/mm3 and ablation speed were, respectively, 19 (14-24) J/mm3 and 0.7 (0.4-0.9)mm3/s. The laser was active during 84% (70-95%) of the total lithotripsy time. HU density > 1000 was associated with reduced efficacy. It is possible to perform laser lithotripsy using a low-power laser device with a virtually continuous laser activity. The estimation of the pre-operative parameters as well as the J/mm3 values are fundamental for a proper pre-operatory planning.

THE INFLUENCE OF PERMEABILITY ON THE ABLATION PROCESS FOR AN ABLATIVE MATERIAL

The heat and mass transfer in the ablation process is of great importance for the ablation protection engineering. Accurate temperature assessment can provide effective support for the design of thermal protection structure and ablative material of reentry hypersonic vehicle. In this work, we studied the effect of permeability on heat and mass transfer and ablation thermal protection of gases produced during ablation. Since the carbide formed by ablation of material is a typical porous medium, its structure has self-similarity and can be described by fractal theory. Taking into account the angle of global coordinates and the local coordinates, this paper derived the permeability in any direction as a function of three different fractal dimensions in [Formula: see text], [Formula: see text] and [Formula: see text] directions. In order to verify the correctness of this method, the new model is introduced into the ablation process. Aiming at the ablation process and the diffusion equation of pyrolysis gas in the carbide layer, the temperature, material density and pyrolysis gas density distribution of three-dimensional spherical head under different permeability were simulated numerically. It is found that the permeability of carbides formed by ablative reaction of ablative materials related to fractal structure has an effect on ablation process. From our preliminary results, the higher the permeability, the faster the ablation speed, and the more obvious the overall temperature rise is.

384 - Comparing short, long, and Moses regimes of Ho:YAG laser vs Super Pulse™ fiber laser in vitro: Ablation speed and retropulsion effect

INTRODUCTION AND OBJECTIVES:Ho:YAG laser is the “gold standard” in the treatment of lower and upper urinary tract stones. Ho:YAG laser with Moses Technology is new technology to reduce retropulsion...

MP24-10 WAVELENGTH AND PULSE SHAPE EFFECTS ON STONE FRAGMENTATION OF LASER LITHOTRIPTERS

You have accessJournal of UrologyStone Disease: Basic Research & Pathophysiology II1 Apr 2018MP24-10 WAVELENGTH AND PULSE SHAPE EFFECTS ON STONE FRAGMENTATION OF LASER LITHOTRIPTERS Andreas Gross, Benedikt Becker, Mark Taratkin, Dmitry Enikeev, Leonid Rapoport, and Christopher Netsch Andreas GrossAndreas Gross More articles by this author , Benedikt BeckerBenedikt Becker More articles by this author , Mark TaratkinMark Taratkin More articles by this author , Dmitry EnikeevDmitry Enikeev More articles by this author , Leonid RapoportLeonid Rapoport More articles by this author , and Christopher NetschChristopher Netsch More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2018.02.763AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Pulsed Holmium:YAG lasers are the energy source of choice in the endoscopic management of urolithiasis. Until recently, pulse frequency and pulse energy were the most investigated parameters to improve efficiency of such lasers. Newer research focusses on the influence of pulse width and pulse shape. Aim of our study was to compare the efficiency of stone dusting of pulsed 2.1µm Holmium:YAG lasers and a pulsed 1.94µm Thulium-fiber laser (TFL) using identical pulse energy, pulse frequency, and average power settings. METHODS The lasers systems tested were the Lumenis Versa Pulse Power Suite P 100 (Ho short pulse), the Lumenis Pulse 120H (Ho long pulse) and a commercially not available prototype of a pulsed TFL (Fig.1, A) to C)). The lasers were tested at 0.2 J and 40 Hz (average power of 8-W). Pulse energies and pulse shapes were measured. Subsequently, efficiency of stone ablation (ablation speed) was compared in vitro on human COM, COM-phosphate, and Uric Acid stones for the three lasers. The in vitro experimental setup included a specially designed cuvette with several levels of metallic meshes allowing for precise quantification of size distribution of stone fragments. RESULTS The pulsewidths (range in ms) of all three lasers are shown in Fig. 1 below. The following values of the peak power were derived from the pulse shape and pulse energy measurements: P100: 1650-W, P120: 1040-W, TFL: 660-W. The measured values of stone ablation speed (in dusting mode, i.e. fragments < 1mm) are summarized in Fig.2. CONCLUSIONS The new pulsed TFL shows a clearly defined pulsewidth with a large area under the curve. This in combination with the wavelength superior in terms of water absorption leads to better efficiency of stone fragmentation in dusting mode. © 2018FiguresReferencesRelatedDetails Volume 199Issue 4SApril 2018Page: e293-e294 Advertisement Copyright & Permissions© 2018MetricsAuthor Information Andreas Gross More articles by this author Benedikt Becker More articles by this author Mark Taratkin More articles by this author Dmitry Enikeev More articles by this author Leonid Rapoport More articles by this author Christopher Netsch More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Efficient and controllable thermal ablation induced by short-pulsed HIFU sequence assisted with perfluorohexane nanodroplets

A HIFU sequence with extremely short pulse duration and high pulse repetition frequency can achieve thermal ablation at a low acoustic power using inertial cavitation. Because of its cavitation-dependent property, the therapeutic outcome is unreliable when the treatment zone lacks cavitation nuclei. To overcome this intrinsic limitation, we introduced perfluorocarbon nanodroplets as extra cavitation nuclei into short-pulsed HIFU-mediated thermal ablation. Two types of nanodroplets were used with perfluorohexane (PFH) as the core material coated with bovine serum albumin (BSA) or an anionic fluorosurfactant (FS) to demonstrate the feasibility of this study. The thermal ablation process was recorded by high-speed photography. The inertial cavitation activity during the ablation was revealed by sonoluminescence (SL). The high-speed photography results show that the thermal ablation volume increased by ∼643% and 596% with BSA-PFH and FS-PFH, respectively, than the short-pulsed HIFU alone at an acoustic power of 19.5 W. Using nanodroplets, much larger ablation volumes were created even at a much lower acoustic power. Meanwhile, the treatment time for ablating a desired volume significantly reduced in the presence of nanodroplets. Moreover, by adjusting the treatment time, lesion migration towards the HIFU transducer could also be avoided. The SL results show that the thermal lesion shape was significantly dependent on the inertial cavitation in this short-pulsed HIFU-mediated thermal ablation. The inertial cavitation activity became more predictable by using nanodroplets. Therefore, the introduction of PFH nanodroplets as extra cavitation nuclei made the short-pulsed HIFU thermal ablation more efficient by increasing the ablation volume and speed, and more controllable by reducing the acoustic power and preventing lesion migration.

High-power Yb-based all-fiber laser delivering 300 fs pulses for high-speed ablation-cooled material removal

We report on a 72W Yb all-fiber ultrafast laser system with 1.6GHz intra-burst and 200kHz burst repetition rate developed to demonstrate ablation-cooled material removal at high speeds. Up to 24W is applied on Cu and Si samples with pulses of ∼300 fs, and record-high ablation efficiencies are obtained, compared to published results to date, despite using only ∼100 nJ pulses. Ablation speeds approaching 1 mm3/s are reported with 24W of average power, limited by available laser power and beam scanning speed. More significantly, these results experimentally confirm the theoretically expected linear scaling of the ablation-cooled regime to higher average powers without sacrificing efficiency, which implies that further scaling is possible with further increases in laser power and scanning speeds.

Impact of γ-Irradiation on the Kinetics of Laser Ablation of Polyamide Under Continuous CO2 Laser Beam

The effect of preliminary γ-irradiation on accelerating the speed of laser ablation of a polyamide is measured for the first time. A linear increase of intensity with a rate of 0.15 mg/s is observed during laser ablation of the polyamide pre-irradiated with γ-rays at a dose of 3,500 kGy. A γ-radiolysis dose of 10 – 20 kGy causes extreme changes in the molecular-topological parameters and the maximum level of growth of the rate of laser ablation. Thus pre-irradiation with γ-rays may be used to optimize the laser ablation of the polymer.

Numerical Response Surfaces of Volume of Ablation and Retropulsion Amplitude by Settings of Ho:YAG Laser Lithotripter.

Objectives Although laser lithotripsy is now the preferred treatment option for urolithiasis due to shorter operation time and a better stone-free rate, the optimal laser settings for URS (ureteroscopic lithotripsy) for less operation time remain unclear. The aim of this study was to look for quantitative responses of calculus ablation and retropulsion by performing operator-independent experiments to determine the best fit versus the pulse energy, pulse width, and the number of pulses. Methods A lab-built Ho:YAG laser was used as the laser pulse source, with a pulse energy from 0.2 J up to 3.0 J and a pulse width of 150 μs up to 1000 μs. The retropulsion was monitored using a high-speed camera, and the laser-induced craters were evaluated with a 3-D digital microscope. The best fit to the experimental data is done by a design of experiment software. Results The numerical formulas for the response surfaces of ablation speed and retropulsion amplitude are generated. Conclusions The longer the pulse, the less the ablation or retropulsion, while the longer pulse makes the ablation decrease faster than the retropulsion. The best quadratic fit of the response surface for the volume of ablation varied nonlinearly with pulse duration and pulse number.

SURFACE ROUGHNESS STUDY ON MICROCHANNELS OF CO2 LASER FABRICATING PMMA-BASED MICROFLUIDIC CHIP

A novel method named soak sacrificial layer ultrasonic method (SSLUM) has been presented for optimizing the surface roughness of the microchannels of polymethyl methacrylate (PMMA)-based microfluidic chips. CO2 laser was used for ablative microchannels on the PMMA sheet, and the effects of key parameters including laser power, laser ablation speed and solution concentration on the surface roughness of microchannels were estimated and optimized by SSLUM. The experimental observation demonstrates that the surface roughness results mainly from the residues on the channel wall, which are produced by the bubbles movement and bursting. The research results show that the surface roughness can be improved effectively by using SSLUM. In our experiment, the best value was Ra [Formula: see text] 110[Formula: see text]nm with laser power 12[Formula: see text]W, laser ablation speed 10[Formula: see text]mm/s, the solution concentration 75%, and the time of ultrasonic vibration 25[Formula: see text]min. SSLUM is proven to be an effective, simple and rapid method for optimizing the surface roughness of microchannels of microfluidic chips.

Online monitoring of nanoparticles formed during nanosecond laser ablation

The particle size distribution of dry aerosol originating from laser ablation of glass material was monitored simultaneously with Laser Ablation – Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) analysis and two aerosol spectrometers – Fast Mobility Particle Sizer (FMPS) and Aerodynamic Particle Sizer (APS). The unique combination of LA-ICP-MS and FMPS offers the possibility of measuring the particle size distribution every 1s of the ablation process in the size range of 5.6–560nm. APS extends the information about particle concentration in the size range 0.54–17μm. Online monitoring of the dry aerosol was performed for two ablation modes (spot and line with a duration of 80s) with a 193nm excimer laser system, using the glass reference material NIST 610 as a sample. Different sizes of laser spot for spot ablation and different scan speeds for line ablation were tested. It was found that the FMPS device is capable of detecting changes in particle size distribution at the first pulses of spot laser ablation and is suitable for laser ablation control simultaneously with LA-ICP-MS analysis. The studied parameters of laser ablation have an influence on the resulting particle size distribution. The line mode of laser ablation produces larger particles during the whole ablation process, while spot ablation produces larger particles only at the beginning, during the ablation of the intact layer of the ablated material. Moreover, spot ablation produces more primary nano-particles (in ultrafine mode size range <100nm) than line ablation. This effect is most probably caused by a reduced amount of large particles released from the spot ablation crater. The larger particles scavenge the ultrafine particles during the line ablation mode.

Magneto-absorption effects in magnetic-field assisted laser ablation of silicon by UV nanosecond pulses

A constant magnetic field can significantly improve the quality and speed of ablation by nanosecond laser pulses. These improvements are usually attributed to the confinement of laser-produced plasma by the magnetic field and specific propagation effects in the magnetized plasma. Here we report a strong influence of constant axial magnetic field on the ablation of silicon by 20-ns laser pulses at wavelength 355 nm, which results in an increase of ablation depth by a factor of 1.3 to 69 depending on laser parameters and magnitude of the magnetic field. The traditional plasma effects do not explain this result, and magneto-absorption of silicon is proposed as one of the major mechanisms of the significant enhancement of ablation.

Fast femtosecond laser ablation for efficient cutting of sintered alumina substrates

Fast, accurate cutting of technical ceramics is a significant technological challenge because of these materials' typical high mechanical strength and thermal resistance. Femtosecond pulsed lasers offer significant promise for meeting this challenge. Femtosecond pulses can machine nearly any material with small kerf and little to no collateral damage to the surrounding material. The main drawback to femtosecond laser machining of ceramics is slow processing speed. In this work we report on the improvement of femtosecond laser cutting of sintered alumina substrates through optimisation of laser processing parameters. The femtosecond laser ablation thresholds for sintered alumina were measured using the diagonal scan method. Incubation effects were found to fit a defect accumulation model, with Fth,1=6.0J/cm2 (±0.3) and Fth,∞=2.5J/cm2 (±0.2). The focal length and depth, laser power, number of passes, and material translation speed were optimised for ablation speed and high quality. Optimal conditions of 500mW power, 100mm focal length, 2000µm/s material translation speed, with 14 passes, produced complete cutting of the alumina substrate at an overall processing speed of 143µm/s – more than 4 times faster than the maximum reported overall processing speed previously achieved by Wang et al. [1]. This process significantly increases processing speeds of alumina substrates, thereby reducing costs, making femtosecond laser machining a more viable option for industrial users.

Three dimensional polymer waveguide using hybrid lithography.

A three dimensional polymer waveguide with taper structure was demonstrated and fabricated by a reliable and effective hybrid lithography. The hybrid lithography consists of lithography to fabricate a polymer waveguide and gray scale lithography to fabricate a polymer taper structure. Laser ablation and shadow aluminum evaporation were designed for gray scale lithography. The length of the gray scale region ranging from 20 to 400 μm could be controlled by the laser power, the ablation speed, and the aluminum thickness. The slope angle was determined by the length of the gray scale region and the thickness of the photoresist. The waveguide taper structure could be transferred to the lower layer by the etching method. The taper structure can be used for integration of the waveguide with different dimensions.

Feasibility of intercostal high intensity focused ultrasound ablation of clinically relevant volumes under the application of beam shaping

Obstruction by the thoracic cage of the high intensity focused ultrasound (HIFU) beam is one of the major challenges in the ablation of abdominal lesions. Several beam shaping methods have been proposed to reduce exposure of the ribs to acoustic energy and to recover focal point intensity. The feasibility of HIFU ablation of a clinically relevant volume applying beam shaping remains however unaddressed. In this study, feasibility was evaluated based on exposure of both the ribs as well as the near-field to acoustic energy. In addition, the volumetric ablation rate was estimated to evaluate whether clinically relevant ablation speeds can be achieved.

Numerical calculation of temperature and surface topology during a laser ablation process for ceramic coatings

In this paper a numerical procedure is presented to calculate a laser ablation process for ceramic thick film coatings. The code is required to cover temperature dependent material data, projected beam intensities and inhomogeneous coating–substrate combinations to calculate the hole shape geometry, the temperature distribution under the surface and the ablation rate per pulse. Therefore, the ablation speed was calculated by an Arrhenius equation while the temperature distribution was simulated by means of the heat conduction equation, which is solvable by a finite differences scheme. Hence, an adaptive mesh is used and the expansion of the code to three spatial dimensions enables the simulation of more complex ablation geometries. The simulation time was held low by introducing actualization frequencies, where critical and time consuming steps were only run if necessary. A validation of the numerical simulation was done by comparing the calculated temperature depth distribution and hole geometry with micrographs of experimental ablations.

High-speed photorefractive keratectomy with femtosecond ultraviolet pulses.

Femtosecond near-infrared lasers are widely used for a number of ophthalmic procedures, with flap cutting in the laser-assisted in situ keratomileusis (LASIK) surgery being the most frequent one. At the same time, lasers of this type, equipped with harmonic generators, have been shown to deliver enough ultraviolet (UV) power for the second stage of the LASIK procedure, the stromal ablation. However, the speed of the ablation reported so far was well below the currently accepted standards. Our purpose was to perform high-speed photorefractive keratectomy (PRK) with femtosecond UV pulses in rabbits and to evaluate its predictability, reproducibility and healing response. The laser source delivered femtosecond 206 nm pulses with a repetition rate of 50 kHz and an average power of 400 mW. Transepithelial PRK was performed using two different ablation protocols, to a total depth of 110 and 150 μm. The surface temperature was monitored during ablation; haze dynamics and histological samples were evaluated to assess outcomes of the PRK procedure. For comparison, analogous excimer ablation was performed. Increase of the ablation speed up to 1.6 s/diopter for a 6 mm optical zone using femtosecond UV pulses did not significantly impact the healing process.

Role of hydrodynamic instability growth in hot-spot mass gain and fusion performance of inertial confinement fusion implosions

In an inertial confinement fusion target, energy loss due to thermal conduction from the hot-spot will inevitably ablate fuel ice into the hot-spot, resulting in a more massive but cooler hot-spot, which negatively impacts fusion yield. Hydrodynamic mix due to Rayleigh-Taylor instability at the gas-ice interface can aggravate the problem via an increased gas-ice interfacial area across which energy transfer from the hot-spot and ice can be enhanced. Here, this mix-enhanced transport effect on hot-spot fusion-performance degradation is quantified using contrasting 1D and 2D hydrodynamic simulations, and its dependence on effective acceleration, Atwood number, and ablation speed is identified.

Etch Rate Characterization of PMMA Via CO2 Laser for Hybrid Micromolding Process

This paper presents fabrication of PMMA micromolds for hybrid soft lithography using laser CO2 ablation system. The system has a CO2 laser system with a maximum rated power of 60 watts that produces an invisible infrared beam at a wavelength of 10.6 μm. The laser system works with vector and raster modes to produce lines and filled shapes, respectively. In this work, the system was set to vector mode for single pass ablation. The control factors that determine the channel depth and width are laser power and speed of ablation, which are set as a percentage via the control software. A CO2 laser emits infrared radiation at a wavelength of 10.6 μm. PMMA has a high absorptance of about 0.92 in the infrared (Absorptance is different from absorbance and is defined as: The ratio of the radiant flux absorbed by a body to that incident upon it.). PMMA also combines a low heat capacity with a low heat conductance, which means that any absorbed heat will result in a rapidly rising temperature. This means that the CO2-laser beam ablates the PMMA photothermally. Unlike UV lasers, a CO2 laser emits radiation continuously. Wherever the focused laser beam meets the PMMA surface, the temperature of the irradiated spot rises rapidly, that the PMMA first melts and then decompose, leaving an V-shape groove. The channels have a V groove due to the temperature distribution within the PMMA substrate [1] The relationship between laser power and the channel depth will be discussed. Initial study indicates that the channel depth increases linearly with the power and decreases exponentially with the beam speed. We observed that the effect of beam speed and power on the channel/groove width is not significant. However, it varies almost linearly with both beam speed and power. Hence, by varying beam speed and power we can achieve different depths and aspect ratios.This novel low cost, large scale, micromold manufacturing technique can be extended to 12 “ x 24” PMMA Sheets [2]. This allows us to batch fabricate very large numbers of micromolded devices at the same time, or very large continuous structures such as long lines for electronic routing on large substrates. Not only does this potentially reduce manufacturing cost through larger batch fabrication, it enables the construction of new very large area devices fabricated by hybrid micromolding process defined by Khosla et al (Hybrid fabrication process for combining micromolded nanocomposite with undoped PDMS polymer) [3, 4], such as electrode arrays, electrical wires, and micromagnets etc.

A 5-mm piezo-scanning fiber device for high speed ultrafast laser microsurgery.

Towards developing precise microsurgery tools for the clinic, we previously developed image-guided miniaturized devices using low repetition rate amplified ultrafast lasers for surgery. To improve the speed of tissue removal while reducing device diameter, here we present a new 5-mm diameter device that delivers high-repetition rate laser pulses for high speed ultrafast laser microsurgery. The device consists of an air-core photonic bandgap fiber (PBF) for the delivery of high energy pulses, a piezoelectric tube actuator for fiber scanning, and two aspheric lenses for focusing the light. Its inline optical architecture provides easy alignment and substantial size reduction to 5 mm diameter as compared to our previous MEMS-scanning devices while realizing improved intensity squared (two-photon) lateral and axial resolutions of 1.16 μm and 11.46 μm, respectively. Our study also sheds light on the maximum pulse energies that can be delivered through the air-core PBF and identifies cladding damage at the input facet of the fiber as the limiting factor. We have achieved a maximum energy delivery larger than 700 nJ at 92% coupling efficiency. An in depth analysis reveals how this value is greatly affected by possible slight misalignments of the beam during coupling and the measured small beam pointing fluctuations. In the absence of these imperfections, self-phase modulation becomes the limiting factor for the maximum energy delivery, setting the theoretical upper bound to near 2 μJ for a 1-m long, 7-μm, air-core PBF. Finally, the use of a 300 kHz repetition rate fiber laser enabled rapid ablation of 150 µm x 150 µm area within only 50 ms. Such ablation speeds can now allow the surgeons to translate the surgery device as fast as ~4 mm/s to continuously remove a thin layer of a 150 µm wide tissue. Thanks to a high optical transmission efficiency of the in-line optical architecture of the device and improved resolution, we could successfully perform ablation of scarred cheek pouch tissue, drilling through a thin slice. With further development, this device can serve as a precise and high speed ultrafast laser scalpel in the clinic.

Features of climate change and their effects on glacier snow melting in Xinjiang, China

The features of climate change and their effects on glacier snow melting in the past 50years (1961–2010) in Xinjiang were studied. Regional climate data for 49 meteorological stations in the Tianshan Mountains and the northern and southern areas of Xinjiang were collected with the aid of techniques such as climatological statistical diagnosis, regional climate models, remote sensing, and geographic information system. The annual average temperature displayed a rising trend across the Tianshan mountainous area and both areas of Xinjiang. The trend was particularly apparent in winter and autumn with the rate of increase in the annual average minimum temperature being significantly higher than that of the maximum temperature. Rainfall also tended to increase in all three areas over the 50-year period, with the magnitude of change being highest in the mountainous area followed by northern Xinjiang and then southern Xinjiang. As a result of the rising temperatures, there was a negative material balance among the region's glaciers, of which the year 1982/1983 was the key year for the development of Tianshan mountain glacier snow. After this date, glacial ablation intensified with an annual change increase in average temperature of 1°C, leading to a glacier material balance change of about 300mm. To establish rainfall and temperature sequences for three regional climate change scenarios in the 2011–2050 period, we adopted the delta method using actual measurements during the 1961–2000 period against corrected data from rainfall and temperature simulations. All three scenarios indicated that temperatures will continue to increase, that the increase in rainfall may decrease in mountainous regions but will increase in the basin, and that the speed of glacial ablation in Xinjiang will continue to accelerate.