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Purpose: To assess the ablation efficiency of the Superpulsed Thulium Fiber Laser (SP-TFL) and investigate the thermal effects of SP-TFL. Methods: A SP-TFLwas employed to evaluate ablation efficiency. Fresh ex-vivo pig kidneys and ureters were utilized to evaluate the renal pelvis and ureter temperature changes, different irrigation rates(0, 15, 38mL/min) and a long pulse width were used. Results: The research indicated that as laser output power increased, ablation rates significantly increased. Ablation rates(mg/min) were higher and the energy per ablated mass(J/mg) was lower at lower frequencies(10–50 Hz). Under the same frequency and single pulse energy, super short and short pulse widths demonstrated higher ablation rates at higher frequencies (exceeding 100 Hz). The temperature of the renal pelvis and ureter decreased with increasing irrigation rates. In the renal pelvis, without irrigation, the temperature quickly reached the critical threshold of 43℃. The irrigation rate was 15 ml/min and power was no more than 18 W, the renal pelvis temperature did not reach 43℃. When the irrigation rate were 38 ml/min, the temperature did not risen to 43℃. In the ureter, without irrigation, the temperature also quickly reached 43℃. The temperature reached 43℃ when the power exceeded to12W with an irrigation rate of 15 ml/min. With an irrigation rate of 38 ml/min, the temperature reached 43℃ at a laser power of 30 W. Conclusions: The SP-TFL demonstrated promising ablation effectiveness especially for lower frequencies and super short and short pulse widths model. Proper irrigation rates, single pulse energy, frequency and pulse width are crucial during lithotripsy. [ABSTRACT FROM AUTHOR]

The results of ablation experiments are given for the case for a scanning beam of nanosecond range pulsed laser radiation using targets made of high-carbon U13 and low-carbon St30 steel grades. The dependence of the depth and power efficiency of ablation on the power density is determined in the range q = 4 × 108–1010 W/cm2. It is established that the maximum efficiency of removing the material is obtained when q = 4 × 109 W/cm2 for a target made of U13 steel and q = 7 × 108–5 × 109W/cm2 for St30 steel. The size distribution is estimated for emitted microparticles. It is established that irradiation of high-carbon steel results in generating a flow of particles deposited on the target surface (back flow). The mechanism of this back flow is associated with formation of nanosized condensate particles. On the basis of the reflectivity measurements and on the studies of the microstructure of the irradiated surface using electron microscopy methods, a hypothesis is put forward that the higher ablation efficiency of high-carbon steel U13 compared to low-carbon steel St30 depends on the process of condensation of supersaturated carbon vapor on the target surface. This process can increase the absorption capacity of the irradiated target surface. As a result, the efficiency of material removal during the subsequent scanning pass is increased. [ABSTRACT FROM AUTHOR]

In order to improve the ablation efficiency of nanosecond pulsed laser (NPL) in the processing of metallic materials, a physical and mathematical model of the NPL induced ablation characteristics in aluminum alloy was established under the auxiliary heating (AH) irradiated by the millisecond pulsed laser (MPL) based on the basic theories of heat transfer and fluid dynamics, and the ablation characteristics were calculated and analyzed, the temperature fields, the vapor recoil pressure and melt pool sizes were obtained under different auxiliary heat temperature (AHT). The results showed that the AH pretreatment will improve the absorptivity of the target because the absorptivity is a function of the temperature, the temperature and the vapor recoil pressure induced by the NPL are higher than that at room temperature(300 K), so the temperature exceeds easily gasification point, and the vapor recoil pressure exceeds easily too the reverse suppression pressure even if irradiated by a low energy NPL, which can cause shock wave or even phase explosion, much more metal vapor and molten material splash into air from the ablation zone, and the depth and the area of the ablation pool are all increased significantly. Therefore, the AH can improve the ablation efficiency of the NPL by improving the energy utilization of the NPL. This work can provide some theoretical basis and technical support for the development of the laser processing metal field. [ABSTRACT FROM AUTHOR]

The high processing efficiency and quality are constant pursuits for modern manufacturing industry. This paper investigated the ablation efficiency and quality of ultrashort pulsed laser ablation of DD6 single crystal alloy based on experiments and theoretical analysis. The experimental results showed that the ablation rate increases with the increase of laser fluence and with the decrease of scanning speed and scanning width, while the ablation efficiency decreases with the increase of laser fluence. A relatively flat and low melted zone ablation surface could be obtained by employing a low laser fluence and high scanning speed. The influence of laser parameters on the ablation diameter, equivalent energy density, and heat accumulation effect was analyzed based on the theory of laser ablation and heat conduction. The theoretical analysis revealed the material removal transforms from plasma or vaporization removal to melt ejection with the pulse energy increases and the scanning speed decreases, which can explain the formation mechanism of surface morphology very well. In addition, the scanning strategy of high efficiency and quality was proposed based on the theoretical analysis and experimental results. [ABSTRACT FROM AUTHOR]

To predict the laser ablation profile on dental hard tissue which will enable the user to optimize laser parameters so as to carry out the laser treatment with minimal tissue damage. The present study constructs a mathematical model to predict the ablation profile based on Gaussian beam distribution of laser intensity and correlates the model with experimentally obtained ablation parameters (effective Gaussian beam radius, ablation threshold fluence, and effective energy penetration depth). To obtain the ablation parameters, laser ablation experiments were carried out on dental hard tissues using Ti:Sapphire femtosecond laser (800 nm, 100 fs, 10 kHz). The method is further extended to predict the ablation rate and efficiency as well. The profile predicted from the mathematical model is compared with that of experimental results. It is found that the predicted ablation profile agrees well with the experimental profile for both enamel and dentin except a slight deviation at higher fluence for dentin. The calculated ablation rate is comparable to that of experimental results whereas for ablation efficiency appreciable deviation is observed in the case of dentin. The model succinctly predicts the ablation profile, ablation rate, and ablation efficiency which will enable to perform dental surgery at optimized laser processing conditions with high precision thus reducing the tissue damage appreciably. Once the details of lesion are known through proper diagnostic tools, the method enables the user to readily obtain optimum laser parameters. It can be used as a handy reference for dentists to perform damage-free surgery, ensuring quicker healing. [ABSTRACT FROM AUTHOR]

Femtosecond laser is an effective and safe tool in many surgeries, but the studies of its effect on oral soft tissue ablation are insufficient. This study aimed to investigate the effect of soft tissue ablation with a 1030-nm femtosecond laser on temperature and depth. Twenty Sprague-Dawley rat tongue specimens were obtained and flat-mounted. The 1030-nm femtosecond laser was controlled by a computer system, with a set distance of 4.7 mm between the laser aperture and soft tissue surfaces. Ten specimens were ablated for > 1 min with or without air-cooling for temperature measurement, while the other 10 specimens were ablated for depth measurements, using the following parameters: (i) 3 W, 2000 mm/s; (ii) 3 W, 4000 mm/s; (iii) 5 W, 2000 mm/s; (iv) 5 W, 4000 mm/s; (v) 8 W, 2000 mm/s; (vi) 8 W, 4000 mm/s. Temperature changes were measured using a type-K thermocouple. The depth attained using different power and scanning speed settings was measured by a three-dimensional morphology measurement laser microscope. Laser power, scanning speed, and air-cooling effects were determined. Higher energy and lower speed induced higher temperatures (p < 0.05), which were significantly decreased by air-cooling (p < 0.05). The lowest ablation depth was obtained at 3 W and 4000 mm/s (72.63 ± 6.47 μm) (p < 0.05). The greatest incision depth was achieved at 8 W and 2000 mm/s (696.19 ± 35.37 μm), or 4000 mm/s (681.16 ± 55.65 μm) (p < 0.05). The 1030-nm femtosecond laser application demonstrates clinically acceptable ablation efficiency, without marked temperature damage, in a controlled manner. [ABSTRACT FROM AUTHOR]

The nail plate forms a barrier that limits the effectiveness of drug delivery in the treatment of nail diseases and prevents the outflow of fluid in the case of subungual hematoma formation. Microperforation of the nail plate through laser radiation can increase the effectiveness of drug delivery and ensure the possibility of blood outflow. This study detected and identified the type and threshold of effects that arise from exposing the nail plate to Yb,Er: Glass ( λ = 1.54 μm) and Er:YLF ( λ = 2.81 μm) laser radiation. The rate and efficiency of nail plate ablation by the radiation of these lasers were studied. The effect of the storage time of a freshly extracted nail plate in open air on its ablation rate by Er:YLF ( λ = 2.81 μm) laser radiation was also investigated. The impact of the Yb,Er:Glass and Er:YLF laser pulses on the nail plate caused bleaching, carbonization, ablation with microcrater formation, and microperforation. The laser energy densities W (thresholds) required for these effects were determined. The maximum ablation rate for Yb,Er:Glass laser radiation was 8 μm/pulse at W = 91±2 J/cm, whereas that for Er:YLF laser radiation was 12 μm/pulse at W = 10.5±0.5 J/cm. The maximum ablation efficiency for Yb,Er:Glass laser radiation was 0.1 μm/mJ at W = 10.5±0.5 J/cm, whereas that for Er:YLF laser radiation was 4.6 μm/mJ at W = 5.3±0.3 J/cm. The laser ablation rate depends on the storage time and conditions of the freshly extracted nail plate. For example, when exposed to Er:YLF laser radiation, the laser ablation rate decreased by half from the initial maximum value in 96 h of air storage and returned to the initial value after 1 h of storage in distilled water. [ABSTRACT FROM AUTHOR]

Laser-assisted lipolysis is routinely used for contouring the body and the neck while modifications of the technique have recently been advocated for facial contouring. In this study, wavelength-dependence measurements of laser lipolysis effect were performed using different lasers at 1,064, 1,320, and 1,444 nm wavelengths that are currently used clinically. Fresh porcine skin with fatty tissue was used for the experiments with radiant exposure of 5-8 W with the same parameters (beam diameter = 600 μm, peak power = 200 mJ, and pulse rate = 40 Hz) for 1,064, 1,320 and 1,444 nm laser wavelengths. After laser irradiation, ablation crater depth and width and tissue mass loss were measured using spectral optical coherence tomography and a micro-analytical balance, respectively. In addition, thermal temporal monitoring was performed with a thermal imaging camera placed over ex vivo porcine fat tissue; temperature changes were recorded for each wavelength. This study demonstrated greatest ablation crater depth and width and mass removal in fatty tissue at the 1,444 nm wavelength followed by, in order, 1,320 and 1,064 nm. In the evaluation of heat distribution at different wavelengths, reduced heat diffusion was observed at 1,444 nm. The ablation efficiency was found to be dependent upon wavelength, and the 1,444 nm wavelength was found to provide both the highest efficiency for fatty tissue ablation and the greatest thermal confinement. [ABSTRACT FROM AUTHOR]

In this study, a thulium (Tm:YAP) laser system was developed for brain surgery applications. As the Tm:YAP laser is a continuous-wave laser delivered via silica fibers, it would have great potential for stereotaxic neurosurgery with highest local absorption in the IR region. The laser system developed in this study allowed the user to set the power level, exposure time, and modulation parameters (pulse width and on-off cycles). The Tm:YAP laser beam (200-600 mW, 69-208 W/cm(2)) was delivered from a distance of 2 mm to cortical and subcortical regions of ex-vivo Wistar rat brain tissue samples via a 200-μm-core optical fiber. The system performance, dosimetry study, and ablation characteristics of the Tm:YAP laser were tested at different power levels by maximizing the therapeutic effects and minimizing unwanted thermal side-effects. The coagulation and ablation diameters were measured under microscope. The maximum ablation efficiency (100 × ablation diameter/coagulation diameter) was obtained when the Tm:YAP laser system was operated at 200 mW for 10 s. At this laser dose, the ablation efficiency was found to be 71.4% and 58.7% for cortical and subcortical regions, respectively. The fiber-coupled Tm:YAP laser system in hence proposed for the delivery of photothermal therapies in medical applications. [ABSTRACT FROM AUTHOR]

PurposeTo explain the origin of changes in corneal asphericity and induced spherical aberration after laser refractive surgery.MethodsA rigorous model, CASIM (corneal ablation simulator), has been developed to model the ablation profile design, the shot-by-shot ablation process and the corneal remodelling that occurs through healing. The dependence of corneal asphericity, induced spherical aberration, and achieved refractive correction on corneal remodelling, and the ablation efficiency reduction caused by the angle of incidence of the excimer beam on the curved cornea are compared to the clinical outcomes reported in the literature.ResultsWhen the exact Munnerlyn formula is used, the CASIM modelling and the clinical data exhibit a high degree of correlation. The modelling predicts that the postoperative cornea will be oblate, with substantial induced spherical aberration. A 6-month postsurgery asphericity is predicted by CASIM with a correlation of R 2=0.94. The corneal remodelling included in CASIM accounts, on the average, for 45 and 69% of the increase in asphericity and spherical aberration, respectively, with the remainder due to the ablation efficiency.ConclusionsThe modelling shows that clinically observed increases in corneal asphericity and induction of spherical aberration can be explained by the effects of corneal remodelling due to healing and by the ablation efficiency reduction due to laser angle of incidence. The model is capable of predicting clinical outcomes for procedures performed with flying spot laser systems and could be used to design compensated ablation profiles to improve the clinical outcomes for custom as well as conventional laser refractive procedures. [ABSTRACT FROM AUTHOR]

High intensity focused ultrasound (HIFU) has been introduced to treat cancers. However, this therapy is a time-consuming procedure; destructing a deeper volume is also difficult as ultrasonic energy attenuates exponentially with increasing depth in tissues. The aim of the present study was to investigate the effects of introducing microbubbles on liver HIFU ablation. Seventeen goats were divided into groups A ( n=8) and B ( n=9). The livers in both groups were ablated using HIFU (1.0 MHz, 22,593 W/cm2) performed in the manner of a clinical regime using a clinical device. A microbubble agent was bolus-injected intravenously before HIFU exposure in group B. All animals in group A and seven goats in group B were euthanased to evaluate the ablation efficiency 24 h after HIFU. The necrosis rate (mm3/s), which was the volume of necrosis tissue per second of HIFU exposure, was used to judge the ablation efficiency. Pathological examinations were performed to determine whether there were residual intact tissues within the exposed volume. The other two goats in group B were used to determine the delayed pathological changes 7 days after ultrasonic ablation. The necrosis rate (mm3/s) was increased in group B (14.4647±4.1960 versus 33.5302±12.4484, P=0.0059). Pathological examinations confirmed that there were no residual unaffected tissue focuses within the exposed volume. Two remarkable changes occurred in the other two goats in group B 7 days after HIFU: there were ghost-cell islands at the periphery of the ablated tissues, and surrounding adjacent tissues outside the reactive zone necrotized. These findings showed that microbubbles could be used to assist liver HIFU ablation. [ABSTRACT FROM AUTHOR]