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Norbert Gutknecht - One of the best experts on this subject based on the ideXlab platform.
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Influence of the pulse duration of an Er:YAG laser system on the Ablation Threshold of dental enamel.
Lasers in Medical Science, 2002Co-Authors: Christian Apel, Rene Franzen, Jorg Meister, H Sarrafzadegan, S Thelen, Norbert GutknechtAbstract:. The present study examines the dependence of the Ablation Threshold on the duration of the applied laser pulses in the dental enamel of human wisdom teeth. To this end, 600 treatments with the Er:YAG laser (λ=2940 nm) were carried out on a total of 50 extracted teeth. The laser light was coupled into a fluoride glass light guide for this purpose, in order to ensure almost gaussian distribution of the light in a radially symmetrical beam. The beam diameter on the specimen was 610 µm. The radiant exposure on the tooth surface was varied between 2 and 20 J/cm2, while the duration of the pulses applied was changed in four steps from 100 µs to 700 µs. The irradiated tooth surfaces were examined for visible signs of Ablation under a reflected-light microscope. The experiments revealed that, when pulses of shorter duration are used, the limit at which Ablation sets in is reduced by up to approx. 3 J/cm2. This expands the Ablation Threshold range of Er:YAG laser radiation to between 6 and 10 J/cm2. In this context, both the pulse duration and the radiant exposure have a statistically significant influence on the Ablation Threshold (logistic regression, p
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influence of the pulse duration of an er yag laser system on the Ablation Threshold of dental enamel
Lasers in Medical Science, 2002Co-Authors: Christian Apel, Rene Franzen, Jorg Meister, H Sarrafzadegan, S Thelen, Norbert GutknechtAbstract:. The present study examines the dependence of the Ablation Threshold on the duration of the applied laser pulses in the dental enamel of human wisdom teeth. To this end, 600 treatments with the Er:YAG laser (λ=2940 nm) were carried out on a total of 50 extracted teeth. The laser light was coupled into a fluoride glass light guide for this purpose, in order to ensure almost gaussian distribution of the light in a radially symmetrical beam. The beam diameter on the specimen was 610 µm. The radiant exposure on the tooth surface was varied between 2 and 20 J/cm2, while the duration of the pulses applied was changed in four steps from 100 µs to 700 µs. The irradiated tooth surfaces were examined for visible signs of Ablation under a reflected-light microscope. The experiments revealed that, when pulses of shorter duration are used, the limit at which Ablation sets in is reduced by up to approx. 3 J/cm2. This expands the Ablation Threshold range of Er:YAG laser radiation to between 6 and 10 J/cm2. In this context, both the pulse duration and the radiant exposure have a statistically significant influence on the Ablation Threshold (logistic regression, p<0.0001). Although the Ablation Threshold of the dental enamel can be changed by varying the pulse duration of the Er:YAG laser, no clinical consequences can be expected, as the shift is only slight.
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the Ablation Threshold of er yag and er ysgg laser radiation in dental enamel
Lasers in Medical Science, 2002Co-Authors: Christian Apel, Rene Franzen, Jorg Meister, R S Ioana, Peter Hering, Norbert GutknechtAbstract:. The scientific investigation of fundamental problems plays a decisive role in understanding the mode of action and the consequences of the use of lasers on biological material. One of these fundamental aspects is the investigation of the Ablation Threshold of various laser wavelengths in dental enamel. Knowledge of the relationships and influencing factors in the laser Ablation of hard tooth tissue constitutes the basis for use in patients and the introduction of new indications. The present paper examines the Ablation Threshold of an Er:YAG laser (λ=2.94 µm) and an Er:YSGG laser (λ=2.79 µm) in human dental enamel. To this end, 130 enamel samples were taken from wisdom teeth and treated with increasing energy densities of 2–40 J/cm2. The sample material was mounted and irradiated on an automated linear micropositioner. Treatment was performed with a pulse duration of τP(FWHM)≈150 µs and a pulse repetition rate of 5 Hz for both wavelengths. The repetition rate of the laser and the feed rate of the micropositioner resulted in overlapping of the single pulses. The surface changes were assessed by means of reflected light and scanning electron microscopy. On the basis of the results, it was possible to identify an energy density range as the Ablation Threshold for both the Er:YAG and the Er:YSGG laser. With the Er:YAG laser, the transition was found in an energy density range of 9–11 J/cm2. The range for the Er:YSGG laser was slightly higher at 10–14 J/cm2.
Cather M Simpson - One of the best experts on this subject based on the ideXlab platform.
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measuring the Ablation Threshold fluence in femtosecond laser micromachining with vortex and bessel pulses
Optics Express, 2018Co-Authors: Reece N. Oosterbeek, Simon Ashforth, Owen Bodley, Cather M SimpsonAbstract:Femtosecond laser micromachining holds significant promise for advanced manufacturing, however uptake has been limited by the low processing speed. Altering the beam shape from its typical Gaussian profile has been attempted to improve efficiency, however virtually all reliable methods for quantifying the efficiency assume a Gaussian beam shape. Here, we describe an approach for quantifying the Ablation Threshold fluence – the key parameter for comparing efficiency – suitable for weakly focused non-Gaussian beams. We successfully demonstrate this method for Bessel and vortex beams, finding that the Ablation Threshold depends not just on the material, but the beam shape as well.
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Ablation Threshold dependence on incident wavelength during ultrashort pulsed laser Ablation
International Journal of Nanotechnology, 2017Co-Authors: Reece N. Oosterbeek, Simon Ashforth, Owen Bodley, Cather M SimpsonAbstract:Ultrashort pulse laser micromachining is an advanced materials processing technique that allows "cold cutting" of almost any material. This is especially of interest in the semiconductor industry, where mechanical cutting of wafers generates large amounts of waste - if laser micromachining could be applied here, there is the potential for huge increases in the efficiency and flexibility of semiconductor manufacturing. The biggest barrier to industrial application of this technology is the cutting speed, however by tailoring the pulse properties, we hypothesise that machining speed can be increased greatly. The commonly used metric for evaluation of laser micromachining is the Ablation Threshold - the energy density required to cause material Ablation. In this study the effect of incident laser wavelength on the Ablation Threshold for materials of interest for microfabrication (e.g., silicon) was investigated. This was achieved using a Ti:Sapphire pumped optical parametric amplifier (TOPAS-C) producing femtosecond pulses (τ = 110 fs, repetition rate = 1 kHz) with wavelengths ranging from 400 nm to 1200 nm using the D-Scan technique. Future work will employ advanced beam shaping technology to tailor pulses in both the spatial and temporal domains to further improve machining efficiency.
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effects of dopant type and concentration on the femtosecond laser Ablation Threshold and incubation behaviour of silicon
Applied Physics A, 2016Co-Authors: Reece N. Oosterbeek, Simon Ashforth, Cather M Simpson, Carsten CorazzaAbstract:In laser micromachining, the Ablation Threshold (minimum fluence required to cause Ablation) is a key performance parameter and overall indicator of the efficiency of material removal. For pulsed laser micromachining, this important observable depends upon material properties, pulse properties and the number of pulses applied in a complex manner that is not yet well understood. The incubation effect is one example. It manifests as a change in the Ablation Threshold as a function of number of laser pulses applied and is driven by photoinduced defect accumulation in the material. Here, we study femtosecond (800 nm, 110 fs, 0.1–1 mJ/pulse) micromachining of a material with well-defined initial defect concentrations: doped Si across a range of dopant types and concentrations. The single-pulse Ablation Threshold (F th,1) was observed to decrease with increasing dopant concentration, from a maximum of 0.70 J/cm2 (±0.02) for undoped Si to 0.51 J/cm2 (±0.01) for highly N-type doped Si. The effect was greater for N-type doped Si than for P-type, consistent with the higher carrier mobility of electrons compared to holes. In contrast, the infinite-pulse Ablation Threshold (F th,∞ ) was the same for all doping levels and types. We attribute this asymptotic behaviour to a maximum defect concentration that is independent of the initial defect concentration and type. These results lend insight into the mechanism of multipulse, femtosecond laser Ablation.
Christian Apel - One of the best experts on this subject based on the ideXlab platform.
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Influence of the pulse duration of an Er:YAG laser system on the Ablation Threshold of dental enamel.
Lasers in Medical Science, 2002Co-Authors: Christian Apel, Rene Franzen, Jorg Meister, H Sarrafzadegan, S Thelen, Norbert GutknechtAbstract:. The present study examines the dependence of the Ablation Threshold on the duration of the applied laser pulses in the dental enamel of human wisdom teeth. To this end, 600 treatments with the Er:YAG laser (λ=2940 nm) were carried out on a total of 50 extracted teeth. The laser light was coupled into a fluoride glass light guide for this purpose, in order to ensure almost gaussian distribution of the light in a radially symmetrical beam. The beam diameter on the specimen was 610 µm. The radiant exposure on the tooth surface was varied between 2 and 20 J/cm2, while the duration of the pulses applied was changed in four steps from 100 µs to 700 µs. The irradiated tooth surfaces were examined for visible signs of Ablation under a reflected-light microscope. The experiments revealed that, when pulses of shorter duration are used, the limit at which Ablation sets in is reduced by up to approx. 3 J/cm2. This expands the Ablation Threshold range of Er:YAG laser radiation to between 6 and 10 J/cm2. In this context, both the pulse duration and the radiant exposure have a statistically significant influence on the Ablation Threshold (logistic regression, p
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influence of the pulse duration of an er yag laser system on the Ablation Threshold of dental enamel
Lasers in Medical Science, 2002Co-Authors: Christian Apel, Rene Franzen, Jorg Meister, H Sarrafzadegan, S Thelen, Norbert GutknechtAbstract:. The present study examines the dependence of the Ablation Threshold on the duration of the applied laser pulses in the dental enamel of human wisdom teeth. To this end, 600 treatments with the Er:YAG laser (λ=2940 nm) were carried out on a total of 50 extracted teeth. The laser light was coupled into a fluoride glass light guide for this purpose, in order to ensure almost gaussian distribution of the light in a radially symmetrical beam. The beam diameter on the specimen was 610 µm. The radiant exposure on the tooth surface was varied between 2 and 20 J/cm2, while the duration of the pulses applied was changed in four steps from 100 µs to 700 µs. The irradiated tooth surfaces were examined for visible signs of Ablation under a reflected-light microscope. The experiments revealed that, when pulses of shorter duration are used, the limit at which Ablation sets in is reduced by up to approx. 3 J/cm2. This expands the Ablation Threshold range of Er:YAG laser radiation to between 6 and 10 J/cm2. In this context, both the pulse duration and the radiant exposure have a statistically significant influence on the Ablation Threshold (logistic regression, p<0.0001). Although the Ablation Threshold of the dental enamel can be changed by varying the pulse duration of the Er:YAG laser, no clinical consequences can be expected, as the shift is only slight.
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the Ablation Threshold of er yag and er ysgg laser radiation in dental enamel
Lasers in Medical Science, 2002Co-Authors: Christian Apel, Rene Franzen, Jorg Meister, R S Ioana, Peter Hering, Norbert GutknechtAbstract:. The scientific investigation of fundamental problems plays a decisive role in understanding the mode of action and the consequences of the use of lasers on biological material. One of these fundamental aspects is the investigation of the Ablation Threshold of various laser wavelengths in dental enamel. Knowledge of the relationships and influencing factors in the laser Ablation of hard tooth tissue constitutes the basis for use in patients and the introduction of new indications. The present paper examines the Ablation Threshold of an Er:YAG laser (λ=2.94 µm) and an Er:YSGG laser (λ=2.79 µm) in human dental enamel. To this end, 130 enamel samples were taken from wisdom teeth and treated with increasing energy densities of 2–40 J/cm2. The sample material was mounted and irradiated on an automated linear micropositioner. Treatment was performed with a pulse duration of τP(FWHM)≈150 µs and a pulse repetition rate of 5 Hz for both wavelengths. The repetition rate of the laser and the feed rate of the micropositioner resulted in overlapping of the single pulses. The surface changes were assessed by means of reflected light and scanning electron microscopy. On the basis of the results, it was possible to identify an energy density range as the Ablation Threshold for both the Er:YAG and the Er:YSGG laser. With the Er:YAG laser, the transition was found in an energy density range of 9–11 J/cm2. The range for the Er:YSGG laser was slightly higher at 10–14 J/cm2.
Reece N. Oosterbeek - One of the best experts on this subject based on the ideXlab platform.
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measuring the Ablation Threshold fluence in femtosecond laser micromachining with vortex and bessel pulses
Optics Express, 2018Co-Authors: Reece N. Oosterbeek, Simon Ashforth, Owen Bodley, Cather M SimpsonAbstract:Femtosecond laser micromachining holds significant promise for advanced manufacturing, however uptake has been limited by the low processing speed. Altering the beam shape from its typical Gaussian profile has been attempted to improve efficiency, however virtually all reliable methods for quantifying the efficiency assume a Gaussian beam shape. Here, we describe an approach for quantifying the Ablation Threshold fluence – the key parameter for comparing efficiency – suitable for weakly focused non-Gaussian beams. We successfully demonstrate this method for Bessel and vortex beams, finding that the Ablation Threshold depends not just on the material, but the beam shape as well.
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Theoretical basis of the diagonal scan method for determining the laser Ablation Threshold for femtosecond vortex pulses
arXiv: Optics, 2018Co-Authors: Reece N. Oosterbeek, Simon Ashforth, Owen Bodley, M. Cather SimpsonAbstract:In femtosecond laser micromachining, the Ablation Threshold is a key processing parameter that characterises the energy density required to cause Ablation. Current techniques for measuring the Ablation Threshold such as the diameter regression and diagonal scan methods are based on the assumption of a Gaussian spatial profile, however no techniques currently exist for measuring the Ablation Threshold using a non-Gaussian beam shape. Here we present a formalism of the diagonal scan method for determining the Ablation Threshold and pulse superposition for femtosecond vortex pulses. To the authors' knowledge this is the first Ablation Threshold technique developed for pulses with non-Gaussian spatial profiles. Using this method, the Ablation Threshold can be calculated using measurement of a single feature (the maximum damage radius $\rho_{max}$), which allows investigations of Ablation Threshold and incubation effects to be carried out quickly and easily. Extending this method to non-Gaussian beams will allow exploration of new avenues of research, enabling characterisation of the Ablation Threshold and incubation behaviour for a material when ablated with femtosecond vortex pulses.
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Ablation Threshold dependence on incident wavelength during ultrashort pulsed laser Ablation
International Journal of Nanotechnology, 2017Co-Authors: Reece N. Oosterbeek, Simon Ashforth, Owen Bodley, Cather M SimpsonAbstract:Ultrashort pulse laser micromachining is an advanced materials processing technique that allows "cold cutting" of almost any material. This is especially of interest in the semiconductor industry, where mechanical cutting of wafers generates large amounts of waste - if laser micromachining could be applied here, there is the potential for huge increases in the efficiency and flexibility of semiconductor manufacturing. The biggest barrier to industrial application of this technology is the cutting speed, however by tailoring the pulse properties, we hypothesise that machining speed can be increased greatly. The commonly used metric for evaluation of laser micromachining is the Ablation Threshold - the energy density required to cause material Ablation. In this study the effect of incident laser wavelength on the Ablation Threshold for materials of interest for microfabrication (e.g., silicon) was investigated. This was achieved using a Ti:Sapphire pumped optical parametric amplifier (TOPAS-C) producing femtosecond pulses (τ = 110 fs, repetition rate = 1 kHz) with wavelengths ranging from 400 nm to 1200 nm using the D-Scan technique. Future work will employ advanced beam shaping technology to tailor pulses in both the spatial and temporal domains to further improve machining efficiency.
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effects of dopant type and concentration on the femtosecond laser Ablation Threshold and incubation behaviour of silicon
Applied Physics A, 2016Co-Authors: Reece N. Oosterbeek, Simon Ashforth, Cather M Simpson, Carsten CorazzaAbstract:In laser micromachining, the Ablation Threshold (minimum fluence required to cause Ablation) is a key performance parameter and overall indicator of the efficiency of material removal. For pulsed laser micromachining, this important observable depends upon material properties, pulse properties and the number of pulses applied in a complex manner that is not yet well understood. The incubation effect is one example. It manifests as a change in the Ablation Threshold as a function of number of laser pulses applied and is driven by photoinduced defect accumulation in the material. Here, we study femtosecond (800 nm, 110 fs, 0.1–1 mJ/pulse) micromachining of a material with well-defined initial defect concentrations: doped Si across a range of dopant types and concentrations. The single-pulse Ablation Threshold (F th,1) was observed to decrease with increasing dopant concentration, from a maximum of 0.70 J/cm2 (±0.02) for undoped Si to 0.51 J/cm2 (±0.01) for highly N-type doped Si. The effect was greater for N-type doped Si than for P-type, consistent with the higher carrier mobility of electrons compared to holes. In contrast, the infinite-pulse Ablation Threshold (F th,∞ ) was the same for all doping levels and types. We attribute this asymptotic behaviour to a maximum defect concentration that is independent of the initial defect concentration and type. These results lend insight into the mechanism of multipulse, femtosecond laser Ablation.
D T A Matthews - One of the best experts on this subject based on the ideXlab platform.
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investigation of the ultrashort pulsed laser processing of zinc at 515 nm morphology crystallography and Ablation Threshold
Materials & Design, 2019Co-Authors: Hasib Mustafa, D T A Matthews, Gertwillem RomerAbstract:Abstract Bulk polycrystalline pure zinc is ablated in air using a picosecond laser source to perform single pulse and multi-pulse processing at a wavelength of 515 nm. The geometries and surface morphologies of the resulting craters are determined by confocal laser scanning microscopy and scanning electron microscopy. Further, the Ablation Threshold and its corresponding incubation coefficient is determined from the ablated volume for multiple laser pulses. Two different thermal Ablation regimes are identified. The single pulse Ablation Thresholds are found to equal 0.1 J/cm2 and 0.68 J/cm2 respectively for the two regimes. It is found that the incubation coefficients are larger than unity, indicating material removal becomes energy expensive for multiple pulse laser irradiation. It is also found that an irradiated area undergoes laser induced preferred crystal orientation.
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picosecond pulsed laser Ablation of zinc crater morphology and comparison of methods to determine Ablation Threshold
Optics Express, 2018Co-Authors: Hasib Mustafa, Robert Otto Pohl, B Pathiraj, D T A Matthews, G R B E RomerAbstract:Ablation of bulk polycrystalline zinc in air is performed with single and multiple picosecond laser pulses at a wavelength of 1030 nm. The relationships between the characteristics of the ablated craters and the processing parameters are analyzed. Morphological changes of the ablated craters are characterized by means of scanning electron microscopy and confocal laser scanning microscopy. Chemical compositions of both the treated and untreated surfaces are quantified with X-ray photoelectron spectroscopy. A comparative analysis on the determination of the Ablation Threshold using three methods, based on ablated diameter, depth and volume is presented along with associated incubation coefficients. The single pulse Ablation Threshold value is found to equal 0.21 J/cm2. Using the calculated incubation coefficients, it is found that both the fluence Threshold and energy penetration depth show lesser degree of incubation for multiple laser pulses.
