| 1. |
- Gaudiuso, Caterina, et al.
(författare)
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Incubation during laser ablation with bursts of femtosecond pulses with picosecond delays
- 2018
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Ingår i: Optics Express. - 1094-4087. ; 26:4, s. 3801-3813
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Tidskriftsartikel (refereegranskat)abstract
- Abstract: We report on an experimental investigation of the incubation effect during irradiation of stainless steel with bursts of ultrashort laser pulses. A series of birefringent crystals was used to split the pristine 650-fs pulses into bursts of up to 32 sub-pulses with time separations of 1.5 ps and 3 ps, respectively. The number of selected bursts was varied between 50 and 1600. The threshold fluence was measured in case of Burst Mode (BM) processing depending on the burst features, i.e. the number of sub-pulses and their separation time, and on the number of bursts. We found as many values of threshold fluence as the combinations of the number of bursts and of sub-pulses constituting the bursts set to give the same total number of impinging sub-pulses. However, existing incubation models developed for Normal Pulse Mode (NPM) return, for a given number of impinging pulses, a constant value of threshold fluence. Therefore, a dependence of the incubation coefficient with the burst features was hypothesized and experimentally investigated. Numerical solutions of the Two Temperature Model (TTM) in case of irradiation with single bursts of up to 4 sub-pulses have been performed to interpret the experimental results. © 2018 Optical Society of America.
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| 2. |
- Gaudiuso, Caterina, et al.
(författare)
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Incubation effect in burst mode fs-laser ablation of stainless steel samples
- 2018
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Ingår i: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 10520
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Tidskriftsartikel (refereegranskat)abstract
- We report on an experimental study of the incubation effect during irradiation of stainless steel targets with bursts of femtosecond laser pulses at 1030 nm wavelength and 100 kHz repetition rate. The bursts were generated by splitting the pristine 650-fs laser pulses using an array of birefringent crystals which provided time separations between sub-pulses in the range from 1.5 ps to 24 ps. We measured the threshold fluence in Burst Mode, finding that it strongly depends on the bursts features. The comparison with Normal Pulse Mode revealed that the existing models introduced to explain the incubation effect during irradiation with trains of undivided pulses has to be adapted to describe incubation during Burst Mode processing. In fact, those models assume that the threshold fluence has a unique value for each number of impinging pulses in NPM, while in case of BM we observed different values of threshold fluence for fixed amount of sub-pulses but different pulse splitting. Therefore, the incubation factor coefficient depends on the burst features. It was found that incubation effect is higher in BM than NPM and that it increases with the number of sub-pulses and for shorter time delays within the burst. Two-Temperature-Model simulations in case of single pulses and bursts of up to 4 sub-pulses were performed to understand the experimental results. © Copyright SPIE.
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| 3. |
- Tricarico, Luigi, et al.
(författare)
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Numerical and experimental investigation of the discrete spot laser hardening of a graphite-coated hypereutectoid steel using a fibre laser
- 2019
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Ingår i: The International Journal of Advanced Manufacturing Technology. - : Springer Science and Business Media LLC. - 0268-3768 .- 1433-3015. ; 104:1-4, s. 1393-1402
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Tidskriftsartikel (refereegranskat)abstract
- The single-pulse laser hardening of a hypereutectoid steel coated by a graphite layer was investigated using a numerical/experimental approach. Experimental tests were conducted on coated samples using a fibre laser source and without any gas shielding aiming to explore the effect of laser power, pulse energy and defocusing distance on the dimensions of the hardened region. The process operating window of the discrete spot laser hardening using the graphite layer was determined through a finite element model and compared with previous results obtained on uncoated samples. For the same laser power and interaction times, an enlargement of the hardened region was found when using the graphite coating, especially when operating at the lowest laser energy level. The process operating window remains similar in shape to the one of the uncoated steel but moves towards larger hardened diameters and much larger defocusing distances. Once the maximum temperature has been fixed, a linear relationship between the hardened diameter and the defocusing distance exists. No obvious surface oxidation occurs since the graphite coating acts as a protective layer. © 2019, Springer-Verlag London Ltd., part of Springer Nature.
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