Pulse energy packing effects on material transport during laser processing of < 1

The effects of energy pulse packing on material transport during single-pulse laser processing of silicon is studied using temporarily shaped pulses with durations from 50 to 150 ns. Six regimes of material transport were identified and disambiguated through energy packing considerations over a range of pulse durations. Energy packing has been shown to shift the interaction to energetically costlier regimes without appreciable benefit in either depth, material removal or crater morphology and quality.The authors would like to thank the UK Technology Strategy Board under project TP14/HVM/6/I/BD5665. The authors acknowledge the EPSRC Centre for Doctoral Training in Photonic Systems Development for their generous support

Investigation of plume dynamics during picosecond laser ablation of H13 steel using high-speed digital holography

Ablation of H13 tool steel using pulse packets with repetition rates of 400 and 1000 kHz and pulse energies of 75 and 44μJ, respectively, is investigated. A drop in ablation efficiency (defined here as the depth per pulse or μm/μJ) is shown to occur when using pulse energies of E$_{pulse}$>44μJ, accompanied by a marked difference in crater morphology. A pulsed digital holographic system is applied to image the resulting plumes, showing a persistent plume in both cases. Holographic data are used to calculate the plume absorption and subsequently the fraction of pulse energy arriving at the surface after traversing the plume for different pulse arrival times. A significant proportion of the pulse energy is shown to be absorbed in the plume for E$_{pulse}$>44μJ for pulse arrival times corresponding to > 1 MHz pulse repetition rate, shifting the interaction to a vapour-dominated ablation regime, an energetically costlier ablation mechanism.This work was collaboratively carried out under EPSRC Grant Number EP/K030884/1, as part of the EPSRC Centre for Innovative Manufacturing in Laser-based Production Processes. One of the authors acknowledges his PhD studentship by the Federal Government of Nigeria (TETFUND) in conjunction with the Federal University of Petroleum Resources Effurun (FUPRE)

Investigation of low nanosecond light-matter interaction mechanisms

Laser ablation of solid Silicon targets using pulsed Yb fiber lasers of pulse duration 1.5-400 ns Yb fiber lasers is studied in this work. Material responses of a range of pulse envelopes are examined including front peak (FP) and double peak (DP) pulses. Theoretical models for the interactions are examined and qualitative explanations of material response experiments are presented

A holographic method for optimisation of laser-based production processes

© 2016 THOSS Media & De Gruyter 2016. A digital holographic system is used to image the plume dynamics of a train of picosecond laser pulses interacting with titanium, aluminium, copper and brass. The recorded process dynamics are used to propose two optimisation strategies: first, by observing the time at which the plume fully dissipates and, second, through calculation of the minimum beam displacement required to maximise energy delivery to the sample by avoiding the plume. The proposed approach could further be applied in real industrial process design, allowing laser users to formulate a processing strategy based on process dynamics rather than lengthy post-process evaluation of a sample

Investigation of pulse shape characteristics on the laser ablation dynamics of TiN coatings in the ns regime

In this work, the ablation dynamics of TiN coating with a ns-pulsed fibre laser in a wide range of pulse durations were studied. Critical time instances within the pulse duration were assessed by reflected pulse analysis. Digital holography was employed to investigate the shock wave expansion dynamics within and beyond the pulse duration. The results depict that the absorption behaviour changes as a function of the pulse rise time. Moreover, planar expansion of the shock wave is observed, which is generally linked to higher machining quality and absence of excessive plasma. The results of the study are interpreted to depict the required characteristics of optimized pulse shapes in the ns-region for improved micromachining performance

Laser micromachining of TiN coatings with variable pulse durations and shapes in ns regime

The micro-structuring of thin surface coatings has become increasingly popular following the discovery of improved performance, especially in terms of the resulting tribological properties. The direct writing of microstructures via laser ablation offers flexibility, extending the applicability of micro-structuring to various materials and machined geometries. However, the laser ablation of coatings requires better comprehension to provide sufficient machining quality with improved productivity to render such processes more viable for industrial applications. This paper presents the processing conditions for the ablation of approximately 4-μm-thick coatings of TiN in the ns pulse regime, which is generally characterised by higher productivity with low machining quality. A range of pulse durations between 12. ns and 200. ns was employed. The effect of pulse duration on ablation threshold fluence and irradiance was investigated. The pulse shape was decomposed into peak and tail regions to investigate their respective effects on the ablation process. The opportune regulation of pulse properties allowed for the maintenance of high productivity and high-quality laser micromachining under delicate processing conditions, in the case of ceramic TiN surface coatings with limited thickness

Monitoring and closed loop feedback control of ultrafast glass welding

Laser based precision processing of micro and nanoscale components is a common manufacturing and prototyping production method given its non-contact nature and well defined energy delivery. However, while laser parameters are highly controllable, laser-material interactions are inherently unstable, resulting in increased rejection rates. Here, swept source optical coherence tomography (SS-OCT) is used to provide feedback control of the position, ensuring that the weld structure will successfully bridge the interface between materials. OCT is also used to monitor the glass weld cycle in-situ, allowing possible control of the structure size by terminating processing once desired results have been achieved. Finally, OCT is able to determine whether or not a successful weld has been created

High resolution laser micromachining of TiN coatings through the regulation of pulse characteristics

The first part of this work presents the study of micro drilling conditions on TiN coatings with a MOPA fibre laser with pulse tuning capability. Pulse shapes with pulse durations varying between 12-200 ns have been employed. Single and multiple-pulse ablation conditions were mapped for different pulse durations to effect greater control of the two main geometrical attributes, namely diameter and depth. In the second part of the work, the mapped conditions were used to design more complicated micro features with dimensions close to the laser beam diameter (36 μm). Elliptical dimple shape was chosen as a demonstrator case