Ultra-short pulsed laser modification points to novel coloration possibilities on a broad range of materials using laser induced periodic surface structures, plasmonic nanoparticles, and thermal oxidation as principles.Here, a general parameter-dependent laser path calculation routine for marking and coloration of complex images is presented.The original image is imported, dependent on size and resolution, down sampled and dithering applied.The color map attained from a laser parameter study is registered and the computer-aided manufacturing routine maps the color space to nearest neighbors of the original image.Thereafter, the laser paths with the adjacent parameters are computed and the numerical code generated.A complex colored pixel graphic is transformed and high-contrast marked in black and grey-scale on a stainless steel plate.Moreover, to demonstrate the capabilities, a titanium alloy is ultra-short pulsed laser colored.A colorful image proves this approach with a pixel size of below 40 µm and no observable cross talk between the colors.

Ultrafast laser processing has shown its advantages characterized by a highly precise ablation with minimal thermal influence in many applications. Many investigations deal with the laser inherent parameters like pulse duration, repetition frequency and scan speed to describe their influence on the machining quality. However, the final machining quality is also determined by the initial surface morphology. To combine the conflicting objectives of productivity and quality a multi-level photonic process chain is established. For this kind of process chain, the knowledge about the influence of the respective surface morphology on the subsequent process step is of importance. For that reason the development of the surface morphology is investigated for several ultrafast laser parameter settings and initial surface morphologies. In our investigations, we were able to establish a mathematical model that describes the development of the roughness as a function of the ablation depth.

In the paper, laser surface texturing process was studied systematically to fabricate riblet array surface structure on Ti64 substrate with 1.06m 10W ps laser which has a pulse duration of 10.3 ps. The optimum laser surface texturing process parameters were identified, under which the desired riblet-array textures were produced on Ti64 substrate with the required specifications in terms of dimension and quality. The fabricated riblets have a trapezoidal shape with a period of 60 m and riblet height of 30 m and a bottom surface roughness (Ra) of 2.115 m. Compared with nontextured sample, the laser-fabricated riblets induced around a 10% reduction in the drag force. Also, it was found that laser surface treatment did not induce any change on the microstructure of Ti64 during ps laser riblet surface texturing of Ti64 substrate. With XRD measurements, the laser riblettextured Ti64 surface was found to exhibit tensile stress of 87.5 MPa, which may be due to the heat shock from laser treatment resulting in larger d-spacing between lattice planes.

High laser-scanning speed and high precision are two opposite parameters for effective laser surface texturing (LST). Application of a sequence of laser pulses (called burst) helps to increase the processing effectivennes and speed, but precision control of laser pulses arriving becomes a difficult task for micro-texturing. In this work, one possible solution for this dilemma is presented: a scan-ning strategy called shifted laser surface texturing (sLST) in burst regime. This burst sLST repre-sents an alternative method, where the inertia of galvanoscan mirrors becomes a useful factor at higher speeds. Physical principles of laser burst interaction with a material surface and resulting subsurface thermal-stress fields are discussed. Heat accumulation was calculated from a semi-planar model of temperature distribution from laser spots in the line of the burst. Residual subsurface temperature and pressure is called positive heat accumulation in the case of minimal output roughness of laser-scanned surfaces. Experimental application of the burst sLST was performed with a pico-second laser with a galvanoscan system. Results were evaluated by newly developed shape analysis of objects detected on contrast images of laser-processed stainless steel surfaces painted with high-emissivity paint. Deviation in sLST precision was determined from larger and smaller diameters of detected microobjects on the surface with LabIR coating. The roughness of depth structure in microobjects was controlled by a contact surface profiler and compared with the goal profile and positive heat accumulation distribution. The sLST method in burst regime enables a significant increase of processing speed while maintaining good precision of the produced texture.

We conducted laser ablation of calcined shell powder and CaO powder dispersed in ethanol. Results showed that laser ablation induced the formation of nanoparticles and the formation of gel-like structures. Observations of the temporal change of the colloidal solution during laser ablation revealed that the gel-like structures formed rapidly after laser ablation for ca. 30 min, suggesting that the gel-like structures form via the agglomeration of CaO nanoparticles formed by laser ablation. Results showed that the gel-like structures (CaO nanoparticle agglomerates) were positively charged, suggesting that the balance between the positive charge of CaO nanoparticles which comes from the source CaO powders and the negative charge provided by ethanol during laser ablation plays a key role in NP agglomeration. It was also demonstrated that the gold-CaO and platinum-CaO nanocomposites are obtainable simply by mixing colloids of positively charged CaO gel-like structures and colloids of negatively charged gold or platinum nanoparticles.

Nondiffracting pulsed beams are well studied nowadays and can be as short as a few femtoseconds. The nondiffracting pulsed beams not only resist diffraction but also propagate without changes due to the dispersion of a linear dispersive medium. A promising member of non-diffracting beam family is the so-called Mathieu beam which is a solution of Helmholtz wave equation in elliptical coordinate system. Zeroth order even Mathieu beams have unique asymmetric cross-section which makes these beams suitable for precise material processing. In this work we derive vectorial Mathieu beams using classical techniques and superpose them to create femtosecond pulsed beams. For these pulsed beams diffraction spreading and dispersive broadening is compensated by a given angular dispersion. Various intensity distributions, durations, angular dispersions and polarization states of different vector Mathieu focus wave modes are presented and discussed in detail.

Under liquid laser ablation is a material removal technique in which a focused laser beam passes through a liquid layer on top of the surface of a sample to be processed. When compared to laser ablation without a liquid layer, material (re)deposition around ablated regions, as well as the size of the Heat Affected Zone (HAZ) is decreased. In addition, the ablation efficiency of the process, in terms of the amount of material removed per pulse, can be optimized by careful variation of the height of the liquid layer: a liquid layer height variation as small as a few tens of millimeters already has a measurable effect on the amount of ablated material. In studies reported in existing literature, the required liquid layer height is typically realized by pouring a pre-defined amount of liquid on top of the sample surface. Surface tension, however, causes the air-liquid interface at the boundaries of the domain to deviate from the planar interface away from the boundaries, which affects the accuracy with which the liquid layer height can be determined. To the best of our knowledge, these accuracy issues have not been studied in previous research. Therefore, an experimental set-up is proposed which circumvents the issues of a curved free surface. Next, a 7 picosecond pulsed laser source (M2≤1.3) at a wavelength of 515nm was employed to study the efficiency of laser ablation of stainless steel for a range of liquid layer heights. Our findings provide a more detailed quantification of crater depth as a function of liquid layer height than is available through existing literature.

Use of lightweight materials to produce automotive body structures is one of the key trends adopted by automotive manufacturers to minimise emission of greenhouse gases, and subsequently, reduction of fuel consumption.Aluminium alloys are one of the promising lightweight materials which are increasingly used for automotive body-in-white structures.Such applications demand both efficient and effective joining/welding methods to produce repeatable, durable and strong joints without significant alteration of material properties.Remote laser welding (RLW) is an emerging joining technology and increasingly being used to produce lightweight joints as it satisfies the demand for high production throughput at low cost.This paper investigates the effects of process parameters when seam tracking remote laser welding is used to create an autogenous fillet edge weld of automotive grade aluminum alloy (AC-170PX) in lap configuration without shielding gas.The effects of laser power and welding speed on the key geometric features are reported together with details of the weld microstructure.Joint strength is evaluated by performing a lap shear test.It is found that the laser power and welding speed have dominant influence on key geometric features and subsequently on the lap shear strength.Relatively larger grain size in the fusion zone reduces the microhardness by up to 20% in comparison with the base material.

Use of lightweight materials to produce automotive body structures is one of the key trends adopted by automotive manufacturers to minimise emission of greenhouse gases, and subsequently, reduction of fuel consumption.Aluminium alloys are one of the promising lightweight materials which are increasingly used for automotive body-in-white structures.Such applications demand both efficient and effective joining/welding methods to produce repeatable, durable and strong joints without significant alteration of material properties.Remote laser welding (RLW) is an emerging joining technology and increasingly being used to produce lightweight joints as it satisfies the demand for high production throughput at low cost.This paper investigates the effects of process parameters when seam tracking remote laser welding is used to create an autogenous fillet edge weld of automotive grade aluminum alloy (AC-170PX) in lap configuration without shielding gas.The effects of laser power and welding speed on the key geometric features are reported together with details of the weld microstructure.Joint strength is evaluated by performing a lap shear test.It is found that the laser power and welding speed have dominant influence on key geometric features and subsequently on the lap shear strength.Relatively larger grain size in the fusion zone reduces the microhardness by up to 20% in comparison with the base material.