The study compares two laser beam intensity distributions, namely the Gaussian beam and the flat-top, for micromachining applications at a UV wavelength of 257 nm (4th). A novel laser system with integrated beam shaping capabilities, including a flat-top intensity profile is introduced. The differences when micromachining materials using the top-hat intensity profile are compared to the conventional Gaussian intensity distribution.
We study the properties of glasses and crystals after an ultraviolet (UV) laser ablation process using 300 fs duration pulses, centered at 206 nm wavelength at the repetition rate of 50 kHz. We show that linear light absorption allows fabricating grooves with a surface roughness in the order of tens of nanometers and even sub-10 nm with low heat affected zones (HAZ) without any post-processing. We produced a single scan laser ablated microchannels’ depth, surface roughness and full width at half maximum maps based on the experimental results. These maps show relations with an overlap of laser pulses and a pulse energy and are useful when considering the working regime for specific applications. Our results depict the minimum channel bottom roughness of 8 nm in Sapphire after one scan. This value represents several times smaller roughness when compared to the nanosecond UV laser ablation. We have also studied a multi shot ablation and by evaluating our results using a scanning electron microscope (SEM) we noticed nanogratings on the walls of the craters of soda-lime and BK7 glasses with a period of 300 nm, that is bigger than the laser wavelength (206 nm). We also show that a precise surface micro patterning can be achieved with our experimental setup. Finally, our theoretical fluence distribution optimization provides a precise fabrication parameters estimate for a small surface roughness condition.
In this study, we present results on direct fiber surface ablation using UV femtosecond laser pulses (206 nm, 50 kHz, 210 fs). The research is carried out experimentally and simulatively. The simulative experiment demonstrates that fringe visibility is best when half of the fiber core is removed. The fringe free spectral range (FSR) decreases as the trench length increases. The experimental study contains the investigation on parameter optimization for trench-like surface formation on the fiber via direct laser ablation, suitable for Mach – Zehnder interferometer (MZI) formation. Linear light absorption allows to fabricate deep, regular structures on the fibers with small (148 ± 12 nm) bottom surface roughness.
Surface roughness is an important parameter that has a great influence on various material properties. It determines the rate of corrosion, wettability, as well as optical properties of different materials. Low roughness (< 100 nm Ra) surfaces are difficult to achieve even with fs pulses, therefore investigation of the theoretical intricacies is of major interest when engraving transparent materials. In our study, we numerically investigate the evolution of the surface roughness when it is scanned with a UV femtosecond laser beam and compare the numerical results to the experimentally acquired values. The study contains a single scan as well as multiple scans (up to 10 scans) on the surface. We found that in the case of a single scan the dominant surface roughness determining factor is the overlap of the pulses in x and y directions. It was found, that parameters such as pulse overlap, laser-scanner synchronization, and initial beam profile strongly influence the resulting surface roughness in a nonlinear manner. In the case of a multi-scanned surface, we determined that the resulting surface roughness can be minimized by introducing rotation of every following layer at a certain angle with respect to the previous one. The angle for minimized surface roughness highly depended on system configuration. The investigated theoretical model is in good relation to the experimentally acquired results and provides valuable information when optimizing the process for minimal-roughness micromachining.
Material surfaces irradiated with laser radiation under specific conditions can lead to laser-induced periodic surface structure (LIPSS) formation. The formation of these surface structures is a robust one-step method that allows for high throughput and cheap surface nano-structuring with spatial periods that can be greatly lower than the irradiating laser wavelength. Typically, a structural size ranges from several micrometers down to less than 100 nm and the structures strongly correlate with the polarization direction of the light used for their formation.
The regularity of LIPSS formation depends on various laser and material parameters. Some metals can exhibit highly regular LIPSS (HR-LIPSS) when the correct conditions are met. One of the main drawbacks of precise LIPSS texturization is the difficulty in controlling the ripple quality. Thus, understanding the processes which lead to HR-LIPSS formation is one step in making laser-based material texturization more prevalent.
The aim of this research was to create highly regular surface structures and investigate how the ripple formation depends on various laser and material properties. The experiment was carried out using femtosecond laser systems. Different laser harmonics modules were used for the LIPSS formation to cover both the IR and UV wavelengths.
Structures were formed on various steel, copper, aluminum, and titanium samples employing different laser wavelengths, pulse energies, pulse overlaps, and polarizations. The resulting surface structures were then examined both visually and with the help of a scanning electron microscope (SEM). LIPSS images taken by SEM were then digitally processed to calculate the distribution of LIPSS orientation angle (DLOA) which characterizes the regularity of the surface structures.
We show that by using ultraviolet femtosecond laser sources, choosing the right pulse energy, pulse overlap values, and sufficiently sharp focusing lens, HR-LIPSS can be formed on metals for which highly regular ripples don’t form using infrared laser radiation.
We investigated GHz pulse bursts ablation on metals, silicon, zirconium dioxide, soda-lime glass and sapphire for surface structuring applications with a commercial laser system providing a burst pulse frequency of 5.4 GHz and a maximum of 25 pulses per burst pulse train. The results on metal show dramatic decrease of the ablation efficiency and a reduction of the machining quality. For silicon we also observed a reduction of the ablation efficiency for GHz pulse bursts but found a strong increase for MHz pulse bursts using a 10 ps laser system. On glass an increase of the ablation rate for GHz pulse bursts was observed, however with pure machining quality indicated by crakes in the surface and boarders. Zirconium oxide was the only investigated material, where a GHz pulse bursts induces a moderate higher ablation efficiency with comparable surface qualities, however a 10% higher ablation rate was obtained with a 10 ps laser system.
Bursts of 230 fs pulses with up to 25 pulses having a time spacing of 180 ps were applied to steel AISI304, copper DHP, brass and silicon in real surface texturing (milling) application by machining squares. The previously reported very high removal rates for GHz bursts could not be confirmed, on the contrary, the specific removal rate tremendously drops down to less than 10% for the metals and 25% for silicon when the number of pulses per burst is increased. This drop is fully in line with shielding effects already observed in case of MHz pulses and double pulse experiments. The increase of the number of pulses per burst directly goes with strongly increased melting effects which are assumed to additionally re-fill the already machined areas in this milling application. Calorimetric experiments show an increasing residual heat with higher number of pulses per burst. Further the removal rates of the GHz bursts directly follow the tendency of single pulses of identical duration. This fosters the hypothesis that in case of metals and silicon only melting and melt ejection lead to the high reported removal rates for GHz bursts in punching applications and that no additional "ablation cooling" effect is taking place.
In this work we present femtosecond laser lift off (LLO) technique for GaN coating separation from sapphire substrates. We demonstrate that using rapid raster scanning technique it is possible to achieve successful delamination of GaN coatings with low surface roughness without any stitching artifacts and at industrial processing rate. Several delamination regimes can be identified in femtosecond LLO: thermal decomposition, stress induced peeling. These results show that femtosecond laser LLO could surpass nanosecond LLO by the achieved quality and overall control of delamination processes.
An approach employing ultrafast laser hybrid subtractive-additive microfabrication, which combines ablation, three-dimensional nanolithography, and welding, is proposed for the realization of a lab-on-chip (LOC) device. A single amplified Yb:KGW femtosecond (fs)-pulsed laser source is shown to be suitable for fabricating microgrooves in glass slabs, polymerization of fine-meshes microfilter out of hybrid organic–inorganic photopolymer SZ2080 inside them, and, finally, sealing the whole chip with cover glass into a single monolithic piece. The created microfluidic device proved its particle sorting function by separating 1- and 10-μm polystyrene spheres in an aqueous mixture. All together, this proves that laser microfabrication based on a single amplified fs laser source is a flexible and versatile approach for the hybrid subtractive-additive manufacturing of functional mesoscale multimaterial LOC devices.
An approach employing ultrafast laser hybrid microfabrication combining ablation, 3D nanolithography and welding is proposed for the realization of Lab-On-Chip (LOC) device. The same laser setup is shown to be suitable for fabricating microgrooves in glass slabs, polymerization of fine meshes inside them, and, lastly, sealing the whole chip with cover glass into one monolithic piece. The created micro fluidic device proved its particle sorting function by separating 1 μm and 10 μm polystyrene spheres from a mixture. Next, a lens adapter for a cell phone's camera was manufactured via thermal extrusion 3D printing technique which allowed to achieve sufficient magnification to clearly resolve <10 μm features. All together shows fs-laser microfabrication technology as a flexible and versatile tool for study and manufacturing of Lab-On-Chip devices.
Glass drilling realized with the help of femtosecond lasers attract industrial attention, however, desired tasks may require
systems employing high numerical aperture (NA) focusing conditions, low repetition rate lasers and complex fast motion
translation stages. Due to the sensitivity of such systems, slight instabilities in parameter values can lead to crack
formations, severe fabrication rate decrement and poor quality overall results. A microfabrication system lacking the
stated disadvantages was constructed and demonstrated in this report. An f-theta lens was used in combination with a
galvanometric scanner, in addition, a water pumping system that enables formation of water films of variable thickness
in real time on the samples. Water acts as a medium for filament formation, which in turn decreases the focal spot
diameter and increases fluence and axial focal length. This article demonstrates the application of a femtosecond (280fs)
laser towards rapid cutting of different transparent materials. Filament formation in water gives rise to strong ablation at
the surface of the sample, moreover, the water, surrounding the ablated area, adds increased cooling and protection from
cracking. The constructed microfabrication system is capable of drilling holes in thick soda-lime, hardened glasses and
sapphire. The fabrication time varies depending on the diameter of the hole and spans from a few to several hundred
seconds. Moreover, complex-shape fabrication was demonstrated.
Glass drilling and welding applications realized with the help of femtosecond lasers attract industrial attention , however, desired tasks may require systems employing high numerical aperture (NA) focusing conditions, low repetition rate lasers and complex fast motion translation stages. Due to the sensitivity of such systems, slight instabilities in parameter values can lead to crack formations, severe fabrication rate decrement and poor quality overall results. A microfabrication system lacking the stated disadvantages was constructed and demonstrated in this report. An f-theta lens was used in combination with a galvanometric scanner, in addition, a water pumping system that enables formation of water films of variable thickness in real time on the samples. Water acts as a medium for filament formation, which in turn decreases the focal spot diameter and increases fluence and axial focal length . This article demonstrates the application of a femtosecond (280fs) laser towards two different micromachining techniques: rapid cutting and welding of transparent materials. Filament formation in water gives rise to strong ablation at the surface of the sample, moreover, the water, surrounding the ablated area, adds increased cooling and protection from cracking. The constructed microfabrication system is capable of drilling holes in thick soda-lime and hardened glasses. The fabrication time varies depending on the diameter of the hole and spans from a few to several hundred seconds. Moreover, complex-shape fabrication was demonstrated. Filament formation at the interface of two glass samples was also used for welding applications. By varying repetition rate, scanning speed and focal position optimal conditions for strong glass welding via filamentation were determined.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.