This manuscript introduces a comprehensive overview in the field of Direct Laser Interference Patterning (DLIP) with a focus on its evolution over the last years, its current status, and the emerging challenges it faces. Starting with the emerging stages of DLIP, attention will be directed towards the role played by the development of innovative optical systems, which have been instrumental in pushing the boundaries of precision and control. Examples of surface functionalization achieved through DLIP techniques are also showcased, emphasizing the transformative impact that DLIP has had across various industries, from the enhancement of material properties to the facilitation of new functionalities. Furthermore, consideration will be given to the evolving landscape of inline monitoring approaches within DLIP. These monitoring techniques are poised to address the intricate challenges associated with real-time quality control and process optimization in DLIP applications.
Surface topography modifications are well-established strategies to improve the biological response of biomaterials and their performance and reliability when used as implants. Studies have shown for instance that surface roughening creates a physical anchorage between the implant and bone and improves its primary and long-term stabilization. This study reports on the fabrication of repetitive periodic structures on CoCrMo and AZ91D magnesium alloys using direct laser interference patterning. An infrared ultra-short, pulsed laser, with a wavelength of 1064 nm and 10 ps laser pulses was combined with a two-beam interference optics to produce line-like patterns. Both, the surface topography and chemical modifications are analyzed using confocal microscopy, scanning electron microscopy and Energy Dispersive Spectroscopy (EDS). By varying the applied laser fluence and pulse overlap different patterns were produced. In particular, homogeneous structures could be achieved for many used process conditions. The used spatial period was 5 μm, and the structure depth was varied up to 0.85 μm and 2.5 μm, for CoCrMo and AZ91D, respectively. For high energy, sub-micrometric secondary structures, so-called LIPSS, could also be observed. In addition, oxidation effects were confirmed by EDS analysis.
Direct Laser Interference Patterning (DLIP) is an established technology for producing textured and functional surfaces using beam-shaped laser radiation. It consists of producing high-intensity interference patterns by overlapping two or more laser beams at the material surface. In this work, new possibilities for producing textured surfaces on metals and polymers using high-throughput concepts for DLIP are presented. The first concept describes the development of a new DLIP optical head (called xDLIP) with an outstanding depth of focus of approximately 10 mm, which can be equipped with fs, ps or ns pulsed laser systems. This approach makes this device ideal to treat large areas as well as three-dimensional parts. In particular, a setup using an industrial robot system is shown. The second approach includes the combination of a new DLIP optical system with a polygon scanner, showing the possibility to treat metallic and polymer surfaces. This includes configurations for reaching 7.0 and 21.0 μm spatial periods at throughputs beyond 1 m2/min. Finally, DLIP is implemented into a roll-to-roll process using a high-power picosecond pulsed laser source, in which the main laser beam is shaped into two elongated beams which go through a scanner system. Using this setup, aluminum and copper foils with thicknesses of 20 μm and 9 μm, respectively, are processed.
This study describes the implementation of a top-hat pulsed laser for high-throughput structuring using Direct Laser Interference Patterning (DLIP). Using two and four laser beams, dot and line-like periodic surface structures were produced, respectively. The top-hat laser profile allows treating the surface of the target materials without the need to overlap the different laser pulses and thus being capable of reducing the processing time compared to Gaussian energy distributions. Similarly, using a burst of pulses, the ablation efficiency of the DLIP process could be significantly improved. Finally, ablation tests on stainless steel samples are presented and discussed.
This study reports on the application of the Direct Laser Interference Patterning method for the fabrication of holographic motives. The advantages of this method over conventional laser processing methods in terms of resolution, flexibility and throughput are analyzed. It is showed that interference approach for formation of diffraction gratings provides faster fabrication speed together with enhanced visual effect of the structural colors. The control of the period of the formed patterns provided the ability to form exact structural colors, which preserved the visibility of the motives across the whole structured area at certain observation conditions. The capability to improve further the fabrication speed, required for several industrial applications, is demonstrated using a Roll-to-Roll hot embossing system, permitting to replicate holographic motives formed by DLIP on PET foils. Finally, the first tests of inline monitoring method are presented, which is proposed for controlling the quality of the imprinted structures.
Surface structuring has attracted great attention due to the rising need of the industrial sector to improve their products through surface functionalization. A very promising technology for this purpose is Direct Laser Interference Patterning, which implements interference of multiple beams to directly form periodical patterns with a single laser pulse. This provides the ability to utilize the whole laser power for high speed structuring of large surface areas. However, in some cases even higher speeds are required. Therefore, alternative technologies like roll-to-roll hot embossing must be utilized. By the synergy of the DLIP technology, which is used for structuring the sleeves (embossing tool) and the roll-to-roll hot-embossing method, the throughput for the fabrication of micro/nano structured polymer foils can be increased at least one order of magnitude. Furthermore, since the sleeves are processed directly, without the need of lithographic methods, the fabrication cost of the textured sleeves can be significantly reduced (up to ~ 90%).
In this study, a unique DLIP-workstation is introduced, consisting of a ps-laser, several DLIP optics and a special positioning system for cylindrical parts. The system allows the patterning of cylindrical parts up to 600 mm in length and 300 mm in diameter. The structures, consisting of line-like or dot-like patterns with periods ranging from 5.5 µm down to 1.0 µm, can be produced with record processing speeds up to 5700 mm²/min. Finally, the implementation of these structured sleeves in a roll-to-roll system is demonstrated for imprinting polymer foils at an impressive surface throughputs of 12.5 m²/min, corresponding to web-speeds of 50 m/min. Additionally, some examples of the decorative elements processed by these technique are presented.
Surfaces with well-defined features (e.g. periodic structures) have shown to exhibit outstanding properties. The design of these textured surfaces often follows a biomimetic approach motivated by living organisms which developed over time through natural selection and evolution. The efficient production of these versatile patterns still represents one of the greatest technical challenges today in the development of new customized surface functionalities. Direct Laser Interference Patterning (DLIP) has been identified as an outstanding technology for the efficient fabrication of tailored surface structures. This method can show impressive processing speeds (up to 1 m²/min) as well as a superior flexibility in producing extremely versatile surface structures. This work gives an overview about recent developments of the DLIP technology by focusing on the topics: structure flexibility, process productivity, technical implementations and recent examples of achieved surface functionalities.
Rimvydas Venckevičius, Linas Minkevičius, Antanas Reklaitis, Vincas Tamošiūnas, Irmantas Kašalynas, Domas Jokubauskis, Dalius Seliuta, Bogdan Voisiat, Gediminas Račiukaitis, Gintaras Valušis
Convenience in use of room-temperature terahertz (THz) imaging systems, reduction of their dimensions and presence of on-chip solutions remains one of prime interests for direct implementation aims. Solid-state-based solutions in miniaturization of spectroscopic THz imaging systems including novel semiconductor nanostructures bias-free emitters, diffractive THz optics components and their on-chip integration with THz detectors are discussed. In particular, pulsed optoelectronic terahertz emitter based on a δ-doped p-i-n-i GaAs/AlxGa1−xAs heterostructure was studied and it is demonstrated that the heterostructure can serve as efficient antenna- and bias-free surface emitter. Diffractive optics elements – Fresnel zone plates –with integrated band-pass filters were simulated employing Finite-difference time domain method. Structures were fabricated using the laser direct writing and investigated using electronic THz sources and an optically pumped terahertz laser. Advantages of on-chip integration of diffractive optics and bow-tie-shaped InGaAs-based terahertz detectors are revealed via detection enhancement. Bow-tie diodes properties in frequency scale and detection sensitivity are considered and compared for different materials. Homodyne detection and imaging of low-absorbing objects at 0.6 THz are demonstrated and discussed.
Zone plates with integrated band-pass filters and binary Fresnel lenses designed for the THz spectral range were fabricated by direct laser ablation in metal films and the silicon substrate. Results on the process performance and quality of the products are reviewed. The focusing performance was measured using the THz source that produces the 580 GHz radiation. The beam was directed to the centre of the fabricated optical elements. Zone plates with integrated band-pass filters have shown the double performance in focusing and spectral selection. The dependence of ablation rate and surface roughness on the laser process parameters was thoroughly investigated on the silicon. The depth of the ablated grooves linearly depends on the number of laser scans number with a particular slope for each scanning speed. The process regime with the 125 mm/s scanning speed provided the most precise control over the ablation depth. The topography measurements of the laser fabricated multilevel phase zone plates (Fresnel lenses) with the 10 mm focal length showed good agreement with the calculated topography. The intensity distribution of the focus spots using the laser fabricated 2, 4 and 8 level binary Fresnel lenses showed better focusing performance when more depth levels were applied in the lens production.
On-chip integrated solutions employing properties of Fresnel zone plates with integrated band-pass filters for the room temperature terahertz imaging systems are discussed. Finite-difference time-domain simulations were used to predict properties of conventional zone plates and ones with resonant filter areas as flat optics components. They are produced employing the laser direct writing and characterized by electronic THz sources and an optically pumped terahertz laser. It was shown that more than one order of magnitude detection enhancement can be observed of bow-tie-shaped InGaAs-based terahertz detectors by on-chip incorporation of the secondary diffractive optics.
New results on development of the Direct Laser Interference Patterning (DLIP) technique using the interference of several beams to directly ablate the material are presented. The method is capable of producing sub-wavelength features not limited by a beam spot size and is an effective method of forming two-dimensional periodic structures on relatively large area with just a single laser shot. Surface texturing speed of DLIP method and the direct laser writing was compared. Fabrication time reduction up to a few orders of magnitude using DLIP was evaluated. The sub-period scanning technique was applied for formation of the complex periodic structures. A new method of laser scanning for fabrication of periodic structures on large areas without any visible stitching signs between laser irradiation spots was tested.
New wavelengths of laser radiation are of interest for material processing. Results of application of the all-fiber ultrashort pulsed laser emitting in 2 µm range, manufactured by Novae, are presented. Average output power was 4.35 W in a single-spatial-mode beam centered at the 1950 nm wavelength. Pulses duration was 40 ps, and laser operated at 4.2 MHz pulse repetition rate. This performance corresponded to 25 kW of pulse peak power and almost 1 µJ in pulse energy. Material processing was performed using three different focusing lenses (100, 30 and 18 mm) and mechanical stages for the workpiece translation. 2 µm laser radiation is strongly absorbed by some polymers. Swelling of PMMA surface was observed for scanning speed above 5 mm/s using the average power of 3.45 W focused with the 30 mm lens. When scanning speed was reduced below 4 mm/s, ablation of PMMA took place. The swelling of PMMA is a consequence of its melting due to absorbed laser power. Therefore, experiments on butt welding of PMMA and overlapping welding of PMMA with other polymers were performed. Stable joint was achieved for the butt welding of two PMMA blocks with thickness of 5 mm. The laser was used to cut a Kapton film on a paper carrier with the same set-up as previous. The cut width depended on the cutting speed and focusing optics. A perfect cut with a width of 11 µm was achieved at the translation speed of 60 mm/s.
Commercial polycrystalline silicon solar cells were textured by the Laser Beam Interference Ablation technique to produce periodical grating in the antireflective and passivation layer. Modeling of periodical hole arrays and refractive index gratings in the antireflective coating on silicon substrate was used to select the fabrication regime and explain alterations in optical properties of the laser treated samples. Visual and elemental analysis of the laser treated areas was performed as well as measurement of photo-electrical characteristics before and after the laser treatment. Two modification regimes were established: ablation and oxidation of the antireflective layer. Changes in surface structure and composition as well as optical and electrical properties of patterned solar cells are discussed.
Silicon remains as the main material used in solar cell production, because of its low cost, abundance in nature and well-established technologies. However, its surface reflects considerable part of light due to its high refraction index. Light harvesting pays an important role for further progress to high-efficient solar cells. Texturing of the substrate surface is an efficient method to enhance the light absorption leading to the higher solar-to-electricity conversion efficiency in crystalline silicon solar cells. We present the novel method for silicon surface texturing using the direct laser beam interference ablation in addition with selective chemical etching. This technique enables production of high aspect ratio structures on a large surface area with just a single laser exposure. Characterization of the laser textured surfaces was performed using SEM. Theoretical simulation of light interaction with such structures was conducted in parallel and was used to adjust the laser process for more efficient light harvesting.
Metal films on transparent substrates are widely applied for mask production in lithography, and lasers are frequently
used for their patterning. Quality of the patterning is limited by fundamental phenomena taking place close to edges of the laser ablated area. We experimentally and numerically investigated transformations in metal films during their
irradiation with the nanosecond laser beam with fluence above the ablation threshold. Ridges of the resolidified metal with non-uniform thickness were always formed on edges of the cleaned area. Instabilities during the ablation process forced the molten metal in the ridges to break up into droplets with the periodicity predicted by the Plateau–Rayleigh instability. The droplets on ridges were starting points for formation of self-organized lines of metal film by irradiation with partially overlapping laser pulses. The initial droplets and later the self-organized parallel lines of chromium metal were heat sinks that cooled down the metal in their close proximity. Temperature modulation along the laser irradiation spot was high enough to initiate the Marangoni effect which resulted in movement of the molten metal from hot to colder areas.
During the recent few years picosecond lasers have been proved as a reliable tool for microfabrication of diverse
materials. We present results of our research on structuring of thin films and surfaces using the direct laser writing and
the laser beam interference ablation techniques. The processes of micro-pattering were developed for metallic, dielectric
films as well as complex multi-layer structures of thin-film solar cells as a way to manufacture frequency-selective
surfaces, fine optical components and integrated series interconnects for photovoltaics. Technologies of nano-structuring
of surfaces of advanced technical materials such as tungsten carbide were developed using picosecond lasers as well.
Experimental work was supported by modeling and simulation of energy coupling and dissipation inside the layers.
Selectiveness of the ablation process is defined by optical and mechanical properties of the materials, and selection of the
laser wavelength facilitated control of the structuring process. Implementation of the technologies required fine
adjustment of spatial distribution of laser irradiation, therefore both techniques are benefiting from shaping the laser
beam with diffractive optical elements. Utilization of the whole laser energy included beam splitting and multi-beam
processing.
Solid oxide fuel cells (SOFC) are widely studied because of their potential usage in power source applications. At
present huge attention is paid to micro solid oxide fuel cells (μ-SOFC) based on thin film technologies with power
capacity in the range of several watts. Porous nickel is an important part in many types of solid oxide fuel cells. This
work presents experimental results of laser micro-channel formation in the 200 nm thick nickel and platinum films for
the fuel cell membranes. The four-beam interference ablation was applied for fast and parallel formation of microchannel
over a large area in thin metal film on a silicon substrate for μ-SOFC. Using this technique, regularly arranged
circular holes with a period of 4.2 μm were formed in the 200 nm thick nickel and platinum films. The diameter of the
holes ranged from 1.7 to 2.7 μm. The area where holes were ablated by a single laser exposure was approximately
250x250 μm. A silicon substrate was chemically etched from backside to release the patterned nickel film.
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