Processing of Transparent Materials (LiM 2019)

Massive Parallelization of Laser Beams with Diffractive Optical Elements for High Speed Two Photon Polymerization
Francisco J. Gontad, Sara M. Vidal, Nerea Otero-Ramudo, Pablo M. Romero-Romero

Repetitive patterns were fabricated by parallel two photon induced photopolymerization (TPP) on Ormocomp®
photoresist. Large patterns were created in one single step of microfabrication by dividing the original laser beam into
51×51 and 101×101 parallel beams using Diffractive Optical Elements (DOEs). A femtosecond pulsed laser, with a
wavelength of 515 nm, was used in order to provide enough peak power to induce TPP within every single parallel
beam. In this way, arrays of micron-sized cones were successfully fabricated in the resin using 0.3 W. However, the
proximity effect limited the maximum number of parallel structures that could be fabricated simultaneously. Still, a very
high fabrication throughput was achieved.


Advanced spatial and temporal shaping for glass cutting application
Konstantin Mishchik, Martin Delaigue, Clemens Hönninger, Eric Mottay

The use of ultrashort lasers combined with Bessel-like beams is becoming an attractive method for glass cutting as
process speed and quality constantly improve. Laser technology potentially offers cutting of the arbitrary complex
shapes even for thick glasses. By combining non-diffractive beam shapes and femtosecond bursts it is possible to
generate crack along the laser trajectory which enables glass cleaving with minimal mechanical force. We show that
flexible optimization of the burst parameters allows to maximize the crack length, which improves the throughput and
minimizes damage while cutting glasses up to 3mm thickness in a single pass.

Keywords: Laser marials processing; Glass processing;In-volume modification; Beam shaping


Creation of Smooth and Flat Surface in Micro-machining of Monocrystalline Diamond by Pulsed Laser
Yasuhiro Okamoto, Takahiro Shimose, Atuya Kajitani, Akira Okada

Both picosecond and nanosecond pulsed lasers enable unique process to obtain smooth and flat surfaces of Ib type
monocrystalline diamond. Picosecond pulsed laser can achieve flat and smooth surface of Ra=0.2 μm at a certain overlap
rate of laser shot. This process is mostly performed by series of crack propagation in parallel direction to top surface of
diamond, and laser scanning area can keep diamond structure. On the other hand, combination of nanosecond pulsed
laser and acid cleaning can perform shiny and flat surface in parallel direction to top surface of diamond at the
transitional region of removal of diamond. Its surface roughness is smaller than Ra=0.2 μm, and Raman spectroscopy
analysis shows glassy carbon structure of processed surface. Combination of these phenomena would contribute shape
creation processes of diamond.

Keywords: monocrystalline diamond; micro machining; smooth surface; pulsed laser


Generation of internal 3D microfluidic architectures in polymers by fs laser processing
Gian-Luca Roth, Bastian Wolf, Cemal Esen, Ralf Hellmann

Microfluidic lab on chip systems require components to transport, mix, separate and analyse small volumes of different
fluids. In this study, we report on the laser generation of internal hollow architectures created by focused 514 nm
femtosecond laser pulses inside PMMA bulk material. Size and cross-sectional shape of a single internal generated
microchannel are determined by the intensity distribution inside the focal voxel and can be controlled either by the
numerical aperture of the focusing objective or by laser beam shaping. As both approaches are practically limited with
respect to the realizable cross-sectional shapes, we present a process based on an internal hatching to expand the
achievable channel cross-sections and thereby enable the possibility to create complex 3D shaped internal structures.
This process is applied to create fully internal functional microfluidic elements such as mixers which are part of most
polymer lab-on-chip systems.

Keywords: laser materials processing; polymer; ultrashort pulse; microfluidics; hollow microchannels


Ultrafast Laser Ablation of Transparent Ceramics: The Role of the Pulse Duration on the Ablation Mechanisms
C. Kalupka, M. Schmalstieg

In recent years, novel transparent ceramics have been developed which combine advantages of high mechanical
strength and thermal capacity with optical transparency and a high refractive index. For this new material class,
conventional processing is a major challenge in particular due to the hardness, therefore ultrashort pulse processing is a
promising technique for high precision and efficient machining of the transparent ceramics. In this study, we report on
the surface laser ablation of three different ceramics – spinel MgAl2O4, aluminum oxide Al2O3, zirconium oxide ZrO2 –
with ultrashort laser pulses. In particular, we vary the pulse energy and the pulse duration from 100 fs up to 10 ps to
investigate the impact of temporal intensity distribution on the ablation mechanism and result. We combine ex situ
investigations of the processed areas with in situ ultrafast pump probe microscopy therefore enabling an extensive study
of the underlying ablation mechanisms.

Keywords: ultrashort pulse processing ; transparent ceramics ; surface ablation ; pulse duration ; ablation mechanism


Ultrafast laser manufacturing of glass microfluidic devices
Krystian L. Wlodarczyk, Richard M. Carter, Omid Shahrokhi, Rumbidzai A. E. Nhunduru,Amir Jahanbakhsh, Duncan P. Hand, M. Mercedes Maroto-Valer

Microfluidic devices can be manufactured from a variety of materials, such as glass, plastics, photoresist or silicon. In
many cases, glass is preferred to the other materials, in particular when a microfluidic device must sustain high
pressures, be fully transparent, and remain chemically inert to injected fluids. Unfortunately, conventional
manufacturing of glass microfluidic devices is a complex, time-consuming, multi-step process that involves the
combination of photolithography, etching and bonding. In this paper, we present a different approach for the fabrication
of glass microfluidic devices. Here, a picosecond laser is the only tool used to manufacture the entire microfluidic device.
It is used for: (i) drilling the inlet/outlet ports, (ii) generating a microfluidic pattern directly on the glass surface, and (iii)
enclosing a microfluidic pattern by welding the glass cover. The whole manufacturing process can be completed within 2
hours, making this method suitable for rapid prototyping of fully-functional microfluidic devices.

Keywords: Microfluidic devices; ultrafast lasers; laser ablation; laser welding; glass;


Direct Fabrication of Micro Lens Arrays by CO2-Lasers
T. Schmidt, D. Conrad, A. Kobylinskiy, M. Kahle

The presented project, promoted by the Federal Ministry for Economic Affairs and Energy (MF160094), shows a new
way of fabricating micro-optics, especially micro lens arrays (MLA’s) with lens heights up to several hundreds of
micrometers. Existing methods of MLA fabrication will be compared to the new approach and applications will be
shown. A short pulse CO2-laser system is used for the processing, which allows pulse lengths down to 200 ns. In
combination with a common galvo-scanner system, the micro lenses are preformed within a very short time, by an
ablation process. Here, different lens diameters, lens radii and array sizes can be produced. In a second step, the MLA is
fire-polished with the same laser source. For this process step the laser is switched to cw-mode and the scanner moves
in a defocused position. The preformed lenses melt and get a defined radius as a result of the surface tension of the
molten glass. Measurements of the resulting geometry are be presented. The results show, that the laser based micro
lens array fabrication process has a high reproducibility, very high flexibility, short processing times and can used with
different glasses like borosilicate, soda lime or fused silica.

Micro processing; Processing of Transparent Materials; Surface functionalization; Glass; CO2-laser; Micro lens arrays


Reflective pump-probe microscopy of ultrashort laser pulses: Energy deposition of burst pulses in alkali aluminosilicate glass
Martin Kratz, Christian Kalupka, Franca auf der Heiden, Stefan Quach

The application of ultrashort laser pulses for processing of wide bandgap materials like glasses is a promising approach in
the glass and semi-conductor industry. Burst pulses have been identified as a key parameter for improving processes like
glass-cutting, surface structuring or involume modification. Undesired damages in the modification region leading to
mechanical stresses, chipping and crack formation are challenging problems. To generate a deeper insight of damage
mechanisms, we investigate the energy deposition using bursts of ultrashort laser pulses in alkali aluminosilicate glass.
The electronic excitation and energy deposition is analyzed in situ during the first 24 ps after illumination by ultrafast
pump-probe microscopy. With an advanced experimental setup, we are able to vary the pulse energy and the temporal
shift between subsequent pulses in a burst train of two pulses. The results of burst pulse processing are compared to
single pulse processing to expose different energy deposition due to the temporal proximity of bursts.

Keywords: ultrashort pulsed laser; pump-probe microscopy; non-linear absorption; microfabrication of glass; burst processing


PDMS laser Thermal Processing for Fabrication of 3D micro structure
Mohammadreza Riahi, Atefeh Ghaffari, Fatemeh Karimi

In this article 3D printing of structures with a new method called selective laser baking (SLB) of PDMS is presented.
PDMS Base is mixed with its hardener and poured into a container. Before it is hardened which occurs after several
hours, a CO2 laser selectively exposes different areas on the surface of the PDMS mixture according to the pattern of a
slice of a 3D model designed on the computer. Once exposed, PDMS heats up and hardens, producing a cured layer of
PDMS which is attached to a base. The base lowers in the container and a new layer of uncured PDMS is spread it. The
laser exposes new areas again and hardens them. This process is repeated until the whole structure is fabricated.

Keywords: CO2 laser; 3D printing ; PDMS; Baking.


Selective ultrashort laser fabrication of thick and thin volume-phase gratings
Julen J. Azkona, Miguel Martínez-Calderon, Mikel Gómez-Aranzadi, Ainara Rodríguez, Santiago M. Olaizola

Volume-phase gratings (VPGs) are fabricated in CdSxSe1-x quantum dot doped borosilicate glass at different repetition
rates. As the heat accumulation effects caused by the repetition rate lead to changes in the diameter of the modified
volume (from 1 to 10 μm), the selective fabrication of thick or thin gratings can be benefitted when the different
repetition rates are exploited. Microscope images of the cross-sections of the laser modified zone at different inscription
distances from the surface, repetion rates and pulse energies are presented. From this images, widths and thicknesses
have been measured. Diffraction properties of VPGs fabricated at different pulse energies have been studied. We
present results on the far-field diffraction efficiencies and the near-field light intensity distribution (Talbot effect).

Keywords: Laser material processing, Ultrashort laser, Integrated Optics Devices, Volume-Phase Gratings, Near-field diffraction, Talbot


Water film assisted picosecond laser ablation of glasses
Edgaras Markauskas, Paulius Gecys, Gediminas Raciukaitis

Ultrashort-pulsed lasers have become a promising tool for fast and high-quality processing of glasses. Rear side drilling
and crack generation in the bulk of the glass material are the two technologies promising the fastest processing of
glasses. However, both suffer when optical glasses coated with laser wavelength matching mirrors are needed to be cut
out into smaller-sized optical elements. This paper investigate
d the laser cutting experiments in SF6 glass plates in
ambient air and water assisted conditions
. For such task a high pulse repetition rate laser with the pulse duration of
13 ps and the radiation wavelength of 1064 nm was utilised in the experiments
. Glass cutting quality and ablation rates
were thoroughly investigated. Water-assisted direct glass ablation significantly improved the processing quality and
ablation rates compared to the laser cuts performed in ambient air.

Keywords: water-assisted; picosecond; glass; ablation; cutting;


Complete manufacturing of microfluidics chip with only one ultra-short pulsed laser
Marc Décultot, Anne Henrotin, Jérôme Patars, Jose Antonio Ramos-de-Campos

The microfluidics field is knowing an important expansion and this is due mainly to its various possibilities in the study of
chemical and biological reactions with only few consumables. To follow this growth, researchers and industrials need
accurate manufacturing tools more flexible, and able to offer the best efficiency for microfluidics chips. In this study we
have developed a new methodology based on an ultra-short pulsed laser in order to fulfil these objectives. Thanks to the
accuracy of the laser machine and the physical properties of ultra-short pulsed laser, we have developed a flexible
solution giving the opportunity to adapt the design for each chip, easily and in an unlimited way, while respecting the
microfluidics expectations. Furthermore, to achieve a complete, hermetical, and resistant welding of microfluidics chips,
this study presents a new methodology, based on the same ultra-short pulsed laser and machine combined with a new
contact free clamping system.

Keywords: ultra-short pulsed laser; micro-machining; welding; transparent polymer; microfluidics


Precision laser cutting of glass for industrial applications in 2 & 3D
S. Höhm, R. Terbrüggen, U. Stute, H. Kiessling

The increasing demand of fast cutting solutions for complex shapes on a variety of transparent and brittle materials in
consumer electronics, automotive and semiconductor industry can be successfully addressed by laser cutting
technology. A stable optical confinement (proven in 24/7 production) can be realized by the presented approach based
on non-diffractive beams and the use of ultrashort pulsed lasers. The nonlinear interaction induces a localized material
modification rather than material removal like ablation processes, resulting in very high quality laser cuts. Trends in
automotive interior design and function are calling for 3D shaped glass. The use of laser will significantly improve the
way 3D formed parts are being processed as laser cutting by itself is contactless and offers outmost flexibility. Most
recently Corning’s unique zero gap process for freeform laser cutting was expanded towards 3D cutting of glass, showing
promising results and fulfilling the requirements for industrial implementation.

Keywords: Laser cutting of glass; ultrafast non-diffractive beam; ultrashort laser material processing


Selective etching of sapphire and fused silica by double pulse femtosecond laser radiation
Valdemar Stankevic, Jonas Karosas, Gediminas Raciukaitis

During the few past years, the laser processing of transparent materials has attracted more and more demand. The new
approaches that can improve the processing efficiency and elucidate unexplained mechanisms are required. The
femtosecond laser-induced selective etching (FLSE) is a promising technology for a wide range of optical mechanical and
microfluidic applications. It is already investigated various etching dependences, and significant optimisations are done.
The most used material for chemical etching is fused silica. However, there are some limitations like position dependent
etching, low processing speed etc. Recently introduced double-pulse processing attracted a lot of attention in the field of
direct materials ablation as a technology that can discover the ultrafast pulse-ablation dynamics. In this work, we
investigate in details the double-pulse processing approach for microchannels formation in fused silica and sapphire with
crossed polarisations. We demonstrate the pulse delay influence on the etching rate inside the fused silica. The etching
rate improvement comparing to the single pulse FLSE technology is demonstrated, and the recording speed of the
microchannels is tending to be increased.

Keywords: Double pulse; femtosecond; chemical etching; fused silica; sapphire


Subsurface modification of semiconductor materials by laser nanosecond pulseswith a wavelength from tail of the absorption edge
A. Grigorev

The results are presented of numerical and experimental investigation of modifying transparent semiconductors
structure induced by focusing into the material the nanosecond laser pulsed with a wavelength at the edge of intrinsic
absorption band. The modification process is based on the thermal shifting of the absorption edge and increasing the
radiation absorption in the focal area that, in turn, results in a local heating and modifying the material structure. It was
obtained, when focusing nanosecond laser pulses into a transparent semiconductor, the following structural changes
may occur: point-type and line-type modifications. Depending on the energy, duration and parameters of the laser pulse
focusing, the first or second modification type can appear.

Keywords: semiconductor materials; absorption edge; laser processing


Selective laser ablation of transparent flexible bi-layer foils
T. Delgado, S.M. Vidal, N. Otero, P. Romero

Flexible electronics is an emerging industry, which requires of a further improvement of specific manufacturing
technologies to process plastic electronic materials. PET-ITO bi-material foils constitute one of the most common
transparent flexible substrates used today in flexible electronics. In this work, we report on the capabilities of a laser
ablation process for micromachining and structuring flexible bi-layer PET-ITO substrates. In particular, a femtosecond
pulsed laser has been employed in order to engrave microchannels with geometrical features in the range of tens of
microns on the PET substrate and to selectively eliminate the ITO coating.

Keywords: Laser ablation; femtosecond; transparent flexible electronics; PET-ITO; micromachining;


Glass processing with different techniques
Juozas Dudutis, Jokubas Pipiras, Paulius Gecys

Precision, speed and quality makes laser glass processing a very attractive technique for industry. However, other
conventional technologies such as mechanical dicing (score and brake method), diamond saw and water jet cutting are
widely used in industry. For this, we conducted a comprehensive investigation to validate the laser based technology
processing in respect to conventional technologies. Two laser glass processing techniques were investigated – rear side
glass processing with tightly focused nanosecond laser pulses and sub-nanosecond laser dicing with Bessel beam.
Furthermore, three conventional glass processing technologies were also considered diamond saw cutting, mechanical
dicing and water jet cutting. Sample processing speed, quality and component resistance to the mechanical load was
investigated. In this work, in-depth investigation of these effects will be introduced.

Keywords: Glass; laser processing; Bessel beam; mechanical processing; water jet processing;


Fs laser micromachining applied to the manufacturing of glass-based devices
A. Champion, A. Henrottin, D. Bruneel, J. A. Ramos-de-Campos, A. Kupisiewicz

Micromachining of glass using femtosecond laser is used in different fields such as micro-fluidic, smartphone and
automotive. The interaction between laser and glass leads to different effects such as volume variation leading to stress,
melting and ablation at the focus point. These effects can be controlled with the laser parameters and allow to weld, to
make channels and to cut the glass along thin and accurate patterns. In this work we present different applications in
glass. At first, glass cutting of plates along curved pattern by controlling cracks propagation. Then channels are engraved
on the surface of the glass using ablation process. To finish, welding of channels in glass is studied targeting applications
for micro-fluidic devices.

Keywords: Femto Second Laser, Welding, Cutting, Micromachining;


Correlation between Joint Strength and Process Temperature in Quasi-Simultaneous Laser Transmission Welding of Polyamide 6
Anton Schmailzl, Benjamin Quandt, Stefan Hierl, Michael Schmidt

The joint strength is gaining importance in quasi-simultaneous laser transmission welds, especially in structural
components. A correlation between the joint strength and a process characteristic is a basic requirement for selecting
the best process parameter setting. In this work, the temperature is measured during welding polyamide 6 by using a
scanner-integrated pyrometer with an InGaAs-detector. The filtering of the heat radiation in the upper joining partner is
taken into account by calibrating the measurement system. By this, the measured temperature signal represents the
temperature in the joining zone. A correlation is found between the measured temperature and the resulting joint
strength. Moreover, high joint strengths are also seen for welds with short welding times, as far as the temperature is
sufficiently high. With this knowledge, a process window can be derived easily in order to produce welds with high
strength and short welding times.

Keywords: laser transmission welding, pyrometer, temperature, joint strength, welding time;