Ultrashort pulse laser phase transition of 2D MoS2 produced by atomic layer deposition
Malte J. M. J. Becher, Leander Willeke, Martin Wilken, Anjana Devi, Claudia Bock and Andreas Ostendorf

2D materials like transition metal dichalcogenides (TMDCs) are promising for flexible electronic devices. Two-dimensional molybdenum disulfide (2D MoS2), with a two-phase system consisting of a semiconductor phase (2H) with a tunable bandgap up to 1,8 eV and a metastable metallic phase (1T), provide the possibility of in plane edge contacts with low contact resistance. By using ultrashort pulse (usp) lasers, a phase transition from the 1T to the 2H phase is possible. In addition, due to the ‘cold’ energy input, more flexible and temperature-sensitive substrates can be used. In this study MoS2 films were deposited by atomic layer deposition (ALD) on SiO2/Si and flexible glass wafers, intercalated with lithium and processed with an NIR fs-laser (λ = 1030 nm, t = 400 fs) with scanning speeds up to v = 10 mm/s. Raman Spectroscopy is used to confirm the phase transition and investigate the effect of the transformation on the electrical resistance of the MoS2 layer.

_____

Inscription of waveguides and beam splitters in borosilicate glass using a femtosecond laser with a long focal length
Theresa Willburger, Max-Jonathan Kleefoot, Sebastian Funken, Harald Riegel

Femtosecond-laser enable the internal fabrication of photonic components in various materials. The extremely high peak intensity due to the ultrashort pulse width leads to a nonlinear interaction in the focal point, which makes the processing of transparent materials such as glass possible. Nonlinear ionization mechanisms can lead to a local, permanent refractive index change of the material, which opens up a promising potential for the fabrication of integrated optics. If the femtosecond laser, which has a long focal length, is moved precisely relative to the glass sample, it is possible to inscribe three-dimensional geometries directly into glass. Thus, a variety of photonic components such as waveguides, beam splitter and other micro-optical components can be fabricated directly in the volume. In this work, the subsurface inscribed micro-optical structures are investigated and demonstrated as a function of the influencing laser parameters.

Keywords: femtosecond laser; integrated micro-optical components; long focal length; borosilicate glass

_____

Dielectric materials cutting using Bessel beams with a femtosecond laser configured in MHz and GHz burst regimes
Ivan Gusachenko, Pierre Balage, Dmitry Nuzhdin, Mahmoud Ziat, Guillaume Bonamis, Adrien Douard, Gwenn Pallier, Clemens Hönninger, John Lopez, Inka Manek-Hönninger

Ultra-Short Pulse (USP) lasers are nowadays widely used in various industrial applications. Femtosecond lasers, in particular, are largely applied in precise micromachining thanks to their ability to process materials without causing thermal damage. For some applications, burst regimes containing trains of femtosecond pulses are advantageous, for example MHz bursts for dielectrics cutting with tailored Bessel beams. These beams offer an efficient cutting process due to their extended focus depth, which is 100 times longer than that of a standard Gaussian beam. Moreover, the central beam size limit is smaller than the diffraction limit by a factor of 2, thanks to their interference-based generation. In this contribution, we show a study on cutting transparent dielectric materials like glass and sapphire exploring various Bessel beam configurations using different types of axicons with a femtosecond laser operating in eighter MHz or GHz burst regime.

Keywords: Laser; Femtosecond; dielectric; cutting; MPLC; beam shaping; Bessel; axicon; pulse; glass; micromachining

_____

Surface topology and shape investigation of soda-lime glass structured by ultrashort pulsed laser with long focal length
Sebastian Funken, Max-Jonathan Kleefoot, Christian Neusüß, Harald Riegel

In recent years, the use of innovative materials such as glass has become increasingly important, especially to substitute polymers in Lab-on-a-Chip applications. This trend is supported by the growing possibilities of laser material processing with ultrashort pulse lasers. In this work, we present the generation of geometrically defined structures on the surface of soda-lime glass by direct laser ablation as an alternative to laser etching with potassium hydroxide. A femtosecond NIR laser with a long focal length of 100 mm was used. Essential parameter correlations, such as pulse energy to ablation depth or pulse-and-track overlap, were investigated. By using direct laser ablation, the flexibility of scanner-based laser ablation can also be utilized through a depth of approximately 160 μm without refocusing. In this process, a slight ablation depth of roughly 5 micrometers could be achieved, compared to only a few tens of nanometers by the laser-etching process.

Keywords: soda-lime glass; long focal length; structuring; ultrashort pulsed laser; direct writing

_____

Femtosecond laser cleaving of polymers with a non-diffracting beam
Bogusz Stępak, Natalia Grudzień, Dariusz Świerad, Yuriy Stepanenko, Michał Nejbauer

High-quality processing of polymers is one of the most important applications of ultrafast lasers. Heat-sensitive polymers with poor thermal conductivity require an ultrashort pulse duration and reduced repetition rate to minimize a heat-affected zone. Cutting thick polymeric samples is challenging because it often requires multi-contour scanning, which slows down the process and promotes thermal accumulation. This work presents a new approach based on non-diffracting beam cleaving using tailored ultrashort pulses.
Cleaving of different polymers, including poly (l-lactide) and poly (methyl methacrylate), with up to 3 mm thickness and a speed exceeding 0.7 m/s is demonstrated. An essential advantage of processing with a non-diffracting beam is negligible HAZ, kerf reduced to single microns, and no taper. This technique has considerable potential in processing polymer samples for special applications like optics and medical devices where the chemical composition of material during the process cannot be altered.

Keywords: polymer cleaving; femtosecond laser; non-diffracting beam

_____

Time-resolved observation of surface temperature distribution of Silicon irradiated by nanosecond laser pulse using a nanosecond imaging technique
Toshifumi Kikuchi, Reiji Koike, Keita Katayama, Hiroshi Ikenoue, Daisuke Nakamura

In nanosecond pulsed laser processing techniques such as laser annealing and laser doping, the surface temperature of the laser-irradiated area and surrounding area changes on a nanosecond scale, which affecting the processing results. Laser energy and pulse width are especially important parameters in the surface microprocessing of semiconductor materials because they dramatically affect the surface temperature. Therefore, surface temperature measurement with nanosecond time resolution is very effective monitoring technique in order to optimize the laser processing conditions. We have developed an in-situ, non-contact, nanosecond time-resolved and micro-scale spatial resolution temperature measurement system by using a nanosecond gated camera and two-color temperature measurement method. In this study, we estimated nanosecond two-dimensional and time-resolved surface temperature of Si wafer irradiated by nanosecond excimer laser pulse using the measurement system.

Keywords: two-color temperature method; surface temperature measurement; nanosecond time-resolved imaging;

_____

Subtleties of machining silicon for inkjet technology
Cary Addington

We will discuss the subtleties of processing silicon for thermal inkjet print cartridges. Topics will range from selecting the proper light source for wafer marking to obtain required quality. The advantages and process set up conditions for stealth dicing wafers, with a deeper dive into aspects around precision micromachining of long, narrow, high aspect ratio channels. Here, we will review how particular laser beam parameters affect the channel quality and their correlation to removal rates for a particular process. To produce these long, narrow features, an assist process is of utmost importance. Details of why this novel assist process is used will also be covered.

Keywords: Laser processing; Silicon; Ablation; Marking; Stealth Dicing; Micromachining; Assist;