We generalize the well-known method of generating nondiffracting beams based on axicons in the near-field using phase modulations with azimuthal dependencies. The enormous benefit of our concept for efficient shaping of nondiffracting beams with arbitrary transverse profiles is shown and optimized processes like cleaving of particularly thin and thick glasses using elliptical Bessel-like beams are discussed.

The modification of transparent materials is enabled by focused ultrashort laser pulses. Single pass processing up to several millimeters can be achieved by the usage of elongated beam profiles. We studied the mechanical separability in dependence of the material thickness. As simulations show, asymmetric beam profiles can cause modifications with preferential direction reducing the necessary breaking force. Pump-probe microscopy is implemented to examine the laser-matter-interaction. We present a measured 3D-reconstruction of the transient interaction inside the material and elucidate the desired crack formation. We demonstrate beam shaping concepts to create a new, efficient and robust class of Bessel-like beams, which can be used to achieve a preferred crack direction. We verify the concept by modification and separation of silicate glasses.

Companies analyse large amounts of data on clusters of machines, using big data analytic tools such as Apache Spark and Apache Flink to analyse the data. Big data analytic tools are mainly tested regarding speed and reliability. Efforts about Security and thus authentication are spent only at second glance. In such big data analytic tools, authentication is achieved with the help of the Kerberos protocol that is basically built as authentication on top of big data analytic tools. However, Kerberos is vulnerable to attacks, and it lacks providing high availability when users are all over the world. To improve the authentication, this work presents first an analysis of the authentication in Hadoop and the data analytic tools. Second, we propose a concept to deploy Transport Layer Security (TLS) not only for the security of data transportation but as well for authentication within the big data tools. This is done by establishing the connections using certificates with a short lifetime. The proof of concept is realized in Apache Spark, where Kerberos is replaced by the method proposed. We deploy new short living certificates for authentication that are less vulnerable to abuse. With our approach the requirements of the industry regarding multi-factor authentication and scalability are met.

In continuous wave keyhole-mode laser welding of high strength steel alloys hot cracking can occur. The hot crack susceptibility depends on the mutual interaction of several factors like the welding parameters, the alloy composition and the weld fixturing. In this paper we focus on the influence of the welding parameters and investigate the dependency of the laser power, the welding speed and the laser wavelength on the crack formation. X-ray images are used to visualize the hot crack patterns, which exhibit a pronounced periodicity. To influence the hot crack formation, the incident energy input into the process was adapted. For specific welding parameters, we show exemplarily the prevention of hot cracking by the use of a twin-spot optics.

For keyhole laser welding of tempered steel, we show that the characteristic formation of eddies in the melt flow significantly depends on the focal position. The local melt flow velocities and accelerations were analyzed in-situ by means of x-ray imaging. It was observed that the keyhole geometry as well as the direction of rotation of the eddy close to the weld pool surface changes when the focal-position is shifted by one Rayleigh length.

In view of the importance of partially softened areas in automotive body components made of press hardened boron steel, further process developments were carried out to improve the heat treating process by means of laser as presented previously [1]. The main issue was to increase the laser-annealed area of the surface in a certain time step. The following report shows that a significant reduction in process time can be achieved when specially designed optics for the laser softening process are used. Due to a highly homogeneous intensity profile of the laser beam and a thus well defined energy deposition into the metal surface, the hardness of the hot formed material can be reduced to values comparable to the thermally untreated material. Hence, applications like e.g. small flaps as mechanical supports in the assembly line, soft areas for rivet points to facilitate joining operations and ductile flange areas or complex 3D-contours to improve crash performance can be realized.In this paper, first, new approaches for the movements of the laser beam to distribute the heat on the surface of the work piece are presented. Second, in-situ pyrometric measurements of the surface temperature in the working field enable a fully closed-loop control and consequently a stable behavior of the annealing process. Third, innovative concepts, which promote high flexibility for the part designs, to integrate the strategies for the softening process into the existing machine systems and into the corresponding workflow of the production line for hot sheet metal forming are shown.

Tempered steel is used in many automotive and aviation parts due to its beneficial material properties such as the combination of high tensile and fatigue strength. Therefore, steel grades like e.g. 42CrMoS4 are used for steering knuckles, axles, connecting rods, drive shafts, pinions, gearwheels, pistons and other highly stressed components (Key to Steel, 2007). Laser welding such parts has the advantage of high welding speed, low heat input, low distortion and high weld seam quality (Huegel and Graf, 2014). However, seam defects may occur which reduce weld seam strength. In that respect, hot cracks are severe weld defects which are not tolerated, according to ISO 13919-1. In general hot crack formation depends on three factors affecting each other (Cross, 2005): energy deposition into the part (heat input; welding parameters), part design (geometry; restraining conditions) and material properties (solidification temperature range). To separate the influence of the above-mentioned factors welding experiments were conducted with varying parameters including beam focusing, beam quality and laser power for partial or full penetration depth. Examining the welding process was done by means of 2D x-ray inspection and longitudinal respective transversal cross sections. In this paper the analysis of continuous crack formation within laser welds in tempered steel will be presented. Additionally, possibilities to reduce and even avoid such severe seam defects will be discussed. Moreover, a new approach of explanation for the formation mechanism of transverse hot cracks will be presented.

Press hardened Boron steel is still gaining importance for automotive body parts because of its advantageous material properties. For forming and hardening the flat metal sheets are heated up to Austenite temperature, transferred to the dye, high speed formed and hardened - while cooling down within the forming tool [1]. This process leads to high strength properties of about 1500 MPa and is used for weight reduction purposes in car design [2]. The combination of heat treatment and forming is also strongly influenced by the cooling gradients within the forming tool. High cooling gradients lead to bainitic and martensitic structure formation - structure parts which show high hardness [3].Car manufacturers look into the application of flaps and cutouts in the design of car body parts. Using flaps within the assembly process would be helpful for part-positioning. Cutouts are used to create pull-throughs with smoothed, rounded edges. The global high hardness has to be reduced in those specific areas in the press hardened part to fulfill their intended task. Implementing this softening process into the forming and heat treatment is complex due to the high temperature differences [4] and cost intensive due to energy costs. TRUMPF as a Laser and Machine Tools manufacturer has developed a heat treating process to reduce hardness in those specific areas of automotive parts. Laser cutting of press hardened automotive body parts, e.g. B-Pillars, is a state of the art process at high production volumes [5]. Besides laser cutting process, a softening process can be applied to the parts with the same machine system, using the same Laser and Laser process head. Due to the defined energy deposition by the Laser, hardness can be reduced more than 50% within seconds with transition zones smaller than 15 mm to the non treated material.This paper shows the Laser softening process steps for diverse purposes and applications e.g. a bending or forming operation is possible without cracks in the flap. Furthermore, in some small areas on the flange, which have to be ductile in a crash situation to absorb kinetic energy, hardness can be reduced the same way.

3D models and applications are of utmost interest in both science and industry. With the increment of their usage, their number and thereby the challenge to correctly identify them increases. Content identification is commonly done by cryptographic hashes. However, they fail as a solution in application scenarios such as computer aided design (CAD), scientific visualization or video games, because even the smallest alteration of the 3D model, e. g. conversion or compression operations, massively changes the cryptographic hash as well. Therefore, this work presents a robust hashing algorithm for 3D mesh data. The algorithm applies several different bit extraction methods. They are built to resist desired alterations of the model as well as malicious attacks intending to prevent correct allocation. The different bit extraction methods are tested against each other and, as far as possible, the hashing algorithm is compared to the state of the art. The parameters tested are robustness, security and runtime performance as well as False Acceptance Rate (FAR) and False Rejection Rate (FRR), also the probability calculation of hash collision is included. The introduced hashing algorithm is kept adaptive e. g. in hash length, to serve as a proper tool for all applications in practice.

Digital watermarking is a promising solution to video game piracy. In this paper, based on the analysis of special challenges and requirements in terms of watermarking textures in video games, a novel watermarking scheme for DDS textures in video games is proposed. To meet the performance requirements in video game applications, the proposed algorithm embeds the watermark message directly in the compressed stream in DDS files and can be straightforwardly applied in watermark container technique for real-time embedding. Furthermore, the embedding approach achieves high watermark payload to handle collusion secure fingerprinting codes with extreme length. Hence, the scheme is resistant to collusion attacks, which is indispensable in video game applications. The proposed scheme is evaluated in aspects of transparency, robustness, security and performance. Especially, in addition to classical objective

The publishers of video games suffer from illegal piracy and information leakage caused by end-consumers, "release groups" or insiders shortly after or even before the official release of a new video game. Mechanisms to prevent or at least postpone this illegal redistribution are DRM or copy protection mechanisms. However, these mechanisms are very unpopular, because they restrict the customers in playing the game and demand a high administration effort from the developers and/or distributors. Even worse, most copy protection mechanisms have proven to be insecure as "patches" for circumvention usually are available quickly and easy to get. To satisfy the challenges of security and usability, this work introduces the idea of using digital watermarking to protect all available and suitable media types and software binaries contained in a video game. A three-layered watermarking deployment approach along the production chain is proposed to detect leakage in the release phase as well as during the development process of a boxed video game. The proposed approach features both copyright watermarking and collusion secure fingerprints embedded as transaction watermark messages in components of video games. We discuss the corresponding new challenges and opportunities. In addition, a prototype watermarking algorithm is presented to demonstrate the adaption necessity of classical image watermarking when applied to video games to satisfy the requirements for transparency, security as well as performance. The watermark capacity is significantly increased while inter-media and inter-file embedding is enabled and the associated synchronization challenge is solved by robust hashes.

This paper proposes a novel digital watermarking algorithm for 3D mesh models that, while developed with focus on video games, operates on a generalized mesh model representation. It combines spectral mesh compression with modifications of the vertex norm distribution in the spatial domain. Furthermore, it uses an optimizer based on evolutionary strategies in order to find the best embedding for the individual 3D model and watermark message. The proposed method is a blind or oblivious watermarking scheme and the embedding is dependent on a secret key. Results from a currently top-selling video game show that the proposed scheme provides satisfactory robustness against various transformations while also retaining good visual quality.

Digital transaction watermarking today is a widely accepted mechanism to discourage illegal distribution of multimedia. The transaction watermark is a user-specific message that is embedded in all copies of one content and thus makes it individual. Therewith it allows to trace back copyright infringements. One major threat on transaction watermarking are collusion attacks. Here, multiple individualized copies of the work are compared and/or combined to attack the integrity or availability of the embedded watermark message. One solution to counter such attacks are mathematical codes called collusion secure fingerprinting codes. Problems arise when applying such codes to multimedia files with small payload, e.g. short audio tracks or images. Therefore the code length has to be shortened which increases the error rates and/or the effort of the tracing algorithm. In this work we propose an approach whether to use as an addition to probabilistic fingerprinting codes for a reduction of the effort and increment of security, as well as a new separate method providing shorter codes at a very fast and high accurate tracing algorithm.

Digital transaction watermarking today is a widely accepted mechanism to trace back copyright infringements. Here, copies of a work are individualized by embedding user-specific watermark messages. One major threat on transaction watermarking are collusion attacks. Here, multiple individualized copies of the work are compared and/or combined to attack the integrity or availability of the embedded watermark message. In this work, we show how Patchwork embedding can be adapted to provide a maximum of resistance against collusion attacks at reduced payload and improved robustness.

Digital transaction watermarking today is a widely accepted mechanism in multimedia security. Here, copies of one work are distributed with individual markings. One major threat on transaction watermarking are collusion attacks. Here multiple individualized copies of the work are mixed in order to create a counterfeited or undetectable watermark. One common countermeasure is the usage of so-called fingerprint codes. The important challenge is to provide fingerprints which are highly secure, reliable and, at the same time, provide a sufficiently compact code length according to the typical payload limitations of common watermarking algorithms. We present an approach that is collusion-secure against two colluders based on special conditions on the Hamming distances between the user fingerprint. Theoretical and empirical analysis shows that our approach provides the false positive rate to be zero although the false negatives remain similar to other approaches in the literature. The respective code length remains smaller than 100 bit such that our approach is applicable in transaction watermarking scenarios.