In recent years additive manufacturing technologies have become widely popular. For complex functional components or low volume production of workpieces, laser powder bed fusion can be used. High safety requirements, e.g. in the aerospace sector, demand extensive quality control. Therefore, offline non-destructive testing methods like computed tomography are used after manufacturing. Recently, for enhanced profitability and practicality online non-destructive testing methods, like optical tomography have been developed. This paper discusses the applicability of eddy current testing with magnetoresistive sensors for laser powder bed fusion parts. For this purpose, high spatial resolution giant magnetoresistance arrays are utilized for testing in combination with a single wire excitation coil. A heterodyne principle minimizes metrology efforts. This principle is compared to conventional signal processing in an eddy current testing setup using an aluminum test sample with artificial surface defects. To evaluate the influence of the powder used in the manufacturing process on eddy current testing and vice versa, a laser powder bed fusion mock-up made from stainless steel powder (316L) is used with artificial surface defects down to 100 μm. This laser powder bed fusion specimen was then examined using eddy current testing and the underlying principles.

Rising popularity of additive manufacturing processes leads to an increased interest in possibilities and methods for related process monitoring. Such methods ensure improved process quality and increase the understanding of the manufacturing process, which in turn is the basis for stable component quality, as e.g. required in the aerospace industry or in the medical sector. For laser powder bed fusion a handful of process monitoring tools already exist such as optical tomography, thermography, pyrometry, imaging, or laser power monitoring. Although these tools provide helpful information about the process, more information is required for an accurate in-depth understanding. In this paper, advanced approaches in eddy current testing are combined such as single wire excitation, magnetoresistive sensor arrays, and heterodyning to build up a system that can be used for online process monitoring of laser powder bed fusion. In addition to detailed information about the developed eddy current testing system and underlying signal processing, first results of magnetoresistance based online eddy current testing during the laser powder fusion process are presented. While producing a step shaped cuboid, each layer is tested during recoating. Test results show that not only the contours of the topmost layer are detected but also contours of previous layers covered by powder. At an excitation frequency of 1 MHz, a penetration depth of approx. 400 μm is obtained. To highlight the possibilities of eddy current testing for online process monitoring of laser powder bed fusion, results are compared to post exposure images of the integrated Layer Control System.

We report on the realization of aluminum oxyfluoride thin films and alumina/silica mixture coatings with different ratios by ion beam sputtering. The atomic compositions quantified by energy dispersive x-ray spectroscopy are correlated with the optical properties calculated from spectrophotometry and laser calorimetry measurements. Furthermore, the femtosecond laser damage resistance ($\tau =400\mathrm{fs}$) of single layers is investigated in the infrared at 1030 nm and in the ultraviolet at 343 nm wavelengths. Experimental results on the wavelength scaling of the laser-induced damage threshold for oxyfluoride and oxide composite coatings are presented.

The challenge in rapid production of high-precision optical coatings is the need to realize a variety of complex coating designs in one process environment. Two approaches to enhance a stable deposition process are presented. First, a virtual deposition system is applied for a pre-selection of coating designs that result in increased process stability using optical broadband monitoring strategies. Second, optical broadband monitoring is combined with additional quartz crystal sensors to realize a hybrid process control for improving layer thickness accuracy. Finally, a successful combination of both approaches is demonstrated by comparative studies on virtual and real deposition processes.

Ion beam sputtering was used to produce Polytetrafluoroethylene (PTFE) thin films for optical coatings. We investigate the chemical structure and the optical parameters such as refractive index, absorption and scattering of these films.