As tensile strength increases, steels tend to react more sensitive to non-metallic inclusions (NMI). Therefore, it is necessary to control the number, size, shape and composition of non-metallic inclusions, the so-called steel cleanness. Common quality assurance methods are mainly focused on inclusions with a size of less than 20 μm and detect larger inclusions only randomly. But just inclusions with a size of more than 20 μm have a devastating effect on the processability of steel and the life cycle of the product. In order to improve process control and quality assurance with regard to the degree of macroscopic and meso-integration, the SILENOS test system was developed by HKM. For this purpose, large format slab and round samples are milled with a defined layer thickness and the respective surface is examined automatically for inclusions. The aim of this thesis is to characterize the performance of the laser spectrometer (LIBS) of the SILENOS test system as well as to test the possibility of error source identification on the basis of a quantitative element determination. After a short general introduction and the description of the process route of steel production at the Hüttenwerken Krupp Mannesmann (HKM), the third chapter of this work briefly explains nonmetallic inclusions, their origin and distinction. This is done especially with respect to the SILENOS test system. The introduction and description of four established methods for determining the steel cleanness follows. An explanation and a comparison of the SILENOS test system, as a new method, is given in the following section. Stereometry is also a section of the chapter, since it is one of the foundations of all test methods. After a first pilot plant of the SILENOS test system has been built in 2015, the current performance and possible improvements of the laser spectrometer are outlined at the beginning of the fourth chapter. Various attempts were made to recognize possible limitations and problems. The visualization of the data generated by the laser spectrometer is also discussed in this chapter. Finally, in the fifth chapter of this thesis, various potential sources of nonmetallic inclusions are investigated with SILENOS and their spectra recorded. One problem was to prepare the samples in such a way that they had to be examined in the laser spectrometer. The recorded spectra are then examined and compared with regard to their suitability for the inclusion classification. The last two chapters give an overview of the results and an outlook on still unresolved questions.