At the Electric Arc Furnace of the Steel and Rolling Mill Marienhütte GesmbH the first laser-based in-situ offgas measurement system LINDARC is installed. The target of this thesis was to investigate the control of the post-combustion in the furnace by using continuous and real-time offgas measurements. A dynamic closed-loop-control of the post-combustion system based on the CO/O2-ratio was developed. The laser lacks the information of the H2 and CH4 content in the offgas. Comparing measurements with a conventional extractive system in the elbow and at the end of the offgas duct were performed. The results of the laser-based measurements corresponded well to the conventionally measured result. Furthermore a good correlation between CO, H2 and CH4 was found. Based on these results a laser-based control was realised. The energy efficiency of the varied operation practices was evaluated by using a statistical model. With the thermodynamic program HSC a comprehensive energy and mass balance was generated. The optimization of the post-combustion system and of the burner and lancing practice increased productivity by more than 5 % and reduced the consumption of electrical energy by 6 %.