I applied online. They initially sent me an online test, similar to an IQ test. After that, I had 3 rounds of online interviews, which were all technical. They have a very specific interview format. They start by introducing themselves, then ask you to introduce yourself. They ask about how to detect light in general, types of detectors, how would you measure a low level signal with a strong DC bias, what lens materials are used in IR etc. The questions gradually evolve into asking how to measure low level signals with a resistive light detector(PbS). What is interesting is they kept asking the same questions over and over again. The difference between different meetings was who was asking the questions. You eventually learn the answers... My interviews went very well and they invited me to their offices in Ludwigshafen. I had another round of the exact same questions, but in-person this time. They also took me in a lab and asked for some simple experimental stuff, like measuring the DC voltage of an adaptor with a multimeter, connecting an optical fiber to a Thorlabs light power meter etc. After the interviews, they said I will be noticed about the final decision within a week. That one week turned into a complete silence for 2 months. I repeatedly asked for an update, but they didn't reply. 2 months later I received a notification that they were not continuing with my application. Keeping me in suspense for 2 months without a notice and not replying to my emails in the meantime tells a lot about the company culture and their lack of respect to people's lives in general.