How do you convert electromagnetic energy into electromagnetic energy?

To convert electromagnetic energy into electromagnetic energy, one can use devices like antennas or photodetectors. For instance, an antenna can receive radio waves (a form of electromagnetic energy) and convert them into electrical signals, which can then be transmitted as electromagnetic waves again. Similarly, photodetectors convert light (photons) into electrical signals, which can be modulated and re-emitted as electromagnetic energy in different forms, such as lasers or radio transmissions. Essentially, the conversion process involves changing the form or frequency of the electromagnetic energy while retaining its fundamental nature.