NbN thin films are promising candidates for the application in hot electron bolometers and superconducting single photon detectors. Due to the small superconducting band gap, they are very sensitive to electromagnetic radiation down to the terahertz region and processed into narrow lines of several hundred nanometers and exhibit very fast response times to a wide range of frequencies. To further understand and optimize the processes of electron heating and the relaxations via electron and phonon scattering in those films, they are studied in this project in the time domain by means of femtosecond laser pulse irradiation.