Different methods for generation of laser radiation in the wavelengthband between 2 and 5 µm have been investigated. Two main methods with OPO seem possible. One method is to use ZnGeP2 that can work in the entire wavelengthband but puts high demands on the pump source. The second method is to use periodically poled LiNbO3 that can be pumped with a simpler laser but can only generate radiation below ca 4 µm. A fiberlaser, with an output wavelength of 1940 nm and a 10 kHz pulse repetition frequency, designated to pump an OPO with ZnGeP2 was evaluated. The wavelength conversion failed since the performance of the fiberlaser did not fulfil the promised specification. A tuneable conversion of a 2 µm pump wavelenght to radiation between 3 and 5 µm succeeded with another kind of pump laser with a pulse repetition frequency of 10-20 Hz and higher pulse energy. Work with the second concept, to convert 1064 nm from an Nd:YVO4 laser with high pulse repetition frequency with periodically poled LiNbO3 to between 2.3 and 3.5 µm, has been initiated.