CW maser with electromagnetic resonant circuit

A maser having an electromagnetic resonant circuit, the electromagnetic resonant circuit of the maser comprising a pick-up coil, a capacitance and a filter coil, an active medium of organic or maser-capable molecules in the pick-up coil as well as a population inversion device for generating a population inversion in the active medium,

• wherein the population inversion device comprises para hydrogen for the generation of the population inversion in the active medium in such a way that the organic or maser-capable molecules can be brought to negative spin temperature.