The invention is a THz waveguide source (3) having a core (9) of great nonlinear coefficient and of a great absorption. The source (3) is adapted to behave as a waveguide in pumping and also in THz range. The THz waveguide source (3) has a cladding of smaller absorption coefficient in the THz range than that of the core. The solution according to the invention diminishes the influence of absorption, while enhances efficiency of generating THz radiation. The waveguide structure and the tilted pulse front excitation together results a greater interaction length and thus a greater THz generating efficiency. According to the solution of the invention highly efficient compact THz waveguide sources can be realized.