As parts of targets used in laser-matter interaction experiments, hydrocarbon plasma polymerized coatings of thickness between 100 nm and 30 mu m with a smooth surface finish (rms less than or equal to 100 nm) are realized. For this work, a mixture of transbutene and hydrogen with the substrate in or out of the discharge is used in a low frequency (2.4 kHz) plasma reactor. The plasma is characterized by emission spectroscopy and mass spectrometry. The best results are obtained in postdischarge conditions : rms = 18 nm for 2.6 mu m thickness.