Narrow dry deep-etched quantum well wires are investigated by Raman scattering (RS) and far infrared (FIR) magnetotransmission experiments. Plasmons and magnetoplasmons dispersions are measured and analysed to extract information about confinement potential, electron density, sidewalls trapped electron density and depletion length of the quasi-one-dimensional electron gas. From RS results, we demonstrate the abruptness of the equilibrium density profile. The corresponding depletion length (200 9) is significantly smaller than the one obtained from FIR measurements (750 9) because of the strong illumination.