System of glow discharge spectrometry and in situ measurement of the etching depth of a sample, comprising: - a glow discharge lamp adapted to receive a solid sample and to form a glow discharge etching plasma, the sample having, on a same face, a first zone exposed to the etching plasma and a second zone protected from the etching plasma, the glow discharge lamp being adapted to provide a first optical path towards the first zone and a second optical path towards the second zone of the sample, the discharge lamp includes a cylindrical anode having a first axial opening adapted for the passage of a first incident beam and wherein the anode includes a second opening, offset with respect to the axis of the anode, the second opening being adapted for the passage of a second incident beam; - a spectrometer coupled to the glow discharge lamp, the spectrometer being adapted to measure, as a function the time of exposure of the first zone to said plasma, at least one signal representative of the glow discharge plasma by optical emission spectrometry and/or by mass spectrometry; - a system of in situ measurement of the depth of the erosion crater generated by etching of the first zone of the sample as a function of the time of exposure to said plasma; the system of measurement of the erosion crater depth including: - a light source adapted to emit a light beam; - an optical splitter (3, 13, 23) adapted to spatially or angularly split the light beam into the first incident beam and the second incident beam; - optical means (4, 14, 24) adapted to direct, respectively, the first incident beam towards the first zone along the first optical path and the second incident beam towards the second zone along the second optical path, so as to form a first reflected beam by reflection on the first zone and, respectively, a second reflected beam by reflection on the second zone; - an optical recombination device (3, 13, 23) adapted to recombine the first reflected beam and the second reflected beam and to form an interferometric beam; - detection means (8, 81, 82, 83, 84) adapted to receive the interferometric beam and to detect an interferometric signal as a function of the time of exposure of the first zone to said plasma; - processing means adapted to process the interferometric signal so as to determine the depth (d) of the erosion carter as a function of the time of exposure of the first zone to said plasma. - a glow discharge lamp adapted to receive a solid sample and to form a glow discharge etching plasma, the sample having, on a same face, a first zone exposed to the etching plasma and a second zone protected from the etching plasma, the glow discharge lamp being adapted to provide a first optical path towards the first zone and a second optical path towards the second zone of the sample, the discharge lamp includes a cylindrical anode having a first axial opening adapted for the passage of a first incident beam and wherein the anode includes a second opening, offset with respect to the axis of the anode, the second opening being adapted for the passage of a second incident beam; - a spectrometer coupled to the glow discharge lamp, the spectrometer being adapted to measure, as a function the time of exposure of the first zone to said plasma, at least one signal representative of the glow discharge plasma by optical emission spectrometry and/or by mass spectrometry; - a system of in situ measurement of the depth of the erosion crater generated by etching of the first zone of the sample as a function of the time of exposure to said plasma; - a light source adapted to emit a light beam; - an optical splitter (3, 13, 23) adapted to spatially or angularly split the light beam into the first incident beam and the second incident beam; - optical means (4, 14, 24) adapted to direct, respectively, the first incident beam towards the first zone along the first optical path and the second incident beam towards the second zone along the second optical path, so as to form a first reflected beam by reflection on the first zone and, respectively, a second reflected beam by reflection on the second zone; - an optical recombination device (3, 13, 23) adapted to recombine the first reflected beam and the second reflected beam and to form an interferometric beam; - detection means (8, 81, 82, 83, 84) adapted to receive the interferometric beam and to detect an interferometric signal as a function of the time of exposure of the first zone to said plasma; - processing means adapted to process the interferometric signal so as to determine the depth (d) of the erosion carter as a function of the time of exposure of the first zone to said plasma.