Method for determining a central wavelength of a spectral line with high accuracy and associated system

A system for measuring a central wavelength of interest (λc) of a spectral line of interest (RSe) measured by a spectrometer, the spectral line of interest corresponding to an emission or an absorption of a sample (Ech) to be characterized, the spectral line of interest having either a bell profile, with said central wavelength of interest then corresponding to the vertex of said bell profile, or a double bell profile, with said central wavelength of interest then corresponding to the trough between the two bells, the measurement system comprising:

• a detection system comprising a spectrometer (Spectro) associated with a detector (Det) comprising a plurality of pixels (Pi) aligned in a direction X, the spectral line of interest being detected on pixels of the detector;
• the system being configured so that the detector detects:
• at a time t1, a first reference measured profile (PS1ref) derived from a reference source (Sref), the reference source (Sref) having a reference spectral line (RSref) having a central wavelength, called reference central wavelength, of known value (λref), the reference wavelength being selected so as to be detected on at least one pixel of the detector;
• then, at a time t0, a measured profile of interest (PSech) derived from said sample of interest;
• then, at a time t2, a second reference measured profile (PS2ref) derived from the reference source (Sref);
• the system further comprising a processing unit (UT) configured to:
• process said first and second reference measured profiles so as to determine a first (P1ref) and a second (P2ref) reference position of the reference wavelength, and process the measured profile of interest so as to determine a position of interest (Pech) of the central wavelength;
• determine a reference position, called intermediate reference position (P0ref), at the time t0 by interpolation, based on the first and second reference positions, and based on a linear variation law of the reference position as a function of time between the times t1 and t2;
• determine a value of the central wavelength of interest based on a difference between said positions of interest (Pech) and intermediate reference positions (P0ref), on said known value of the reference wavelength and on a linear dispersion (DL) of the detection system.