Abstract: A method for the wavelength calibration of echelle spectra, in which the wavelengths are distributed across number of orders is characterised by the steps: recording of a line-rich reference spectrum with known wavelengths for a number of the lines, determination of the position of a number of peaks of the reference spectrum in the recorded spectrum, selection of at least two first lines of known order, position and wavelength, determination of a wavelength scale for the order in which the known lines lie, by means of a fit function ?m(x), determination of a provisional wavelength scale ??m 1(x) for at least one neighboring order m 1, by means of addition/subtraction of a wavelength difference ?FSR which corresponds to a free spectral region, according to ?m 1 ?(x)=?m(x)?FSR with ?FSR=?m(x)/m, determination of the wavelengths of lines in said neighboring order m 1, by means of the provisional wavelength scale ? 1(x), replacement of the provisional wavelength of at least two lines by the reference wavelength f

Abstract: A spectrometer assembly (10) is disclosed. The assembly includes a light source (11) with a continuous spectrum. A pre-monochromator (2) generates a spectrum with a relatively small linear dispersion from which a spectral portion is selectable, the spectral bandwidth of the spectral portion being smaller than or equal to the bandwidth of the free spectral range of the order in the echelle spectrum. The centre wavelength of the selected spectral interval is measurable with maximum blaze efficiency. The assembly also includes an echelle spectrometer (4) with means for wavelength calibration, an entrance slit (21) at the pre-monochromator (2), an intermediate slit assembly (50) with an intermediate slit (3) and a spatially resolving light detector (5) in the exit plane of the spectrometer for the detection of wavelength spectra.