Echelles: scalar, electromagnetic, and real-groove properties

Abstract

For lack of alternatives, echelle-grating diffraction behavior has in the past been modeled on scalar theory, despite observations that indicate significant deviations. To resolve this difficulty a detailed experimental, theoretical, and numerical study is performed for several echelles that work at low (18-13), medium (35-55), high (84-140), and very-high (to 660) diffraction orders. Noticeable deviations from the scalar model were detected both experimentally and numerically, on the basis of electromagnetic theory: (1) the shift of the observed blaze position was shown to decrease with the wavelength-to-period ratio, and it tends to zero more rapidly than the decrease of the maximum width, so that the TE- and TM-plane responses tend to merge into each other; (2) cut-off effects (Rayleigh anomalies) were found to play a significant role for high groove angles, where passing-off orders are close to the blaze order. A possibility for evaluation of the blaze angle from angular, rather than from spectral, measure nts is discussed.Several reasons for the differences between real and ideal echelles (material-index deviations, profile deformations, and groove-angle errors) are analyzed, and their effects on the performance of echelles is studied.

An improved microcarb dispersive instrumental concept for the measurement of greenhouse gases concentration in the atmosphere

“…This is why we developed a grating polarization model [7] and studied very precise characterisation of the instrument polarization as well as its main contributing factors. Nevertheless, a polarization scrambler (optical depolarising component) needs to be inserted in the MicroCarb design to meet the required specification level,.…”

A new space instrumental concept based on dispersive components for the measurement of CO2 concentration in the atmosphere

“…A development was made with Institut Fresnel [6] to build a grating model in order to predict grating performances for our instrument.…”

Independent electromagnetic optimization of the two coating thicknesses of a dielectric layer on the facets of an echelle grating in Littrow mount

“…The deviation with measured data is less than two percent, proving that this method works correctly. The observed deviations with the efficiency results of another BIM [6] underline the fact that even for BIMs echelle grating investigation was still a challenging task in the 1990s.…”

“…In this sense, BIMs have more favourable computation time behaviour than other rigorous diffraction methods which make them capable of solving demanding echelle diffraction problems. Publication [6] is the first and most extensive theoretical electromagnetic and experimental investigation on echelle gratings with the number of diffraction orders ranging from low (8)(9)(10)(11)(12)(13) to very high (660). Several imperfections of echelles and their effects on the performance were studied.…”