Evaluation of a multilayer mirror spectrometer in the 230-304 Å wavelength range

The reflective properties of a flat Mo/Si multilayer mirror (MLM) optimized for the 230 Å<λ<304 Å range (2d=373.2 Å, N=25, 25 Å<Δλ<50 Å) have been measured. A near-normal incidence spectrometer using the MLM as the dispersive element, a beryllium foil as a light blocking filter, and a channel electron multiplier as the photodetector has been built. The interest in such a device is related to its possible application as a monitor of alpha particles by imaging the whole plasma using the Lyman series of He II. In the laboratory experiment described here, the Lyman series of He II, emitted from a Penning ionization discharge, were scanned with a θ-2θ goniometer. In parallel, high-resolution (Δλ≈1 Å) spectra were also recorded using a 1 m grazing incidence (GI) spectrometer. Comparisons are made between the high-resolution (GI) spectrum modeled to the bandpass of the MLM and the low-resolution (MLM) spectrum in the range of interest.