The laboratory calibration of the SOHO Coronal Diagnostic Spectrometer

The laboratory end-to-end testing of the Coronal Diagnostic Spectrometer (CDS) experiment on the ESA/NASA SOHO mission is reported. A brief overview of CDS, which operates in the extreme-ultraviolet wavelength range, is given. Pertinent details of the calibration source are presented, followed by an account of the source beam characterization. A section is devoted to the determination of the instrument apertures and this includes an outline of the measurements, the results from both the grazing incidence and normal incidence aperture scans and their interpretation to yield estimated aperture areas. Next the measurement of spectrometer bandwidths and their comparison with expected values are described. Then the pre-launch wavelength calibrations are obtained. The section on sensitivity starts with an evaluation of the effects of polarization on the measurements. The expected sensitivities are then derived. The measurements, their analysis and a comparison of measured and expected sensitivities are presented for both the normal incidence and grazing incidence spectrometers. The application of the laboratory calibration to in-flight solar data is discussed.