Figure testing and calibration of the ISOON Fabry-Perot etalons

摘要

We present the methods and results for the figure testing and spectral calibration of the narrow- and wide-band etalons for the Improved Solar Observing Optical Network's dual-etalon tunable imaging filters. The ISOON system comprises a distributed network of ground-based patrol telescopes that gather full-disk data for the monitoring of solar activity and for the development of more reliable space weather models. The etalon figure testing consists mainly of testing the cavity flatness and coating uniformity of each etalon. For this testing a series of exposures is taken as the etalon is tuned through a stable spectral line and a full-aperture line profile correlation method is employed to map the variations in the effective cavity thickness. Calibration of the etalons includes absolute calibration of the cavity mean spacing change corresponding to a controller step and calibration of plate parallelism and spacing settings for each spectral region of interest. Developmental acceptance testing and calibration procedures were performed in a laboratory environment using a HeNe laser source. A calibration method that uses illumination in the telluric lines is also described. This latter method could be used to conduct calibration in the field without the use of an artificial light source.