Characteristic evaluation of a near-infrared Fabry-Perot filter for the InfraRed Imaging Magnetograph (IRIM)

摘要

The InfraRed Imaging Magnetograph (IRIM) is a high temporal resolution, high spatial resolution, high spectral resolving power, and high magnetic sensitivity solar two-dimensional narrow-band spectrc-polarimeter working in the near infrared from 1.0 μm to 1.7 yum at Big Bear Solar Observatory (BBSO). It consists of an interference filter, a polarization analyzer, a birefringent filter, and a Fabry-Perot etalon. As the narrowest filter of IRIM, the infrared Fabry-Perot plays a very important role in achieving the narrow band transmission of ~ 10 pm and high throughput between 85% and 95% for the full wavelength range, maintaining wavelength tuning ability from 1.0 to 1.7 μm, and assuring stability and reliability. As the third of a series of publications describing IRIM, this paper outlines a set of methods to evaluate the near infrared Fabry-Perot etalon. Two-dimensional characteristic maps of the near infrared Fabry-Perot etalon, including the bandpass AA, effective finesse F_(eff), peak transmission τ_(max), along with free spectral range, flatness, roughness, and stability and repeatability were obtained with laboratory equipment. These measured results will benefit the optimization of IRIM design and observational mode of the future.