Development of new tunable filter for solar observation in Hida observatory

摘要

Solar Magnetic Activity Research Telescope (SMART) at Hida observatory is in operational to monitor the solar activity. As a new solar Ha observing instrument for SMART, we developed "Solar Dynamics Doppler Imager (SDDI)", which can measure the three-dimensional motion of solar eruptive phenomena. These eruptive events could be affective to the earth magnetism and cause serious damage to our society. The purpose of SMART/SDDI is monitoring and forecasting the geo-affective solar eruptions. In this paper, we present the development of the tunable filter "TF40", the key component of SDDI. The features of TF40 are, (1) fast tuning of observation wavelength. (2) narrow transmission width and large free spectral range (FSR), (3) large field-of-view that covers the entire solar disk with a 20 cm objective lens. TF40 has 7 stages of optical blocks. Each stage consists of a linear polarizer, calcites, a quartz as half waveplate and a Liquid Crystal Variable Retarder (LCVR), and has the periodic transmission profile with 0.05, 0.1, 0.2, 0.4, 0.8, 1.6 and 3.2 nm period at Hα line (656.2808 nm), respectively. Combining the 7 stages, the 0.025 nm transmission width and 3.2 nm FSR arc achieved. Retardation of each LCVR and its dependence on applied voltage and temperature were measured for modeling its characteristics, with which we calculate the voltage for desired retardation. Best-shaped transmission profile is obtained by further adjustment of voltages of individual LCVRs using the real solar light. We report the performance and current observing status of the TF40.