The tunable near InfraRed Lyot filter (TNIRLF) is one of the focal plane instruments for Advanced Technology Solar Telescope (ATST) project of the National Solar Observatory (NSO). Achromatic half waveplate and quarter waveplates working from 1000 nm to 1700 nm will be used in this filter. In this paper, we give a description of the design and development for the synthesized achromatic waveplates using quartz plates. The retardance variation is within 1% over the full spectral range and we discuss the variance of optical axis.
The InfraRed Imaging Magnetograph (IRIM) is an innovative magnetograph system for near-infrared (NIR)observations of the Sun. IRIM will provide high spatial resolution (0.2" per pixel image scale), high temporal resolution (1-2 minutes), moderate spectral resolution (14.0 pm), and high magnetic sensitivity covering a substantial field-of-view (FOV: 170" circular). The bandpass of the instrument is reduced in three steps while still providing high transmission: (1) a 4 nm interference filter, (2) a 0.25 nm Lyot-filter, and (3) a 14.0 pm tunable Fabry-Perot etalon. The innovative NIR Lyot-filter was developed at the New Jersey Institute of Technology (NJIT) and is currently being assembled at Cambridge Research Instruments. It is the first of its kind and provides a large angle of acceptance, thus solving many problems encountered with dual Fabry-Perot systems. The two-dimensional line profiles will be recorded by a 1024 × 1024 pixel, 12-bit Complex Metal Oxide Semiconductor (CMOS) focal plane array (FPA) manufactured by Rockwell Scientific Imaging, which can obtain images at a rate of 50 fps. IRIM will utilize the remodelled Coude-feed of the 65 cm vacuum telescope at the Big Bear Solar Observatory (BBSO) and will benefit from an image stabilization and correction system of independently operating Correlation Tracking (CT) and Adaptive Optics (AO) systems.
In this paper, we present an optical design of a near- infrared (at FeI 15648.5A) birefringent filter system which is used to obtain the chromatic images of the sun and measure the solar magnetic field at the Big Bear Solar Observatory (BBSO). This system consists of a prefilter,a liquid crystal analyzer, a wavelength-tunable birefringent filter and a Fabry-Perot Etalon. This system is expected to achieve a clean narrow pass band (1/8A). It can also be tuned across the spectral line to obtain line profiles of two0dimensional fields of view. During the design of the tunable near-IR birefringent filter and the test of its components, we found the value of birefringence index μ(ne-no) of calcite at spectral range near 15648.5A is very different from the value in literature. Because the birefringence index is important for the design of birefringent optical components, the birefringence index of calcite and its thermal coefficient are measured. Some test results of the four pairs of calcite plate used in the birefringent filter are presented.