We design an omnidirectional optical system that is composed of pseudo-Cassegrain collecting mirror part making narrow field of view(FOV) and a reverse pseudo-Cassegrain imaging mirror part, which can be used simultaneously in visible and long wavelength infrared(LWIR) light. The FOV is set to 40° to 110° and the F/number is 1.55. Because a CMOS sensor (CMOSIS, CMV2000) for visible and a micro bolometer sensor (semiconductor device, Bird 384) for LWIR are chosen, respectively, the common size of image should be determined by 5.9 mm × 5.9 mm. After the optimizing design, the ratio of the image height about two cases of 40° and 110° is 48.97 %. We can obtain that two MTFs for visible and LWIR at 20 lp/mm about the FOV of 110° are 0.425 and 0.385, respectively. The total length of this system is about 280 mm. When the MTF at 20 lp/mm and 110° is 0.3, the cumulative probabilities of the tolerance in visible and LWIR are 90.69 % and 99.79 %, respectively. After the athermalization analysis in the temperature range of - 32°C to 55°C, we choose the secondary mirror of the imaging part as a compensator to improve the collapsed MTF.
A polarization-preserving optical system that includes a dual photoelastic modulator (PEM) has been designed and fabricated for the motional Stark effect (MSE) diagnostic system which measures internal magnetic field structures inside the tokamak for the Korea Superconducting Tokamak Advanced Research. The collection optics located outside the vacuum window is composed of four lenses, a dielectric coated mirror, and a dichroic beam splitter in addition to the PEM and a polarizer. The fiber dissector is designed based on the focal plane that aligns 25 lines of sight, each of which constitutes a bundle of 19 600-μm fibers. The fibers run about 40 m from the front optics in the tokamak vacuum vessel to the detector in the diagnostic area remote from the tokamak hall. This takes the advantage of the fact that the polarization information is intensity-modulated once going through the PEM and the polarizer. The polarization signals measured by the MSE diagnostic successfully demonstrates its proof-of-principle physics that is critical in the stable and steady-state operation of the tokamak plasmas.
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