Design and analysis of radial supports for a large aperture prism

Abstract

WFOS (Wide-field Optical Spectrograph) will be seriously affected by atmospheric dispersion on imaging quality in its operating wavelength range¹ (0.31-1.0 micron). ADC (Atmospheric Dispersion Corrector)² can compensate atmospheric dispersion for light deflection of different wavelengths. The main optical elements of a LADC³ (Linear Atmospheric Dispersion Corrector) are two large aperture transmission prisms whose optical axes are placed horizontally. The prisms are placed opposite to 180° and separated by a certain distance in the direction of the optical axis to generate the amount of dispersion compensation. the large-diameter wedge prisms not only make a linear motion in the optical axis direction but also operate rotary motion separately. Because of the non-rotational symmetry and large mass of the wedge prism, gravity has a serious effect on the surface deformation of the prism. In addition, the prisms have to withstand ±20°C temperature change when they work. a support system is proposed and a comparative analysis is operated to estimate performance of support forms with different number of supports. Different circumferential support positions three, four, six, and eight schemes are analyzed and compared. in addition, the influence of different supports layouts based on the six supports scheme are analyzed. The 3D models are established and finite element analyses are conducted to evaluate the support performance via the surface RMS values which show that the design can meet the current design requirements for the support scheme.