Indian astronomers are aiming to build a large 10m class optical-NIR telescope, equipped with state-of art instruments. After exploring many potential design options, we ended up with two mirror Ritchey-Chretien (RC) type design, which provide diffraction limited performance over a sufficiently large field and delivers decent image quality over fairly extended field. The segmented primary mirror is a natural choice for the proposed 10m class telescope. However, unlike monolithic primary mirror, various factors linked with the segmentation plays very critical role to decide the performance of the telescope. In great detail, we have also studied the effect of the segment piston, tip and tilt, clocking, the radius of curvature, the shear, the segment size, inter-segment gap as well as figuring error on the telescope performances. All these studies are conducted using a custom developed generic python-based tool that can be used along with ZEMAX ray-tracing software. In this paper we present the optical design of proposed 10m class telescope as well as our extensive study on segmentation and alignment related effects.
Use of aspheric mirrors is common practice to design astronomical telescope with just a few optical elements. For an example in the most preferred telescope optical design, Ritchy Chretien (RC) both primary and secondary mirrors are hyperbola. Nowadays large telescopes are being built using small mirror segments, however, making aspheric off-axis mirror segment is a challenge. We have conducted a study in which we have explored a possibility to mimic aspheric hyperbolic primary mirror by making use of smaller spherical mirror segments. In this paper we present results of our study on designing an RC type telescope optics for an 10m class optical-NIR telescope
Alignment and Phasing system (APS) is one of essential device for any segmented mirror telescope. It helps to align and phase mirror segments, so that all together they works like a monolithic surface. Over last two years we have been exploring a possibility of using pyramid based wave-front sensor in the APS of a Prototype Segmented Mirror Telescope (PSMT), being developed in India. As a first step, we have derived the basic mathematical formulations required for the pyramid sensor and then after simulated the functional aspects of the pyramid sensor in the MATLAB. In order to carry out experimentation on pyramid sensor, we have also designed an optical setup using the ZEMAX. Since manufacturing of a high quality pyramid is a challenge, therefore, we have come up with a simple scheme in which the PSF is divided into multiple pupils using a rotating mask. In this paper, we briefly present the mathematical formulation, the technique of wave-front reconstruction, various simulations using the MATLAB and the ZEMAX as well as results obtained through a preliminary experimentation.
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