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.
To cater the need of growing astronomical community of India, there is a proposal to install 10-12m size optical-NIR telescope, equipped with state of the art back-end instruments . A telescope of this size is possible only, when primary mirror is made of smaller mirror segments. In order to get acquainted with segmented mirror telescope technology, at Indian Institute of Astrophysics Bangalore, we have initiated a project to develop a small prototype telescope made of small mirror segments. The proposed prototype telescope will use seven hexagonal mirrors, which will be supported by simple mirror support assembly and driven by indigenously developed voice coil based actuators. We also plan to make use of in-house developed inexpensive inductive edge sensor, which can precisely sense inter-segment relative displacement. The telescope mount is supposed to be Alt-Az and secondary mirror will be supported by trusses made of steel. The primary axes like elevation, azimuth and field de-rotator will be driven by direct drive motors. Though the primary objective of this telescope is to demonstrate the segmented mirror technology, however, we have designed the telescope in such way that it can also be used to a few dedicated science cases. The telescope is planned to be installed at Hanle, Ladakh India which is also a potential site for India's large telescope project. In this paper, we will present the progress made in opto-mechanical design as well development of other sub-systems required for the PSMT. The prototyping effort is one step toward realization of a large telescope in India and it is expected to be completed in two years period.
The primary mirror for a 10 meter class telescope will be made of many individual segments rather than a
monolithic mirror, because of the ease with which the segments can be made, transported and replaced. An
f1 primary mirror with an RoC of 20 meter is modeled using Zemax. The theoretical evaluation of the basic
properties of the individual segments such as dimensions, orientation and location, has been carried out. The
dimensions of each segment is different because the primary mirror is curved and aspheric. These parameters
are further optimised with respect to the image spot size and also to minimise the narrow, uniform gap between
the segments. The results of this optimisation is discussed in this paper.
In the new era of astronomy, we go for bigger telescopes having segmented primary and secondary mirrors. But once
segmentation is done, aligning and phasing mirror segments so that altogether they act like a monolithic mirror of a large
diameter, becomes critical. Co-phasing is a complex task that needed to be done after aligning the segments. Diffraction
limited resolution is only possible by a large segmented telescope, if mirror segments are co-phased. Co-phasing techniques
rely on physical optics and in one of the technique implemented in Keck telescope is based on analysis of diffraction pattern
generated by Shack Hartmann sensor. This same technique is being further explored by us in laboratory experimentation.
In this paper we present our effort to develop a simple but robust phasing technique for a large segmented mirror telescope
proposed to be installed in India. After rigorous mathematical exercise , analytical formulation for the phasing technique is
derived, which is further used to simulate in MATLAB. The MATLAB results are cross checked with the ZEMAX. There
after, a preliminary laboratory experiment has been conducted to check the feasibility of using this technique for phasing