Integrated M.Tech-Ph.D (Tech.) projects

Ultraviolet imagers for space flight

Lunar Ultraviolet Cosmic Imager (LUCI) is an innovative all-spherical mirror telescope, expected to fly as part of the Team-Indus entry to the Google X-prize competition and will be deployed as part of the Lander on the Lunar surface. LUCI will observe at a fixed elevation angle and will detect stars in the near ultraviolet (200–320 nm) to a limiting magnitude of 12, with a field of view of 28 × 20 arcmin2. The instrument is being tested at the M.G.K. Menon Space Laboratory, CREST.

LUCI assembly and Calibration set-up at MGK Menon Laboratory clean room facility, CREST campus at Hosakote field station.
Stabilized Fabry-Perot wavelength calibrator for precision Doppler spectroscopy.

High precision spectroscopy is bounded by two major challenges, first being instrument instability, mainly caused by temperature and pressure variations. Second is due to the limitations of traditional calibration methods. Spectrographs require suitable calibration sources for precise Radial velocity (RV) measurements.Emission lamps do not provide homogenous line distributions and intensities, giving limited wavelength coverage and spectrum contamination from different sources.A wavelength calibrator based on Fabry-Perot (FP) etalon can provide stable transmission lines covering full wavelength range and can achieve 1-10 m/s RV precision. In the lab, students are developing a FP based wavelength calibrator.

Laboratory set-up of wavelength calibrator.

Polarimeter is a device used to identify the polarization states of incoming light. In astronomy, a typical detectable polarimetric accuracy is 10-4. In ground based instruments, seeing induced spurious polarization limits the achieved precision. Increase in modulation frequency systematically reduces the seeing-induced cross-talk. Therefore, a Liquid Crystal (LC) retarder in combination with waveplates can be used as a modulator as they can be modulated at high frequencies. One such polarimeter is being developed and tested in the laboratory at IIA by the student.

Laboratory set-up for testing of liquid crystal retarder.
The laboratory model of low-order adaptive optics system

AO is now being considered to be part of standard instrument suite at many ground based observatories, enabling telescopes to reach diffraction limit. It improves the spatial resolution to a considerable extent. Currently, the spatial resolution of 1.3 m telescope at Kavalur is limited by local atmosphere seeing. A development of low-order AO system is going on at the IIA’s laboratory. This system is intended to work for a wavelength range of 0.48 - 0.7 μm to provide an image of 1.2 arcmin field-of-view for science imaging.

Solar Ultraviolet Imaging Telescope-ADITY-L1

Solar Ultraviolet Imaging Telescope (SUIT), on-board ADITYA-L1, aims at imaging full-disc of the sun with about 1.4” angular resolution in NUV (200-400nm) through 11 narrow-band and wideband filters. It is being developed at IUCAA in collaboration with different institutes such as IIA and ISRO.

SUIT components internal layout (front, top and right covers removed). [courtesy: IUCAA & IIA]
Inductive Edge Sensor for segmented mirror telescopes

Edge sensor is a vital component of any segmented mirror telescope. The telescope performance highly depends on the performance of edge sensor. In order to achieve very high spatial resolution and sensitivity, all mirror segments of segmented mirror telescope must be precisely positioned with respect to each other to form a single primary mirror. Each mirror segment is usually supported by a complex segment support assembly (SSA) and is driven by 3 actuators.

An edge sensor test station showing inductive edge sensor and its related electronics.
Pointing system for balloon borne astronomical payloads

Development of a light-weighted, fully autonomous 2-axis pointing and stabilization system designed for balloon-borne astronomical payloads is being done at IIA. The system is developed using off-the-shelf components such as Arduino Uno controller, HMC 5883L magnetometer, MPU-9150 Inertial Measurement Unit (IMU) and iWave GPS receiver unit. It is a compact and rugged system which can also be used to take images/video in a moving vehicle, or in areal photography.

The pointing system inside vacuum chamber during the thermo-vac test. The payloads (a star sensor camera and UV spec-trograph) can also be seen in the image.
High altitude balloon experiments at Indian Institute of Astrophysics
Top: Balloon experiments carried out at Hosakote field station. Bottom: Image of the Earth taken from ballon floating at 25 km above the ground (left) and Earth’s atmospheric glow at high altitude (right).
Multilayer mirrors for Astronomical X-ray optics

Conventional mirrors for X-ray telescopes operate at very low grazing incidence angles. This is a severe limitation in building large numerical aperture telescopes and telescopes observing at Hard X-rays. Hence, A developmental work on multilayer mirrors is being carried out at IIA. Multilayer mirrors consist of periodic repetitive coatings of low and high refractive index materials which work on the principle of X-ray Bragg reflection. A typical multilayer mirror with high reflectivity is made up of a large number of bi-layers (∼100) on a highly polished substrate. At angles larger than the critical angle for a multilayer mirror, most X-rays get transmitted through the top layer and are subsequently gets divided into transmitted and reflected components at every bi-layer interface. The specifications of the bi-layer coatings can be optimized to interfere all the reflected components from each bilayer constructively, and thus enhance the overall reflectivity of the mirror.

Schematic of a multilayer mirror (left) Reflectivity response of the multilayer mirror (right)

Spherical W/B4C multilayer mirror fabricated using magnetron sputtering system.
High Precision Radial Velocity Studies using VBT Echelle Spectrograph

The Echelle spectrograph operational at 2.3 m Vainu Bappu Telescope (VBT), Kavalur is designed conventionally for high resolution spectroscopic observations. The students at IIA, aim to extend the science goals of the spectrograph to high precision Radial Velocity (RV) measurements. In order to implement precision spectroscopic studies, a stable high-resolution spectrograph has to be complemented with a stabilized wavelength calibration source. The primary objective is to develop and implement a simultaneous calibration technique using Iodine absorption cell. This method is expected to track and minimize the errors arising from instrumental drift and other systematics in the spectrograph.

VBT Echelle Spectrograph (R = 60,000) at Kavalur Observatory.

Iodine absorption cell installed at the entrance slit of the Echelle Spectrograph.
Scalable Generic Platform for Adaptive Optics Control using FPGAs

A generic low-cost easily replicable FPGA platform for future AO systems is being developed at IIA by the int. Mtech-PhD students. The platform is scalable across different sizes of AO systems, and works with varying number of subapertures, pixels per subaperture, AO geometry, size of the telescope and atmospheric conditions. It desirable to develop an FPGA platform that can compete in processing and hardware interface requirements with GPGPUs and multi-core CPUs (which dominate the current
landscape for implementing AO on large telescopes).

The present platform consists of a Wavefront Processing Unit and a core AO reconstructor. The Wavefront Processing Unit is a scalable fast pixel acquisition unit capable of handling different sizes of WFS CCDs and computes the local WF slope as part
of a highly pipelined algorithm. The AO reconstructor is a robust MVM (Matrix Vector Multiplier) type reconstructor which can work with multiple memory interfaces(for storing the reconstruction matrix) of different sizes according to the nature of the
AO system used.

A prototype is being tested on an inexpensive off-the-shelf Xilinx VC-709 development board. The students were able to obtain a real time performance of 21.4 GFlops(for AO reconstruction) using 2 DDR3 modules which can give a maximum combined
memory bandwidth of 21.4 GBps. For a target reconstruction time of 1 ms, the system works for a 32x32 subaperture system with on-chip memory and works with a 42x42 subaperture system with external DDR3-RAM. The system is limited by the bandwidth of external memory on the development board and the current prototype is indicative of the performance which can be achieved for larger telescopes. The platform is meant to be scalable and compatible with the next generation of Virtex UltraScale FPGAs which offer a much higher logic density with faster memory options.

Xilinx VC-709 development board. Results after interfacing with Robo-AO.
Last updated on: January 17, 2019