Prof. Anamparambu N. Ramaprakash Profile

Prof. Anamparambu N. Ramaprakash

Dean, Core Academic Programmes at Inter-Univ Centre for Astronomy and Astrophysics

SPIE Involvement:

Conference Program Committee | Author

Area of Expertise:

Adaptive Optics , Detector Arrays and Controllers , Optical Fibres , Transients

Publications (41)

SPIE Journal Paper | 30 October 2024

Wide Area Linear Optical Polarimeter North instrument I: optical design, filter design, and calibration

John Andrew Kypriotakis, Siddharth Maharana, Ramya Anche, Chaitanya Rajarshi, Anamparambu Ramaprakash, Bhushan Joshi, Artem Basyrov, Dmitry Blinov, Tuhin Ghosh, Eirik Gjerløw, Sebastian Kiehlmann, Nikolaos Mandarakas, Georgia Panopoulou, Katerina Papadaki, Vasiliki Pavlidou, Timothy Pearson, Vincent Pelgrims, Stephen Potter, Anthony C. S. Readhead, Raphael Skalidis, Konstantinos Tassis

JATIS, Vol. 10, Issue 04, 044005, (October 2024) https://doi.org/10.1117/12.10.1117/1.JATIS.10.4.044005

KEYWORDS: Equipment, Tunable filters, Polarimetry, Optical filters, Polarization, Calibration, Design, Telescopes, Point spread functions, Stars

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Proceedings Article | 25 July 2024 Presentation + Paper

Presentation + Paper

The WALOP software

John Kypriotakis, Bhushan Joshi, Dmitry Blinov, Sebastian Kiehlmann, Siddharth Maharana, Chaitanya Rajarshi, A. Ramaprakash, Artem Basyrov, Myrto Falalaki, Tuhin Ghosh, Eirik Gjerløw, Ioannis Liodakis, Nikolaos Mandarakas, Georgia Panopoulou, Vasiliki Pavlidou, Timothy Pearson, Vincent Pelgrims, Stephen Potter, Anthony C. Readhead, Raphael Skalidis, Konstantinos Tassis, Namita Uppal

Proceedings Volume 13101, 131011A (2024) https://doi.org/10.1117/12.3018100

KEYWORDS: Databases, Calibration, Polarizers, Observatories, CCD cameras, Control software, Web services, Control systems, Robotics, Internet imaging, Instrumentation control

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Proceedings Article | 18 July 2024 Poster + Paper

Poster + Paper

Systems design, assembly, integration, and lab testing of WALOP-South Polarimeter

Siddharth Maharana, A. Ramaprakash, Chaitanya Rajarshi, Pravin Khodade, Bhushan Joshi, Pravin Chordia, Abhay Kohok, Ramya Anche, Deepa Modi, John Kypriotakis, Amit Deokar, Aditya Kinjawadekar, Stephen Potter, Dmitry Blinov, Hans Kristian Eriksen, Myrto Falalaki, Hitesh Gajjar, Tuhin Ghosh, Eirik Gjerløw, Sebastian Kiehlmann, Ioannis Liodakis, Nikolaos Mandarakas, Georgia Panopoulou, Vasiliki Pavlidou, Timothy Pearson, Vincent Pelgrims, Anthony C. Readhead, Raphael Skalidis, Konstantinos Tassis, Namita Uppal, Ingunn Wehus

Proceedings Volume 13096, 130967P (2024) https://doi.org/10.1117/12.3016144

KEYWORDS: Equipment, Cameras, Polarimetry, Polarizers, Collimators, Telescopes, Cements, Polarization, Calibration, Optomechanical design, Optical design, Calcite

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Wide-Area Linear Optical Polarimeter (WALOP)-South is the first wide-field and survey-capacity polarimeter in the optical wavelengths. On schedule for commissioning in 2024, it will be mounted on the 1 m SAAO telescope in Sutherland Observatory, South Africa to undertake the PASIPHAE sky survey. PASIPHAE program will create the first polarimetric sky map in the optical wavelengths, spanning more than 2000 square degrees of the southern Galactic region. In a single exposure, WALOP-South’s innovative design will enable it to measure the linear polarization (Stokes parameters q and u) of all sources in a field of view (FoV) of 35 × 35 arc-minutes-squared in the SDSS-r broadband and narrowband filters between 500-750 nm with 0.1 % polarization accuracy. The unique goals of the instrument place very stringent systems engineering goals, including on the performance of the optical, polarimetric, optomechanical, and electronic subsystems. In particular, the major technical hurdles for the project included the development of: (a) an optical design to achieve imaging quality PSFs across the FoV, (b) an optomechanical design to obtain high accuracy optical alignment in conjugation with minimal instrument flexure and stress birefringence on optics (which can lead to variable instrumental polarization), and (c) an on-sky calibration routine to remove the strong polarimetric cross-talk induced instrumental polarization to obtain 0.1% across the FoV. All the subsystems have been designed carefully to meet the overall instrument performance goals. As of May 2024, all the instrument optical and mechanical subsystems have been assembled and are currently getting tested and integrated. The complete testing and characterization of the instrument in the lab is expected to be completed by August 2024. While the instrument was initially scheduled for commissioning in 2022, it got delayed due to various technical challenges; WALOP-South is now on schedule for commissioning in second half of 2024. In this paper, we will present (a) the design and development of the entire instrument and its major subsystems, focusing the instrument’s opto-mechanical design which has not been reported before, and (b) assembly and integration of the instrument in the lab and early results from lab characterization of the instrument’s optical performance.

Proceedings Article | 18 July 2024 Poster + Paper

Poster + Paper

Improving polarimetric accuracy of RoboPol to < 0.05 % using a half-wave plate calibrator system

Siddharth Maharana, Dmitry Blinov, A. N. Ramaprakash, Vasiliki Pavlidou, Konstantinos Tassis

Proceedings Volume 13096, 130963A (2024) https://doi.org/10.1117/12.3021523

KEYWORDS: Polarimetry, Calibration, Polarization, Equipment, Stars, Telescopes, Design, Astrophysics, Observatories

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SPIE Journal Paper | 6 September 2022

WALOP-South: a four-camera one-shot imaging polarimeter for PASIPHAE survey. Paper II – polarimetric modeling and calibration

Siddharth Maharana, Ramya Anche, Anamparambu Ramaprakash, Bhushan Joshi, Artem Basyrov, Dmitry Blinov, Carolina Casadio, Kishan Deka, Hans Kristian Eriksen, Tuhin Ghosh, Eirik Gjerløw, John Kypriotakis, Sebastian Kiehlmann, Nikolaos Mandarakas, Georgia V. Panopoulou, Katerina Papadaki, Vasiliki Pavlidou, Timothy Pearson, Vincent Pelgrims, Stephen Potter, Anthony C. Readhead, Raphael Skalidis, Trygve Leithe Svalheim, Konstantinos Tassis, Ingunn Wehus

JATIS, Vol. 8, Issue 03, 038004, (September 2022) https://doi.org/10.1117/12.10.1117/1.JATIS.8.3.038004

KEYWORDS: Polarimetry, Calibration, Polarization, Instrument modeling, Stars, Telescopes, Sensors, Zemax, Performance modeling, Systems modeling

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Proceedings Article | 31 August 2022 Poster + Paper

Poster + Paper

The thermal filter for the Solar Ultraviolet Imaging Telescope (SUIT) on-board Aditya-L1

Avyarthana Ghosh, Ravi Kesharwani, Aafaque Khan, Sreejith Padinhatteeri, Durgesh Tripathi, A. Ramaprakash, Ketan Patel, Tayaramma D. P. V. Jalluri, G. R. Madhumalathi, R. Venkateshwaran, S. Elumalai, Kinshuk Gupta, J. P. Nair, H. Sparrow, R. S. Worlikar, Anit Gupta, Sanjoy Sen

Proceedings Volume 12181, 121813O (2022) https://doi.org/10.1117/12.2629760

KEYWORDS: Optical filters, Telescopes, Coating, Charge-coupled devices, Ultraviolet telescopes, Reflection, Ultraviolet radiation, Sun, Visible radiation, Space telescopes, Bandpass filters, Gamma radiation

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The solar ultraviolet imaging telescope (SUIT) is an imaging telescope on-board the Aditya-L1 satellite, which is India’s maiden space mission dedicated solely to solar observations. The spatially resolved, high cadence observations are designed to be taken in eleven science filters with full width half maxima ranging between 0.1–58 nm and spread over the near-ultraviolet (NUV) domain of the solar spectrum (200–400 nm). The huge incoming solar flux, limited by the linearity regime performance of the charge coupled device (CCD) as well as the thermal operational constraints, mandate the use of an entrance aperture filter, the thermal filter (TF), for SUIT. The design of this filter is, further, constrained by exposure time and enhanced emission of the sun during eruptive events. From performance perspective, the TF reflects ∼50% of the incident radiation and allows only 0.1–0.45% of the incoming flux to pass within 200–400 nm. The transmission on either side of the operational range is satisfactorily reduced, so as to ensure minimum unwanted light leaking into the imaging system. Therefore, the TF plays a significant role in increasing the photometric efficiency as well as maintaining the operational temperature of the telescope. To the best of our knowledge, this is the first time any attempt of designing and manufacturing any such rejection filter aiming optimized performance in the NUV range is being done for a space-based imaging solar telescope. The choice of materials for substrate and coating for the filter poses several challenges in terms of contamination, corrosion/ oxidation, durability during manufacturing process, long-term exposure to harsh space environment as well as formation of pinholes. The transmission and reflection profiles of the fabricated TF is satisfactory to meet our design and technical constraints. The TF is also qualified for various environmental and radiation conditions. The transmission of the TF is seen to be well within our allowed margins (±10% of the design value) even after being exposed to these qualification tests.

Proceedings Article | 30 August 2022 Poster + Paper

Poster + Paper

Speckle simulation tool for automated modelling of a large range of telescope aperture to fried parameter ratios

Sorabh Chhabra, Abhay Kohok, Bhushan Joshi, A. Ramaprakash, Chaitanya Rajarshi, Rani Bhandare

Proceedings Volume 12185, 1218566 (2022) https://doi.org/10.1117/12.2628032

KEYWORDS: Turbulence, Telescopes, Speckle, Device simulation, Lenses, Zemax, Collimation, Cameras, Atmospheric turbulence, Monte Carlo methods

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Proceedings Article | 30 August 2022 Presentation + Paper

Presentation + Paper

Towards the development of the Infrared Guide Star Catalogue for the adaptive optics observations by the Thirty Meter Telescope

Sarang Shah, Smitha Subramanian, G. Anupama, Francisco Delgado, Kim Gillies, Maheshwar Gopinathan, Rajalakshmi Narayanan, A. Ramaprakash, Suhasini Rao, B. Reddy, Warren Skidmore, T. Sivarani, Annapurni Subramaniam

Proceedings Volume 12185, 1218506 (2022) https://doi.org/10.1117/12.2629775

KEYWORDS: Near infrared, Stars, Atmospheric modeling, Adaptive optics, Thirty Meter Telescope, Data modeling, Infrared radiation, Photometry, Infrared telescopes, Telescopes

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Proceedings Article | 29 August 2022 Presentation + Paper

Presentation + Paper

Stress-induced birefringence in the lenses of Wide-Area Linear Optical Polarimeter-South

Ramya M. Anche, Siddharth Maharana, A. N. Ramaprakash, Pravin Khodade, Deepa Modi, Chaitanya Rajarshi, John A. Kypriotakis, Dmitry Blinov, Hans Kristian Eriksen, Tuhin Ghosh, Georgia V. Panopoulou, Vincent Pelgrims, Raphael Skalidis, Timothy J. Pearson, Eirik Gjerløw, Nikolaos Mandarakas, Vasiliki Pavlidou, Stephen B. Potter, Anthony C. S. Readhead, Konstantinos Tassis, Artem Basyrov, Katerina Papadaki, Trygve Leithe Svalheim, Ingunn K. Wehus

Proceedings Volume 12188, 121882C (2022) https://doi.org/10.1117/12.2629515

KEYWORDS: Birefringence, Polarization, Polarimetry, Telescopes, Finite element methods

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Two unique wide-field and high-accuracy polarimeters named WALOP (Wide-Area Linear Optical Polarimeter)- North and WALOP-South are currently under development at the Inter-University Center for Astronomy and Astrophysics (IUCAA), India, to create a large area optical polarization map of the sky for the upcoming PASIPHAE sky survey. These instruments are designed to achieve a linear polarimetric measurement accuracy of 0.1% across a field of view (FoV) of 30×30 arcminutes. The WALOP-South instrument will be installed first on a 1 m telescope at the Sutherland Observatory, where the temperatures during the night can vary between 10 to -5°C. These temperature variations and the instrument’s pointing to various non-zenithal positions in the sky can introduce stress birefringence in the lenses, leading to time-varying instrumental polarization. This work estimates stress-induced birefringence due to thermal, and gravity stresses on WALOP-South lenses. Using the optomechanical model of the WALOP-South, we carried out Finite Element Analysis (FEA) simulations in SolidWorks software to estimate the stresses for various scenarios of temperature, telescope pointing airmass, and lens mount material (aluminum and titanium). Further, we use the stress tensor analysis to estimate the principal stresses and their directions and consequent birefringence and retardance introduced in the lenses. The stressinduced birefringence will change the optical path length for orthogonal polarization states of the beam passing through the lenses and introduce phase retardation. Overall, with the lens mount design of the instrument, we find that the retardation and consequent instrumental polarization will be within the instrumental accuracy requirements. Additionally, the stress birefringence is found to be higher for aluminum compared to titanium mounts. We further incorporated this retardance in the instrument Mueller matrix estimation to understand its effects on the polarization measurements.

Proceedings Article | 29 August 2022 Paper

Paper

Design and fabrication of a silicon based micro fiber holder for DOTIFS Integral field unit and associated IFU tests

Annu Jacob, A. N. Ramaprakash, Chaitanya Rajarshi, Pravin Khodade, Hillol Das, Sabyasachi Chattopadhyay, Amitesh Omar

Proceedings Volume 12184, 121847D (2022) https://doi.org/10.1117/12.2629966

KEYWORDS: Semiconducting wafers, Spectrographs, Polishing, Microlens, Photomasks, Optical alignment, Manufacturing, Cameras, Calibration, Optical fibers

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Devasthal Optical Telescope Integral Field Spectrograph (DOTIFS) is a new multi-object integral field spectrograph being built by the Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune, India for the 3.6m Devasthal Optical Telescope, (DOT). Spectrographs, which disperse the light to study various aspects of the source, traditionally follow long slit to enter the light into to the instrument. However, varying slit width, atmospheric dispersion, crowded object field etc, causes this approach to lose its efficiency. A 2D field access using optical fibres solves most of these issues and introduces additional modularity. However, the circular shape of the fibre tip causes light loss as the fill factor < 80 %. There are mainly two ways to solve these issues, one is with 2D field splicers which are usually mirrors which break the field and reflect the beams in different directions, the other a more convenient alternative is using micro lens arrays (MLA) coupled with optical fibres, increasing the fill factor < 90 %. Even with this advantage, the miss alignment of the optical fibre with the MLA can cause increase in optical entropy and hence loss of effective transmission. Therefore, making a precise fiber to micro-lenslet array holder is a necessity. In DOTIFS which uses a combination of MLA and fibers to transmit the light, the IFU unit of the spectrograph consist of fiber array held on a mask and glued to a micro lenslet array. The plano-convex MLA (PCMLA) forms a hexagonal honeycomb structure of 12×12 spaxels. The on-sky footprint of an IFU is designed to be 8.7”×7.4” for a spatial sampling of 0.8”/300µm. The PCMLA has a thickness of 2.32 mm to create the pupil at its flat surface where fibers would be butted to sample the pupil. Each microlens curved side will receive a f/21.486 beam from the magnifier optics assembly sitting between IFU assembly and the Cassegrain side port selection mirror of the telescope. The microlens converts the incoming beam from the magnifier to f/4.5 beam and creates an ideal pupil of 76µm diameter at its at back surface. In this paper we present deep reactive ion etching technique based fibre holder manufacturing for holding the fibres of IFU of DOTIFS spectrograph. We present the design details, fiber routing scheme, manufacturing and gluing and polishing concepts for fibre holder and the tests and results on the IFU deployment system.

SPIE Journal Paper | 17 June 2021 Open Access

Open Access

Generalized approach to compensate for low- and high-frequency errors in fast Fourier transform-based phase screen simulations

Sorabh Chhabra, Jyotirmay Paul, Anamparambu Ramaprakash, Avinash Surendran

JATIS, Vol. 7, Issue 02, 025007, (June 2021) https://doi.org/10.1117/12.10.1117/1.JATIS.7.2.025007

KEYWORDS: MATLAB, Fourier transforms, Telescopes, Matrices, Device simulation, Atmospheric turbulence, Atmospheric propagation, Astrophysics, Astronomy, Zernike polynomials

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SPIE Journal Paper | 9 March 2021

WALOP-South: a four-camera one-shot imaging polarimeter for PASIPHAE survey. Paper I—optical design

Siddharth Maharana, John Kypriotakis, Anamparambu Ramaprakash, Chaitanya Rajarshi, Ramya Anche, Shrish Shrish, Dmitry Blinov, Hans Eriksen, Tuhin Ghosh, Eirik Gjerløw, Nikolaos Mandarakas, Georgia Panopoulou, Vasiliki Pavlidou, Timothy Pearson, Vincent Pelgrims, Stephen Potter, Anthony C. Readhead, Raphael Skalidis, Konstantinos Tassis, Ingunn Wehus

JATIS, Vol. 7, Issue 01, 014004, (March 2021) https://doi.org/10.1117/12.10.1117/1.JATIS.7.1.014004

KEYWORDS: Polarimetry, Polarization, Sensors, Telescopes, Cameras, Prisms, Point spread functions, Optical design, Optical filters, Stars

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Proceedings Article | 13 December 2020 Poster + Presentation + Paper

Poster + Presentation + Paper

Gaussian phase autocorrelation as an accurate compensator for FFT-based atmospheric phase screen simulations

Sorabh Chhabra, Jyotirmay Paul, A. Ramaprakash, Avinash Surendran

Proceedings Volume 11448, 114487U (2020) https://doi.org/10.1117/12.2575934

KEYWORDS: Atmospheric turbulence, Large screens

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Proceedings Article | 13 December 2020 Poster + Presentation + Paper

Poster + Presentation + Paper

WALOP-South: A wide-field one-shot linear optical polarimeter for PASIPHAE survey

Siddharth Maharana, John Kypriotakis, A. Ramaprakash, Pravin Khodade, Chaitanya Rajarshi, Bhushan Joshi, Pravin Chordia, Ramya Anche, Shrish Mishra, Dmitry Blinov, Hans Kristian Eriksen, Tuhin Ghosh, Eirik Gjerløw, Nikolaos Mandarakas, Georgia Panopoulou, Vasiliki Pavlidou, Timothy Pearson, Vincent Pelgrims, Stephen Potter, Anthony C. Readhead, Raphail Skalidis, Konstantinos Tassis, Ingunn Wehus

Proceedings Volume 11447, 114475E (2020) https://doi.org/10.1117/12.2554396

KEYWORDS: Polarimetry, Polarization, Telescopes, Stars, Astronomy, Optical filters, Photometry, Prisms, Vignetting, Optomechanical design

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SPIE Journal Paper | 25 July 2019 Open Access

Open Access

Design and development of an adaptive optics system in visible and near-infrared for Inter-University Centre for Astronomy and Astrophysics 2-meter telescope

Jyotirmay Paul, Hillol Kanti Das, Anamparambu Ramaprakash, Mahesh Burse, Pravinkumar Chordia, Kalpesh Chillal, Gaurav Datir, Bhushan Joshi, Pravin Khodade, Abhay Kohok, Vilas Mestry, Sujit Punnadi, Chaitanya Rajarshi, Chikku Shekhar

JATIS, Vol. 5, Issue 03, 039002, (July 2019) https://doi.org/10.1117/12.10.1117/1.JATIS.5.3.039002

KEYWORDS: Adaptive optics, Telescopes, Prisms, Cameras, Projection systems, Ultraviolet radiation, Mirrors, Infrared cameras, Zemax, Atmospheric modeling

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SPIE Journal Paper | 31 July 2018

Scalable platform for adaptive optics real-time control, part 1: concept, architecture, and validation

Avinash Surendran, Mahesh Burse, Anamparambu Ramaprakash, Jyotirmay Paul, Hillol Das, Padmakar S. Parihar

JATIS, Vol. 4, Issue 03, 039001, (July 2018) https://doi.org/10.1117/12.10.1117/1.JATIS.4.3.039001

KEYWORDS: Adaptive optics, Field programmable gate arrays, Interfaces, Wavefronts, Actuators, Adaptive control, Computer simulations, Telescopes, Logic, Wavefront sensors

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SPIE Journal Paper | 31 July 2018

Scalable platform for adaptive optics real-time control, part 2: field programmable gate array implementation and performance

Avinash Surendran, Mahesh Burse, Anamparambu Ramaprakash, Padmakar Parihar

JATIS, Vol. 4, Issue 03, 039002, (July 2018) https://doi.org/10.1117/12.10.1117/1.JATIS.4.3.039002

KEYWORDS: Adaptive optics, Field programmable gate arrays, Clocks, Digital signal processing, Reconstruction algorithms, Interfaces, Logic, Adaptive control, Computing systems, Telescopes

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SPIE Journal Paper | 11 July 2018

Noise characterization of IUCAA digital sampling array controller

Sabyasachi Chattopadhyay, A. N. Ramaprakash, Bhushan Joshi, Pravinkumar Chordia, Mahesh Burse, Kalpesh Chillal, Sakya Sinha, Sujit Punnadi, Ketan Rikame, Sungwook Hong, Dhruv Paranjpye, Haeun Chung, Changbom Park, Amitesh Omar

JATIS, Vol. 4, Issue 03, 036002, (July 2018) https://doi.org/10.1117/12.10.1117/1.JATIS.4.3.036002

KEYWORDS: Interference (communication), Charge-coupled devices, Electrons, Analog electronics, Clocks, Amplifiers, Power supplies, Sensors, Field programmable gate arrays, Statistical modeling

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The IUCAA digital sampling array controller (IDSAC) is a flexible and generic yet powerful CCD controller that can handle a wide range of scientific detectors. Based on an easily scalable modular backplane architecture consisting of single board controllers (SBC), IDSAC can control large detector arrays and mosaics. Each of the SBCs offers the full functionality required to control a CCD independently. The SBCs can be cold swapped without the need to reconfigure them. IDSAC is also available in a backplane-less architecture. Each SBC can handle data from up to four video channels with or without dummy outputs at speeds up to 500-kilo pixels per second (kPPS) per channel with a resolution of 16 bits. Communication with a Linux-based host computer is through a USB3.0 interface, with the option of using copper or optical fibers. A field programmable gate array (FPGA) is used as the master controller in each SBC, which allows great flexibility in optimizing performance by adjusting gain, timing signals, bias levels, etc., using user-editable configuration files without altering the circuit topology. Elimination of thermal kTC noise is achieved via digital correlated double sampling (DCDS). The number of digital samples per pixel (for both reset and signal levels) is user configurable. We present the results of noise performance characterization of IDSAC through simulation, theoretical modeling, and actual measurements. The contribution of different types of noise sources is modeled using a tool to predict noise of a generic DCDS signal chain analytically. The analytical model predicts the net input referenced noise of the signal chain to be 5 electrons for 200-k pixels/s per channel readout rate with three samples per pixel. Using a cryogenic test setup in the lab, the noise is measured to be 5.4 e (24.3 μV), for the same readout configuration. With a better-optimized configuration of 500-kPPS readout rate, the measured noise is down to 3.8 electrons RMS (17 μV), with three samples per interval.

Proceedings Article | 11 July 2018 Paper

Paper

Design and development of IR camera

Jyotirmay Paul, A. Ramaprakash, Hillol Das, Mahesh Burse, Pravin Chordia, Pravin Khodade, Abhay Kohok, Vilas Mestry , Deepa Modi , Sujit Punnadi, Chaitanya Rajarshi

Proceedings Volume 10703, 1070368 (2018) https://doi.org/10.1117/12.2311457

KEYWORDS: Infrared cameras, Cameras, Sensors, Optical filters, Adaptive optics, Infrared sensors, Telescopes, Infrared telescopes, Infrared radiation

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Proceedings Article | 10 July 2018 Paper

Paper

Multiple rooks of chess: a generic integral field unit deployment technique

Sabyasachi Chattopadhyay, A. Ramaprakash, Pravin Khodade, Kabir Chakravarti, Shabbir Shaikh, Haeun Chung, Sungwook Hong

Proceedings Volume 10706, 107065S (2018) https://doi.org/10.1117/12.2313798

KEYWORDS: Detection and tracking algorithms, Target acquisition, Telescopes, Robots, Space telescopes, Astronomy, Spectrographs, Computer simulations, Astronomical imaging

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Proceedings Article | 10 July 2018 Presentation + Paper

Presentation + Paper

A new photolithography based technique to mass produce microlens+fibre based integral field units (IFUs) for 2D spectroscopy

Sabyasachi Chattopadhyay, Vishal Joshi, A. Ramaprakash, Deepa Modi, Abhay Kohok, Haeun Chung

Proceedings Volume 10706, 107062D (2018) https://doi.org/10.1117/12.2313729

KEYWORDS: Photomasks, Optical lithography, Microlens array, Polishing, Microlens, Metals, Spectrographs, Ultraviolet radiation, Photoresist materials, Back illuminated sensors

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Long-slit astronomical spectroscopy has various limitations when dealing with optimum slit width, atmospheric dispersion, extended source spectroscopy, etc. to name a few. Most of these issues can be solved by the use of optical fibers as the light carrier from the telescope focal plane to the spectrograph. The approach is technically and scientifically flexible in terms of instrument modularity and target acquisition. Implementation of Integral Field Unit (IFU) provides a continuous sampling of extended objects and has a distinct advantage over the single fiber. Using a microlens array in front of the fibers improves the sky coverage by increasing the fill factor. Devasthal Optical Telescope Integral Field Spectrograph (DOTIFS) is a novel instrument being built by the Inter-University Centre for Astronomy and Astrophysics, Pune for the 3.6m Devasthal Optical Telescope (DOT) constructed by Aryabhatta Research Institute of Observational Sciences, Nainital. Each of the 16 DOTIFS IFUs consist of 12x12 spatial elements (spaxels) distributed in a hexagonal honeycomb structure covering 8.7"x7.8" in the sky. Each IFU is made by a photolithography technique to transfer the corresponding microlens array pattern to create a mask which holds the fibers at the focal plane end of an integral field unit. These masks are aligned with the microlens array and fibers are inserted before gluing and polishing. The fiber array can be positioned with a peak positioning error less than 5 μm from the desired position within a fiber array, compared to a requirement of 10 μm. The slit end is made by wire EDM cutting technology and fibers are placed with an accuracy of ~0.3 pixels compared to a 6.75 pixel center-to-center gap between two spectra on the detector. In this paper we provide details of deriving requirements and error budgets. The process of photolithography and the use of generated masks to create an IFU are also discussed. The technique allows very cost effective mass production of IFUs which are very accurately matched with the corresponding microlens array.

Proceedings Article | 9 July 2018 Presentation

Presentation

MIRADAS: the facility multi-object medium-resolution NIR spectrograph for the GTC (Conference Presentation)

Stephen Eikenberry, Steven Raines, R. Deno Stelter, Alan Garner, Yigit Dallilar, Kendall Ackley, J. Greg Bennett, Brian Chinn, Scott Mullin, Sidney Schofield, Craig Warner, Frank Varosi, Bo Zhao, Sophia Eikenberry, Claudia Vega, H. Veronica Donoso, Christian Carrera, Denisse Almeida, Gabriel Fuentes, Josep Sabater, José María Gomez, Francisco Garzón, Pablo Lopez, Josefina Rosich, Anthony Russo, Antonio Marin-Franch, Arkaitz Larman, Miguel-Angel Carrera, Greg Fitzgerald, Ian Prees, Todd Stolberg, Peter Kornik, Anamparambu Ramaprakash, Mahesh Burse, Sujit Punnadi, Peter Hammersley

Proceedings Volume 10702, 107021E (2018) https://doi.org/10.1117/12.2313482

KEYWORDS: Spectrographs, Astronomical imaging, Near infrared, Infrared telescopes, Multiplexing, Cryogenics, Infrared astronomy, Mid-IR, Infrared spectroscopy, Infrared radiation

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Proceedings Article | 9 July 2018 Paper

Paper

DOTIFS: fore-optics and calibration unit design

Haeun Chung, A. Ramaprakash, Pravin Khodade, Chaitanya Rajarshi, Sabyasachi Chattopadhyay, Pravin Chordia, Amitesh Omar, Changbom Park

Proceedings Volume 10702, 107027U (2018) https://doi.org/10.1117/12.2312394

KEYWORDS: Calibration, Telescopes, Lamps, Mirrors, Integrating spheres, Spectrographs, Lenses, Light, Optical instrument design, Optomechanical design

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Proceedings Article | 8 July 2018 Paper

Paper

DOTIFS: spectrograph optical and opto-mechanical design

Haeun Chung, A. N. Ramaprakash, Pravin Khodade, Deepa Modi, Chaitanya Rajarshi, Sabyasachi Chattopadhyay, Pravin Chordia, Vishal Joshi, Sungwook Hong, Amitesh Omar, Swara Ravindranath, Yong-Sun Park, Changbom Park

Proceedings Volume 10702, 107027A (2018) https://doi.org/10.1117/12.2311594

KEYWORDS: Spectrographs, Cameras, Charge-coupled devices, Optical design, Collimators, Optical filters, Spectral resolution, Tolerancing, Optomechanical design, Optical fibers, Thermal analysis

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Proceedings Article | 6 July 2018 Paper

Paper

Design and results for the SAAO wide-field nasmyth camera

Pieter Swanevelder, Dave Carter, James O'Connor, Hannah Worters, Willie Koorts, Briehan Lombaard, Egan Loubser, Keegan Titus, Carel van Gend, Michael Rust, Craig Sass, Hitesh Gajjar, Amanda Sickafoose, A. N. Ramaprakash, Pravin Chordia, Mahesh Burse, Sujit Punnadi, Bhushan Joshi, Sakya Sinha

Proceedings Volume 10702, 107022K (2018) https://doi.org/10.1117/12.2312540

KEYWORDS: Camera shutters, Charge-coupled devices, Cameras, Telescopes, Astronomy

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Proceedings Article | 19 August 2016 Paper

Paper

First results and future plans for the Canarias Infrared Camera Experiment (CIRCE) for the Gran Telescopio Canarias

Alan Garner, Stephen Eikenberry, Miguel Charcos, Yigit Dallilar, Michelle Edwards, Nestor Lasso-Cabrera, Richard Stelter, Antonio Marin-Franch, S. Nicholas Raines, Kendall Ackley, John Bennett, Javier Cenarro , Brian Chinn, Veronica Donoso, Raymond Frommeyer, Kevin Hanna, Michael Herlevich, Jeff Julian, Paola Miller, Scott Mullin, Charles Murphey, Christopher Packham, Frank Varosi, Claudia Vega, Craig Warner, Anamparambu Ramaprakash, Mahesh Burse, Sujit Punnadi, Pravinkumar Chordia, Andreas Gerarts, Héctor de Paz Martín, María Martín Calero, Riccardo Scarpa, Sergio Fernandez Acosta, William Miguel Hernández Sánchez, Benjamin Siegel, Francisco Francisco Pérez, Himar Viera Martín, José Rodríguez Losada, Agustín Nuñez, Álvaro Tejero, Carlos E. Martín González, César Cabrera Rodríguez, Jordi Molgó Sendra, J. Esteban Rodriguez, J. Israel Fernádez Cáceres, Luis A. Rodríguez García, Manuel Huertas Lopez, Raul Dominguez, Tim Gaggstatter, Antonio Cabrera-Lavers, Stefan Geier, Peter Pessev, Ata Sarajedini, A. J. Castro-Tirado

Proceedings Volume 9908, 99084Q (2016) https://doi.org/10.1117/12.2232672

KEYWORDS: Infrared cameras, Polarimetry, Astronomy, X-rays, Stars, Spectroscopy, Spectroscopes, Sensors, Galactic astronomy, Binary data

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Proceedings Article | 4 August 2016 Paper

Paper

MIRADAS for the Gran Telescopio Canarias

Stephen Eikenberry, Steven Nicholas Raines, Richard Deno Stelter, Alan Garner, Yigit Dallilar, Kendall Ackley, John Greg Bennett, Charles Murphey, Paola Miller, David Tooke, Luke Williams, Brian Chinn, Scott Mullin, Sidney Schofield, Craig Warner, Frank Varosi, Bo Zhao, Sophia Eikenberry, Claudia Vega, Hipatia Donoso, Josep Sabater, José María Gómez, Jordi Torra, Josefina Rosich Minguell, Francisco Garzón López, Nicolás Cardiel, Jesús Gallego Maestro, Antonio Marín-Franch, Julio Galipienzo, Miguel Ángel Carrera Astigarraga, Greg Fitzgerald, Ian Prees, Todd Stolberg, Peter Kornik, Anamparambu Ramaprakash, Mahesh Burse, Sujit Punnadi, P. Hammersley

Proceedings Volume 9908, 99081L (2016) https://doi.org/10.1117/12.2232533

KEYWORDS: Infrared telescopes, Infrared radiation, Spectrographs, Astronomical imaging, Mirrors, Sensors, Astronomy, Telescopes, Spectral resolution, Relays

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Proceedings Article | 27 July 2016 Paper

Paper

Evaluating noise performance of the IUCAA sidecar drive electronics controller (ISDEC) based system for TMT on-instrument wavefront sensing (OIWFS) application

Mahesh Burse, Sabyasachi Chattopadhyay, A. Ramaprakash, Sakya Sinha, Swapnil Prabhudesai, Sujit Punnadi, Pravin Chordia, Abhay Kohok

Proceedings Volume 9915, 991520 (2016) https://doi.org/10.1117/12.2232265

KEYWORDS: Sensors, Wavefront sensors, Control systems, Analog electronics, Multiplexers, Stars, Field programmable gate arrays, Power supplies, Electrons, Interfaces

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Proceedings Article | 27 July 2016 Paper

Paper

IDSAC-IUCAA digital sampler array controller

Sabyasachi Chattopadhyay, Pravin Chordia, A. Ramaprakash, Mahesh Burse, Bhushan Joshi, Kalpesh Chillal

Proceedings Volume 9915, 991524 (2016) https://doi.org/10.1117/12.2232477

KEYWORDS: Charge-coupled devices, Video processing, Cadmium sulfide, Video, Analog electronics, Interference (communication), Clocks, Sensors, Power supplies, Signal to noise ratio

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In order to run the large format detector arrays and mosaics that are required by most astronomical instruments, readout electronic controllers are required which can process multiple CCD outputs simultaneously at high speeds and low noise levels. These CCD controllers need to be modular and configurable, should be able to run multiple detector types to cater to a wide variety of requirements. IUCAA Digital Sampler Array Controller (IDSAC), is a generic CCD Controller based on a fully scalable architecture which is adequately flexible and powerful enough to control a wide variety of detectors used in ground based astronomy. The controller has a modular backplane architecture that consists of Single Board Controller Cards (SBCs) and can control up to 5 CCDs (mosaic or independent). Each Single Board Controller (SBC) has all the resources to a run Single large format CCD having up to four outputs. All SBCs are identical and are easily interchangeable without needing any reconfiguration. A four channel video processor on each SBC can process up to four output CCDs with or without dummy outputs at 0.5 Megapixels/Sec/Channel with 16 bit resolution. Each SBC has a USB 2.0 interface which can be connected to a host computer via optional USB to Fibre converters. The SBC uses a reconfigurable hardware (FPGA) as a Master Controller. IDSAC offers Digital Correlated Double Sampling (DCDS) to eliminate thermal kTC noise. CDS performed in Digital domain (DCDS) has several advantages over its analog counterpart, such as - less electronics, faster readout and easier post processing. It is also flexible with sampling rate and pixel throughput while maintaining the core circuit topology intact. Noise characterization of the IDSAC CDS signal chain has been performed by analytical modelling and practical measurements. Various types of noise such as white, pink, power supply, bias etc. has been considered while creating an analytical noise model tool to predict noise of a controller system like IDSAC. Several tests are performed to measure the actual noise of IDSAC. The theoretical calculation matches very well with practical measurements within 10% accuracy.

Proceedings Article | 27 July 2016 Paper

Paper

ISDEC-2 and ISDEC-3 controllers for HAWAII detectors

Mahesh Burse, A. Ramaprakash, Pravinkumar Chordia, Sujit Punnadi, Kalpesh Chillal, Vilas Mestri, Rupali Bharti, Sakya Sinha, Abhay Kohok

Proceedings Volume 9915, 991526 (2016) https://doi.org/10.1117/12.2232510

KEYWORDS: Sensors, Electronics, Astronomy, Observatories, Telescopes, Field programmable gate arrays, Interfaces, Clocks, Control systems, Analog electronics

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Proceedings Article | 18 July 2016 Paper

Paper

The Solar Ultraviolet Imaging Telescope onboard Aditya-L1

Avyarthana Ghosh, Subhamoy Chatterjee, Aafaque Khan, Durgesh Tripathi, A. Ramaprakash, Dipankar Banerjee, Pravin Chordia, Achim Gandorfer, Natalie Krivova, Dibyendu Nandy, Chaitanya Rajarshi, Sami Solanki, S. Sriram

Proceedings Volume 9905, 990503 (2016) https://doi.org/10.1117/12.2232266

KEYWORDS: Space operations, Ultraviolet radiation, Space telescopes, Telescopes, Space telescopes, Solar processes, Sensors, X-ray imaging, Plasma, Ions, Magnetosphere

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Proceedings Article | 15 June 2015 Paper

Paper

Development of a scalable generic platform for adaptive optics real time control

Avinash Surendran, Mahesh Burse, A. Ramaprakash, Padmakar Parihar

Proceedings Volume 9654, 965425 (2015) https://doi.org/10.1117/12.2180704

KEYWORDS: Adaptive optics, Field programmable gate arrays, Clocks, Wavefront sensors, Control systems, Charge-coupled devices, Telescopes, Wavefronts, Logic, Sensors

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Proceedings Article | 15 June 2015 Paper

Paper

Analytical modelling of Thirty Meter Telescope optics polarization

Ramya Anche, G. Anupama, Krishna Reddy, Asoke Sen, K. Sankarasubramanian, A. Ramaprakash, Sujan Sengupta, Warren Skidmore, Jenny Atwood, Sivarani Tirupathi, Shashi Bhushan Pandey

Proceedings Volume 9654, 965408 (2015) https://doi.org/10.1117/12.2181397

KEYWORDS: Mirrors, Polarization, Telescopes, Zemax, Modeling, Instrument modeling, Mueller matrices, Polarimetry, Coating, Thirty Meter Telescope

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Proceedings Article | 18 July 2014 Paper

Paper

DOTIFS: a new multi-IFU optical spectrograph for the 3.6-m Devasthal optical telescope

Haeun Chung, A. Ramaprakash, Amitesh Omar, Swara Ravindranath, Sabyasachi Chattopadhyay, Chaitanya Rajarshi, Pravin Khodade

Proceedings Volume 9147, 91470V (2014) https://doi.org/10.1117/12.2053051

KEYWORDS: Spectrographs, Optical fibers, Galactic astronomy, Iterated function systems, Telescopes, Microlens, Charge-coupled devices, Optical telescopes, Software development, Astronomy

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Proceedings Article | 8 July 2014 Paper

Paper

Project status of the Robert Stobie spectrograph near infrared instrument (RSS-NIR) for SALT

Marsha Wolf, Mark Mulligan, Michael Smith, Douglas Adler, Curtis Bartosz, Matthew Bershady, David Buckley, Mahesh Burse, Pravin Chordia, J. Christopher Clemens, Harland Epps, Kristine Garot, Briana Indahl, Kurt Jaehnig, Ron Koch, William Mason, Gregory Mosby, Kenneth Nordsieck, Jeffrey Percival, Sujit Punnadi, Anamparambu Ramaprakash, J. Alan Schier, Andrew Sheinis, Stephen Smee, Donald Thielman, Mark Werner, Theodore Williams, Jeffrey Wong

Proceedings Volume 9147, 91470B (2014) https://doi.org/10.1117/12.2056736

KEYWORDS: Sensors, Cameras, Near infrared, Diffraction gratings, Beam splitters, Optical filters, Collimators, Received signal strength, Spectroscopes, Telescopes

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Proceedings Article | 13 September 2012 Paper

Paper

Robo-AO: autonomous and replicable laser-adaptive-optics and science system

C. Baranec, R. Riddle, A. Ramaprakash, N. Law, S. Tendulkar, S. Kulkarni, R. Dekany, K. Bui, J. Davis, M. Burse, H. Das, S. Hildebrandt, S. Punnadi, R. Smith

Proceedings Volume 8447, 844704 (2012) https://doi.org/10.1117/12.924867

KEYWORDS: Adaptive optics, Telescopes, Mirrors, Cameras, Imaging systems, Infrared cameras, Laser systems engineering, Observatories, Stars, Sensors

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Proceedings Article | 13 September 2012 Paper

Paper

The Robo-AO software: fully autonomous operation of a laser guide star adaptive optics and science system

Reed Riddle, Mahesh Burse, Nicholas Law, Shriharsh Tendulkar, Christoph Baranec, Alexander Rudy, Marland Sitt, Ankit Arya, Athanasios Papadopoulos, A. Ramaprakash, Richard Dekany

Proceedings Volume 8447, 84472O (2012) https://doi.org/10.1117/12.925475

KEYWORDS: Telescopes, Adaptive optics, Control systems, Laser guide stars, Robotic systems, Cameras, Robotics, Astronomy, Imaging systems, Telecommunications

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Proceedings Article | 20 July 2010 Paper

Paper

Controller and data acquisition system for SIDECAR ASIC driven HAWAII detectors

Anamparambu Ramaprakash, Mahesh Burse, Pravin Chordia, Kalpesh Chillal, Abhay Kohok, Vilas Mestry, Sujit Punnadi, Sakya Sinha

Proceedings Volume 7742, 77422I (2010) https://doi.org/10.1117/12.858455

KEYWORDS: Sensors, Data acquisition, Human-machine interfaces, Staring arrays, Field programmable gate arrays, Cryogenics, Astronomy, Electrons, Interfaces, Readout integrated circuits

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Proceedings Article | 1 October 2009 Paper

Paper

Two-channel wavefront sensor arrangement employing moire deflectometry

Saifollah Rasouli, Anamparambu Ramaprakash, H. K. Das, C. V. Rajarshi, Yasser Rajabi, M. Dashti

Proceedings Volume 7476, 74760K (2009) https://doi.org/10.1117/12.829962

KEYWORDS: Wavefronts, Wavefront sensors, Deflectometry, Turbulence, Atmospheric propagation, Beam splitters, CCD cameras, Moire patterns, Atmospheric sensing, Sensors

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A wavefront sensor which takes advantage of the moire deflectometry has been constructed for measuring atmosphere induced wavefront distortions. In this sensor a collimated laser beam propagates through turbulent atmosphere, then a beam splitter splits it into two beams and the beams pass through a pair of moire deflectometers. Directions of the grating's rulings are parallel in each moire deflectometer but are perpendicular in the two beams. Using a suitable array of lenses and mirrors two sets of moire patterns are projected on a CCD camera. A suitable spatial filter removes the unwanted frequencies. Recording the successive moire patterns by the CCD camera and feeding them to a computer, allow temporal fluctuations of the laser beam wavefront phase to be measured highly accurately. Displacements of the moire fringes in the recorded patterns correspond to the fluctuations of two orthogonal components of the angle of arrival (AA) across the wavefront. The fluctuations have been deduced in successive frames, and then evolution of the wavefront shape is determined. The implementation of the technique is straightforward and it overcomes some of the technical difficulties of the Schlieren and Shack-Hartmann techniques. The sensitivity of detection is adjustable by merely changing the distance between two gratings in both moire deflectometers and relative grating ruling orientation. This overcomes the deficiency of the Shack-Hartman sensors in that these require expensive retrofitting to change sensitivity. Besides, in the moire deflectometry, the measurement is relatively insensitive to the alignment of the beam into the device. Hence this setup has a very good potential for adaptive optics applications in astronomy. Since tilts are measured in the Shack-Hartmann method at discrete locations, it cannot detect discontinuous steps in the wavefront. By this method discontinuous steps in the wavefront are detectable, because AA fluctuations are measured across the wavefront.

Proceedings Article | 16 August 2000 Paper

Paper

CIRPASS: a NIR integral field and multi-object spectrograph

Ian Parry, Craig Mackay, Rachel Johnson, Richard McMahon, Andrew Dean, Anamparambu Ramaprakash, David King, Jim Pritchard, Steve Medlen, Chris Sabbey, Richard Ellis, Alfonso Aragon-Salamanca

Proceedings Volume 4008, (2000) https://doi.org/10.1117/12.395438

KEYWORDS: Sensors, Spectrographs, Cameras, Gemini Observatory, Optical filters, Telescopes, Mirrors, Scattering, Spectral resolution, Astronomical imaging

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Proceedings Article | 26 May 1998 Paper

Paper

Flexible off-axis acquisition and guidance system

Anamparambu Ramaprakash, Ranjan Gupta, S. Tandon

Proceedings Volume 3351, (1998) https://doi.org/10.1117/12.308808

KEYWORDS: Telescopes, Stars, Charge-coupled devices, Image intensifiers, Polarimetry, Imaging systems, Lenses, Relays, Signal to noise ratio, CCD cameras

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Showing 5 of 41 publications

Conference Committee Involvement (5)

Space Telescopes and Instrumentation 2024: Optical, Infrared, and Millimeter Wave

16 June 2024 | Yokohama, Japan

Ground-based and Airborne Telescopes X

16 June 2024 | Yokohama, Japan

Ground-based and Airborne Telescopes IX

17 July 2022 | Montréal, Québec, Canada

Ground-based and Airborne Telescopes VIII

14 December 2020 | Online Only, California, United States

Ground-based and Airborne Telescopes VIII

13 December 2020 | San Diego, California, United States

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