Mr. Chaitanya V. Rajarshi Profile

Chaitanya V. Rajarshi

at Inter-Univ Ctr for Astronomy and Astrophysics

SPIE Involvement:

Author

Publications (15)

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

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

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 | 30 August 2022 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 | 29 August 2022 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

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 | 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

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

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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Proceedings Article | 11 July 2018 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 | 9 July 2018 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

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 | 18 July 2016 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 | 18 July 2014 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 | 1 October 2009 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.

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