Prof. Stephen B. Potter Profile

Prof. Stephen B. Potter

at South African Astronomical Observatory

SPIE Involvement:

Author

Publications (19)

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

Instrumentation at the SAAO for autonomous rapid-response observing

Nicolas Erasmus, Stephen Potter, Carel H.D. van Gend, Egan Loubser, Kathryn Rosie, Keegan Titus, Sunil Chandra, Hannah Worters, Hitesh Gajjar, Moloko Hlakola, Roufurd Julie

Proceedings Volume 13096, 130968K (2024) https://doi.org/10.1117/12.3015250

KEYWORDS: Equipment, Telescopes, Observatories, Cameras, Imaging systems, Spectrographs

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SPIE Journal Paper | 27 April 2024

Mookodi: multi-purpose low-resolution spectrograph and multi-filter photometric imager for rapid follow-up observations of astronomical transient events

Nicolas Erasmus, Iain Steele, Andrzej Piascik, Stuart Bates, Christopher Mottram, Kathryn Rosie, Carel H. D. van Gend, Ulrich Geen, Magaretha L. Pretorius, Stephen Potter, Egan Loubser, Willie Koorts, Hitesh Gajjar, Keegan Titus, Hannah Worters, Amanda Sickafoose, Sunil Chandra, James E. O’Connor, Kgothatso Matlala, Justine Crook-Mansour, Ali Ranjbar, Robert Smith, Helen Jermak, Shalom Abiodun, Okwudili Egbo

JATIS, Vol. 10, Issue 02, 025005, (April 2024) https://doi.org/10.1117/12.10.1117/1.JATIS.10.2.025005

KEYWORDS: Telescopes, Equipment, Spectrographs, Tunable filters, Cameras, Stars, Imaging systems, Sensors, Optical filters, 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 | 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 Presentation + Paper

Presentation + Paper

Software architecture of the Intelligent Observatory Local Control Unit

Carel H De R van Gend, Stephen Potter, Roufurd Julie, Paul Swart, Nicolas Erasmus, Hannah Worters, Sunil Chandra, Kgothatso Matlala

Proceedings Volume 12189, 121890R (2022) https://doi.org/10.1117/12.2629978

KEYWORDS: Telescope instrument control software, Telescopes, Observatories, Computer architecture, Control systems, Information operations, Domes, Stars, Human-machine interfaces, Astronomy

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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

SALT transient science with TOMs

Ruby Van Rooyen, Deneys Maartens, David Buckley, Marissa Kotse, Christian Hettlage, Stephen Potter, Rachel Street

Proceedings Volume 11452, 114523L (2020) https://doi.org/10.1117/12.2562250

KEYWORDS: Visibility, Satellites, X-rays, Telescopes, Earth observing sensors, Prototyping, Visualization, Lanthanum, Observatories, Astronomical telescopes

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One aspect of the SALT X-ray transient program is the identification of SALT observation time that overlaps with scheduled X-ray satellite observations. This is particularly relevant to the optical study of X-ray transients. Since SALT is a fixed elevation telescope, the target visibility is restricted to a circular annulus on the sky covering a total of 1 380 square degrees. In order to identify satellite targets that overlap with SALT visibility, a custom Python program was developed to scrape daily schedules of a number of satellites, and calculate the SALT annulus visibility period of the satellite targets to find overlapping observation time between the satellites and SALT. If a target observation time overlaps in visibility, the relevant information is published to a web page, as well as summarised in an email for dissemination by a mailing list. Transient alerts by email is an old established method, but it clogs inboxes and requires time during the day to evaluate for scheduling — followed by an independent process to request or submit a target for observation to a telescope. It also requires a human in the loop, which will become increasingly challenging as the frequency of alerts increase over time. To streamline the process, from evaluation to submission, SALT (and by extension the SAAO intelligent observatory) is in the midst of developing a prototype TOM for the X-ray transient observations. The aim of the prototype development is to identify and implement the components that will make SALT observations more easily undertaken for the transient community using TOMs1 for target management and observation. The current SALT X-ray transient email alert software, Xsats, contains all the components necessary to migrate to a TOM transient alert interface. Additionally, because the current email alerts have been running for a while, user needs and requirements are already folded into the code; thereby permitting a straight-up mapping onto new technology, using the existing system as independent verification. This paper presents the overall design describing the migration process, as well as application-based development that will be required.

Proceedings Article | 13 December 2020 Presentation + Paper

Presentation + Paper

Design of telescope and instrument control and interface software at the South African Astronomical Observatory: building blocks of the intelligent observatory

Carel H. D. van Gend, Amanda Sickafoose, Stephen Potter, Briehan Lombaard, Pieter Swanevelder, Hitesh Gajjar, Hannah Worters, Willie Koorts, Keegan Titus, Craig Sass, Egan Loubser, Nicolas Erasmus, James O'Connor, Ramotholo Sefako, Roufurd Julie, Freya Bovim

Proceedings Volume 11452, 1145206 (2020) https://doi.org/10.1117/12.2562161

KEYWORDS: Telescopes, Observatories, Astronomical telescopes, Astronomy, Optical instrument design, Control systems, Software development, Computer architecture, Large telescopes, Cameras

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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 | 14 May 2019

SpUpNIC (Spectrograph Upgrade: Newly Improved Cassegrain): a versatile and efficient low- to medium-resolution, long-slit spectrograph on the South African Astronomical Observatory’s 1.9-m telescope

Lisa Crause, David Gilbank, Carel van Gend, Hannah Worters, Craig Sass, Enrico Kotze, Stephen Potter, Amanda Sickafoose, Ramotholo Sefako, John Southworth, Lucas Macri, John Thorstensen, Cezary Galan, Patricia Skelton, Chris Engelbrecht, Ian Braker, Hartmut Winkler, Daniel Pieńkowski, Derya Sürgit, Ahmet Erdem, Matt Burleigh

JATIS, Vol. 5, Issue 02, 024007, (May 2019) https://doi.org/10.1117/12.10.1117/1.JATIS.5.2.024007

KEYWORDS: Spectrographs, Cameras, Telescopes, Stars, Astronomy, Charge-coupled devices, Lamps, Mirrors, Astronomical telescopes, Sensors

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Proceedings Article | 10 July 2018 Presentation + Paper

Presentation + Paper

SALT and SAAO strategy, focusing on the time-domain: process, plans, and challenges

Petri Väisänen, Lisa Crause, David Gilbank, David Buckley, Chris Coetzee, Steven Crawford, Stephen Potter, Retha Pretorius, Encarni Romero Colmenero, Ramotholo Sefako, Michael Shara, Amanda Sickafoose, Theodore Williams

Proceedings Volume 10704, 107040A (2018) https://doi.org/10.1117/12.2313272

KEYWORDS: Telescopes, Galactic astronomy, Astronomy, Spectrographs, Observatories, Stars, Exoplanets, Large telescopes, Spherical lenses, Spectral resolution, Software development

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Proceedings Article | 9 August 2016 Paper

Paper

Commissioning the polarimetric modes of the Robert Stobie spectrograph on the Southern African Large Telescope

S. Potter, Ken Nordsieck, Encarni Romero-Colmenero, Steve Crawford, Petri Vaisanen, Éric Depagne, David Buckley, Anthony Koeslag, Janus Brink, Christian Hetlage, Keith Browne, Lisa Crause, Alan Schier, James Allington

Proceedings Volume 9908, 99082K (2016) https://doi.org/10.1117/12.2232391

KEYWORDS: Polarimetry, Beam splitters, Calcite, Spectrographs, Large telescopes, Received signal strength, Imaging spectroscopy, Polarimetry, Spectrographs, Polarization, Prisms, Stars

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Proceedings Article | 9 August 2016 Paper

Paper

SpUpNIC (Spectrograph Upgrade: Newly Improved Cassegrain) on the South African Astronomical Observatory's 74-inch telescope

Lisa Crause, Dave Carter, Alroy Daniels, Geoff Evans, Piet Fourie, David Gilbank, Malcolm Hendricks, Willie Koorts, Deon Lategan, Egan Loubser, Sharon Mouries, James O'Connor, Darragh O'Donoghue, Stephen Potter, Craig Sass, Amanda Sickafoose, John Stoffels, Pieter Swanevelder, Keegan Titus, Carel van Gend, Martin Visser, Hannah Worters

Proceedings Volume 9908, 990827 (2016) https://doi.org/10.1117/12.2230818

KEYWORDS: Spectrographs, Cameras, Collimators, Mirrors, Telescopes, Diffraction gratings, Charge-coupled devices, Spectrographs, Cameras, Collimators, Diffraction gratings, Lamps, Optical alignment, CCD cameras

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Proceedings Article | 15 July 2016 Paper

Paper

Genetically optimizing weather predictions

S. Potter, Kai Staats, Encarni Romero-Colmenero

Proceedings Volume 9910, 99102H (2016) https://doi.org/10.1117/12.2232306

KEYWORDS: Databases, Telescopes, Observatories, Photometry, Space telescopes, Cameras, Data acquisition, Robotics, Electron multiplying charge coupled devices, Sensor networks

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Proceedings Article | 30 July 2010 Paper

Paper

PySALT: the SALT science pipeline

Steven Crawford, Martin Still, Pim Schellart, Luis Balona, David A. Buckley, Garith Dugmore, Amanda A. Gulbis, Alexei Kniazev, Marissa Kotze, Nicola Loaring, Kenneth Nordsieck, Timothy Pickering, Stephen Potter, Encarni Romero Colmenero, Petri Vaisanen, Theodore Williams, Ewald Zietsman

Proceedings Volume 7737, 773725 (2010) https://doi.org/10.1117/12.857000

KEYWORDS: Telescopes, Imaging spectroscopy, Received signal strength, Fabry–Perot interferometers, Data archive systems, Spectroscopy, Software development, Photometry, Spectrographs, Polarimetry

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Proceedings Article | 21 July 2010 Paper

Paper

Time resolved astronomy with the SALT

D. A. Buckley, S. Crawford, A. A. Gulbis, J. McPhate, K. Nordsieck, S. Potter, D. O'Donoghue, O. H. Siegmund, P. Schellart, M. Spark, B. Welsh, E. Zietsman

Proceedings Volume 7735, 773559 (2010) https://doi.org/10.1117/12.858039

KEYWORDS: Stars, Telescopes, Astronomy, Charge-coupled devices, Sensors, X-rays, Cameras, Magnetism, Photometry, Photon counting

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Proceedings Article | 15 July 2010 Paper

Paper

Spectropolarimetry with the SALT RSS

Janus Brink, David A. Buckley, Kenneth Nordsieck, Stephen Potter

Proceedings Volume 7735, 773517 (2010) https://doi.org/10.1117/12.856932

KEYWORDS: Polarization, Polarimetry, Received signal strength, Telescopes, Wave plates, Error analysis, Astronomy, Stars, Polarizers, Sensors

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Proceedings Article | 11 July 2008 Paper

Paper

A new two channel high-speed photo-polarimeter (HIPPO) for the SAAO

Stephen Potter, David Buckley, Darragh O'Donoghue, James O'Conner, Piet Fourie, Geoff Evans, Craig Sass, Lisa Crause, O. Butters, Andrew Norton, Koji Mukai, Martin Still

Proceedings Volume 7014, 70145E (2008) https://doi.org/10.1117/12.789716

KEYWORDS: X-ray astronomy, Astronomy, Beam splitters, Modulation, Polarization, Ultraviolet astronomy, X-rays, Ultraviolet radiation, Optical filters, Wave plates

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Showing 5 of 19 publications

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