Mr. Pasko Roje Profile

Pasko Roje

at Leibniz-Institut für Astrophysik Potsdam

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Publications (2)

Proceedings Article | 25 July 2024 Presentation + Paper

The fibre target alignment process of the 4MOST instrument

Roland Winkler, Ingo Stilz, Alexander Pramskiy, Weijia Sun, Pasko Roje, Thomas Liebner, Daniel Sablowski, Steffen Frey, Gerard Zins, Scott Smedley

Proceedings Volume 13101, 131010L (2024) https://doi.org/10.1117/12.3020482

KEYWORDS: Telescopes, Metrology, Cameras, Device simulation, Equipment, Calibration, Sensors

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The 4-meter Multi-Object Spectroscopic Telescope (4MOST) instrument uses 2436 individually positioned optical fibres to couple the light of targets into its spectrographs. The Fibre Target Alignment (FTA) software controls all aspects of the 4MOST instrument that are involved to position the 2448 spines of the AESOP positioner to their target locations closer than 10µm RMS, within 90 seconds. The AESOP fibre positioner provides a HTML interface which is used by the FTA software to command spine movements. The metrology system consists of four cameras, and a sophisticated software package to measure the location of fibres, which are moved by the AESOP spines. Spines reach their target typically after six to eight iterative movements, which are interlaced with metrology frames. The metrology software is capable of taking 4 images simultaneously, and reconstructing fibre positions to within 3μm RMS within five seconds. We present the FTA control software architecture, the interaction of sub-components and the different operation modes of the system. Especially the concurrent and simultaneous control of four metrology camera processes. Due to the complexity of the system, comprehensive debugging and visualization tools have been developed which allow a detailed understanding and interaction of the entire system. The graphical tool provides feedback for each individual camera stream and their combined result. It provides statistics and tools to manipulate individual spines, especially to recover them in case of entanglement. To develop the control software, a full end-to-end simulator has been created, which closes the loop between metrology image simulation, simulated fibre positioning and all control aspects in between. The metrology system uses the current spine position as presented by the AESOP positioner to render metrology camera images. Analysis and downstream computation is identical to the live software. When commanded to move spines, The AESOP simulator executes the identical steps to move spines, except sending electrical signals. After which it returns the expected spine positions after their move, which is taken as input for the next FTA iteration.

Proceedings Article | 18 July 2024 Poster + Paper

4MOST low-resolution spectrographs AIT at AIP

Florence Laurent, Didier Boudon, Eric Daguisé, Karen Disseau, Steffen Frey, Rémi Giroud, Aurélien Jarno, Jens-Kristian Krogager, Jean-Emmanuel Migniau, Matthew Lehnert, Arlette Pecontal, Emmanuel Pécontal, Alban Remillieux, Johan Richard, Pasko Roje, Carlos E. Rodriguez Alvarez, Deborah Sobiella

Proceedings Volume 13096, 130966C (2024) https://doi.org/10.1117/12.3020061

KEYWORDS: Lawrencium, Spectrographs, Lamps, Collimators, Sensors, Optical alignment, Light emitting diodes, Interfaces, CCD image sensors, Spectral resolution

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4MOST, the 4m Multi Object Spectroscopic Telescope, is an upcoming optical, fibre-fed, MOS facility for the VISTA telescope at ESO's Paranal Observatory in Chile. Its main science drivers are in the fields of galactic archeology, high-energy physics, galaxy evolution and cosmology. The 4MOST consortium consists of several institutes in Europe and Australia under leadership of the Leibniz-Institut für Astrophysik Potsdam (AIP). 4MOST is currently in its Assembly, Integration and Tests Phase with an expected start of science operations in 2025. The design of 4MOST features 2436 fibres split into two low-resolution spectrographs (1624 fibres, three arms, 370-950 nm, R > 4000) and one high-resolution spectrograph (812 fibres, three arms, ~44-69 nm coverage each, R > 18000). The fibre positioner covers a hexagonal field of view of ~4.1 deg². The fibers are 85μm core with an output beam at f/3. CRAL has the full responsibility of the two Low Resolution Spectrographs. Each of them is composed of a 200mm beam for an off-axis collimator associated to its Schmidt corrector, three “color” arms hosting f/1.73 cameras with standard 6k x 6k 15μm pixel CCD detectors. The local acceptance reviews at CRAL for the both 4MOST Low Resolution Spectrographs were successfully passed respectively in December 2021 and October 2022. In 2022, two SPIE papers described the process performed at CRAL from the integration and alignment of the sub-assemblies up to the procedures developed to test the spectrograph and demonstrate its compliance with the requirements. Then the two LRS were partially disassembled and sent to Potsdam. They have now been fully integrated, aligned and tested at Potsdam by the CRAL team. The integration of both LRS with the others sub-systems in order to validate the global end-to-end tests is foreseen in 2024 and an installation at VISTA telescope is expected in 2025. This paper describes the assembly, integration and performances achieved at Postdam for the both Low Resolution Spectrographs. Special emphasis is put on the update of procedures and components to improve performances and meet the top-level requirements.

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