1 / 10

B-Pol Satellite experiment: HWP technologies comparison

This presentation discusses the critical requirements and performance characteristics of Half-Wave Plates (HWPs) in sensitive multi-pixel array applications, conducted by the Radioastronomy Technology Group at the University of Manchester. Key requirements such as large dimensions, robust and lightweight design, anti-reflection coatings, and low absorption losses are highlighted. The study compares the effectiveness of sapphire achromatic HWPs with mesh designs, demonstrating promising results in terms of polarization control and systematic understanding. Insights into recent advancements and material properties are presented, showcasing future directions in HWP research.

clark
Télécharger la présentation

B-Pol Satellite experiment: HWP technologies comparison

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. B-Pol Satellite experiment: HWP technologies comparison The University of Manchester Giampaolo Pisano Radioastronomy Technology Group Jodrell Bank Centre for Astrophysics, University of Manchester, UK B-Pol Meeting - Paris, 29-30 July 2010

  2. Half-Wave Plates: Requirements • In sensitive multi-pixel array applications there are many demanding • requirements for the HWP characteristics, let’s mention the most general ones: Large dimensions: (up to 30 cm in diameter) to achieve meaningful sensitivities. 1 Robust and light device: mechanical rotation needed; should not vibrate. 2 Anti-reflection coatings (ARCs): to achieve broadband performance. 3 Low absorption losses: to minimise the thermal emission seen by the detectors ( also very low differential losses between fast/slow axes). 4 Polarisation systematic effects introduced by the device: deep understanding and good control both needed. 5

  3. Sapphire Achromatic HWPs: Pancharatnam designs G. Pisano et al., Applied Optics v45, n26 (2006) G. Savini et al., Applied Optics v45, n35 (2006) - Recipes based on birefringent plates: • Limited maximum diameters • Very expensive plates 1 (Quartz Ø ~110mm; Sapphire Ø ~280 mm)  Very robust but heavy 2 (Ex: 3-plates sapphire, no ARC) • New ARCs to be synthesised • - For sapphire (n~3.4) •  new materials needed (n~1.8) 3 ~10cm •  Low absorption (2-4%) • Can be achieved by cooling at • cryogenic temperatures but : • differential loss axes ~0.1% • (not reducible) 4

  4. G. Pisano et al., Applied Optics v45, n26 (2006) G. Savini et al., Applied Optics v45, n35 (2006) Sapphire Achromatic HWPs: Modelling & FTS Tests Results Fast axis Transmission Absorption calculation Results Extrapolated Minimum Cross Polarisation Measured Cross-Polarisation X-pol ~-25/-30dB  We have excellent understanding of the polarisation systematics 5

  5. Sapphire Achromatic HWPs: Quasi-Optical Tests Co-Pol & Cross-Pol Beams - VNA measurements: Horn-OMT pixel + HWP Averaged Cross-Pol: -29dB (Across beam and frequency band)  We can characterise/control the polarisation systematics with high accuracy 5

  6. Mesh Half-Wave Plate: Air-gap design G. Pisano et al., Applied Optics v47, n33 (2008) Capacitive Stack Dj = p • Limits in diameter ~100mm 1 • ARCs not required ! 3 • It is very fragile and can vibrate ! 2 Inductive Stack • Absorption can be very low at room T (1.5%) • Differential losses (0.6%) could be equalised 4

  7. Mesh HWP : Air-gap design results G. Pisano et al., Applied Optics v47, n33 (2008) Fast Axis Transmission Slow Axis Transmission Differential Phase-Shift Cross-Polarisation X-pol ~ -25dB  We have very good understanding of the polarisation systematics 5

  8. Mesh HWP: Dielectrically embedded design(v.1) G. Pisano et al., to be submitted to Appl. Opt. Capacitive Stack Dj = p • Present diameter ~200mm (soon 300mm !) 1 • ARC commercially available 3 Pol 1 • Very robust & light 2 Inductive Stack Pol 2 • Absorption should be low at room T • Differential loss could be equalised 4

  9. Mesh HWP: Dielectrically embedded design(v.2) G. Pisano et al., to be submitted to Appl. Opt. 20cm Recipe with Inductive and Capacitive lines on the same grid • One C/L stack only •  Grids # reduced by a factor 2 • Grids easier to align  should have lower losses

  10. Conclusions • HWP studies: • Birefringent vs Mesh options • We know how to model and build both • Mesh HWP the most promising •  We should be able to meet all the requirements

More Related