Cophasing elements. Dispersive sensing. Cophasing process

20 Abril 2026, 14:00 • José Manuel Rebordão

Co-phasing hardware: PIL, WL and Dispersive Hartman Sensors.
Overview of the JWST cophasing process.
 
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Gravitational waves observatories.

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Phase retrieval: parametric and curvature sensing methods

17 Abril 2026, 09:00 • José Manuel Rebordão

Phase retrieval approaches:
Phase diversity. Modelling propagation and defocusing. Examples
Curvature sensing: description of Shack-Hartman and Pyramid sensors.
 
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Co-phasing hardware: PIL, WL and Dispersive Hartman Sensors
JWST Cophasing process

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Wavefront metrology (class 1 of 3)

15 Abril 2026, 17:00 • Bachar Wehbe

A Shack-Hartmann wavefront sensor was built based on an array of lenses that divide / sample the incoming wavefront into small sub-apertures, focusing independently the light from each lens in a 2D sensor that captures the focal plane pattern. This pattern was processed to obtain the position of each focus point from each individual lens.

An incident plane wave was created using a spatial filter and a collimated lens to produce a grid of equidistant focal points, the reference position, while several distorted waves (corresponding to a point source from an optical fibre in controlled positions) result in an uneven distribution of points that were referenced to the ideal plan wave situation in order to determine with the sensor the position of the fibre tip, using the Shack-Hartman sensor to measure an unknown wavefront based of the focus shifts from the calibration. 

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Michelson interferometry (class 1 of 3)

15 Abril 2026, 15:00 • Alexandre Pereira Cabral

Setup of a Michelson Interferometer (MI), using amplitude splitting, and analysis of the generated interferograms in several configurations.
Usage of cube beam splitters and polarisation optics to control laser beam polarization.

Assessment of how the MI can be used to measure relative displacements of one of the mirrors, using a piezo electric stage actuator to move one of the mirrors.

Analysis of several polarization optical elements (polarizers, polarizing beam splitters and wave plates) using a polarimeter (an instruments that measure the polarisation state of light).

Assembly of a homodyne quadrature detection configuration to achieve higher resolution compared to the previous simple homodyne detection.
Acquisition of interferograms using a CMOS 2D camera for post processing.

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NIRISS – AMI. Webb cophasing

13 Abril 2026, 14:00 • José Manuel Rebordão

NIRISS AMI – Conclusion
JWST COPHASING: HW and SW elements available to co-phase.
Phase retrieval: The Gerchber-Saxton/IFTA algorithm; kinoforms; examples similar to JWST needs.
 
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Hartman sensors. Phase diversity. Webb cophasing process

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