Sumários

Review: Resonant cavities. Gaussian Beams. Modes. Mode-matching.

8 Maio 2026, 09:00 • José Manuel Rebordão

Resonant cavities, Finesse, FSR, Airy function.
Gaussian beams, higher order Hermite and Laguerre modes. Gouy phase.
Resonant cavities as mode cleaners, basics.
 
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Detection architectures
Layered media – matrix methods, transfer and scattering matrices, examples.

Wavefront metrology (3 of 3)

6 Maio 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. 

Michelson interferometry (class 3 of 3)

6 Maio 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.

Measurement concept. Noise factors and their evolution

4 Maio 2026, 14:00 • José Manuel Rebordão

Principle of measurement. Optical Gain. Dark fringe concept. Impact of using resonant arms to gain sensitivity. Active FP cavities driven by intracavity power concept
Architecture of the Interferometers: Michelson and Sagnac, pros and cons.
Noise factors in GWO. Intrinsic and technical noises. Analysis of the intrinsic factors. Evolution of overall noise curves since initial LIGO (2010) to current implementations or being under development. Thermal noise: comparative analysis between thermal properties of silicon, fused silica and sapphire; exquisite properties of Si, therefore justifying its selection for LIGO Voyager, despite the need to change the laser and reducing temperature to 123 K.
 
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Reviewing: Gaussian waves. Mode-matching. Mode cleaning

Wavefront metrology (class 2 of 3)

29 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.