PhD Defence Viola Spagnuolo

Keywords: Gravitational Waves, Mirrors for Gravitational-Wave Detectors, Coating Thermal Noise, Material investigations for mirrors of gravitational-wave detectors
 

"Mirror, Mirror on the Wall: Pushing the Boundaries of Gravitational-wave Detection"
 

Viola Spagnuolo studied materials to make gravitational-wave detectors more sensitive, especially for future projects like the Einstein Telescope. Gravitational waves are tiny ripples in spacetime caused by massive objects like black holes colliding. Detecting them is very difficult and requires incredibly precise instruments called laser interferometers.

An interferometer uses laser light to measure tiny changes in distance, but it can be affected by "noise"—unwanted disturbances that make detection harder. One major source of noise is thermal noise, which comes from the natural vibrations of materials due to heat. Viola’s research focused on understanding and reducing this noise, especially by studying how energy dissipates within materials, and how materials lose energy when they vibrate (mechanical loss).

To study this, Viola developed and tested a new setup called the Gentle Nodal Suspension system, which helps measure mechanical loss very precisely. She tested several materials used for the coatings of interferometer mirrors, such as amorphous silicon, TiO₂:SiO₂ (titanium dioxide and silicon dioxide), and TiO₂:GeO₂ (titanium dioxide and germanium dioxide). Among these, TiO₂:SiO₂ was especially promising because it reduced thermal noise more effectively than the materials currently in use.

In the final part of her research, Viola studied thermoelastic loss, a type of noise that occurs when temperature changes cause materials to expand and contract. She explored how different mirror shapes could reduce this effect. Her work helps improve the materials and techniques used in gravitational-wave detectors, making them better at spotting these faint signals from space.

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