\section{Friction dampers and noise reduction} \label{sec:dampers}
Due to the unique construction of our cavity to achieve the goals outlined in Section \ref{sec:apparatus}, we are unable to incorporate a spacer made out of ultralow expansion glass (ULE) or fused sillica (FS) to provide stability against thermal and vibration drifts \cite{didier2016ule}. 
Instead, we aim to `stiffen' the mechanical modes by introducing friction dampers to reduce the mechanical vibrations. 
These friction dampers are thin light strips of aluminum which we cut from a larger sheet and milled to the desired thickness.

With strategically chosen points of placement, we find that we can suppress the noise by an order of magnitude to $\sim0.1$~nm \cite{neville2020thesis}.
We observe an improvement in the suppression as the number of dampers increase, with a maximal improvement at three friction dampers. 
The ideal locations of the dampers are shown in Figure \ref{fig:metal strips}.
We observe that populating the top of the structure with more than two dampers did not yield any discernible improvements.
It is important to note that the dampers are effective only when they are in contact with both mirrors.

\begin{figure}
    \centering
    \includegraphics[width=\columnwidth]{figures/cuvtop.png}
    \caption{Top view of the friction dampeners placed on the cavity, housed in a curvette. The dampeners weigh around 0.2~g, and have a thickness of approximately 0.5~mm to fit within the 1~mm gap between the cavity and the curvette. Two dampeners are placed at the top, whereas a third can be spotted at the bottom corner.}
    \label{fig:metal strips}
\end{figure}

This approach is advantageous for several reasons. 
Firstly, the friction dampers are very lightweight and compact. 
They weigh a mere 0.2~g and have a thickness of around 0.5~mm. 
Hence, they do not restrict the movement range of the piezo scanner and are easily implemented in systems that face stringent space or load constraints.
Secondly, they are readily available at practically no cost since they are made from a common material, and they do not require any technical expertise to prepare. 
Lastly, it is a vacuum-compatible material, which is crucial for applications where the system will be placed in a vacuum, such as ours.  
