@@ -216,7 +216,7 @@ The performances of the setup depend strongly on the HoQIs because they are the
...
@@ -216,7 +216,7 @@ The performances of the setup depend strongly on the HoQIs because they are the
\paragraph*{Tested noise sources}
\paragraph*{Tested noise sources}
There are several noise sources to take into account: air currents and vibrations from electronics and cables have been reduced placing the optical setup into a foam box and moving the electronic devices suitably. Cables have been isolated from the table and the breadboard by rubber feet.\\
There are several noise sources to take into account: air currents and vibrations from electronics and cables have been reduced placing the optical setup into a foam box and moving the electronic devices suitably. Cables have been isolated from the table and the breadboard by rubber feet.\\
\noindent
\noindent
The test in Fig. \ref{sound} shows that the setup is sensitive to acoustic noise: we injected a sound at 75 Hz and both HoQIs clearly detected it. Moreover, we found out that HoQI1 is detected some noise around 22 Hz that HoQI2 is not able to sense: the two peaks in the figure are present in every condition of the laboratory and part of the day. The source of this noise is still under investigation: it could be a permanent sound in the lab non audible by humans. The fact that only HoQI1 can detected could be due to its position with respect to the noise source: it might be closer to it than HoQI2. Imperfections in the optics and general setup of the HoQIs are also taken into account.\\
The test in Fig. \ref{sound} shows that the setup is sensitive to acoustic noise: we injected a sound at 75 Hz and both HoQIs clearly detected it. Moreover, we found out that HoQI1 is detecting some noise around 22 Hz that HoQI2 is not able to sense: the two peaks in the figure are present in every condition of the laboratory and time of the day. The source of this noise is still under investigation: it could be a permanent sound in the lab non audible by humans. The fact that only HoQI1 can detected could be due to its position with respect to the noise source: it might be closer to it than HoQI2. Imperfections in the optics and general setup of the HoQIs are also taken into account.\\
\begin{figure}[h!]
\begin{figure}[h!]
\centering
\centering
...
@@ -237,7 +237,7 @@ The behaviour of the two HoQIs has been tested in loop and out of loop, to check
...
@@ -237,7 +237,7 @@ The behaviour of the two HoQIs has been tested in loop and out of loop, to check
This test shows that HoQI2 is in general noisier than HoQI1, especially above 1 Hz: this affects laser stabilization measurement and loop stability, thus it has been deeply investigated. The higher intensity fluctuations of laser2 can partially explain the reason of HoQI2 noise.
This test shows that HoQI2 is in general noisier than HoQI1, especially above 1 Hz: this affects laser stabilization measurement and loop stability, thus it has been deeply investigated. The higher intensity fluctuations of laser2 can partially explain the reason of HoQI2 noise.
\begin{figure}[h!]
\begin{figure}[h!]
%\centering
\centering
\includegraphics[scale=0.3]{images/hoqisOLCL.png}
\includegraphics[scale=0.3]{images/hoqisOLCL.png}
\caption[In-loop test of HoQIs performances]{In-loop test of HoQIs performances. The out-of-loop traces (cyan and purple) are following the free running frequency noise trace (blue) as expected, while when the loop is closed the HoQI outputs (green and red) show that the controllers are pushing the expected gain (orange). There is an evident un-match with the orange trace below 0.4 Hz and this is likely due to loop leakage.}
\caption[In-loop test of HoQIs performances]{In-loop test of HoQIs performances. The out-of-loop traces (cyan and purple) are following the free running frequency noise trace (blue) as expected, while when the loop is closed the HoQI outputs (green and red) show that the controllers are pushing the expected gain (orange). There is an evident un-match with the orange trace below 0.4 Hz and this is likely due to loop leakage.}
@@ -135,31 +135,6 @@ UoB = University of Birmingham\\
...
@@ -135,31 +135,6 @@ UoB = University of Birmingham\\
\mainmatter
\mainmatter
\chapter*{Structure of this thesis}
This thesis presents a study for the enhancement of the detectors for gravitational waves. It is then divided in two parts: Part 1 introduces the context of the work done and frames the study into the specific field of the low frequency window; this part is crucial to fully embrace the study performed in the laboratories. Part 2 is entirely focussed on the work done during the years between 2017 and 2021, covering the experience at LIGO Hanford and at the Albert Einstein Institute. This part includes the details of the experiments performed and their results.\\
\noindent
Chapter 1. This chapter briefly introduces the gravitational waves as the astrophysical phenomenon proposed by Albert Einstein in 1915 and discovered in 2017.\\
\noindent
Chapter 2. In this chapter we will see that there are some gravitational-wave sources emitting at lower frequency for which the current detectors are blind: it is in this frame that the experiments proposed in this thesis have been done. The final and ambitious goal is to improve the sensitivity of the detectors at lower frequencies.\\
\noindent
Chapter 3. This chapter describes briefly how an interferometric detector for gravitational waves works. In particular, the detector LIGO for which this work collaborated is illustrated. Specific details of the instruments on which the author has contributed are explained and referred to throughout the experimental work of the following chapters.\\
\noindent
Chapter 4. In this chapter there is the first experimental study performed in the first year of my PhD study: an optical lever for the reduction of tilt motion has been design and build at UoB, and then tested at the AEI. The details of the experiment and the results are explained in details.\\
\noindent
Chapter 5. This chapter is focussed entirely on the work done during my collaboration at LIGO Hanford site in 2019: during the O3a and O3b runs I had the chance to contribute to the improvement of the detectors by studying a new configuration of the seismic system in order to make the instrument more stable and allow a longer observing time. The details of this study includes original computations and tests on LIGO sites.\\
\noindent
Chapter 6. During the last year of the PhD studies, I contributed to the development of a new device for seismic control; in particular, I focussed on the stabilization in frequency of the laser source of the device, making use of new technology and advanced techniques. The experiment has been fully carried out at UoB between September 2020 and September 2021 and it is described in details.\\
\noindent
There are three appendices useful to make the work more complete: appendix A illustrates the work done at LIGO Hanford laboratory in building the suspensions for the A+ upgrade; appendix B gives some useful directions about control loops and block diagrams; appendix C aims to celebrate the first gravitational wave discovery.
\part{Gravitational-wave frontiers}
\part{Gravitational-wave frontiers}
\include{GW}
\include{GW}
\include{LF}
\include{LF}
...
@@ -183,10 +158,10 @@ There are three appendices useful to make the work more complete: appendix A ill
...
@@ -183,10 +158,10 @@ There are three appendices useful to make the work more complete: appendix A ill
\bibitem{wei} S. Weinberg \textit{Gravitation and Cosmology: principles and applications of the General Theory of Relativity}, John Wiley \& Sons, Inc., 1972
\bibitem{wei} S. Weinberg \textit{Gravitation and Cosmology: principles and applications of the General Theory of Relativity}, John Wiley \& Sons, Inc., 1972
\bibitem{nar} J. V. Narlikar \textit{An introduction to Relativity}, Cambridge University Press, 2011
\bibitem{mag} M. Maggiore \textit{Gravitational waves - Vol. 1: Theory and Experiments}, Oxford University Press, 2013
\bibitem{mag} M. Maggiore \textit{Gravitational waves - Vol. 1: Theory and Experiments}, Oxford University Press, 2013
\bibitem{nar} J. V. Narlikar \textit{An introduction to Relativity}, Cambridge University Press, 2011
%chapt 2
%chapt 2
\bibitem{first} B. P. Abbott, \textit{Observation of Gravitational Waves from a Binary Black Hole Merger}, Phys. Rev. Lett. 116, 061102, 2016
\bibitem{first} B. P. Abbott, \textit{Observation of Gravitational Waves from a Binary Black Hole Merger}, Phys. Rev. Lett. 116, 061102, 2016
