updates to oplev chapter

main/LIGO.tex

@@ -179,7 +179,7 @@ The main disturbance affecting the stabilization of the resonators is the ground
 The most important cavity lengths to keep stable are highlighted in Fig. \ref{lsc}; each length path between optics contributes to a specific signal monitored to keep the cavities in resonance. The signals are the Signal Recycling Cavity Length (SRCL), the Power Recycling Cavity Length (PRCL), the MICHelson (MICH), the Common Arm length (CARM) and the Differential Arm Length (DARM) and are described by the following relations between lengths:
 
 \begin{equation*}
-DARM = \frac{L_x - L_y}{2}
+DARM = L_x - L_y
 \end{equation*}
 
 \begin{equation*}

main/main.tex

@@ -5,6 +5,7 @@
 \usepackage{bookman}
 \usepackage[english]{babel} 
 \usepackage{graphicx}
+\usepackage{pdfpages}
 \usepackage[font=small,hang]{caption}
 \usepackage{subfigure}
 \usepackage{float}
@@ -38,7 +39,7 @@ A brief summary of the project goes here, with main results.
 \chapter{Acknowledgements}
 
 Here I need to acknowledge for any funding (UoB, RAS, IOP, Caltech).
-
+%ricordati anche di ringraziare per l'estensione
 
 \tableofcontents
 \listoffigures
@@ -190,6 +191,8 @@ Beginning of Gravitational Wave Astronomy}
 
 \bibitem{sina} S. M. Köhlenbeck, \textit{Towards the SQL Interferometer Length Stabilization at the AEI 10 m-Prototype}, PhD thesis, Gottfried Wilhelm Leibniz Universität Hannover, 2018
 
+\bibitem{luise} L. KranzHoff for the AEI group, \textit{A novel vertical inertial sensor for with phasemeter readout}, poster, LVK September 2021
+
 \bibitem{tuyen} D. Tuyenbayev, \textit{Extending the scientific reach of Advanced LIGO by compensating for temporal variations in the calibration of the detector.}, PhD thesis, University of Texas, 2017
 
 \bibitem{venka} Venkateswara et al., \textit{Subtracting tilt from a horizontal-seismometer using a ground-rotation-sensor}, Bulletin of the Seismological Society of America (2017) 107 (2): 709-717

main/oplevs.tex

@@ -21,7 +21,7 @@ The most important problem, in order to achieve good isolation, is the sensitivi
 
 \begin{figure}[h!]
 \centering
-\includegraphics[scale=0.7]{images/hor.PNG}
+\includegraphics[scale=1.6]{images/hor.pdf}
 \caption{Basic sketch of horizontal sensor tilting.}
 \label{a}
 \end{figure}
@@ -97,7 +97,7 @@ If $\theta \ll$ 1, $\cos \theta \rightarrow$ 1: this means that the vertical sen
 
 \begin{figure}[h!]
 \centering
-\includegraphics[scale=0.8]{images/vert.PNG}
+\includegraphics[scale=1.6]{images/vert.pdf}
 \caption[Tilting of vertical sensor]{Tilting of vertical sensor.}
 \label{v}
 \end{figure}
@@ -109,8 +109,8 @@ When the optic is tilted by an angle $\theta$, we have the situation illustrated
 
 \begin{figure}[h!]
 \centering
-\includegraphics[scale=0.5]{images/opt2.PNG}
-\caption{Tilt of the optic.}
+\includegraphics[scale=0.8]{images/opt2.pdf}
+\caption{Concept of the optical lever working principle: when the optic is tilted by a known angle, the displacement is detected by the photodiode.}
 \label{opt2}
 \end{figure}
 \noindent
@@ -123,7 +123,7 @@ The device described in this chapter should involve sensing and actuation for th
 
 \begin{figure}[h!]
 \centering
-\includegraphics[scale=0.75]{images/opt3.PNG}
+\includegraphics[scale=0.9]{images/opt3.pdf}
 \caption{Basic principle of the optical lever used for sensing and actuation for seismic isolation.}
 \label{z}
 \end{figure}
@@ -427,14 +427,14 @@ The focussing lens of focal length 150 mm is inserted 10 cm before the photodiod
 
 \begin{figure}[h!]
 \centering
-\includegraphics[scale=0.7]{images/syst.PNG}
-\caption{Basic sketch of the optical lever system (not in scale).}
+\includegraphics[scale=0.9]{images/syst.pdf}
+\caption{Basic sketch of the lever optical design (not in scale).}
 \label{syst}
 \end{figure}
 \noindent
-The prototype and its own pre-amplifying electronics has been built at UoB (Fig. \ref{oplev20}) and tested in air and in vacuum at the AEI.
+The prototype and its own pre-amplifying electronics have been built at UoB (Fig. \ref{oplev20}) and tested in air and in vacuum at the AEI. The purpose is to calibrate the prototype with the electronics from UoB in vacuum conditions and test the sensitivity of the device to angular displacements. This first step is necessary for a good sensing system characterization.
 
-\begin{figure}
+\begin{figure}[h!]
 \centering
 \includegraphics[scale=0.55]{images/OpLev20.jpg}
 \caption[Photo of the optical lever prototype]{Photo of the optical lever prototypes as built at UoB. In this picture, the devices are not connected to electronics. Each platform hosts a laser source and a sensor. Each sensor is covered by a tube to avoid spurious light on the active area, and the focusing lens in placed at the suitable distance from it.}
@@ -493,12 +493,12 @@ Op-amp noise              & OP = 8,8 nV/$\sqrt{Hz}$
 %\end{table}
 
 \paragraph*{Preliminary test in air}
-To test if everything was set in the best way, we performed a first measurement in air, using one of the AEI pre-amp boxes connected to the CDS. Fig. \ref{inair} shows the trend of pitch, yaw and the sum of the QPD quadrants.
+To test if everything was set in the best way, we performed a first measurement in air, using one of the AEI pre-amp boxes connected to the CDS. Fig. \ref{inair} shows the trend of pitch P = (Q1+Q4)-(Q2+Q3) and yaw Y = (Q1+Q2)-(Q3+Q4).
 
 \begin{figure}[h!]
 \centering
 \includegraphics[scale=0.3]{images/inair_test.PNG}
-\caption[OpLev test in air]{Preliminary test in air: the traces show the trend of the pitch, yaw and the sum of all QPD quadrants (Q) as from the output of the pre-amp box built at UoB.}
+\caption[OpLev test in air]{Preliminary test in air: the traces show the trend of the pitch and as from the output of the pre-amp built at UoB.}
 \label{inair}
 \end{figure}
 
@@ -513,17 +513,15 @@ Also, the alignment of the optical fibre has been checked during the process.\\
 %\subsection{Temperature trend}
 
 \subsection{30mbar test}
-Fig. \ref{LVDT} shows the movement of South bench along z axis, that we use as a reference measurement for bench adjustments with temperature variations. The variable under examination is displacement tested by a Linear Variable Displacement Transformer (LVDT).
 
-\begin{figure}[h!]
-\centering
-\includegraphics[scale=0.3]{images/LVDT_Z.PNG}
-\caption[30 mbar LVDT test]{Motion along z axis of the South bench during vacuum pump to 30 mbar.}
-\label{LVDT}
-\end{figure}
+%\begin{figure}[h!]
+%\centering
+%\includegraphics[scale=0.3]{images/LVDT_Z.PNG}
+%\caption[30 mbar LVDT test]{Motion along z axis of the South bench during vacuum pump to 30 mbar.}
+%\label{LVDT}
+%\end{figure}
 \noindent
-Fig. \ref{QPD} shows the measurements taken with the QPD. The 4 quadrants and the Pitch, Yaw and Sum values show an expected behaviour.\\
-There are some peaks due to intensity fluctuations: we do not expect they disappear at lower pressure, because they are due to power fluctuation of the fibre itself.\\
+Fig. \ref{QPD} shows the measurements taken with the QPD. There are some peaks due to intensity fluctuations: we do not expect they disappear at lower pressure, because they are due to power fluctuation of the fibre itself.\\
 Some peaks at lower frequencies may be due to bench motion: if the assumption is correct, at lower pressure and more stable temperature, these peaks should be less visible.
 
 \begin{figure}[h!]
@@ -532,19 +530,21 @@ Some peaks at lower frequencies may be due to bench motion: if the assumption is
 \caption[In vacuum QPD test: 30 mbar]{QPD signals during 30 mbar pressure conditions.}
 \label{QPD}
 \end{figure}
+\noindent
+The movement of South bench along z axis is used as a reference to monitor the bench adjustments with temperature variations. The variable under examination is displacement tested by a Linear Variable Displacement Transformer (LVDT).
 
 \subsection{Final vacuum set up}
-The pressure has been set at 5 $\times$ 10$^{-3}$ mbar. What we expect is to find no variations in terms of the peaks we think are due to power fluctuations. Variations in LVDT trend can be due to temperature stabilization and related variations of Pitch and Yaw are then due to the more stable bench conditions.\\
+The pressure has been set at 5 $\times$ 10$^{-3}$ mbar. What we expect is to find no variations in terms of the peaks we think are due to power fluctuations. Variations in LVDT trend can be due to temperature stabilization and related variations of pitch and yaw are then due to the more stable bench conditions.\\
 
 \begin{figure}[H]
 \centering
-\includegraphics[scale=0.3]{images/LVDT.PNG}\\
-\includegraphics[scale=0.3]{images/ULVDT.PNG}
-\caption[Different pre-amps test: bench LVDT motion]{Bench motion long z axis at 5 $\times$ 10$^{-3}$ mbar pressure conditions. Blue curve is the trend measured by AEI pre-amp, red curve is measured with UoB pre-amp.}
+\includegraphics[scale=0.3]{images/LVDT_T.PNG}
+\caption[Different pre-amps test: bench LVDT motion]{Bench motion long z axis during the vacuum pump from 30 mbar to at 5 $\times$ 10$^{-3}$ mbar pressure conditions. Pressure has been set at 30 mbar at first stage to let temperature to stabilize faster. The two-step vacuum procedure was a good idea: it improved the temperature gradient by two times faster.}
 \label{LVDT_FIN}
 \end{figure}
+
 \noindent
-In this conditions, also the signals from the L4C seismometers and accelerometers placed on the Central bench have been measured.
+In this conditions, also the signals from the L4C seismometers and accelerometers (Watt's Leakage) placed on the Central bench have been measured. The plots with the UoB electronics show that there is some leakage below 10 Hz, probably due to saturation, in the measurement of the accelerometers.
 
 \begin{figure}[H]
 \centering
@@ -554,24 +554,24 @@ In this conditions, also the signals from the L4C seismometers and accelerometer
 \label{central}
 \end{figure}
 \noindent
-QPD performances are shown in the following pictures. With AEI boxes we had expected results: no variations in the power fluctuation peaks and expected behaviour of Pitch and Yaw with single quadrants.\\
-However, with UoB box the measurements do not seem consistent with what we expected: despite the behaviour of each quadrant seems to follow the expected trend (even if differently from AEI trend), the curves of Pitch and Yaw do not match with the quadrants trend. We think that some non-linearities in UoB box could be the cause of the problem: this is still under investigation at UoB.
+QPD performances are shown in the plots \ref{qpd_fin}. With AEI boxes we had expected results: no variations in the power fluctuation peaks and expected behaviour of pitch and yaw.\\
+However, with UoB pre-amp the measurements do not seem consistent with what we expected: we think that some non-linearities in UoB pre-amp could be the cause of the problem. This is still under investigation at UoB.
 
 \begin{figure}[H]
 \centering
 \includegraphics[scale=0.3]{images/AEI_QPD_TEST.PNG}\\
 \includegraphics[scale=0.3]{images/UOB_QPD_TEST.PNG}
-\caption[In vacuum QPD test]{QPD performance, with AEI and UoB pre-amps. There is an evident difference between the measurements taken with thw two different electronics: UoB electronics is under investigations to overcome the issue.}
+\caption[In vacuum QPD test]{QPD performance, with AEI and UoB pre-amps. There is an evident difference between the measurements taken with the two different electronics: pitch signal is ~5x noisier than yaw with UoB electronics.}
 \label{qpd_fin}
 \end{figure}
 
 \paragraph*{Electronic noise}
-Noise measurements of CDS with unplugged electronics have been taken, to check if there could be issues related to it. However, they do not show any unexpected behaviour.
+Noise measurements of CDS with unplugged electronics have been taken, to check if there could be issues related to it. However, they do not show any unexpected behaviour:  CDS dominates nearly everywhere and the CDS noise is lower than any of our optical measurements everywhere, typically by at least a factor of 10.
 
 \begin{figure}[H]
 \centering
 \includegraphics[scale=0.3]{images/EL_NOISE.PNG}
-\caption[Electronic noise]{Electronic noise measurements of CDS and unplugged electronics.}
+\caption[Electronic noise]{Measurements of CDS noise and output of unplugged electronics.}
 \label{noise}
 \end{figure}
 
@@ -592,5 +592,6 @@ Noise measurements of CDS with unplugged electronics have been taken, to check i
 %\end{equation}
 
 \section*{Conclusions}
-The measurements have shown that the device was problematic to calibrate due to issues probably related to electronics and due to the very short time of the visit it was not possible to take more in-depth tests. Other possible reasons to investigate might lie in the structure of the prototype: further tests might be useful to understand if the performances of the device can be improved by changing the position of the lens with respect to the QPD, and let the diode sit at the focus on the lens. This solution will concentrate the power and decrease the size of the beam.\\
-The device is currently not suitable for the purposes we tested for, but it opened the way to further tests to improve the technology. 
+The measurements have shown that we had issues when calibrating the device due to problems highly related to electronics from UoB, since the tests with the AEI electronics showed that the optical setup was well built and aligned. The very short time of the visit did not allow to take more in-depth tests.\\
+Other possible reasons to investigate for better performances might lie in the structure of the prototype: further tests might be useful to understand if the device can be improved by changing the position of the lens with respect to the QPD, and let the diode sit at the focus on the lens. This solution will concentrate the power and decrease the size of the beam.\\
+The device is currently not suitable for the purposes we tested for, but it opened the way to further tests to improve the technology: since the pitch and yaw tests have shown that the optical lever might be sensitive to the vertical motion of the bench, a reduction of this motion might be of great impact to improve the sensitivity of the levers \cite{luise}. With a good sensing system of tilt motion, the addition of an actuation system able to reduce this motion will be crucially helpful to stabilize the suspension points of the optical chains and then of the whole cavity.