cps_diff and laserstab updates

main/CPSdiff.tex

@@ -525,6 +525,6 @@ After every simulation which could possibly work for the system, we locked the i
 \end{figure}
 
 \section*{Conclusions}
-Due to the stretched time, it was not possible to take further measurements of ISI motion and LSC signals, especially with an accurate study of the blending filters. The study is however promising to be of great help in the improvement of the LSC signals of LIGO and its stabilization when in observing mode.\\
-LIGO Livingston site has also actuated a similar process, following the progression at LHO during 2019 collaboration and since the software skeleton of the new configuration has been built and installed on LIGO CDS, further studies and tests were due in 2020 to complete the last steps and test it fully on the interferometer. However the pandemic and the correlated travel restrictions have moved forward in the future the schedule for these tests.
+This study is promising to give an impactful contribution to the improvement of the LSC signals of LIGO and its stabilization when in observing mode. As we saw, the implications go straight to the basics of the instrument: a more stable detector produces a less noisy signal which can last longer into the cavities, assuring a longer observing time and giving the possibility to observe more gravitational waves, in lower ranges of frequency.\\
+LIGO Livingston site has also actuated a similar process, following the progression at LHO during 2019 collaboration. Due to the stretched time, it was not possible to take further measurements of ISI motion and LSC signals, especially with an accurate study of the blending filters, but since the software skeleton of the new configuration has been built and installed on both LIGO CDSs, further studies and tests were due in 2020 to complete the last steps and test it fully on the interferometer. However the pandemic and the correlated travel restrictions have moved forward in the future the schedule for these tests.
 

main/laserstab.tex

@@ -72,11 +72,11 @@ The laser chosen as source for 6D is a 1064 nm RIO ORION Laser Module (see Fig.
 \label{rio}
 \end{figure}
 \noindent
-What we want from this source is a low-noise readout for the HoQIs inside the 6D tank, and thus the laser source needs to be as low noise in frequency fluctuations as possible at frequencies below 1Hz, because this is the range of frequencies where the 6D isolator is aimed to detect and control seismic noise: we are going to use two Rio Orion lase modules to obtain a frequency stabilization suitable for 6D requirements. Constraints to these requirements are mainly given by the HoQIs. For 6D readout, HoQIs are built in such a way that the arm length is L$_{6D}$ $<$ 3 mm. Limitations to this number are given by BOSEM size ($\pm$ 2 mm) and the ability to adjust it, once the devices are in vacuum. Another parameter to take into account is the ADC noise of HoQIs, which is ADC = 2 $\times$ 10$^{-14}$ m/$\surd{Hz}$ at about 10 Hz \cite{hoqi}. Frequency fluctuations depend on both these parameters and we want it to meet the following requirement:
+What we want from this source is a low-noise readout for the HoQIs inside the 6D tank, and thus the laser source needs to be as low noise in frequency fluctuations as possible at frequencies below 1Hz, because this is the range of frequencies where the 6D isolator is aimed to detect and control seismic noise: we are going to use two Rio Orion laser modules to obtain a frequency stabilization suitable for 6D requirements. Constraints to these requirements are mainly given by the HoQIs. For 6D readout, HoQIs are built in such a way that the arm length mismatch is L$_{6D}$ $<$ 3 mm. Limitations to this number are given by BOSEM size ($\pm$ 2 mm) and the ability to adjust it, once the devices are in vacuum. Another parameter to take into account is the noise of HoQIs, which is H = 6 $\times$ 10$^{-14}$ m/$\surd{Hz}$ at about 1 Hz \cite{hoqi}. Frequency fluctuations depend on both these parameters and we want it to meet the following requirement:
 
 \begin{equation}
 \centering
-\delta f_{6D} \ll f \times \frac{ADC}{L_{6D}} = 2000 \frac{Hz}{\surd{Hz}}.
+\delta f_{6D} \ll f \times \frac{H}{L_{6D}} \simeq 5000 \frac{Hz}{\surd{Hz}}.
 \end{equation}\\
 The technique we are going to adopt to stabilize the laser in frequency, as anticipated, is to use HoQIs, because we can associate frequency fluctuations to fluctuations of arm length:\\
 \begin{equation}
@@ -85,10 +85,11 @@ The technique we are going to adopt to stabilize the laser in frequency, as anti
 \label{df}
 \end{equation}\\
 and this arm length can belong to a HoQI placed on the optical bench. The use of compact interferometers to stabilize solid-state lasers in frequency is new and allows the whole set up to be small in size. This technique, in combination with cheap laser sources, makes the set up competitive with other more expensive products.\\
-We can then apply the same relation of. eq. \ref{df} to the arm length of the HoQI used for the laser stabilization, remembering that the requirement of $\delta$f $\ll$ 2000 Hz/$\surd{Hz}$ must remain valid. So, constraints to the arm length in this case are due also to the size of the bench and the whole set up.\\ We said we want a compact setup, but the arm length of this HoQI (say L$_{stab}$) can have a wider range of sizes to fit the requirement. For example, for L$_{stab}$ = 0.1 m we have:\\
+We can then apply the same relation of. eq. \ref{df} to the arm length of the HoQI used for the laser stabilization, remembering that the requirement of $\delta$f $\ll$ 5000 Hz/$\surd{Hz}$ must remain valid. So, constraints to the arm length in this case are due also to the size of the bench and the whole set up.\\ We said we want a compact setup, but the arm length of this HoQI (say L$_{stab}$) can have a wider range of sizes to fit the requirement. For example, for L$_{stab}$ = 1 m we have:\\
+
 \begin{equation}
 \centering
-\delta f_{stab} = f \times \frac{ADC}{L_{stab}} \simeq 55 \frac{Hz}{\surd{Hz}},
+\delta f_{stab} = f \times \frac{H}{L_{stab}} \simeq 16 \frac{Hz}{\surd{Hz}},
 \end{equation}\\
 which is still much lower than the threshold.\\
 Since we want the setup to be as much compact as possible, we need to find the lowest possible L$_{stab}$ which gives an interesting $\delta f_{stab}$, compared to the current performances of RIO Orion and the best products available.\\
@@ -101,7 +102,7 @@ In the plot in Fig. \ref{perf} there is the analysis and comparison with two of
 \label{perf}
 \end{figure}
 \noindent
-It is evident that we cannot build a HoQI with L=10 m. If we want our device to be competitive even with the best product (ADJUSTIK X15, shown in blue line), we will need a L=30 cm. However, our purpose is to make the set up \textit{compact} and \textit{competitive} with most of the available products, so the best compromise is choosing L=10 cm. With this configuration, the device will still be competitive with ADJUSTIK X15 in terms of price.\\
+It is evident that we cannot build a HoQI with L=10 m. If we want our device to be competitive even with the best product (ADJUSTIK X15, shown in orange line), we will need a L=30 cm. However, our purpose is to make the set up \textit{compact} and \textit{competitive} with most of the available products, so the best compromise is choosing L=10 cm. With this configuration, the device will still be competitive with ADJUSTIK X15 in terms of price.\\
 Fig. \ref{free} shows a plot of the measured frequency noise of the Rio Orion laser modules and the level of stabilization required by the 6D with the chosen L$_{stab}$.
 
 \begin{figure}[h!]
@@ -157,7 +158,7 @@ In Fig. \ref{chia} there is a photo of the HoQI built for this experiment.\\
 
 \begin{figure}[h!]
 \centering
-\includegraphics[scale=0.5]{images/HoQIChia.png}
+\includegraphics[scale=0.5]{images/HoQIChia.jpg}
 \caption[Photo of a HoQI]{Photo of one of the HoQIs built for the laser stabilization experiment.}
 \label{chia}
 \end{figure}