laserstab updates

main/laserstab.tex

@@ -270,15 +270,23 @@ This test confirms that HoQI2 is in general noisier than HoQI1, especially above
 
 \section{Laser stabilization: tests and results}
 The tests have been performed measuring the stability of the beat-note peak around the 60 Hz setpoint: the frequency counter used for this measurements is a Keysight 53230A 350 MHz - 20 ps. The output of the fast photoreceiver is DC-coupled and can be directly connected to the counter. The measurements has been recorded on a USB drive: the data provided by the counter are in frequency (Hz).\\
-Several tests have been taken in different conditions for noise hunting along the frequency range of interest. %QUI CI VANNO I TEST COL COUNTER DI CUI PARLAVA CONOR: LO SCOPO E' DIMOSTRARE CHE IL SETUP E' STATO ADEGUATAMENTE TESTATO
+Several tests have been taken in different conditions for noise hunting along the frequency range of interest, the best measurements are shown in Fig. \ref{test}. The tests with the heterodyne detection revealed that the system is very sensitive to the external noise sources described above and that the two HoQIs are nor robust and stable enough to assure the stability of the loop, despite the robustness of the controller filter. The solution for reducing these noises might be placing the HoQIs in vacuum.\\
+A picture of the experiment is in Fig. \ref{expsetup}.
 
 \begin{figure}[h!]
 \centering
 \includegraphics[scale=0.3]{images/result.png}
-\caption[Results of frequency stabilization tests]{Results of frequency stabilization: the in-loop red trace shows the frequency stabilization process as detected by the frequency counter monitoring the beat-note between the two lasers; the black trace is the expected gain activated by the controllers, which is set to maximise the stabilization below 1 Hz.}
+\caption[Results of frequency stabilization tests]{Results of frequency stabilization with respect to th free running frequency noise: the in-loop red trace shows the frequency stabilized lasers as detected by the frequency counter, monitoring the beat-note between the two lasers in the lower frequency range. This trace is the best measurement we obtained below 1 Hz, where we reached 1.67 $\times$ 10$^4$ Hz/$\sqrt{Hz}$ at 0.05 Hz; The green trace is a test taken with the counter set to a higher frequency range: this test shows a result of 3.6 $\times$ 10$^4$ Hz/$\sqrt{Hz}$ at 1 Hz. This is also the test which showed the quietest results above 10 Hz, demonstrating that the HoQIs can reach a good level of stability in air. The black trace is the expected gain activated by the controllers, which is set to maximise the stabilization below 1 Hz.}
 \label{test}
 \end{figure}
 
+\begin{figure}[h!]
+\centering
+\includegraphics[scale=0.7]{images/experiment.jpg}
+\caption[Photo of the experiment setup]{Photo of the experiment setup for frequency stabilization of the 6D laser source. Only the optical setup has been placed inside the foam box, which suitable apertures to let the beams go to the power photodiodes and the photoreceiver outside the box. The gaps inside the box have been filled in order to reduce the air currents along the OPL in free air and a lid covers the whole box.}
+\label{expsetup}
+\end{figure}
+
 \section{An alternative test}
 An alternative test has been made to make sure that the input modulation is effectively reducing the frequency noise of the lasers. Since we found that HoQI2 is noisier than HoQI1 and that laser2 has larger power fluctuations, we decided to use laser1 to feed both lasers. The new concept is to let only HoQI1 be the in-loop sensor, while HoQI2 will act as the out-of-loop sensor.\\
 Results are shown in Fig. \ref{alt} and are encouraging: the frequency noise of the out-of-loop sensor is lowered by about one order of magnitude when the controller on laser1 is active. This means that the control loop works well and that there are still more external noise sources that are reducing the performances of the HoQIs, impacting also on the measurement through the heterodyne detection.\\

main/main.tex

@@ -16,6 +16,7 @@
 \usepackage{verbatim}
 \usepackage{lscape}
 \usepackage{amsmath,amssymb}
+%\usepackage{hyperref}
 %\mathrm
 \linespread{2}
 \subject{A Thesis submitted for the degree of PHILOSOPHIAE DOCTOR}