• Suspensions
• MagneticSuspension
• PhaseIII
• Goal

Goal

The final goal of this stage is to set up a Fabry-Perot cavity of which the two mirrors are magnetically levitated. We want to characterize the seismic isolation performance and also other noises, e.g., the effect of ambient magnetic field. To start with, we will first work with one mirror before setting up the entire cavity.

Plan

This stage lasts for approximately half to one year, which depending on the time scale for achieving a successful levitation with this new scheme. The lessons we learn from the second-stage experiment could be very helpful, but the new sensing scheme introduces additional uncertainty. The plan for this stage goes as follows:

1. Design the scheme which contains the mechanical part (details) and the electronics part (details). [Time scale: one month and a half].

2. During the lead time for the mechanical setup, test the critical components before the final assembly. [Time scale: one month].

   1. The QPD and associate electronics for position sensing (details);

   2. The fiber optics and associate components (details);

   3. The strain gauge for force measurement (details);

   4. The Hall-effect sensor (details);

   5. Linear DC motor (details);

   6. Analog electronics (details);

   7. Digital part (details).

3. Assemble the scheme for a single mirror. [Time scale: two weeks]

4. Achieve full levitation, and the envisioned locking procedure goes as follow: [Time scale: one or two months (uncertain)]

   1. We first use the Hall-effect sensors and associated feedback loop to lock the floating plate;
   2. We then try to align the fibre optics and also the QPD, and characterize the cross couplings among different degrees of freedom by using optical sensors;
   3. Lock the floating plate with optical sensors, and the Hall-effect sensors can provide preliminary damping if necessary before the system is stable.
5. Tune the magnetic potential by using the three auxiliary coils to achieve a low resonant frequency and characterize it;

6. Set up the the other mirror with the same scheme and achieve full levitation; [Time scale: few weeks up to one month]

7. Try to lock the FP cavity; [Time scale: few weeks up to one month (uncertain)]

8. Measure the noise and have a full characterization of the system [Time scale: one month].

9. Report writing [Time scale: one month].