It has been a great effort completely driven by IFAE scientists and the whole IFAE technical department including precise mechanics, electronics, DAQ and the need for intense optical tests and detailed simulations.

The basic requirements of the instrumented baffles are rather challenging. The total reflectivity of the surface at 1064 nm has been maintained at the level of 0.5% and the total scattering within about 500 ppm. This required precise material polishing and the application of anti-reflective coating layers. As suspended by a couple of wires, no active cooling is possible and the readout cables have been minimised to avoid affecting the performance of the payload and seismic attenuation systems. Therefore, both wired and wireless DAQ solutions have been implemented. Most importantly, the ultra-high vacuum conditions in the towers (with a vacuum level of 1E-9 mbars) imposed stringent constraints to all the materials to avoid contaminants affecting the mirrors, and forced a rather novel PCB design with low power consumption and efficient heat dissipation.

In addition, the baffle DAQ system should not interfere with the rest of the electronics in the tower, governing the feedback loop systems that control the position of the mirror. Finally, the total weight of the new device met within 100 g the weight of the non-instrumented version to facilitate the integration in the suspension system. The baffle is equipped with 76 Si-based photosensors suitable for ultra-high vacuum conditions and complemented with anti-reflective coating, as the result of a two-years long R&D process triggered by IFAE and carried out together with Hamamatsu in Japan.