Set of slides can be found here

Open questions / other approaches:

• Can we get aSi-based coatings <1ppm absorption?

• 120 K operation? Some more work needed. Silica loss potentially lower than at 10 / 20 K (depending on annealing state). Cooling by radiation, less limited by heat extraction. Less TN benefit from cooling.

• 2um may allow use of a-Ge coatings – higher index than aSi, thinner coatings. What is loss, absorption?

• Crystalline coatings still of interest (both AlGaAs and AlGaP) – may be scalable to large diameters on the timescale of ET? Similar potential TN reduction to aSi/SiN. AlGaAs already has <1ppm absorption.

• Nano-layer coatings to suppress crystallisation and enable higher heat-treatment temperatures May be useful for squeezing best possible performance out of amorphous oxide coatings