1. PRELIMINARY DATA ON THE COATING AT THE LIQUID NITROGEN TEMPERATURE Flavio Travasso Virgo-Perugia Group

2. Samples TiO 2 /SiO 2 caoted slab (50 layers evaporated by SILO) (Measured) TiO 2 doped Ta 2 O 5 coated slab (Sputtering by LMA) (Work in progress) Co doped Ta2O5 coated slab (Sputtering by LMA) (Next months) Uncoated fused silica (311) slab supplied by LMA (Next months) Dimension of the slabs: Silo TiO 2 /SiO 2 : 25mm x 25mm x 50 μm with a coating of 5 μm LMA doped samples: 5mm x 41mm x 104 μm with a coating of about 5 μm

3. Labview Interface Ni He Ni He Cu Laser HV Amplifier Clamp tightened using a spring

4. Preliminary data: TiO 2 /SiO 2 coating Loss angle vs. Temperature: coated and uncoated sample have a minimum at about 160K The trend of the coated sample seems to be driven by the behaviour of substrate of fused sillica The trend of the coated sample seems to be driven by the behaviour of substrate of fused sillica Levin model (using a FEM model): we need a good database about the thermal trend of E TiO2 (loss angle of the coating at room temperature is about 10 -3 ) Coated Sample Uncoated Sample The silica has a peak at the lower temperature…maybe we are seeing the first part (?)

5. Preliminary data: TiO2-doped Ta2O5 coating (1) Coated sample:same trend of the TiO 2 /SiO 2 coated sample Uncoated sample: work in progress Work done in collaboration with LMA/Virgo laboratory

6. Preliminary data: TiO2-doped Ta2O5 coating (2) Increasing of the loss angle decreasing the temperature The loss angle seems to be frequency dependent: we need much more data to increase the statistics

7. Temperature hysteresis Cool down Warm up The dispersion of the data and the value of the Φ Tot have a minimum around 160K cooling down and aroud 120K warming up

8. Open problem Short term upgrade: change present clamp Short term upgrade: change present clamp New suspension system: MIT likeNew suspension system: MIT like Thermalization of the sample: moving contact, gas of He inside the chamber(?)Thermalization of the sample: moving contact, gas of He inside the chamber(?) Reading of the temperature: twin systemReading of the temperature: twin system Long term upgrade Long term upgrade Pulse tube: evaluation of the noisePulse tube: evaluation of the noise Ni He Ni He Cu Laser Labview Interface

9. Summary Trend of the data versus the temperature maybe driven by the substrate Trend of the data versus the temperature maybe driven by the substrate Frequency dependency of the loss angle at temperature lower than 160K Frequency dependency of the loss angle at temperature lower than 160K Need to improve the system: short and long term upgrades Need to improve the system: short and long term upgrades