1. Review on thermal noise related activities in Perugia
Flavio Travasso
N.i.P.S. Laboratory, Dip. Fisica – Università di Perugia and INFN Perugia
Virgo - Perugia

2. Activities in Perugia Cryogenic Coating Measurements:
Changes in the coating Фcoat(T): to find a change in the coating changing the temperature
Different coatings: to measure the different loss angles of different coatings
Measured Slabs (3 samples – provided and coated by LMA-Virgo Lion):
Uncoated Slab
Titania doped tantala coated slab (slab A)
Cobalt doped tantala coated slab (slab B)
Dimension:
A & B: mm x 5 mm x 104 μm
Uncoated: 45mm x 5 mm x 104 μm
Different frequencies
Coatings:
A: 520 nm TiO2 doped Ta2O5 mono-layer coating
B: 500 nm Co doped Ta2O5 mono-layer coating
2. Fused silica Substrate cryogenic behavior
Experimental activity:
about 20 modes studied for 3 uncoated slabs
Theoretical activity:
For the amorphous material the classical laws used for the crystalline materials are not so easy to use or to support that’s why is usefull and hard find a:
theory to explain the Ф frequency trend of the modes at each temperature above 140K
theory to explain the Ф temperature peak around 20K

3. Activities in Perugia Silicate bonding: Monolithic suspension:
Different materials: studies for future cryogenic suspension
Ice and flame: to see the answer of the SB to the thermal stress
Monolithic suspension:
Fiber production: flame
Monolithic suspension Collaboration: see Puppo Paola talk
Non equilibrium thermal noise:
Purpose:
to measure the dynamics of a perturbed system at thermal equilibrium
to improve the sensibility of an optical system
Work in progress: to check the sensibility with the new cavity to stabilize the laser in frequency

4. Coatings

5. Sample holds

6. Measurement Apparatus
Labview Interface Ni He Cu
Clamp tightened using a spring
HV Amplifier
Laser
Cooling down rate: 1-2 K/h
…to avoid particular thermal/mechanical stress

7. Summury on coating activity
Coating Results:
The coating ФCoat is almost costant in the temperature range of 300K-90K
The Cobalt doped tantala coating shows a ФCoat better than the titania doped tantala coating:
ФCoat Mean Value = 3.4E-3 ± 1E-3
ФCoat Mean Value = 7E-4 ± 2E-4
The measurements are limited by the substrates losses… (see Work in progress)
..too high
Work in progress:
To improve the measurements of coating at low temperature we plan on testing the same coating on new substrates
To design a new clamping system and/or new geometry for the samples: see the “New clamping system” session
New materials for the coating

8. Fused Silica Substrates at low temperature

9. Introduction What we are going to see:
Φ vs temp: choosing a mode of the slab, how change the loss angle of this mode changing the temperature
We found 2 peaks
Φ vs freq: selecting a temperature, what is the loss angle of the first 20 modes of the slabs (or rather how the loss angle changes with the frequency)
• We found 3 different scenarious in 3 temperature ranges => 3 different dissipative processes

10. Summary of situations The frequency dependent trend is clear…
…but it’s also clear that the data for T<30K have a slope smaller than the data between 140K-40K.

11. Power law (Kramers formula)
…that comes from a double well potential model
What we can do?
We can fit the data with a general power law (the fist one) and compare that with few specific power laws coming from different physical models. In literature the most accredited one is the double well potetial model

12. Exponent of power law: B
These results are interesting because
In literature the explored frequency range is 500Hz-MHz (there are no infos on our frequency range)
In literature K = 0 …we have to consider another process to improve the actual physical models
Sharp transition? System instability? Work in progress…
The freq. Dependent process is becoming more active
A different dissipative mechanism comes into play: dissipative quantum tunnelling , that is quantum tunnelling assisted by thermal fluctuations
Above 140K the loss angle appears to be NOT frequency dependent

13. Linear Fit of B: 110K-40K In literature K=0
…as you remind the BWP forseen a liner law for B(T)

14. Fit A Using for B the value evaluated in the previous slide
At low temperature (T<30K) the data have a different trend respect the fits: a different dissipative mechanism comes into play, dissipative quantum tunnelling , that is quantum tunnelling assisted by thermal fluctuations
The losses are higher than what forseen by the double well potential model: 2 competive dissipative processes

15. Comments SiO2 Results: Work in progress: Bibliography:
The measurements show a clear behaviour with temperature:
-  an almost constant loss angle above 140K
  - between 140K and 30K the loss angle has a significant increase that can be interpreted by calling for thermally activated relaxation dynamics (in multi-stable potentials)
  - below 30K the loss angle starts decreasing: the thermally activated dissipation is less effective and a different dissipative mechanism starts driving the dynamics (quantum tunnelling effects become active at very low temperature… that is quantum tunnelling assisted by thermal fluctuations )
- The clamp adds a quite costant dissipation and has a smoothing effect
Work in progress:
A new refined dynamical model for the interpretation of the losses in the low frequency and temperature region is in preparation (F. Marchesoni)
In literature the most accredited model is the double well potetial model deriving from a lot of different concurrent processes (tetrahedron links that rotate from an quasi-equilibrium state to another, region of collaboration defects => the dimension of those regions define the time scale (energy activation) of the process…and so on) and those make the exponent B dipendent by the temperature.
But for the DWP model it´s not important the physical reason of the processes but just the existence of 2 or more quasi-static position…that’s the nice thing and the limit of that theory
Bibliography:
Low-frequency internal friction in silica glass
Travasso,F. /Amico,P. /Bosi,L. /Cottone,F. /Dari,A. /Gammaitoni,L. /Vocca,H./Marchesoni,F.
Submitted

16. New clamping system

17. Welded slab

18. The clamp adds a quite costant dissipation and has a smoothing effect
The 2 slabs have the same trend and the same slope for T<190K
Work in progress
I would test this new clamping system on a coated sample in order to see if the old copper clamp add only a costant loss to each sample.
If so, it should be better to use the old clamp because for the new clamp we have to weld the sample using a flame risking to damage the sample

19. The fit at low temperature is the Kramers formula (see slide 14) while the fit at high temperature is the error function. Here is clear the extra loss added by the copper clamp

20. Comments Clamps: Work in progress:
The copper clamp clearly adds an extra loss to the loss angle
We would evaluate that extra loss in order to use that clamp with the very thin sample: the flame could be destructive (no problem with the sample with a thickness of 1 mm at least)
Work in progress:
New data on the coated samples with the new clamping system
New geometry for the samples: cylindrical windows

21. Heating data

22. The sample was heating to 340K
The loss angle shows a flat region till this temperature

23. Silicate bonding

24. Si – Si

25. Si – Al2O3

26. Al2O3 – Al2O3

27. Mean Values
There is no evidence thet the breaking strength has a clear trend over the time or over the lambda: that´s why we report here the mean value over the samples

28. Work in progress ICE FLAME
We made just one test on a Silicon-Sapphire SB We put the sample in a liquid nitrogen tank for few minutes. That sample showed the usual breaking strength
FLAME
The SB seems to be very sensitive to the high temperature. Few test are mede using samples cooking in an oven an samples with a SB of few month and welding in a very slow way

29. Comments
The silicate bonding seems to work very well if one of the material we want to glue has the Si atom in its formula
There is no evidence that the breaking strength has a real trend with the time or with the lambda

30. Fiber production for the Monolithic Suspension

31. Fiber production machines

32. Cascina fiber pulling machine
The facility at the west middle arm building, is a newer copy of the Perugia one.
The facility is now operative.
As soon as the laser CO2 will be operative we will compare the two results.
The fused silica bar is contemporary heated in the center part of the “flame stove” and cooled near it to limit the melted volume (better control of the fiber tapers). We will install an upgrade of it in few days…

33. Cascina fiber pulling machine (2)

34. Validation procedure
We improved our control on the fiber surface quality using a portable very thin flame welding machine. It is possible to check and repair the fiber surface and increase the validated fiber quality.
80 mm fiber
It is possible to:
rearrange the surface defects and cracks;
weld fibers in the low diameter part accurately;
We are evaluating the optimum diameter for the welding to minimize the losses induced.

35. Validation procedure (2)
A 3D Laser Caliper is used to measure the diameter and shape of the fiber produced.
It is possible to verify the circularity of the fiber section and to measure the diameter with a precision up to 0.1 microns.

36. ..for the monolithic suspension status see the Paola Puppo´s talk

37. Non-stationary thermal noise

38. Non-stationary thermal noise
Schema ottico
Purpose
To understand the dynamics of a perturbed system at thermal equilibrium or rather:
- read directly the thermal noise of a thin slab
reduce a TN peak with a sine in counter-phase with the oscillation of the slab
see how the peak comes back to the equilibrium: it should absorb energy from the other modes reducing the thermal noise
see if the system changes its dynamics
to improve the sensibility of an optical system driving the dinamics of the optics
Cavità
Misura
P=10-6 mbar
l/4
Pico-motore
Segnale in
riflessione X
Pbs
Modulatore
Elettro-ottico
Nd-Yag
1064 nm
l/2
12.5 MHz

39. Non-Stationary Thermal Noise: stabilized cavity
P=10-6 mbar
Pico-motore
Segnale in
trasmissione
Cavità stabilizzazione
Cella
peltier
Segnale in
riflessione
Cavità
Misura ò
telescopio
l/4
Segnale in
riflessione X
Pbs
Modulatore
Elettro-ottico
Nd-Yag ò
1064 nm
l/2
12.5 MHz X

40. New sensitivity
Not stabilized cavity Electronic Noise Stabilized Cavity
Displacement [m]
Frequency [Hz]

41. Comments Results: Work in progress:
Without the cavity to stabilized the laser it´s possible to see the peaks, to reduce their amplitude and to see how the system comes back to the thermal equilibrium => the dynimics of the system changes:
there is a crosstalk between the modes => it´s very hard to understand if the perturbed peak is stealing energy from the slab improving the sensibility on the other region: new exciter
the rigidity of the slab seems to change: if we could understand how to change this parameter we could move the peaks in order to free a region of the spectrum with a particulare interest
Work in progress:
To test the new stabilized cavity to see directly the thermal noise

42. The End