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

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: 41mm 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

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

Coatings

Sample holds

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

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

Fused Silica Substrates at low temperature

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

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.

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

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

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

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

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. 2007 - Submitted

New clamping system

Welded slab

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

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

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

Heating data

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

Silicate bonding

Si – Si

Si – Al2O3

Al2O3 – Al2O3

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

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

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

Fiber production for the Monolithic Suspension

Fiber production machines

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…

Cascina fiber pulling machine (2)

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.

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.

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

Non-stationary thermal noise

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

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

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

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

The End