STREGA WP1/M1 mirror substrates GEO LIGO ISA • Scientific motivation: Mechanical dissipation from dielectric mirror coatings is predicted to be a significant source of thermal noise for advanced detectors. Coatings must also be of low optical loss. • Main workpackage outcomes/long term aim: – Measurement of the thermal expansion, thermal conduction and mechanical losses of CaF2 (Calcium Fluorite) and Si (Silicon), varying the temperature from 300K down to 4K. – Investigation of the alteration of thermo- mechanical properties of silicon as a function of quantity and nature of dopants – Realisation and test of prototypes in connection with the tasks M4 and M5
STREGA WP1/M1 mirror substrates. Scientific motivation: Mechanical dissipation from dielectric mirror coatings is predicted to be a significant source of thermal noise for advanced detectors. Coatings must also be of low optical loss. Main workpackage outcomes/long term aim: - PowerPoint PPT Presentation
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STREGA WP1/M1 mirror substrates
GEO
LIGO
ISA
• Scientific motivation: Mechanical dissipation from dielectric mirror coatings is predicted to be a significant source of thermal noise for advanced detectors. Coatings must also be of low optical loss.
• Main workpackage outcomes/long term aim:– Measurement of the thermal expansion, thermal conduction
and mechanical losses of CaF2 (Calcium Fluorite) and Si (Silicon), varying the temperature from 300K down to 4K.
– Investigation of the alteration of thermo-mechanical properties of silicon as a function of quantity and nature of dopants
– Realisation and test of prototypes in connection with the tasks M4 and M5
Status at last meeting
To high voltage
Excitation plate(behind mass)
Silicon samples cut along different crystal axes, [111] and [100].
The [111] sample was boron-doped.
Preliminary room T measurements of mechanical dissipation of two silicon samples of identical geometry, supplied by Stanford, was measured over a range of frequencies.
Clamp
Suspension thread/wire
Schematic diagram of front view of suspended test mass.
Test mass
Status at last meeting
• Lowest loss obtained so far = (9.6±0.3)10-9
• Comparable with the lowest loss factors measured at room temperature
Reason for difference seen in measured loss factors (eg crystalline orientation, dopant, other?) is under investigation
Some evidence to suggest may be due to crystalline orientation
Measured loss factors fortwo samples of bulk silicon
30 40 50 600.0
2.0x10-8
4.0x10-8
6.0x10-8
8.0x10-8
1.0x10-7
1.2x10-7
1.4x10-7
Silicon (111) doped Silicon (100) undoped
[a]
[b]
Consider the [100] sample
Q of two modes of the sample studied as a function of orientation of sample in suspension loop
FE model of relative displacement of surface for 2 modes of sample
Friction at suspension points is clearly significant and dependent on position of crystalMode shapes are dependent on crystal axis
Future plans
• Constructing a prototype ‘nodal support’ system to attempt to reduce suspension losses for these samples
• Several sets of samples purchased of various aspect ratios and different crystal cuts for further study
• Measurements of bulk silicon at cryogenic temperature– Second cryostat being commissioned
in Glasgow
– Sample suspended – initial cooling taking place this week
STREGA WP1/M5 suspension substrates
• Suspension technology status:
– To achieve the desired sensitivities of future long-baseline gravitational wave detectors will require a reduction in thermal noise associated with test masses and their suspensions
– Requirement to develop ultra-low thermal noise suspensions for 3rd generation detections (cryogenic temperatures)
Currenteg. GEO600
Advancedeg. AdLIGO
Futureeg. EGO Silicon
suspension technology
Silicon cantilever fabrication
• Initial samples have been fabricated by etching from silicon wafers at Stanford (Stefan Zappe)