Nessun titolo diapositiva

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Experimental investigation of dynamic
Photothermal Effect
M. De Rosa INOA, LENS, INFN F. Marin University
of Florence, LENS, INFN F. Marino INFN O.
Arcizet, A. Heidmann, M. Pinard, Laboratoire
Kastler Brossel, Paris
Work performed in the framework of the ILIAS
project STREGA
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Photothermal effect
Photon absorption ? Local heating ? Thermal
expansion

• Depends on
• laser power impinging on the mirrors
• absorption coefficient
• material - thermal expansion
• - thermal conductivity and capacitance
• temperature (through the above parameters)
• mirror size and shape/suspension
• beam waist
• detection frequency

3
Mirror ? half space approximation Braginsky et
al., Phys. Lett. A 264, 1 (1999) Cerdonio et al.,
Phys. Rev. D 63, 082003 (2001)
dL L0 K(w/wc)
? 1/W
a thermal expansion coefficient s Poisson
ratio k thermal conductivity cs volumetric
thermal capacitance w beam waist
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Mirror ? half space approximation Braginsky et
al., Phys. Lett. A 264, 1 (1999) Cerdonio et al.,
Phys. Rev. D 63, 082003 (2001)
dL L0 K(w/wc)
? 1/W
a thermal expansion coefficient s Poisson
ratio k thermal conductivity cs volumetric
thermal capacitance w beam waist
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• Calculated nc (Hz)
• Fused silica Sapphire
• w/?2 300K 1K 300K 1K
• 10mm 0.0015 4.8 0.02 19000
• 0.1mm 15 48000 200 1.9108
• Cut-off depending on the mirror shape and
  suspension (heat dispersion)
• Large timescale and size spread ? necessity of
  accurate and verified model over a complete
  frequency range

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Reference cavity
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Probed Cavities
Mirrors substrate Fused Silica Coatings
SiO2/Ta2O5
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Long cavity
a) half-infinite mirror b) finite size effects c)
coating effect
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IMPROVED MODEL - 1
Low frequency finite size effect
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IMPROVED MODEL - 2
High frequency coating effect One-dimensional
model K KFS Kcoat
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Short cavity
Frequency scaling with waist as predicted
Phase at high frequency to be improved (coating
depth comparable with waist)
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• Conclusions
• beam waist dependence of cut-off frequency is
  verified
• finite size effects at low frequency
• coating effects at high frequency
• improvement of the half-infinite mirror model
  including finite size and coating effect
  (material properties)