Mechanical properties of coating materials for use in the mirrors of interferometric gravitational wave detectors

[摘要] This thesis contains measurements of temperature dependent mechanical loss, Young's modulus, and coefficient of thermal expansion of various amorphous optical coating materials of interest to gravitational wave detectors. The materials focused upon here are hafnia and titania-doped tantala. Measurements of the mechanical loss of hafnia indicate that at temperatures below 100 K, hafnia with heat treatments between As Deposited and 400 C have lower loss than tantala. However, the hafnia was found to be partially crystalline, which must be removed in order to meet the requirements of gravitational wave detectors. This may also improve the mechanical loss. Loss measurements of 25 and 55% As Deposited titania-doped tantala indicate that the activation energy of the two-level system loss mechanism is greatly different between the two doping concentrations. The Young's modulus of the coating materials was carried out using nano-indentation. The Young’s modulus of un-doped tantalum dioxide is reduced with increasing heat-treatment until the sample crystallizes between 600 and 800 C. The 25% doped samples exhibit similar trends, while the 55% doped samples have the opposite trend. Additional measurements have also been made for IBS hafnia and amorphous silicon coatings. The coefficient of thermal expansion was measured using a thermal bending setup, which extracts a combination of Young's modulus and coefficient of thermal expansion. The Young's modulus from the nano-indentation measurements was then used to extract the thermal expansion. For the 25 and 55% tantalum dioxide doped coatings did not vary with heat-treatment; however, it did appear to vary for the hafnia coatings.

[发布机构] University:University of Glasgow;Department:School of Physics and Astronomy

[关键词] Gravitation, Gravitational Waves, Optical coatings, Young's modulus, mechanical loss, thermal noise, nano-indentation, thermal expansion, hafnia, tantala, hafnium dioxide, tantalum pentoxide, mechanical properties, coating materials