Temperature dependent electrical and mechanical loss in gravitational wave detectors

Gravitational wave astronomy has changed how we understand the universe ever since the 2015 gravitational wave detection of two black holes colliding 1.3 billion light years away.

Expanding the range of a gravitational detector requires making these highly sensitive instruments even more sensitive. One way to do this is to reduce thermal noise by keeping the detector test masses at low temperatures, around 123 Kelvin.

Klochkov and Mitrofanov investigated how this low temperature impacts the mechanical loss induced by the electric field of an electrostatic actuator in the vibration mode of a commercial silicon wafer.

“Mechanical oscillations of the wafer in the actuator’s electric field cause redistribution of electrical charges in silicon,” said author Valeriy Mitrofanov. “Ohmic electrical losses cause mechanical energy loss and associated thermal noise.”

High-purity monocrystalline silicon is often used as a test mass due to its high thermal conductivity, low mechanical losses, and low optical absorption at the necessary wavelengths.

The electric field-induced loss increases with resistivity of undoped silicon used for test masses. However, for the desired low detector temperature, the resistivity decreases due to an increase in the mobility of charge carriers.

The researchers measured the temperature dependence of the losses and compared results with and without an applied electric field. They found the mechanical loss decreased as the wafer’s temperature decreased and observed two different time-dependent behaviors of the electric field-induced mechanical loss in undoped silicon wafers.

“The results are interesting and important not only for gravitational-wave detectors but are important for high-performance MEMS/NEMS systems made of silicon,” Mitrofanov said. “Undoped or high-resistivity silicon also has applications in high-frequency telecommunication systems.”

Source: “Measurement of the temperature dependence of mechanical losses induced by an electric field in undoped silicon disk resonators,” by Yaroslav Yu Klochkov and Valeriy P. Mitrofanov, Applied Physics Letters (2023). The article can be accessed at https://doi.org/10.1063/5.0143587 .

This paper is part of the Gravitational Wave Detectors Collection, learn more here .