An inventive technique has been created to enhance the optical spring in gravitational wave detectors (GWDs) by utilizing the Kerr effect. This new approach harnesses the optical non-linear effects from the Kerr effect in the Fabry-Perot cavity to achieve high signal amplification ratios and optical spring constant. It has the potential for use in various optomechanical systems, not just limited to GWDs. The detection of gravitational waves is a notable achievement in modern physics, with the 2017 discovery of gravitational waves from the merger of a binary neutron star being a key example.Gravitational waves were recently discovered for the first time, revealing important information about the universe. However, detecting waves from post-merger remnants has been difficult due to their frequency range being outside of the capabilities of modern gravitational wave detectors (GWDs). These waves are important for understanding the internal structure of neutron stars and are only visible once every few decades with current GWDs. Therefore, there is a need for next-generation GWDs to improve sensitivity.WDs use an optical spring for signal amplification, which is different from traditional mechanical springs as it relies on the force of radiation pressure from light to create a spring-like effect. The stiffness of optical springs, as seen in GWDs, depends on the power of the light within the optical cavity. Therefore, increasing the resonant frequency of optical springs involves increasing the power of the light within the cavity. However, this can lead to harmful thermal effects and disrupt the detector’s functionality.
In response to this challenge, a group of researchers from Japan, led by Associate Professor Kentaro Somiya and Dr. Sotatsu Otabe from the Department, has been working on a solution.The Department of Physics at Tokyo Tech has created a revolutionary solution known as the Kerr-enhanced optical spring. Professor Somiya explains that they have found a promising way to boost the impact of optical springs without increasing the power within the cavity. This is achieved through intracavity signal amplification, which utilizes non-linear optical effects to enhance the signal amplification ratio and the optical spring constant. The team’s research has shown that the optical Kerr effect is a key element in the successful implementation of this technique. Their findings have been published in the journal Physical Review Letters and the letter has been recognized for its significance.This week’s Editors’ Suggestion promotes interdisciplinary engagement. The innovative design involves creating an intracavity signal amplification effect in a Fabry-Perot type optomechanical cavity by adding a Kerr medium. The Kerr medium induces an optical Kerr effect, which changes the refractive index of the medium when an optical field is applied. This leads to a significant gradient of the radiation pressure force in the cavity, increasing the optical spring constant without the need to increase intracavity power. Experiments have shown that the optical Kerr effect successfully enhances the optical spring constant.The optical spring was increased by a factor of 1.6, resulting in a resonant frequency increase from 53 Hz to 67 Hz. The researchers are expecting an even larger signal amplification ratio with further technical refinement.
Dr. Otabe believes that the proposed design is easy to implement and provides a new tunable parameter for optomechanical systems. They anticipate that this technique will be important not only in gravitational wave detectors but also in other optomechanical systems for cooling macroscopic oscillators to their quantum ground state.
In summary, the new optical spring design represents a significant development.The full potential of optomechanical systems and enhanced GWDs capable of unraveling the mysteries of the universe cannot be realized.
Journal Reference:
- Sotatsu Otabe, Wataru Usukura, Kaido Suzuki, Kentaro Komori, Yuta Michimura, Ken-ichi Harada, Kentaro Somiya. Kerr-Enhanced Optical Spring. Physical Review Letters, 2024; 132 (14) DOI: 10.1103/PhysRevLett.132.143602