Demonstration of a Dual Cavity Configuration for next Generation Light-Shining-Through-a-Wall Experiments

Abstract

Based on peculiarities within the Standard Model of particle physics, such as the strong CPproblem, and on the observation of astrophysical phenomena, such as dark matter (DM), a group of particles, axions and axion-like particles (ALPs), is postulated. These particles are associated with a very light mass and weakly-interacting characteristics with ordinary matter. Their potential existence is the motivation for the so-called Light-Shining-Through-a-Wall (LSW) experiments. These experiments are based on the hypothesis that photons can oscillate into ALPs in the presence of magnetic fields and vice versa. The fundamental principle is to shine an intense laser beam onto a wall that is opaque to photons in the presence of a magnetic field. The interaction of the photons with the magnetic field can lead to an oscillation into ALPs that pass the wall due to their weak interaction with ordinary matter. In the presence of another magnetic field behind the wall, the reverse process can take place and the ALPs oscillate into photons that can be detected with a single photon or heterodyne detector. The ALPS II experiment (Any Light Particle Search) is a laboratory-based experiment that exploits the mechanisms described above for the ALPs-photon conversion. To increase the probability of the production of ALPs and the regeneration of photons in front and behind the wall, two 122 m long optical resonators, called the Production Cavity (PC) and Regeneration Cavity (RC), are used. The circulating field in each cavity is directed through a string of 12 superconducting dipole magnets. In order to achieve the intended probability of production of ALPs and regeneration of photons, the frequency of the laser beam incident on the PC needs to be matched to the resonance frequency of the cavity. In addition, the cavities have to be tuned and maintained such that the field from the PC would resonate within the RC, which poses a particular challenge, since no light can reach the RC directly from the PC during the science run. This problem can be addressed by frequency doubling part of the light and injecting it into the RC for stabilization purposes. Furthermore, the eigenmodes of both cavities have to be matched spatially with high precision. Therefore, strict requirements on the lateral and angular alignment of the two eigenmodes to each other as well as on the alignment and long-term stability of the optical and mechanical components have to be fulfilled. In the framework of this thesis, a miniaturized experiment based on ALPS II is conducted to experimentally verify some fundamental requirements for ALPS II. In contrast to ALPS II, this setup contains neither magnets nor a high power laser or a wall. First of all, the setup is used to test and verify the alignment concept, which is used to realize the desired angular alignment of the two eigenmodes. Furthermore, the long-term stability of the mechanical components that maintain the angular alignment is verified. In a further step, the methodology with which the position of the eigenmode is laterally tracked is verified and the long-term stability of the associated components is tested. In a final step, the concept of the dichroic stabilizationis demonstrated as a proof-of-concept experiment. With this concept, the cavities are tuned and maintained such that the field from the PC resonates within the RC. Therefore, the frequencies of the lasers used are stabilized to the respective eigenfrequencies of the cavities and a phaselocked loop is implemented to ensure that the PC field resonates within the RC.