Karlsruhe 2024 – scientific programme

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T: Fachverband Teilchenphysik

T 28: Search for new particles 3 (ALPS)

T 28.5: Talk

Tuesday, March 5, 2024, 17:00–17:15, Geb. 20.30: 1.067

Precision Optics and Control for the ALPS II Experiment — •Daniel Brotherton for the ALPS collaboration — University of Florida

The Any Light Particle Search II (ALPS II) is an experiment at DESY which searches for axions via a ``light-shining-through-a-wall'' scheme. Namely, light is directed through a region of magnetic field where it has a probability of conversion into axions. A barrier beyond this region impedes the light, but axions converted from the light may traverse the barrier and reconvert back into light in a second magnetic field region. The experiment employs 120-meter long high-finesse optical cavities to improve the final photon-axion-photon coupling sensitivity. Currently a ``regeneration cavity'' (RC) amplifies the reconverted light's amplitude by a demonstrated factor > 7000. A future ``production cavity'' (PC) will aim to store 150 kW of power to increase the flux of generated axions. This requires a control scheme to maintain the resonance of laser light within the cavities while also mitigating stray light from entering the RC. This talk will discuss the precision optics techniques utilized in ALPS II, including optical offset phase-locking and heterodyne interferometric sensing of ultra-low power fields. Some initial results of the optics performance from ALPS II's current data-taking campaign will also be discussed. Work at Florida is supported by the NSF PHY-2309918.

Keywords: Axion; ALPS; DESY; dark matter; optics