Development of laser system for atom interferometric detection of gravitational waves and dark matter

Long-baseline atom interferometers (AIs) are rapidly developing tools for precise and accurate tests of fundamental physics. This work focuses on a 100 meter baseline AI known as the Matter-wave Atomic Gradiometer Interferometric Sensor (MAGIS-100). The ultimate goal of instruments in the MAGIS family, with progressively longer baselines (e.g. 1 kilometer) in newer generations, is the detection of gravitational waves (GWs) and dark matter (DM). For GW detection, MAGIS-100 exploits the clock transition in Strontium-87 (⁸⁷Sr) at 698 nm. For DM detection, two isotopes ⁸⁷Sr/⁸⁸Sr will be simultaneously driven using the Bragg transition near 679 nm.

The AI laser system has the following requirements: (a) high power (> 8 W), (b) tunability (679-698 nm), (c) stable absolute frequency (< 10 Hz linewidth), (d) low wavefront imperfections (< λ/1000), and (e) stable and controllable pointing (< 30 nrad). This talk will focus on our efforts to achieve target specifications for (a)-(c). These specifications are achieved using two low-noise Titanium:Sapphire lasers and a frequency comb. In the GW mode, output from each laser (> 4 W) is coherently combined to drive the clock transition at > 8 W. In the DM mode, the two lasers are offset-locked to the frequency comb to perform AC-Stark-shift-compensated Bragg transitions. This talk will cover this laser system’s architecture, design principles, some preliminary test results.