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arXiv:2310.08500

Progress towards ultracold Sr for the AION project -- sub-microkelvin atoms and an optical-heterodyne diagnostic tool for injection-locked laser diodes

Elizabeth Pasatembou, Charles F. A. Baynham, O. Buchmüller, David E. Evans, Richard Hobson, L. Iannizzotto-Venezze, A. Josset

Published Oct 12, 2023• 0 citations
arXivHTMLPDF

Abstract

Long-baseline atom interferometers, such as the one to be built by the AION collaboration, require ultra-cold atomic clouds. These are produced by trapping the atoms in Magneto-Optical Traps (MOTs) using high-power, narrow-linewidth lasers. We report on the laser and optical master-slave injection locked system used to address the 1S0 - 3P1 strontium transition at 689 nm, and on the trapping of strontium atoms in a narrowband MOT. We demonstrate the quality of the injection through the characterisation of the injection lock using a novel, easy-to-assemble method which uses a double pass acousto-optic modulator (AOM) to generate and detect a heterodyne beatnote. The reported system is used to produce an atomic cloud at a temperature of 812 +/- 43 nK in a narrowband red MOT.

DOI
10.48550/arxiv.2310.08500

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Long-baseline atom interferometers, such as the one to be built by the AION collaboration, require ultra-cold atomic clouds. These are produced by trapping the atoms in Magneto-Optical Traps (MOTs) using high-power, narrow-linewidth lasers. We report on the laser and optical master-slave injection locked system used to address the 1S0 - 3P1 strontium transition at 689 nm, and on the trapping of strontium atoms in a narrowband MOT. We demonstrate the quality of the injection through the characterisation of the injection lock using a novel, easy-to-assemble method which uses a double pass acousto-optic modulator (AOM) to generate and detect a heterodyne beatnote. The reported system is used to produce an atomic cloud at a temperature of 812 +/- 43 nK in a narrowband red MOT.
Long-baseline atom interferometers, such as the one to be built by the AION collaboration, require ultra-cold atomic clouds. These are produced by trapping the atoms in magneto-optical traps (MOTs) using high-power, narrow-linewidth lasers. We report on the laser and optical master–slave injection-locked system used to address the 1S0–3P1 strontium transition at 689 nm and on the trapping of strontium atoms in a narrowband MOT. We demonstrate the quality of the injection through the characterization of the injection lock using an easy-to-assemble method that uses a double-pass acousto-optic modulator to generate and detect a heterodyne beatnote. The reported system is used to produce an atomic cloud at a temperature of 812(43) nK in a narrowband red MOT.
Abstract The realization of compact high-power narrow-linewidth laser sources in the visible range has been a long-standing interest for the atomic physics community, especially in the field of laser cooling and trapping of alkaline-earth and alkaline-earth-like atoms. We report a simple master-slave injection-locked laser system capable of generating 500 mW at 460.86 nm with a linewidth of 1.6 MHz to realize magneto-optical trapping of strontium atoms on the 5s2 1S0−5s5p 1P15s^{2} \ ^{1}\mathrm {S}_{0}-5s5p \ ^{1}\mathrm {P}_{1}5s2 1S0​−5s5p 1P1​ 5 s 2 1 S 0 - 5 s 5 p 1 P 1 transition. The master laser used is an external cavity diode laser built with an anti-reflection coated laser diode in a Littrow configuration and the slave laser is built with a recently launched single mode high power GaN laser diode. We characterized the frequency noise, injection stability, spectral purity and relative intensity noise of the laser system. The reported laser system is used routinely to produce 10710^7107 10 7 strontium atoms at a temperature of 10 mK in a magneto-optical trap. The laser system offers a prominent alternative to the existing frequency-doubled laser systems in terms of cost, design flexibility, electrical power consumption, ease of scaling, intensity stability, and frequency tunability. The proposed system is also an effective solution for space-based experiments where a laser system’s size, weight, and electrical power consumption are crucial design parameters.
Advancing our knowledge of the universe increasingly relies on technologies capable of extremely precise measurement. Quantum sensors have emerged as promising tools for searching for new physics by pushing the boundaries of precision in measuring time, acceleration, and gravity. Two promising platforms are long-baseline atom interferometers and atomic clocks, both of which rely on cold atoms. This thesis lies at the intersection of cold-atom physics, quantum technology, and particle phenomenology. We report experimental progress from the AION project, a next-generation atom interferometer for the detection of ultra-light dark matter and mid-frequency gravitational waves. Within the collaboration, we present the first results from a red magneto-optical trap (MOT) for strontium-88 atoms. A seed–amplifier injection-locked laser system was developed to address the 1S0–3P1 transition at 689 nm, delivering 13.8 mW of light to the science chamber. Using this setup, we produced an atomic cloud at a temperature of (812 ± 4) nK in the narrowband red MOT, marking a critical milestone in the project. Secondly, the potential of next-generation atomic and molecular clocks in constraining theories that violate the weak equivalence principle (EP) is investigated. A search for variations in the electron–proton mass ratio is performed using publicly available data from UTC. A statistical framework is then developed to model clock noise and forecast sensitivity to signals arising in theories of dark matter, dark energy, unification, and other EP-violating scenarios, providing new and improved constraints. The framework is packaged into a tool that translates clock noise characteristics into constraints on fundamental physics theories. A preliminary study investigating the effect of data gaps in signal recovery shows that annual signals with amplitudes above 10⁻¹⁶ can be recovered even with up to 83% missing data.
We report recent progress in sub-kHz-linewidth operation of AlGaInP-based SDL systems designed for neutral Strontium optical clocks. Overall system performance is presented, including intensity, frequency and phase noise characterisation. Two almost identical SDLs, each with >150 mW output at 689 nm, were frequency locked and an optical beat note measurement produced a linewidth of 160 Hz with fractional frequency stability reaching below 2×〖10〗^(-15) for averaging times from 60-400 s. Spectroscopic measurements of a blue magneto-optical trap (MOT) of Strontium with one SDL resulted in a reduction of the atomic sample fluorescence and revealed Zeeman splitting of the 3P1 electronic level.
Laser cooling has become a powerful tool for producing quantum gases and has enabled the study of a wide range of phenomena only accessible at ultracold temperatures. This thesis will describe the implementation and characterization of a magneto-optical trap (MOT) for laser cooling strontium to microkelvin temperatures operating on the narrow 689nm transition (the “red” MOT). The red MOT is the second cooling stage required to create quantum degenerate gases of strontium, bridging the temperatures and densities produced by the first cooling stage (the 461 nm “blue” MOT) and the shallow conservative traps for evaporation to quantum degeneracy.
We report the experimental realization of strontium magneto-optical trap (MOT) operating on the intercombination transition 1 S 0 − 3 P 1 at 689 nm, namely red MOT. A 689 nm laser used for cooling and trapping is injection locked to a master laser, whose linewidth is narrowed to 150 Hz by locking to a high finesse optical reference cavity. 88 Sr atoms pre-cooled and trapped by the broad 1 S 0 − 1 P 1 transition at 461 nm are transferred to the red MOT with the help of a time sequence controller. The transfer ratio is about 20% and the red MOT's temperature is estimated to be less than 20 μK by the time-of-flight (TOF) image analysis.