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Stabiles UV-Licht für optische Uhren

Stable UV light for optical clocks

Frequency quadrupling unit

Optical clocks based on trapped single ions require at least one phase-stable laser that interrogates the electronic transitions of the clock ion over several seconds. If the interrogation time is too short, the statistical uncertainty of the measurement increases. Supported by the Cluster of Excellence QuantumFrontiers, six researchers at the Physikalisch-Technische Bundesanstalt have succeeded in developing a compact laser system that delivers phase-stable UV light for an optical clock with aluminium ions. They published their results in the journal Opics Express.

For some optical atomic clocks, such as a clock based on aluminium ions, the crucial transitions are in the UV spectrum. To generate frequency-stable UV light, the frequency of an infrared laser is first stabilised to a reference cavity. Then the frequency of the IR laser is doubled twice so that UV light is generated.

A key challenge is to transfer the frequency stability from the infrared to the ultraviolet. In their construction of a transportable aluminium ion clock, the researchers of the Cluster of Excellence QuantumFrontiers use non-linear crystals for the twofold frequency doubling. In their setup, the to-be-doubled light passes through each of the crystals only once. Unlike traditional setups, this configuration enables uninterrupted interferometric phase stabilisation of the IR pump laser and thus also of the generated UV light.

"With our setup, we have managed to build a compact, transportable and very phase-stable UV laser for the clock transition of the aluminium ion. In the future, this will allow us to interrogate the clock transition for a longer period of time and to operate the aluminium ion clock at different locations," says doctoral student Benjamin Kraus, responsible for the construction and commissioning of the laser system.


Original publication:

B. Kraus, F. Dawel, s. Hannig et al.
Phase-stabilized UV light at 267 nm through twofold second harmonic generation.
Optics Express 30, 44992-45007 (2022).