Generation of continuous-wave laser light at 148.4 nm using cavity-enhanced second harmonic generation in $BaMgF_4$

Keerthan Subramanian; Hiroki Tanaka; Simon J. Herr; Nutan Kumari Sah; Gaurav Jha; Florian Zacherl; Srinivasa Arasada Pradeep; Valerii Andriushkov; Ke Zhang; Darius Fenner; Yumiao Wang; Milena Hugenschmidt; Frank Kühnemann; Gaetano G. M. Bonetti; Shoichi Ui; Matthias Bickermann; Chenxi Ma; Xian Zheng; Michael Zopf; Bettina Lommel; Jan C. Müller; Stephan Hannig; Dmitry Budker; Ferdinand Schmidt-Kaler; Lars von der Wense

arXiv · 2606.25046

Generation of continuous-wave laser light at 148.4 nm using cavity-enhanced second harmonic generation in $BaMgF_4$

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Abstract

We experimentally investigate the potential of $BaMgF_4$ crystals to create a continuous-wave (CW) solid state laser at the vacuum ultraviolet (VUV) wavelength of 148.4 nm via cavity-enhanced second harmonic generation. This investigation is motivated by the development of a nuclear optical clock based on a transition between the ground and isomeric state in the $^{229}Th$ nucleus. For this purpose, a $BaMgF_4$ crystal was grown, optically polished and periodically poled. The crystal was inserted into a power-enhancement cavity, resonant at the fundamental wavelength of 296.8 nm and the generated laser light at 148.4 nm was characterized. Within this proof-of-concept investigation, a VUV output power of typically ($16\pm1$) pW is obtained. This marks the first time that this type of crystal is used to generate VUV laser light. The experimental findings are compared to theoretical expectations and provide a clear path for future improvements.

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Keerthan Subramanian, Hiroki Tanaka, Simon J. Herr, Nutan Kumari Sah, Gaurav Jha, Florian Zacherl, Srinivasa Arasada Pradeep, Valerii Andriushkov, Ke Zhang, Darius Fenner, Yumiao Wang, Milena Hugenschmidt, Frank Kühnemann, Gaetano G. M. Bonetti, Shoichi Ui, Matthias Bickermann, Chenxi Ma, Xian Zheng, Michael Zopf, Bettina Lommel, Jan C. Müller, Stephan Hannig, Dmitry Budker, Ferdinand Schmidt-Kaler, Lars von der Wense. 2026-06-23. Generation of continuous-wave laser light at 148.4 nm using cavity-enhanced second harmonic generation in $BaMgF_4$. https://arxiv.org/abs/2606.25046

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