Long-term performance of a mid-IR laser system for muonic hydrogen spectroscopy in the FAMU experiment

Year: 2026

Authors: Baruzzo M., Fasci E., Moretti L., Subrez-Vargas J.J., Cabrera H., Toci G., Capra S., Gianfrani L., Pizzolotto C., Mocchiutti E., Danailov M.B., Vacchi A.

Autors Affiliation: Sez INFN Trieste, Via A Valerio 2, Trieste, Italy; Complesso Univ Monte S Angelo, Sez INFN Napoli, 6 Via Cintia, Naples, Italy; Univ Campania Luigi Vanvitelli, Dipartimento Matemat & Fis, Viale Lincoln 5, Caserta, Italy; Abdus Salam Int Ctr Theoret Phys, Str Costiera 11, Trieste, Italy; Consiglio Nazl Ric CNR, Ist Nazl Ottica INO, Via Madonna Del Piano 10, Sesto Fiorentino, Italy; Sez INFN Milano, Via Celoria 16, Milan, Italy; Univ Milan, Dipartimento Fis, Via Celoria 16, Milan, Italy; Elettra Sincrotrone Trieste, SS14,Km 163 5, Basovizza, Italy; Univ Udine, Dipartimento Sci Matemat Informat & Fis, Via Sci 206, Udine, Italy.

Abstract: We report, to the best of our knowledge, the first long term operation of a 1-2 mJ pulsed laser system operating at 6.78 mu m. The laser system has been employed during the data acquisition campaigns of FAMU (Fisica Atomi MUonici) experiment. The laser was used continuously for at least one week on four occasions. Recent improvements have further enhanced the stability of the laser, notably through the implementation of active feedback systems that maintain single-mode operation and ensure wavelength precision. This paper discusses the stability of the laser in terms of wavelength, laser-muon beam delay, energy, and linewidth, and also examines the factors that influence these characteristics during long-term laser operation. Through the implementation of active feedback systems on the single-mode operation, the standard deviation of the central wavelength is 2.5 pm, the pulse linewidth 15 pm and the average pulse energy ranges from 1 to 1.7 mJ with a standard deviation of 0.08 mJ over 24 h. This outstanding stability was complemented by excellent laser operation throughout the campaigns, with a 95% uptime.

Journal/Review: OPTICS COMMUNICATIONS

Volume: 608      Pages from: 133082-1  to: 133082-8

More Information: This work was partially performed within the PRIN 2022 (project code n. 2022KMNSR9) , entitled MEtrology and Nonlinear optics for Precision muonic HYdrogen physicS (MENPHYS) . Authors would like to thank the skillful help of the INFN Trieste mechanical workshop for the experimental setup as well as the precious contribution by INFN Trieste electronic service.
KeyWords: Mid-IR Laser; FAMU; Muonic hydrogen spectroscopy; BaGa4Se7; DFG
DOI: 10.1016/j.optcom.2026.133082