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

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 μm. 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.