A mid-IR laser source for muonic hydrogen spectroscopy: The FAMU laser system.

A pulsed, tunable, narrow linewidth mid-infrared (mid-IR) laser radiation source was developed to meet the needs of the FAMU project (Fisica Atomi MUonici). The main goal of this experiment is to measure the hyperfine splitting of the ground state of muonic hydrogen using pulsed laser spectroscopy. The experiment requires a high energy, mid-IR source around the resonance energy Δ E1S h f s ∼ 0.1828 eV (6. 79 μ m) of the muonic hydrogen atom to excite it from the para (F = 0) to the ortho (F = 1) spin state. The laser system designed to fulfill these requirements is based on Difference Frequency Generation (DFG) using a non-linear crystal pumped by two laser beams at 1064 nm and 1262 nm. For the first time, the details of the entire laser system are described in this paper. The laser light at 6. 79 μ m , generated with a BaGa 4 Se 7 non-linear crystal, is being directed into the FAMU target multi-pass optical cavity. To date, an energy above 1 mJ, a linewidth below 30 pm, and a tunability step of 9 pm have all been attained. Here, we present the unique features of the laser system and the characterization results. • As the core of a crucial spectroscopy experiment on muonic hydrogen the FAMU laser has complied with the basic specifications and will be used during the next data taking. • This mid-IR laser source is based on nonlinear optics using a BaGa 4 Se 7 crystal and DFG process. • The FAMU mid-IR laser is tuneable and produces a narrow linewidth beam between 6730 and 7135 nm. • The energy produced by the FAMU laser exceeds 1,1 mJ at 6,79 nm and linewidth below 30 pm. [ABSTRACT FROM AUTHOR]