According to an aspect, the present description concerns a frequency-tunable laser source comprising: a set of N elementary sources (101-k), each elementary source being suitable for emitting a beam at a given central frequency (fk); an optical coupler (12) for coupling the beams emitted by each of the elementary sources in order to form a multi-spectral incident beam (Bin) regrouping all the frequencies of the N elementary sources in a same optical beam; a beam splitter (15) for forming, from the incident beam (Bin), a first beam (B1) and a second beam (B2), each regrouping all the frequencies of the elementary sources; a first tunable filter (16) for selecting, from the first beam (B1), a third beam (B3) at a first frequency (Fj); a second tunable filter (17) for selecting, from the second beam (B2), a fourth beam (B4) at a second frequency (Fl); a nonlinear frequency doubling crystal (18) for generating, from the third beam at the first frequency (Fj), a fifth beam (B5) having a frequency (F2j) which is twice the first frequency; a nonlinear sum-frequency generation crystal (19) for generating, from the fifth beam coming from the nonlinear frequency doubling crystal and from the fourth beam at the second frequency (Fl), a beam (Bout) having a frequency (F2j+1) equal to the sum of twice the first frequency (F2j) and the second frequency (Fl).