A laser device (100), comprising: a source of electromagnetic radiation (S) that comprises at least one reflecting surface (RS), said source (S) being configured to generate a light beam that follows an optical path (OPa; OP) external to said source (S); a dispersive stage (6) located outside said source (S) along said optical path (OP) of said light beam generated by said source (S), said dispersive stage (6) comprising at least one axis of reflection that forms an angle (Θ; cp) with said optical path (OPa; OP) of said light beam and being configured to reflect: at least a first spectral portion of said light beam generated by said source (S) towards said source (S); and a second spectral portion of said light generated by the source (S) along said axis of reflection, wherein said at least one reflecting surface (RS) and said dispersive stage (6) form at least one variable-length external optical cavity (RS, L, 6); at least one collimating lens (C) located along said optical path (OPa; OP) and configured to collimate said light beam coming from said source (S); a collimator module (3), in which said source (S) and said at least one collimating lens (C) are mounted; and an actuator (24) configured to vary a length (L) of said a variable-length external optical cavity (RS, L, 6). In said device: said actuator (24) is mechanically coupled to said collimator module (3); and said actuator (24) is configured to vary the length (L) of said at least one external optical cavity of the variable-length gain medium (RS, L, 6) by moving said collimator (3).