A middle infrared femtosecond mode-locked laser, comprising a collimator lens (2), a focusing lens (3), an input spherical lens (4), a laser medium (5) and a spherical high-reflection lens (6) sequentially disposed in a pumping light beam direction outputted by a laser diode (1); the input spherical lens (4), the spherical high-reflection lens (6), a spherical high-reflection focusing lens (7), an output coupling lens (11) and a graphene mode-locked element (8) form a five-lens laser resonator; a laser in the five-lens laser resonator is reflected onto the spherical high-reflection focusing lens (7) via the input spherical lens (4), is focused on the graphene mode-locked element (8), goes back along the original path, then sequentially passes through the spherical high-reflection focusing lens (7), the input spherical lens (4), a laser crystal (5) and the spherical high-reflection lens (6), is deflected and reflected onto a dispersion compensation prism pair (9) by the spherical high-reflection lens (6), and is outputted from the output coupling lens (11) through a slit (10). In the manufacturing process, the graphene grown by adopting a CVD method is transferred to a laser wavelength high-reflection lens, and is protected by an inert gas, thus a stable mode-locked laser pulse is outputted within the middle infrared wave band. The laser is simple to adjust and is easy to realize single layer (with low non-saturated loss).
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