Method for determining the separation distance between a working head in a machine for laser processing of a material, operating by means of a high power processing laser beam emitted by said head and led along a working trajectory on the material comprising a succession of working areas, and the surface of the material at said working areas, comprising the steps of: - generating a measurement low coherence optical radiation beam, leading said measuring beam towards a working area through said working head, and leading the measuring beam reflected or diffused from the surface of the material in said working area through said head and towards optical interferometric sensor means along a first direction of incidence, in which the measuring beam travels a measurement optical path from a respective source to said optical interferometric sensor means including a first section comprised between said source and the working head and a second section comprised between said working head and the interferometric sensor means having a respective predetermined and invariant geometric length; - generating a reference beam of said low coherence optical radiation, and leading said reference beam towards said optical interferometric sensor means along a second direction of incidence, at a predetermined angle of incidence with respect to the first direction of incidence of said measurement beam, wherein the reference beam travels a reference optical path whose optical length is equivalent to the optical length of the measurement optical path in a nominal operating condition in which the distance between the working head and the surface of the material corresponds to a predetermined nominal separation distance; - superimposing the measurement beam and the reference beam on a common region of incidence of said optical interferometric sensor means, along a predetermined illumination axis; - detecting the position of a pattern of interference fringes between the measurement beam and the reference beam along said illumination axis on said common region of incidence, wherein the extension of said pattern of interference fringes along the illumination axis corresponds to the coherence length of said low coherence optical radiation; and - determining a difference in optical length between the measurement optical path and the reference optical path - indicative of a difference between the current separation distance between the working head and the surface of the material at the working area and a predetermined nominal separation distance - as a function of the position of said pattern of interference fringes along said illumination axis of said region of incidence. - generating a measurement low coherence optical radiation beam, leading said measuring beam towards a working area through said working head, and leading the measuring beam reflected or diffused from the surface of the material in said working area through said head and towards optical interferometric sensor means along a first direction of incidence, in which the measuring beam travels a measurement optical path from a respective source to said optical interferometric sensor means including a first section comprised between said source and the working head and a second section comprised between said working head and the interferometric sensor means having a respective predetermined and invariant geometric length; - generating a reference beam of said low coherence optical radiation, and leading said reference beam towards said optical interferometric sensor means along a second direction of incidence, at a predetermined angle of incidence with respect to the first direction of incidence of said measurement beam, wherein the reference beam travels a reference optical path whose optical length is equivalent to the optical length of the measurement optical path in a nominal operating condition in which the distance between the working head and the surface of the material corresponds to a predetermined nominal separation distance; - superimposing the measurement beam and the reference beam on a common region of incidence of said optical interferometric sensor means, along a predetermined illumination axis; - detecting the position of a pattern of interference fringes between the measurement beam and the reference beam along said illumination axis on said common region of incidence, wherein the extension of said pattern of interference fringes along the illumination axis corresponds to the coherence length of said low coherence optical radiation; and - determining a difference in optical length between the measurement optical path and the reference optical path - indicative of a difference between the current separation distance between the working head and the surface of the material at the working area and a predetermined nominal separation distance - as a function of the position of said pattern of interference fringes along said illumination axis of said region of incidence.