A method for determining the pressure in an assist gas chamber associated with a nozzle for supplying an assist gas flow, carried by a working head of a machine for laser cutting, drilling or welding of a material, or for the additive manufacturing of three-dimensional structures by laser, characterized in that it includes the steps of:
- i) determining the local position of an optical element of protection or delimitation of the assist gas chamber, interposed along the optical transport path for the processing laser beam or of an optical assistance element facing said assist gas chamber, optionally outside the axis of the processing laser beam, by means of a method comprising the steps of:
- a) generating a respective measurement low coherence optical radiation beam, leading said measurement beam towards said optical element, and leading the measurement beam reflected or diffused by at least one back-reflective surface of said optical element, on which said measurement beam impinges with at least a partial back-reflection, towards optical interferometric sensor means, wherein the measurement beam travels a measurement optical path from a respective source to said optical interferometric sensor means including a first section between said source and said back-reflective surface of said optical element and a second section between said back-reflective surface of said optical element and the interferometric sensor means, having a respective predetermined nominal geometric length when said optical element is in a predetermined nominal position corresponding to a predetermined reference pressure value of the assist gas in the assist gas chamber,
- b) generating a respective reference beam of said low coherence optical radiation, and leading said reference beam towards said optical interferometric sensor means, wherein the reference beam travels a reference optical path having an optical length, or optical path, equivalent to the optical length of the measurement optical path in a nominal operating condition including a partial back-reflection of the measurement beam at a surface of said optical element when it is in the predetermined nominal position;
- c) 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;
- d) 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, or the frequency of a pattern of fringes in the wavelength spectrum, obtained by the interference between the measurement beam and the reference beam by wavelength dispersion of said beams, whose extension in the frequency domain is determined by the coherence length of said low coherence optical radiation;
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- e) determining a difference in optical length between the measurement optical path and the reference optical path-indicative of a difference between (a) the current local position of said optical element and (b) the predetermined nominal local position of said optical element along the axis of the measurement beam—as a function respectively of the position of said pattern of interference fringes along said illumination axis of said region of incidence, or of the frequency of said pattern of interference fringes in the frequency domain, and
- ii) determining the pressure of the assist gas in the assist gas chamber according to a predetermined reference model indicative of a nominal relationship between the position of said optical element with respect to said predetermined nominal position and the assist gas pressure.