A method for printing a desired uniform periodic pattern of linear features into a photosensitive layer on a substrate, which method includes: a) providing a mask bearing a mask pattern of linear features that are parallel to a first direction and have a period that is twice that of the desired pattern; b) arranging the substrate parallel to the mask and with a separation from the mask pattern; c) generating an elongated beam of monochromatic light and directing it to the mask so that the light of the elongated beam illuminates the mask with a range of angles of incidence in a plane that is orthogonal to the direction of elongation and is parallel to the first direction, and so that the light of the elongated beam in a plane parallel to the direction of elongation is collimated and has a power per incremental distance along the length of the elongated beam that is uniform except at the two ends of the elongated beam where the power per incremental distance falls to zero according to respectively a first profile over a fall-off distance and a second profile over the fall-off distance, wherein the range of angles is selected in relation to the wavelength of the light, the separation of the mask and substrate and the period of the mask pattern so that the light diffracted by the mask forms an intensity distribution at the substrate that is uniform in the direction orthogonal to the plane of mask; d) scanning said elongated beam in a first sub-exposure in a direction parallel to the first direction across a first part of said mask pattern so as to print a first part of the desired pattern on the substrate; e) scanning said elongated beam in a second sub-exposure in a direction parallel to the first direction across a second part of said mask pattern that is offset from the first part of the mask pattern in the direction of the beam elongation, such that the first and second parts of the mask pattern overlap by the fall-off distance, and such that the angle of incidence of the beam in the plane parallel to the direction of elongation in the area of the mask pattern where the first and second parts overlap is the same in the first and second sub-exposures; and wherein the first and second profiles are selected so that the summation of the two profiles across the fall-off distance where the profiles are overlapped in the first and second sub-exposures produces a uniform power per incremental distance. a) providing a mask bearing a mask pattern of linear features that are parallel to a first direction and have a period that is twice that of the desired pattern; b) arranging the substrate parallel to the mask and with a separation from the mask pattern; c) generating an elongated beam of monochromatic light and directing it to the mask so that the light of the elongated beam illuminates the mask with a range of angles of incidence in a plane that is orthogonal to the direction of elongation and is parallel to the first direction, and so that the light of the elongated beam in a plane parallel to the direction of elongation is collimated and has a power per incremental distance along the length of the elongated beam that is uniform except at the two ends of the elongated beam where the power per incremental distance falls to zero according to respectively a first profile over a fall-off distance and a second profile over the fall-off distance, wherein the range of angles is selected in relation to the wavelength of the light, the separation of the mask and substrate and the period of the mask pattern so that the light diffracted by the mask forms an intensity distribution at the substrate that is uniform in the direction orthogonal to the plane of mask; d) scanning said elongated beam in a first sub-exposure in a direction parallel to the first direction across a first part of said mask pattern so as to print a first part of the desired pattern on the substrate; e) scanning said elongated beam in a second sub-exposure in a direction parallel to the first direction across a second part of said mask pattern that is offset from the first part of the mask pattern in the direction of the beam elongation, such that the first and second parts of the mask pattern overlap by the fall-off distance, and such that the angle of incidence of the beam in the plane parallel to the direction of elongation in the area of the mask pattern where the first and second parts overlap is the same in the first and second sub-exposures; and