A wavelength separating element for separating a second beam from a first beam configured to be used in a nonlinear frequency conversion, NLFC, device, which NLFC device is configured to generate a first beam and a second beam, wherein the second beam has a wavelength different from a wavelength of the first beam, the wavelength separating element comprising: a first mirror surface; a second mirror surface opposite to the first mirror surface; wherein: the first and second mirror surfaces have a high reflectivity of the second beam relative to a reflectivity of the first beam, and the first and second mirror surfaces are configured such that the first and second beams undergo multiple reflections between the first mirror surface and the second mirror surface to separate the second beam from the first beam; wherein the first and second mirror surfaces are configured such that the first and second beams undergo at least three reflections at the first and second mirror surfaces; and the wavelength separating element being characterized in that at least one plate element having a first surface and a second surface opposite to the first surface, wherein the first surface is one of the first or second mirror surfaces and the second surface includes a scattering element that scatters a portion of the first beam that is transmitted through the first or second mirror surface. a first mirror surface; a second mirror surface opposite to the first mirror surface; wherein: the first and second mirror surfaces have a high reflectivity of the second beam relative to a reflectivity of the first beam, and the first and second mirror surfaces are configured such that the first and second beams undergo multiple reflections between the first mirror surface and the second mirror surface to separate the second beam from the first beam; wherein the first and second mirror surfaces are configured such that the first and second beams undergo at least three reflections at the first and second mirror surfaces; and the wavelength separating element being characterized in that at least one plate element having a first surface and a second surface opposite to the first surface, wherein the first surface is one of the first or second mirror surfaces and the second surface includes a scattering element that scatters a portion of the first beam that is transmitted through the first or second mirror surface. the first and second mirror surfaces have a high reflectivity of the second beam relative to a reflectivity of the first beam, and the first and second mirror surfaces are configured such that the first and second beams undergo multiple reflections between the first mirror surface and the second mirror surface to separate the second beam from the first beam; wherein the first and second mirror surfaces are configured such that the first and second beams undergo at least three reflections at the first and second mirror surfaces; and the wavelength separating element being characterized in that at least one plate element having a first surface and a second surface opposite to the first surface, wherein the first surface is one of the first or second mirror surfaces and the second surface includes a scattering element that scatters a portion of the first beam that is transmitted through the first or second mirror surface.