Two-Photon Laser Lithography for Fabricating X-ray Optics: Advantages, Challenges, and Solutions

The advantages and shortcomings of two-photon laser lithography (TPL) technology for fabricating X-ray compound refractive lenses (CRLs) are discussed. A CRL consisting of 15 one-dimensional refractive lenses with an aperture of 185 µm was fabricated and then tested at the “Microfocus” beamline (KISI-Kurchatov) for photon energies of 8 and 12 keV. Factors affecting the focal spot size and focal length are discussed. TPL technology provides acceptable surface roughness of the lenses and the required radius of curvature, but the lenses are inhomogeneous internally due to the presence of uncured photocurable composition in the gaps between polymerized areas. This inhomogeneity is one of the reasons for the broadening of the focal spot, as well as undesirable effects of synchrotron radiation (SR). The combination of TPL and nanoimprint technology is proposed, which would simultaneously preserve the best characteristics of the lenses and eliminate the disadvantages of the TPL method.