Borate nonlinear optical single crystal surface finishing by argon cluster ion sputtering

Due to its distinctive features, gas cluster ion beams offer unique capabilities to improve the performance of optical devices based on nonlinear single crystals. In this work, the applicability of the argon cluster ion sputtering at different incident energies for finishing the LiB3O5 surface has been studied. It is demonstrated that a combination of high- and low-energy treatment modes (energy per atom of about 100 eV and several eV, respectively) provides an efficient etching rate comparable to that of a monoatomic ion beam. Besides, the surface roughness is reduced to the angstrom level in a wide range of spatial frequencies (nu = 0.3 100 mu m(-1)). Using XPS measurements, the preferential sputtering of oxygen and, to a lesser extent, boron, and an increase in the concentration of lithium cations in both modes were revealed. Although a chemical alteration of the treated materials could not be fully prevented, chemical and physical damages after a cluster bombardment are much less than that from a monoatomic ion beam.