Diamond-like carbon (DLC) films have potential applications in infrared transmission enhancement. Reducing or eliminating mechanical stress and optical absorption of DLC is important in such applications because relatively thick films are necessary. In this work, DLC was deposited in an unbalanced magnetron sputtering (UBMS) system. Mechanical and optical properties of the DLC films were analysed. Thick DLC films were deposited which satisfied applications for the infrared windows at 3-5 and 8-10 mu m. At optimised conditions, the stress in the DLC films decreased with increasing thickness, approaching 1 GPa. For single side DLC coated silicon substrate, about 69% transmittance was achieved at wavelengths near 5 mu m, close to the theoretical value for non-absorbing DLC material. Other properties such as surface roughness, wetting angle, and stability were also studied, which showed that the DLC films produced in the UBMS system were excellent for infrared transmission enhancement applications in tough environments. (c) 2005 Elsevier B.V. All rights reserved.