Laser thermochemical method (LTM) of writing the information on thin Cr films is used for fabricating of diffractive optical elements (DOE). LTM is based on local laser oxidation of thin Cr films and following selective etching. It seems to be an alternative method to photolithography and laser ablation of thin films. The quantity of technological operations is much less then at photolithography and there are no thermal and hydrodynamic distortions at LTM as at laser ablation. Nowadays, DOEs are widely used in different devices, especially in modern telescopes, micro lens arrays, laser optics etc. The main parameter for all types of DOE is high spatial resolution. It implies a tendency to reduce the pulse duration up to femtosecond range. This, in turn, requires the detail knowledge of the physical and chemical processes in thin Cr films under ultrashot laser irradiation, to study them is the aim of present work.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.