cw‐laser‐induced local oxidation of ultrathin (3–60 nm) titanium films on glass in air is studied. It is shown, that the brightening of the films upon through‐oxidation forms a negative feedback to this highly nonlinear process. It offers the possibility of stable writing of oxide line structures narrower than the diffraction limited focused laser spot. The optimum metal film thickness is of the order of the light absorption length in the metal. Transparent isolated oxide lines and gratings with periods down to 250 nm and line width down to 165 nm were recorded in 6–15 nm thick Ti films on glass by using the radiation of the Ar ion laser (&lgr;=488, 514 nm). ©1996 American Institute of Physics.