[en] A technique has been established to accurately determine the position of a high velocity liner as it slides past or impinges on another surface. A small diameter optical fiber is accurately positioned relative to a target or liner. A bright light source (such as a small He--Ne laser) illuminates one end. The output from the other end is passed through a bandpass filter to a gated photomultiplier tube. Loss of the light signal thus accurately determines the time and position at which th fiber is broken by a passing liner. This technique is especially useful in environments where the presence of large magnetic fields or large circulating currents make the use of other techniques difficult (e.g., electrical shorting pins). This optical system is completely decoupled from environments having large electromagnetic noise levels. Shock waves in solid materials have been found to turn the fiber opaque during passage so that shock wave time of arrival studies are also feasible using the TOFS system