A computerized in situ optical reflectivity measurement system for the quantitative determination of material parameter changes of a substrate during the process of ion implantation, is presented. These changes are related to the extent and nature of the induced crystal disorder in the substrate. The system comprises an optical reflectometer, with data acquisition and signal processing capabilities. For each sample a case history of the implant is obtained in the form of a continuous graph of reflectivity vs. a desired implantation parameter (e.g., dose). Examples regarding the implantation of 3fP +, 48Ar +, and 14N +are presented. Additional suggestions for further system development and applications are also made. Among the advantages of in situ measurements are the time-effort-expenses savings, higher yield of experimental data per sample, higher accuracy, repeatability, and various possibilities of process control.