The present invention relates to a device to photocure and/or photoactivate a photosensitive material. The device comprises several subsystems to transmit light towards an area of interest where a photosensitive material is applied as well as to collect light reflected by the applied photosensitive material. Reflected light is analyzed by an optical detector to monitor the photocuring and/or photoactivation process. Further means to inject or otherwise apply a photosensitive material can be combined in the same device. Methods for applying a fluent polymerizable material to a target site and for effecting polymerization of the fluent light- sensitive material in situ are also disclosed.