Multiphoton process investigation in silica by UV femtosecond laser

•Non-linear deposition of the light investigated by online photoluminescence induced by UV femtosecond laser exposition.•Clarification of the strong-field ionization limit (multiphoton regime) which leads to the generation of point defects under femtosecond laser irradiation.•Understanding of the OH content impact on the silica-femtosecond laser interaction monitoring the optical signatures of the PL-active induced defects.•Evidence of the importance of online investigation to better understand the fs laser-silica interaction processes compared to the post mortem one.