In situ spectroscopic measurement of defect formation in SiO2 induced by femtosecond laser irradiation

We measured real-time spectra of light transmitted through SiO2 specimens during irradiation of amplified ultrashort laser. The real-time spectra exhibit a peak at around 400 rim. The observation and identification of defects were performed by measurements of electron spin resonance (ESR). Both dependences of the peak at around 400 nm on irradiation time and laser power are in good agreement with those of the ESR signal intensity of positively charged oxygen vacancies (E' center: O(3)dropSi(.)). This strong correlation shows that self-trapped excitons are created followed by the formation of the E' center and finally that of ESR inactive centers, namely, oxygen-deficiency centers (ODCs: O(3)dropSi-SidropO(3) or O(3)dropSi:). (C) 2003 Elsevier B.V. All rights reserved.