Refractive index modification using fs-laser double pulses

Buried waveguides in glass are manufactured by irradiation with femtosecond laser double pulses. The refractive index change Delta n is determined by measuring the numerical aperture NA of the waveguides and by through light microscopy. The value of Delta n shows a significant dependency on the time delay Delta t of the fs-laser double pulses. A Delta n of up to 2×10(sup)-3 in fused silica is reached at a Delta t between 400 and 800 ps. Based on the results of the double pulse experiments the initial effects of the refractive index change are discussed, taking into account thermal effects and the formation of self trapped excitons (STE) and transient color centers and their interaction with the next laser pulse