[OPTICAL REVIEW Vol. 7, No. 1 (2000) 14-17]

Estimation of the Refractive Index Change in Glass Induced by Femtosecond Laser Pulses

Tadamasa TOMA,1 Yoshio FURUYA,1 Wataru WATANABE,1 Kazuyoshi ITOH,1 Junji NISHII2 and Ken-ichi HAYASHI3

1Department of Applied Physics, Graduate School of Engineering, Osaka University, 2-1, Yamadaoka, Suita, Osaka, 565-0871 Japan, 2Optical Material Division, Osaka National Research Institute, Agency of Industrial Science and Technology, 1-8-31, Midorigaoka, Ikeda, Osaka, 563-8577 Japan, 3Planning and Management Development, Research and Development Center, Sumitomo Heavy Industries, Ltd., 63-30, Yuhigaoka, Hiratsuka, Kanagawa, 254-00806 Japan

(Received July 24, 1999; Accepted October 14, 1999)

It is known that local refractive index change occurs when femtosecond laser pulses with extremely high peak power are launched into glass. We focused 130-femtosecond laser pulses of 800 nm into the bulk of glass and examined the shape of the induced refractive index change. We found that the length of the spot of the refractive index change along the optical axis reached about 30 μm despite the diameter being about 2 μm. To estimate the distribution of induced refractive index change, we fabricated Bragg grating by scanning the focused spot and calculated the amount of the change by applying Kogelnik's coupled mode theory to the measured diffraction efficiencies of the higher order diffracted beams.

Key words : Bragg grating, ultrashort pulses, refractive index change, self-focusing, zone plate, fabrication