Structural Modification in Borosilicate Glass by Use of Femtosecond Fiber Laser at 1.56 µm

By focusing intense femtosecond laser pulses inside a transparent material, one can induce localized structural modifications including a refractive-index change. This technique can be applied to the fabrication of three-dimensional photonic devices. In this paper, we study on the structural modifications in borosilicate glass by using an amplified femtosecond Er-fiber laser system producing 947-fs optical pulses at a repetition rate of 155.1 kHz and a wavelength of 1.56 m. In order to optimize the irradiation condition, we investigate the dependence of structural modification on the incident pulse energy, exposure time, and focusing condition. In a static exposure experiment, it is found that refractive-index change can be induced with a wider range of pulse energies compared to silica glass. The magnitude of refractive-index change is estimated to be 1.2 10 -2 by measuring the diffraction efficiencies of a Raman-Nath grating fabricated in borosilicate glass.