펨토초 레이저를 이용한 실리카 내부의 다층 회절격자 가공 기술

Direct writing of multi-layer diffraction grating inside fused silica glass by using a femtosecond laser

We fabricated a multi-layer diffraction grating inside fused silica glass by using a femtosecond laser direct writing method. The femtosecond laser with a wavelength of 515 ㎚, a pulse width of 250 fs, a repetition rate of 100 ㎑, and an average output power of 6 W was used. Two layer diffraction grating with a grating period of 6 ㎛ was successfully fabricated with the layer gap of 0.5, 1, 2, 3, and 5 ㎛, respectively. Also, we investigated the diffraction pattern by illuminating a He-Ne laser beam. Finally, we demonstrated the diffraction grating with a grating period of 3 ㎛ by adjusting the gap of each layer with a grating period of 6 ㎛. Femtosecond laser direct writing technology of multi-layer has a potential to fabricate the diffraction grating with a grating period of below 1.5 ㎛.