This thesis details with the fabrication of microholes and change of refractive index of materials, in-duced by femtosecond laser. The experimental results present two series of investigations, which are divided into two categories: (1) femtosecond laser induced ablation of photosensitive glass; (2) fabrication of micro-holes in fused silica glass using femtosecond laser glass.
The first series of experiments dealt with the analysis of single shot and trepanning method. During the first set of investigations, I inspect the fabrication of microholes using single shot and trepanning method on the surface of photosensitive glass. The single shots are applied from the IFRIT laser system with the average pulse energy ranging from 10 nJ/pulse to 30μJ/pulse. From the experimental results, we obtain that the abla-tion threshold for photosensitive glass is 320 nJ/pulse. The percussion methods are also executed using the same IFRIT laser system with the average pulse energy of 10 μJ/pulse. By controlling the exposure time of the internal shutter, 1 to 500 pulses are overlapped at the same tiny spot. The microholes’ diameter and depth have been saturated after the overlap of 100 pulses. The second set of experiments is trepanning. A 50?? objective lens and a 100?? objective lens are used for the experiments to focus the laser beam on the surface of and inside the glass sample. The average pulse energy is varied in the range between 650 nJ/pulse to 27 μJ/pulse and the scanning speed is fixed at 3 μm/s. The third set of investigations deal with the fabrication of microholes inside the photosensitive glass. The laser beam is focused perpendicularly 100 μm below the glass surface. The average pulse energy is either 10 μJ/pulse or 20 μJ/pulse. After the laser micromachining, the sample is baked in furnace. Baked sample is etched with hydrofluoric acid 49% solution.
The second series of experiments dealt with the fabrication of microholes in fused silica glass. The mi-croholes are fabricated in the perpendicular direction of the sample surface. The experiments are performed with the IFRIT laser system with the average pulse energy ranging from 46 nJ/pulse to 1.2 μJ/pulse. The an-gles between the polarization direction of the laser beam and the scanning direction are 0??, 45?? and 90??. In the first set of investigations, I investigate the formation of optical waveguides inside the sample glass using an optical microscope. Below the average pulse energy of 160 nJ/pulse, we are unable to fabricate optical waveguide inside the sample glass. The diameter of the optical waveguides those are fabricated with an angle of 90?? is the widest compared to other optical waveguides those are fabricated with different angles. The diameter of the narrowest waveguide is below 1μm. The optical waveguides have been etched using hydrofluoric acid 5% solution. The optical waveguides those are fabricated with an angle of 90?? has the fastest etching rate compared to other fabrication angles. In the second set of investigations, fabrication of microholes using hydrofluoric acid etching technique is investigated. The longest depth of the microholes is 630 μm, which has a diameter of 5μm. The highest aspect ratio of the fabricated microholes is ~ 126.
본 석사논문은 펨토초 레이저를 이용한 홀 가공방법과 굴절률 변화에 관한 논문이다. 본 실험 결과는 크게 감광 유리에 관한 부분과 용융 실리카에 관한 부분으로 나누어져 있다.
첫번째 실험들은 감광유리에 홀 가공방법에 관한 것이다. 10nJ/pulse 에서 30uJ/pulse의 레이저를 이용하여 단일 가공을 실험 하였다. 감광유리의 가공 역치는 320nJ/pulse이다. 충격가공 방법으로 최대 500펄스가 중첩되었다. 100펄스 이후로는 가공양이 포화되었다. 10uJ/pulse와 20uJ/pulse의 에너지를 이용하여 광도파로를 형성하였다. 생성된 도파로는 베이크 과정 후 49%의 불산 용액을 이용하여 식각을 하였다.
두번째 실험은 실리카 유리에 관한 것이다. 46nJ/pulse에서 1.2uJ/pulse의 에너지가 사용되었다. 160nJ/pulse 이하에서는 가공이 되지 않았다. 레이저의 편광방향은 레이저의 진행방향과 0,45,90도를 이루도록 조사되었다. 편광방향이 90도를 이루는 경우 생성된 광 도파로의 직경이 그렇지 않은 경우에 비해 크다. 0,45도로 조사된 부분에 비해 90도로 조사된 부분에 식각 속도가 매우 빠르다. 식각 후 630um길이에 5um직경의 홀을 가공하였다. 종횡비가 최대 126:1에 달한다.
