펨토초 레이저로 제작된 회절격자의 CO2 레이저 표면 연마 특성 연구

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We fabricated a two-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 , a repetition rate of 100 , and an average output power of 6 was used. The 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 .
When writing grating inside fused silica using femtosecond laser, we find filament phenomenon which is engraved toward Z-axis direction. To reduce this phenomenon, we use objective lenses which have ×20 (NA=0.4), ×50 (NA=0.42), and ×100 (NA=0.5) magnification. We do experiment with 4.3 fixed pulse energy and changing of processing speed from 1 to 10 . As lens magnification and processing speed were increased, filament phenomenon is decreased and its length is 4 5 with 100 magnification of objective lens.
After fabrication of diffraction grating on the surface of fused silica by using a femtosecond laser, its surface with CO2 laser was polished. We measured a surface and cross-section with optical microscope and SEM by changing polishing repetition rate of CO2 laser, respectively. We found that the efficiency of the diffraction grating with surface treatment less than 1 3 steps of the surface treatment by using a CO2 laser is increased by 7 %.
A laser beam array is generated by using a phase hologram (Kinoform) and spatial light modulation (SLM). The beam size was 2.78 for the objective lens of ×40 magnification. This method will be applied to make complex 3D shapes by using a femtosecond laser beam.
Alternative Title
Study on CO2 laser surface treatment of diffraction grating fabricated by using a femtosecond laser
Alternative Author(s)
Hun kook, Choi
일반대학원 광기술공학과
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Table Of Contents
목 차


제 1장 서 론 1
제 1절 연구 배경 1
제 2절 연구 목적 3

제 2장 이 론 5
제 1절 레이저 가공 5
1. 펨토초 레이저 5
제 2절 회절격자 7
제 3절 필라멘트 현상 9
제 4절 위상 홀로그램 10
1. 키노폼 10
2. 반복 푸리에 변환방법을 적용한 위상추출 방법 10

제 3장 실험장치 및 방법 12
제 1절 실험 장치 12
1. 펨토초 레이저 12
2. CO2 레이저 14
3. 공간광변조기 (SLM) 15
4. 레이저 가공 시스템 17
5. 키노폼 점 배열 재생 시스템 24

제 4장 실험 결과 26
제 1절 회절격자 효율 향상 26
1. 회절격자 제작 26
2. CO2 레이저 연마 28
3. 연마 전·후 회절격자 특성 비교 30
제 2절 다중 회절격자 36
1. 다중 회절격자 제작 (격자주기 6um ) 36
2. 제작된 다중 회절격자 (격자주기 6um ) 측정 및 비교 39
3. 다중 회절격자 제작 (격자주기 2um ) 44
4. 제작된 다중 회절격자 (격자주기 2um ) 측정 및 비교 47
제 3절 필라멘트 현상 51
1. 가공 및 깊이 비교 51
제 4절 키노폼 점 배열 재생 56
1. 키노폼 점 배열 제작 56
2. 키노폼 점 배열 재생 57

제 5장 결 론 63

【참고 문헌】 65
최훈국. (2011). 펨토초 레이저로 제작된 회절격자의 CO2 레이저 표면 연마 특성 연구.
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