Mr. Yen Chun Tung Profile

Yen Chun Tung

at National Taiwan Univ

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Proceedings Article | 12 March 2015 Paper

Design and fabrication of sub-wavelength annular apertures for femtosecond laser machining

Kuan-Yu Hsu, Yen-Chun Tung, Ming-Han Chung, Chih-Kung Lee

Proceedings Volume 9351, 93510U (2015) https://doi.org/10.1117/12.2078804

KEYWORDS: Micromachining, Femtosecond phenomena, Bessel beams, Laser development, Optical simulations, Transmittance, Glasses, Surface roughness, Finite-difference time-domain method, Silicon

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Many research teams have begun pursuing optical micromachining technology in recent years due to its associated noncontact and fast speed characteristics. However, the focal spot sizes and the depth of focus (DOF) strongly influenced the design requirements of the micromachining system. The focal spot size determines the minimum features can be fabricated, which is inversely proportional to the DOF. That is, smaller focal spot size led to shorter DOF. However, the DOF of the emitted visible or near-infrared light beam is typically limited to tens of nanometers for traditional optic system. The disadvantages of using nanosecond laser for micromachining such as burrs formation and surface roughness were found to further influence the accuracy of machined surfaces. To alleviate all of the above-mentioned problems, sub-wavelength annular aperture (SAA) illuminated with 780 nm femtosecond laser were integrated to develop the new laser micromachining system presented in this paper. We first optimized the parameters for high transmittance associated with the SAA structure for the 780 nm femtosecond laser used by adopting the finite difference time domain simulations method. A lateral microscope was modified from a traditional microscope to facilitate the measurement of the emitted light beam optical energy distribution. To verify the newly developed system performance the femtosecond laser was used to illuminate the SAA fabricated on the metallic film to produce the Bessel light beam so as to perform micromachining and process on silicon, PCB board and glass. Experimental results were found to match the original system design goals reasonably well.

Proceedings Article | 7 March 2014 Paper

Design and fabrication of sub-wavelength annular apertures on fiber tip for femtosecond laser machining

Yen-Chun Tung, Ming-Han Chung, I-Hui Sung, Chih-Kung Lee

Proceedings Volume 8973, 89730M (2014) https://doi.org/10.1117/12.2039148

KEYWORDS: Femtosecond phenomena, Surface plasmons, Metals, Optical fibers, Near field optics, Micromachining, Gold, Silicon, Diffraction, Laser processing

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Adopting optical technique to pursue micromachining must make a compromise between the focal spot sizes the depth of focus. The focal spot size determines the minimum features can be fabricated. On the other hand, the depth of focus influences the ease of alignment in positioning the fabrication light beam. A typical approach to bypass the diffraction limit is to adopt the near-field approach, which has spot size in the range of the optical fiber tip. However, the depth of focus of the emitted light beam will be limited to tens of nanometers in most cases, which posts a difficult challenge to control the distance between the optical fiber tip and the sample to be machined optically. More specifically, problems remained in this machining approach, which include issues such as residue induced by laser ablation tends to deposit near the optical fiber tip and leads to loss of coupling efficiency. We proposed a method based on illuminating femtosecond laser through a sub-wavelength annular aperture on metallic film so as to produce Bessel light beam of sub-wavelength while maintaining large depth of focus first. To further advance the ease of use in one such system, producing sub-wavelength annular aperture on a single mode optical fiber head with sub-wavelength focusing ability is detailed. It is shown that this method can be applied in material machining with an emphasis to produce high aspect ratio structure. Simulations and experimental results are presented in this paper.

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