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△ [7p-S45-10] Characteristics of repetition rate and number of pulse shots of near UV femtosecond laser drilling in a glass fiber optic
Keywords:femtosecond laser processing, fiber optic sensor
We have observed shape and inner surface of microhole fabricated by a near UV (NUV) femtosecond laser drilling in the middle of a glass fiber optic. The microhole was fabricated by the NUV femtosecond laser without breaking off. The microhole works as inline/picoliter fiber optic spectrometer cell. The attractive feature of the spectrometer cell is very small sensing volume which has several tens of picoliter. A second harmonic 400 nm femtosecond laser with 350 fs pulse duration and 30 μJ pulse energy launched into the glass fiber optic. The diameters of core and cladding layer of the glass fiber optic were 62.5 and 125 μm, respectively. A high aspect ratio of the microhole was fabricated after 1000 pulse shots, but there was inner surface roughness. Although the repetition rate was changed 10 to 1000 Hz in order to control the inner surface roughness, the inner surface roughness was occurred in each case. It was confirmed that ablated fused silica particles deposited on the inner surface of microhole. The depth of microhole was deepened with 1 kHz of repetition rate and number of 1000 shots. In comparison to 10 Hz, the depth of microhole was increased by approximately 80%. It was assumed that heat accumulation effect enlarged the length of drilling. In order to minimize inner surface roughness, the best method is to use low number laser shots. After 100 pulse shots with 30 μJ of pulse energy, an optical inner surface quality of microhole was obtained with the 1 kHz of repetition rate which had the depth of 60 μm. The deepened microhole was not occurred under the condition of 100 Hz.