A Deep Through-Microhole Fabricated Inside a Glass Optical Fiber by Use of a Near Ultraviolet Femtosecond Laser

We have demonstrated an inline/picoliter fiber optic spectrometer cell for providing a new method of optical fiber sensing. The spectrometer cell consisted of a microhole fabricated by femtosecond laser drilling. Sample solutions were introduced into the spectrometer cell which had a sensing volume of several picoliters. The microhole was preferable as penetrating through the optical fiber because of introducing the liquid samples smoothly. In this paper, the parameters of laser system in order to make the microhole penetrating through a glass optical fiber were unraveled. A near ultraviolet 400 nm of femtosecond laser pulse launched into the glass optical fiber. A pulse duration and a repetition rate were 350 fs and 500 Hz, respectively. The femtosecond laser pulses with energy of 70 μJ were focused by an objective lens with numerical aperture of 0.65. After 180 shots, the through-microhole which corresponded the depth of 125 μm was structured.