Fabrication of microfluidic channels with a circular cross section using spatiotemporally focused femtosecond laser pulses

Abstract

We report on the fabrication of hollow microfluidic channels with a circular cross-sectional shape embedded in fused silica by spatiotemporally focusing the femtosecond laser beam. We demonstrate both theoretically and experimentally that the spatiotemporal focusing of femtosecond laser beam allows for the creation of a three-dimensionally symmetric spherical intensity distribution at the focal spot.

Progress in ultrafast laser processing and future prospects

“…The most typical device used to both temporally and spatially tailor the ultrafast laser beam is an SLM. In addition, spatiotemporal manipulation by the use of optical gratings, in which the wavelength components in the ultrafast laser pulse are spatiotemporally dispersed, offers excellent performance for internal modification and 3D fabrication because of the more spatially localized confinement of multiphoton absorption [141,142].…”

“…This method was applied to 3D internal processing with an ultrafast laser to improve the depth fabrication resolution (resolution along the laser beam axis) [141]. One of the issues with optical waveguide writing and microfluidic channel formation inside transparent materials using ultrafast lasers is the longitudinally elongated cross-sectional shapes of the formed structures, because of the mismatch between the focal radius and the Rayleigh length.…”

“…In the spatiotemporal focusing method, the femtosecond laser pulse is first spatially dispersed to elongate the pulse width using a pair of parallel gratings before introduction onto the focal lens, as schematically illustrated in Fig. 20(a) [141]. Temporal focusing is achieved at the focus position because different frequency components spatially overlap only near the focus, so that the original ultrashort pulse width is reproduced to maximize the peak intensity at the focus.…”

Femtosecond laser induced tunable surface transformations on (111) Si aided by square grids diffraction

“…25 By solving the Fresnel diffraction equations (Equation (S6) in the supplementary material 24 ), we can get the intensity distribution. For D ¼ 25 lm, the corresponding calculated relative intensity distribution is presented in Fig.…”

“…This is not consistent with the previous classical theory of Fresnel diffraction that the diffraction pattern is determined by the diffraction distance. 25 The formation of the multiple dots can be considered as the repetition of the two-step process (as shown in Fig. S2 in the supplementary material 24 ).…”