3D microstructuring inside photosensitive glass by use of a femtosecond laser for lab-on-chip applications

In this paper we show that a femtosecond laser enables us to form true three-dimensional microstructures embedded in a photosensitive glass Foturan for lab.-on-chip applications. The Foturan glass has superior properties on transparency, hardness, chemical and thermal resistances, and biological compatibility. After exposure to the tightly focused laser beam, latent images are written inside the glass. Modified regions are developed by a post baking process and then preferentially etched away in an ultrasonic solution of 10% hydrofluoric acid in water. By use of this technique, we fabricated various true 3D microstructures including microfluidic components and microoptics inside the Foturan glass. However, the microchannel fabricated inside glass by scanning focal spot of a femtosecond laser perpendicularly to the direction of laser propagation gets an elliptical shape with a cross section of large aspect ratio, owing essentially to a longitudinal distribution of the focal spot produced by an objective lens with numerical aperture of 0.46. We demonstrate that the aspect ratio can be effectively improved by use of a slit-assisted irradiation method. Lastly, we show that 3D microoptics are fabricated inside the Foturan glass, which enhances the function of lab.-on-chip.