  Large-scale, high-precision, and high-transparency microchannels hold great
potential for developing high-performance continuous-flow photochemical
reactions. We demonstrate ultrafast laser-enabled fabrication of 3D
microchannel reactors in ultraviolet (UV) grade fused silica which exhibit high
transparency under the illumination of UV light sources of wavelengths well
below 300 nm with excellent mixing efficiency. With the fabricated glass
microchannel reactors, we demonstrate continuous-flow UV photochemical
synthesis of vitamin D3 with low power consumption of the UV light sources.
