SiO2-based nonplanar structures fabricated using femtosecond laser lithography

Fabrication Methods for Microfluidic Devices: An Overview

Microfluidic devices offer the potential to automate a wide variety of chemical and biological operations that are applicable for diagnostic and therapeutic operations with higher efficiency as well as higher repeatability and reproducibility. Polymer based microfluidic devices offer particular advantages including those of cost and biocompatibility. Here, we describe direct and replication approaches for manufacturing of polymer microfluidic devices. Replications approaches require fabrication of mould or master and we describe different methods of mould manufacture, including mechanical (micro-cutting; ultrasonic machining), energy-assisted methods (electrodischarge machining, micro-electrochemical machining, laser ablation, electron beam machining, focused ion beam (FIB) machining), traditional micro-electromechanical systems (MEMS) processes, as well as mould fabrication approaches for curved surfaces. The approaches for microfluidic device fabrications are described in terms of low volume production (casting, lamination, laser ablation, 3D printing) and high-volume production (hot embossing, injection moulding, and film or sheet operations).

Design and fabrication of complicated diffractive optical elements on multiple curved surfaces

Fabrication of multiple arbitrary diffractive optical elements (DOEs) on multiple curved surfaces is always a challenge; here we propose an effective optimization method to fabricate complicated DOEs on several curved surfaces at the same time. First we design phase distribution to modulate complicated three-dimensional (3D) intensity distribution on multiple curved surfaces simultaneously, and then by exposure, the intensity distribution is transferred into the pure-phase or depth distribution. Numerical simulations and optical fabrication are performed for different intensity distributions: 3D binary patterns and 3D gray level patterns, on two or three curved surfaces, and both are in nice agreement. Since multiple DOEs are fabricated on curved surfaces simultaneously, the collimation of different curved surfaces is avoided, and it could improve the fabrication efficiency. It is expected that this proposed method would be employed in various precision 3D optical fabrication and processing in the future.

Large refractive index changes of a chemically amplified photoresist in femtosecond laser nonlinear lithography

We found that marked increases in refractive index of chemically amplified photoresists induced by highly repetitive femtosecond laser irradiation without post-exposure baking treatment. For laser writing speed less than 30 μm/s, the refractive index change of the nonlinear absorption region was as large as 8 × 10(-3). Moreover, cross-linking reactions of the resists were induced. The refractive index changes can generate optical confinement and subsequent channel propagations of femtosecond laser pulses. The coupling efficiency was estimated as high as 87% using a low numerical aperture objective lens. The peak intensities of the guiding modes exceeded the polymerization threshold of the resist.