One-step 3D microstructure fabrication inside pmma by using a femtosecond laser

Femtosecond laser induced locally optical breakdown inside some transparent bulk material have been widely studied in recent two decades. Nowadays, hollow structures can be precisely designed and fabricated inside photosensitive glass, fused silica and porous glass. However, PMMA, as a important polymeric material with superior optical property which is widely used in Micro Total Analysis System (μTAS) was rarely reported in recent studies about laser bulk manufacturing. Only a few reports indicated hollow structures can be made inside PMMA in one-step with the help of femtosecond laser focused by a high NA objective lens . The channel of which was in a diameter of several hundreds of nanometer, which is regarded as a premature product of microfluidic chips because only a few injection techniques and liquid driven methods can be used in nanofluidic systems. In this paper, we present a method to fabricate a 7 mm long 3D hollow channel inside a 1 mm thick PMMA slice with a diameter among 100∼150 µm with the help of a Ti: sapphire regenerative amplifier laser system focused by a long working distance (3.4 mm), low NA (100×/0.8) objective. High power density of femtosecond laser induced optical breakdown is regarded as the main factor to fulfill hollow structure inside PMMA. Heat accumulation effect also play an important role in this process.