Preparation of high-quality three-dimensional microstructures on polymethyl methacrylate surfaces by femtosecond laser micromachining and thermal-induced micro-leveling

• A modified layer composed of low-weight chains exists on fs laser machined surfaces. • The modified layer melts more quickly than the bulk substrate during the annealing. • Smoot inner walls can be obtained by thermal-induced micro-leveling. • Low pulse energy and suitable feed rate are the keys to obtain high-quality surfaces. As a maskless method, femtosecond (fs) laser micromachining has been used to fabricate microstructures on polymethyl methacrylate (PMMA) substrates, but the fs laser ablation promotes the formation of pores and redeposited debris, generating high surface roughness ranging from hundreds of nanometers to several micrometers. Herein, high-quality three-dimensional microstructures are prepared on PMMA surfaces by fs micromachining under suitable parameters followed by a short annealing treatment. Thermogravimetric analysis coupled with Fourier transform infrared analysis (TG-FTIR) and Raman spectra results reveal that a modified layer may exist on the laser-machined surfaces, which melts more rapidly during the annealing. Improved surface quality is probably caused by the micro-leveling effect of the modified layer. Laser processing parameters greatly affect the final surface morphology. Under optimal parameters, the surface microstructures prepared by this method have sharp edges and smooth inner walls with an average profile surface roughness of 45 ± 15 nm.