Sapphire is a widely used material, but is difficult to process by using mechanical or chemical methods. We used a femtosecond laser to fabricate highly curved periodic micro/nano grating structures on a sapphire surface. The effects of laser repetition rate, laser scanning speed, laser polarization direction and scanning direction, and laser fluence on the resulting curved grating were studied. Finite difference time domain (FDTD) simulation software was used to investigate the formation of the curved grating and explain the reason for the formation of the structure being dependent on the distance between two adjacent pulses, which is determined by the scanning speed. This method can be used to process complex patterns with structural colors on a sapphire surface, and different colors could be observed from different angles under white light.
Fabrication inside transparent materials using femtosecond laser has important applications in optical storage, microfluidic devices, and other fields. However, the manufacturing efficiency and quality are limited due to the Rayleigh-length of Gaussian beam and the saturation effect in multi-pulses processing. In this paper, plasma distribution and morphology inside PMMA was modulated by adjusting the focus depth (0~ 200 μm) of femtosecond laser single pulse, which realized the fabrication of modification lines with controllable length and high efficiency. Ultrafast pumpprobe imaging system was used to investigate the evolution of filaments and shockwave inside PMMA during processing. The results showed that the filaments and shockwave inside PMMA transformed from the combination of hemispherical shockwave and filaments into only filaments gradually. Besides, it was observed that the length of filaments extended from 50 μm to 325 μm with the increasing focus depth. The simulation of finite-different time-domain was executed and the results agreed well with the observation results. It indicated the changed optical field distribution inside PMMA caused by different focus depth resulted in the corresponding changes of filaments and the effects of self-focusing and spherical aberration dominated in the mechanism of filaments extension on both sides. The morphology of structure processed inside PMMA was further characterized by optical microscope. It showed that uniform modification lines can be fabricated by single pulse with all focus depth and the length of which increased from 73 μm to 135 μm. These controllable modification lines have great potential in fields like optical waveguide, optical storage and hologram.
With ultrashort pulse durations and ultrahigh power densities, femtosecond laser presents unique advantages of high precision and high quality fabrication of microchannels in transparent materials. In our study, by shaping femtosecond laser pulse energy distribution in temporal or spatial domains, localized transient electrons dynamics and the subsequent processes, such as phase changes, can be controlled, leading to the dramatic increases in the capability of femtosecond laser microchannels fabrication. The temporally shaped femtosecond laser pulse trains can significantly enhance the material removal rate in both water-assisted femtosecond laser drilling and femtosecond laser irradiation followed by chemical etching. Besides, high-aspect-ratio and small-diameter microchannels are drilled by spatially shaped femtosecond laser pulses.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.