Abstract
We developed an efficient fabrication method of high-quality concave microarrays on fused silica substrates based on temporal shaping of femtosecond (fs) laser pulses. This method involves exposures of fs laser pulse trains followed by a wet etching process. Compared with conventional single pulses with the same processing parameters, the temporally shaped fs pulses can enhance the etch rate by a factor of 37 times with better controllability and higher quality. Moreover, we demonstrated the flexibility of the proposed method in tuning the profile of the concave microarray structures by changing the laser pulse delay, laser fluence, and pulse energy distribution ratio. Micro-Raman spectroscopy was conducted to elucidate the stronger modification induced by the fs laser pulse trains in comparison with the single pulses. Our calculations show that the controllability is due to the effective control of localized transient free electron densities by temporally shaping the fs pulses.
Highlights
Etch rate enhancement and high controllability can be explained by the control of the localized transient free electron density and the corresponding change in photon absorption efficiency
A drastic increase in the diameter took place at a late stage, which means that the pulse train increasingly reveals its effect in etch rate enhancement compared with a single pulse (see Fig. 1(d–e,i,j))
During the ablation of fused silica by a fs laser, the peak free electron densities generated by the double pulse are less than those generated by a single pulse at the same total fluence, leading to smaller ablated structures
Summary
Etch rate enhancement and high controllability can be explained by the control of the localized transient free electron density and the corresponding change in photon absorption efficiency. We can obtain that at te = 150 min, the etch rate of the fs laser pulse train is about 37 times greater than that of the conventional single pulse.
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