Abstract
We report control possibilities over ultrafast laser-induced periodic void lines in porous glass. Instead of high intensity regime leading to filaments, multi-pulse irradiation with high repetition rate (500 kHz) and various writing speed is used here in a transverse geometry. The formation of a perfectly controlled periodic void structure is shown to rely on such parameters as laser energy per pulse and scanning speed. In particular, both the threshold energy required for this effect and the period of the fabricated void arrays are shown to rise linearly with the number of the applied laser pulses per spot, or with a decreasing writing speed. To explain these results, a thermodynamic analysis is performed. The obtained dependencies are correlated with linear energy losses, whereas the periodicity of the observed structures is attributed to a static energy source formation at the void location affecting both material density and laser energy absorption.
Highlights
The capacity of femtosecond laser systems to locally modify transparent materials has been used for many promising applications in different areas ranging from photonics to microfluidics [1]
Laser machining can be performed in volume of different glasses enabling three-dimensional inscription of numerous structures, such as photonics crystals, optical memories, waveguides, gratings, couplers, chemical and biological membranes and other devises [2, 3]
Material modifications are obtained by varying sample moving speed, Vs, from 0.0125 − 3.75mm/s with respect to the focused laser beam and by changing laser pulse energy Ep from 1.5 to 2.34 μJ at a constant repetition rate (ν = 500kHz)
Summary
The capacity of femtosecond laser systems to locally modify transparent materials has been used for many promising applications in different areas ranging from photonics to microfluidics [1]. Laser machining can be performed in volume of different glasses enabling three-dimensional inscription of numerous structures, such as photonics crystals, optical memories, waveguides, gratings, couplers, chemical and biological membranes and other devises [2, 3]. Previous studies have already revealed major mechanisms of femtosecond laser irradiation of typical glasses, such as fused silica, BK7 and calcium fluoride [4–9]. Such phenomena as photoionization and avalanche ionization leading to laser-induced breakdown were in focus of both experimental and theoretical studies starting from the invention of highpower systems [4, 10]. It was shown that very small regions could be efficiently treated in a well-determined way by using only a central part of the Gaussian radial distribution of the laser beam [11]
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