Scattering effects of glass-embedded microstructures by roughness controlled fs-laser micromachining

Abstract

We report a full roughness analysis carried out upon the internal walls of fs-fabricated micro-structures embedded in fused silica glass. In addition to the standard mapping methods based on RMS evaluation, we performed a spectral analysis to compare different types of surface morphology. In detail, introducing the correlation length Lc as a key parameter to describe the profile periodicity, we highlight that the bottom- top- and side-wall of a square micro-channel show a different surface order and differently affect the light scattering. This is further validated by fast Fourier transform calculations and supported by beam transmission holograms. Here we suggest that proper beam shaping could ensure uniform energy distribution and low scattering effects.

Optofluidic platform using liquid crystals in lithium niobate microchannel

“…In the microfluidic platforms in which quartz is the ideal material the most common method of femtosecond pulse laser microfabrication is the formation of periodic nanoplanes that are later etched by hydrofluoric (HF) acid. Although this technique has shown amazing ability to quickly fabricate precise and controllable-roughness 3D microfluidic circuits, also buried in the substrate 16 , it is not suitable for all materials. Laser assisted etching in lithium niobate has never been reported and attempts of etching LiNbO 3 :Fe crystals with HF after laser ablation, made at CNST did not give any result.…”

“…In this way the low size debris created by femtosecond ablation (tens of nanometers in diameter) are free to “fly” away from the unprocessed area thanks to the increase in their average free path and to the low kinetic energy possessed. The writing parameters (as well as the used objective) deeply affect the residual roughness so that the one of the side walls results almost an order of magnitude lower than that of bottom and top sides 16 . Worthy of note, surface roughness reduction in lithium niobate thin films by femtosecond micromachining in water were also proposed, showing that the ablation debris can be more efficiently removed with the assistance of water and the cavitation process triggered by the ultra-short pulse significantly reduces the size of the debris 17 .…”

Large Scale Indium Tin Oxide (ITO) One Dimensional Gratings for Ultrafast Signal Modulation in the Visible

“…It is well known that direct laser ablation typically creates a large number of debris. In order to overcome those problems a particular precaution has been used: the sample has placed in a controlled atmosphere chamber in which the working condition is maintained slightly below the atmosphere pressure (2×10 -2 bar) via a flux provided by a gas tank and a vacuum pump [16]. The low pressure avoids the debris deposition and significantly improve the ablation quality by promoting the separation of the ablated material from the crystal bulk.…”

Large scale indium tin oxide (ITO) one dimensional gratings for ultrafast signal modulation in the visible spectral region

“…In order to overcome this problem, a particular precaution has been used: the sample was placed in a controlled atmosphere chamber in which the working condition is maintained slightly below the atmosphere pressure (2 Â 10 À2 bar) via a flux provided by a gas tank and a vacuum pump. 16 The low pressure avoids debris deposition and significantly improves the ablation quality by promoting the separation of the ablated material from the crystal bulk. In this way, the low size debris created by femtosecond ablation (tens of nanometers in diameter) is free to ''fly'' away from the unprocessed area, thanks to the increase in its average free path and its low kinetic energy.…”