Formation of rectangular channels in fused silica by laser-induced chemical etching

Abstract

In this paper, we report results of our research on the formation of micro-channels with the rectangular cross section inside bulk fused silica. The selective etching of channels was performed by the technique called the femtosecond laser induced chemical etching. Hydrofluoric acid was used as an agent for selective removal of laser-modified regions in fused silica samples. The method of the channel cross section control based on multiple scanning is proposed. The effect of scanning speed, laser pulse energy, and polarization on the etching selectivity was investigated and discussed.

Fabrication of Tuning-Fork Gyroscope Resonator using Directed Chemical Etching of Fused Silica

“…The obtained difference in the etching rate can be connected with the differences in orientation of the modified structures due with the direction of radiation polarization (the laser system has linearly polarized output radiation, respectively, in the considered case the polarization is directed at a zero angle to axis X and 90 to axis Y). This assumption is confirmed by the data provided for example in [16,20]. Besides, practically in all considered works devoted to the directed etching of fused silica the significant influence of orientation of structures on quality of process is noted: the most effective etching is observed for cases when modification of fused silica is made by the radiation with circular polarization, or the linear polarization focused at an angle 90 towards the movement of the sample [18].…”

“…3 from the work [18]. The formation of structures in fused silica is possible at rather high density of energy of laser radiation which in certain cases reaches 20 J/cm 2 [16]. Such density is reached when the radiation is focused by lenses with a numerical aperture (NA) not less than 0.2.…”

“…It is known from a number of sources [16][17][18][19][20][21][22] that there can be various structural changes in fused silica under the influence of ultra-short pulse laser radiation. The nature of these changes depends on the modification mode: density of radiation energy, duration and repetition rate of pulses, etc.…”

“…The quality of the selective etching process is estimated on selectivity of sthe dimensionless parameter characterizing the efficiency of etching of the modified material in comparison with the initial one. The etimation of selectivity can be obtained from the expression [16,22]:…”

Femtosecond Beam Transformation Effects in Water, Enabling Increased Throughput Micromachining in Transparent Materials

“…Therefore, it is necessary to increase the efficiency (ablated material/unit energy/unit of time) of the micromachining process as much as possible to fulfil the necessary requirements. Several techniques exist for processing materials with femtosecond pulses which include: direct ablation in air [14,15], back side wet etching [16][17][18], spatiotemporally enhanced focusing [19,20], laser-assisted etching (LAE) [21][22][23][24][25][26], and gas-assisted processing [27][28][29]. Although the techniques presented above all have their advantages and disadvantages, when talking about cutting/drilling deep (> 500 µm) structures inside the material, all of the stated techniques fall short (with the exception of LAE), and ultimately fall victim to slow processing and heat-affected zones around the cut.…”