Speaker
Description
In this work, we report the experimental results of studies aimed at producing electrodes for glass-based Gaseous Electron Multiplier (GEM) detectors, employing different approaches of femtosecond laser processing. The fabrication of micro-holes in fused silica glass was achieved via two approaches - selective laser etching and direct laser ablation. The first approach is a two-step process. It starts with laser-induced modification of the fused silica substrate in the form of a micro cylinder array through the whole thickness using a tightly focused second harmonic (515 nm) Yb:KGW femtosecond laser beam of 290-fs pulse length, with an average power of 300 mW. After exposure using the XYZ stage, the sample is etched in high-concentration (10 M) 90°C KOH. Laser irradiation induces the local formation of nanogratings, which are etched in KOH several times faster than the untreated glass. The drawback of this approach is that both the laser processing and the etching steps are time-consuming processes, as the full thickness needs to be irradiated, which makes them hardly applicable on an industrial scale. Expediting the formation of holes is necessary to enable the formation of larger array of microscopic holes. This was achieved by direct femtosecond laser ablation of fused silica using irradiation with a fundamental harmonic (1030 nm) and 1.3 W average power. In this approach, a XY galvanometric scanner with a low numerical aperture f-Theta objective was used, and the sample height was controlled with a motorized Z stage. Laser ablation was performed from the bottom up, with the bottom of the substrate in contact with water throughout the entire ablation process. The conditions of glass laser exposure and scanning geometry required for through-hole formation were studied. The latter laser ablation approach allows to omit an etching step, and the exposure process itself is faster due to the faster-moving beam geometry and bigger laser spot size. The second approach allowed the formation of arrays of micro holes in glass with an area of 30 x 30 mm, which enabled further investigation into scaling up the fabrication process. Despite the selective etching being a slower process, it provides steeper side walls than the ablation process, which intrinsically induces some tapering. We expect the formed through micro holes in electrically insulating glass substrates will provide a more stable detector operation, avoiding discharges between the anode and cathode that are usually recorded at high gains.
| Name of the speaker | Asta Tamulevičienė |
|---|---|
| Eligible for the Georges Charpak Young Scientist Award. | no |