Sub-Picosecond Micromachining of Monocrystalline Silicon for Solar Cell Manufacturing

In this study a prototype sub-picosecond laser was investigated for cutting and scribing of silicon wafers. The Yb:KYW laser used for this investigation, unlike ultrashort systems used previously, generates pulses of 650 fs, i.e., between the pico and femtosecond range. The laser was placed in a micromachining setup, involving a galvo scanner and a telecentric lens. A study of the influence of the processing parameters on the crater width, depth, and quality of machining was carried out. The optimal parameters were found to be 343 nm, 200 kHz, 7 mm/s, and 15 pattern repetitions. The experiments were performed using samples of a silicon wafer of 210-µm thickness. The experimental results show that the sub-picosecond laser can be a promising and competitive tool for solar cell micromachining. In comparison to the commercially available ultrashort pulse laser systems, we find the sub-picosecond laser to be a more cost efficient and reliable source, than a femtosecond one. In addition, the prototype Yb:KYW design offers some unique parameters, such as repetition rate in the range of 100–400 kHz, UV wavelength or obtainable laser fluence close to the silicon ablation thresholds

Experimental Investigations on Laser Ablation of Aluminum in Sub-Picosecond Regimes

Due to high power and ultrashort pulses, femtosecond lasers excel at (but are not limited to) processing materials whose thicknesses are less than 500 microns. Numerous experiments and theoretical analyses testify to the fact that there are solid grounds for the applications of ultrafast laser micromachining. However, with high costs and complexity of these devices, a sub-picosecond laser that might be an alternative when it comes to various micromachining applications, such as patterns and masks in thin metal foils, micro-nozzles, thermo-detectors, MEMS (micro electro-mechanical systems), sensors, etc. Furthermore, the investigation of sub-picosecond laser interactions with matter could provide more knowledge on the ablation mechanisms and experimental verification of existing models for ultrashort pulse regimes. In this article, we present the research on sub-picosecond laser interactions with thin aluminum foil under various laser pulse parameters. Research was conducted with two types of ultrafast lasers: a prototype sub-picosecond Yb:KYW laser (650 fs) and a commercially available femtosecond Ti:S laser (35 fs). The results show how the variables such as pulse width, energy, frequency, wavelength and irradiation time affect the micromachining process

Ozone Generation by Surface Dielectric Barrier Discharge

Surface dielectric barrier discharge (SDBD) is used in a variety of different applications; however, the ozone generated in the discharge can be toxic to people in the vicinity. In this paper, we study the SDBD (using generators with smooth-edge, serrated and thin-wire high-voltage electrodes) in terms of ozone generation. The electrical measurements and the time-resolved plasma imaging revealed differences in the discharge current, dissipated power and plasma morphology for the different types of SDBD generators and showed significant suppression of the streamer formation from the thin-wire electrode. We determined the amount of ozone produced by each generator and found that despite the observed differences in discharge between the generators, the ozone production yield and the maximum volumetric concentration of ozone for all three generators is a linear function of only one parameter—the discharge active power. We also found that the ozone production efficiency of 9.66 g/kWh is constant for all three generators. Our results show that SDBD generators can be safely used in the enclosed space if the SDBD discharge operates with relatively low active power (the SDBD generator working with the active power of 1.7 W did not exceed the ozone concentration of 0.1 ppm in the 60 m3 room)

Update on the neuromonitoring procedures applied during surgeries of the spine – observational study

Introduction Motor evoked potentials (MEPs) are currently considered as a more useful method for neurophysi-ological intraoperative monitoring than somatosensory evoked potentials in cases of surgery applied to patients with adolescent idiopathic scoliosis. The non-invasive approach is preferred to modify MEP recordings, criticizing, in many cases, the fundamentalism for neurophysiological monitoring based only on needle recordings. The aim of the review is to provide our own experience and prac-tical guidelines with reference to neuromonitoring innovations. Material and Methods Recordings of MEPs with surface electrodes instead of needle electrodes including nerve instead of muscle combinations during neurophysiological monitoring associated with surgical interventions to the spine have become more relevant for pediatric purposes, avoiding the anesthesiology-related influences. Observations on 280 patients with Lenke A–C types of spine curvature are presented before and after the surgical correction. Results The MEPs recorded from nerves do not undergo fluctuations at different stages of scoliosis correc-tions and the anesthesia effect more than MEPs recorded from muscles. The use of non-invasive surface electrodes during neuromonitoring for MEP recordings shortens the total time of the surgical procedure without diminishing the precision of the neural transmission evaluation. The quality of MEP recordings during intraoperative neuromonitoring from muscles can be significantly influ-enced by the depth of anesthesia or administration of muscle relaxants but not those recorded from nerves. Conclusions The proposed definition of “real-time” neuromonitoring comprises the immediate warning from a neurophysiologist about the changes in a patient’s neurological status during scoliosis surgery (es-pecially during pedicle screws’ implantation, corrective rods’ implantation, correction, distraction and derotation of the spine curvature) exactly during the successive steps of corrective procedures. This is possible due to the simultaneous observation of MEP recordings and a camera image of the surgical field. This procedure clearly increases safety and limits financial claims resulting from possible complications