A 310 nm Optically Pumped AlGaN Vertical-Cavity Surface-Emitting Laser

Ultraviolet light is essential for disinfection, fluorescence excitation, curing, and medical treatment. An ultraviolet light source with the small footprint and excellent optical characteristics of vertical-cavity surface-emitting lasers (VCSELs) may enable new applications in all these areas. Until now, there have only been a few demonstrations of ultraviolet-emitting VCSELs, mainly optically pumped, and all with low Al-content AlGaN cavities and emission near the bandgap of GaN (360 nm). Here, we demonstrate an optically pumped VCSEL emitting in the UVB spectrum (280-320 nm) at room temperature, having an Al0.60Ga0.40N cavity between two dielectric distributed Bragg reflectors. The double dielectric distributed Bragg reflector design was realized by substrate removal using electrochemical etching. Our method is further extendable to even shorter wavelengths, which would establish a technology that enables VCSEL emission from UVA (320-400 nm) to UVC (<280 nm)

Aviation Applications: Hybrid Navigation Techniques and Safety-of-Life Requirements, Part 1

This paper describes some key results of the UniTaS IV project, a publicly funded effort to investigate special problems in the application of satellite navigation for aviation. Among the subjects covered: adaptive beamforming antennas, a GNSS landing system that incorporates inertial sensors with a ground-based augmentation system (GBAS), multiconstellation RAIM (receiver autonomous integrity monitoring), and jamming, spoofing, and authentication of signals

Laparoscopic varicocelectomy in male infertility

Background!#!The suitability of laparoscopic varicocelectomy for assisted reproductive technology depends on the improvement of semen parameters. The present study analyzed the improvement of semen parameters following laparoscopic varicocele ligation.!##!Material and methods!#!A retrospective study of the laparoscopic varicocele clippings at the Department of Urology of University Hospital of Kiel between the years 2007 and 2019 was conducted. The semen analyses according to WHO standards (sperm count, density, motility and morphology) were conducted before and 12 months after surgery. Screening for surgical complications took place at the time of the follow-up seminal analysis. Included were patients with oligozoospermia, asthenozoospermia and/or teratozoospermia (group 1, OAT) or with nonobstructive azoospermia (group 2, NOA).!##!Results!#!This study included data of 27 patients and 22 patients presented preoperative OAT (81%, group 1). Another 5 patients showed NOA (19%, group 2). Data of group 1 showed that semen parameters normalized in 32% of the patients after surgery. Significant improvement in total sperm count (p < 0.005), sperm density (p < 0.005) and total motile sperm count (p < 0.005) was observed. No deterioration of semen parameters was observed. In group 2 we detected spermatozoa in 1 case in the postoperative ejaculate. None of the patients showed complications according to the Clavien-Dindo classification, postoperative hydrocele formation or recurrence of varicocele at the time of control spermiogram.!##!Conclusion!#!Laparoscopic varicocelectomy is a valid therapeutic approach to improve semen parameters for further assisted reproductive techniques. Spermatogenesis may be induced for patients with NOA. Normalization of semen parameters can be achieved for patients with OAT

Auger recombination in AlGaN quantum wells for UV light-emitting diodes

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 113, 071107 (2018) and may be found at https://doi.org/10.1063/1.5044383.We show that the often observed efficiency droop in AlGaN quantum well heterostructures is an internal carrier loss process, analogous to the InGaN system. We attribute this loss process to Auger recombination, with C = 2.3 × 10−30 cm6 s−1; a similar value found commonly in InGaN-based devices. As a result, the peak internal quantum efficiency (IQE) of our structures is limited to 66%. These values were obtained by resonant excitation (time-resolved) photoluminescence (PL), avoiding common error sources in IQE measurements. The existence of strong Auger recombination implies that simple methods employed for IQE determination, such as temperature-dependent PL, may lead to erroneous values. Auger losses will have to be considered once the challenges regarding carrier injection are solved.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement

Out of the blue: ultraviolet vertical-cavity surface-emitting lasers

Out of the blue: ultraviolet vertical-cavity surface-emitting laser

Single-mode lasing in optically pumped UVB VCSELs with circular relief structures

Single-mode lasingSingle-mode lasing in optically pumped UVB VCSELs with circular relief structures in optically pumped UVB VCSELs with circular relief structure