Star Formation and Dynamics in the Galactic Centre

The centre of our Galaxy is one of the most studied and yet enigmatic places in the Universe. At a distance of about 8 kpc from our Sun, the Galactic centre (GC) is the ideal environment to study the extreme processes that take place in the vicinity of a supermassive black hole (SMBH). Despite the hostile environment, several tens of early-type stars populate the central parsec of our Galaxy. A fraction of them lie in a thin ring with mild eccentricity and inner radius ~0.04 pc, while the S-stars, i.e. the ~30 stars closest to the SMBH (<0.04 pc), have randomly oriented and highly eccentric orbits. The formation of such early-type stars has been a puzzle for a long time: molecular clouds should be tidally disrupted by the SMBH before they can fragment into stars. We review the main scenarios proposed to explain the formation and the dynamical evolution of the early-type stars in the GC. In particular, we discuss the most popular in situ scenarios (accretion disc fragmentation and molecular cloud disruption) and migration scenarios (star cluster inspiral and Hills mechanism). We focus on the most pressing challenges that must be faced to shed light on the process of star formation in the vicinity of a SMBH.Comment: 68 pages, 35 figures; invited review chapter, to be published in expanded form in Haardt, F., Gorini, V., Moschella, U. and Treves, A., 'Astrophysical Black Holes'. Lecture Notes in Physics. Springer 201

Grundlagenuntersuchungen von Festkoerperlasern im Spektralbereich 1 bis 3 Mikrometer Schlussbericht

Solid-state lasers have been fundamentally investigated in the spectral region 1 to 3 microns in a cooperation between the Institute of Laser Physics/Hamburg and the Eastern partners International Laser Centre/Minsk, General Physics Institute/Moscow and the company FIRN/Krasnodar. The cooperation had a duration of 2 years (1995-1996). The main aim was the characterization and evaluation of new laser materials. Several new lasers (Nd&quot;3&quot;+, Tm&quot;3&quot;+, Er&quot;3&quot;+, Yb&quot;3&quot;+) were realized with Russian laser crystals and published in 20 international papers. Krasnodar mainly worked on the growth of Er:YSGG for 3 #mu#m-lasers. Nd:GdVO_4-crystals (Moscow) don't have yet the quality of commercially available YVO_4 from Japan or USA; however the parameters of these crystals are principally superior (absorption coefficient and cross section). In the cooperation with Minsk a lot of crystals were investigated: Silicates, tungstates, berrylates, and aluminates. From the application point of view, the most interesting results are new Yb&quot;3&quot;+-lasers with very high efficiency (80%.) on the basis of tungstates and a new Er&quot;3&quot;+-laser on the basis of Er, Yb-tungstate. The laser application of the investigated crystals is in the spectral region 1 to 3 #mu#m, which is especially interesting for applications in measurements techniques and medicine. (orig.)SIGLEAvailable from TIB Hannover: F97B1619+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman

A 3-μm Laser Perforator for Ophthalmic Surgery

An Er:YAG laser device for effective perforation of narrow channels in biological tissues was developed. Ophthalmic application of this device for chalazion surgery demonstrated its high efficiency for treatment of young and middle-aged patients. © 2019, Springer Science+Business Media, LLC, part of Springer Nature

Mode-locked diode-pumped vanadate lasers operated with PbS quantum dots

The use of glasses doped with PbS nanocrystals as intracavity saturable absorbers for passive Q-switching and mode locking of c-cut Nd:Gd0.7Y0.3VO4, Nd:YVO4, and Nd:GdVO4 lasers is investigated. Q-switching yields pulses as short as 35 ns with an average output power of 435 mW at a repetition rate of 6–12 kHz at a pump power of 5–6 W. Mode locking through a combination of PbS nanocrystals and a Kerr lens results in 1.4 ps long pulses with an average output power of 255 mW at a repetition rate of 100 MHz

Use of a 1.43-μm Laser Coagulator for Treating Corneal Ulcers

It is a common current practice in ophthalmology to use laser for coagulating deep-lying tissues. Laser techniques are sufficiently simple and accurate to be used in outpatient settings. Despite a limited penetration depth, laser coagulators are also widely used for treating corneal pathologies. The article discusses the therapeutic use of a 1.43-μm laser coagulator. © 2020, Springer Science+Business Media, LLC, part of Springer Nature