202 research outputs found
Synoecologie van wegbermvegetaties : biomassa en soortensamenstelling van een aantal plantengemeenschappen in wegbermen in relatie tot abiotische factoren
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Characterization of bubble core and cloudiness in Yb3+:Sr5(PO4)3F crystals using Micro-Raman spectroscopy
Ytterbium doped strontium fluoroapatite Yb{sup 3+}:Sr{sub 5}(PO{sub 4}){sub 3}F (Yb: S-FAP) crystals have been used in High Average Power Laser systems as gain medium. Growth induced defects associated with the crystal often affect their performance. In order to improve the crystal quality and its optical applications, it is imperative to understand the nature of these defects. In this study, we utilize Micro-Raman spectroscopy to characterize two common growth-induced defects: bubble core and cloudiness. We find the bubble core consist of voids and microcrystals of Yb: S-FAP. These microcrystals have very different orientation from that of the pure crystal outside the bubble core. In contrast to a previous report, neither Sr{sub 3}(PO{sub 4}){sub 2} nor Yb{sub 2}O{sub 3} are observed in the bubble core regions. On the other hand, the cloudy regions are made up of the host materials blended with a structural deformation along with impurities which include CaCO{sub 3}, YbPO{sub 4}, SrHPO{sub 4} and Sr{sub 2}P{sub 2}O{sub 7}. The impurities are randomly distributed in the cloudy regions. This analysis is necessary for understanding and eliminating these growth defects in Yb:S-FAP crystals
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Laser damage initiation and growth of antireflection coated S-FAP crystal surfaces prepared by pitch lap and magnetorheological finishing
Antireflection (AR) coatings typically damage at the interface between the substrate and coating. Therefore the substrate finishing technology can have an impact on the laser resistance of the coating. For this study, AR coatings were deposited on Yb:S-FAP [Yb{sup 3+}:Sr{sub 5}(PO{sub 4}){sub 3}F] crystals that received a final polish by both conventional pitch lap finishing as well as magnetorheological finishing (MRF). SEM images of the damage morphology reveals laser damage originates at scratches and at substrate coating interfacial absorbing defects. Previous damage stability tests on multilayer mirror coatings and bare surfaces revealed damage growth can occur at fluences below the initiation fluence. The results from this study suggest the opposite trend for AR coatings. Investigation of unstable HR and uncoated surface damage morphologies reveals significant radial cracking that is not apparent with AR damage due to AR delamination from the coated surface with few apparent cracks at the damage boundary. Damage stability tests show that coated Yb:S-FAP crystals can operate at 1057 nm at fluences around 20 J/cm{sup 2} at 10 ns; almost twice the initiation damage threshold
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New tunable lasers for potential use in LIDAR systems
We discuss the optical and laser properties of two new tunable laser crystals, Ce:LiSrAlF{sub 6} and Cr:ZnSe. These crystals are unique in that they provide a practical alternative to optical parametric oscillators as a means of generating tunable radiation in the near ultraviolet and mid-infrared regions (their tuning ranges are at least 285-315 nm and 2.2-2.8 microns, respectively). While these crystals are relatively untested in field deployment, they are promising and likely to be useful in the near future
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Removal of Lattice Imperfections that Impact the Optical Quality of Ti:Sapphire using Advanced Magnetorheological Finishing Techniques
Advanced magnetorheological finishing (MRF) techniques have been applied to Ti:sapphire crystals to compensate for sub-millimeter lattice distortions that occur during the crystal growing process. Precise optical corrections are made by imprinting topographical structure onto the crystal surfaces to cancel out the effects of the lattice distortion in the transmitted wavefront. This novel technique significantly improves the optical quality for crystals of this type and sets the stage for increasing the availability of high-quality large-aperture sapphire and Ti:sapphire optics in critical applications
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Removal of Lattice Imperfections that Impact the Optical Quality of Ti:Sapphire using Advanced Magnetorheological Finishing Techniques
Ti:sapphire has become the premier lasing medium material for use in solid-state femtosecond high-peak power laser systems because of its wide wavelength tuning range. With a tuneable range from 680 to 1100 nm, peaking at 800 nm, Ti:sapphire lasing crystals can easily be tuned to the required pump wavelength and provide very high pump brightness due to their good beam quality and high output power of typically several watts. Femtosecond lasers are used for precision cutting and machining of materials ranging from steel to tooth enamel to delicate heart tissue and high explosives. These ultra-short pulses are too brief to transfer heat or shock to the material being cut, which means that cutting, drilling, and machining occur with virtually no damage to surrounding material. Furthermore, these lasers can cut with high precision, making hairline cuts of less than 100 microns in thick materials along a computer-generated path. Extension of laser output to higher energies is limited by the size of the amplification medium. Yields of high quality large diameter crystals have been constrained by lattice distortions that may appear in the boule limiting the usable area from which high quality optics can be harvested. Lattice distortions affect the transmitted wavefront of these optics which ultimately limits the high-end power output and efficiency of the laser system, particularly when operated in multi-pass mode. To make matters even more complicated, Ti:sapphire is extremely hard (Mohs hardness of 9 with diamond being 10) which makes it extremely difficult to accurately polish using conventional methods without subsurface damage or significant wavefront error. In this presentation, we demonstrate for the first time that Magnetorheological finishing (MRF) can be used to compensate for the lattice distortions in Ti:sapphire by perturbing the transmitted wavefront. The advanced MRF techniques developed allow for precise polishing of the optical inverse of lattice distortions with magnitudes of about 70 nm in optical path difference onto one or both of the optical surfaces to produce high quality optics from otherwise unusable Ti:sapphire crystals. The techniques include interferometric, software, and machine modifications to precisely locate and polish sub-millimeter sites onto the optical surfaces that can not be polished into the optics conventionally. This work may allow extension of Ti:sapphire based systems to peak powers well beyond one petawatt
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Mercury: A High Repetition Rate Laser for High Energy Density Physics
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Frequency Conversion Activation on the Mercury Laser
High efficiency frequency conversion while operating at average power is critical for the Mercury laser. We will demonstrate average power frequency conversion of face-cooled DKDP and YCOB crystals using a sapphire heat spreader approach
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