Latest advances of high intensity laser facilities enable the beam transport of petawatt laser pulses and can provide novel fundamental insights in high energy plasma physics or laser fusion. The very high peak intensities put enormous demands on the required large sized optics. Beam transport mirrors reflect pulses with only several tens of fs and maintain their phase while providing best possible laser induced damage threshold. State of the art, such mirrors are mostly manufactured by thermal evaporation techniques as they provide a large and uniform deposition area. Their porous layer structure causes changing spectral characteristics and wavefront when vacuum-air cycled. Especially large sized mirrors can show crazing and thereby decrease up-time of PW beamlines. In contrast, sputtered layers are very compact and provide non changing characteristics. Stable and reproducible sputter processes enable the deposition of more complex design structures necessary for further optimization of the laser induced damage threshold. However, deposition rate is slow and an uniform large sized area difficult to achieve for sputtered coatings. In our study, we show a self-constructed and built-up ion beam sputtering (IBS) machine capable to deposit large sized substrates up to a diameter of 550 mm. A design study is presented to evaluate best HR810nm mirror to meet demanding spectral requirements and providing maximized laser damage threshold for HAPLS at ELI beamlines. In the end, a field optimized design is applied with a measured LIDT of 0.9 J/cm2 at 42 fs and 1 kHz. This design is used to manufacture beam transport mirrors for HAPLS applying IBS.
This contribution describes an approach to realize dichroic mirrors for fifth-harmonic separation with a diameter of 12”. The optics will be used at the National Ignition Facility to build a diagnostic based on Optical Thomson Scattering, which requires a high energy, pulsed laser operating at 211nm wavelength. Since the ultra-violet absorption edge of the most commonly used high refractive coating materials is above 211nm, only a few oxide materials as for example alumina are suitable for this wavelength. The applied material combination Al2O3/SiO2 provides a small refractive index contrast of about 0.2, which requires a coating process with a very high precision and uniformity to realize complex thin film designs. To achieve a physical layer thickness uniformity better than 0.5%, the linear motion concept of the MAXIMA ion beam sputtering machine [1] is combined with an additional substrate rotation. The layer thickness is controlled precisely by optical broad band monitoring in the wavelength range from 220nm to 1050nm. To realize a surface figure of λ/10 at 633nm for a clear aperture of 250mm diameter, the multi-antireflection coating on the backside is utilized for stress compensation. Experimental results regarding the spectral performance, the mechanical stress, the surface roughness and the laser damage resistance will be presented and discussed.
Optical thin films are essential for many laser applications in industry and science. The increasing demand for highest quality laser optics, requires the enhancement of existing coating technology as for example Ion Beam Sputtering (IBS). By facing new challenges like the large area deposition for line beam optics with up to two-meter edge length, LASEROPTIK is already pushing the limits of coating technology. This contribution describes an approach to combine Glancing Angle Deposition (GLAD) with IBS utilizing the MAXIMA deposition machine. To analyse the dependence of the refractive index, the ultra violet absorption edge, the mechanical stress and the laser damage resistance on the mean deposition angle to the substrate surface, single layers as well as multilayer coatings are realized at five different mean deposition angles between 30° and 90°. By coating one substrate at each of the five different mean deposition angles in the same batch the influence of run to run process variations is minimized. Besides fundamental research regarding this coating technology the results of this experiment will gain further insight into the deposition of thin films on strongly curved surfaces applying curvature dependent velocity profiles.
Laser material processing plays an important role in the fabrication of the crucial parts for state-of-the-art smartphones and tablets. With industrial line beam systems a line shaped beam with a length above one meter and an average power of several thousand watts can be realized. To ensure excellent long axis beam homogeneity, demanding specifications regarding the substrate surface form tolerances and the coating uniformity have to be achieved for each line beam optic. In addition, a high laser damage threshold and a low defect density are required for the coatings. In order to meet these requirements, the MAXIMA ion beam sputtering machine was developed and built by LASEROPTIK. This contribution describes the functional principle of MAXIMA deposition machine, which adapts the ion beam sputtering technology with its highest coating quality to the field of large area deposition. Furthermore, recent developments regarding the process control by optical broadband monitoring are discussed. Finally experimental results on different thin film characteristics as for example the coating uniformity, the microstructure and the laser damage resistance of multilayers are presented.
Optical coatings are essential for many applications of excimer or solid state lasers in industry and science. An increasing demand for larger optics of highest quality, mainly generated by the display industry processing active matrix organic light emitting diode (AMOLED) backplanes, is posing new challenges for substrate and coating suppliers. For the deposition process development principally the coating uniformity, but also the handling and the cleaning steps of optics with one edge length (L) above 1 meter and several kilograms of weight have to be considered. To provide coatings for optics up to 2 meter edge length, a new ion beam sputtering (IBS) machine was developed and built at LASEROPTIK. This contribution describes an approach to adapt the IBS technology with its advanced coating quality for small optics (L≤50mm) to the field of large area deposition (L≥1m). Applying a customized linear drive, the MAXIMA deposition machine is able to coat optics of up to 100kg weight sequentially. Experimental results on the uniformity, the spectral characteristics and the laser damage resistance of dielectric single- and multilayer coatings are presented and compared with the performance of standard IBS thin films. Furthermore, the deposition of thin films on convex curved surfaces applying curvature dependent movement profiles is discussed. Finally the run to run stability is evaluated on the basis of concrete coating examples.
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