In the past years the usage of mixed oxides coatings lead to an important improvement of laser damage threshold and
quality of optical elements. In this study influence of post treatment procedure - ex-situ annealing - is examined in terms
of quality, optical constants and laser induced damage threshold (LIDT) of mixed HfO2 and SiO2 coatings. Monolayer
thin films containing different fractions of HfO2 are deposited with ion beam sputtering technology (IBS.) All samples
are post annealed at different temperatures and optimal regimes are defined. Refractive index and absorption coefficient
dispersion is evaluated from transmission spectra measurements. Surface roughness of all samples is characterized
before and after deposition and annealing, using atomic force microscopy (AFM). Microstructural changes are identified
from changes in surface topography. Further, optical resistance was characterized by 5.7 ns duration pulses for 355 nm
wavelength laser radiation, performing 1-on-1 sample exposure tests with high resolution micro-focusing approach for
monolayer samples and S-on-1 tests for multilayer reflectors. Morphology of damaged sites was analyzed through
optical microscopy. Finally, conclusions about annealing effect for mixed HfO2 and SiO2 monolayer and multilayer
coatings are made.
In this work we report an experimental investigation of subsurface damage (SSD) in conventionally polished fused silica
(FS) substrates which are widely used in laser applications and directly influence performances of optical elements.
Two procedures were developed: 1 - acid etching and 2 - superpolishing. Additionally, surface roughness and total
integrated scattering (TIS) measurements were performed to find correlation between the main surface properties and
laser induced damage threshold (LIDT) as circumstantial evidence of elimination of SSD.
Different durations of acid etching have been used to study LIDT of FS substrates. These experiments revealed that the
optimal etching time is ~1 min. for a given acid concentration. Laser induced damage threshold of etched and SiO2 layer
coated FS samples increased ~3 times, while of the ones that were not coated - 4 times. It has been revealed that for nonetched
surface a single nano- to micro-scale absorbing defect ensemble most likely associated with polishing particles
within Beilby layer was dominant, while damage morphology in ~1 min etched FS sample had no point defects
More than 5 times lower roughness value (RMS) was obtained by superpolishing procedure using colloidal silica
abrasive particles. LIDT of such superpolished fussed silica substrates was also strongly increased and compared with
conventional CeO2 abrasive polishing.
Despite the growing improvement in optical polishing and deposition technologies optical resistance of the laser
components used for high-power UV applications remains insufficient in many cases. In this study influence of different
fused silica substrate preparation, post treatment processing and deposition techniques are examined in terms of surface
roughness, optical scattering and laser damage performance. The conventional techniques of polishing, etching, and
finally surface cleaning of substrates have been investigated. Further, a part of samples were also coated with SiO2
monolayer by Ion Beam Sputtering (IBS) technique. Surface quality was characterized prior to and after the treatment
and deposition processes by the means of total integrated scattering (TIS) and atomic force microscopy (AFM). The
experimental results of surface roughness measurements exhibited a good correlation between AFM and TIS methods.
Further optical resistance was characterized with 10 ns duration pulses for 355 nm wavelength laser radiation performing
1-on-1 sample exposure test with high resolution micro-focusing approach. A dominating damage precursor ensembles
produced during manufacturing processes were identified and directly compared. Finally, the conclusions about the
quality influencing factors of investigated processes were drawn.
The stability of thin film coatings for applications especially in the UV spectral range is oftentimes a limiting factor in
the further development of radiation sources and beam delivery systems. Particularly, functional coatings on laser and
conversions crystals as well as resonator mirrors show an insufficient lifetime due to laser-induced degradation. Previous
investigations in the power handling capability of UV coatings mostly concentrate on the properties of pure oxide
materials and particle mitigation.
Recent innovations in ion beam sputtering technology enabled efficient deposition of mixture coatings of different oxide
materials. In combination with an advanced thickness monitoring equipment, the described IBS deposition systems are
capable of employing designs with sub-layers of a few nm thickness. In the present investigation, the stability of classical
designs using pure oxide materials is compared with gradient index design concepts based on mixture materials.
Reflecting and transmitting thin film coatings employing classical and gradient index approaches manufactured under
comparable conditions are characterized in respect to their power handling capability. The results are analyzed before the
background of theoretical expectations regarding contributions from field enhancement and absorptance effects.
In recent years, there has been a growing interest in further development of sol-gel method which can produce ceramics
and glasses using chemical precursors at relative low-temperatures. The applications for sol-gel derived products are
numerous. Department of General and Inorganic Chemistry with Laser Research Center of Vilnius University and
Institute of Physics continues an ongoing research effort on the synthesis, deposition and characterization of porous solgel.
Our target is highly optically resistant anti-reflective (AR) coatings for general optics and nonlinear optical crystals.
In order to produce AR coatings a silica (SiO2) sol-gel has been dip coated on the set of fused silica substrates. The
optical properties and structure of AR-coatings deposited from hydrolysed tetraethylorthosilicate (TEOS) sol were
characterized in detail in this study. The influence of different parameters on the formation of colloidal silica
antireflective coatings by dip-coating technique has been investigated. All samples were characterized performing,
transmission electron microscopy, UV-visible spectroscopy, atomic force microscopy, ellipsometric, total scattering and
laser-induced damage threshold measurements. Herewith we present our recent results on synthesis of sol-gel solvents,
coating fabrication and characterization of their optical properties.