Laser systems dedicated to space missions require durable and well-characterized optics, that could ensure long-term operation under high average output power. If any of optical elements in such system experiences light-induced fatigue, the performance of whole laser system suffers. Thus, any delayed failure of the optical element would also endanger the entire space mission as repairing optic in the orbit is rather complicated. Up to now, the ability to predict optic’s longevity required by space programs was difficult and expensive, because of limited experimental data and lack of validated prediction models and methods. In order to address this problem, Lidaris and ESA joined forces for a two years cooperation project ESPRESSO. The overall aim of the project is to carry out research and development work required for essential preparation of reliable longevity qualification procedure to evaluate high power laser optics with intended use in space applications. Main elements of chosen methodology for optics lifetime prediction is reported in this paper. The essence of the proposed method lies in online video detection, failure mode (damage mechanism) separation and subsequent search of appropriate extrapolation models and methods. Main experimental findings confirm the suitability of the suggested approach for prediction of laser-induced damage threshold (LIDT) from a limited set of data to the extrapolated higher number of incident laser pulses.
Band-gap and refractive index are known as fundamental properties determining intrinsic optical resistance of multilayer dielectric coatings. By considering this fact we propose novel approach to manufacturing of interference thin films, based on artificial nano-structures of modulated porosity embedded in high band-gap matrix. Next generation all-silica mirrors were prepared by GLancing Angle Deposition (GLAD) using electron beam evaporation. High reflectivity (HR) was achieved by tailoring the porosity of highly resistant silica material during the thin film deposition process. Furthermore, the proposed approach was also demonstrated to work well in case of anti-reflection (AR) coatings. Conventional HR HfO2 and SiO2 as well as AR Al2O3 and SiO2 multilayers produced by Ion Beam Sputtering (IBS) were used as reference coatings. Damage performance of experimental coatings was also analyzed. All-silica based GLAD approach resulted in significant improvement of intrinsic laser damage resistance properties if compared to conventional coatings. Besides laser damage testing, other characteristics of experimental coatings are analyzed and discussed – reflectance, surface roughness and optical scattering. We believe that reported concept can be expanded to virtually any design of thin film coatings thus opening a new way of next generation highly resistant thin films well suited for high power and UV laser applications.
Presented study addresses the nano-size defects acting as damage precursors in nanosecond laser pulse irradiation regime. Defects embedded within the surface of glass are investigated in terms of defect ensembles. Damage frequency method and raster scan procedure are directly compared on the set of two samples: uncoated fused silica substrates and SiO2 monolayer films. The extracted defect ensembles appear to be different from each other. The limitations of compared methods such as pulse-to-pulse variation of laser intensity and sample contamination induced by laser ablation were identified as the main causes of observed differences.
We characterize laser-induced damage threshold (LIDT) in transparent photopolymers by a sub-ps laser pulses of 515 nm wavelength representing case of high light intensities. Five different photopolymers (SZ2080, OrmoComp, SU-8, PDMS and PMMA) widely used in the laser lithography are investigated. The relationship of the damage threshold and optical band-gap energy of the polymers indicating possible damage mechanism is considered. Incubation model validating damage threshold dependence on the number of laser pulses is studied as well. The obtained characteristic values of LIDT reveal potential of photopolymers and their possible applications in high power laser systems.
In this paper new laser-induced damage threshold testing system operating in broad range of pulse repetition
rates (from 0.02 Hz up to 200 kHz) is introduced. The system is capable to test either bare or coated optical
components, used for high average and peak power femtosecond laser applications. Pulses of tunable duration
(300 - 5000 fs) from diode pumped Yb:KGW solid state laser are employed at fundamental wavelength (1030 nm)
and its II-IV harmonics (515 nm, 343 nm and 258 nm). Thanks to advanced adaptive damage detection technique
so called S-on-1 tests are performed with single shot resolution. The capabilities of the system were characterized
and demonstrated on niobia and zirconia - single layer dielectric coatings at different repetition rates.
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.
Group III nitrides are wide band-gap semiconductors which are commonly used in high power and high frequency
electronics and optoelectronics. A rapid development of GaN/InGaN devices is in progress however many technological
improvements are still demanded. One of them is a convenient formation of electrical contacts attached to appropriate
layers. Currently a selective etching step of GaN and InGaN layers is performed by using quite expensive methods such
as plasma, chemical-lithographic or electron beam exposure. However, very little research has been done towards
investigation of an alternative selective laser etching possibility. Therefore in this work we study optical resistance and
damage morphology of thin film GaN and InxGa1-xN layers grown on sapphire substrates in the femtosecond regime.
Laser induced damage threshold (LIDT) tests were carried out in both S-on-1 and 1-on-1 regimes by exposing samples
from front (deposited) and rear (substrate) sides. For optical resistance testing a femtosecond Yb:KGW laser combined
with harmonic generator covering near IR spectrum to visible and UV was used. Experimental results of optical
resistance dependence on band-gap in InxGa1-xN layers with different indium concentration (X up to 22%) are presented.
Also detailed morphology study for different laser wavelengths is performed and discussed.
We report on the fabrication of the minimized conventional microoptical components out of the hybrid organic-
inorganic SZ2080 and SG4060 photoresins using laser direct writing technique. An ascending laser focus multiscan
approach is introduced as a method for the structuring of 2D nanolines. The diameters and heights of the
nanolines are comparable to the ones written with the electron beam lithography. Using our proposed laser
direct writing approach one can write 3D microstructures with the 2D nanofeatures in a single step procedure.
As demonstration of this technology, microlenses with 1D, 2D and circular transmission gratings were fabricated.
Additionally, for the rst time, ISO certied laser-induced damage testing was applied to determine the optical
breakdown threshold of the SZ2080 photoresin used for the laser direct writing.
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