In this work, an all-dielectric light polarizing element with 0 angle of incidence was fabricated and investigated. Linear polarizer for 1064 nm wavelength was formed by conformal deposition of dielectric thin films on the structured substrate. Its potential in laser applications was tested with laser-induced damage threshold evaluation for single-shot nanosecond pulses. Despite only dielectric materials, the optical resistance of the periodically structured element is several times inferior to that of the planar element. Differences in optical resistance correlate with formed electric field peaks within the modulated structure, revealing the problem to be solved in the ongoing work.
Anti-reflective (AR) coatings are widely utilized to minimize reflections from optical components. Laser direct writing (LDW) is employed to fabricate complex and multi-level micro-optical elements, such as micro-triplets. Conventional physical vapor deposition methods are insufficient to produce conformal coatings on complex shape and stacked substrates. The atomic layer deposition (ALD) technique offers a promising solution for achieving conformal coatings on free-form components. In this work, we demonstrate the deposition of an AR coating by ALD on LDW-fabricated microstructures and micro-lenses. The ALD-deposited AR coating successfully reduced reflection from 3.3% to 0.1% at 633 nm for one surface of SZ2080.
The compactization of lasers is an ongoing challenge in increasing their effectiveness and integrability of other systems, from nanosatellites to medical devices. The need to decrease their dimensions, especially, for diode-pumped solid-state microchip laser systems causes significant problems with beam quality. Such lasers feature an additional problem of Brightness to output power scaling power. We report an approach where we used a thin film dielectric Fano-like resonance structure as a replacement to a conventional output coupler to overcome this challenge. The structure is engineered to function as a flat spatial filter element for selecting the fundamental transverse mode of the cavity. We achieved an increase of 2x over a conventional setup in CW operation. The data matches well with the numerical analysis performed for a single longitudinal mode model. We predict that this discovery could lead to advanced power scaling in submillimeter cavities, while maintaining the beam quality.
This work presents the investigation of 2D periodic structures made by conformal deposition of dielectric thin films on the modulated surface, where the deposited layers repeat the primary surface. Depending on the architecture, spatial filtering and polarization control may be performed in transmission or reflection with the incidence of radiation perpendicular to the surface.
In the presentation, the overview of different technologies to form conformal coatings on periodically modulated surfaces will be presented. As the proposed 2D photonic structure can be considered a promising component for intracavity spatial filtering, the integration into a microchip laser will be presented. A significant reduction of M2 and brightness increase of two times was recorded for the microchip laser when the fabricated spatial filter was used as one of the resonator mirrors.
Multi-photon lithography empowers additive manufacturing of free-form 3D structures. Currently it is being established for production of miniature optical elements including stacked compound components: diffractive, refractive, guiding, filtering, polarizing, and many other optical functions can be merged into monolith devices with super-wavelength and sub-wavelength features. Still such optics are limited to polymers which are low grade in context of optical materials.
We present improvements in their transparency and increasing their laser induced damage threshold (LIDT). This is made by covering the micro-optics with anti-reflective coating employing atomic layer deposition (ALD) method. In contrast to previous reports, the employed material is hybrid organic-inorganic SZ2080TM substance, which be calcinated and turn the objects into glass-ceramics. The transparency after ALD is improved for a single, doublet, and triplet micro-lenses at 633 nm. The calcination increases LIDT for the micro-lenses by several times validated by S-on-1 tests.
The research work opens additive manufacturing of transparent and durable 3D micro-optical components by combining ALD and calcination.
Laser 3D nanolithography enables the fabrication of complex shape micro-optical elements. The freedom of multi-surface designs of such components has cost them to suffer from reflection losses. This work presents the deposition of an Antireflective (AR) coating, using Atomic Layer Deposition (ALD), on hybrid organic-inorganic polymer SZ2080™ microstructures and micro-lenses fabricated using Laser Direct Writing (LDW). The single-wavelength AR coating produced using ALD successfully reduced reflection from 3.3 % to 0.1 % at 633 nm for one surface of SZ2080™.
This study was aimed to investigate the formation of thin films on a nanostructured surface. Optical characterization revealed the presence of Fano-like resonance phenomenon in such single-layer structure, surrounded by a lower refractive index media. Also, we demonstrate a 5 µm thick photonic multilayer structure composed of alternating high- and low-index materials, providing angular selectivity of light. The proposed 2D structure can be considered as a promising component for intracavity spatial filtering even in high power microlasers. Moreover, the possibility to control polarization with such photonic structures will be presented.
We report on the 3D printing of high transparency and resiliency free-form micro-optics. The fabrication is realized employing combining femtosecond laser direct write 3D nanolithography (fs-LDW or a.k.a. two-photon polymerization) with high temperature calcination (sintering) and atomic layer deposition (ALD) techniques. The developed approach allows production of diverse single optical elements and stacked components ranging in dimensions from 10 to 100 µm. Produced micro-optic objects are characterized of their optical performance (focusing, imaging, transparency) and determining their laser induced damage threshold (LIDT). This opens novel applications of laser 3D printed microoptics under harsh conditions: radiation, temperature, acidic environment, pressure variations.
The laser beam shaping is a practical problem in both information transmission, detection and material processing. Many applications focus on beam intensity and phase control in the so-called near-field, but far-field phenomena in microsystems should be no less interesting. One new way to control far-field distributions is by applying what is called “supercollimation”.
It can be observed in systems consisting of periodically arranged phase gratings made from concentric features that repeat along the optical axis. Supercollimation is defined as the transformation of a broad-angular-intensity profile beam into a very thin well-defined high-peak-intensity and low-divergence beam. Such a beam can be compared to a Bessel Beam, however, a sharp central peak does not appear in the near field, but on the contrary: in the far field.
There is no simple way to understand how a supercollimated beams are formed because it does not occur with 1D or 2D periodic systems. What is clear is that it is a cascading process that requires multiple diffraction. In sufficiently, long structures, plane waves diffracted from 0-order to higher diffraction orders are diffracted back resonantly with a broadened angular distribution that can overlap with the zero-angle component in the spatial spectrum.
Thus, the aim of this paper is to reveal how such a phenomenon can occur in periodic systems with rotational (axial) symmetry, such as photonic crystals and resonators with concentric gratings. Finally, I will discuss how to use the “broken” symmetry of asymmetric photonic crystals in interpreting this phenomenon in practical contexts.
This study was aimed to investigate the growth process of thin films on a pre-structured surface using different optically transparent materials and their optical properties. As results of conformal deposition of ion beam sputtered dense single layers on nano-modulated surfaces showed, replicability of surface modulation depends on the layer’s material itself. Among investigated metal oxides, namely tantalum, niobium, hafnium, and silicon oxides, materials with higher molecular weight tend to better repeatability of the initial structure. As an example, the surface modulation depth of tantalum oxide single layer of ~1 μm thickness has preserved almost 97 % of the initial structure, while the silica layer showed the most rapid smoothening of modulation since preserved only ~ 65 %. Considering that tantalum oxide single layers showed the best replicability results, its optical properties were investigated in a more detailed way. Optical characterization revealed the presence of Fano-like resonance phenomenon in such single-layer structure with high refractive index, surrounded by a lower refractive index media. Due to the coupling of thin film's waveguided modes with excited Fabry-Perot modes this phenomenon results in extremely low transmittance lines in the transmittance maps in a plane of the angle of incidence θ and wavelength λ. Moreover, these resonance lines show sensitivity to the angle and the wavelength of the incident light, which can serve as a demonstration of spatial and spectral filtering properties in such compact photonic single-layer structures.
Optical components are the main parts in laser systems, which limits the total generated output power due to laser-induced damage. At nanosecond laser pulses materials experiences thermal expansion phenomena, therefore optical coatings gain stress leading to breakdown. Moreover, the main resistance to laser radiation is limited by material itself (band gap). Glancing angle deposition method is presented to produce porous nanostructured coatings, which are characterized by low inner stress. Optical resistivity dependance on porosity of several materials such as aluminium, niobium and silicium oxides singlelayers was evaluated. Furthermore, all-silica Bragg mirror is formed and optical properties investigated in different environments to achieve stable and superior optical resistance.
In this work we present a new all-silica coating - polarizer, which is also capable to withstand high density of radiation. In order to demonstrate the versatility of presented approach, several coating designs have been modelled and two of them fabricated together with the full-scale measurements and analysis necessary for polarizers implementation into high power microlaser systems. Two polarizing coatings at the wavelength of 355 nm have been formed using two stepper motors based GLAD system. Afterwards optical and structural analysis have been performed including spectrophotometric, atomic-force microscopy (AFM), scanning electron microscopy (SEM) and optical resistivity measurements.
In this study, we report Fano-like coupling of electromagnetic radiation to infinitely extended planar waveguiding modes of a spatially unbounded system, which specifically is a nanostructured thin film. Proposed design differs from conventional Fano-resonant systems, since conventional ones emerge from coupling to compact resonators with discrete spectrum. In this context, nanostructured thin films are explored by numerical simulations along with an analytical study, followed by the fabrication of the films by the ion beam sputtering method on nano-modulated substrates. Experimental results showed Fano-like resonances of high sensitivity to wavelength and incidence angle of the radiation. Hence, proposed design can be a potential candidate for frequency- and spatial filtering of light in transmission/reflection through/from such nanostructured thin films.
Optical components are the main parts in laser systems and also the limiting factor for high power laser. All-silica based optical components proved to have extremely high laser induced damage threshold and were already tested on standard glass substrates. Such coatings are fabricated by employing glancing angle deposition method, combination of nanostructured porous low refractive index and dense high refractive index thin films were fabricated. Anti-reflection coatings and mirrors with required reflection were achieved, which have superior LIDT values (50.7 J/cm2). Antireflection coating was deposited directly on BBO crystal and results are demonstrated. In this work, the possibility to improve microlaser systems with all-silica coatings is presented.
In this work, a novel multi-layer approach of high band-gap birefringent columnar coatings was proposed and investigated. The growth of anisotropic columnar nano-structures with elliptical shape cross-section was initiated by self-shadowing effect, which was induced by placing the substrate at oblique angle during the deposition process. Amorphous silica was deposited in so-called serial bi-deposition manner to form anisotropic films with high thickness uniformity. The combination of birefringent nano-structured and isotropic layers allows to form zero-order wave-plates with desirable phase delay difference (as an example, λ/4). Low optical losses and high transparency (T~99%) are demonstrated while indicating the potential to withstand laser fluences of 40 J/cm2 and 15 J/cm2 in nanosecond regime at 355 nm and 266 nm wavelengths, respectively.
Standard high reflectivity coatings consist of materials with high and low refractive indexes. Typically, optical resistivity of such elements is limited by the threshold value of material with high index. Combination of two deposition methods, namely ion-beam sputtering and oblique angle deposition, was used to form high reflectivity coatings for the wavelength of 355 nm. Variation of the design of standard coating and the number of top layers, deposited at oblique angle have been investigated. Laser induced damage thresholds, optical scattering, surface roughness, spectral performance etc. were tested for the experimental samples. Analysis indicate that combination of both deposition methods allows to enhance the optical resistivity of typical high reflictivity mirrors. Introducing standard method also allows to stabilize the spectra and reduce the losses of total optical component.
In present work, oblique angle deposition technique was employed to form nano-structured anisotropic layers evaporating amorphous materials. The combination of birefringent nano-structured and isotropic layers allows to form highly transparent (T ~ 99 %) wave-plates. Furthermore, such combination can be used to form two spectrally separated Bragg reflection zones for perpendicular polarizations. This feature allows to form polarizers for zero angle applications. Both elements can be manufactured using only one material by changing only its structural morphology what leads to superior LIDT value. In this work, the possibility to evaporate waveplates and polarizers for zero angle applications was shown.
Standard high reflectivity mirrors consist of layers with high and low refractive indexes. Typically, optical resistivity of such elements is limited by the threshold value of material with high index. Combination of two deposition methods, namely ion-beam sputtering and glancing angle deposition, was used to form high reflectivity mirrors for the wavelength of 355 nm. Variation of the design for standard coating and the number of top layers, deposited at oblique angle have been investigated. Laser induced damage thresholds, surface roughness, spectral performance etc. were tested for all the experimental samples. Analysis indicate that combination of both deposition methods allows to enhance the optical resistivity of typical high reflictivity mirrors. Fully sculptured thin film based mirrors also exhibit spectral instability and optical losses. Introducing standard method allows to stabilize the spectra and reduce the losses of total optical component.
Laser induced damage of optical coatings has been one of the most important targets during many decades of intensive research. Different techniques were used and explored with the aim to increase the resistance of multilayer systems to laser pulses. In this work, LIDT results of different “base” structures made by ion beam sputtering of Al2O3, SiO2 and their mixtures are presented, and further enhancement possibilities are discussed by applying additional layer structure using higher bandgap material – fluorides and glancing angle deposited SiO2.
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.
Optical elements for polarization control are one of the main parts in advanced laser systems. The state and intensity of polarized light is typically controlled by optical elements, namely waveplates. Polymers, solid or liquid crystals and other materials with anisotropic refractive index can be used for production of waveplates. Unfortunately, most of aforementioned materials are fragile, unstable when environmental conditions changes, difficult to apply in microsystems and has low resistance to laser radiation. Retarders, fabricated by evaporation process, do not consist any of these drawbacks. In order to manufacture such optical components with high quality, characterisation of deposition parameters are essential. A serial bi-deposition method was employed to coat anisotropic layers for polarisation control. Such waveplate can be deposited on micro optics or other optical elements, essentially improving compact optical systems. The range of available materials is limited by absorption losses for waveplates in UV spectral region. Therefore, the investigation was accomplished with four eligible candidates – TiO2, LaF3, Al2O3 and SiO2. Structural (XPS, XRD) and optical (spectrophotometry, ellipsometry) analysis have shown Al2O3 and SiO2 as the most applicable materials for UV spectral region.
Laser resistance of optical elements is one of the major topics in photonics. Various routes have been taken to improve optical coatings, including, but not limited by, materials engineering and optimisation of electric field distribution in multilayers. During the decades of research, it was found, that high band-gap materials, such as silica, are highly resistant to laser light. Unfortunately, only the production of anti-reflection coatings of all-silica materials are presented to this day. A novel route will be presented in materials engineering, capable to manufacture high reflection optical elements using only SiO2 material and GLancing Angle Deposition (GLAD) method. The technique involves the deposition of columnar structure and tailoring the refractive index of silica material throughout the coating thickness. A numerous analysis indicate the superior properties of GLAD coatings when compared with standard methods for Bragg mirrors production. Several groups of optical components are presented including anti-reflection coatings and Bragg mirrors. Structural and optical characterisation of the method have been performed and compared with standard methods. All researches indicate the possibility of new generation coatings for high power laser systems.
Technological developments in laser technology require advancements in optical components. Such demand is particularly important in UV spectral region. Antireflection coatings (AR) and waveplates as a widely used optical elements were produced based on glancing angle deposition (GLAD) method. Superior optical performance was measured for AR thin films. Broadband and broad-angle antireflection coatings were manufactured by using multilayer system when changing the refractive index profile by varying the porosity of material. SiO2, Al2O3 and LaF3 materials were used for formation of waveplates for UV region. An investigation of optical and resistant performance were conducted. All materials showed optical losses at the wavelength of 355 nm. Possible technological solutions are presented and investigated.
The stresses in thin films are one of the main problems in the development of small dimensions or thin optical components. In order to produce low-tension anisotropic coatings, the characterization of serial bideposition is essential. Structural and optical performance have been tested for anisotropic TiO2 thin films deposited by serial bideposition technique. Three-dimensional surface interferometric measurements were performed for samples deposited at various angles. Also experimental observations of anisotropic tensions in annealed two-dimensional sculptured thin films of TiO2 material are presented. The deposition angle of 80 deg is considered to be the most applicable for developing optical components due to the befitting optical performance and the lowest tensions before and after the annealing.
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