Highly resistant all-silica polarizing coatings for normal incidence applications.

Several fundamental restrictions limit the implementation of microlasers in high power systems, low resistivity of coatings and compactness of elements, especially if control of polarization is necessary. Thin-film-based coatings with extremely high optical resistivity and polarizing properties for normal incidence could become a preferable solution. In this Letter, a novel multilayer approach to form all-silica polarizing coatings for normal incidence angle applications is proposed. Laser induced damage thresholds (test one-on-one) at the wavelength of 355 nm were 39J/cm2 and 48.5J/cm2 for the reflected and transmitted polarizations, respectively. Such elements can essentially improve tolerated radiation power and allow for production of more compact laser systems.

Correlation of structural and optical properties using virtual materials analysis.

Thin film growth of ${\textrm{TiO}}_2$TiO2 by physical vapor deposition processes is simulated in the Virtual Coater framework resulting in virtual thin films. The simulations are carried out for artificial, simplified deposition conditions as well as for conditions representing a real coating process. The study focuses on porous films which exhibit a significant anisotropy regarding the atomistic structure and consequently, to the index of refraction. A method how to determine the effective anisotropic index of refraction of virtual thin films by the effective medium theory is developed. The simulation applies both, classical molecular dynamics as well as kinetic Monte Carlo calculations, and finally the properties of the virtual films are compared to experimentally grown films especially analyzing the birefringence in the evaluation.

Anti-Reflective Coatings Produced via Atomic Layer Deposition for Hybrid Polymer 3D Micro-Optics.

The increasing demand for optics quality requires the lowest optical power loss, which can occur from unwanted reflections. Laser direct writing (LDW) allows for the fabrication of complex structures, which is particularly advantageous in micro-optic applications. This research demonstrates the possibility of forming an anti-reflective coating on hybrid polymer micro-lenses fabricated by employing LDW without changing their geometry. Such coating deposited via atomic layer deposition (ALD) decreased the reflection from 3.3% to 0.1% at a wavelength of 633 nm for one surface of hybrid organic-inorganic SZ2080™ material. This research validates the compatibility of ALD with LDW 3D multiphoton lithography synergistically, expanding its applications on optical grade sub-100 µm scale micro-optics.

Anisotropy of 3D Columnar Coatings in Mid-Infrared Spectral Range.

Polarisation analysis in the mid-infrared fingerprint region was carried out on thin (∼1 µm) Si and SiO2 films evaporated via glancing angle deposition (GLAD) method at 70∘ to the normal. Synchrotron-based infrared microspectroscopic measurements were carried out on the Infrared Microspectroscopy (IRM) beamline at Australian Synchrotron. Specific absorption bands, particularly Si-O-Si stretching vibration, was found to follow the angular dependence of ∼cos2θ, consistent with the absorption anisotropy. This unexpected anisotropy stems from the enhanced absorption in nano-crevices, which have orientation following the cos2θ angular dependence as revealed by Fourier transforming the image of the surface of 3D columnar films and numerical modeling of light field enhancement by sub-wavelength nano-crevices.

Next generation highly resistant mirrors featuring all-silica layers.

A principal possibility to overcome fundamental (intrinsic) limit of pure optical materials laser light resistance is investigated by designing artificial materials with desired optical properties. We explore the suitability of high band-gap ultra-low refractive index material (n less than 1.38 at 550 nm) in the context of highly reflective coatings with enhanced optical resistance. The new generation all-silica (porous/nonporous) SiO2 thin film mirror with 99% reflectivity was prepared by glancing angle deposition (GLAD). Its damage performance was directly compared with state of the art hafnia/silica coating produced by Ion-Beam-Sputtering. Laser-Induced Damage Thresholds (LIDT) of both coatings were measured in nanosecond regime at 355 nm wavelength. Novel approach indicates the potential for coating to withstand laser fluence of at least 65 J/cm2 without reaching intrinsic threshold value. Reported concept can be expanded to virtually any design thus opening a new way of next generation thin film production well suited for high power laser applications.