Total Internal Reflection Ellipsometry Approach for Bloch Surface Waves Biosensing Applications.

A one-dimensional photonic crystal with an additional TiO2 layer, supporting Bloch surface waves (BSW), was used for enhanced signal sensitivity for the detection of protein interaction. To compare the optical response of BSW and photonic crystals (PC), bovine serum albumin and specific antibodies against bovine serum were used as a model system. The results obtained show the enhanced sensitivity of p- and s-BSW components for the 1D PC sample with an additional TiO2 layer. Furthermore, a higher sensitivity was obtained for the BSW component of p-polarization in the PC sample with an additional TiO2 layer, where the sensitivity of the ellipsometric parameter Ψ was five times higher and that of the Δ parameter was eight times higher than those of the PC sample. The capabilities of BSW excitations are discussed from the sensitivity point of view and from the design of advanced biosensing.

Large area ion beam sputtered dielectric ultrafast mirrors for petawatt laser beamlines.

The latest advances in petawatt laser technology within the ELI Beamlines project have stimulated the development of large surface area dielectrically coated mirrors meeting all demanding requirements for guiding the compressed 30 J, 25 fs HAPLS laser beam at 10 Hz repetition rate and a center wavelength of 810 nm entirely in vacuum. We describe the production and evaluation of Ta2O5/HfO2/SiO2 ion beam sputtered coated (440 × 290 × 75) mm3 beam transport mirrors. No crazing was observed after thirty vacuum-air cycles. A laser induced damage threshold of 0.76 J/cm2 (fluence on mirror surface) was achieved and maintained at high shot rates.

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.

Broadband chirped mirrors with a porous top layer for smooth group delay dispersion.

The effectiveness of ultrashort pulse compression depends on the coatings group delay dispersion (GDD) characteristics in chirped mirror (CM)-based optical systems. Current porous-layer-based CMs with low GDD oscillations are limited to less than half optical octave spectral bandwidth and the stability of their spectral parameters is still unknown. In order to address these limitations, a broadband CM (covering 400 nm bandwidth) with a porous top layer was deposited and spectral parameters were measured at different environmental conditions. The modeled refractive index of the porous layer varied by approximately 1% due to the changes in humidity. Deposited coatings exhibited low sensitivity of GDD oscillations to deposition errors of porous layer and humidity in the surrounding environment.

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.

Hybrid Tamm-surface plasmon polaritons mode for detection of mercury adsorption on 1D photonic crystal/gold nanostructures by total internal reflection ellipsometry.

Spectroscopic ellipsometry was used for the generation and study of the hybrid TPP-SPP mode as a sensor probe for the real-time formation of amalgam structures on the surface of a plasmon active gold layer. The Au/Hg amalgam formation features and the mercury atoms' penetration into the gold layer were determined by means of the experimental TIRE data and a regression analysis of a multi-layer model containing the index-profile amalgam layer. The hybrid TPP-SPP mode behavior of the coupled excitations provided more information about the mercury atoms' penetration into the gold layer than the single TPP and SPP resonances did. The present study demonstrated the possibility of using the hybrid TPP-SPP mode to design advanced optical gas sensor technologies.

Enhancement of laser-induced damage threshold in chirped mirrors by electric field reallocation.

In this paper, the relation between the laser-induced damage threshold (LIDT) and the electric field intensity (EFI) distribution inside a CM is investigated experimentally. We show that it is possible to increase the LIDT values by slightly modifying the electric field of a standing wave distribution without loss of spectral and dispersion performance. Suggested CM design improvement could increase reliability and LIDT performance of both CM elements and high-power systems they are used in.

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.

Femtosecond laser damage resistance of oxide and mixture oxide optical coatings.

We report on the laser damage resistance of ion beam-sputtered oxide materials (Al2O3, Nb2O5, HfO2, SiO2, Ta2O5, ZrO2) and mixtures of Al2O3-SiO2, Nb2O5-SiO2, HfO2-SiO2, Ta2O5-SiO2, and ZrO2-SiO2, irradiated by single 500 fs pulses at 1030 nm. Laser-induced damage threshold (LIDT), refractive index, and bandgaps of the single-layer coatings are measured. For pure oxide materials a linear evolution of the LIDT with bandgap is observed. The results are in accordance with our simulations based on photo-ionization and avalanche-ionization. In the case of mixtures, however, deviations from the previous behaviors are evidenced. The evolution of the LIDT as a function of the refractive index is analyzed, and an empirical description of the relation between refractive index and LIDT is proposed.

Characterization of zirconia- and niobia-silica mixture coatings produced by ion-beam sputtering.

ZrO2-SiO2 and Nb2O5-SiO2 mixture coatings as well as those of pure zirconia (ZrO2), niobia (Nb2O5), and silica (SiO2) deposited by ion-beam sputtering were investigated. Refractive-index dispersions, bandgaps, and volumetric fractions of materials in mixed coatings were analyzed from spectrophotometric data. Optical scattering, surface roughness, nanostructure, and optical resistance were also studied. Zirconia-silica mixtures experience the transition from crystalline to amorphous phase by increasing the content of SiO2. This also results in reduced surface roughness. All niobia and silica coatings and their mixtures were amorphous. The obtained laser-induced damage thresholds in the subpicosecond range also correlates with respect to the silica content in both zirconia- and niobia-silica mixtures.