Durability of stochastic antireflective structures--analyses on damage thresholds and adsorbate elimination.

We fabricated stochastic antireflective structures (ARS) and analyzed their stability against high power laser irradiation and high temperature annealing. For 8 ps pulse duration and 1030 nm wavelength we experimentally determined their laser induced damage threshold to 4.9 (±0.3) J/cm(2), which is nearly as high as bulk fused silica with 5.6 (±0.3) J/cm(2). A commercial layer stack reached 2.0 (±0.2) J/cm(2). An annealing process removed adsorbed organics, as shown by XPS measurements, and significantly increased the transmission of the ARS. Because of their monolithic build the ARS endure such high temperature treatments. For more sensitive samples an UV irradiation proved to be capable. It decreased the absorbed light and reinforced the transmission.

Tungsten wire grid polarizer for applications in the DUV spectral range.

In this paper, we present a broadband wire grid polarizer with a spectral working range down to a wavelength of 193 nm. Tungsten is chosen as grating material because it provides a high extinction ratio and transmission compared with other common grating materials. The fabrication of the grating with 100 nm period was accomplished using a spatial frequency doubling approach based on ultrafast electron beam lithography and a sophisticated deposition technique. At a wavelength of 193 nm, a transmission of about 44% and an extinction ratio of 20 was measured.

Antireflective subwavelength structures on microlens arrays-comparison of various manufacturing techniques.

Antireflective subwavelength structures (ARS) resembling nanostructures found on the cornea of night-active insects reduce the reflection of light by providing a gradual change in the refractive index at the interface. These artificial ARS have mainly been fabricated by a combination of conventional lithography and reactive ion etching, which constrains their application to planar substrates. We report on the fabrication of ARS using three different techniques including bottom-up and top-down methods as well as their combination on microlens arrays (MLAs) made of fused silica. The optical performance of the resulting ARS on the MLAs is as good as ARS fabricated on planar substrates with increased transmission of up to 96% at certain wavelengths.

Simulating different manufactured antireflective sub-wavelength structures considering the influence of local topographic variations.

Laterally structured antireflective sub-wavelength structures show unique properties with respect to broadband performance, damage threshold and thermal stability. Thus they are superior to classical layer based antireflective coatings for a number of applications. Dependent on the selected fabrication technology the local topography of the periodic structure may deviate from the perfect repetition of a sub-wavelength unit cell. We used rigorous coupled-wave analysis (RCWA) to simulate the efficiency losses due to scattering effects based on height and displacement variations between the individual protuberances. In these simulations we chose conical and Super-Gaussian shapes to approximate the real profile of fabricated structures. The simulation results are in accordance with the experimentally determined optical properties of sub-wavelength structures over a broad wavelength range. Especially the transmittance reduction in the deep-UV could be ascribed to these variations in the sub-wavelength structures.

Flexible replication technique for high-aspect-ratio nanostructures.

A flexible, nondestructive, and cost-effective replication technique for nanostructures is presented. The advantages of the process are: 1) it allows for tailoring structural parameters of the replica (e.g., line width) nearly independent of the structural geometry of the master; 2) it allows for replication of high-aspect-ratio structures also in polymer materials from solution (especially noncurable polymers) such as polystyrene and polymethylmethacrylate; 3) it includes an easy separation process, thus preserving the master for repeated use. Linear grating replicas with line widths ranging from 88 to 300 nm are obtained using a single nanostructured master. Nanofibers and complex nanopatterned replicas are achievable. The presented technique and its flexibility show that atomic layer deposition is a unique tool for the preparation of high-efficiency polarizer diffractive optics, photonics, electronics, and catalysts.

Tailored antireflective biomimetic nanostructures for UV applications.

Antireflective surfaces composed of biomimetic sub-wavelength structures that employ the 'moth eye principle' for reflectance reduction are highly desirable in many optical applications such as solar cells, photodetectors and laser optics. We report an efficient approach for the fabrication of antireflective surfaces based on a two-step process consisting of gold nanoparticle mask generation by micellar block copolymer nanolithography and a multi-step reactive ion etching process. Depending on the RIE process parameters nanostructured surfaces with tailored antireflective properties can easily be fabricated that show optimum performance for specific applications.

Atomic layer deposition of Al2O3 and TiO2 multilayers for applications as bandpass filters and antireflection coatings.

Al(2)O(3) and TiO(2) thin films have been deposited on Si wafers, quartz, BK7 glass, and polycarbonate substrates by atomic layer deposition (ALD). The refractive indices and growth rates of the materials have been determined by spectroscopic ellipsometry and transmission electron microscopy. The influence of substrate temperature and precursor on the refractive indices has been investigated. The refractive index of TiO(2) significantly increases with temperature, whereas the Al(2)O(3) films are temperature insensitive. The films deposited using H(2)O(2) as oxygen source show a slightly higher refractive index than the films prepared with H(2)O. Multilayer narrow-bandpass filters and broadband antireflective coatings have been designed and produced by ALD.

Biomimetic interfaces for high-performance optics in the deep-UV light range.

We report an innovative approach for the fabrication of highly light transmissive, antireflective optical interfaces. This is possible due to the discovery that metallic nanoparticles may be used as a lithographic mask to etch nonstraightforward structures into fused silica, which results in a quasihexagonal pattern of hollow, pillar-like protuberances. The far reaching optical performance of these structures is demonstrated by reflection and transmission measurements at oblique angles of incidence over a broad spectral region ranging from deep-ultraviolet to infrared light.