Demonstration of a high extinction ratio TiN-based TM-pass waveguide polarizer

A high extinction ratio transverse magnetic (TM)-pass plasmonic waveguide polarizer has been designed and optimized. This device exploits two parallel TiN strips embedded in a silicon dioxide cladding to cut off the transverse electric (TE) polarization state, which is either reflected or absorbed, while the TM mode can pass through the main silicon waveguide with significant low losses. Given a device of 5 μm length, an extinction ratio as high as 60.7 dB and an insertion loss of 2.23 dB were achieved at the target wavelength of 1.55 μm. To our knowledge, this extinction ratio is one of the highest values ever reported. In the wavelength of 1.45–1.59 μm, the proposed device provides an optical bandwidth of 140 nm for an extinction ratio more than 30 dB and an insertion loss less than 3 dB. This device is relatively simple and is easier to be fabricated than other architectures that are found in the literature

Long term stability of optical coatings in close solar environment

Close observations of the solar atmosphere and surface are required in order to understand the solar activity and its influence on Earth. This task will be performed from Solar Orbiter mission which will reach a very close distance from the Sun: the minimum perihelion distance will be only 0.28 AU. At these distances, the spacecraft and instruments are immersed in a very harsh environment characterized by high temperature, solar wind particles and ions. The stability of the optical coatings at these working conditions are a crucial point in an instrument design and a thorough investigation of the environment effects must be carried out for a secure validation. In this work we present the first experiment carried on in laboratory to establish the effect of solar wind low energy particles bombardment in some optical coatings

Extreme-ultraviolet multilayer coatings with high spectral purity for solarimaging

Future solar experiments designed to perform solar plasma diagnostics will also be based on extreme-ultravilet observations. Multilayer (ML) optics are essential in this spectral region since these coatings have high reflectivity at normal incidence. Typically, the reflectivity curve of a ML coating has a small but finite bandwidth, and this can be a serious drawback when several spectral lines fall within the bandwidth. In fact, spectral lines emitted by different ion species can correspond to different plasma conditions. We present the design, realization, and characterization of an innovative ML structure with high reflectivity coupled with a strong rejection ratio for two adjacent spectral features. The key element is an optimized capping layer structure deposited on top of the ML that preserves the performance reflectance at the target wavelength and at the same time suppresses the reflectance at specific adjacent wavelengths. Application to the Fe xv3 7106 K coronal emission line at 28.4 nm with rejection of the He ii Lyman-\u3b1 line at 30.4 nm is presented

Systematic investigation of the optical coatings damages induced in harsh space environment

The scientific goals required to the next-generation space missions lead the development of innovative instrumentation, conceived to operate in increasingly harsh environments. Optical coatings are among the sub-systems which can highly suffer the agents in such environments. In particular, as recently demonstrated, the accelerated ions and particles can potentially jeopardize the coatings optical performances, with a consequent degradation of the overall functionality of an instrument. Despite its importance, this issue is still poorly investigated. In fact, the fragmentary knowledge of the space environments and the low number of previous ground testing experiments complicates the definition of clear procedures to investigate the behavior of the optical coatings in space. A systematic approach devoted to identify a methodology for the validation of optical coatings under ions irradiation is presented. Monte Carlo simulations are used to evaluate the effects induced by different ion species and energies on both layers and multilayers of different materials, getting an accurate overview of the main criticalities. Such results are then used to plan representative irradiation experiments and the subsequent analysis procedures needed for a proper characterization of the exposed samples. In this paper, a summary of the experiments performed so far is presented. Thanks to these studies we have identified three main damage mechanisms which can be used to explain most of the degradation effects observed when an optical coating is irradiated with low energy particles. A brief discussion of such mechanisms is reported