Search Results (3)

Remote sensing is critical for a wide range of applications, including ocean and wave monitoring, planetary exploration, agriculture, and astronomy. We demonstrate a polariscopy concept that is able to determine orientation of patterns below the optical resolution limit of a system. This technique relies on measuring at least four different polarisation angles and calculating the orientation from this set of intensity information. It was initially demonstrated on the Infrared Microspectroscopy Beamline at the Australian Synchrotron using IR light in transmission. Using a monochrome polarising camera mounted onto a drone as a remote sensing platform analogue, orientation information was extracted from 3D-printed targets in reflection. The images were taken at an altitude where conventional imaging could not resolve the test patterns. The system had a 3.33 mm ground resolution. Patterns consisting of 0.5 mm lines spaced 0.5 mm apart were detected using the method, demonstrating the capability of detecting features over six times smaller than the resolution limit. In the interest of moving towards high-speed data acquisition and processing, two methods for processing the image are compared—an analytical and a curve fitting method. Full article

Capabilities of the attenuated total reflection (ATR) at THz wavelengths for increased sub-surface depth characterisation of (bio-)materials are presented. The penetration depth of a THz evanescent wave in biological samples is dependent on the wavelength and temperature and can reach 0.1–0.5 mm depth, due to the strong refractive index change ∼0.4 of the ice-water transition; this is quite significant and important when studying biological samples. Technical challenges are discussed when using ATR for uneven, heterogeneous, high refractive index samples with the possibility of frustrated total internal reflection (a breakdown of the ATR reflection mode into transmission mode). Local field enhancements at the interface are discussed with numerical/analytical examples. Maxwell’s scaling is used to model the behaviour of absorber–scatterer inside the materials at the interface with the ATR prism for realistic complex refractive indices of bio-materials. The modality of ATR with a polarisation analysis is proposed, and its principle is illustrated, opening an invitation for its experimental validation. The sensitivity of the polarised ATR mode to the refractive index between the sample and ATR prism is numerically modelled and experimentally verified for background (air) spectra. The design principles of polarisation active optical elements and spectral filters are outlined. The results and proposed concepts are based on experimental conditions at the THz beamline of the Australian Synchrotron. Full article

Polariscopy is demonstrated using hyperspectral imaging with a focal plane array (FPA) detector in the infrared (IR) spectral region under illumination by thermal and synchrotron light sources. FPA Fourier-transform IR (FTIR) imaging microspectroscopy is useful for monitoring real time changes at specific absorption bands when combined with a high brightness synchrotron source. In this study, several types of samples with unique structural motifs were selected and used for assessing the capability of polariscopy under this FPA-FTIR imaging technique. It was shown that the time required for polariscopy at IR wavelengths can be substantially reduced by the FPA-FTIR imaging approach. By using natural and laser fabricated polymers with sub-wavelength features, alignment of absorbing molecular dipoles and higher order patterns (laser fabricated structures) were revealed. Spectral polariscopy at the absorption peaks can reveal the orientation of sub-wavelength patterns (even when they are not spatially resolved) or the orientation of the absorbing dipoles. Full article