![]() ![]() The intensities in copolarization and cross-polarization were recorded and fitted to determine the four parameters of the related Jones matrix. The transmission intensity was recorded under illumination of linearly polarized light at different angles at infrared wavelengths. 27 experimentally determined the transmission coefficients of a manufactured 2D metasurface to confirm their analytical model. 26,27 While the absolute values of the Jones matrix parameters are usually easily derived for most systems when characterized under linearly polarized illumination, 24,25,28–30 determining the complex elements of the Jones matrix is demanding and requires a careful analysis of the optical response under a range of illumination conditions. Jones matrices describing metamaterials have been determined experimentally 24,25 or by analytic modeling. 14,15 In general, the intensity and the polarization state of light after traveling through a chiral medium strongly depend on the initial polarization state of the light. 9,13 By carefully controlling the deposition angle, helices can be grown from gold nanoparticle seeds, yielding sub-100 nm gold helices with a material-based tuneable CD at visible frequencies. 10,11,12 Employing focused ion beam-induced deposition techniques, helices with a smaller radius were fabricated, exhibiting a strong CD between 5 nm. 7 These helical structures and their circular dichroism can be further optimized by increasing the number of intertwined helices within the unit cell that makes up the metamaterial. ![]() demonstrated periodic gold helices exhibiting a strong CD at mid-infrared wavelengths in transmission, which were manufactured by direct laser writing followed by gold electrodeposition. ![]() Periodically arranged 3D spirals are the typical example of a chiral metamaterial in which the handedness of the helices dictates the sign of the CD. 4 Both CD and optical activity are generally pronounced in chiral metamaterials. These metamaterials can additionally exhibit a strong optical activity, which is defined as the effect of the rotation of linearly polarized light propagating through a chiral medium. This characterization requires expensive optical components, such as quarter-wave plates with minimal retardation errors over the wavelength range of interest. 4–6 The performance of these materials is often characterized based on the circular dichroism (CD), the difference in transmission of right-handed (RH) and left-handed (LH) circularly polarized light. 1–3 Many 3D chiral metamaterials have emerged as novel optical materials, e.g., efficient broadband circular polarizers at infrared and optical wavelengths. Metamaterials, various optical materials including plasmonic metasurfaces and three-dimensional (3D), structured plasmonic arrays, have recently attracted attention as they are extremely efficient in tailoring a material’s optical response and controlling the polarization of incident light. This approach is versatile, allowing to calculate the optical response in intensity and phase of any generalized chiral metamaterial upon linear, circular, or elliptical polarized illumination. A coordinate transformation then enabled the calculation of the gyro-optical response of the sample, i.e., its circular dichroism and circular polarization conversion, which is shown to be in good agreement with direct measurements. Using the advantage of symmetry considerations, all parameters of the complex Jones matrix associated with the metamaterial were determined by two linear-polarization experiments. Here, we demonstrate a new method to fully characterize any generalized chiral medium without the use of optical phase-retarding elements, such as quarter-wave plates. ![]() Efficient broadband circular polarizers can be implemented through chiral nanostructures that are periodic and possess certain spatial symmetries. Due to their strong optical activity, chiral metamaterials are attractive optical elements for the control of the polarization of light. ![]()
0 Comments
Leave a Reply. |