Proposed method for phase retardation measurements using polarimetric techniques

Phase retardance elements such as quarter, half and full waveplates are essential elements in the most of the polarization systems. So, they should be determined precisely. Accurate determination of the phase retardation for these elements are necessary and critical due to its effect on the optical polarization measurements. In this paper we measure two-dimensional phase retardation distribution of half wave plate using four step phase shifting technique for accurate retardance measurements through the whole surface of the wave plate. By using this technique, four images are captured, which are related to different orientation of the azimuth angle of the analyzer, and mathematically analyzed to obtain the phase retardance measurements. The mean value of the phase retardance measurements is 182.57˚ with uncertainty 0.6˚.

Black phosphorus phase retarder based on anisotropic refractive index dispersion

Black phosphorus (BP) has gained wide interest as a promising layered material for its unique physical properties. In particular, the anisotropic optical property of BP can act as a retarder or a polarizer in nano-optoelectronic devices, for which quantitative qualification of the phase retardation and the anisotropic refractive index dispersion are essential. Here, we report the anisotropic refractive index and extinction coefficient dispersions of BP in the visible and near infrared range of 540–1500 nm, and then characterize optical phase retardation in a BP flake. Cauchy absorbent equations are provided for the refractive index dispersions along both armchair and zigzag directions, which well reproduce the experimentally measured reflectance and transmittance contrast spectra of BP flakes. Furthermore, we demonstrate that a linear polarized light through BP becomes elliptical, a finding that agrees well with simulation results using the obtained anisotropic refractive index dispersions. The two-dimensional phase retarder in this work is expected to find various applications in novel polarization-sensitive nano-optoelectronic devices.

Design of reflective phase retarders in the extreme ultraviolet based on chirped Mo/Si multilayer mirrors

The extreme ultraviolet (EUV) phase retarder is an important optical element for polarization analysis and conversion of EUV synchrotron radiation. In this paper, a linearly chirped Mo/Si multilayer mirror is used to design an EUV phase retarder. With increasing thickness variation of the chirped multilayer, the reflective phase retardation between s- and p-polarized light increases at first and then reaches its maximum value. When the bilayer number increases from 2 to 20, the maximum phase retardation for an EUV source with a photon energy of 90 eV increases from 5.97° to 245.10° for a linearly chirped Mo/Si multilayer with 14.7 nm central thickness. In addition, the phase retardations of chirped mirrors at different photon energies (80 eV, 85 eV and 90 eV) are also investigated and compared. Furthermore, the physical mechanism of reflective phase retardation improvement is also studied by investigating the field intensity distributions inside chirped mirrors.

Bideposited silver nanocolloid arrays with strong plasmon-induced birefringence for SERS application

Silver nano-rod, nano-zigzag, nano-saw, and nano-particle arrays are fabricated with glancing angle bideposition. The structure-dependent anisotropic optical properties of those bideposited nanostructured arrays are measured and investigated. The equivalent birefringence values of nano-rod and nano-zigzag arrays are much larger than crystals found in nature and liquid crystal used in display products. The fact that induced localized plasmon-magnetic field between nanorods dominates the strong phase retardation between p-polarized and s-polarized transmitted wave. For the nano-saw, the strong localized electric field induced between the saw teeth leads to strong SERS signals. Although the bideposited nanoparticles own weak morphological anisotropy, strong optical phase retardation is still detected at wavelengths near 400 nm.

Topological charge of optical vortices devoid of radial symmetry

Here we theoretically obtain values of the topological charge (TC) for vortex laser beams devoid of radial symmetry: asymmetric Laguerre-Gaussian (LG) beams, Bessel-Gaussian (BG) beams, Kummer beams, and vortex Hermite-Gaussian (HG) beams. All these beams consist of conventional modes, namely, LG, BG, or HG modes, respectively. However, all these modes have the same TC equal to that of a single constituent mode n. Orbital angular momenta (OAM) of all these beams, normalized to the beam power, are different and changing differently with varying beam asymmetry. However, for arbitrary beam asymmetry, TC remains unchanged and equals n. Superposition of just two HG modes with the adjacent numbers (n, n+1) and with the phase retardation of (pi)/2 yields a modal beam with the TC equal to – (2n+1). Numerical simulation confirms the theoretical predictions.