Nonexhibition of Bragg phenomenon by chevronic sculptured thin films: experiment and theory

Abstract

The unit cell of a chevronic sculptured thin film (ChevSTF) comprises two identical columnar thin films (CTFs) except that the nanocolumns of the first are oriented at an angle χ and nanocolumns of the second are oriented at an angle π − χ with respect to the interface of the two CTFs. A ChevSTF containing 10 unit cells was fabricated using resistive-heating physical vapor deposition of zinc selenide. Planewave reflectance and transmittance spectrums of this ChevSTF were measured for a wide variety of incidence conditions over the 500-900-nm range of the free-space wavelength. Despite its structural periodicity, the ChevSTF did not exhibit the Bragg phenomenon. Theoretical calculations with the CTFs modeled as biaxial dielectric materials indicated that the Bragg phenomenon would not be manifested for normal and near-normal incidence, but vestigial manifestation was possible for sufficiently oblique incidence. Thus, structural periodicity does not always lead to electromagnetic periodicity that underlies the exhibition of the Bragg phenomenon.

Highly Resistant Zero‐Order Waveplates Based on All‐Silica Multilayer Coatings

“…Fresnel reflections between interfaces are inseparable in optical systems with different refractive indexes. Even reducing the columnar broadening in anisotropic silica film (using chevronic thin film structure with, possibly, lower birefringence would result in interference between the porous silica layer and the fused silica substrate. Also, the final waveplate must contain at least two layers: anisotropic film for retardance and a dense layer on top for mechanical protection.…”

Hybrid Nanostructured Porous Silicon-Silver Layers for Wideband Optical Absorption

“…The first subscript on a specular reflectance denotes the linear polarization state of light collected by the detector, while the second subscript denotes the linear polarization state of light impinging on the sample. Care was taken to remove the effects of ambient light, as described elsewhere 14 .…”

Chiral sculptured thin films for circular polarization of mid-wavelength infrared light

“…The transmittance-measurement apparatus for λ 0 ∈ [600 nm, 900 nm] is described in detail elsewhere [28,35]. Briefly, light from a halogen source (HL-2000, Ocean Optics, Dunedin, Florida) was passed through a fiber-optic cable and then through a linear polarizer (GT10, ThorLabs, Newton, New Jersey); it was transmitted through the sample to be characterized and then passed through a second linear polarizer (GT10, ThorLabs) and a fiber-optic cable to a CCD spectrometer (HRS-BD1-025, Mightex Systems, Pleasanton, California) [35]. The linear transmittances were thus measured for normal incidence.…”