Mingdong Kong

Optimization of thickness uniformity of optical coatings on a conical substrate in a planetary rotation system.

For a coating machine with a planetary rotation system and counterrotating shadowing mask configuration, a shadowing mask was designed using a numerical optimization algorithm to control the thickness uniformity of optical coatings formed on conical substrate. Single-layer magnesium fluoride (MgF(2)) and antireflective (AR) coating at 193 nm were fabricated on a convex conical substrate holder (with diameter 225 mm, apex angle 140 deg, and height 41 mm) by thermal evaporation. Thickness distribution determined from the transmittance spectra of single-layer MgF(2) thin films on BK7 slices showed that uniformities better than 99.3% were experimentally achieved with the designed counterrotating shadowing mask. From the reflectance spectra, uniform optical performance was also obtained for the 193 nm AR coating deposited on fused-silica substrates.

Theoretical design of shadowing masks for uniform coatings on spherical substrates in planetary rotation systems.

A straightforward theoretical routine is proposed to design shadowing masks which are used for preparing uniform coatings on flat as well as strongly curved spherical substrates with large diameters in planetary rotation system. By approximating a spherical substrate in planetary rotation to a corresponding flat substrate in simple rotation around the revolution axis, the initial shape of a shadowing mask is determined. The desired uniformity for the spherical substrate is further realized through expanding appropriately the arc length of the initial shadowing mask. Utilizing the shadowing masks designed with the theoretical routine, film uniformities better than 97% are experimentally achieved for large-diameter spherical substrates with ratios of clear aperture to radius of curvature range from approximately -1.0 to 1.3.

Simultaneous determination of optical constants, thickness, and surface roughness of thin film from spectrophotometric measurements.

A model taking into consideration the refractive index inhomogeneity and surface roughness of a film was proposed for the simultaneous determination of the optical constants, thickness, and surface roughness of a single-layer thin film from spectrophotometric measurements. In the model, the rough surface was treated as an effective absorbing layer. The model was applied to determine simultaneously the parameters of single-layer MgF(2) thin films deposited on fused silica substrates by the oblique-angle deposition technique. The film thicknesses and rms surface roughnesses extracted from spectrophotometric measurements with the proposed model were in good agreement with the values measured by a spectroscopic ellipsometer and an atomic force microscope, respectively.

Microstructure-related properties of magnesium fluoride films at 193nm by oblique-angle deposition

Magnesium fluoride (MgF2) films deposited by resistive heating evaporation with oblique-angle deposition have been investigated in details. The optical and micro-structural properties of single-layer MgF2 films were characterized by UV-VIS and FTIR spectrophotometers, scanning electron microscope (SEM), atomic force microscope (AFM), and x-ray diffraction (XRD), respectively. The dependences of the optical and micro-structural parameters of the thin films on the deposition angle were analyzed. It was found that the MgF2 film in a columnar microstructure was negatively inhomogeneous of refractive index and polycrystalline. As the deposition angle increased, the optical loss, extinction coefficient, root-mean-square (rms) roughness, dislocation density and columnar angle of the MgF2 films increased, while the refractive index, packing density and grain size decreased. Furthermore, IR absorption of the MgF2 films depended on the columnar structured growth.

Anomalous optical Anderson localization in mixed one dimensional photonic quasicrystals

Anomalous optical Anderson localization (AOAL) in mixed one-dimensional (1D) photonic quasicrystals with matching impedance is obtained when the average refractive index of left- and right-handed layers is approximately zero. The transport properties of ordinary and anomalous localization are investigated and compared. The difficulties in expressing analytically the scaling factors of the mixed photonic quasicrystals are illustrated from Hamiltonian-map analysis. An approach based on transfer matrix method is proposed to simulate the localization behavior. From the simulation, it is found that the narrow distribution of the phase shift is responsible for AOAL in the mixed photonic structures. The scaling factors of AOAL decrease with the broadening of the phase shift distribution. The maximum phase shifts of the mixed photonic structures determine the lower boundary of the anomalous localization.

Tamm plasmon-polariton with negative group velocity induced by a negative index meta-material capping layer at metal-Bragg reflector interface

Influence of a negative refractive index meta-material (NIM) capping layer on properties of Tamm plasmon-polariton at the interface of metal-Bragg reflector structure is investigated. Conditions for excitation of the plasmon-polariton is determined from reflectivity mapping calculation and analyzed with cavity mode theory. For specific thicknesses of capping layers, Tamm plasmon-polariton with negative group velocity is revealed in a wide region of frequency. Different from backward optical propagation induced by negative effective-group-refractive-index in dispersive media, negative group velocity of Tamm plasmon-polariton results from opposite signs of cross-section-integrated field energy and Poynting vector.

Fluoride coatings for vacuum ultraviolet reflection filters

LaF3/MgF2 reflection filters with a high spectral-discrimination capacity of the atomic-oxygen lines at 130.4 and 135.6 nm, which were employed in vacuum ultraviolet imagers, were prepared by molybdenum-boat thermal evaporation. The optical properties of reflection filters were characterized by a high-precision vacuum ultraviolet spectrophotometer. The vulnerability of the filters microstructures to environmental contamination and the recovery of the optical properties of the stored filter samples with ultraviolet ozone cleaning were experimentally demonstrated. For reflection filters with the optimized nonquarter-wave multilayer structures, the reflectance ratios R135.6 nm/R130.4 nm of 92.7 and 20.6 were achieved for 7° and 45° angles of incidence, respectively. On the contrary, R135.6 nm/R130.4 nm ratio of 12.4 was obtained for a reflection filter with a standard π-stack multilayer structure with H/L=1/4 at 7° AOI.

Comparison on properties of LaF3 films by Mo boat evaporation on stationary and planetary rotating substrates

Investigation and comparison are made for LaF3 films deposited on stationary and planetary rotating fused-silica substrates by Mo boat evaporation. Influences of substrate movement manners on the film structures and optical properties are discussed.