Design and fabrication of blazed gratings for a waveguide-type head mounted display.

In a waveguide-type display for augmented reality, the image is injected in the waveguide and extracted in front of the eye appearing superimposed on the real-world scene. An elegant and compact way of coupling these images in and out is by using blazed gratings, which can achieve high diffraction efficiencies. We report the design of blazed gratings for green light (λ = 543 nm) and a diffraction angle of 43°. The blazed gratings with a pitch of 508 nm and a fill factor of 0.66 are fabricated using grayscale electron beam lithography. We outline the subsequent replication in a polymer waveguide material with ultraviolet nanoimprint lithography and confirm a throughput efficiency of 17.4%. We finally show the in- and outcoupling of an image through two blazed gratings appearing sharp and non-distorted in the environment.

Vertical distribution of natural radionuclides in soil: assessment of external exposure of population in cultivated and undisturbed areas.

In the present work, naturally occurring radionuclides ²³8U, ²³²Th and 4°K were measured in soil samples from the cultivated and undisturbed areas in Rudovci, municipality of Lazarevac, Serbia. There were three profiles, each profile divided into four horizons, giving the twelve soil samples. The specific activity of ²³8U, ²³²Th and 4°K in soil and sediment samples was determined by gamma spectrometry using the HPGe semiconductor detector. Obtained activity concentrations ranged from 28.0 to 44.0 Bq/kg for ²³8U, from 59.4 to 71.4 Bq/kg for ²³²Th and from 335.0 to 517.0 Bq/kg for 4°K. The evaluation of the radiological hazards originated from ²³8U, ²³²Th and 4°K in the samples, the absorbed dose rate (D) and the annual effective dose rate (E), calculated in accordance with the UNSCEAR 2000 report, are presented in this paper.