Changes of optical properties of retroreflector installed in LHD.

This article describes changes of optical properties of retroreflectors installed on the inner wall of the vacuum vessel of the Large Helical Device. They were made of stainless steel and were used for a CO(2) laser polarimeter. The reflectivity for a CO(2) laser beam dropped up to 40% after the start of glow discharge cleanings and main plasma experiments. Then it decreased gradually. The reflectivity in a wavelength range shorter than 10 mum decreased significantly through one experimental campaign (about 4 months). On the other hand the reflectivity in a wavelength range longer than 50 mum was larger than 70%. Decrease in the reflectivity in the central region of mirrors was more significant (the reflectivity for visible beams became almost zero) than that in the edge. The distribution of the reflectivity along the radial direction is expected to be related to the shape of the retroreflector. The parallelism of the reflected beam to an incident one also deteriorated. The changes in the polarization angle and in the ellipticity of reflected light polarization were not observed from the visible to the far infrared range.

Bifurcation, birooted primary canines: a case report.

A rare case of birooted primary canines is reported. A male patient aged 6 years 4 months of age presented with pain and swelling related to the upper right first primary molar. Radiographic examination revealed an incidental finding of bifurcation of the roots of all four primary canines. This represents a rare finding. The prevalence of birooted permanent canines in the Japanese population has been reported, but the prevalence of this abnormality of primary canines in other populations is unknown. This report discusses the findings in the context of the available literature. The possible aetiology, possible inferences for the developing dentition, and the need for careful assessment prior to root canal therapy or extraction are highlighted.