Oblique astigmatism and field curvature measured with light-field imaging.

The testing of astigmatism and field curvature of an optical system with light-field imaging is proposed. The method consists in measuring the depth map, obtained with a plenoptic camera, of the image of a test pattern formed by the optical system. To demonstrate the accuracy of the method, the virtual image formed by a plano-convex lens was tested. The resulting depth map was compared with the sagittal and tangential foci distances calculated with the Coddington theory. The proposed method could be applied to the quality testing of ocular optics, including eyeglasses, eyepieces, virtual reality goggles, and augmented reality devices.

Luminescence studies on green emitting InGaN/GaN MQWs implanted with nitrogen.

We studied the optical properties of metalorganic chemical vapour deposited (MOCVD) InGaN/GaN multiple quantum wells (MQW) subjected to nitrogen (N) implantation and post-growth annealing treatments. The optical characterization was carried out by means of temperature and excitation density-dependent steady state photoluminescence (PL) spectroscopy, supplemented by room temperature PL excitation (PLE) and PL lifetime (PLL) measurements. The as-grown and as-implanted samples were found to exhibit a single green emission band attributed to localized excitons in the QW, although the N implantation leads to a strong reduction of the PL intensity. The green band was found to be surprisingly stable on annealing up to 1400°C. A broad blue band dominates the low temperature PL after thermal annealing in both samples. This band is more intense for the implanted sample, suggesting that defects generated by N implantation, likely related to the diffusion/segregation of indium (In), have been optically activated by the thermal treatment.