Photoacoustic (PA) tomography (PAT) is a rapidly developing imaging modality that can provide high contrast and spatial-resolution images of light-absorption distribution in tissue. However, reconstruction of the absorption distribution is affected by nonuniform light fluence. This paper introduces a reconstruction method for reducing amplification of noise and artifacts in low-fluence regions. In this method, fluence compensation is integrated into model-based reconstruction, and the absorption distribution is iteratively updated. At each iteration, we calculate the residual between detected PA signals and the signals computed by a forward model using the initial pressure, which is the product of estimated voxel value and light fluence. By minimizing the residual, the reconstructed values converge to the true absorption distribution. In addition, we developed a matrix compression method for reducing memory requirements and accelerating reconstruction speed. The results of simulation and phantom experiments indicate that the proposed method provides a better contrast-to-noise ratio (CNR) in low-fluence regions. We expect that the capability of increasing imaging depth will broaden the clinical applications of PAT.

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A scattering-type cell projection method is proposed and its characteristics are estimated by simulation and experiment. In this method, a mask consisting of thin scatterers and apertures is used to shape an electron beam. Thus, this method has advantages over the conventional cell projection method. First, a high aspect ratio is not necessary to fabricate the mask. Thus, the mask pattern is easily fabricated and its experimental dimensional accuracy is better than 0.2 µ m. Second, the simulated heat deposition on the mask drastically decreases. In addition, simulation and experiment show good contrast of over 105 related to using a limiting aperture to intercept scattered electrons. As a result, this method is considered to be a key technology in future electron beam lithography systems.

The magnetic limiter and helical divertor geometry predicted by vacuum magnetic field calculations has been confirmed by measurements with various probe and calorimeter arrays in Heliotron-E. The effect of modification of these configurations with auxiliary magnetic fields or a material limiter on the edge plasma profile is studied. The relation of the edge plasma properties with the main plasma parameters (density, heating power, etc.) are described. The amount of total heat loss to the divertor region is almost the same as that of the heating power. The edge plasma density is approximately proportional to the core plasma density.

Electron and ion optical design software for integrated circuit manufacturing equipmentA novel single-column multi-electron-beam system, called a beam-split array, has been developed for a high-resolution, high-throughput lithography tool. In this system, a single electron beam is divided into 1024 beams by a multisource module ͑MSM͒ composed of an aperture array ͑a beam-dividing aperture͒, a static lens array ͑Einzel lenses for each divided beam͒, and a blanker array ͑BLA, blanking electrode pairs for each focused beam͒. The MSM is used to form multiple intermediate images of the electron source at the BLA. These images are demagnified to form final images through a projection optics consisting of a double lens doublet with a blanking aperture and deflector. To align the multiple beam paths in the MSM, aligners between these arrays are used, and the aligner conditions are determined by monitoring the blanking-aperture image. Moreover, because each beam current is about 0.1% of the total beam current on the specimen, a high-contrast transmission detection method is used to detect the electrons at the final image plane. As a result, 1024 point beams are successfully formed. In the final image, the measured beam size is less than 55 nm, and the displacement due to distortion is less than 56 nm, even on the off-axial beams. In addition, individual beam blanking by BLA is verified, and cross-talk at the BLA is confirmed to be negligible at present accuracy. Moreover, 65 nm patterns can be simultaneously delineated by nearand off-axial beams. These results verify the concept of their single-column multibeam formation and indicate that this optics can be applied to lithography for manufacturing on semiconductor devices.