Provided is an illumination optical system includes: a light source; and a light guiding member configured to guide a light flux emitted from the light source to an illuminated surface, the light guiding member having: an incident surface into which the light flux from the light source enters; an ellipsoidal reflection surface configured to reflect the light flux from the incident surface; and an exit surface from which the light flux reflected by the ellipsoidal reflection surface exits, in which the light source is arranged so as to be separated from a first focal point of the ellipsoidal reflection surface at a position farther from the illuminated surface, in a direction perpendicular to a light emitting surface of the light source.

Embodiments for optical diffusion devices are provided. In one example, an optical diffusion device comprises a first optical element including a first diffusing surface, a second optical element including a second diffusing surface, and an adhesive layer optically coupling the first diffusing surface to the second diffusing surface.

A photocathode is formed on a monocrystalline silicon substrate having opposing illuminated (top) and output (bottom) surfaces. To prevent oxidation of the silicon, a thin (e.g., 1-5 nm) boron layer is disposed directly on the output surface using a process that minimizes oxidation and defects, and a low work-function material layer is then formed over the boron layer to enhance the emission of photoelectrons. The low work-function material includes an alkali metal (e.g., cesium) or an alkali metal oxide. An optional second boron layer is formed on the illuminated (top) surface, and an optional anti-reflective material layer is formed on the boron layer to enhance entry of photons into the silicon substrate. An optional external potential is generated between the opposing illuminated (top) and output (bottom) surfaces. The photocathode forms part of novel sensors and inspection systems.

The number of stimulated spots and/or the area of a stimulated spot is easily increased or decreased while keeping the irradiation power for each stimulated spot constant. Provided is a light stimulation device (3) that includes an objective lens (23) that radiates stimulation light emitted from a stimulation laser (11) onto a specimen (S); an LCOS-SLM (17) that is located at a position conjugate to the pupil of the objective lens (23) and that can modulate the phase of stimulation light to be made to enter the objective lens (23) based on a predetermined pupil modulation pattern; an AOM (13) that adjusts the amount of stimulation light to be made to enter the LCOS-SLM (17); a mouse (26) that is used to specify the number of spots and the position of a spot of light to be radiated onto the specimen (S); and a controller main unit (28) that determines the pupil modulation pattern for the LCOS-SLM (17) according to the number of spots and the position of a spot specified by means of the mouse (26) and that controls the AOM (13) such that, when the number of spots specified by means of the mouse (26) is changed, the amount of light to be radiated onto each spot before and after the change in the number of spots becomes constant.