A device comprises a housing, a detector for receiving solar irradiance and for providing a detector signal providing an indication of an amount of solar irradiance received by the detector and a shield transparent to at least part of the solar irradiance to be detected, the shield and the housing providing a detector space for housing at least part of the detector. The device further comprises a first light source for emitting light to the shield and a first light sensor arranged to receive light from the first light source, arranged to provide a first signal providing an indication for an amount of light received by the first light sensor. Particles will and reflect light back to the detector space. The reflected light is received by the light sensor. Hence, a signal generated by the sensor is an indication for pollution of the shield.

An inspection system having a light source able to illuminate a transparent cylinder, a mask able to block at least part of the light from the light source, the light source and the mask arranged such that, when the transparent cylinder is positioned in the system for inspection, the light source, the mask and the transparent cylinder are substantially aligned along an inspection axis perpendicular to the longitudinal axis of said transparent cylinder and the mask is interposed between the light source and the transparent cylinder to prevent illumination of a first portion of the transparent cylinder having a width smaller than the diameter of the transparent cylinder while allowing illumination of a second portion of the transparent cylinder, the mask configured to provide a contrast with a particle present in the first portion of the cylinder and illuminated by light refracted by the second portion of the cylinder.

An inspection information generation device includes a design information acquirer configured to acquire design information of a sample to be inspected, a candidate region extractor configured to use the design information to extract multiple candidate regions, an image capturer configured to capture images of the multiple candidate regions, a similarity calculator configured to use the images of the multiple candidate regions to calculate a similarity or distance between the multiple candidate regions, and a region determiner configured to use the similarity or the distance to determine, as inspection information, at least one reference region corresponding to a region to be inspected.

A surface inspection system (10) for inspecting the surface of sheet elements (4) present in an inspection area (20). The system includes an image evaluation unit (18), a camera (12), a dark-field illuminator (14) and a bright-field illuminator (16). The image evaluation unit (18) subtracts a line image captured under bright-field illumination conditions from a line image captured under dark-field illumination conditions. A method of identifying highly reflective surface areas on a sheet element (4) being moved through a sheet element processing machine, wherein first a line image (I.sub.16) of the surface of the sheet element (4) in the viewing area (20) is captured under bright-field illumination conditions and a line image (I.sub.14) of the same surface of the sheet element (4) in the viewing area (20) is captured under dark-field illumination conditions, and then the two line images (I.sub.14, I.sub.16) are compared, in particular subtracted from each other, wherein the surface is identified as being reflective if the difference (S.sub.n) between the two line images (I.sub.14, I.sub.16) is above a predefined threshold.

An inspection system utilizing an air scatter standard includes one or more illumination sources to generate a beam of illumination, illumination optics configured to focus the beam of illumination into a volume of air contained within a chamber of an inspection chamber, one or more collection optics configured to collect a portion of illumination scattered from the volume of air, a detector configured to receive the collected portion of illumination from the one or more collection optics, a controller including one or more processors, communicatively coupled to the detector, configured to execute a set of program instructions to receive one or more signals from the detector and determine a state of the beam of illumination at one or more times based on a comparison between at least one of the intensity or polarization of the illumination scattered from the volume of air and a predetermine air scatter standard.

A system may include illumination optics to direct an illumination beam to a sample at an off-axis angle, collection optics to collect scattered light from the sample, and a phase mask located at a first pupil plane to provide different phase shifts for light in two or more pupil regions of a collection area to reshape a point spread function of light scattered from one or more particles on a surface of the sample. The system may further include a polarization rotator located at a second pupil plane, where the polarization rotator provides a spatially-varying polarization rotation angle selected to rotate light scattered from the surface of the sample to a selected polarization angle, a polarizer to reject light polarized along the selected polarization angle, and a detector to generate a dark-field image of the sample based on light passed by the polarizer.

In a method for modeling a darkfield candidate image at a sensor, a plurality of darkfield images of the sensor is captured, wherein each darkfield image of the plurality of darkfield images is associated with a different operational condition of the sensor. An operational condition of the sensor is determined. A darkfield candidate image comprising a combination of the plurality of darkfield images is modeled based at least in part on the operational condition of the sensor, wherein a contribution of each darkfield image of the plurality of darkfield images is dependent on the operational condition.

A photomultiplier tube (PMT) detector assembly includes a PMT and an analog PMT detector circuit. The PMT includes a photocathode configured to emit an initial set of photoelectrons in response to an absorption of photons. The PMT includes a dynode chain with a plurality of dynodes. The dynode chain is configured to receive the initial set of photoelectrons, generate at least one amplified set of photoelectrons, and direct the at least one amplified set of photoelectrons. The PMT includes an anode configured to receive the at least one amplified set of photoelectrons, with a digitized image being generated based on a measurement of the final amplified set of photoelectrons. The digitized image is corrected by applying an output of the signal measured by the analog PMT detector circuit to the digitized image.

A dark field inspection system may include an illumination source to generate an illumination beam, one or more illumination optics to direct the illumination beam to a sample at an off-axis angle along an illumination direction, a detector, one or more collection optics to generate a dark-field image of the sample on the detector based on light collected from the sample in response to the illumination beam, and a radial polarizer located at a pupil plane of the one or more collection optics, where the radial polarizer rejects light with radial polarization with respect to an apex point in the pupil plane corresponding to specular reflection of the illumination beam from the sample.

A dark-field inspection system may include an illumination source to generate an illumination beam, illumination optics configured to direct the illumination beam to a sample at an off-axis angle along an illumination direction, collection optics to collect scattered light from the sample in response to the illumination beam in a dark-field mode, a polarization rotator located at a pupil plane of the one or more collection optics, where the polarization rotator provides a spatially-varying polarization rotation angle selected to rotate light scattered from a surface of the sample to a selected polarization angle, a polarizer aligned to reject light polarized along the selected polarization angle to reject the light scattered from a surface of the sample, and a detector to generate a dark-field image of the sample based on scattered light from the sample passed by the polarizer.