An optical element reflects radiation, such as EUV radiation. The optical element includes a substrate with a surface to which a reflective coating is applied. The substrate has at least one channel through which a coolant can flow. The substrate is formed from fused silica, such as titanium-doped fused silica, or a glass ceramic. The channel has a length of at least 10 cm below the surface to which the reflective coating is applied. The cross-sectional area of the channel varies by no more than +/−20% over the length of the channel.

Optical system includes front group, light-shielding member, and rear group that are arranged from object side toward image side. The light-shielding member is provided with opening elongated in first direction. The front group has aspherical surface, does not image the object at the opening in first section parallel to the first direction, and forms intermediate image of the object at the opening in second section perpendicular to the first direction. The rear group has diffractive surface that splits light beam that passes through the opening into light beams at different wavelengths in the second section and focuses the light beams on different locations in the second section. The curvature radius of the aspherical surface in the second section at on-axis position in the first direction differs from that at outermost off-axis position in the first direction.

A hybrid reflective/refractive HMD includes a structural frame, refractive optical lens elements, and optics housings coupled to the structural frame and positioned in front of a user's first and second eyes. Light-emitting visual sources and reflective optical surfaces are contained in the optics housings. Visual content is transmitted from light-emitting visual sources to the reflective optical surfaces. The visual content is reflected within the reflective optical surfaces at least four times without passing through a refractive optical lens element. The visual content is transmitted to the user's first eye or the user's second eye. Simultaneous with the transmission of the visual content to the user's first eye or the user's second eye, a real-world view of the outside surrounding environment is transmitted to the user's first eye or the user's second eye. The visual content is overlaid onto the real-world view of the outside surrounding environment.

A projection optical unit for microlithography includes a plurality of mirrors and has a numerical aperture having a value larger than 0.5. The plurality of mirrors includes at least three grazing incidence mirrors, which deflect a chief ray of a central object field point with an angle of incidence of greater than 45°. Different polarized light beams passing the projection optical unit are rotated in their polarization direction by different angles of rotation. The projection optical unit includes first and second groups of mirrors. The second group of mirrors includes the final two mirrors of the plurality of mirrors at the image side. A linear portion in the pupil dependence of the total geometrical polarization rotation of the projection optical unit is less than 20% of a linear portion in the pupil dependence of the geometrical polarization rotation of the second group of mirrors.

A catoptric system having a reference axis and including a reflective pattern-source (carrying a substantially one-dimensional pattern) and a combination of two optical reflectors disposed sequentially to transfer EUV radiation incident onto the first optical component to the pattern-source the substantially one-dimensional pattern of which is disposed in a curved surface. In one case, such combination includes only two optical reflectors (each may contain multiple constituent components). The combination is disposed in a fixed spatial and optical relationship with respect to the pattern-source, and represents an illumination unit (IU) of a 1D EUV exposure tool that additionally includes a projection optical sub-system configured to form an optical image of the pattern-source on an image plane with the use of only two beams of radiation. These only two beams of radiation originate at the pattern-source from the EUV radiation transferred onto the pattern-source.

An example method includes recording dark images on an image sensor on-board an orbital vehicle during flight, which include a first image recorded before the orbital vehicle is over a predefined location on the Earth and a second image recorded after the orbital vehicle is over the predefined location; and recording third and fourth images on the image sensor during flight based on illumination from a light source that is on-board, with the third image being recorded before the orbital vehicle is over the predefined location and the fourth image being recorded after the orbital vehicle is over the predefined location. A fifth image is recorded on the image sensor during flight while the predefined location on the Earth is visible to the image sensor. The fifth image is based on light from a ground-based calibration system. The light source is calibrated during flight based on the five images.

An example method includes recording dark images on an image sensor on-board an orbital vehicle during flight, which include a first image recorded before the orbital vehicle is over a predefined location on the Earth and a second image recorded after the orbital vehicle is over the predefined location; and recording third and fourth images on the image sensor during flight based on illumination from a light source that is on-board, with the third image being recorded before the orbital vehicle is over the predefined location and the fourth image being recorded after the orbital vehicle is over the predefined location. A fifth image is recorded on the image sensor during flight while the predefined location on the Earth is visible to the image sensor. The fifth image is based on light from a ground-based calibration system. The light source is calibrated during flight based on the five images.

An optical system 10 includes a front group 11, a light shielding member 4, and a rear group 12 disposed in order from a side of an object to a side of an image. The light shielding member 4 has an opening. The rear group 12 has a diffraction surface 5 and an aspherical surface 6. The aspherical surface 6 in a first section has a non-circular-arc shape. The grating spacing of the diffraction surface 5 in the first section changes from a center portion toward a peripheral portion to include an extremum value at the center portion. In the first section, the shape of at least one of a base surface of the diffraction surface 5 and an optical surface disposed closer than the diffraction surface 5 to the side of the object is asymmetric with respect to a normal line at a vertex thereof.

The disclosure provides a method and to an apparatus for determining the heating state of a mirror in an optical system, in particular in a microlithographic projection exposure apparatus. A method for determining the heating state of an optical element includes: measuring values of a first temperature that the optical element has at a first position using a temperature sensor; and estimating a second temperature that the optical element has at a second position, which is located at a distance from the first position, on the basis of the measured values, wherein estimating the second temperature is accomplished while taking into account a temporal change in the previously measured values.

A telescope system (100) comprises a steering minor (M5) arranged in a part of its optical path (L5-L6) between a first telescope stage (10) and a second telescope stage (20). The steering mirror (M5) is configured to controllably rotate over a rotation angle (θm) for controlling a view angle (θv) of the telescope system (100) from the entrance aperture (A1). The steering mirror (M5) is disposed at an intermediate pupil (Pi) of the telescope system (100), at which position an image of the aperture stop (As) is formed by one or more of the optical components (M7,M6) there between.