There is provided a wavefront measuring method for obtaining wavefront information of an optical system. The method including: irradiating the optical system with a light beam; allowing the light beam passed via the optical system to come into a diffraction grating having periodicity in a first direction; and obtaining the wavefront information based on an interference fringe formed by light beams generated from the diffraction grating. The diffraction grating including: first portions which allow light to pass therethrough; and second portions which shield light, each of the second portions being provided between two of the first portions. A ratio between a width of one of the first portions in the first direction and a width of one of the second portions in the first direction is changed in the first direction, the one of the first portions and the one of the second portions being adjacent to each other.

An interference fringe pattern generator forms an interference fringe pattern from the light rays diffused from a region of an object positioned against a background. A planar array of detector pixels is arranged to capture an image of the interference fringe pattern. A storage medium records information indicative of intensity values of the image of the interference fringe pattern captured by a selected group of pixels of the planar array of detector pixels. The information is recorded as a function of the optical path difference values traversed by the diffused light rays through the interference fringe pattern generator for each of the pixels in the selected group of pixels. A processor determines the spectral characteristics of the object based on the information indicative of the intensity values recorded by the storage medium and the optical path difference values traversed by the diffused light rays.

The present invention describes methods and apparatuses for creating superposition shape images by superposed base and revealing layers of lenslet gratings. The superposition shape images form a message recognizable by a human observer or by an image acquisition and computing device such as a smartphone. The superposition shape images may be created by different superposition techniques ranging from 1D moir, 2D moir and level-line moir superposition techniques to lenticular image and phase shift superposition techniques. Moir superposition techniques enable creating superposition shape images at different apparent depth levels. Applications comprise the protection of documents and valuable articles against counterfeits, the creation of eye-catching advertisements as well as the decoration of buildings and exhibitions.

The present invention describes methods and apparatuses for creating superposition shape images by superposed base and revealing layers of lenslet gratings. The superposition shape images form a message recognizable by a human observer or by an image acquisition and computing device such as a smartphone. The superposition shape images may be created by different superposition techniques ranging from 1D moir, 2D moir and level-line moir superposition techniques to lenticular image and phase shift superposition techniques. Moir superposition techniques enable creating superposition shape images at different apparent depth levels. Applications comprise the protection of documents and valuable articles against counterfeits, the creation of eye-catching advertisements as well as the decoration of buildings and exhibitions.

A new projector design combines one spatial light modulator that affects only the phase of the illumination, and one spatial light modulator that only affects its amplitude (intensity). The phase-only modulator curves the wavefront of light and acts as a pre-modulator for a conventional amplitude modulator. This approach works with both white light and laser illumination, generating a coarse image representation efficiently, thus enabling, within a single image frame, significantly elevated highlights as well as darker black levels while reducing the overall light source power requirements.

An electrically variable lens comprising a variable Fresnel lens and a variable phase corrector plate. A liquid crystal variable Fresnel lens and liquid crystal phase corrector plate are varied in concert to compensate for wavefront discontinuities that would otherwise be produced by the Fresnel lens. The same principle is also used to provide a device capable of imposing an arbitrary spatial and temporal phase modulation on a wavefront.

An electrically variable lens comprising a variable Fresnel lens and a variable phase corrector plate. A liquid crystal variable Fresnel lens and liquid crystal phase corrector plate are varied in concert to compensate for wavefront discontinuities that would otherwise be produced by the Fresnel lens. The same principle is also used to provide a device capable of imposing an arbitrary spatial and temporal phase modulation on a wavefront.

A multiple mirror for multiplying a single incident wavefront of electromagnetic radiation into a plurality of outgoing wavefronts, including at least one first mirror, onto which the incident wavefront first falls, and a second mirror, on which the wavefront is last reflected, wherein the mirror planes are superimposed in the direction of movement of the first wavefront. The first mirror is partially transparent to the electromagnetic radiation and the second mirror is fully reflective.

A radiation source includes a nozzle configured to direct a stream of fuel droplets along a droplet path towards a plasma formation location, and is configured to receive a gaussian radiation beam having gaussian intensity distribution, having a predetermined wavelength and propagating along a predetermined trajectory, and further configured to focus the radiation beam on a fuel droplet at the plasma formation location. The radiation source includes a phase plate structure including one or more phase plates. The phase plate structure has a first zone and a second zone. The zones are arranged such that radiation having the predetermined wavelength passing through the first zone and radiation having the predetermined wavelength passing through the second zone propagate along respective optical paths having different optical path lengths. A difference between the optical path lengths is an odd number of times half the predetermined wavelength.

A radiation source includes a nozzle configured to direct a stream of fuel droplets along a droplet path towards a plasma formation location, and is configured to receive a gaussian radiation beam having gaussian intensity distribution, having a predetermined wavelength and propagating along a predetermined trajectory, and further configured to focus the radiation beam on a fuel droplet at the plasma formation location. The radiation source includes a phase plate structure including one or more phase plates. The phase plate structure has a first zone and a second zone. The zones are arranged such that radiation having the predetermined wavelength passing through the first zone and radiation having the predetermined wavelength passing through the second zone propagate along respective optical paths having different optical path lengths. A difference between the optical path lengths is an odd number of times half the predetermined wavelength.