The invention relates to a method for acquiring an image by an imager (20) comprising a matrix of pixels configured to generate an electric response when exposed to an incident light flux travelling through an optical path (21) in which is arranged a wavefront correction element (22), comprising the following steps: 1) initiating the exposure of the pixels to the incident light flux; 2) for a plurality of iterations during the exposure: 2.1) non-destructive reading of the electric responses of pixels of a region of interest; 2.2) determining an evolution of the spatial distribution of pixels in logarithmic mode previous iteration with respect to the previous iteration; 2.3) based on said evolution, establishing a command for the wavefront correction element (22) in order to correct the wavefront; 2.4) configuring the wavefront correction element, 3) reading the electric responses of the pixels resulting in an image.

Apparatus and method for detecting wavefront aberration of an objective lens, comprising a wavefront detection system, a planar mirror, and a planar mirror adjusting mechanism; the objective lens is placed between planar mirror and wavefront detection system; planar mirror is positioned at focal point of the objective lens. A test wavefront emitted by wavefront detection system passes through the objective lens, gets reflected by the planar mirror, and t passes through the objective lens again; the wavefront detection system receives and detects the test wavefront to derive a phase distribution thereof; an angle of the planar mirror tilts at is adjusted to obtain different return wavefronts; a polynomial for expressing wavefront aberration is selected, and expressions corresponding to all the return wavefronts are calculated; result of fitting the wavefront aberration of the objective lens when expressed by the selected polynomial is derived through fitting with the polynomial.

A metrology apparatus (302) includes a higher harmonic generation (HHG) radiation source for generating (310) EUV radiation. Operation of the HHG source is monitored using a wavefront sensor (420) which comprises an aperture array (424, 702) and an image sensor (426). A grating (706) disperses the radiation passing through each aperture so that the image detector captures positions and intensities of higher diffraction orders for different spectral components and different locations across the beam. In this way, the wavefront sensor can be arranged to measure a wavefront tilt for multiple harmonics at each location in said array. In one embodiment, the apertures are divided into two subsets (A) and (B), the gratings (706) of each subset having a different direction of dispersion. The spectrally resolved wavefront information (430) is used in feedback control (432) to stabilize operation of the HGG source, and/or to improve accuracy of metrology results.

Disclosed is a wavefront sensor for measuring a tilt of a wavefront at an array of locations across a beam of radiation, wherein said wavefront sensor comprises a film, for example of Zirconium, having an indent array comprising an indent at each of said array of locations, such that each indent of the indent array is operable to perform focusing of said radiation. Also disclosed is a radiation source and inspection apparatus comprising such a wavefront sensor.

An optical detection system for detecting data on the optical mutual coherence function of input field. The system comprising an encoder having similar unit cells, and an array of sensor cells located at a distance downstream of said unit cells with respect to a general direction of propagation of input light. The array defines a plurality of sub-array unit cells, each sub-array corresponding to a unit cell of the encoder, and each sub-array comprising a predetermined number M of sensor elements. The encoder applies predetermined modulation to input light collected by the system, such that each unit cell of said encoder directs a portion of the collected input light incident thereon onto sub-array unit cell corresponding therewith and one or more neighboring sub-array unit cells within a predetermined proximity region. The number M is determined in accordance with a predetermined number of sub-arrays unit cells within the proximity region.

The present application provides a virtual image display apparatus. The virtual image display apparatus includes an image source configured to produce imaging illumination; an optical relay configured to receive the imaging illumination from the image source, and configured to transmit a detection light having an aberrated wavefront representing imaging distortion in a virtual image displayed by the virtual image display apparatus; a wavefront sensor configured to receive the detection light, and configured to detect wavefront aberration information from the detection light; and a wavefront correction processor configured to receive the wavefront aberration information from the wavefront sensor, and configured to adjust in real time the imaging illumination produced by the image source to reduce the imaging distortion in real time.

A device for analysing a wavefront may be connected to a fluorescence microscopy imaging system with optical sectioning, equipped with a microscope objective including a pupil in a pupil plane, the analysis device including a two-dimensional detector including a detection plane; a two-dimensional arrangement of microlenses, arranged in an analysis plane, each microlens forming, on the detection plane, when the analysis device is connected to the microscopic imaging system, an image of an object situated in a focal plane of the microscope objective, with a given analysis field; an optical relay system optically conjugating the analysis plane and the pupil plane; a field diaphragm positioned in a plane optically conjugated with the plane of detection, and defining said analysis field; a processing unit that determines, based on the set of images formed by the microlenses, a two-dimensional map of a characteristic parameter of the wavefront in said analysis plane.

An example deformable mirror includes a number of cells defining an aperture plane of the mirror. Each of the cells includes a first transparent electrode layer and a second reflective electrode layer, with a solid crystal electro-optical (EO) active layer between the electrode layers. The deformable mirror includes a reflective layer optically coupled to each of the cells on the reflective side of the cell.

A method for high-accuracy wavefront measurement based on grating shearing interferometry, which adopts a grating shearing interferometer system comprising an illuminating system, an optical imaging system under test, an object plane diffraction grating plate, an image plane diffraction grating plate, a two-dimensional photoelectric sensor, and a calculation processing unit. The object plane diffraction grating plate and the image plane diffraction grating plate are respectively arranged on the object plane and the image plane of the optical imaging system under test. The shearing phase of 1.sup.st-order diffracted beam and −1.sup.st-order diffracted beam is exactly extracted through phase shifting method, and the original wavefront is obtained by carrying out reconstruction algorithm according to a shear ratio of 2s, such that the accuracy of wavefront measurement of the optical imaging system under test is improved, wherein s is the shear ratio of the grating shearing interferometer.

The present application provides a virtual image display apparatus. The virtual image display apparatus includes an image source configured to produce imaging illumination; an optical relay configured to receive the imaging illumination from the image source, and configured to transmit a detection light having an aberrated wavefront representing imaging distortion in a virtual image displayed by the virtual image display apparatus; a wavefront sensor configured to receive the detection light, and configured to detect wavefront aberration information from the detection light; and a wavefront correction processor configured to receive the wavefront aberration information from the wavefront sensor, and configured to adjust in real time the imaging illumination produced by the image source to reduce the imaging distortion in real time.