Method and systems are presented for analysing a wavefront using a spectral wavefront analyser to extract optical phase and spectral information at a two dimensional array of sampling points across the wavefront, wherein the relative phase information between the sampling points is maintained. Methods and systems are also presented for measuring an eye by reflecting a wavefront of an eye and measuring the wavefront at a plurality of angles to provide a map of the off-axis relative wavefront curvature and aberration of the eye. The phase accuracy between wavelengths and sample points over a beam aperture offered by these methods and systems have a number of ocular applications including corneal and anterior eye tomography, high resolution retinal imaging, and wavefront analysis as a function of probe beam incident angle for determining myopia progression and for designing and testing lenses for correcting myopia.

A device and a method for wavefront analysis. The device is designed for analyzing the wavefront of at least one light wave passing through an optical system, and has at least one illumination mask (105, 205, 305, 405, 406, 407), at least one first grating (120, 220, 320, 420), at least one second grating (130, 230, 330, 430) arranged in the predefined plane and at least one detector (140, 240, 340, 440) for detecting said superimposition pattern. The at least one first grating has at least one first grating structure and generates an interferogram in a predefined plane from a wavefront to be analyzed which proceeds from the illumination mask and passes through the optical system. The at least one second grating has at least one second grating structure and generates a superimposition pattern by the superimposition of the second grating structure with the interferogram generated by the first grating.

The imaging quality of an optical imaging system is interferometrically measured. A wavefront measurement has a first imaging scale .sub.1 in a first direction and a second imaging scale .sub.2 in a second, perpendicular direction. The second imaging scale differs from the first imaging scale by a scale ratio (.sub.1/.sub.2)1 (anamorphic imaging system). A first measurement structure (MS1) on a first structure carrier arranged on the object side of the imaging system has a two-dimensional mask structure suitable for shaping the coherence of measurement radiation. A second measurement structure (MS2) on a second structure carrier arranged on the image side of the imaging system has a diffraction grating. The first and second measurement structures are mutually adapted, taking account of the scale ratio so that an interference pattern arises upon imaging the first measurement structure onto the second measurement structure using the anamorphic imaging system.

A shearing interferometer includes first and second shearing plates disposed opposite to each other. The first shearing plate includes a first front surface and a first back surface, and splits an input beam input to the first front surface into first and second beams reflected at the first front and back surfaces, respectively. The second shearing plate includes a second front surface and a second back surface. The second shearing plate splits the first beam into third and fourth beams reflected at the second front and back surfaces, respectively, and splits the second beam into fifth and sixth beams reflected at the second front and back surfaces, respectively. Each of the first and second shearing plates has a thickness which limits a phase delay between the fourth beam and the fifth beam to a degree determined to allow interference to occur between the fourth beam and the fifth beam.

A device and a method for wavefront analysis. The device is designed for analysing the wavefront of at least one light wave passing through an optical system, and has at least one illumination mask (105, 205, 305, 405, 406, 407), at least one first grating (120, 220, 320, 420), at least one second grating (130, 230, 330, 430) arranged in the predefined plane and at least one detector (140, 240, 340, 440) for detecting said superimposition pattern. The at least one first grating has at least one first grating structure and generates an interferogram in a predefined plane from a wavefront to be analysed which proceeds from the illumination mask and passes through the optical system. The at least one second grating has at least one second grating structure and generates a superimposition pattern by the superimposition of the second grating structure with the interferogram generated by the first grating.

Method and systems are presented for analysing a wavefront using a spectral wavefront analyser to extract optical phase and spectral information at a two dimensional array of sampling points across the wavefront, wherein the relative phase information between the sampling points is maintained. Methods and systems are also presented for measuring an eye by reflecting a wavefront of an eye and measuring the wavefront at a plurality of angles to provide a map of the off-axis relative wavefront curvature and aberration of the eye. The phase accuracy between wavelengths and sample points over a beam aperture offered by these methods and systems have a number of ocular applications including corneal and anterior eye tomography, high resolution retinal imaging, and wavefront analysis as a function of probe beam incident angle for determining myopia progression and for designing and testing lenses for correcting myopia.

Method and systems are presented for analyzing a wavefront using a spectral wavefront analyzer to extract optical phase and spectral information at a two dimensional array of sampling points across the wavefront, wherein the relative phase information between the sampling points is maintained. Methods and systems are also presented for measuring an eye by reflecting a wavefront of an eye and measuring the wavefront at a plurality of angles to provide a map of the off-axis relative wavefront curvature and aberration of the eye. The phase accuracy between wavelengths and sample points over a beam aperture offered by these methods and systems have a number of ocular applications including corneal and anterior eye tomography, high resolution retinal imaging, and wavefront analysis as a function of probe beam incident angle for determining myopia progression and for designing and testing lenses for correcting myopia.

Interferometry-based methods and apparatus are presented for analyzing one or more wavefronts from a sample, in which the sample wavefronts are interfered with two or more reference wavefronts to produce two or more interferograms in a sufficiently short time period for the interferograms to be captured in a single exposure of an image capture device such as a CCD array. Each interferogram has a unique carrier frequency dependent on the angle between a respective pair of sample and reference wavefronts. In certain embodiments multiple sample and/or reference wavefronts are generated using scanning mirrors, while in other embodiments utilizing multi-wavelength beams multiple sample and/or reference wavefronts are generated with wavelength dispersive elements. The methods and apparatus are suitable for measuring aberrations at one or more positions on the retina of an eye.

Methods, and corresponding systems for, determining one or more aberrations of a projection system (for example a projection system of a lithographic apparatus) are disclosed. One method includes performing a phase stepping or phase scanning process using a first patterning device (at object level) that includes a specular diffraction grating. Also disclosed is a calibration method for determining calibration data which characterizes any differences between: aberrations of a projection system determined using a diffusive grating at object level and aberrations of a projection system determined using a specular grating at object level.