A low-coherence interferometer apparatus for determining information on interfaces of an object including: a polychromatic light source; an optical system generating a measurement optical beam and a reference optical beam; a delay line introducing a variable optical delay between the optical beams; detection optics combining the beams, and producing a spectral signal representative of an optical-power spectral density of the resulting interference signal; a control and processing module acquiring a plurality of spectral signals for a plurality of optical delays, determining, for each spectral signal, optical retardation information between interfering beams within a spectral measurement range, analyse the variation in the retardations, and assign the optical retardation determined on the basis of the different spectral signals to interface curves, corresponding to straight lines with positive, negative, zero or almost-zero gradient, depending on the respective optical delay of the acquisition of the spectral signals, and to deduce information of the object.

Methods, apparatus and systems for processing interferograms in metrology applications are described. In one example aspect, a method includes obtaining an input phase image based on the interferograms, segmenting the input phase image by classifying the input phase image into multiple regions based on the phase value and a location of each pixel, assigning an integer value to each of the multiple regions, and constructing an output phase image based on the input phase image and the phase offset of each of the multiple regions.

The disclosure provides a device for detecting a wavefront error by modal-based optimization phase retrieval using an extended Nijboer-Zernike (ENZ) theory. The detection device includes a point light source (1), a half mirror (2), a lens (3) to be tested, a plane mirror (4) and an image sensor (5). The wavefront error of the component under test is characterized by using a Zernike polynomial, and a Zernike polynomial coefficient is solved based on an ENZ diffraction theory. The present disclosure realizes the one-time full-aperture measurement on the wavefront error of a large-aperture optical component, and can use a partially overexposed image to achieve accurate wavefront error retrieval. Meanwhile, the present disclosure overcomes the contradiction between underexposure and high signal-to-noise ratio (SNR) caused by a limited dynamic range when the image sensor (5) acquires an image. The detection device is simple and does not have high requirements for the experimental environment.

In some embodiments, systems, methods, and media for multiple reference arm spectral domain optical coherence tomography are provided which, in some embodiments, includes: a sample arm coupled to a light source; a first reference arm having a first path length; a second reference arm having a longer second path length; a first optical coupler that combines light from the sample arm and the first reference arm; a second coupler that combines light from the sample arm and the second reference arm; and an optical switch comprising: a first input port coupled to the first optical coupler; a second input coupled to the second coupler via an optical waveguide that induces a delay at least equal to an acquisition time of an image sensor; and an output coupled to the image sensor.

In some embodiments, systems, methods, and media for multiple reference arm spectral domain optical coherence tomography are provided which, in some embodiments, includes: a sample arm coupled to a light source; a first reference arm having a first path length; a second reference arm having a longer second path length; a first optical coupler that combines light from the sample arm and the first reference arm; a second coupler that combines light from the sample arm and the second reference arm; and an optical switch comprising: a first input port coupled to the first optical coupler; a second input coupled to the second coupler via an optical waveguide that induces a delay at least equal to an acquisition time of an image sensor; and an output coupled to the image sensor.

In some embodiments, systems, methods, and media for multiple reference arm spectral domain optical coherence tomography are provided which, in some embodiments, includes: a sample arm coupled to a light source; a first reference arm having a first path length; a second reference arm having a longer second path length; a first optical coupler that combines light from the sample arm and the first reference arm; a second coupler that combines light from the sample arm and the second reference arm; and an optical switch comprising: a first input port coupled to the first optical coupler; a second input coupled to the second coupler via an optical waveguide that induces a delay at least equal to an acquisition time of an image sensor; and an output coupled to the image sensor.

An inspection system is disclosed. In one embodiment, the inspection system includes an interferometer sub-system configured to acquire an interferogram of a sample. The inspection system may further include a controller communicatively coupled to the interferometer sub-system. The controller is configured to: receive the interferogram from the interferometer sub-system; generate a phase map of the sample based on the received interferogram, wherein the phase map includes a plurality of pixels; select a sub-set of pixels of the plurality of pixels of the phase map to be used for phase unwrapping procedures; perform one or more phase unwrapping procedures on the sub-set of pixels of the phase map to generate an unwrapped phase map; and generate a surface height map of the sample based on the unwrapped phase map.

An inspection system is disclosed. In one embodiment, the inspection system includes an interferometer sub-system configured to acquire an interferogram of a sample. The inspection system may further include a controller communicatively coupled to the interferometer sub-system. The controller is configured to: receive the interferogram from the interferometer sub-system; generate a phase map of the sample based on the received interferogram, wherein the phase map includes a plurality of pixels; select a sub-set of pixels of the plurality of pixels of the phase map to be used for phase unwrapping procedures; perform one or more phase unwrapping procedures on the sub-set of pixels of the phase map to generate an unwrapped phase map; and generate a surface height map of the sample based on the unwrapped phase map.

A low-coherence interferometer apparatus for determining information on interfaces of an object including: a polychromatic light source; an optical system generating a measurement optical beam and a reference optical beam; a delay line introducing a variable optical delay between the optical beams; detection optics combining the beams, and producing a spectral signal representative of an optical-power spectral density of the resulting interference signal; a control and processing module acquiring a plurality of spectral signals for a plurality of optical delays, determining, for each spectral signal, optical retardation information between interfering beams within a spectral measurement range, analyse the variation in the retardations, and assign the optical retardation determined on the basis of the different spectral signals to interface curves, corresponding to straight lines with positive, negative, zero or almost-zero gradient, depending on the respective optical delay of the acquisition of the spectral signals, and to deduce information of the object.

An inspection system is disclosed. In one embodiment, the inspection system includes an interferometer sub-system configured to acquire an interferogram of a sample. The inspection system may further include a controller communicatively coupled to the interferometer sub-system. The controller is configured to: receive the interferogram from the interferometer sub-system; generate a phase map of the sample based on the received interferogram, wherein the phase map includes a plurality of pixels; select a sub-set of pixels of the plurality of pixels of the phase map to be used for phase unwrapping procedures; perform one or more phase unwrapping procedures on the sub-set of pixels of the phase map to generate an unwrapped phase map; and generate a surface height map of the sample based on the unwrapped phase map.