Abstract: An apparatus (10) for spoiling banknotes (103) arranged in a block formation within a cassette (100). The apparatus (10) comprises a cassette (100) for carrying a block of banknotes (103), a main housing (20) in which is located at least one cartridge (31) containing a spoiling fluid, and first and second spray bars (61, 62) extending from the housing (20). The spray bars (61, 62) are in fluid communication with the at least one cartridge (31), and the main housing (20) further comprises a valve (40) configured to release the spoiling fluid from the at least one cartridge (31) and into the spray bars (61, 62). In use, the first spray bar (61) extends across the length and proximate a first end of the block of banknotes (103) within the cassette (100) and the second spray bar (62) extends across the length and proximate a second end of the block of banknotes (103) within the cassette (100).

Abstract: In general, in a first aspect, the invention features a method that includes using an interferometry assembly to provide three different output beams, each output beam including an interferometric phase related to an optical path difference between a corresponding first beam and a corresponding second beam, each first beam contacting a measurement object at least once, monitoring the interferometric phases for each of the three different output beams, and deriving information about variations in the optical properties of a gas in the first beam paths from the three monitored phases.

Abstract: A test object including: an arrangement of optical elements defining a first partially reflecting surface and a second partially reflecting surface, at least one of the first and second partially reflecting surfaces being curved, wherein the first partially reflecting surface is arranged to receive a substantially collimated input beam and produce therefrom a first transmitted beam that passes on to the second partially reflecting surface, wherein the second partially reflecting surface is arranged to receive the first transmitted beam from the first partially reflecting surface and produce a collimated second transmitted beam and a first reflected beam therefrom, wherein the first partially reflecting surface is arranged to receive the first reflected beam and produce a second reflected beam therefrom, and wherein the first and second reflecting surfaces are configured to cause the second reflecting beam to converge onto a spot on a back surface to produce a diverging beam traveling in the same direction as

Abstract: We disclose acousto-optic modulators that include: (a) an optical element configured to receive an input optical beam that propagates along a first direction; and (b) a transducer extending along the first direction and positioned on one or more surfaces of the optical element, the transducer having a transducer material positioned between two electrodes configured to apply a potential difference across the transducer to cause the transducer to generate an acoustic waveform propagating in a second direction in the optical element, and the input optical beam undergoing diffraction in a region of the optical element that includes the acoustic waveform.

Abstract: An interferometric method including: generating a variable frequency source beam; from the source beam, generating a collimated beam propagating at an angle ? relative to an optical axis; introducing the collimated beam into an interferometer that includes a reference object and a measurement object, wherein at least a portion of the collimated beam interacts with the reference object to generate a reference beam, at least a portion of the collimated beam interacts with the measurement object to generate a return measurement beam, and the reference beam and the return measurement beam are combined to generate a combined beam; causing the angle ? to have a first value and at a later time a second value that is different from the first value; and causing the variable frequency F to have a first value that corresponds to the first value of the angle ? and at the later time to have a second value that corresponds to the first value of the angle ?.

Abstract: Methods and systems for determining information about the incident angle of a beam are disclosed, the method including directing a beam having an s-polarized component and a p-polarized component to reflect from an interface at a non-normal angle, where the non-normal reflection introduces for each component a phase change upon reflection that is different for each component, and measuring an optical interference signal related to the phase change between the components of the reflected beam.

Abstract: A wavefront interferometry system including: a wavefront interferometer that during operation combines a reference beam from a reference object and a measurement beam from a measurement object to generate a combined beam; and a processor system programmed to processes the combined beam to concurrently generate therefrom a control signal and information about the difference in wavefront profiles of the reference and measurement objects, wherein the control signal controls a system parameter so as to maintain an optical path length difference between a spot on the reference object and a corresponding spot on the measurement object at a constant value mod 2?.

Abstract: A method of operating a wavefront interferometry system that generates an array of interference signals that contains information about relative wavefronts of measurement and reference beams, the method involving: from the array of interference signals, computing a first array of phase measurements for a first time and a second array of phase measurements for a second time; computing a difference of the first and second arrays of phase measurements to determine an array of rates of phase changes; and from the array of rates of phase changes, computing an array of atmospheric turbulence effect values which is a measure of atmospheric turbulence effects in the wavefront interferometry system.

Abstract: In certain aspects, the invention features interferometry systems that include an input assembly positioned to receive a beam emitted from a light source comprising a first component beam and a second component beam, the input assembly being configured to change a dimension of one of the component beams relative to the dimension of the other component beam, an interferometer positioned to receive the component beams propagating from the input assembly, the interferometer being configured to direct the component beams along different paths and to produce an output beam by directing the component beams along a common path, wherein the output beam comprises information about an optical path difference between the different component beam paths, and an output assembly positioned in the path of the output beam and configured to change a dimension of the component beam that contacts the measurement object.

Abstract: An external cavity structure including: a light source for generating a light beam; a dispersive system which in combination with the light source defines a cavity, the dispersive system for directing a selected wavelength of the light beam back into the light source, the dispersive system including a grating for selecting said wavelength of the light beam; and a beam-conditioner positioned within the cavity along a light path between the light source and the dispersive system, the beam conditioner including a beam deflecting element for changing the direction of propagation of the light beam as that light beam that travels between the light source and the dispersive system.

Abstract: An interference signal S(t) is provided from interference between two beams directed along different paths. The signal S(t) is indicative of changes in an optical path difference n{tilde over (L)}(t) between the different paths, where n is an average refractive index along the different paths, {tilde over (L)}(t) is a total physical path difference between the different paths, and t is time. An error signal is provided to reduce errors in an estimate of {tilde over (L)}(t). The error signal is derived at least in part based on one or more collective properties of a distribution of multi-dimensional values. At least one of the multi-dimensional values in the distribution is generated from a plurality of samples of the signal S(t) (e.g., samples of the signal captured at different times).

Abstract: In general, in one aspect, the invention features interferometry systems that include an interferometer configured to direct a first beam and a second beam derived from common light source along different paths and to combine the two beams to form an output beam including information related to an optical path difference between the different paths, wherein the path of the first beam contacts a measurement object. The interferometry systems also include an afocal system positioned in the path of the first beam and configured to increase a dimension of the first beam as it propagates from the interferometer towards the measurement object and reduces the dimension of the first beam as it returns from the measurement object propagating towards the interferometer.

Abstract: Apparatus and methods for in situ and ex situ measurements of spatial profiles of the modulus of the complex amplitude and intensity of flare generated by an optical system. The in situ and ex situ measurements comprise interferometric and non-interferometric measurements that use an array of diffraction sites simultaneously located in an object plane of the optical system to increase signals related to measured properties of flare in a conjugate image plane. The diffraction sites generate diffracted beams with randomized relative phases. In general, the interferometric profile measurements employ phase-shifting point-diffraction interferometry to generate a topographical interference signal and the non-interferometric measurements are based on flare related signals other than topographic interference signals.

Abstract: In general, in a first aspect, the invention features a method that includes using an interferometry assembly to provide three different output beams, each output beam including an interferometric phase related to an optical path difference between a corresponding first beam and a corresponding second beam, each first beam contacting a measurement object at least once, monitoring the interferometric phases for each of the three different output beams, and deriving information about variations in the optical properties of a gas in the first beam paths from the three monitored phases.

Abstract: A point diffraction interferometer for measuring properties of a spatial impulse response function, the interferometer including: a source for generating a source beam; an optical system; an optical element including a test object located in an object plane of the optical system, the test object including a diffraction point for generating from the source beam a measurement beam that passes through the optical system, wherein the optical element also generates from the source beam a reference beam that is combined with the measurement beam to generate an interference pattern in an image plane of the optical system, the interference pattern representing the spatial impulse response function of the optical system.

Abstract: In general, in one aspect, the invention features methods that include locating a plurality of alignment marks on a moveable stage, interferometrically measuring a position of a measurement object along an interferometer axis for each of the alignment mark locations, and using the interferometric position measurements to derive information about a surface figure of the measurement object. The position of the measurement object is measured using an interferometry assembly and either the measurement object or the interferometry assembly are attached to the stage.

Abstract: In general, in one aspect, the invention features methods that include interferometrically monitoring a distance between an interferometry assembly and a measurement object along each of three different measurement axes while moving the measurement object relative to the interferometry assembly. The methods also include monitoring an orientation angle of the measurement object with respect to a rotation axis non-parallel to the three different measurement axes while the measurement object is moving, determining values of a parameter for different positions of the measurement object from the monitored distances, wherein for a given position the parameter is based on the distances of the measurement object along each of the three different measurement axes at the given position, and deriving information about a surface figure profile of the measurement object from a frequency transform of at least the parameter values.

Abstract: An interferometric system including: an interferometer that directs a measurement beam at an object point to produce a return measurement beam, focuses the return measurement beam to an image point in an image plane, and mixes the return measurement beam with a reference beam at the image point to form a mixed beam; a beam combining layer located at the image plane which is responsive to the mixed beam and produces an optical beam therefrom, wherein the layer comprises a thin film with an array of transmissive openings formed therein and further comprises a fluorescent material associated with each of the openings of the array of openings; a detector that is responsive to the optical beam from the beam combining layer; and an imaging system that directs the optical beam from the beam combining layer onto the detector.

Abstract: An interferometric system including: an interferometer that directs a measurement beam at an object point to produce a return measurement beam, focuses the return measurement beam to an image point in an image plane, and mixes the return measurement beam with a reference beam at the image point to form a mixed beam; a beam combining layer located at the image plane which is responsive to the mixed beam and produces an optical beam therefrom, wherein the layer comprises a thin film with an array of transmissive openings formed therein and further comprises a fluorescent material associated with each of the openings of the array of openings; a detector that is responsive to the optical beam from the beam combining layer; and an imaging system that directs the optical beam from the beam combining layer onto the detector.

Abstract: In general, in one aspect, the invention features methods that include using an interferometer to produce an output beam having a phase related to an optical path difference between a path of a first beam and a path of a second beam, wherein the first beam contacts a measurement object and either the measurement object or the interferometer are coupled (e.g., directly attached) to a stage that is moveable within a reference frame. The methods further include monitoring variations in the phase while both varying an orientation of the stage with respect to at least one degree of freedom in the reference frame and keeping a reference mark on the stage in a common position with respect to the reference frame, and determining information based on the monitored variations, the information being related to a contribution to the optical path difference caused by a deviation of the path of the first or second beam from a nominal beam path.