WO2016087393A1

WO2016087393A1 - Multi-wavelength generalized phase contrast system and method

Info

Publication number: WO2016087393A1
Application number: PCT/EP2015/078106
Authority: WO
Inventors: Jesper GLÜCKSTAD
Original assignee: Danmarks Tekniske Universitet
Priority date: 2014-12-01
Filing date: 2015-11-30
Publication date: 2016-06-09

Abstract

A new generalized phase contrast (GPC) system is provided that is designed for non-monochromatic electromagnetic waves, comprising • a source (12) of electromagnetic waves for emission of electromagnetic waves with a plurality of wavelengths A, • a phase modifying element (18) with an input surface (x, y) positioned so that the electromagnetic waves are incident upon it and configured for phase modulation of the electromagnetic waves impinging on the surface (x, y) by phasor values eⁱ ^{ϕ(λ, x, y)} • first Fourier or Fresnel optics (29) positioned so that the phase modulated electromagnetic waves are incident upon it and configured for Fourier or Fresnel transforming the phase modulated electromagnetic waves, • a spatial phase filter (22) with a surface S positioned at the Fourier or Fresnel plane of the first Fourier or Fresnel optics, respectively, and having phase shifting regions (x^s, y^S) configured for phase shifting Fourier or Fresnel transformed electromagnetic waves with different wavelengths A incident on the respective phase shifting regions (x^s, y^S) by predetermined respective phase shift values 6(h, x^s, y^S) with relation to the remaining part of the respective Fourier or Fresnel transformed electromagnetic waves incident on parts of the surface S without a phase shifting region, and second Fourier or Fresnel optics (26) configured for forming the intensity pattern I (A, x', y') by Fourier or Fresnel transforming the Fourier or Fresnel transformed electromagnetic waves.

Description

MULTI-WAVELENGTH GENERALIZED PHASE CONTRAST SYSTEM AND METHOD

[0001] The present invention relates to a new Generalized Phase Contrast method and a system.

[0002] Generalized Phase Contrast (GPC) methods and systems are well-known in the art. In the known GPC systems an image is formed by phase modulation of light which is subsequently converted into intensity modulation. As opposed to intensity modulation, phase modulation does not involve loss of energy.

[0003] The basic principles of the generalized phase contrast (GPC) method and system were originally disclosed in WO 96/34307 A1 . A comprehensive introduction to the GPC method is provided in the textbook by Jesper Gliickstad and Darwin Palima: "Generalized Phase Contrast: Applications in Optics and Photonics", Springer, 2009, ISBN 978-90-481 -2839-6.

[0004] The GPC method is not based on the so-called Zernike approximation that the phase shift φ is less than 1 radian. The GPC method has been provided without this assumption.

[0005] In WO 96/34307 A1 , a GPC method and system are disclosed that include an imaging operation with a simple one-to-one mapping between resolution elements or pixels of a spatial phase modulator and resolution elements of the generated intensity pattern.

[0006] The disclosed GPC method of synthesizing a prescribed intensity pattern l(x',y'), comprises the steps of:

dividing the intensity pattern l(x',y') into pixels in accordance with the disposition of resolution elements (x,y) of a spatial phase mask having a plurality of individual resolution elements (x,y), each resolution element (x,y) modulating the phase of electromagnetic waves incident upon it with a predetermined phasor value e'*** ^, radiating electromagnetic waves towards the spatial phase mask,

Fourier or Fresnel transforming the modulated electromagnetic waves, · phase shifting with a spatial phase filter (SPF) in a region of spatial frequencies comprising DC in the Fourier or Fresnel plane, the modulated electromagnetic waves by a predetermined phase shift value Θ in relation to the remaining part of the electromagnetic waves, and forming the intensity pattern by Fourier or Fresnel transforming, respectively, the phase shifted Fourier or Fresnel transformed modulated electromagnetic waves, whereby each resolution element (x,y) of the phase mask is imaged on a corresponding resolution element (x' ,y') of the image,

calculating the phasor values e'*** ^ of the phase mask and the phase shift value Θ in accordance with

I(x' , y' ) = β^ίφ(χ'^γ) + a(e^w - I) ²

for selected phase shift values Θ, being the average of the phasors eⁱ⁽p^(x.y⁾ of the resolution elements of the phase mask,

selecting, for each resolution element, one of two phasor values which represent a particular grey level, and supplying the selected phasor values e'*** ^ to the resolution elements (x,y) of the spatial phase mask.

[0007] In one embodiment disclosed in WO 96/34207, the spatial phase mask is positioned at the front focal plane of a lens while the spatial phase filter is positioned in the back focal plane of the lens, whereby a first electromagnetic wave at the spatial phase mask is Fourier transformed by the lens into a second electromagnetic wave at the spatial phase filter. Thus, specific spatial frequencies of the first electromagnetic wave will be transmitted through the spatial phase filter at specific positions of the spatial phase filter. For instance, the energy of the electromagnetic waves at zero frequency (DC) is modified by the input phase modulator and transformed onto the intersecting point of the Fourier plane and the optical axis of the lens also denoted the zero-order diffraction region.

[0008] Typically, the spatial phase filter is adapted to phase shift the DC-part of the electromagnetic waves and to leave the remaining part of the electromagnetic waves unchanged. Alternatively, the DC-part of the electromagnetic waves remains unchanged and the remaining part of the electromagnetic waves is phase shifted. This alternative is preferred when the energy level of the DC-part of the

electromagnetic waves is so high that the phase shifting part of the spatial phase filter will be destroyed by it. For example in laser cutting, the DC level of the laser beam can be so high that a phase shifting dot positioned at the intersecting point of the DC part of the laser beam at the spatial phase filter would deteriorate. It is also possible to block the electromagnetic waves (no transmittance) in the zero-order diffraction region, however, the DC energy of the radiation is then lost.

[0009] Further developments of the GPC method are disclosed in WO 00/02339 A1 , WO 02/23794 A2, WO 02/052332 A2, WO 03/0341 18 A1 , WO 2004/1 13993 A1 , WO 2005/0961 15 A1 , WO 2006/097101 A1 , WO 2007/147407 A1 , WO 2009/036761 A1 , WO 2012/146257 A1 , and WO 2013/102464 A1 .

[0010] In the disclosed applications of the GPC method, the electromagnetic waves are monochromatic or quasi-monochromatic, i.e. the energy of the electromagnetic waves is concentrated in a narrow frequency bandwidth, and lasers are typically selected as the light source in GPC systems.

[0011] Since the phase modulation of the input wave front and the phase shift value Θ of the phase shifting region of the spatial phase filter depend on the wavelength λ of the electromagnetic waves, the robustness of a known GPC system was investigated in Darwin Palima and Jesper Gliickstad: "Multi-wavelength spatial light shaping using generalized phase contrast", Optics Express, Vol. 16, No. 2, p. 1331 - 1342, 21 January 2008. It was shown that the wavelength dependency of the phase shifting in the Fourier plane counteracted to some extent the wavelength dependency of the phase modulation of the input wave front so that the known GPC systems maintained image quality over a wavelength range from approximately 0.75λο to 1 .5λο, where λο is the characteristic design wavelength for which the phasor value e'*** ^ and the phase shift Θ were determined.

[0012] It is an object of the present invention to provide new GPC methods and systems with improved performance with a non-monochromatic source of

electromagnetic radiation.

[0013] Thus, a new GPC method and a new GPC system are provided for synthesizing an intensity pattern and operating on more complex electromagnetic waves than the known GPC methods and systems with improved performance, e. g., to be able to utilize sources of electromagnetic radiation that is not monochromatic, e.g. sources with a larger bandwidth than, e.g., single mode continuous wave lasers.

[0014] According to the new GPC method and in the new GPC system more than one wavelength λ is included in the determination of phase shift values

θ(λ) of the spatial phase filter. [0015] Thus, a new GPC system is provided, comprising

a) a source of electromagnetic waves for emission of electromagnetic

waves with a plurality of wavelengths λ,

b) a phase modifying element with an input surface (x, y) positioned so that the electromagnetic waves are incident upon it and configured for phase modulation of the electromagnetic waves impinging on the surface (x, y) by phasor values e'^*^,

c) first Fourier or Fresnel optics positioned so that the phase modulated electromagnetic waves are incident upon it and configured for Fourier or Fresnel transforming the phase modulated electromagnetic waves, d) a spatial phase filter with a surface S positioned at the Fourier or Fresnel plane of the first Fourier or Fresnel optics, respectively, and having phase shifting regions (x^s, y^s) configured for phase shifting Fourier or Fresnel transformed electromagnetic waves with different wavelengths λ incident on the respective phase shifting regions (x^s, y^s) by predetermined respective phase shift values θ(λ, x^s, y^s) with relation to the remaining part of the respective Fourier or Fresnel transformed electromagnetic waves incident on parts of the surface S without a phase shifting region, and

e) second Fourier or Fresnel optics configured for forming the intensity pattern I (λ, χ', y') by Fourier or Fresnel transforming the Fourier or Fresnel transformed electromagnetic waves.

[0016] The source of electromagnetic waves may emit electromagnetic waves with a spectrum that is broader than and includes a spectrum of a monochromatic source such as a single mode continuous wave laser, and the source may be arranged so that at least some parts of the electromagnetic waves with different wavelengths propagate along different propagation paths through the GPC system and illuminate different regions of a surface S of the spatial phase filter.

[0017] Apart from the fact that the source of electromagnetic waves may be arranged so that the emitted electromagnetic waves with different wavelengths λ propagate along respective different propagation paths through the GPC system and illuminate respective different phase shifting regions (x^s, y^s) of the surface S of the spatial phase filter, the main components a) - e) of the new GPC system may be positioned in the same way with relation to each other as in a conventional 4f phase contrast imaging system, or, as in a conventional 2f phase contrast imaging system; or, as in a conventional 1f phase contrast imaging system.

[0018] A new GPC method is also provided, comprising the steps of

(i) emitting electromagnetic waves with a plurality of wavelengths λ,

(ii) phase modulating the electromagnetic waves by phasor values e'^*^,

(iii) Fourier or Fresnel transforming the phase modulated electromagnetic waves,

(iv) phase shifting parts of the Fourier or Fresnel transformed

electromagnetic waves with different wavelengths λ by predetermined respective phase shift values θ(λ, x^s, y^s) with relation to the remaining part of the respective Fourier or Fresnel transformed electromagnetic waves incident on parts of the surface S without a phase shifting region, and

(v) forming an intensity pattern I (λ, χ', y') by Fourier or Fresnel transforming the respective phase shifted Fourier or Fresnel transformed electromagnetic waves.

[0019] The electromagnetic waves or radiation may be of any frequency range of the electromagnetic spectrum, i. e. the gamma frequency range, the ultraviolet range, the visible range, the infrared range, the far infrared range, the X-ray range, the microwave range, the HF (high frequency) range, etc. The present invention is also applicable to particle radiation, such as electron radiation, neutron radiation, etc.

[0020] The source of electromagnetic waves may comprise a plurality of sources of electromagnetic waves, each of which is monochromatic or quasi-monochromatic, emitting in combination electromagnetic waves within a wavelength range that is larger than the wavelength range of one of the individual sources of electromagnetic waves.

[0021] An individual source of the plurality of sources of electromagnetic waves may be a laser, a semi-conductor laser, a strained multi-quantum well laser, a vertical cavity surface emitting laser (VCSEL), a maser, a phase-locked laser diode array, a light emitting diode, a pulsed laser, such as a sub-picosecond laser, etc. An array of such sources may form the source of electromagnetic waves of the new GPC system.

[0022] The source of electromagnetic waves may be arranged so that at least some electromagnetic waves with different wavelengths propagate along different propagation paths through the GPC system and illuminate different regions of the surface S of the spatial phase filter, by provision of an assembly of individually positioned sources, each of which emits electromagnetic waves of wavelengths, wherein at least two of the wavelengths emitted by different sources, are different.

[0023] For example, the assembly may comprise a plurality of semiconductor lasers, at least two of which emit electromagnetic waves of different wavelengths. For example, the assembly may comprise three semiconductor lasers, one of which emits red light, another of which emits green light, and yet another of which emits blue light.

[0024] Electromagnetic waves with different wavelengths emitted by differently positioned sources propagate along different propagation paths through the GPC system and illuminate different regions of the surface S of the spatial phase filter.

[0025] The source of electromagnetic waves may be arranged so that at least some electromagnetic waves with different wavelengths propagate along different propagation paths through the GPC system and illuminate different regions of the surface S of the spatial phase filter, by provision of a first dispersing element positioned so that the electromagnetic waves are incident upon it and configured for dispersing the electromagnetic waves into wavelength dependent propagation paths, so that electromagnetic waves with different wavelengths propagate along different propagation paths upon interaction with the first dispersing element.

[0026] The first dispersing element disperses the electromagnetic waves incident upon it, i.e. it changes the direction of the propagation path of the electromagnetic waves as a function of the wavelength of the electromagnetic waves.

[0027] The GPC system may comprise a second dispersing element configured for compensating the dispersion performed by the first dispersing element so that intensity patterns I (λ, χ', y') of different wavelengths λ coincides; or, substantially coincides.

[0028] Each of the first and second dispersing elements may comprise a prism and disperse the electromagnetic waves by refraction, and/or each of the first and second dispersing elements may comprise a diffractive optical element, a hologram, a computer generated hologram, etc., wherein a diffraction grating disperses the electromagnetic waves by diffraction. The diffraction grating may be an amplitude grating, or a phase grating, or a combination of an amplitude grating and a phase grating. [0029] The source of electromagnetic waves may comprise a high-pressure arc lamp, such as an Hg lamp, a Xenon lamp, an incandescent lamp, etc.

[0030] The source of electromagnetic waves may comprise a supercontinuum laser, which is a source of electromagnetic waves utilizing supercontinuum generation. Supercontinuum generation is a process where laser light is converted to light with a very broad spectral bandwidth i.e. with low temporal coherence, whereas the spatial coherence usually remains high. The spectral broadening is usually accomplished by propagating wave pulses through a strongly nonlinear device, such as propagating intense (amplified) ultra-short pulses through a piece of bulk glass; or, propagating pulses with much lower pulse energy through an optical fibre having a much higher nonlinearity and also a waveguide structure which ensures a high beam quality. The nonlinear device may be a photonic crystal fibre that has chromatic dispersion characteristics providing strong nonlinear interaction over a significant length of fibre. Very broad spectra have been achieved with moderate pulse energy. In some cases, tapered fibres can also be used.

[0031] The source of electromagnetic waves may comprise an ultrafast pulsed laser.

[0032] The phasor values β'^φ<^{λ χ} ^ of the phase modifying element and the phase shift values θ(λ) may be calculated in accordance with the equations disclosed in the above-mentioned previous publications on the GPC method; however generalized to include the dependency on the wavelength λ. For example, the phasor values β'^φ<^{λ χ} ^ of the phase modifying element and the phase shift values θ(λ) may substantially fulfil that

wherein

Α(λ) is an optional amplitude modulation of the spatial phase filter outside the phase shifting regions,

Β(λ, X^s, y^s) is an optional amplitude modulation of the spatial phase filter in the respective phase shifting regions (x^s, y^s), α(λ) = |a|exp(i ^) is the average of the phasors β'^φ<^{λ χ} ^ across the surface of the phase modifying element,

Φ = Φ— φ- , and

Isource (A,x,y) is the intensity of the electromagnetic waves incident on the phase modifying element, and g(A,x,y) is the spatially varying synthetic reference wave SRW

12%

fK

i.2%

^~ JJ S (ξ_λ. i x i) A (f_sJL , f_yJi ; K ) exp [^χ ξχ +y ⁱi )

fK

See equation (23) in Darwin Palima and Jesper Gliickstad: "Multi-wavelength spatial light shaping using generalized phase contrast", Optics Express, Vol. 16, No. 2, p. 1331 - 1342, 21 January 2008.

[0033] The spatial phase filter may not attenuate the electromagnetic waves incident upon it outside the phase shifting regions, i.e. Α(λ) is equal to one or approximately equal to one.

[0034] Further, the spatial phase filter may not attenuate the electromagnetic waves incident upon it inside the phase shifting regions, i. e. Β(λ) is equal to one or approximately equal to one.

[0035] The phase modifying element modulates, i.e. changes, the phase of electromagnetic waves incident upon it. Optionally, it also changes the amplitude of the electromagnetic waves incident upon it.

[0036] Preferably, the electromagnetic waves incident upon the phase modifying element are substantially collimated; or, collimated.

[0037] The first dispersing element and the phase modifying element may be integrated into one component performing both the phase modulation of the electromagnetic waves and the dispersing of the electromagnetic waves. [0038] Each of the first and second dispersing elements may transmit or reflect the incident electromagnetic waves.

[0039] The phase modifying element may transmit or reflect the incident electromagnetic waves.

[0040] The phase modifying element may comprise a component having a plurality of individual resolution elements (x, y), wherein each resolution element (x, y) is configured to modulate the phase of electromagnetic waves incident upon it with a predetermined phasor value e'^*^.

[0041] The predetermined phasor values e'^ y⁾ are assigned to each resolution element in different ways depending upon the technology applied in the component. For example, the component may be a spatial light modulator (SLM).

[0042] In SLMs, each resolution element may be addressed either optically or electrically. The electrical addressing technique may resemble the addressing technique of solid-state memories in that each resolution element can be addressed through electronic circuitry to receive a control signal corresponding to the phase change to be generated by the addressed resolution element. The optical addressing technique may address each resolution element by pointing a light beam on it, the intensity of the light beam corresponding to the phase change to be generated by the resolution element illuminated by the light beam.

[0043] The phase modulation may also be realized utilizing fixed phase mask, a liquid crystal device based on liquid crystal display technology, a MEMS (micro electro-mechanical system), a MOEMS (micro opto-electro-mechanical system), such as a dynamic mirror device, a digital micro-mirror array, a deformable mirror device, etc., a membrane spatial light modulator, a laser diode array (integrated light source and phase modulator), smart pixel arrays, etc.

[0044] Seiko-Epson produces a transmitting liquid crystal SLM (LC-SLM) having a high resolution matrix of transparent liquid crystal elements wherein the relative permittivity of each element can be electrically modulated in order to vary the refractive index and thereby the optical path length of the element.

[0045] Meadowlark produces a parallel-aligned liquid crystal (PAL-SLM) with a high fill factor, but this device has a very low resolution in that it contains only 137 phase- modulating elements.

[0046] Hamamatsu Photonics produces a dynamically controllable PAL-SLM with VGA or XGA resolution.

[0047] Texas Instruments produces a Digital Mirror Device (DMD) having an array of mirrors each of which can be tilted between two positions.

[0048] The phasor values may also be contained in an object that is not controlled by the system, e. g. a specimen in a slide; instead they are detected in the system.

[0049] The phase modifying element may comprise a phase modulating component configured for phase modulation of the electromagnetic waves impinging on its surface (x, y) by phasor values e'***^ that are independent of the wavelength λ.

[0050] Phase modulation independent of wavelength λ, at least in a first order approximation, may be obtained by displacement of a grating of an otherwise regular diffraction grating with continuous grating lines, see WO 2012/146257 A1. For example, a conventional regular diffraction grating may be divided into pixels, i.e. a regular array of small rectangles, within which the grating lines may be displaced with relation to the grating lines of neighbouring pixels, whereby broken grating lines are created. Due to the displacement of the grating lines, a dispersed electromagnetic wave will be phase shifted correspondingly. Thus, if a regular diffraction grating with unbroken grating lines with the grating line spacing L between all grating lines is taken as a starting point and used as a reference grating, then displacement of the grating lines in one pixel (i, j) by a displacement distance d will result in a

corresponding phase modulation of electromagnetic waves incident on that pixel (i, j) by

<Pij = ^2π - with relation to the reference grating.

[0051] Gratings can be made in which various properties of incident electromagnetic waves are modulated by grating patterns, e.g. transparency by transmission amplitude gratings, reflectance by reflection amplitude gratings, refractive index or optical path length by phase gratings, direction of optical axis (optical axis gratings), etc.

[0052] The first dispersing element and the phase modifying element may be integrated in a SLM that is configured for provision of a diffraction grating as disclosed above and providing the desired dispersion and the phase modulation.

[0053] The spatial phase filter may be a fixed phase mask, such as an optically flat glass plate coated with a dielectric layer in the regions where it is desired to phase shift incident electromagnetic waves with relation to electromagnetic waves incident on the spatial phase filter outside the regions. However, the various types of phase modulators mentioned above may also be used for the spatial phase filter. In addition, non-linear materials providing for self-phase modulation such as Kerr-type materials can also be used for introducing the desired phase shifts θ(λ).

[0054] For example, when a Fourier lens is positioned in the propagation paths of the phase modulated electromagnetic waves for Fourier transforming the phase modulated electromagnetic waves, the spatial phase filter is positioned with its surface S in the Fourier plane of the lens, and parts of the electromagnetic waves are focussed onto the surface S of the spatial phase filter at the Fourier plane.

[0055] A part of the surface S onto which electromagnetic waves are focussed by the Fourier lens is denoted a focus region throughout the present disclosure.

[0056] For example, collimated electromagnetic waves propagating along the optical axis of the Fourier lens is focussed onto a focus region centred on the intersection of the optical axis and the Fourier plane also denoted the zero-order diffraction region in the art. Collimated electromagnetic waves incident on the Fourier lens at another angle of incidence is focussed onto a focus region that is displaced with relation to the zero-order diffraction region.

[0057] In the new GPC system, electromagnetic waves incident on the Fourier lens at different angles of incidence may have different wavelengths so that

electromagnetic waves of different wavelengths are focussed onto different focus regions with different centres. The focus regions may overlap. One phase shifting region (x₀ ^s, y₀ ^s) of the spatial phase filter preferably comprises the focus region of electromagnetic waves of a specific wavelength λο, and the phase shifting value Θ for the phase shifting region (x_o ^s, yo^s) is preferably determined for the specific

wavelength λο.

[0058] In this way, the desired phase shifts θ(λ) for different wavelengths λι and λ2 may be designed and determined independently for the different wavelengths λι and λ₂, whereas the individual phase shift value θ(λ) of a specific phase shifting region of the spatial phase filter may depend on the wavelength λ of the electromagnetic waves. For example, when a phase shifting region introduces a difference Ad in optical path length, e.g. due to a difference in thickness and/or a difference in refractive index, in the propagation path of the electromagnetic waves with a certain wavelength λ, the resulting phase shift is given by θ(λ) = ^-^. [0059] For example, for each wavelength λ of the electromagnetic waves, the electromagnetic waves may be focussed onto focus regions at the surface S of the spatial phase filter, with different centres for different wavelengths λ, and for all wavelengths λ of the electromagnetic waves, a respective phase shifting region (x^s, y^s) of the spatial phase filter may comprise the corresponding focus region.

[0060] A plurality of phase shifting regions (x^s, y^s) of the spatial phase filter may form a continuous phase shifting region of the surface S of the spatial phase filter. A continuous phase shifting region may have any arbitrary shape as defined by the source and dispersing element(s).

[0061] A plurality of phase shifting regions (x^s, y^s) of the spatial phase filter may form separate phase shifting regions delimited by parts of the surface S of the spatial phase filter without phase shifting regions. The separate phase shifting regions may be distributed along a line or may be distributed in two dimensions across the surface S.

[0062] The positioning and/or shaping of the phase shifting region or regions of the spatial phase filter are preferably matched to the corresponding focus regions of the electromagnetic waves so that a phase shifting region (x^s, y^s) preferably coincides, or substantially coincides, with the corresponding focus region of the electromagnetic waves.

[0063] If the phase shifting regions do not match the geometry of the respective focus regions, artefacts in the synthesized intensity pattern may result. If a phase shifting region is larger than the corresponding focus region, part of the

electromagnetic waves that is not part of the focussed electromagnetic waves is also phase shifted resulting in artefacts in the synthesized intensity pattern, and if the phase shifting region is smaller than the corresponding focus region, part of the focussed electromagnetic waves is not phase shifted as desired also resulting in artefacts in the synthesized intensity pattern.

[0064] For example, if a one-dimensional array or two-dimensional array of VCSELs forms the source, the phase shifting regions of the spatial phase filter preferably form a corresponding one-dimensional or two-dimensional array, respectively, of phase shifting regions, each of the regions being positioned at the focus region of electromagnetic waves emitted by a respective VCSEL in the VCSEL array. Further, each phase shifting region preferably coincides, or substantially coincides, with the focus region of the electromagnetic waves emitted by the respective VCSEL. [0065] Likewise, the spatial phase filter may match a source with a specific geometrical shape with a continuous phase shifting region covering an area of the spatial phase filter that corresponds to the focus region of the electromagnetic waves emitted by the source.

[0066] Thus, the energy of the electromagnetic waves of the system may be distributed over a large area of the spatial phase filter as compared to the area of a focus region of a single plane electromagnetic wave of a known GPC system.

[0067] Thus, the phase shifting regions of the spatial phase filter may form a rectangular array, a circular array, a linear array, two linear crossing arrays, a continuous region, a continuous tapered region, a ring, etc.

[0068] An imaging system maps the phase modulating surface (x, y) of the phase modifying element onto a target surface (χ', y') of the reconstructed intensity pattern l(x', y'), such as a 4f imaging system with two Fourier transforming lenses utilizing transmission of light; or a 2f imaging system with one Fourier transforming lens utilizing reflection of light. However, any optical imaging system providing a filtering plane for the spatial phase filter may be applied in the new GPC system.

[0069] The intensity pattern I (λ, χ', y') may be generated by superposition of electromagnetic waves in the image plane (χ', y') of the imaging system. The phase modifying element changes the phase values of electromagnetic waves incident upon it, and the imaging system directs the electromagnetic waves with changed phases reflected from or transmitted through the phase modifying element and optionally the first dispersing element towards the spatial phase filter. The spatial phase filter phase shifts parts of the electromagnetic waves, and the imaging system is configured to superimpose in the image plane the phase shifted parts of the electromagnetic waves with the parts of the electromagnetic waves that are not phase shifted by the spatial phase filter.

[0070] Intensity patterns I (λ, χ', y') for different wavelengths λ may be displaced with relation to each other. The displacement may be compensated optically by addition of appropriate dispersing elements; or, the intensity patterns may be captured and processed electronically in a processor that is configured for electronically moving the intensity pattern of each wavelength so that the intensity patter of different wavelengths λ coincide and configured to output the processed intensity pattern to a display system.

[0071] The phase modifying element may have an input for reception of signals for addressing specific points or parts of the phase modulation surface (x, y) and for adjusting the phasor values e'^ y⁾ of the respective addressed point or part (x, y).

[0072] The system may further comprise a controller with a first output that is connected to the input of the phase modifying element, and a second output that is connected to the spatial phase filter and being adapted for adjusting phasor values _θ ^ίφ^{(λ ,}γ⁾ of th_e phase modifying element and phase shift values θ(λ) of the spatial phase filter.

[0073] The controller may include the processor.

Proposed applications:

[0074] A multi-photon fluorescence microscope may advantageously comprise the new GPC system. The multi-photon excitation technique is widely applied in the biological imaging and micro-fabrication fields. With its superior axial sectioning capability and long excitation wavelength, MPE results in lower photo-bleaching and minimum invasiveness, and is, therefore, particularly suitable for imaging thick tissues. Further, with the two-photon absorption confined to the focal volume, multi- photon excitation provides an ideal solution for the fabrication of high-precision microstructures. Further, multi-photon excitation with temporal focusing can generate wide-field and axially resolved excitation on a plane-by-plane basis. Recombination of the femto-pulsed dispersed and monochromatic electromagnetic waves, preferably in the infrared wavelength range, at the front focal plane of an objective lens produces a short, high-peak power pulse in the focal plane, whereby multi-photon excitation is provided simultaneously over an area in the focal plane.

[0075] A cinema laser projector may advantageously comprise the new GPC system.

[0076] A wavelength-division multiplexing communication system may

advantageously comprise the new GPC system.

[0077] An endoscope may advantageously comprise the new GPC system.

[0078] A super resolution microscope, such as a stimulated emission depletion (STED) microscope, a photo-activated localization microscope (PALM), a stochastic optical reconstruction microscope (STORM), etc., may advantageously comprise the new GPC system.

[0079] The new GPC system may also advantageously be utilized in:

■ Spatially shaping of super-continuum light ^■ Spatially shaped multi-colour lasers in one integrated system

^■ Unique module for parallel opto-genetics using ultra-fast pulsed lasers

^■ Fluorescence excitation approach in a variety of applications

^■ Laser machine tools e. g. for shaping, forming, assembling, etc., such as cutting, drilling, milling, planning, marking, branding, trimming, hardening, scribing, labelling, welding, soldering, two-and three-dimensional surfaces especially by use of CO2 and Nd:YAG laser based systems. The main advantage is that energy is not absorbed in the system according to the present invention (thereby preventing damage of the optical hardware) and this non-absorbed energy is instead utilized to increase the intensity level of the desired light distribution in the image plane. High power can be delivered to selected regions on a work piece simultaneously.

^■ Optical tweezer arrays for manipulation of micro-objects, such as micro- components, biological cells, etc., using electromagnetic gradient forces proportional to the optical intensity pointing in the direction of the intensity gradient.

^■ Efficient and dynamic spot-array generators based on phase contrast imaging. In order to provide bias or holding beams for arrays of optoelectronic elements, such as bi-stable elements, photonic switches and smart pixels.

^■ Generation of structured light (loss less) for machine vision applications. E. g. periodic and skew periodic mesh grid illumination that can be updated in parallel.

^■ Photolithographic applications (laser 3D direct writing in parallel without the need for sequential scanning). E. g. high power laser direct writing of waveguides in Ge-doped silica.

^■ Spatial light intensity modulation in general by use of pure phase

modulation (radiation focusators).

^■ Laser beam shaping (dynamic).

■ Highly efficient parallel image projection without the need for a laser- scanning device.

^■ Dynamic Infrared Scene Projection (DIRSP). Exposure device for grating and mask production.

LIDAR applications.

Laser printing in parallel.

Laser show applications.

Atmosphere research, and

Potentially many more rapidly emerging broad-band or multi-colour light applications.

[0080] Below, the new GPC method and system according to the appended claims are explained in more detail with reference to the drawings in which various examples of the new GPC system are shown. In the drawings:

Fig. 1 schematically illustrates optical signal processing of a known GPC system,

Fig. 2 schematically illustrates an example of the new GPC system with a plurality of light sources with different wavelengths,

Fig. 3 schematically illustrates an example of the new GPC system with a point light source emitting red, green, and blue light; and a prism,

Fig. 4 schematically illustrates an example of the new GPC system with a point light source emitting white light, and a prism.

Fig. 5 schematically illustrates an example of the new GPC system with a point light source emitting white light, and a combined phase modifying and dispersing element,

Fig. 6 schematically illustrates an example of the new GPC system with a point light source emitting red, green, and blue light; and a combined Fourier lens and dispersing element,

Fig. 7 schematically illustrates an example of the new GPC system with a point light source emitting white light; and a combined Fourier lens and dispersing element,

Fig. 8 schematically illustrates an example of the new GPC system with a point light source emitting red, green, and blue light; and a diffraction grating,

Fig. 9 schematically illustrates an example of the new GPC system with a point light source emitting white light; and a diffraction grating, and

Fig. 10 schematically illustrates an example of the new GPC system with a femto- second pulsed laser and a diffraction grating.

[0081] The drawings illustrate the design and utility of embodiments, in which similar elements are referred to by common reference numerals. Like elements may, thus, not be described in detail with respect to the description of each figure. In order to better appreciate how the above-recited and other advantages and objects are obtained, a more particular description of the embodiments will be rendered, which are illustrated in the accompanying drawings. It should be noted that the figures are only intended to facilitate the description of the features. They are not intended as an exhaustive description of the claimed invention or as a limitation on the scope of the claimed invention. In addition, an illustrated feature needs not have all the aspects or advantages shown. An aspect or an advantage described in conjunction with a particular feature is not necessarily limited to that feature and can be practiced in any other features even if not so illustrated or explicitly described.

[0082] The new GPC system and method according to the appended claims may be embodied in different forms not shown in the accompanying drawings and should not be construed as limited to the examples set forth herein.

[0083] It should be noticed that the elements shown in the drawings are not drawn to scale. For example, the sizes of the phase shifting regions have been enlarged for illustration purposes. Typically, the size of a phase shifting region is in the order of μ m.

[0084] Fig. 1 shows a known 4f phase contrast imaging system 10 embodied in a 4f common path interferometer as disclosed in WO 96/34307 A1 , see e.g. Fig. 1 and page 18, line 14 - page 19, line 21 of WO 96/34307 A1 . A corresponding 2f phase contrast imaging system 10 is shown in Fig. 2 and further disclosed in page 19, line 22 - page 20, line 9; and a corresponding 1f phase contrast imaging system is shown in Fig. 3 and further disclosed in page 20, lines 10 - 22.

[0085] The source of electromagnetic waves is a laser 12 that emits a light beam 14, which is collimated by lens 16 into a plane light wave of uniform intensity and directed towards a phase modifying element 18. The light beam 14 is transmitted through the phase modifying element 18 and a Fourier transforming lens 20. The phase modifying element 18 is positioned in the front focal plane of the lens 20 and a spatial phase filter 22 is positioned in the back focal plane of the lens 20 that is also the front focal plane of a lens 26. The Fourier transforming lenses 20, 26 need not have identical focal lengths. Different focal lengths lead to a magnification ratio different from one. The spatial phase filter 22 phase shifts by Θ, and optionally attenuates (by a factor B), the zero order diffraction waves 24 of the light that has been phase modulated by the phase modifying element 18. Optionally, the remaining part of the electromagnetic waves modulated by the phase modifying element may be attenuated by a factor A. The reconstructed intensity pattern I (χ', y') is generated in the back focal plane of the lens 26.

[0086] Fig. 2 schematically illustrates an exemplary new GPC system 10 in a 4f common path interferometer configuration wherein, apart from the fact that a source 12 of electromagnetic waves 14 is arranged so that electromagnetic waves 14 with different wavelengths λ propagate along respective different propagation paths through the generalized phase contrast system 10 and illuminate respective different phase shifting regions (x^s, y^s) of a surface S of a spatial phase filter 22, the main components a) - e) of the new GPC system 10 are positioned in the same way with relation to each other as in a conventional 4f phase contrast imaging system.

Obviously, the function of the illustrated GPC system 10 may also be obtained with a system wherein the main components a) - e) of the new GPC system 10 are positioned in the same way with relation to each other as in a conventional 2f phase contrast imaging system; or, as in a conventional 1f phase contrast imaging system.

[0087] An assembly 12 of three individual semiconductor lasers 12R, 12G, 12B forming a linear equidistant array of laser sources with the illustrated layout 12a constitutes the source of electromagnetic waves. The semiconductor laser 12R emits a beam of red light 14_R, the semiconductor laser 12_G emits a beam of green light 14_G, and the semiconductor laser 12_B emits a beam of blue light 14_B.

[0088] The emitted light beams are collimated by lens 16 into a plurality of plane light waves 14R, 14G, 14B directed towards a phase modifying element 18 to be incident upon the phase modifying element 18 at different respective angles of approach. The phase modifying element 18 has an input surface (x, y), wherein (x, y) are coordinates of the resolution elements or pixels of the phase modifying unit 18, positioned so that the light beams 14_R, 14_G, 14_B are incident upon it, and the phase modifying element is configured for phase modulation of the light beams 14R, 14G, 14B impinging on the surface at resolution element (x, y) by phasor values e^w⁾, wherein λ is the wavelength of the laser light beam 14R, 14G, 14B in question. The phase modifying element 18 may be a spatial light modulator adjusted to provide a predetermined changed optical path length d(x, y) for each resolution element (x, y) resulting in different phasor values e^id<^x y^)A for different wavelengths of light passing though the resolution element (x, y) in question.

[0089] The light beams 14_R, 14_G, 14_B propagate through the phase modifying element 18 and a Fourier transforming lens 20. The Fourier transforming lens 20 refracts the non-scattered parts of the light beams 14R, 14G, 14B into converging beams 24R, 24G, 24B. The phase modifying element 18 is positioned in the front focal plane of the lens 20 so that the electromagnetic field exiting the phase modifying element 18 is Fourier transformed at the back focal plane of the lens 20.

[0090] A spatial phase filter 22 is positioned with its surface S at the back focal plane, i.e. the Fourier plane, of the lens 20 with a layout 22a of phase shifting regions 22R, 22G, 22B positioned at respective focus regions of the respective light beams 24R, 24G, 24B that are conjugate positions of the positions of the respective semiconductor lasers 12R, 12G, 12B; or in other words, the centres of the semiconductor lasers 12R, 12G, 12B are imaged onto the centres of the respective focus regions of converging light beams 24R, 24G, 24B by lens 16 and lens 20 in cooperation. In Fig. 2, the phase shifting regions 22_R, 22_G, 22_B form a linear array; however, if the source of

electromagnetic waves comprises a two-dimensional array of sources, the phase shifting regions will be arranged in a corresponding two-dimensional array forming an image of the two-dimensional array of sources.

[0091] At the phase shifting regions 22R, 22G, 22B, the spatial phase filter is configured for phase shifting the respective focussed electromagnetic waves 24R, 24G, 24B by predetermined respective phase shift values θ(λ, x^s, y^s) with relation to the remaining part of the respective Fourier transformed light waves outside the respective phase shifting regions 22_R, 22_G, 22_B. (x^s, y^s) are coordinates of the surface S of the spatial phase filter 22. In the illustrated example, the optical path length through the phase shifting regions 22R, 22G, 22B is different for the different wavelengths λ of the red, green and blue light beams impinging at the respective phase shifting region with the respective optical path length, e.g. resulting in the same phase shift Θ for all three wavelengths. However, any value may be selected independently for each of the wavelengths.

[0092] The position, shape, and area of each of the phase shifting regions 22R, 22G, 22B of the spatial phase filter is fitted to the position, shape, and area of the respective focus regions of the focussed electromagnetic waves 24R, 24G, 24B SO that the focussed electromagnetic waves 24R, 24G, 24B illuminate the respective phase shifting region 22R, 22G, 22B and are phase shifted with the desired phase shift values θ(λ, X^s, y^s) with relation to the remaining part of the electromagnetic waves (not shown) propagating through the illustrated GPC system 10. Preferably, each of the phase shifting regions 22_R, 22_G, 22_B of the spatial phase filter coincides with the respective focus region.

[0093] If the phase shifting regions 22R, 22G, 22B do not match the geometry of the respective focus regions, artefacts in the synthesized intensity pattern l(x', y') may result. If the phase shifting region is larger than the corresponding focus region, part of the light that is not part of the focussed light beam is also phase shifted resulting in artefacts in the synthesized intensity pattern, and if the phase shifting region is smaller than the corresponding focus region, part of the focussed light beam is not phase shifted as desired also resulting in artefacts in the synthesized intensity pattern.

[0094] The spatial phase filter 22 with layout 22a is positioned in the back focal plane of the lens 20 that is also the front focal plane of a second Fourier transforming lens 26. The Fourier transforming lenses 20, 26 need not have identical focal lengths. Different focal lengths lead to a magnification ratio different from one.

[0095] An intensity pattern I (χ', y') is generated in the back focal plane 28 of the lens 26 as a result of the Fourier transformation of the electromagnetic field exiting the spatial phase filter 22.

[0096] The illustrated system 10 may be controlled by a computer (not shown) comprising interface means for addressing each of the resolution elements of the phase modifying element 18 and transmitting a phasor value e'^^y) to the addressed resolution element (x, y). Further, the computer may comprise control means for controlling the output of the source 12. The computer may also comprise input means, such as a keyboard, a mouse, a diskette drive, an optical disc drive, a network interface, a modem, etc., for receiving an image pattern to be synthesized by the system 10. From the received image pattern, the computer may be adapted to calculate phasor values to be transmitted to the resolution elements (x, y) of the phase modifying element 18, e. g. based on a histogram technique as is well-known in the art of GPC-systems.

[0097] Optionally, the phase shifts of the spatial phase filter 22 may be adjustable and controllable by optional phase control means of the computer, which may be further adapted to adjust the phase shift. An optional imaging system captures the synthesized intensity pattern l(x', y') and transmits it to the computer (not shown) for display to the user and for possible automatic adjustment. Fig. 3 schematically illustrates an exemplary new GPC system 10 in a 4f common path interferometer configuration, wherein, apart from the fact that a source 12 of electromagnetic waves 14 is arranged so that electromagnetic waves 14 with different wavelengths λ propagate along respective different propagation paths through the generalized phase contrast system 10 and illuminate respective different phase shifting regions (x^s, y^s) of a surface S of a spatial phase filter 22, the main components a) - e) of the new GPC system 10 are positioned in the same way with relation to each other as in a conventional 4f phase contrast imaging system. Obviously, the function of the illustrated GPC system 10 may also be obtained with a system wherein the main components a) - e) of the new GPC system 10 are positioned in the same way with relation to each other as in a conventional 2f phase contrast imaging system; or, as in a conventional 1f phase contrast imaging system.

[0098] A point source of electromagnetic waves 12 emits red light, green light, and blue light. The emitted light is collimated by lens 16 into plane light waves 14 directed towards a phase modifying element 18. The phase modifying element 18 has an input surface (x, y), wherein (x, y) are coordinates of resolution elements or pixels of the phase modifying unit 18, positioned so that the plane light waves 14 are incident upon it, and the phase modifying element 18 is configured for phase modulation of the light waves 14 impinging on the surface at resolution element (x, y) by phasor values _θίφ(λ wherein λ is the wavelength. The phase modifying element 18 may be a spatial light modulator adjusted to provide a predetermined changed optical path length d(x, y) for each resolution element (x, y) resulting in different phasor values _eid(x,y) for different wavelengths of light passing though the resolution element (x, y) in question.

[0099] The light waves 14 propagate through the phase modifying element 18 towards a first dispersing element constituted by a prism 30. The prism 30 disperses the phase modulated light waves into wavelength dependent propagation paths as indicated for the red light 14_R, the green light 14_G, and the blue light 14_B, so that light waves with different wavelengths propagate along different propagation paths upon interaction with the prism 30.

[0100] The dispersed light waves 14R, 14G, 14B propagate towards a Fourier transforming lens 20. The phase modifying element 18 is positioned in the front focal plane of the lens 20 as defined by the lens 20 in combination with the prism 30. The Fourier transforming lens 20 refracts the non-scattered parts of the light waves 14_R, 14G, 14B into converging waves 24R, 24G, 24B. The phase modifying element 18 is positioned in the front focal plane of the lens 20 so that the electromagnetic field exiting the phase modifying element 18 is Fourier transformed at the back focal plane of the lens 20.

[0101] A spatial phase filter 22 is positioned with its surface S at the back focal plane, i.e. the Fourier plane, of the lens 20 with a layout 22a of phase shifting regions 22R, 22G, 22B positioned at respective focus regions of the respective dispersed light waves 24R, 24G, 24B. In Fig. 3, the phase shifting regions 22R, 22G, 22B form a linear array; however, the surfaces of the prism 30 may also be shaped so that the phase shifting regions form a two-dimensional array.

[0102] At the phase shifting regions 22R, 22G, 22B, the spatial phase filter is configured for phase shifting the respective focussed electromagnetic waves 24R, 24G, 24B by predetermined respective phase shift values θ(λ, x^s, y^s) with relation to the remaining part of the respective Fourier transformed light waves outside the respective phase shifting regions 22_R, 22_G, 22_B. (x^s, y^s) are coordinates of the surface S of the spatial phase filter 22. In the illustrated example, the optical path length through the phase shifting regions 22R, 22G, 22B is different for the different wavelengths λ of the red, green and blue light waves impinging at the respective phase shifting region with the respective optical path length, e.g. resulting in the same phase shift Θ for all three wavelengths. However, any value may be selected independently for each of the wavelengths.

[0103] The position, shape, and area of each of the phase shifting regions 22_R, 22_G, 22_B of the spatial phase filter is fitted to the position, shape, and area of the respective focus regions of the focussed electromagnetic waves 24R, 24G, 24B SO that the focussed electromagnetic waves 24R, 24G, 24B illuminate the respective phase shifting region 22R, 22G, 22B and are phase shifted with the desired phase shift values θ(λ, X^s, y^s) with relation to the remaining part of the electromagnetic waves (not shown) propagating through the illustrated GPC system 10. Preferably, each of the phase shifting regions 22_R, 22_G, 22_B of the spatial phase filter coincides with the respective focus region.

[0104] If the phase shifting regions 22R, 22G, 22B do not match the geometry of the respective focus regions, artefacts in the synthesized intensity pattern l(x', y') may result. If the phase shifting region is larger than the corresponding focus region, part of the light that is not part of the focussed electromagnetic waves is also phase shifted resulting in artefacts in the synthesized intensity pattern, and if the phase shifting region is smaller than the corresponding focus region, part of the focussed electromagnetic waves is not phase shifted as desired also resulting in artefacts in the synthesized intensity pattern.

[0105] The spatial phase filter 22 with layout 22a is positioned in the back focal plane of the lens 20 that is also the front focal plane of a second Fourier transforming lens 26. The Fourier transforming lenses 20, 26 need not have identical focal lengths. Different focal lengths lead to a magnification ratio different from one.

[0106] An intensity pattern I (λ, χ', y') is generated in the back focal plane 28 of the lens 26 as a result of the Fourier transformation of the electromagnetic field exiting the spatial phase filter 22. Due to the wavelength dispersion by the prism 30, the intensity patterns formed by the red, green, and blue light are displaced with relation to each other; however, this may be compensated optically or electronically or by a combination of optical and electronic compensation. In the illustrated example, a second dispersing element 32, e.g. a grating or a second prism, is provided for compensation of the dispersion of the first dispersing element 30 so that the intensity patterns formed by the red, green, and blue light coincide. Alternatively, or in combination, an optional imaging system (not shown) may capture the synthesized intensity patterns Ι(λ, χ', y') and may be configured to electronically displace the respective intensity patterns so that the intensity patterns formed by the red, green, and blue light coincide, e.g. in a computer (not shown), and output the combined intensity pattern l(x', y') for display to the user and for possible automatic adjustment.

[0107] The illustrated system 10 may be controlled by a computer (not shown) comprising interface means for addressing each of the resolution elements of the phase modifying element 18 and transmitting a phasor value e'^^' to the addressed resolution element (x, y). Further, the computer may comprise control means for controlling the output of the source 12. The computer may also comprise input means, such as a keyboard, a mouse, a diskette drive, an optical disc drive, a network interface, a modem, etc., for receiving an image pattern to be synthesized by the system 10. From the received image pattern, the computer may be adapted to calculate phasor values to be transmitted to the resolution elements (x, y) of the phase modifying element 18, e. g. based on a histogram technique as is well-known in the art of GPC-systems.

[0108] Optionally, the phase shifts of the spatial phase filter 22 may be adjustable and controllable by optional phase control means of the computer, which may be further adapted to adjust the phase shift. An optional imaging system may capture the synthesized intensity pattern l(x', y') and transmit it to the computer (not shown) for display to the user and for possible automatic adjustment.

[0109] Fig. 4 schematically illustrates an exemplary new GPC system 10 in a 4f common path interferometer configuration, wherein, apart from the fact that a source 12 of electromagnetic waves 14 is arranged so that electromagnetic waves 14 with different wavelengths λ propagate along respective different propagation paths through the generalized phase contrast system 10 and illuminate respective different phase shifting regions (x^s, y^s) of a surface S of a spatial phase filter 22, the main components a) - e) of the new GPC system 10 are positioned in the same way with relation to each other as in a conventional 4f phase contrast imaging system.

[0110] A source of electromagnetic waves 12 emits visible substantially white light with a continuous spectrum including red light, green light, and blue light. The emitted white light is collimated by lens 16 into plane light waves 14 directed towards a phase modifying element 18. The phase modifying element 18 has an input surface (x, y), wherein (x, y) are coordinates of resolution elements or pixels of the phase modifying unit 18, positioned so that the plane light waves 14 are incident upon it, and the phase modifying element 18 is configured for phase modulation of the light wave 14 impinging on the surface at resolution element (x, y) by phasor values

wherein λ is the wavelength. The phase modifying element 18 may be a spatial light modulator adjusted to provide a predetermined changed optical path length d(x, y) for each resolution element (x, y) resulting in different phasor values e^id<^x y^)A for different wavelengths of light passing though the resolution element (x, y) in question.

[01 11] The light waves 14 propagate through the phase modifying element 18 towards a first dispersing element constituted by a prism 30. The prism 30 disperses the phase modulated light waves into wavelength dependent propagation paths as indicated for the red light 14R, the green light 14G, and the blue light 14B, SO that light waves with different wavelengths propagate along different propagation paths upon interaction with the prism 30. The white light waves 14 contains all the wavelengths of the visible spectrum; however, for illustration purposes only the dispersed red light waves 14R, the dispersed green light waves'! 4G, and the dispersed blue light waves 14_B are shown in Fig. 4.

[0112] The dispersed light waves including the dispersed red light waves 14_R, the dispersed green light waves14G, and the dispersed blue light waves 14B, propagate towards a Fourier transforming lens 20. The phase modifying element 18 is positioned in the front focal plane of the lens 20 as defined by the lens 20 in combination with the prism 30. The Fourier transforming lens 20 refracts the non- scattered parts of the dispersed light waves 14R, 14G, 14B into converging light waves as illustrated for light waves 24_R, 24_G, 24_B of the red, green and blue wavelengths, respectively. The phase modifying element 18 is positioned in the front focal plane of the lens 20 so that the electromagnetic field exiting the phase modifying element 18 is Fourier transformed at the back focal plane of the lens 20.

[0113] A spatial phase filter 22 is positioned with its surface S at the back focal plane, i.e. the Fourier plane, of the lens 20 with a layout 22a of overlapping phase shifting regions forming a continuous tapered phase shifting region including phase shifting regions 22_R, 22_G, 22_B positioned at respective focus regions of the respective focussed light waves 24R, 24G, 24B. The width of the continuous tapered phase shifting region increases with increased wavelength of light incident upon it. In Fig. 4, the phase shifting regions form a tapered region; however, the surfaces of the prism 30 may also be shaped so that the phase shifting regions form an arbitrary two- dimensional shape.

[0114] At the phase shifting regions, e.g. 22_R, 22_G, 22_B, the spatial phase filter is configured for phase shifting the respective focussed electromagnetic waves, e.g. 24R, 24G, 24B, by predetermined respective phase shift values θ(λ, x^s, y^s) with relation to the remaining part of the respective Fourier transformed light waves outside the tapered continuous phase shifting region. (x^s, y^s) are coordinates of the surface S of the spatial phase filter 22. In the illustrated example, the optical path length through the phase shifting regions 22R, 22G, 22B increases with increased wavelength λ of the focussed light waves impinging at the respective area of the phase shifting region with the respective optical path length, e.g. resulting in the same phase shift Θ for all wavelengths. However, any variation of the optical path length as a function of the wavelength λ may be selected.

[0115] The position, shape, and area of each of the phase shifting (overlapping) regions, e.g. 22R, 22G, 22B, of the spatial phase filter 22 is fitted to the position, shape, and area of the respective focus regions of the focussed light waves 24R, 24G, 24B SO that the focussed light waves 24_R, 24_G, 24_B illuminate the respective phase shifting region 22_R, 22_G, 22_B and are phase shifted with the desired phase shift values θ(λ, x^s, y^s) with relation to the remaining part of the light waves (not shown) propagating through the illustrated GPC system 10. Preferably, each of the phase shifting regions, e.g. 22R, 22G, 22B, of the spatial phase filter coincides with the respective focus region.

[01 16] If the phase shifting regions, e.g. 22R, 22G, 22B, do not match the geometry of the respective focus regions, artefacts in the synthesized intensity pattern l(x', y') may result. If the phase shifting region is larger than the corresponding focus region, part of the light that is not part of the focussed electromagnetic waves is also phase shifted resulting in artefacts in the synthesized intensity pattern, and if the phase shifting region is smaller than the corresponding focus region, part of the focussed electromagnetic waves is not phase shifted as desired also resulting in artefacts in the synthesized intensity pattern.

[0117] The spatial phase filter 22 with layout 22a is positioned in the back focal plane of the lens 20 that is also the front focal plane of a second Fourier transforming lens 26. The Fourier transforming lenses 20, 26 need not have identical focal lengths. Different focal lengths lead to a magnification ratio different from one.

[0118] An intensity pattern I (λ, χ', y') is generated in the back focal plane 28 of the lens 26 as a result of the Fourier transformation of the electromagnetic field exiting the spatial phase filter 22. Due to the wavelength dispersion by the prism 30, the intensity patterns I (λ, χ', y') formed at the back focal plane 28 are displaced with relation to each other as a function of the wavelength λ; however, this may be compensated optically or electronically or by a combination of optical and electronic compensation. In the illustrated example, a second dispersing element 32, e.g. a grating or a second prism, is provided for compensation of the dispersion of the first dispersing element 30 so that the intensity patterns formed by the light of all the wavelengths coincide, or substantially coincide. Alternatively, or in combination, an optional imaging system (not shown) may capture the synthesized intensity patterns l( λ, χ', y') and may be configured to electronically displace the respective intensity patterns so that the intensity patterns formed by the light of all the wavelengths coincide, or substantially coincide, e.g. in a computer (not shown), and output the combined intensity pattern l(x', y') for display to the user and for possible automatic adjustment. [0119] The illustrated system 10 may be controlled by a computer (not shown) comprising interface means for addressing each of the resolution elements of the phase modifying element 18 and transmitting a phasor value e'^ y⁾ to the addressed resolution element (x, y). Further, the computer may comprise control means for controlling the output of the source 12. The computer may also comprise input means, such as a keyboard, a mouse, a diskette drive, an optical disc drive, a network interface, a modem, etc., for receiving an image pattern to be synthesized by the system 10. From the received image pattern, the computer may be adapted to calculate phasor values to be transmitted to the resolution elements (x, y) of the phase modifying element 18, e. g. based on a histogram technique as is well-known in the art of GPC-systems.

[0120] Optionally, the phase shifts of the spatial phase filter 22 may be adjustable and controllable by optional phase control means of the computer, which may be further adapted to adjust the phase shift. An optional imaging system may capture the synthesized intensity pattern l(x', y') and transmit it to the computer (not shown) for display to the user and for possible automatic adjustment.

[0121] Fig. 5 schematically illustrates a GPC system 10 as claimed in a 4f common path interferometer configuration, wherein, apart from the fact that a source 12 of electromagnetic waves 14 is arranged so that electromagnetic waves 14 with different wavelengths λ propagate along respective different propagation paths through the generalized phase contrast system 10 and illuminate respective different phase shifting regions (x^s, y^s) of a surface S of a spatial phase filter 22, the main

components a) - e) of the new GPC system 10 are positioned in the same way with relation to each other as in a conventional 4f phase contrast imaging system.

[0122] A source of electromagnetic waves 12 emits visible substantially white light with a continuous spectrum including red light, green light, and blue light. The emitted white light is collimated by lens 16 into plane light waves 14 directed towards a phase modifying element 18. The phase modifying element 18 has an input surface (x, y), wherein (x, y) are coordinates of resolution elements or pixels of the phase modifying unit 18, positioned so that the plane light waves 14 are incident upon it, and the phase modifying element 18 is configured for phase modulation of the light wave 14 impinging on the surface at resolution element (x, y) by phasor values e'*** ^ independent of the wavelength λ.

[0123] The phase modifying element 18 also constitutes the first dispersing element. The phase modifying and dispersing element 18 disperses the light waves 14 into wavelength dependent propagation paths as indicated for the red light 14R, the green light 14G, and the blue light 14B, SO that light waves with different wavelengths propagate along different propagation paths upon interaction with the phase modifying and dispersing element 18.

[0124] The phase modifying and dispersing element 18 comprises gratings that are displaced with relation to each other as indicated with layout 18a in Fig. 5, so that phase modulation of the electromagnetic waves impinging on its surface (x, y) is performed by phasor values e'*** ^ that are independent of the wavelength λ, at least in a first order approximation.

[0125] Phase modulation independent of wavelength λ may, e.g., be obtained by displacement of a grating of an otherwise regular diffraction grating with continuous grating lines as disclosed in WO 2012/146257 A1. For example, a conventional regular diffraction grating may be divided into pixels, i.e. a regular array of small rectangles, within which the grating lines may be displaced with relation to the grating lines of neighbouring pixels, whereby broken grating lines are created. Due to the displacement of the grating lines, a dispersed electromagnetic wave will be phase shifted correspondingly. Thus, if a regular diffraction grating with unbroken grating lines with the grating line spacing L between all grating lines is taken as a starting point and used as a reference grating, then displacement of the grating lines in one pixel (i, j) by a displacement distance dy will result in a corresponding phase modulation of electromagnetic waves incident on that pixel (i, j) by = 2π - with relation to the reference grating.

[0126] The dispersed light waves including the dispersed red light waves 14R, the dispersed green light waves14G, and the dispersed blue light waves 14B, propagate towards a Fourier transforming lens 20. The Fourier transforming lens 20 refracts the non-scattered parts of the dispersed light waves 14R, 14G, 14B into converging light waves as illustrated for light waves 24_R, 24_G, 24_B of the red, green and blue wavelengths, respectively. The phase modifying and dispersing element 18 is positioned in the front focal plane of the lens 20 so that the electromagnetic field exiting the phase modifying and dispersing element 18 is Fourier transformed at the back focal plane of the lens 20.

[0127] A spatial phase filter 22 is positioned with its surface S at the back focal plane, i.e. the Fourier plane, of the lens 20 with a layout 22a of overlapping phase shifting regions forming a continuous tapered phase shifting region including phase shifting regions 22R, 22G, 22B positioned at respective focus regions of the respective focussed light waves 24R, 24G, 24B. The width of the continuous tapered phase shifting region increases with increased wavelength of light incident upon it. In Fig. 5, the phase shifting regions form a tapered region; however, the phase modifying and dispersing element 18 may be configured to disperse the electromagnetic waves so that the phase shifting regions form another arbitrary two-dimensional shape.

[0128] At the phase shifting regions, e.g. 22R, 22G, 22B, the spatial phase filter is configured for phase shifting the respective focussed electromagnetic waves, e.g. 24R, 24G, 24B, by predetermined respective phase shift values θ(λ, x^s, y^s) with relation to the remaining part of the respective Fourier transformed light waves outside the tapered continuous phase shifting region. (x^s, y^s) are coordinates of the surface S of the spatial phase filter 22. In the illustrated example, the optical path length through the phase shifting regions 22R, 22G, 22B increases with increased wavelength λ of the focussed light waves impinging at the respective area of the phase shifting region with the respective optical path length, e.g. resulting in the same phase shift Θ for all wavelengths. However, any variation of the optical path length as a function of the wavelength λ may be selected.

[0129] The position, shape, and area of each of the phase shifting (overlapping) regions, e.g. 22_R, 22_G, 22_B, of the spatial phase filter 22 is fitted to the position, shape, and area of the respective focus regions of the focussed light waves 24R, 24G, 24B SO that the focussed light waves 24R, 24G, 24B illuminate the respective phase shifting region 22R, 22G, 22B and are phase shifted with the desired phase shift values θ(λ, x^s, y^s) with relation to the remaining part of the light waves (not shown) propagating through the illustrated GPC system 10. Preferably, each of the phase shifting regions, e.g. 22_R, 22_g, 22_b, of the spatial phase filter coincides with the respective focus region.

[0130] If the phase shifting regions, e.g. 22R, 22G, 22B, do not match the geometry of the respective focus regions, artefacts in the synthesized intensity pattern l(x', y') may result. If the phase shifting region is larger than the corresponding focus region, part of the light that is not part of the focussed electromagnetic waves is also phase shifted resulting in artefacts in the synthesized intensity pattern, and if the phase shifting region is smaller than the corresponding focus region, part of the focussed electromagnetic waves is not phase shifted as desired also resulting in artefacts in the synthesized intensity pattern.

[0131] The spatial phase filter 22 with layout 22a is positioned in the back focal plane of the lens 20 that is also the front focal plane of a second Fourier transforming lens 26. The Fourier transforming lenses 20, 26 need not have identical focal lengths. Different focal lengths lead to a magnification ratio different from one.

[0132] An intensity pattern I (λ, χ', y') is generated in the back focal plane 28 of the lens 26 as a result of the Fourier transformation of the electromagnetic field exiting the spatial phase filter 22. Due to the wavelength dispersion by the prism 30, the intensity patterns I (λ, χ', y') formed at the back focal plane 28 are displaced with relation to each other as a function of the wavelength λ; however, this may be compensated optically or electronically or by a combination of optical and electronic compensation. In the illustrated example, a second dispersing element 32, e.g. a grating or a second prism, is provided for compensation of the dispersion of the first dispersing element 30 so that the intensity patterns formed by the light of all the wavelengths coincide, or substantially coincide. Alternatively, or in combination, an optional imaging system (not shown) may capture the synthesized intensity patterns l( λ, χ', y') and may be configured to electronically displace the respective intensity patterns so that the intensity patterns formed by the light of all the wavelengths coincide, or substantially coincide, e.g. in a computer (not shown), and output the combined intensity pattern l(x', y') for display to the user and for possible automatic adjustment.

[0133] The illustrated system 10 may be controlled by a computer (not shown) comprising interface means for addressing each of the resolution elements of the phase modifying and dispersing element 18 and transmitting a phasor value e'^*^ to the addressed resolution element (x, y). Further, the computer may comprise control means for controlling the output of the source 12. The computer may also comprise input means, such as a keyboard, a mouse, a diskette drive, an optical disc drive, a network interface, a modem, etc., for receiving an image pattern to be synthesized by the system 10. From the received image pattern, the computer may be adapted to calculate phasor values to be transmitted to the resolution elements (x, y) of the phase modifying and dispersing element 18, e. g. based on a histogram technique as is well-known in the art of GPC-systems. [0134] Optionally, the phase shifts of the spatial phase filter 22 may be adjustable and controllable by optional phase control means of the computer, which may be further adapted to adjust the phase shift. An optional imaging system may capture the synthesized intensity pattern l(x', y') and transmit it to the computer (not shown) for display to the user and for possible automatic adjustment.

[0135] Fig. 6 schematically illustrates an exemplary new GPC system 10 in a 4f common path interferometer configuration, wherein, apart from the fact that a source 12 of electromagnetic waves 14 is arranged so that electromagnetic waves 14 with different wavelengths λ propagate along respective different propagation paths through the generalized phase contrast system 10 and illuminate respective different phase shifting regions (x^s, y^s) of a surface S of a spatial phase filter 22, the main components a) - e) of the new GPC system 10 are positioned in the same way with relation to each other as in a conventional 4f phase contrast imaging system.

[0136] A multi-wavelength point source constitutes the source of electromagnetic waves. In the illustrated example, the multi-wavelength point source is formed by an optical fibre transmitting red, green and blue light and emitting the light from its end surface.

[0137] The emitted electromagnetic waves constituted by red, blue and green light waves, are collimated by lens 16 into plane electromagnetic waves 14 directed towards a phase modifying element 18. The phase modifying element 18 has an input surface (x, y), wherein (x, y) are coordinates of resolution elements or pixels of the phase modifying unit 18, positioned so that the plane light waves 14 are incident upon it, and the phase modifying element 18 is configured for phase modulation of the light waves 14 impinging on the surface at resolution element (x, y) by phasor values _θίφ(λ wherein λ is the wavelength. The phase modifying element 18 may be a spatial light modulator adjusted to provide a predetermined changed optical path length d(x, y) for each resolution element (x, y) resulting in different phasor values _eid(x,y) for different wavelengths of light passing though the resolution element (x, y) in question.

[0138] The electromagnetic waves 14 propagate through the phase modifying element 18 and a Fourier transforming lens 20. The phase modifying element 18 is positioned in the front focal plane of the lens 20 so that the electromagnetic field exiting the phase modifying element 18 is Fourier transformed at the back focal plane of the lens 20.

[0139] The Fourier transforming lens 20 is combined with a first dispersing element 30 for combined dispersing the phase modulated electromagnetic waves into wavelength dependent propagation paths so that the red, green, and blue light of the electromagnetic waves are focussed onto different focus regions in the Fourier plane of the lens 20.

[0140] A spatial phase filter 22 is positioned with its surface S at the back focal plane, i.e. the Fourier plane, of the lens 20 with a layout 22a of phase shifting regions 22R, 22G, 22B positioned at respective focus regions of the respective red, green, and blue light waves that have been phase modulated. In Fig. 6, the phase shifting regions 22R, 22G, 22B form a linear array; however, the combined Fourier transforming lens 20 and first dispersing element 30 may disperse the electromagnetic waves so that the phase shifting regions form a two-dimensional array.

[0141] At the phase shifting regions 22R, 22G, 22B, the spatial phase filter is configured for phase shifting the respective focussed red, green, and blue light waves by predetermined respective phase shift values θ(λ, x^s, y^s) with relation to the remaining part of the respective Fourier transformed light waves outside the respective phase shifting regions 22R, 22G, 22B. (X^s, y^s) are coordinates of the surface S of the spatial phase filter 22. In the illustrated example, the optical path length through the phase shifting regions 22_R, 22_G, 22_B is different for the different wavelengths λ of the red, green and blue light waves impinging at the respective phase shifting region with the respective optical path length, e.g. resulting in the same phase shift Θ for all three wavelengths. However, any value may be selected independently for each of the wavelengths.

[0142] The position, shape, and area of each of the phase shifting regions 22R, 22G, 22B of the spatial phase filter is fitted to the position, shape, and area of the respective focus regions of the focussed red, green, and blue light waves so that the focussed red, green, and blue light waves illuminate the respective phase shifting region 22R, 22G, 22B and are phase shifted with the desired phase shift values θ(λ, x^s, y^s) with relation to the remaining part of the electromagnetic waves (not shown) propagating through the illustrated GPC system 10. Preferably, each of the phase shifting regions 22R, 22G, 22B of the spatial phase filter coincides with the respective focus region.

[0143] If the phase shifting regions 22_R, 22_G, 22_B do not match the geometry of the respective focus regions, artefacts in the synthesized intensity pattern l(x', y') may result. If the phase shifting region is larger than the corresponding focus region, part of the light that is not part of the focussed electromagnetic waves is also phase shifted resulting in artefacts in the synthesized intensity pattern, and if the phase shifting region is smaller than the corresponding focus region, part of the focussed electromagnetic waves is not phase shifted as desired also resulting in artefacts in the synthesized intensity pattern.

[0144] The spatial phase filter 22 with layout 22a is positioned in the back focal plane of the lens 20 that is also the front focal plane of a second Fourier transforming lens 26. The Fourier transforming lenses 20, 26 need not have identical focal lengths. Different focal lengths lead to a magnification ratio different from one.

[0145] An intensity pattern I (λ, χ', y') is generated in the back focal plane 28 of the lens 26 as a result of the Fourier transformation of the electromagnetic field exiting the spatial phase filter 22. Due to the wavelength dispersion by the dispersing element 30, the intensity patterns I (λ, χ', y') formed at the back focal plane 28 are displaced with relation to each other as a function of the wavelength λ; however, this may be compensated optically or electronically or by a combination of optical and electronic compensation. In the illustrated example, the second Fourier transforming lens 26 is combined with a second dispersing element 32, e.g. a grating, for compensation of the dispersion of the first dispersing element 30 so that the intensity patterns formed by the light of the red, green, and blue light waves coincide, or substantially coincide. Alternatively, or in combination, an optional imaging system (not shown) may capture the synthesized intensity patterns Ι(λ, χ', y') and may be configured to electronically displace the respective intensity patterns so that the intensity patterns formed by the red, green and blue light waves coincide, or substantially coincide, e.g. in a computer (not shown), and output the combined intensity pattern l(x', y') for display to the user and for possible automatic adjustment.

[0146] The illustrated system 10 may be controlled by a computer (not shown) comprising interface means for addressing each of the resolution elements of the phase modifying and dispersing element 18 and transmitting a phasor value e'^*^ to the addressed resolution element (x, y). Further, the computer may comprise control means for controlling the output of the source 12. The computer may also comprise input means, such as a keyboard, a mouse, a diskette drive, an optical disc drive, a network interface, a modem, etc., for receiving an image pattern to be synthesized by the system 10. From the received image pattern, the computer may be adapted to calculate phasor values to be transmitted to the resolution elements (x, y) of the phase modifying and dispersing element 18, e. g. based on a histogram technique as is well-known in the art of GPC-systems.

[0147] Optionally, the phase shifts of the spatial phase filter 22 may be adjustable and controllable by optional phase control means of the computer, which may be further adapted to adjust the phase shift. An optional imaging system may capture the synthesized intensity pattern l(x', y') and transmit it to the computer (not shown) for display to the user and for possible automatic adjustment.

[0148] Fig. 7 schematically illustrates an exemplary new GPC system 10 in a 4f common path interferometer configuration, wherein, apart from the fact that a source 12 of electromagnetic waves 14 is arranged so that electromagnetic waves 14 with different wavelengths λ propagate along respective different propagation paths through the generalized phase contrast system 10 and illuminate respective different phase shifting regions (x^s, y^s) of a surface S of a spatial phase filter 22, the main components a) - e) of the new GPC system 10 are positioned in the same way with relation to each other as in a conventional 4f phase contrast imaging system.

[0149] A multi-wavelength point source constitutes the source of electromagnetic waves. In the illustrated example, the multi-wavelength point source is formed by an optical fibre transmitting visible substantially white light with a continuous spectrum including red light, green light, and blue light, and emitting the light from its end surface.

[0150] The emitted white light is collimated by lens 16 into plane light waves 14 directed towards a phase modifying element 18. The phase modifying element 18 has an input surface (x, y), wherein (x, y) are coordinates of resolution elements or pixels of the phase modifying unit 18, positioned so that the plane light waves 14 are incident upon it, and the phase modifying element 18 is configured for phase modulation of the light waves 14 impinging on the surface at resolution element (x, y) by phasor values e'^*^, wherein λ is the wavelength. The phase modifying element 18 may be a spatial light modulator adjusted to provide a predetermined changed optical path length d(x, y) for each resolution element (x, y) resulting in different phasor values e^id<^x y^)M for different wavelengths of light passing though the resolution element (x, y) in question.

[0151] The electromagnetic waves 14 propagate through the phase modifying element 18 and a Fourier transforming lens 20. The phase modifying element 18 is positioned in the front focal plane of the lens 20 so that the electromagnetic field exiting the phase modifying element 18 is Fourier transformed at the back focal plane of the lens 20.

[0152] The Fourier transforming lens 20 is combined with a first dispersing element 30 for combined dispersing the phase modulated light waves into wavelength dependent propagation paths so that the light waves are focussed onto different focus regions in the Fourier plane of the lens 20 in dependence of the wavelength λ.

[0153] A spatial phase filter 22 is positioned with its surface S at the back focal plane, i.e. the Fourier plane, of the lens 20 with a layout 22a of overlapping phase shifting regions forming a continuous tapered phase shifting region including phase shifting regions 22R, 22G, 22B positioned at respective focus regions of the focussed light waves with red, green and blue wavelengths, respectively. The width of the continuous tapered phase shifting region increases with increased wavelength of light incident upon it. In Fig. 7, the phase shifting regions form a tapered region; however, the Fourier lens 20 and dispersing element 30 may be configured to disperse the electromagnetic waves so that the phase shifting regions form another arbitrary two- dimensional shape.

[0154] At the phase shifting regions, e.g. 22R, 22G, 22B, the spatial phase filter is configured for phase shifting the respective focussed electromagnetic waves by predetermined respective phase shift values θ(λ, x^s, y^s) with relation to the remaining part of the respective Fourier transformed light waves outside the tapered continuous phase shifting region. (x^s, y^s) are coordinates of the surface S of the spatial phase filter 22. In the illustrated example, the optical path length through the phase shifting regions, e.g. 22R, 22G, 22B, increases with increased wavelength λ of the focussed light waves impinging at the respective area of the phase shifting region with the respective optical path length, e.g. resulting in the same phase shift Θ for all wavelengths. However, any variation of the optical path length as a function of the wavelength λ may be selected.

[0155] The position, shape, and area of each of the phase shifting regions, e.g. 22_R, 22_G, 22B, of the spatial phase filter is fitted to the position, shape, and area of the respective focus regions of the focussed light waves so that the focussed light waves illuminate the respective phase shifting regions, e.g. 22R, 22G, 22B, and are phase shifted with the desired phase shift values θ(λ, x^s, y^s) with relation to the remaining part of the electromagnetic waves (not shown) propagating through the illustrated GPC system 10. Preferably, each of the phase shifting regions, e.g. 22R, 22G, 22B, of the spatial phase filter coincides with the respective focus region.

[0156] If the phase shifting regions, e.g. 22R, 22G, 22B, do not match the geometry of the respective focus regions, artefacts in the synthesized intensity pattern l(x', y') may result. If the phase shifting region is larger than the corresponding focus region, part of the light that is not part of the focussed electromagnetic waves is also phase shifted resulting in artefacts in the synthesized intensity pattern, and if the phase shifting region is smaller than the corresponding focus region, part of the focussed electromagnetic waves is not phase shifted as desired also resulting in artefacts in the synthesized intensity pattern.

[0157] The spatial phase filter 22 with layout 22a is positioned in the back focal plane of the lens 20 that is also the front focal plane of a second Fourier transforming lens 26. The Fourier transforming lenses 20, 26 need not have identical focal lengths. Different focal lengths lead to a magnification ratio different from one.

[0158] An intensity pattern I (λ, χ', y') is generated in the back focal plane 28 of the lens 26 as a result of the Fourier transformation of the electromagnetic field exiting the spatial phase filter 22. Due to the wavelength dispersion by the first dispersing element 30, the intensity patterns I (λ, χ', y') formed at the back focal plane 28 are displaced with relation to each other as a function of the wavelength λ; however, this may be compensated optically or electronically or by a combination of optical and electronic compensation. In the illustrated example, the second Fourier transforming lens 26 is combined with a second dispersing element 32, e.g. a grating, for compensation of the dispersion of the first dispersing element 30 so that the intensity patterns formed by the light waves of various wavelengths λ coincide, or substantially coincide. Alternatively, or in combination, an optional imaging system (not shown) may capture the synthesized intensity patterns Ι(λ, χ', y') and may be configured to electronically displace the respective intensity patterns so that the intensity patterns formed by the light waves of various wavelengths λ coincide, or substantially coincide, e.g. in a computer (not shown), and output the combined intensity pattern l(x', y') for display to the user and for possible automatic adjustment.

[0159] The illustrated system 10 may be controlled by a computer (not shown) comprising interface means for addressing each of the resolution elements of the phase modifying and dispersing element 18 and transmitting a phasor value e'^*^ to the addressed resolution element (x, y). Further, the computer may comprise control means for controlling the output of the source 12. The computer may also comprise input means, such as a keyboard, a mouse, a diskette drive, an optical disc drive, a network interface, a modem, etc., for receiving an image pattern to be synthesized by the system 10. From the received image pattern, the computer may be adapted to calculate phasor values to be transmitted to the resolution elements (x, y) of the phase modifying and dispersing element 18, e. g. based on a histogram technique as is well-known in the art of GPC-systems.

[0160] Optionally, the phase shifts of the spatial phase filter 22 may be adjustable and controllable by optional phase control means of the computer, which may be further adapted to adjust the phase shift. An optional imaging system may capture the synthesized intensity pattern l(x', y') and transmit it to the computer (not shown) for display to the user and for possible automatic adjustment.

[0161] Fig. 8 schematically illustrates an exemplary new GPC system 10 in a 4f common path interferometer configuration, wherein, apart from the fact that a source 12 of electromagnetic waves 14 is arranged so that electromagnetic waves 14 with different wavelengths λ propagate along respective different propagation paths through the generalized phase contrast system 10 and illuminate respective different phase shifting regions (x^s, y^s) of a surface S of a spatial phase filter 22, the main components a) - e) of the new GPC system 10 are positioned in the same way with relation to each other as in a conventional 4f phase contrast imaging system.

[0162] A point source of electromagnetic waves 12 emits red light, green light, and blue light. The emitted light is collimated by lens 16 into plane light waves 14 directed towards a phase modifying element 18. The phase modifying element 18 has an input surface (x, y), wherein (x, y) are coordinates of resolution elements or pixels of the phase modifying unit 18, positioned so that the plane light waves 14 are incident upon it, and the phase modifying element 18 is configured for phase modulation of the light wave 14 impinging on the surface at resolution element (x, y) by phasor values

wherein λ is the wavelength. The phase modifying element 18 may be a spatial light modulator adjusted to provide a predetermined changed optical path length d(x, y) for each resolution element (x, y) resulting in different phasor values _eid(x,y) for different wavelengths of light passing though the resolution element (x, y) in question.

[0163] The light waves 14 propagate through the phase modifying element 18 towards a first dispersing element constituted by a diffraction grating 30. The diffraction grating 30 disperses the phase modulated light waves into wavelength dependent propagation paths as indicated for the red light 14R, the green light 14G, and the blue light 14B, SO that light waves with different wavelengths propagate along different propagation paths upon interaction with the diffraction grating 30.

[0164] The dispersed light waves 14_R, 14_G, 14_B propagate towards a Fourier transforming lens 20. The phase modifying element 18 is positioned in the front focal plane of the lens 20 as defined by the lens 20 in combination with the diffraction grating 30. The Fourier transforming lens 20 refracts the non-scattered parts of the light waves 14R, 14G, 14B into converging waves 24R, 24G, 24B. The phase modifying element 18 is positioned in the front focal plane of the lens 20 so that the

electromagnetic field exiting the phase modifying element 18 is Fourier transformed at the back focal plane of the lens 20.

[0165] A spatial phase filter 22 is positioned with its surface S at the back focal plane, i.e. the Fourier plane, of the lens 20 with a layout 22a of phase shifting regions 22R, 22G, 22B positioned at respective focus regions of the respective light waves 24R, 24G, 24B. In Fig. 8, the phase shifting regions 22R, 22G, 22B form a linear array;

however, the dispersing element 30 may also be configured so that the phase shifting regions form a two-dimensional array.

[0166] At the phase shifting regions 22R, 22G, 22B, the spatial phase filter is configured for phase shifting the respective focussed electromagnetic waves 24R, 24G, 24B by predetermined respective phase shift values θ(λ, x^s, y^s) with relation to the remaining part of the respective Fourier transformed light waves outside the respective phase shifting regions 22R, 22G, 22B. (X^s, y^s) are coordinates of the surface S of the spatial phase filter 22. In the illustrated example, the optical path length through the phase shifting regions 22_R, 22_G, 22_B is different for the different wavelengths λ of the red, green and blue light waves impinging at the respective phase shifting region with the respective optical path length, e.g. resulting in the same phase shift Θ for all three wavelengths. However, any value may be selected independently for each of the wavelengths.

[0167] The position, shape, and area of each of the phase shifting regions 22R, 22G, 22B of the spatial phase filter is fitted to the position, shape, and area of the respective focus regions of the focussed electromagnetic waves 24_R, 24_G, 24_B so that the focussed electromagnetic waves 24R, 24G, 24B illuminate the respective phase shifting region 22R, 22G, 22B and are phase shifted with the desired phase shift values θ(λ, X^s, y^s) with relation to the remaining part of the electromagnetic waves (not shown) propagating through the illustrated GPC system 10. Preferably, each of the phase shifting regions 22R, 22G, 22B of the spatial phase filter coincides with the respective focus region.

[0168] If the phase shifting regions 22_R, 22_G, 22_B do not match the geometry of the respective focus regions, artefacts in the synthesized intensity pattern l(x', y') may result. If the phase shifting region is larger than the corresponding focus region, part of the light that is not part of the focussed electromagnetic waves is also phase shifted resulting in artefacts in the synthesized intensity pattern, and if the phase shifting region is smaller than the corresponding focus region, part of the focussed electromagnetic waves is not phase shifted as desired also resulting in artefacts in the synthesized intensity pattern.

[0169] The spatial phase filter 22 with layout 22a is positioned in the back focal plane of the lens 20 that is also the front focal plane of a second Fourier transforming lens 26. The Fourier transforming lenses 20, 26 need not have identical focal lengths. Different focal lengths lead to a magnification ratio different from one.

[0170] An intensity pattern I (λ, χ', y') is generated in the back focal plane 28 of the lens 26 as a result of the Fourier transformation of the electromagnetic field exiting the spatial phase filter 22. Due to the wavelength dispersion by the diffraction grating 30, the intensity patterns formed by the red, green, and blue light are displaced with relation to each other; however, this may be compensated optically or electronically or by a combination of optical and electronic compensation. In the illustrated example, a second dispersing element 32, e.g. a second grating, is provided for compensation of the dispersion of the first dispersing element 30 so that the intensity patterns formed by the red, green, and blue light coincide. Alternatively, or in combination, an optional imaging system (not shown) may capture the synthesized intensity patterns Ι(λ, χ', y') and may be configured to electronically displace the respective intensity patterns so that the intensity patterns formed by the red, green, and blue light coincide, e.g. in a computer (not shown), and output the combined intensity pattern l(x', y') for display to the user and for possible automatic adjustment.

[0171] The illustrated system 10 may be controlled by a computer (not shown) comprising interface means for addressing each of the resolution elements of the phase modifying element 18 and transmitting a phasor value e'^ y⁾ to the addressed resolution element (x, y). Further, the computer may comprise control means for controlling the output of the source 12. The computer may also comprise input means, such as a keyboard, a mouse, a diskette drive, an optical disc drive, a network interface, a modem, etc., for receiving an image pattern to be synthesized by the system 10. From the received image pattern, the computer may be adapted to calculate phasor values to be transmitted to the resolution elements (x, y) of the phase modifying element 18, e. g. based on a histogram technique as is well-known in the art of GPC-systems.

[0172] Optionally, the phase shifts of the spatial phase filter 22 may be adjustable and controllable by optional phase control means of the computer, which may be further adapted to adjust the phase shift. An optional imaging system may capture the synthesized intensity pattern l(x', y') and transmit it to the computer (not shown) for display to the user and for possible automatic adjustment.

[0173] Fig. 9 schematically illustrates an exemplary new GPC system 10 in a 4f common path interferometer configuration, wherein, apart from the fact that a source 12 of electromagnetic waves 14 is arranged so that electromagnetic waves 14 with different wavelengths λ propagate along respective different propagation paths through the generalized phase contrast system 10 and illuminate respective different phase shifting regions (x^s, y^s) of a surface S of a spatial phase filter 22, the main components a) - e) of the new GPC system 10 are positioned in the same way with relation to each other as in a conventional 4f phase contrast imaging system.

Obviously, the function of the illustrated GPC system 10 may also be obtained with a system wherein the main components a) - e) of the new GPC system 10 are positioned in the same way with relation to each other as in a conventional 2f phase contrast imaging system; or, as in a conventional 1f phase contrast imaging system. [0174] A source of electromagnetic waves 12 emits visible substantially white light with a continuous spectrum including red light, green light, and blue light. The emitted white light is collimated by lens 16 into plane light waves 14 directed towards a phase modifying element 18. The phase modifying element 18 has an input surface (x, y), wherein (x, y) are coordinates of resolution elements or pixels of the phase modifying unit 18, positioned so that the plane light waves 14 are incident upon it, and the phase modifying element 18 is configured for phase modulation of the light wave 14 impinging on the surface at resolution element (x, y) by phasor values e'^*^, wherein λ is the wavelength. The phase modifying element 18 may be a spatial light modulator adjusted to provide a predetermined changed optical path length d(x, y) for each resolution element (x, y) resulting in different phasor values e^id<^{x y)A} for different wavelengths of light passing though the resolution element (x, y) in question.

[0175] The light waves 14 propagate through the phase modifying element 18 towards a first dispersing element constituted by a diffraction grating 30. The diffraction grating 30 disperses the phase modulated light waves into wavelength dependent propagation paths as indicated for the red light 14_R, the green light 14_G, and the blue light 14B, SO that light waves with different wavelengths propagate along different propagation paths upon interaction with the diffraction grating 30. The white light waves 14 contains all the wavelengths of the visible spectrum; however, for illustration purposes only the dispersed red light waves 14R, the dispersed green light waves14G, and the dispersed blue light waves 14B are shown in Fig. 4.

[0176] The dispersed light waves including the dispersed red light waves 14_R, the dispersed green light waves14_G, and the dispersed blue light waves 14_B, propagate towards a Fourier transforming lens 20. The phase modifying element 18 is positioned in the front focal plane of the lens 20 as defined by the lens 20 in combination with the diffraction grating 30. The Fourier transforming lens 20 refracts the non-scattered parts of the dispersed light waves 14R, 14G, 14B into converging light waves as illustrated for light waves 24R, 24G, 24B of the red, green and blue wavelengths, respectively. The phase modifying element 18 is positioned in the front focal plane of the lens 20 so that the electromagnetic field exiting the phase modifying element 18 is Fourier transformed at the back focal plane of the lens 20.

[0177] A spatial phase filter 22 is positioned with its surface S at the back focal plane, i.e. the Fourier plane, of the lens 20 with a layout 22a of overlapping phase shifting regions forming a continuous tapered phase shifting region including phase shifting regions 22_R, 22_G, 22_B positioned at respective focus regions of the respective focussed light waves 24R, 24G, 24B. The width of the continuous tapered phase shifting region increases with increased wavelength of light incident upon it. In Fig. 9, the phase shifting regions form a tapered region; however, the dispersing element 30 may be configured to disperse the electromagnetic waves so that the phase shifting regions form another arbitrary two-dimensional shape.

[0178] At the phase shifting regions, e.g. 22R, 22G, 22B, the spatial phase filter is configured for phase shifting the respective focussed electromagnetic waves, e.g. 24R, 24G, 24B, by predetermined respective phase shift values θ(λ, x^s, y^s) with relation to the remaining part of the respective Fourier transformed light waves outside the tapered continuous phase shifting region. (x^s, y^s) are coordinates of the surface S of the spatial phase filter 22. In the illustrated example, the optical path length through the phase shifting regions 22R, 22G, 22B increases with increased wavelength λ of the focussed light waves impinging at the respective area of the phase shifting region with the respective optical path length, e.g. resulting in the same phase shift Θ for all wavelengths. However, any variation of the optical path length as a function of the wavelength λ may be selected.

[0179] The position, shape, and area of each of the phase shifting (overlapping) regions, e.g. 22R, 22G, 22B, of the spatial phase filter 22 is fitted to the position, shape, and area of the respective focus regions of the focussed light waves 24R, 24G, 24B SO that the focussed light waves 24R, 24G, 24B illuminate the respective phase shifting region 22R, 22G, 22B and are phase shifted with the desired phase shift values θ(λ, x^s, y^s) with relation to the remaining part of the light waves (not shown) propagating through the illustrated GPC system 10. Preferably, each of the phase shifting regions, e.g. 22R, 22G, 22B, of the spatial phase filter coincides with the respective focus region.

[0180] If the phase shifting regions, e.g. 22R, 22G, 22B, do not match the geometry of the respective focus regions, artefacts in the synthesized intensity pattern l(x', y') may result. If the phase shifting region is larger than the corresponding focus region, part of the light that is not part of the focussed electromagnetic waves is also phase shifted resulting in artefacts in the synthesized intensity pattern, and if the phase shifting region is smaller than the corresponding focus region, part of the focussed electromagnetic waves is not phase shifted as desired also resulting in artefacts in the synthesized intensity pattern.

[0181] The spatial phase filter 22 with layout 22a is positioned in the back focal plane of the lens 20 that is also the front focal plane of a second Fourier transforming lens 26. The Fourier transforming lenses 20, 26 need not have identical focal lengths. Different focal lengths lead to a magnification ratio different from one.

[0182] An intensity pattern I (λ, χ', y') is generated in the back focal plane 28 of the lens 26 as a result of the Fourier transformation of the electromagnetic field exiting the spatial phase filter 22. Due to the wavelength dispersion by the diffraction grating 30, the intensity patterns I (λ, χ', y') formed at the back focal plane 28 are displaced with relation to each other as a function of the wavelength λ; however, this may be compensated optically or electronically or by a combination of optical and electronic compensation. In the illustrated example, a second dispersing element 32, e.g. a second diffraction grating, is provided for compensation of the dispersion of the first dispersing element 30 so that the intensity patterns formed by the light of all the wavelengths coincide, or substantially coincide. Alternatively, or in combination, an optional imaging system (not shown) may capture the synthesized intensity patterns l( λ, χ', y') and may be configured to electronically displace the respective intensity patterns so that the intensity patterns formed by the light of all the wavelengths coincide, or substantially coincide, e.g. in a computer (not shown), and output the combined intensity pattern l(x', y') for display to the user and for possible automatic adjustment.

[0183] The illustrated system 10 may be controlled by a computer (not shown) comprising interface means for addressing each of the resolution elements of the phase modifying element 18 and transmitting a phasor value e'^ y⁾ to the addressed resolution element (x, y). Further, the computer may comprise control means for controlling the output of the source 12. The computer may also comprise input means, such as a keyboard, a mouse, a diskette drive, an optical disc drive, a network interface, a modem, etc., for receiving an image pattern to be synthesized by the system 10. From the received image pattern, the computer may be adapted to calculate phasor values to be transmitted to the resolution elements (x, y) of the phase modifying element 18, e. g. based on a histogram technique as is well-known in the art of GPC-systems.

[0184] Optionally, the phase shifts of the spatial phase filter 22 may be adjustable and controllable by optional phase control means of the computer, which may be further adapted to adjust the phase shift. An optional imaging system may capture the synthesized intensity pattern l(x', y') and transmit it to the computer (not shown) for display to the user and for possible automatic adjustment. [0185] Fig. 10 schematically illustrates an exemplary new GPC system 10 in a 4f common path interferometer configuration, wherein, apart from the fact that a source 12 of electromagnetic waves 14 is arranged so that electromagnetic waves 14 with different wavelengths λ propagate along respective different propagation paths through the generalized phase contrast system 10 and illuminate respective different phase shifting regions (x^s, y^s) of a surface S of a spatial phase filter 22, the main components a) - e) of the new GPC system 10 are positioned in the same way with relation to each other as in a conventional 4f phase contrast imaging system.

[0186] The illustrated GPC system 10 is particularly well suited for multi-photon fluorescence microscopy, including two-photon excitation microscopy. The source of electromagnetic waves 12 is a femto-second pulsed laser wherein the short duration of the pulses of emitted electromagnetic waves broadens the spectrum of the longitudinal mode(s) of the laser. The multi-photon excitation technique is widely applied in the biological imaging and micro-fabrication fields. With its superior axial sectioning capability and long excitation wavelength, MPE results in lower photo- bleaching and minimum invasiveness, and is, therefore, particularly suitable for imaging thick tissues. Further, with the two-photon absorption confined to the focal volume, multi-photon excitation provides an ideal solution for the fabrication of high- precision microstructures. Further, multi-photon excitation with temporal focusing can generate wide-field and axially resolved excitation on a plane-by-plane basis.

Recombination of the femto-pulsed dispersed and monochromatic electromagnetic waves, preferably in the infrared wavelength range, at the front focal plane of an objective lens produces a short, high-peak power pulse in the focal plane, whereby multi-photon excitation is provided simultaneously over an area in the focal plane.

[0187] The emitted electromagnetic waves are collimated by lens 16 into plane electromagnetic waves 14 directed towards a phase modifying element 18. The phase modifying element 18 has an input surface (x, y), wherein (x, y) are coordinates of resolution elements or pixels of the phase modifying element 18, positioned so that the plane electromagnetic waves 14 are incident upon it, and the phase modifying element 18 is configured for phase modulation of the

electromagnetic waves14 impinging on the surface at resolution element (x, y) by phasor values e'^^Kx^ wherein λ is the wavelength. The phase modifying element 18 may be a spatial light modulator adjusted to provide a predetermined changed optical path length d(x, y) for each resolution element (x, y) resulting in different phasor values e^id<^{x y)M} for different wavelengths of electromagnetic waves passing though the resolution element (x, y) in question.

[0188] The electromagnetic waves 14 propagate through the phase modifying element 18 towards the dispersing element constituted by the ruled grating 30. The ruled grating 30 disperses the electromagnetic waves 14 into wavelength dependent propagation paths as indicated by electromagnetic waves 14i, 14₂, 14₃ (in the order of decreasing wavelength), so that electromagnetic waves with different wavelengths propagate along different propagation paths upon interaction with the ruled grating 30.

[0189] The dispersed electromagnetic waves 14i, 142, 143 propagate towards a Fourier transforming lens 20. The phase modifying element 18 is positioned in the front focal plane of the lens 20 as defined by the lens 20 in combination with the ruled grating 30. The Fourier transforming lens 20 refracts the non-scattered parts of the dispersed electromagnetic waves, e.g. as illustrated for electromagnetic waves 14i, 142, 143 into converging electromagnetic waves, e.g. as illustrated for electromagnetic waves 24i, 242, 243. The phase modifying element 18 is positioned in the front focal plane of the lens 20 so that the electromagnetic field exiting the phase modifying element 18 is Fourier transformed at the back focal plane of the lens 20.

[0190] A spatial phase filter 22 is positioned with its surface S at the back focal plane, i.e. the Fourier plane, of the lens 20 with a layout 22a of overlapping phase shifting regions forming a continuous tapered phase shifting region including phase shifting regions 22i , 222, 223 positioned at respective focus regions of the respective electromagnetic focussed electromagnetic waves 24i, 242, 243 that have been phase modulated. The width of the continuous tapered phase shifting region increases with increased wavelength of electromagnetic waves incident upon it. The dimensions of the tapered phase shifting region are in the order of

μηη. In Fig. 10, the phase shifting regions form a tapered region; however, the dispersing element 30 may be configured to disperse the electromagnetic waves so that the phase shifting regions form another arbitrary two-dimensional shape.

[0191] At the phase shifting regions, e.g. 22i, 222, 223, the spatial phase filter is configured for phase shifting the respective focussed electromagnetic waves, e.g. 24ι , 242, 243, by predetermined respective phase shift values θ(λ, x^s, y^s) with relation to the remaining part of the respective Fourier transformed electromagnetic waves outside the tapered continuous phase shifting region. (x^s, y^s) are coordinates of the surface S of the spatial phase filter 22. In the illustrated example, the optical path length through the phase shifting regions 22i , 222, 223 increases with increased wavelength λ of the focussed electromagnetic waves impinging at the respective area of the phase shifting region with the respective optical path length, e.g. resulting in the same phase shift Θ for all wavelengths. However, any variation of the optical path length as a function of the wavelength λ may be selected.

[0192] The position, shape, and area of each of the phase shifting (overlapping) regions, e.g. 22i , 222, 223, of the spatial phase filter 22 is fitted to the position, shape, and area of the respective focus regions of the focussed electromagnetic waves, e.g. 24i , 242, 243 so that the focussed electromagnetic waves 24i , 242, 243 illuminate the respective phase shifting region 22i , 222, 223 and are phase shifted with the desired phase shift values θ(λ, x^s, y^s) with relation to the remaining part of the

electromagnetic waves (not shown) propagating through the illustrated GPC system 10. Preferably, each of the phase shifting regions, e.g. 22i , 222, 223, of the spatial phase filter coincides with the respective focus region.

[0193] If the phase shifting regions, e.g. 22i , 222, 223, do not match the geometry of the respective focus regions, artefacts in the synthesized intensity pattern l(x', y') may result. If the phase shifting region is larger than the corresponding focus region, part of the electromagnetic waves that is not part of the focussed electromagnetic waves is also phase shifted resulting in artefacts in the synthesized intensity pattern, and if the phase shifting region is smaller than the corresponding focus region, part of the focussed electromagnetic waves is not phase shifted as desired also resulting in artefacts in the synthesized intensity pattern.

[0194] The spatial phase filter 22 with layout 22a is positioned in the back focal plane of the lens 20 that is also the front focal plane of a second Fourier transforming lens 26. The Fourier transforming lenses 20, 26 need not have identical focal lengths. Different focal lengths lead to a magnification ratio different from one.

[0195] An intensity pattern I (λ, χ', y') is generated in the back focal plane 28 of the lens 26 as a result of the Fourier transformation of the electromagnetic field exiting the spatial phase filter 22. Due to the wavelength dispersion by the diffraction grating 30, the intensity patterns I (λ, χ', y') formed at the back focal plane 28 are displaced with relation to each other as a function of the wavelength λ; however, this may be compensated optically or electronically or by a combination of optical and electronic compensation. In the illustrated example, a second dispersing element 32, e.g. a second diffraction grating, is provided for compensation of the dispersion of the first dispersing element 30 so that the intensity patterns formed by the electromagnetic waves of all the wavelengths coincide, or substantially coincide. Alternatively, or in combination, an optional imaging system (not shown) may capture the synthesized intensity patterns Ι(λ, χ', y') and may be configured to electronically displace the respective intensity patterns so that the intensity patterns formed by the

electromagnetic waves of all the wavelengths coincide, or substantially coincide, e.g. in a computer (not shown), and output the combined intensity pattern l(x', y') for display to the user and for possible automatic adjustment.

[0196] The illustrated system 10 may be controlled by a computer (not shown) comprising interface means for addressing each of the resolution elements of the phase modifying element 18 and transmitting a phasor value e'^^y) to the addressed resolution element (x, y). Further, the computer may comprise control means for controlling the output of the source 12. The computer may also comprise input means, such as a keyboard, a mouse, a diskette drive, an optical disc drive, a network interface, a modem, etc., for receiving an image pattern to be synthesized by the system 10. From the received image pattern, the computer may be adapted to calculate phasor values to be transmitted to the resolution elements (x, y) of the phase modifying element 18, e. g. based on a histogram technique as is well-known in the art of GPC-systems.

[0197] Optionally, the phase shifts of the spatial phase filter 22 may be adjustable and controllable by optional phase control means of the computer, which may be further adapted to adjust the phase shift. An optional imaging system may capture the synthesized intensity pattern l(x', y') and transmit it to the computer (not shown) for display to the user and for possible automatic adjustment.

Claims

A generalized phase contrast system comprising

a) a source of electromagnetic waves for emission of electromagnetic waves with a plurality of wavelengths λ,

c) first Fourier or Fresnel optics positioned so that the phase modulated

electromagnetic waves are incident upon it and configured for Fourier or Fresnel transforming the phase modulated electromagnetic waves, d) a spatial phase filter with a surface S positioned at a Fourier or Fresnel plane of the first Fourier or Fresnel optics, respectively, and having phase shifting regions (x^s, y^s) configured for phase shifting Fourier or Fresnel transformed electromagnetic waves incident on the respective phase shifting regions (x^s, y^s) by predetermined respective phase shift values θ(λ, X^s, y^s) with relation to the remaining part of the respective Fourier or Fresnel transformed electromagnetic waves incident on parts of the surface S without a phase shifting region, and

e) second Fourier or Fresnel optics positioned so that the spatial phase filter is positioned at a Fourier or Fresnel plane of the second Fourier or Fresnel optics, respectively, and configured for forming the intensity pattern I (λ, χ', y') by Fourier or Fresnel transforming the Fourier or Fresnel transformed electromagnetic waves,

c h a r a c t e r i z e d in that

f) the source of electromagnetic waves is arranged so that electromagnetic waves with different wavelengths λ propagate along respective different propagation paths through the generalized phase contrast system and illuminate respective different phase shifting regions (x^s, y^s) of the surface S of the spatial phase filter.

A generalized phase contrast system according to claim 1 , wherein at least one of the phase shifting regions (x^s, y^s) substantially coincides with a region of the surface S that is illuminated by a focussed part of the phase modulated electromagnetic waves with a specific wavelength λ.

3. A generalized phase contrast system according to claim 1 or 2, wherein the

source of electromagnetic waves comprises an assembly of individually positioned sources, wherein at least two of the sources emit electromagnetic waves with spectra with different centre wavelengths.

4. A generalized phase contrast system according to any of the previous claims, comprising a supercontinuum laser.

5. A generalized phase contrast system according to any of the previous claims, comprising an ultrafast pulsed laser.

6. A generalized phase contrast system according to any of the previous claims, comprising a first dispersing element positioned so that the electromagnetic waves are incident upon it and configured for dispersing the electromagnetic waves into wavelength dependent propagation paths.

7. A generalized phase contrast system according to any of the previous claims, wherein the phase modulating element comprises a regular grating divided into regions with continuous grating lines and wherein at least one region has grating lines that are displaced with relation to the grating lines of at least one

neighbouring region so that broken grating lines are provided along the border between the respective regions and electromagnetic waves incident on the respective regions are phase shifted with respect to each other with an amount that is substantially independent of the wavelength λ of the electromagnetic waves.

8. A generalized phase contrast system according to claim 7, wherein the phase modulating element with the grating is divided into pixels with continuous grating lines and wherein at least one pixel has grating lines that are displaced with relation to the grating lines of at least one neighbouring pixel.

9. A generalized phase contrast system according to any of the previous claims, comprising a second dispersing element configured for compensating the dispersion performed by the first dispersing element so that intensity patterns I (λ, χ', y') of different wavelengths λ substantially coincides.

10. A generalized phase contrast system according to any of the previous claims, comprising a controller having a first output that is connected to an input of the phase modifying element and a second output that is connected to an input of the spatial phase filter, and wherein the controller is configured for adjusting phasor values e'^ y⁾ of the phase modifying element and phase shift values θ(λ) of the spatial phase filter.

1 1. A multi-photon fluorescence microscope comprising a generalized phase contrast system according to any of the previous claims.

12. A cinema laser projector comprising a generalized phase contrast system

according of claims 1 - 10.

13. A wavelength-division multiplexing communication system comprising a

generalized phase contrast system according to any of claims 1 - 10.

14. An endoscope comprising a generalized phase contrast system according to any of claims 1 - 10.

15. A super resolution microscope comprising a generalized phase contrast system according to any of claims 1 - 10.

16. A method comprising the steps of

a) emitting electromagnetic waves with a plurality of wavelengths λ,

b) phase modulating the electromagnetic waves by phasor values

θίφ(λ,χ,γ)_ι c) Fourier or Fresnel transforming the phase modulated electromagnetic waves, d) phase shifting parts of the Fourier or Fresnel transformed electromagnetic waves with different wavelengths λ incident on different respective phase shifting regions (x^s, y^s) by predetermined respective phase shift values θ(λ, X^s, y^s) with relation to the remaining part of the respective Fourier or Fresnel transformed electromagnetic waves, and e) forming an intensity pattern I (λ, χ', y') by Fourier or Fresnel transforming the respective phase shifted Fourier or Fresnel transformed electromagnetic waves,

c h a r a c t e r i z e d in f) propagating electromagnetic waves with different wavelengths λ along

respective different propagation paths thereby illuminating respective different phase shifting regions (x^s, y^s).