WO2004031838A1 - Device for reducing the coherence of a beam of light - Google Patents
Device for reducing the coherence of a beam of light Download PDFInfo
- Publication number
- WO2004031838A1 WO2004031838A1 PCT/EP2003/010075 EP0310075W WO2004031838A1 WO 2004031838 A1 WO2004031838 A1 WO 2004031838A1 EP 0310075 W EP0310075 W EP 0310075W WO 2004031838 A1 WO2004031838 A1 WO 2004031838A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- beam splitter
- arrangement according
- light beam
- incident light
- radiation
- Prior art date
Links
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/10—Beam splitting or combining systems
- G02B27/14—Beam splitting or combining systems operating by reflection only
- G02B27/144—Beam splitting or combining systems operating by reflection only using partially transparent surfaces without spectral selectivity
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/10—Beam splitting or combining systems
- G02B27/14—Beam splitting or combining systems operating by reflection only
- G02B27/143—Beam splitting or combining systems operating by reflection only using macroscopically faceted or segmented reflective surfaces
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/48—Laser speckle optics
Definitions
- the invention relates to an arrangement for reducing the coherence of a light beam, in particular a laser light beam for illuminating an image area or a sample.
- Light bundles are used to illuminate the sample in a microscope or to display light images on picture walls. Due to the relatively high temporal and spatial coherence of the laser light, interferences occur, which the observer perceives as different luminance levels or as annoying glitter. Such lighting structures are often referred to as "speckle".
- DE 195 01 525 C2 describes a method which is used to reduce the temporal coherence of the laser light. It is provided that the light be passed through an optical plate which has a microstructured, phase-shifting radiation or radiation surface or to direct the light onto a plate, which is provided with such a surface structure and has a reflective effect.
- the disadvantage here is that, due to the relatively large individual reflectors compared to the wavelength of the light, shadowing occurs, which results in an undesired weakening of the radiation intensity.
- honeycomb capacitors are used to implement the different optical path lengths, which have differently thick glass paths in the individual honeycombs, or optical prisms, with different glass paths being specified depending on the position of the prism, the success only occurs with radiation sources whose temporal coherence is relatively low , otherwise considerable glass path differences have to be realized and this is not possible with these means.
- the object of the invention is to find a further possibility for reducing coherence and thus for reducing speckle. the one in which the radiation intensity is weakened as little as possible.
- such an arrangement for reducing the coherence of a light bundle comprises a beam splitter on which an incident light bundle is split into two orthogonal partial bundles, and two reflecting elements, at least one of which is designed as a reversing prism.
- a partial bundle is aimed at a reflecting element and is thrown back from there to the beam splitter.
- the reflecting elements are positioned at different distances from the beam splitter, so that the partial beams pass the beam splitter in the opposite direction again and are combined to form an outgoing light beam.
- the different distances between the beam splitter and the respective reflecting element ensure different optical path lengths of the sub-beams and, to that extent, that the temporal coherence between the two arms is exceeded, so that the interference capability is at least reduced and therefore interference patterns are no longer or only in small, negligible extent.
- the previously interference-capable phase space cells or wave trains are mixed by the inversion to non-interference-capable radiation components.
- both reflecting elements are designed as reversing prisms and are aligned perpendicular to one another, ie they are rotated by 90 ° relative to each other in relation to the direction of radiation of the respective sub-bundle.
- the solution according to the invention is particularly suitable for laser sources whose coherence lengths are greater than 1 mm. This applies to F 2 excimer lasers, such as those used in inspection systems in microlithography.
- the beam splitter advantageously has a division ratio of 50:50, ie the incident light bundle is split into two sub-bundles with essentially the same radiation components.
- the distances measured between the beam splitter and the reflecting elements should differ by at least 14 mm if the F 2 excimer laser is used as the radiation source, so that the temporal coherence between the two arms is exceeded and interference patterns can no longer arise.
- At least one deflection prism is arranged in the beam path of the incident light beam in front of the beam splitter, through which the incident light beam passes before it strikes the beam splitter. Line separation in the light beam is thus achieved, and the variable optical paths over the beam cross section due to the deflection prism lead to a further reduction in coherence.
- a partially reflecting layer can be placed in the beam path of the incident light bundle, which ensures that those coming from the beam splitter are falling light beams, reflected radiation components are directed back onto the beam splitter and thus included in an optical cycle. The light that would have made its way back into the radiation source without this partially reflecting layer is thus used again for the superposition.
- the partially reflecting layer can be formed, for example, on the surface of a glass plate or on the surface of a deflection prism.
- a device for pupil division is provided in the beam path of the incident light bundle, consisting of a mirror which couples a radiation component out of the light bundle, and a telescope through which the remaining, uncoupled radiation component passes, the decoupled radiation component is deflected via further mirrors and finally combined again with the radiation component emerging from the telescope in reverse.
- the two radiation components are now offset from one another by more than the temporal coherence length due to the different optical path lengths, so that the interference capability of the resulting light beam, which now strikes the splitting surface of the beam splitter as an incident light beam, is reduced.
- the radiation source is an F 2 - Excimer laser is concerned, the optical path lengths in turn differ by at least 14 mm.
- a device for homogenizing the radiation intensity can be arranged downstream of the beam splitter, through which the emerging light bundle passes and the principle mode of operation of which can be found in the prior art.
- a device for homogenization can be, for example, a transparent optical element with a microstructured, diffractive or refractive radiation and / or radiation surface.
- Fig.l the basic structure of the arrangement according to the invention in a first embodiment
- FIG. 2 shows the basic structure of the arrangement according to the invention in a second exemplary embodiment with an illustration of the superimposition of beam components by inversion
- FIG. 3 shows the structure of the arrangement according to the invention according to FIG. 2, but with a deflection prism arranged upstream of the beam splitter and an upstream partly reflecting mirror
- FIG .4 an embodiment of the invention with an arrangement upstream of the beam splitter for pupil division.
- the basic structure of the arrangement according to the invention is shown in a first embodiment.
- An incident light beam 1 is directed onto a beam splitter 2 with a splitter layer 3.
- a first sub-bundle 4 is deflected towards a first reversing prism 5, while a second sub-bundle 6 passes through the divider layer 3 and meets a second reversing prism 7.
- the divider layer 3 is designed in such a way that the incident light beam is divided in a ratio of 50:50, i.e. the two sub-beams 4 and 6 have approximately the same radiation components or the same radiation intensities.
- the two prisms 5 and 7 are rotated relative to one another in relation to the respective direction of irradiation of the partial bundles by 90 °.
- the longitudinal orientation (roof edge) of the first reversing prism 5 lies in the plane of the drawing, while the longitudinal orientation of the second reversing prism 7 is oriented perpendicular to the plane of the drawing.
- the two reversing prisms 5 and 7 are positioned at different distances from the beam splitter 2.
- the distance li between the first reversing prism 5 and the beam splitter 2 is approximately 14 mm greater than the distance 1 2 between the second reversing prism 7 and the beam splitter 2.
- the first sub-bundle 4 is inverted in the first reversing prism 5, is again directed onto the divider layer 3 and passes through it.
- the second sub-bundle 6 inverts in the second reversing prism 7 and is deflected at the dividing layer 3 in the direction which the first sub-bundle 4 has to pass through the dividing layer 3.
- the two sub-beams 4 and 6 combine to form an outgoing light beam 8.
- the outgoing light beam 8 has a reduced coherence, which has the consequence that the interference capability of the phase space cells or wave trains is reduced or eliminated.
- FIG. 2 The mixing of the inverted radiation components is illustrated below using a second exemplary embodiment shown in FIG. 2, in which a plane mirror 9 is located at the location of the first inverting prism 5 (see FIG. 1).
- the radiation components a to e of the incident light bundle 1 from the plane mirror 9 meet the divider layer 3 with the correct side and pass through it, while a reversal of the sides takes place in the reversing prism 7 and thereby, for example, the radiation components e of the first Sub-bundle 4 after the Combine flexion at the plane mirror 9 and after passing through the divider layer 3 with the radiation components a of the second sub-beam 6 deflected at the divider layer 3.
- the radiation components b of the first sub-beam 4 combine with the radiation components d of the second sub-beam 6, etc.
- the radiation components previously capable of interference mix after exceeding the time coherence and inversion on the plane mirror 9 or in the inverting prism 7 to form non-interference-capable radiation components.
- a laser with a coherence length> 1 mm for example an F 2 excimer laser, is provided here as the radiation source for the incident light beam.
- FIG 3 shows an embodiment variant in which a deflection prism 10 is arranged in the beam path of the incident light bundle 1 in front of the beam splitter 2, the purpose of which is to achieve a line separation in the light bundle 1, thereby overcoming the optical paths of the individual lines to vary the beam cross-section and thus additionally reduce the coherence.
- an optical element 11 with a partially reflecting layer 12 can also be provided in the beam path of the incident light bundle 1 or as an alternative to the deflecting prism 10.
- the partially reflecting layer 12 ensures that radiation components which are reflected back into the light beam 1 at the splitting layer 3 of the beam splitter 2 opposite to the direction of irradiation, at least partially invert at the partially reflecting layer 12, thereby again reaching the beam splitter 2 with the incident light beam 1 and can be used again for the overlay.
- a device for pupil division can be provided in the path of the incident light bundle 1, as shown in FIG.
- a mirror 13 is used to decouple a significant portion of the radiation from the light bundle 1, while the remaining portion of the radiation passes through a telescope 14 and thereby experiences a side reversal, as is illustrated by the designations g and h.
- the outcoupled radiation component is deflected via further mirrors 15 and 16 and finally coupled back into the light path of the light bundle 1 with a mirror 17, with the coupling in an offset of this radiation component taking place laterally to the optical axis, as can be seen from the designations f and g is.
- the telescope can it is, for example, a Kepler telescope (preferably 1: 1).
- This device for pupil division also serves to reduce the coherence of the incident light beam 1 and thus in cooperation with the arrangements according to FIGS. 1 and 2 to increase the efficiency of these arrangements.
- Such homogenization devices are sufficiently known from the prior art and can consist, for example, of a transparent optical element which is microstructured on the irradiation and / or the radiation surface, in such a way that the microstructure has a diffractive or refractive effect.
Abstract
Description
Claims
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP03798901A EP1543375A1 (en) | 2002-09-27 | 2003-09-11 | Device for reducing the coherence of a beam of light |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
DE10245229.6 | 2002-09-27 | ||
DE10245229A DE10245229A1 (en) | 2002-09-27 | 2002-09-27 | Arrangement for reducing the coherence of a light beam |
Publications (1)
Publication Number | Publication Date |
---|---|
WO2004031838A1 true WO2004031838A1 (en) | 2004-04-15 |
Family
ID=31969668
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/EP2003/010075 WO2004031838A1 (en) | 2002-09-27 | 2003-09-11 | Device for reducing the coherence of a beam of light |
Country Status (3)
Country | Link |
---|---|
EP (1) | EP1543375A1 (en) |
DE (1) | DE10245229A1 (en) |
WO (1) | WO2004031838A1 (en) |
Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5048926A (en) * | 1988-02-29 | 1991-09-17 | Nikon Corporation | Illuminating optical system in an exposure apparatus |
US5153773A (en) * | 1989-06-08 | 1992-10-06 | Canon Kabushiki Kaisha | Illumination device including amplitude-division and beam movements |
US5233460A (en) * | 1992-01-31 | 1993-08-03 | Regents Of The University Of California | Method and means for reducing speckle in coherent laser pulses |
GB2304923A (en) * | 1995-09-02 | 1997-03-26 | Renishaw Plc | Detector system for an interferometric measuring apparatus |
US6238063B1 (en) * | 1998-04-27 | 2001-05-29 | Nikon Corporation | Illumination optical apparatus and projection exposure apparatus |
Family Cites Families (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4511220A (en) * | 1982-12-23 | 1985-04-16 | The United States Of America As Represented By The Secretary Of The Air Force | Laser target speckle eliminator |
JP2565134B2 (en) * | 1994-06-06 | 1996-12-18 | 日本電気株式会社 | Lighting optics |
US6956878B1 (en) * | 2000-02-07 | 2005-10-18 | Silicon Light Machines Corporation | Method and apparatus for reducing laser speckle using polarization averaging |
JP2001296503A (en) * | 2000-04-13 | 2001-10-26 | Mitsubishi Heavy Ind Ltd | Device for reducing speckle |
-
2002
- 2002-09-27 DE DE10245229A patent/DE10245229A1/en not_active Withdrawn
-
2003
- 2003-09-11 EP EP03798901A patent/EP1543375A1/en not_active Withdrawn
- 2003-09-11 WO PCT/EP2003/010075 patent/WO2004031838A1/en not_active Application Discontinuation
Patent Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5048926A (en) * | 1988-02-29 | 1991-09-17 | Nikon Corporation | Illuminating optical system in an exposure apparatus |
US5153773A (en) * | 1989-06-08 | 1992-10-06 | Canon Kabushiki Kaisha | Illumination device including amplitude-division and beam movements |
US5233460A (en) * | 1992-01-31 | 1993-08-03 | Regents Of The University Of California | Method and means for reducing speckle in coherent laser pulses |
GB2304923A (en) * | 1995-09-02 | 1997-03-26 | Renishaw Plc | Detector system for an interferometric measuring apparatus |
US6238063B1 (en) * | 1998-04-27 | 2001-05-29 | Nikon Corporation | Illumination optical apparatus and projection exposure apparatus |
Also Published As
Publication number | Publication date |
---|---|
EP1543375A1 (en) | 2005-06-22 |
DE10245229A1 (en) | 2004-04-01 |
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