Optical system for reducing cross-track errors

Abstract

An optical system (100) is provided, comprising: a scanning mirror (103) having a reflective surface (105); and a plurality of optical elements (M1, 117, M2) defining an optical beam path (P) from a first position (109) to a second position (111) via a plurality of surface reflections (FR1, FR2) on the surface (105), the plurality of optical elements (M1, 117, M2) comprising relay segments (P2 to P4) from one surface reflection (FR1) to a next surface reflection (FR2). A method is also provided, comprising: directing light from a light source (109) along the optical beam path (P) from the first position (109) to the second position (111) via the plurality of surface reflections (FR1, FR2) on the rotating reflective surface (105) of the scanning mirror (103); and relaying light from one surface reflection (FR1) to a next surface reflection (FR2) on the surface (105) while the surface (105) is rotating.

Description

[Technical Field]

[0001] The present application relates to an optical system comprising a scanning mirror having a reflective surface and a plurality of optical elements defining a light beam path from a first position to a second position. The scanning mirror may comprise a rotating polygon mirror. [Background technology]

[0002] Scanning mirrors are commonly known for scanning a light beam from a light source across a target area by reflecting the light beam off the mirror's reflective surface and rotating (also referred to as "scanning") the mirror head (and thus the reflective surface). A rotating polygon mirror (also referred to as a polygon scanner) is a high-speed scanner that includes a mirror head with multiple mirror surface(s) mounted on a shaft that rotates about a central axis. The mirror head is mounted on the shaft that rotates about a central axis. The shaft may be mounted by suitable bearings, such as air bearings, magnetic bearings, and / or ball bearings, for high-speed applications. In raster scanning applications, the rotation of the mirror may define a fast axis and a slow axis perpendicular to it. The rotation of the facets generates scan lines, and when using a polygon mirror, each passing, reflective polygon facet generates a separate (fast-axis) scan line. However, due to imperfections in the mirror head's machining and / or imperfections in the bearings, scanning mirrors tend to exhibit a certain cross-scan error in the direction perpendicular to the fast-axis scan direction defined by the axis of rotation. In the case of polygon mirrors, cross-scan errors (or "dynamic track errors") can be particularly due to imperfections in the polygon faces. In some applications, excessive amounts of this error can be problematic.

[0003] WO 2020 / 263094 discloses the use of a polygon scanner for raster scanning for confocal microscopy. In such cases, if the dynamic track error is constant but not identical on each side, each fast axis scan line will move laterally relative to the scan line. This can result in an unevenly illuminated raster scan pattern, which can cause noticeable brightness banding in the final image.

[0004] Several methods already exist for reducing dynamic tracking errors of polygon mirrors. For example, G. Marshall and G. Stutz, Handbook of Optical and Laser Scanning, Second Edition, ser. Optical Science and Engineering. Taylor & Francis, 2011, disclose the use of retroreflecting prisms; EP 0 465 136 discloses the use of cylindrical lenses; and DE 4 300 739 discloses the use of active beam steering, e.g., acousto-optic beam steering or galvanometers, to correct (known) surface errors. See also U.S. Pat. No. 5,614,961 and AS Khattak et al. "Refractive scanner removes tracking errors economically," Laser Focus World, 28(3), March 1992, pp. 73-77, 79, ISSN: 1043-8092.

[0005] However, these solutions have problems such as not being able to completely correct errors, requiring larger polygon face sizes, or requiring precise timing. For a given size polygon, increasing the polygon face size may require a reduction in the number of faces. While it is possible to reduce machining errors by applying tighter tolerances to the machining of polygons, this increases the cost of such units.

[0006] Therefore, it is desirable to reduce the cross-scan error of the scan mirror. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2020 / 263094 [Patent Document 2] European Patent Application Publication No. 0465136 [Patent Document 3] DE 4300739 A1 [Patent Document 4] U.S. Patent No. 5,614,961 [Non-patent literature]

[0008] [Non-Patent Document 1] G. Marshall and G. Stutz, Handbook of Optical and Laser Scanning, Second Edition, ser. Optical Science and Engineering. Taylor & Francis, 2011 [Non-patent document 2] AS Khattak et al. “Refractive scanner removes tracking errors economically”, Laser Focus World, 28(3), March 1992, p. 73-77, 79, ISSN: 1043-8092 Summary of the Invention [Problem to be solved by the invention]

[0009] In view of the above, there is provided herein an optical system comprising: a scanning mirror having a reflective surface; and a plurality of optical elements defining a light beam path from a first position to a second position via a plurality of surface reflections on the surface, the optical system comprising a relay segment from one surface reflection to a next surface reflection.

[0010] The provision of a relay segment from one surface reflection to the next on the surface allows light from the light source to be directed along a light beam path from a first position to a second position via multiple surface reflections on the rotating reflective surface of the scanning mirror, by relaying one surface reflection to the next, thereby reversing the angle of the beam from one surface reflection to the next. Therefore, reflection angle errors can be nullified. This can prevent or at least reduce position errors at the second position due to reflection errors due to (the rotation of) the surface. The relay allows optical properties of the light beam that may otherwise be unaffected.

[0011] Thus, illumination of an object at a second location with light from a first location can be suitably controlled. Illumination may be used for one or more of illuminating, writing, printing, cutting, welding, melting, curing, etc. at least a portion of the object. The object may be or comprise an object and / or one or more flowable substances (such as, for example, photocurable substances for additive manufacturing). Illumination may include causing the object to emit light at a wavelength different from that of the light of the light beam, particularly by fluorescence and / or phosphorescence. Additionally or alternatively, other optical effects may occur, such as reflection and / or emission of light with a polarization different from that of the incident light.

[0012] The next surface reflection preferably occurs directly on that surface, with no other surface reflections in between, so that no further or other track errors are accumulated.

[0013] The scanning mirror may comprise a rotating polygon mirror having multiple reflective surfaces, where the reflection from one surface to the next may be the same surface, thereby reducing or eliminating cross-scan errors at each surface and from one surface to the next, and reducing dynamic scanning errors across the polygon.

[0014] The reflections from one surface may be co-located with the next, e.g., the surfaces may partially or fully overlap, which may accomplish one or more of the following: simplifying alignment, aiding in alignment checks, minimizing (preventing the introduction of) other errors, and / or reducing the size of the system.

[0015] The scanning mirror may be a first scanning mirror, and the optical system may include a second scanning mirror having a reflective surface between the first scanning mirror and the second position, where the scanning mirror may be positioned for scanning in a different direction than the first scanning mirror, preferably a vertical direction. Thus, scanning of surface areas other than line scans may be facilitated, which may support (use of the system for) confocal microscopy of samples wider than a scan line. Vertical scanning may support, for example, one or more of: improved resolution, reduced error, shorter scan time, easier alignment, and / or aiding in alignment checks.

[0016] The system may further include multiple optical elements defining an additional relay segment from the surface reflection of the first scanning mirror to the surface reflection of the second scanning mirror. As above, this may prevent cross-scan errors and improve scan quality. This system may be particularly useful in confocal microscopes, where the second scanning mirror may be used to reflect the scanning light and the object light in opposite directions. This may also improve the image quality of the object.

[0017] The system may include a detector and / or an aperture, and may further include a beam splitter, such as a dichroic mirror, and / or a polarizing beam splitter for directing (e.g., reflecting) light from a light source having a first optical property (e.g., a first wavelength and / or a first polarization) along an optical beam path from a first location to a second location, and directing (e.g., transmitting) light having a second optical property (e.g., a second wavelength and / or a second polarization) in a different direction along the optical beam path, through the beam splitter, to the detector and / or aperture.

[0018] Such a system may be used for scanning imaging, particularly confocal imaging, and may use light having a first optical property (e.g., a first wavelength) to illuminate at least a portion of an object, and light having a second optical property (e.g., a second wavelength) may be detected by a detector, which may be positioned behind an aperture that may be used for spatial filtering of the light having the second optical property, and which may further be positioned at the focus of a lens.

[0019] Herein, unless otherwise specified, the term "lens" may refer to a single lens element or a compound lens comprising multiple individual lens elements, such as, for example, an eyepiece, an achromat (such as an achromatic doublet), a collimating beam expander, etc.

[0020] An embodiment may include a detector and aperture as described above, and may also include a dichroic element, such as a dichroic mirror, and / or a beamsplitter, such as a polarizing beamsplitter, for directing light from a light source having a first optical characteristic (e.g., a first wavelength and / or polarization) from a first location to a second location and for directing light having a second optical characteristic (e.g., a second wavelength and / or polarization), preferably from the second location, through the aperture toward the detector, and a plurality of second optical elements defining a second light beam path from the aperture to the detector via a plurality of second surface reflections, the second optical element comprising a second relay segment from one second surface reflection to a next second surface reflection. Further, if the scanning mirror includes a rotating polygon mirror having multiple reflective surfaces, the one second surface reflection and the next second surface reflection may be on the same surface of the rotating polygon mirror, preferably on the same surface as the one surface reflection and the next surface reflection, as specified above.

[0021] Such a system allows for rescanning of a confocal microscope. The optical beam path and any additional elements and aspects mentioned above may also be associated with the scanning path and rescanning path. The subsequent second surface reflection may preferably be a direct subsequent second surface reflection on that surface.

[0022] Such an embodiment may include a third scanning mirror between the scanning mirror and the detector, the third scanning mirror having a reflective surface that scans in a direction perpendicular to the first scanning mirror (particularly, in a direction parallel to the second scanning mirror, if present).

[0023] Such a system may further comprise a plurality of optical elements defining an additional second relay beam path segment from the first scanning mirror to the third scanning mirror.

[0024] One or more of the second optical beam path, second relay segment, plurality of second optical elements, third scanning mirror, additional second relay beam path segment, etc. may provide, mutatis mutandis, any features and / or advantages defined for any one of the (first) optical beam path, second scanning mirror, (first and / or further) relay segment, plurality of (first) optical elements, etc. in any embodiment of the system described above.

[0025] The system may include a light source for directing light along a light beam path from a first location to a second location, and / or an object holder configured to hold an object at the second location. Such an object holder may be configured to hold a microscope object at the second location and may include an objective lens system.

[0026] The surface reflection may be located on one side of the scanning mirror, and the relay segment and / or, if applicable, the second relay segment may further be located at least partially on the opposite side of the scanning mirror, for example, extending around the periphery of the scanning mirror and, if applicable, extending in a plane perpendicular to the scanning axis of the scanning mirror.

[0027] Yet another aspect related to the above and providing related advantages comprises an optical method.

[0028] The method includes directing light from a light source along a light beam path from a first location to a second location through multiple surface reflections on a rotating reflective surface of a scanning mirror, and relaying one surface reflection to a next surface reflection on the surface while rotating the surface.

[0029] By relaying one surface reflection to the next on the surface while rotating the surface (included in the mirror head), cross-scan errors can be reduced or prevented, as described elsewhere in this specification.

[0030] The scanning mirror may comprise a rotating polygonal mirror having multiple reflective surfaces, with one surface reflection and the next surface reflection being on the same surface.

[0031] The use of a polygonal mirror facilitates providing uniform illumination across a scan line on an object. When a scanning mirror performs a reciprocating scan, the rotational speed tends to be sinusoidal due to acceleration and deceleration as the mirror head oscillates about the scan axis. Therefore, illuminating an object via surface reflection can result in local variations in average illumination power along the scan line. A polygonal mirror facilitates scanning at a constant rotational speed, which results in constant average illumination along the scan line.

[0032] One surface reflection and the next surface reflection may be at the same location.

[0033] The scanning mirror may be a first scanning mirror, and the method may further include the steps of directing light from the first scanning mirror to a second scanning mirror having a reflective surface, and scanning with the second scanning mirror in a second direction perpendicular to the first scanning direction of the first scanning mirror between the first scanning mirror and the second position.

[0034] The method may further comprise relaying the surface reflection on the first scanning mirror to a subsequent surface reflection on a second scanning mirror.

[0035] The method may include directing light from a light source having a first optical characteristic (e.g., a first wavelength and / or a first polarization) using a beam splitter, such as a dichroic mirror and / or a polarizing beam splitter; directing the directed light from a first location to a second location along a light beam path; and sending light having a second optical characteristic (e.g., a second wavelength and / or a second polarization) along the light beam path through the dichroic mirror toward a detector and / or an aperture.

[0036] The method may comprise detecting light at a second wavelength to detect a particular process (e.g., writing, printing, cutting, welding, melting, curing, etc.) in at least a portion of the object placed at the second location. In particular, the method may be used for confocal microscopy. The aperture may be used for spatial filtering and / or imaging of (light at) the second wavelength.

[0037] The method comprises the steps of: directing light from a light source having a first optical characteristic (e.g., a first wavelength and / or a first polarization) along a light beam path from a first location to a second location via a beam splitter, such as a dichroic element (e.g., a dichroic mirror); directing light having a second optical characteristic (e.g., a second wavelength and / or a second polarization) along the light beam path through an aperture using the beam splitter to a detector; and directing the light having the second optical characteristic (e.g., a second wavelength) from the aperture to the detector via multiple second surface reflections on a rotating reflective surface of a scanning mirror, comprising relaying one second surface reflection to a next second surface reflection as the surface is rotated; where the scanning mirror comprises a rotating polygon mirror having multiple reflective surfaces, the one second surface reflection and the next second surface reflection may be on the same surface of the rotating polygon mirror, and are preferably on the same surface as the one surface reflection and the next surface reflection in the method described above.

[0038] The scanning mirror may be a first scanning mirror, and the method may include the steps of directing light from the first scanning mirror to a third scanning mirror having a reflective surface, and using the third scanning mirror to scan between the first scanning mirror and the detector in a third scanning direction perpendicular to the first scanning direction of the first scanning mirror, and in particular, the third scanning direction is parallel to the second scanning direction mentioned above.

[0039] The method may comprise holding the object in a second position and illuminating a portion of the object with light.

[0040] The object may comprise a microscope sample and the method may further comprise, if a detector is provided, imaging at least some of the sample light with the detector.

[0041] Therefore, performance improvements in rescanning confocal imaging, and in particular confocal microscopy, can be achieved not only in the scanning and descanning light beam paths, but also in the rescanning light beam path.

[0042] In the method, relaying from one surface reflection to the next surface reflection may comprise directing light from one surface reflection to the next surface reflection on an opposite side of the scanning mirror, e.g., on a plane perpendicular to at least a portion of the circumference of the scanning mirror and preferably to a scan axis of the scanning mirror. Additionally or alternatively, if applicable, relaying one second surface reflection to the next second surface reflection may comprise directing light from one second surface reflection to the next second surface reflection on an opposite side of the scanning mirror, e.g., on a plane perpendicular to at least a portion of the circumference of the scanning mirror and preferably to a scan axis of the scanning mirror.

[0043] Accordingly, there is provided herein an optical system comprising a scanning mirror having a reflective surface, in particular a polygonal mirror having multiple reflective surfaces.

[0044] The one or more first optical elements define a first beam path segment directed from the light source to a surface location on the scanning mirror to provide a first surface reflection of the light from the light source, providing the single-reflected light.

[0045] The one or more second optical elements define a second beam path segment from and back to the surface location to provide a second surface reflection of the light from the light source, providing twice-reflected light.

[0046] One or more third optical elements define a third light beam path segment from the surface location to the target location for directing the twice-reflected light towards the target location.

[0047] The one or more second optical elements comprise a relay optical system arranged to define a second beam path segment as a relay beam path from the first reflection to the second reflection.

[0048] The scanning mirror may be a polygonal mirror having multiple reflective surface(s), and the surface position may be determined by at least a portion of the surface(s) and / or a polygonal mirror surface position at a rotational position of the polygonal mirror that produces the surface reflection, or a polygonal mirror surface position that is expected to produce the surface reflection.

[0049] The third optical element may comprise a second scanning mirror having a reflective surface, and the third optical element may further optionally comprise a further relay optical system arranged to define a portion of the third light beam path segment as a relay beam path from the surface location reflection to the surface reflection location on the second scanning mirror, to provide further reflected light from the twice reflected light, and to direct the further reflected light to the target location.

[0050] The optical system may comprise a detector and / or an aperture, which may have a fixed size or may have an adjustable size, for example, an adjustable diaphragm.

[0051] One or more of the first optical element, the second optical element, or the third optical element may comprise a beam splitter for directing (e.g., sending) light having a first optical characteristic (e.g., a first wavelength and / or a first polarization) in one direction along a respective one of the first light beam path segment, the second light beam path segment, and the third light beam path segment, and for directing (e.g., reflecting) light having a second optical characteristic (e.g., a second wavelength and / or a second polarization) in a different direction along a respective one of the first light beam path segment, the second light beam path segment, and the third light beam path segment.

[0052] The optical system may comprise one or more fourth optical elements defining a fourth beam path segment directed from the aperture to a second surface position (possibly similar to the (first) surface position) of the scanning mirror to provide a third surface reflection, providing triple-reflected light.

[0053] The one or more fifth optical elements define a fifth beam path segment from and back to the surface location to provide a fourth surface reflection, providing four times reflected light.

[0054] The one or more sixth optical elements define a sixth beam path segment from the fourth surface location towards the second object location, in particular the detector location, for directing the four times reflected light towards the second object location.

[0055] The one or more fifth optical elements comprise a relay optical system arranged to define a fifth beam path as a relay beam path from the third surface reflection to the fourth surface reflection.

[0056] The sixth optical element may comprise a third scanning mirror having a reflective surface, and optionally a further second relay optical system arranged to define a portion of the sixth beam path segment as a relay beam path from the fourth surface position reflection to a surface reflection position on the third scanning mirror to provide a further second reflected light from the four times reflected light and direct the further second reflected light to a second target position.

[0057] The above-mentioned aspects, together with further details and advantages, will be explained in more detail below with reference to the drawings showing, by way of example, a number of embodiments. [Brief explanation of the drawings]

[0058] [Figure 1] Illustrates polygonal mirrors and some basic concepts. [Figure 2] Illustrates the use of polygonal mirrors. [Figure 3] 1 shows a relay system. [Figure 4]1 shows a first embodiment of an improved optical system. [Figure 5] 2 shows a second embodiment of an improved optical system. [Figure 6A] As a comparative example, the cross-scan error measurement results for the system of FIG. 3 are shown. [Figure 6B] 6 shows cross-scan error measurement results for the embodiment of FIG. 5. [Figure 7] 1 shows a third embodiment of an improved optical system. [Figure 8] 1 shows a fourth embodiment of an improved optical system. DETAILED DESCRIPTION OF THE INVENTION

[0059] It should be noted that the drawings are schematic and not necessarily to scale, and that details not necessary for understanding the present invention may be omitted. Terms such as "upward," "downward," "below," and "above" refer to the embodiments oriented in the drawings, unless otherwise specified. Furthermore, elements that are at least substantially identical, or that perform at least substantially the same functions, are designated by the same numerals and usefully distinguished by alphabetical suffixes.

[0060] Additionally, unless otherwise specified, terms such as "detachable" and "removably connected" are intended to mean that parts can essentially be separated without damaging or destroying either part. For example, it excludes structures in which parts are unitary (e.g., welded or molded together), but includes structures in which parts are attached by or as mating connectors, fasteners, releasable self-fastening features, etc. The verb "to facilitate" is intended to mean "to make easier and / or less complicated," rather than "to enable."

[0061] FIG. 1 shows an exemplary scanning mirror, a polygonal mirror 1, having a mirror head 3 provided with a plurality of mirror surfaces 5, for example eight surfaces 5, and mounted on a shaft 7 that rotates about a central axis A.

[0062] Each surface 5 is planar and has a surface normal. A light beam incident on the surface is reflected from the surface. To distinguish from other reflections, the term "surface reflection" is used herein to refer to reflection on the reflective surface of a scanning mirror, for example, a polygonal mirror surface. Ideally, the surface normal of each surface 5 is radial and lies in a plane radial to the axis A.

[0063] 2 is an axial view (hereinafter also referred to as a "top view") along axis A of a portion of polygon 3, showing a light source 9, here a laser, emitting a light beam along beam path P (light beam segments P1, P2) from light source 9 to camera 11 or other target via surface reflection FR on face 5 of polygon mirror 3. In FIG. 2, the light beam path is further defined by lenses 13, 15, such as collimator lens 13 and imaging lens 15.

[0064] Cross-scan error may be caused by deviation of the normal from its ideal direction, as shown, by an elevation angle ε or −ε (up or down in FIG. 1, where the error is shown as symmetrical), which is related to the mechanical angle of the surface plane relative to a pure tangent plane to axis A. Thus, a light beam L1 incident radially on surface 5 is reflected as a reflected light beam R1 (R1') offset from the radial plane by an angle 2ε (−2ε), as shown.

[0065] Cross-scan errors may be caused by surface wobble relative to ideal and fixed axial directions, and / or, in the case of polygon mirrors, by different orientations of the surface normals for different faces of the polygon mirror. The dynamic track error of the entire polygon scanner may be defined as the sum of the mechanical angular variations of the faces perpendicular to the scan direction, according to Marshall and Stutz, supra. This is the peak-to-peak (P2P) mechanical variation, and twice that of the optical variation.

[0066] Therefore, each surface passed through will have an optical "zero-to-peak" (Z2P) error at a certain angle from the "intended" surface normal. Cross-scan errors due to surface normal elevation axis errors, particularly Z2P errors, can be inverted and rescanned using a relay optical system.

[0067] FIG. 3 illustrates a relay optical system 17 (or, for short, "relay system" / "relay optical system"), which is known per se. For example, it may comprise a set of two lenses 19 with a front-to-back focal length f operatively arranged to have coincident foci along the optical axis and along the optical axis (not shown) that generate three focal planes FP1, FP2, and FP3 perpendicular to the optical axis. The lenses 19 may or may not be identical, but are preferably identical. A collimated beam propagating along the optical axis is focused between the lenses 19 on the optical axis and, after traversing the relay segment 19, propagates in a reversed direction relative to the optical axis (OA). As shown in FIG. 2, a collimated beam CB propagating at an angle 2ε relative to the optical axis is focused between the lenses 19 offset from the optical axis and, after traversing the relay segment 19, propagates at a reversed angle relative to the optical axis. Thus, the angle 2ε is relayed through four focal lengths f along the optical axis, changing sign to -2ε.

[0068] This angle is equal in absolute value at that point compared to the starting position, but is negative. These two properties of the relay optical system (relaying and the sign reversal of any incident angle) can be used to eliminate unwanted cross-scan errors by simply relaying a beam scanned by a polygonal facet back to the same polygonal facet, as will be shown below. As explained in connection with FIG. 1, a light beam reflecting at a reflection position on a reflecting surface 5 having a directional error relative to the optical axis, e.g., an elevation error of +ε, will acquire an error of +2ε in its direction relative to the optical axis. If the first focal plane FP1 of the relay optical system 17 coincides with the reflection position, the beam will be focused at a second focal plane FP2 offset from the optical axis. After traversing the relay optical system 17, the light beam will propagate at a reverse angle of -2ε relative to the optical axis. If the third focal plane FP3 coincides with the reflection position on a reflecting surface 5 having an elevation error of -ε opposite to that which caused the initial reflection, the light beam will further reflect, nullifying the initial error, so that the light beam will then propagate again along the optical axis.

[0069] 4 shows a first embodiment of an optical system 100. It should be noted that in this specification, to clarify the general structure of any figure, the figures are schematic and not to scale, and beam angles may be incorrect when reflected.

[0070] Optical system 100 includes a scanning mirror 103 having a reflective surface 105 and a plurality of optical elements (e.g., static mirrors M1, M2) that define a light beam path P (having path segments P1 to P5) from a light source 109 at a first location to a target 111 at a second location via a plurality of surface reflections FR1, FR2 on surface 105. Optical system 100 further includes a relay optical system 117 that provides relay segments P2 to P4 from one surface reflection FR1 to the next surface reflection FR2. The reflection positions of surface reflections FR1, FR2 on surface 105 are located at the respective focal planes of relay optical system 117.

[0071] As indicated by the arrow, scan mirror 103 may rotate about a scan axis (not shown), causing an associated rotation of the beam path segments. A scan rotation of surface 105 about the scan axis by a scan angle 2ζ, with a possible angular error ε, doubles the scan deflection of the light beam segments due to each surface reflection FR1, FR2, but the angular error ε is removed by relay segments P2 to P4.

[0072] FIG. 5 shows an optical system 200 according to a second embodiment, which includes a rotating polygon mirror 203 as a scanning mirror having a reflective surface 205 and multiple optical elements (e.g., mirrors M1 and M2) that define an optical beam path P (having path segments P1 to P5) from a laser as a light source 209 at a first location to a camera 211 at a second location via multiple surface reflections FR1 and FR2 on the surface 205. Unlike FIG. 4, here, the surface reflections FR1 and FR2 are at the same position on the surface. The optical system 200 further includes a relay system 217 that provides relay segments (P2 to P4) from one surface reflection FR1 to the next surface reflection FR2. The reflection positions of the surface reflections R1 and R2 on the surface 205 are located in the respective focal planes of the relay system 217. Note that the relay segments (P2 to P4) optionally cross at least one other beam segment (here, beam path segment P1). This facilitates a compact configuration.

[0073] To test the effectiveness of the proposed method, we compared the setups shown in Figures 2 and 5 using an eight-sided rotating polygon scanner. For each facet, a collimated beam is reflected from the polygon facet and measured directly (Figure 2), or first relayed back to the same polygon facet and measured (Figure 5). The light beam (finally) reflected from the polygon is focused onto the camera's image plane, and the position of the focused spot thus formed is determined. Figures 6A and 6B show the measurement results: the deviation of the eight faces from the average trend line of the comparative example shown in Figure 2 in Figure 6A, and the deviation of the embodiment shown in Figure 5 with a relay system in Figure 6B. The relay system significantly reduces the cross-axis error.

[0074] FIG. 7 shows a schematic of an optical system 300 for a rescanning confocal microscope according to the concepts of the present application.

[0075] The system 300 comprises a rotating mirror 303 with a reflective surface 305. Here, the mirror 303 is a polygonal mirror, and the mirror 303, and therefore the surface 305, rotates in the XZ plane about an axis in the Y direction.

[0076] A plurality of optical elements including a dichroic mirror DM define an optical beam path P (having segments P1 to P8) from the laser light source 309 to the microscope 311 along beam path segments P1 to P8 via a plurality of surface reflections FR1, FR2 on the surface 305, and includes a first relay segment 317A from one surface reflection to the next on the surface.

[0077] The system 300 further comprises a dichroic mirror DM as a beam splitter, a pinhole PH as an aperture, and a CMOS (Complementary Metal Oxide Semiconductor) camera 321 as an exemplary detector.

[0078] The plurality of second optical elements define a second optical beam path R having segments R1 to R8 from the aperture PH to the detector 321 via a plurality of second surface reflections FR3, FR4, with a second relay segment 317B from one second surface reflection FR3 to the next second surface reflection FR4 on the same surface as the surface reflections FR1, FR2.

[0079] In system 300, scanning mirror 303 is the first scanning mirror. Optical system 300 also includes a second scanning mirror 323 having a reflective surface and disposed along light beam path P between first scanning mirror 303 and microscope 311. Second scanning mirror 323 is disposed to scan light along light beam path P in a direction perpendicular to first scanning mirror 303 and rotates about an axis in the XZ plane. Multiple optical elements 317C define further relay segments P6 to P7 from surface reflection FR2 on first scanning mirror 303 to surface reflections on second scanning mirror 323.

[0080] The optical system 300 also includes a third scanning mirror 325 having a reflective surface and disposed along the light beam path R between the first scanning mirror 303 and the detector 321. The third scanning mirror 325 is disposed to scan light along the light beam path R in a direction perpendicular to the first scanning mirror 303 and rotates about an axis in the XZ plane. A plurality of optical elements 317D define further second relay segments R6 to R7 from the surface reflection FR4 on the first scanning mirror 303 to the surface reflection on the third scanning mirror 325.

[0081] Laser 309 illuminates a sample (not shown) in microscope 311 with light at a first wavelength along segments P1-P8 of optical beam path P. Sample light emitted from the sample is collected and directed backward along segments P8 to P1 of optical beam path P, and sample light at a second wavelength is transmitted through dichroic mirror DM along beam path segments P9 to P10 to an aperture PH. Pinhole PH is positioned in a spatial filtering setup between lenses BP and AP, which are focused on pinhole PH.

[0082] The sample light passing through the pinhole PH is directed by a plurality of second optical elements along second light beam paths R (R1 to R8) to the camera 321.

[0083] As explained above, the scanning angle 2ζ, as indicated by the arrow, and the possible variations ε ζ The scanning rotation of plane 305 by causes an associated scanning rotation of each light beam segment P3 to P7, as indicated by the respective arrows, to second scanning mirror 323 and from there to a suitably positioned (e.g., in the focus) sample of microscope 311. By scanning second scanning mirror 323 (or "second scanning / reverse scanning mirror") vertically, the light beam is scanned in two directions across the sample (i.e., 2D scanning).

[0084] Conversely, emission light from the sample is counter-scanned in both directions on its reverse path to pinhole PH by both scanning mirrors 323, 303. Sample light then passes through pinhole PH and is directed along second light beam path R (R1 through R8) to camera 321, which is also scanned across the image plane of camera 321 by scanning first mirror surface 305, and then scanned vertically by third scanning mirror 325, or "second re-scanning mirror," in a manner similar to that described for scanning above.

[0085] The light beam path segment P2-P10-R1-R2 forms a static path, while all other path segments are dynamic upon rotation of the first mirror 303 and, possibly, the second scanning mirror 323 and / or the third scanning mirror 325.

[0086] Relay optical systems 317A and 317C / relay segments P3-P5 and P6-P7, respectively, are provided so that cross-scan errors of the first mirror (facet) are nullified on the second mirror facet reflection, allowing the second mirror to scan the sample. In accordance with the present principles, additional optical elements may be provided to convert the illustrated optical beam path P8 from the second scanning mirror 323 to the microscope 311 via multiple facet reflections on the reflective facet of the second scanning mirror 323, with relay segments from one facet reflection to the next on that reflective facet, to reduce or eliminate cross-scan errors from the second scanning mirror 323. The same applies mutatis mutandis to relay systems 317B and 317D / relay segments R3-R5 and R6-R7 and optical beam path R8 from the third scanning mirror 325 and to the camera 321.

[0087] Figure 7 shows several horse heads. The horse heads represent the "sample image" of a sample emission beam incident at that point along the optical path. It is important to "look" at the horse heads in the same direction as the (re)scanning beam is traveling. Please note again that for clarity, the image is not to scale and the beam angles on the surface are not necessarily correct.

[0088] FIG. 8 shows another optical system for a rescanning confocal microscope according to the present concepts.

[0089] System 400 includes a scanning mirror 403 with a reflective surface 405 that rotates about a scan axis perpendicular to the plane of the drawing. Mirror 403 may be a rotating polygon mirror. System 400 includes a dichroic mirror DM as a beam splitter and a pinhole PH. Also shown in Figure 8 are a light source 409 that emits excitation light at a first wavelength, a microscope 411, and a detector 321.

[0090] The multiple optical elements include a dichroic mirror DM, static mirrors SM1 to SM4, and lenses SL1 to SL2, and excitation light from light source 409 is directed along beam path segments P1 to P7 via multiple surface reflections PF on surface 405 to define an optical beam path P to (a sample within) microscope 411, providing a scanning beam path. Note that in this embodiment, the dichroic mirror directs the light of light source 409.

[0091] Lenses SL1 and SL2 provide a relay optical system defining a first relay segment P2 to P6 from one surface reflection PF on the surface of the light beam path P to the next surface reflection PF.

[0092] Similar to the system and description of Figure 7, sample light from the sample at the second wavelength is directed in the reverse direction along the optical beam path P, from segment P7 to P1, and after reflection by the dichroic mirror DM, P8 above the pinhole PH, thus providing a reverse scanning beam path.

[0093] The sample light passing through pinhole PH is directed by a plurality of second optical elements, including static mirrors SPM, RM1 to RM4, and lenses RL1, RL2, along a second optical beam path R (having path segments R1 to R8) defined by the plurality of second optical elements to detector 321, thereby forming a rescanned beam path. Lenses RL1 and RL2 provide a second relay system defining second relay segments R3 to R7 in optical beam path R from one surface reflection PF to the next surface reflection PF on the surface.

[0094] The route P1-P8-R1-R2 is a static route.

[0095] Relay segments P2 to P6 and second relay segments R3 to R7 are located partially on the opposite side of the scanning mirror 403 from the surface reflection and extend around the scanning mirror 406, optionally in a plane perpendicular to the scanning axis of scanning mirror 403. The relay beam segments optionally intersect with other beam path segments.

[0096] The disclosure of the present application is not limited to the above-described embodiments, but can be modified in various ways within the scope of the claims.

[0097] For example, elements and aspects discussed with or in connection with a particular embodiment may be suitably combined with elements and aspects of other embodiments, unless expressly stated otherwise.

Claims

1. a rotating scanning mirror (103, 203, 303, 403) having a reflective surface (105, 205, 305, 405); a plurality of optical elements (117, 213, 215, 217, 317A, 323, M1 to M2, CL, SL, SL1 to SL2, SM1 to SM4) defining an optical beam path (P) from a first position (109, 209, 309, 409) to a second position (111, 211, 311, 411) via a plurality of surface reflections (FR1, FR2, PF) on surfaces (105, 205, 305, 405); An optical system (100, 200, 300, 400) comprising a relay segment (P2 to P4 for 100 and 200, P3 to P5 for 300, P2 to P6 for 400) from one surface reflection (FR1, FR2, PF) to the next surface reflection (FR2, FR1, PF).

2. the rotating scanning mirror (103, 203, 303, 403) comprises a rotating polygonal mirror having a plurality of reflective surfaces (105, 205, 305, 405); 2. The optical system (100, 200, 300, 400) of claim 1, wherein the one surface reflection (FR1, FR2, PF) and the next surface reflection (FR2, FR1, PF) are on the same surface (105, 205, 305, 405).

3. 3. The optical system (100, 200, 300, 400) of claim 1 or 2, wherein the one surface reflection (FR1, FR2, PF) and the next surface reflection (FR2, FR1, PF) are at the same location.

4. The rotating scanning mirror (303) is a first scanning mirror, The optical system further includes a second scanning mirror (323) having a reflective surface between the first scanning mirror (303) and the second position (311); 4. The optical system (300) of claim 1, wherein the second scanning mirror (323) is arranged to scan in a different direction than the first scanning mirror (303), preferably in a perpendicular direction.

5. 5. The optical system (300) of claim 4, further comprising a plurality of optical elements (317C) defining further relay segments (P6, P7) from a surface reflection (FR2) on the first scanning mirror (303) to a surface reflection on the second scanning mirror (323).

6. a detector (321, 421) and / or an aperture (PH) such as a pinhole; A beam splitter (DM), directing, e.g., reflecting, light from a light source (309, 409) having a first optical characteristic from said first location (309, 409) to said second location (311, 411) along said light beam path (P); and 6. The optical system (300, 400) of claim 1, further comprising a beam splitter (DM) for directing light having a second optical property in different directions, for example sending it along the light beam path (P) and through the beam splitter (DM) to the detector (321, 421) and / or the aperture (PH).

7. a detector (321, 421); An opening (PH) such as a pinhole, Optionally, an optical system (300, 400) according to claim 6, A beam splitter (DM) such as a dichroic element, for example a dichroic mirror, directing light from a light source (309, 409) having a first optical characteristic, such as a first wavelength, from the first location (309, 409) to the second location (311, 411); and a beam splitter (DM) for directing light having a second optical characteristic, such as a second wavelength, preferably from said second location (311, 411) through said aperture (PH) to said detector (321, 421); A plurality of second optical elements (AP, M4 to M6, 317B, 317D, 325, RL), defining a second light beam path (R) from said aperture (PH) to said detector (321) via a plurality of second surface reflections (FR3, FR4); the second optical beam path (R) further comprises a plurality of second optical elements (AP, M4 to M6, 317B, 317D, 325, RL) comprising a second relay segment (R3 to R5) from one second surface reflection (FR3) to the next second surface reflection (FR4); An optical system (300, 400) according to any one of claims 1 to 6, wherein when the scanning mirror (303) comprises a rotating polygonal mirror having a plurality of reflective surfaces (305), the one second surface reflection (FR3) and the next second surface reflection (FR4) are on the same surface (305) of the rotating polygonal mirror, preferably on the same surface as the one surface reflection (FR1) and the next surface reflection (FR2) according to claim 2.

8. a third scanning mirror (325) between the scanning mirror (303) and the detector (321) and having a reflective surface that scans in a direction perpendicular to the first scanning mirror (303); In particular, at least when the optical system (300) is the optical system (300) described in claim 4, the optical system (300) described in any one of claims 1 to 7 further comprises a third scanning mirror (325) oriented parallel to the second scanning mirror (323).

9. 9. The optical system (300) of claim 8, further comprising a plurality of optical elements (317D) defining a further second relay beam path segment (R6 to R7) from the first scanning mirror (303) to the third scanning mirror (325).

10. 10. The optical system (100, 200, 300, 400) of any one of claims 1 to 9, further comprising a light source (109, 209, 309, 409) for directing light along the light beam path (P) from the first position (109, 209, 309, 409) to the second position (111, 211, 311, 411).

11. The optical system (100, 200, 300, 400) of any one of claims 1 to 10, further comprising an object holder configured to hold an object at the second position (111, 211, 311, 411).

12. the object holder is configured to hold a microscope object at the second position (111, 211, 311, 411); 12. The optical system (100, 200, 300, 400) of claim 11, wherein the object holder optionally comprises an objective lens system.

13. The surface reflection (PF) is disposed on one side of the scanning mirror (403), An optical system (400) according to any one of claims 1 to 12, wherein the relay segments (P2 to P6) and / or, if applicable, the second relay segments (R3 to R7) are at least partially located on opposite sides of the scanning mirror (403), for example extending around the scanning mirror (403), preferably extending in a plane perpendicular to the scanning axis of the scanning mirror (X-Z plane).

14. directing light from a light source from a first location (109, 209, 309, 409) to a second location (111, 211, 311, 411) along a light beam path (P) via a plurality of surface reflections (FR1, FR2, PF) on a rotating reflective surface (105, 205, 305, 405) of a scanning mirror (103, 203, 303, 403); relaying one surface reflection (FR1, FR2, PF) to a next surface reflection (FR2, FR1, PF) on the surface while rotating the surface (105, 205, 305, 405).

15. the scanning mirror (103, 203, 303, 403) comprises a rotating polygonal mirror having a plurality of reflective surfaces (105, 205, 305, 405); 15. The method of claim 14, wherein the one surface reflection (FR1, FR2, PF) and the next surface reflection (FR2, FR1, PF) are on the same surface (105, 205, 305, 405).

16. 16. The method of claim 14 or 15, wherein the one surface reflection (FR1, FR2, PF) and the next surface reflection (FR2, FR1, PF) are at the same location.

17. The scanning mirror (303) is a first scanning mirror, The method further comprises: directing light from the first scanning mirror (303) onto a second scanning mirror (323) having a reflective surface; and using the second scanning mirror (323) to scan in a second scanning direction perpendicular to the first scanning direction of the first scanning mirror (303) between the first scanning mirror (303) and the second position (311).

18. 18. The method of claim 17, further comprising relaying a surface reflection (FR2) on the first scanning mirror (303) to a next surface reflection (FR2) on the second scanning mirror (323).

19. - directing, e.g., reflecting, light from a light source (309, 409) having a first optical characteristic, e.g., a first wavelength, using a beam splitter (DM); directing the directed light from the first location (309, 409) to the second location (311, 411) along the light beam path (P); 19. The method of any one of claims 14 to 18, further comprising the step of directing light having a second optical property, such as a second wavelength, in another direction, for example by sending it along the light beam path (P) and through the beam splitter (DM) to a detector (321, 421) and / or an aperture (PH), such as a pinhole.

20. directing light from a light source (309, 409) having a first optical characteristic, e.g., a first wavelength, along the light beam path (P) from the first location (309, 409) to the second location (311, 411) via a beam splitter (DM), e.g., a dichroic element, e.g., a dichroic mirror; directing light having a second optical property, e.g., a second wavelength, along the light beam path (P) and using the beam splitter (DM) to a detector (321, 421) through an aperture (PH), such as a pinhole; directing light having a second optical characteristic, e.g., a second wavelength, from the aperture (PH) to the detector (321, 421) via a plurality of second surface reflections (FR3, FR4, PF) on a rotating reflective surface (305, 405) of the scanning mirror (303, 403), relaying one second surface reflection (FR3) to a next second surface reflection (FR4) while rotating the surfaces (305, 405); 20. The method of any one of claims 14 to 19, wherein when the scanning mirror (303, 403) comprises a rotating polygonal mirror having a plurality of reflective surfaces (305, 405), the one second surface reflection (FR3, PF) and the next second surface reflection (FR4, PF) are on the same surface (305, 405) of the rotating polygonal mirror (303, 403), preferably at least on the same surface as the one surface reflection and the next surface reflection of the method of claim 15.

21. The scanning mirror (303) is a first scanning mirror, The method further comprises: directing light from the first scanning mirror (303) onto a third scanning mirror (325) having a reflective surface; a step of scanning the third scanning mirror (325) between the first scanning mirror (303) and a detector (321) in a third scanning direction perpendicular to the first scanning direction of the first scanning mirror (303), 21. The method according to any one of claims 14 to 20, comprising the step of: in particular, the third scanning direction being at least parallel to the second scanning direction of the method according to claim 17.

22. holding the object in said second position (111, 211, 311, 411); 22. The method of any one of claims 14 to 21, further comprising illuminating a portion of the object with light.

23. the object comprises a microscope sample; 23. The method of any one of claims 14 to 22, when at least as defined in claim 19 or 20, further comprising imaging at least a portion of the sample light onto the detector (321, 421).

24. The step of relaying the one surface reflection (PF) to the next surface reflection (PF) further comprises directing light from the one surface reflection (PF) to the next surface reflection (PF) on an opposite side of the scanning mirror (403), for example, in at least a part of the periphery of the scanning mirror (403), preferably in a plane perpendicular to the scanning axis of the scanning mirror (403) (X-Z plane); and / or 24. The method of any one of claims 14 to 23, wherein, if applicable, the step of relaying from one second surface reflection (PF) to the next second surface reflection (PF) further comprises directing light from the one second surface reflection (PF) to the next second surface reflection (PF) on an opposite side of the scanning mirror (403), for example in at least a part of the periphery of the scanning mirror (403), preferably in a plane perpendicular to a scanning axis of the scanning mirror (403) (X-Z plane).

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