Compact Laser Scanning Microscope System

Abstract

A laser scanning imaging system comprises: a first beam scanner; a first group of relay lenses; a second beam scanner; a second group of relay lenses; an objective lens; the first beam scanner is configured to receive an input laser beam and scan the laser beam around one or more axes; the first group of relay lenses is configured to expand the laser beam scanned by the first beam scanner and conjugate the scanning plane of the first beam scanner with the scanning plane of the second beam scanner; the second beam scanner is configured to scan the laser beam relayed by the first group of relay lenses around one or more axes; the second group of relay lenses is configured to expand the laser beam scanned by the second beam scanner and project the scanning plane of the second beam scanner onto the pupil of the objective lens.

Description

Technical Field

[0001] The present invention relates generally to microscopic systems and more particularly to a laser scanning microscopy system that uses multiple conjugated repeater pairs to form a set of composite beam expansion optics to enable the laser scanning microscopy system to use a smaller scanner, fiber laser delivery, or a more compact form factor. Background Art

[0002] For in vivo imaging in life sciences, there is a growing need for microscopy systems that can adapt to the living environment being studied. It is imperative to have a compact, lightweight, and spatially manipulable multiphoton microscopy system to allow easy access to a variety of positions and angles. Summary of the invention

[0003] One embodiment of the present invention provides a compact, lightweight and spatially manipulable imaging system. In one embodiment, the system is composed of a MEMS (Micro-Electro Mechanical System) scanner, a robotic arm and a fiber-coupled ultrafast laser source. Please note that the microscope is also referred to as a "stick scope" in this document.

[0004] One embodiment of the present invention provides a laser scanning imaging system, comprising: a first beam scanner; a first group of relay lenses; a second beam scanner; a second group of relay lenses; and an objective lens; wherein the first beam scanner is configured to receive an input laser beam and scan the laser beam around one or more axes; wherein the first group of relay lenses is configured to expand the laser beam scanned by the first beam scanner and conjugate the scanning plane of the first beam scanner with the scanning plane of the second beam scanner; wherein the second beam scanner is configured to scan the laser beam relayed by the first group of relay lenses around one or more axes; and wherein the second group of relay lenses is configured to expand the laser beam scanned by the second beam scanner and project the scanning plane of the second beam scanner onto the pupil of the objective lens.

[0005] One embodiment of the present invention provides a laser scanning imaging system, comprising: a first beam scanner; a first group of relay lenses; a second beam scanner; a second group of relay lenses; a third beam scanner; a third group of relay lenses; and an objective lens; wherein the first beam scanner is configured to receive an input laser beam and scan the laser beam around one or more axes; wherein the first group of relay lenses is configured to expand the laser beam scanned by the first beam scanner and conjugate the scanning plane of the first beam scanner with the scanning plane of the second beam scanner; wherein the second beam scanner is configured to scan the laser beam relayed by the first group of relay lenses around one or more axes; wherein the second group of relay lenses is configured to expand the laser beam scanned by the second beam scanner and conjugate the scanning plane of the second beam scanner with the scanning plane of the third beam scanner; wherein the third beam scanner is configured to scan the laser beam relayed by the second group of relay lenses around one or more axes; wherein the third group of relay lenses is configured to expand the laser beam scanned by the third beam scanner and project the scanning plane of the third beam scanner onto the pupil of the objective lens.

[0006] One embodiment of the present invention provides a laser scanning imaging system, comprising: a liquid crystal polarization zone plate (LCPZP) lens stack; a first group of relay lenses; a beam scanner; a second group of relay lenses; and an objective lens; wherein the LCPZP lens stack is configured to receive an input laser beam and move the focus of the laser beam; wherein the first group of relay lenses is configured to receive a laser beam from the LCPZP lens stack and expand the laser beam so that the aperture of the LCPZP lens stack matches the aperture of the beam scanner; wherein the beam scanner is configured to scan the laser beam relayed by the first group of relay lenses around one or more axes; and wherein the second group of relay lenses is configured to expand the laser beam scanned by the beam scanner and project the scanning plane of the beam scanner onto the pupil of the objective lens. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 The optical path of the laser scanning system according to an embodiment of the present invention is shown.

[0008] Figure 2 A repeater in a laser scanning system according to an embodiment of the present invention is shown.

[0009] Figure 3 A repeater in a laser scanning system according to an embodiment of the present invention is shown.

[0010] Figure 4The optical layout in the laser scanning system according to the embodiment of the present invention is shown.

[0011] Figure 5 A simulated Strehl ratio of a laser scanning system according to an embodiment of the present invention is shown.

[0012] Figure 6 A laser scanning system mounted on a robot arm according to an embodiment of the present invention is shown.

[0013] Figure 7 The optical path of the confocal laser scanning system according to an embodiment of the present invention is shown.

[0014] Figure 8 The optical path of a laser scanning system with MEMS scanner position tracking according to an embodiment of the present invention is shown.

[0015] Fig. 9 An LCPZP lens is shown in a laser scanning system according to an embodiment of the present invention.

[0016] Fig.10 An image of 16 discrete focal points along the optical axis is shown according to an embodiment of the present invention, with a 4-stage LCPZP lens preceding a 10x objective.

[0017] Fig.11 An LCPZP lens is shown placed in front of a scanner for remote focus control in accordance with an embodiment of the present invention.

[0018] Fig.12 A remote focus control of an LCPZP lens with a wavefront spherical aberration compensator according to an embodiment of the present invention is shown.

[0019] Fig.13 The pre-compensation of spherical aberration introduced by using a diverging beam according to an embodiment of the present invention is shown.

[0020] Fig.14 The pre-compensation of spherical aberration introduced by a converging beam according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0021] The description of the illustrative embodiments according to the principles of the present invention is intended to be read in conjunction with the accompanying drawings, which are considered part of the entire written description. In the description of the embodiments of the invention disclosed herein, any reference to direction or orientation is only for the convenience of description and does not limit the scope of the invention in any way. Relative terms such as "lower", "upper", "horizontal", "vertical", "above", "below", "upward", "downward", "top" and "bottom" and their derivatives (e.g., "horizontal", "downward", "upward", etc.) should be interpreted as referring to the orientation described at the time or shown in the figure in question. These relative terms are only for convenience of description and do not require the device to be constructed or operated in a specific orientation unless explicitly stated. Terms such as "attach", "attach", "connect", "couple", "interconnect" refer to the relationship of fixing or connecting structures together directly or indirectly through intermediate structures, as well as movable or rigid connections or relationships, unless otherwise explicitly stated. In addition, the features and advantages of the present invention are illustrated by reference to exemplary embodiments. Therefore, the present invention should not be explicitly limited to such exemplary embodiments, which illustrate some possible non-limiting feature combinations that may exist alone or in other feature combinations; the scope of the present invention is defined by the claims attached hereto.

[0022] The present disclosure describes the best mode currently contemplated for carrying out the invention. The description is not intended to be understood in a limiting sense, but rather provides examples of the invention, which are presented for illustrative purposes only by reference to the accompanying drawings to suggest the advantages and configurations of the invention to those of ordinary skill in the art. In the various views of the drawings, like reference numerals represent like or similar parts.

[0023] The optical path of the laser scanning microscope system according to an embodiment of the present invention is as follows: Figure 1 As shown. An input laser enters the system and the light is received and scanned by a scanner 110. The scanner can be either a single axis scanner or a dual axis scanner. The light passes through a repeater 120 and is then reflected by a folding mirror 130 to a dual axis scanner 140. The folding mirror allows the microscope system to be aligned. The light scanned by the dual axis scanner 140 then passes through a repeater 150, through a dichroic beam splitter 160, and then to an objective lens 170. Optomechanical components (not shown) may be used for input laser alignment control, for example, a kinematic mount for a fiber collimator that directs light to a single axis scanner in the microscope.

[0024] In one embodiment, the microscope can be used for multiphoton EPI fluorescence detection with a non-de-scanning detection scheme. The objective lens focuses the scanned light onto the sample. The sample interacts with the incident light and emits fluorescence back to the objective lens 170. A dichroic beam splitter 160 is placed next to the objective pupil to deflect the fluorescence signal laterally. A lens or a set of lenses 180 focuses the fluorescence into a light detector 190, such as a photomultiplier tube or a silicon photomultiplier tube.

[0025] The optical path of the confocal microscope system according to an embodiment of the present invention is as follows: Figure 7 As shown. The input laser enters the confocal microscope system, the light passes through the beam splitter 210, and is then received and scanned by the scanner 110. The scanner can be a single-axis scanner or a dual-axis scanner. The light passes through the repeater 120 and is then reflected by the folding mirror 130 to the dual-axis scanner 140. The light scanned by the dual-axis scanner 140 then passes through the repeater 150 and then reaches the objective lens 170. The light signal received from the objective lens 170 is de-scanned back to the optical path, the light signal is deflected by the beam splitter 210, and through the lens and pinhole 220, the light signal is detected by the detector 230.

[0026] The key elements in the above system according to the embodiment are two MEMS scanners. The first MEMS scanner is a single-axis resonant scanner, which can also be a dual-axis scanner. It has a smaller-sized mirror with a diameter of about 1.2 to 2 mm. The smaller mirror, therefore lighter weight and lower inertia has a higher resonant frequency in the range of 4–12kHz. When the mirror is driven at the resonant frequency, the mirror can also be tilted at a larger mechanical angle of ±8 degrees (optical ±16 degrees). The second MEMS scanner is a dual-axis point-to-point scanner. It has a mirror with a diameter of about 5 mm and a tilt angle of up to ±5 degrees (optical ±10 degrees) in both the X and Y directions. The scanning planes of the two MEMS scanners are optically conjugated with a 4f relay lens system with a magnification ratio of 1:4. After the second MEMS scanner, a second relay lens system is inserted to project the scanning plane onto the entrance pupil of the microscope objective.

[0027] An important feature in embodiments of the present invention is that the beam expansion is different between the first mirror in the first scanner and the mirror in the second scanner. This arrangement not only creates a conjugate pair, but also allows the mirror in the first scanner to be significantly smaller, and then the conjugation between the mirrors not only makes the mirrors conjugate, but also allows the system to act as a scan lens and beam telescope. The use of small mirrors in the first scanner allows the use of MEMS devices, which are significantly simpler to use and still have similar performance. This creates a more compact and simpler system.

[0028] In one embodiment, one or more additional MEMS scanners and relay systems are used to further extend the length of the imaging system. For example, in a system with 3 MEMS scanners, a first beam scanner scans the laser beam around one or more axes, and a first group of relay lenses conjugates the scanning plane of the first beam scanner with the scanning plane of the second beam scanner. A second beam scanner scans light around one or more axes, and a second group of relay lenses conjugates the scanning plane of the second beam scanner with the scanning plane of the third beam scanner. A third beam scanner scans light around one or more axes, and a third group of relay lenses projects the scanning plane of the third beam scanner onto the pupil of the objective lens. Although not shown, it should be understood that the arrangement of one or more additional MEMS scanners and relay systems is similar to Figure 1 and 7 -9 shows a repeated arrangement of a second MEMS scanner and a second set of relay lenses.

[0029] The system according to the embodiment has three imaging modes. The first mode is a fast raster scanning mode running at video frame rates. In this mode, the first MEMS scans in a resonant mode on the fast X axis. The second MEMS scans on the slow Y axis. With appropriate electronic control, the raster scan can run at 30–45 frames per second (fps) for an image pixel size of 512×512. The second mode is slow point-to-point scanning. In this mode, the first MEMS remains stationary at the center. The second MEMS scans in the X and Y directions to build an image. Although the point-to-point mode scans a 512×512 image size at a slower frame rate of 2 or 3fps, it provides a larger field of view, is more flexible in pixel dwell time, and is capable of randomly shaped ROI (Region of Interest) scans. In the third mode, multiple raster scans can be performed within a given FOV (Field ofview) to increase the frame rate of a subset of the area. This is typically done using an X and Y resonant scanning system.

[0030] Scanning optics

[0031] To achieve optimal imaging resolution and 2-photon excitation efficiency, the optical system needs to be diffraction limited. Figure 2 and 3 Example layouts are shown for Repeater 1 and Repeater 2. Both are achromatically corrected for 910–950nm and are diffraction limited.

[0032] Figure 2An example embodiment of a repeater with a 1:4 beam expansion is shown. Repeater 1 consists of a scan lens with an effective focal length of 12.5 mm and a tubular lens with an effective focal length of 50 mm. It has an entrance pupil diameter of 1.3 mm and an exit pupil diameter of 5.2 mm. It allows scan angles of up to ±16 degrees, matching the scan range of the resonant MEMS scanner.

[0033] Figure 3 An example embodiment of a repeater with 1:2 beam expansion is shown. Repeater 2 consists of a scan lens with an effective focal length of 25 mm and a tube lens with an effective focal length of 50 mm. It has an entrance pupil diameter of 5 mm and an exit pupil diameter of 10 mm. It allows scan angles up to ±7.5 degrees. At the exit pupil, the scan angle is reduced by half to ±3.75 degrees, matching the incidence angles of most commercial objective lenses.

[0034] Figure 4 The layout of the entire rod microscope optical system is shown. For simulation purposes, paraxial lenses representing ideal objectives are inserted at the ends of the layout. The Strehl ratios for different field positions are plotted as 2D diagrams, as shown in Figure 5 shown.

[0035] System Specifications

[0036] The following are example system specifications for a microscope according to an embodiment.

[0037] Assuming a 20x objective lens with a focal length of 9mm:

[0038] Fast scanning FOV: 600μm (424μm×424μm)

[0039] Slow scanning FOV: 1mm (700μm×700μm)

[0040] Input beam: Maximum

[0041] Effective NA (Numerical Aperture): 0.53

[0042] Design wavelength: 910nm–950nm

[0043] Laser source and fiber coupling

[0044] In one embodiment, laser light is delivered to the system via photonic crystal hollow core fiber, which ensures high throughput and manageable group delay dispersion. The fiber is essential to allow the rod microscope's 6-DOF maneuverability.

[0045] Mechanical systems and robotic arms

[0046] Some advantages of a microscope according to one embodiment include light weight and compact size, and the rod microscope can be mounted and manipulated by a tabletop robotic arm, such as Figure 6 shown.

[0047] MEMS Scanner Position Tracking

[0048] According to one embodiment, an additional laser 240 may be added to track the scanning position to close the loop of the MEMS mirror control, thereby allowing precise control of the amplitude, scanning angle, or phase of the MEMS scanner. For example, a low-power continuous wave visible light or NIR (Near Infrared) laser may be selected for such tasks. Figure 8 As shown, the dichroic beam combiner 250 directs the tracking laser beam into the optical path of the laser scanning imaging system. The tracking laser beam can be extracted from the optical path at a desired position. In one embodiment, a position detector (PSD) 260 after the focusing lens 270 can be placed next to the dichroic BS (Beam Splitter) 160 opposite to the fluorescence detector 190 to detect the tracking laser beam. Through the PSD of the MEMS scanner and appropriate control electronics, the system can track the angle of each MEMS mirror in real time and allow the control electronics to compensate for thermal drift caused by ambient temperature fluctuations or excitation laser power modulation.

[0049] Liquid Crystal Polarization Zone Plate (LCPZP)

[0050] LCPZP consists of a nematic liquid crystal (LC) film that is surface aligned to present a permanent, continuously changing concentric polarization grating pattern. The pattern is arranged to act as a diffraction lens. Note that the use of LCPZP for beam control stages has been discussed in US2021 / 0188467A1. For incident light with a single chirality of circular polarization, the LCPZP will focus the incident beam, while for the opposite chirality, the light passing through the LCPZP will diverge. Therefore, the focus of the LCPZP can be adjusted by changing the handedness of the incident circularly polarized light. Therefore, a switchable variable focal length lens can be created by inserting a stack of LC half-wave switches between multiple LCPZPs with selected power. This technology can be combined in the above embodiments to add fast laser focus control along the objective axis for three-dimensional image acquisition.

[0051] like Fig. 9As shown, according to one embodiment, the LCPZP lens stack 280 is placed after the relay 2 tube lens 150 and before the dichroic beam splitter 160. With this configuration, the LCPZP can control the divergence of the excitation laser without affecting the fluorescence signal collection throughput. The number of discrete focal planes of the LCPZP lens is 2 N , where N is the order of the LCPZP lens. Fig.10 The two-photon excitation focus in a fluorescein dye cell using a quadrupole LCPZP lens and a 10x objective is shown. Fig.10 In this case, 16 discrete foci are recorded one by one but presented in one image.

[0052] There are several advantages to using an LCPZP lens for focus control in a laser scanning imaging system according to one embodiment:

[0053] Lightweight and smaller size, suitable for compact microscope systems.

[0054] Rapidly switch focus within milliseconds.

[0055] No mechanical moving parts.

[0056] Another configuration for implementing the LCPZP lens, not limited to the compact system described herein, is to place the LCPZP lens before the scanning mirror. Fig.11 A scanning system with a set of scanning mirrors according to an embodiment and a position where the LCPZP lens stack 280 can be arranged to provide focus control remotely are shown. A relay 120 can be used between the LCPZP lens stack 280 and the scanning mirror 140 to match the apertures of the two. An input laser enters the system, the light passes through the LCPZP lens stack 280 and the relay 120, and is then reflected by the folding mirror 130 to the scanner 140. The light scanned by the scanner 140 then passes through the relay 150, through the dichroic beam splitter 160, and then reaches the objective lens 170. In one embodiment, the scanning system can be used for multi-photon EPI fluorescence detection with a non-de-scanning detection scheme. The objective lens focuses the scanned light onto the sample. The sample interacts with the incident light and emits fluorescence back to the objective lens 170. The dichroic beam splitter 160 is placed next to the target pupil to deflect the fluorescence signal laterally. A lens or a group of lenses 180 focuses the fluorescence into the photodetector 190.

[0057] Since the LCPZP lens causes the beam focus to deviate from the nominal focal plane of the objective lens, a certain amount of spherical aberration will be generated. In the case of such aberration, a pair of spherical compensators 291, 292 can be introduced into the optical repeater to pre-compensate and improve the final PSF (Point Spread Function) quality, such as Fig.12 As shown in the embodiment.

[0058] A pair of aspheric lenses separated by a certain distance act as spherical aberration compensators. The separation is fixed, so no mechanical moving parts are required. The aspheric surfaces of the two compensators are custom made, one compensating for positive spherical wavefront aberration and the other compensating for negative spherical aberration. At neutral LCPZP power, the beam width through both compensator surfaces is the same, so the positive and negative compensations cancel each other out. At negative LCPZP power, the beam diverges, so the beam width at the negative (concave) compensator is larger than the beam width at the positive (convex) compensator, as shown in Figure 1. Fig.13 As shown in Figure 2, the net spherical aberration compensation is negative. Under positive LCPZP power conditions, the beam converges, so the beam width at the negative (concave) compensator is smaller than the beam width at the positive (convex) compensator, as shown in Figure 2. Fig.14 Therefore, the net spherical aberration compensation is positive.

[0059] Although the present invention has been described with some length and particularity in several of the described embodiments, the present invention is not limited to any such details or embodiments or to any particular embodiment, but should be interpreted with reference to the appended claims so as to provide the broadest possible interpretation of those claims in light of the prior art, and therefore, effectively encompass the intended scope of the present invention. In addition, the foregoing describes the present invention in terms of the embodiments foreseen by the inventors, although non-substantial modifications of the present invention not yet foreseen may represent equivalents thereof.

Claims

1. A laser scanning imaging system, comprising: First beam scanner; The first set of relay lenses; a second beam scanner; The second relay lens; and Objective lens; wherein the first beam scanner is configured to receive an input laser beam and scan the laser beam about one or more axes; wherein the first group of relay lenses is configured to expand the laser beam scanned by the first beam scanner and conjugate a scanning plane of the first beam scanner with a scanning plane of the second beam scanner; wherein the second beam scanner is configured to scan the laser beam relayed by the first set of relay lenses about one or more axes; as well as wherein the second group of relay lenses is configured to expand the laser beam scanned by the second beam scanner and project a scan plane of the second beam scanner onto a pupil of the objective lens; Also includes: a beam splitter located next to a pupil of the objective lens, configured to deflect light signals received from the objective lens out of an optical path, and one or more collection lenses configured to focus the deflected light signals into a light detector; A liquid crystal polarization zone plate LCPZP lens stack is located between the second group of relay lenses and the beam splitter, so that the LCPZP lens stack can control the divergence of the laser beam without affecting the collection of the optical signal.

2. The system of claim 1, wherein the first beam scanner is a resonant micro-electromechanical system (MEMS) device that scans in a single axis; The second beam scanner is a non-resonant MEMS device that scans in two axes, one of which is parallel to the scanning axis of the first beam scanner.

3. The system of claim 2, further comprising an optical fiber coupled to the optomechanical component configured to guide input light from the laser source.

4. The system of claim 3, further comprising a beam splitter located between the input of the optical fiber and the first beam scanner, configured to deflect the de-scanned light signal from the objective lens to a pinhole assembly, the pinhole assembly comprising a pinhole configured to limit light to light from a focal point of the objective lens.

5. The system according to claim 1, further comprising: Tracking laser beam source; Position detector; a beam combiner configured to combine and direct the input laser beam and the tracking laser beam onto the first beam scanner; a beam splitter configured to deflect the tracking laser beam out of an optical path; and A lens is configured to focus the deflected tracking laser beam into the position detector. 6 . The system of claim 5 , further comprising a control circuit configured to control the first beam scanner and the second beam scanner based on the signal detected by the position detector.

7. The system of claim 1, wherein the LCPZP lens stack comprises a lens configured to provide 2 N N levels of discrete focal planes.

8. A laser scanning imaging system, comprising: First beam scanner; The first set of relay lenses; a second beam scanner; The second relay lens; a third beam scanner; The third relay lens; and Objective lens; wherein the first beam scanner is configured to receive an input laser beam and scan the laser beam about one or more axes; wherein the first group of relay lenses is configured to expand the laser beam scanned by the first beam scanner and conjugate a scanning plane of the first beam scanner with a scanning plane of the second beam scanner; wherein the second beam scanner is configured to scan the laser beam relayed by the first set of relay lenses about one or more axes; wherein the second group of relay lenses is configured to expand the laser beam scanned by the second beam scanner and conjugate a scanning plane of the second beam scanner with a scanning plane of the third beam scanner; wherein the third beam scanner is configured to scan the laser beam relayed by the second set of relay lenses around one or more axes; and wherein the third group of relay lenses is configured to expand the laser beam scanned by the third beam scanner and project a scanning plane of the third beam scanner onto a pupil of the objective lens; Also includes: a beam splitter located next to a pupil of the objective lens, configured to deflect light signals received from the objective lens out of an optical path, and one or more collection lenses configured to focus the deflected light signals into a light detector; A liquid crystal polarization zone plate LCPZP lens stack is located between the third group of relay lenses and the beam splitter, so that the LCPZP lens stack can control the divergence of the laser beam without affecting the collection of the optical signal.

9. The system of claim 8, wherein the first beam scanner is a resonant micro-electromechanical system (MEMS) device that scans in a single axis; The second beam scanner is a non-resonant MEMS device that scans in two axes, one of which is parallel to the scan of the first beam scanner; The third beam scanner is a non-resonant MEMS device that scans in two axes, one of which is parallel to the scanning axis of the first beam scanner, or one of which is parallel to one of the scanning axes of the second beam scanner.

10. The system of claim 9, further comprising an optical fiber coupled to the optomechanical component configured to guide input light from the laser source.

11. The system of claim 10, further comprising a beam splitter located between the input of the optical fiber and the first beam scanner, configured to deflect a de-scanned optical signal from the objective lens to a pinhole assembly, the pinhole assembly comprising a pinhole configured to limit light to light from a focal point of the objective lens.

12. The system of claim 8, further comprising: Tracking laser beam source; Position detector; a beam combiner configured to combine and direct the input laser beam and the tracking laser beam onto the first beam scanner; a beam splitter configured to deflect the tracking laser beam out of an optical path; and a lens configured to focus the deflected tracking laser beam into the position detector. 13 . The system of claim 12 , further comprising a control circuit configured to control the first beam scanner, the second beam scanner, and the third beam scanner based on the signal detected by the position detector.

14. The system of claim 12, wherein the LCPZP lens stack comprises a lens configured to provide 2 N N levels of discrete focal planes.

15. A laser scanning imaging system, comprising: Liquid crystal polarization zone plate LCPZP lens stack; The first set of relay lenses; beam scanner; The second relay lens; and Objective lens; wherein the LCPZP lens stack is configured to receive an input laser beam and move a focus of the laser beam; wherein the first group of relay lenses is configured to receive a laser beam from the LCPZP lens stack and expand the laser beam to match an aperture of the LCPZP lens stack with an aperture of the beam scanner; wherein the beam scanner is configured to scan the laser beam relayed by the first set of relay lenses about one or more axes; and wherein the second group of relay lenses is configured to expand the laser beam scanned by the beam scanner and project a scanning plane of the beam scanner onto a pupil of the objective lens; Also included is a pair of spherical compensators separated by a fixed distance and configured to compensate for spherical aberration associated with the laser beam focus being moved away from the nominal focal plane of the objective lens by the LCPZP lens stack.

16. The laser scanning imaging system according to claim 15, wherein: In the spherical compensator, one is configured to compensate for positive spherical wavefront aberration and the other is configured to compensate for negative spherical aberration, so that: (a) under neutral LCPZP power conditions, positive compensation and negative compensation cancel each other out; (b) under negative LCPZP power adjustment, negative compensation is greater than positive compensation; (c) under positive LCPZP power adjustment, negative compensation is less than positive compensation.

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