WO2019109071A1

WO2019109071A1 - System and method for preparing laser light for microscopy

Info

Publication number: WO2019109071A1
Application number: PCT/US2018/063594
Authority: WO
Inventors: Henry SCHEK, III
Original assignee: Chroma Technology Corp.
Priority date: 2017-12-01
Filing date: 2018-12-03
Publication date: 2019-06-06

Abstract

A device is provided for treating laser light so that the laser light can be used as a light source for illuminating samples for various forms of microscopy while retaining the beneficial characteristics of a laser light source such as intensity and directionality. The device receives a laser beam from a laser light source and sends the beam into conditioning optics that focus the light into homogenizing optics that expand the etendue of the light beam. The conditioned, homogenized light beam is eye-safe and enters output optics that deliver the light beam to a microscope.

Description

SYSTEM AND METHOD FOR PREPARING LASER LIGHT FOR MICROSCOPY

FIELD OF THE INVENTION

[0001] The present invention generally relates to microscopy. In particular, the present invention is directed to modifying laser light so that it is eye-safe and appropriate for microscopy, including widefield microscopy, stereo microscopy, mesoscopy, or macroscopy.

BACKGROUND

[0002] In order to produce an even field of illumination of samples, many microscopes use a technique called Kohler illumination. Kohler illumination is a technique that seeks to prevent uneven illumination of a sample caused by the formation on the sample of an image of the light source (e.g., a filament of an incandescent bulb). This is accomplished through the use of optical elements that place the image of the light source in the back focal plane of the objective. The back focal plane of the objective can accept up to a 4-15 mm spot at about a 3 degree half-cone. This means that, when using Kohler illumination, the largest cone of light that is useful for imaging is about a 3 mm light source with a divergence half-angle of 15-18 degrees. A major challenge with LEDs as light sources is that a 3 mm LED source emits into a full 180 degree cone and only the central solid angle is useful for imaging, which limits the average power that can be delivered for illuminating the sample.

[0003] In the field of microscopy, the use of lasers as light sources has been limited to advanced techniques. Generally, laser systems used for microscopy are Class 3 or Class 4 lasers, which can present a legitimate danger to the human eye. Further, Class 3 and Class 4 lasers are not well-suited for most types of microscopy, in which the entirety'- of the field of view is illuminated simultaneously or nearly simultaneously. In widefield microscopy, for example, many users prefer to view samples by looking through the eye-pieces of the microscope, but laser safety generally demands that the user not look through the eye-pieces of the microscope when lasers are used as the source of illumination. In addition, laser illumination is often spatially and temporally uneven, resulting in poor imaging. Further, laser systems have generally been more expensive to users than the more common non coherent extended sources found in lamps and LEDs, which also tend to present fewer hazards.

[0004] Lasers offer many advantages, however, when used as light sources for microscopy. Light management is easier, as intensity can be quite high and easy to direct. Cost, especially for laser diodes, is in line with high-end LEDs, making that less of a factor. Nevertheless, the broadest swath of microscopy techniques cannot accommodate a laser as the light source for use in a microscope with eye-pieces because laser safety regulations require that any device that could allow the viewing by eye of the emission of a Class 3 or 4 laser be interlocked such that opening the eye- pieces for viewing stops the emission of the light source.

[0005] Laser safety regulations are mostly aimed at determining the potential of a laser to damage the human eye. The eye is built to optically focus light from distant objects, which generally arrives at the eye in the form of parallel rays (i.e., as collimated light) onto the retina. Lasers emit collimated light that is generally much more intense than light from distance objects. Laser light is therefore dangerous to eyes because an intense beam of collimated light will be focused by the eye into a tiny spot with high power per area on the retina where it can do great, and potentially permanent, damage.

[0006] In general, for the purposes of laser safety regulations, any light generated by a laser is always treated as laser light, regardless of how it is conditioned. However, it is possible to build a system for conditioning laser light that will make it unfocusable without expanding the beam to a full 180 degrees. Some systems can make laser light diffuse enough so that the light can be treated as non-laser light for safety' purposes. Such systems are primarily used for general architectural illumination or projected illumination, such as for creating images on a movie screen.

[0007] What is needed is a way to make laser light suitable in terms of eye safety for use as a light source in microscopes while retaining, to at least some extent, the favorable properties of laser light in terms of intensity and control that are advantageous for microscope light sources.

SUMMARY OF THE DISCLOSURE

[0008] In an exemplary embodiment, a device for preparing laser light for microscopy is provided that includes an input conduit designed and configured to receive a light beam from a laser light source, a conditioning optic including a lens having a focal length, the conditioning optic configured to receive the light beam from the input conduit, a homogenizing optic having a receiving aperture and being designed and configured to homogenize and to expand an etendue of the light beam when the conditioned light beam passes through the homogenizing optic such that an exiting homogenized light beam is eye-safe for use in microscopy, and an output optic positioned and configured to guide the homogenized light beam to an external destination.

[0009] Additionally or alternatively, the conditioning optic directs the received light beam to the receiving aperture such that rays of the light beam are internally reflected within the homogenizing optic.

[0010] Additionally or alternatively, the homogenizing optic is a light rod or pipe.

[0011] Additionally or alternatively, the light rod is a hexagonal rod.

[0012] Additionally or alternatively, the light rod is a pentagonal rod.

[0013] Additionally or alternatively, the light rod is a heptagonal rod.

[0014] Additionally or alternatively, the light rod has an aperture between about 0.4 mm and 5 mm and a length between about 10 mm and 200 mm.

[0015] Additionally or alternatively, the conditioning optic is an aspheric lens, and wherein the focal length is between about 5 mm and 50 mm.

[0016] Additionally or alternatively, a half-angle of the light beam is between about 5 degrees and 22 degrees when the conditioning optic receives the light beam.

[0017] Additionally or alternatively, the half-angle of the light beam is decreased upon exiting the conditioning optic.

[0018] Additionally or alternatively, the output optic is a liquid light guide.

[0019] In another exemplary embodiment, a method of preparing laser light for microscopy is provided that includes receiving a light beam from a laser light source, passing the light beam through a conditioning optic to modify an angular distribution of the light beam, expanding an etendue of the modified light beam by passing the modified light beam through a homogenizing optic, homogenizing the modified light beam by passing the modified light beam through the homogenizing optic, and delivering the homogenized light beam to illuminate a sample in a microscope. [0020] Additionally or alternatively, homogenizing the modified light beam includes internally reflecting at least a portion of the light beam within the homogenizing optic.

[0021] Additionally or alternatively, passing the light beam through the conditioning optic includes increasing a half-angle of the light beam.

[0022] Additionally or alternatively, the homogenizing optic is a light rod with an aperture between about 0.4 mm and 5 mm and a length between about 10 mm and 200 mm.

[0023] Additionally or alternatively, the conditioning optic is an aspheric lens having a focal length between about 5 mm and 50 mm.

[0024] Additionally or alternatively, the light rod is a hexagonal light rod.

[0025] Additionally or alternatively, the light rod is a pentagonal light rod.

[0026] Additionally or alternatively, the light rod is a heptagonal light rod.

[0027] In another exemplary embodiment, a system for preparing laser light for microscopy is provided that includes an input optic for receiving a light beam from a laser light source, the light beam having an etendue, a conditioning optic with a focal length, the conditioning optic positioned to receive the light beam from the input optic and configured to increase a half-angle of the light beam, a homogenizing optic positioned to receive the light beam after the light beam passes through the conditioning optic, the homogenizing optic designed and configured to expand the etendue of the light beam when the conditioned light beam passes through the homogenizing optic such that a resulting homogenized light beam is eye-safe for use in microscopy, and an output optic positioned and configured to deliver the homogenized light beam to a microscope.

[0028] Additionally or alternatively, the homogenizing optic and conditioning optic are configured such that at least a portion of the light beam is internally reflected within the

homogenizing optic.

[0029] Additionally or alternatively, the homogenizing optic is a light rod.

[0030] Additionally or alternatively, the light rod is a hexagonal rod. [0031] Additionally or alternatively, the light rod is a pentagonal rod.

[0032] Additionally or alternatively, the light rod is a heptagonal rod.

[0033] Additionally or alternatively, the light rod has an aperture between about 0.4 mm and 5 mm and a length between about 10 mm and 200 mm.

[0034] Additionally or alternatively, the conditioning optic is an aspheric lens, wherein the focal length is between about 5 mm and 50 mm.

[0035] Additionally or alternatively, the light rod has an odd number of internally reflecting faces.

[0036] In another embodiment, a method of modifying laser light for use in microscopy is provided that includes receiving laser light and passing the laser light through optical components, the optical components designed and configured to modify the laser light such that the laser light is eye-safe for use in microscopy.

[0037] Additionally or alternatively, the laser light is from a Class 4 laser source.

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] For the purpose of illustrating the invention, the drawings show aspects of one or more embodiments of the invention. However, it should be understood that the present invention is not limited to the precise arrangements and instrumentalities shown in the drawings, wherein:

FIG. 1 is a schematic of components that may be included in a system for preparing laser light in accordance with an embodiment of the present invention;

FIG. 2 is a device for preparing laser light in accordance with an embodiment of the present invention;

FIG. 3. is a cross-sectional view of a device for preparing laser light in accordance with an embodiment of the present invention;

FIG. 4A depicts light-rays passing through optical components of an exemplary device from a side view in accordance with an embodiment of the present invention; FIG. 4B depicts light-rays passing through optical components of an exemplary device from a perspective view in accordance with an embodiment of the present in vention;

FIG. 5 depicts two light rays, for clarity, passing through optical components of an exemplar}' device from a side view in accordance with an embodiment of the present invention; and

FIG. 6 is a perspective view of a pentagonal light rod that may be used as an optical component of a homogenizing module in another embodiment of the present inven tion.

DESCRIPTION OF THE DISCLOSURE

[0039] Tire present invention modifies light produced by a laser in order to make the light suitable for use in microscopy, both in terms of eye-safety and in terms of sample illumination. In this way, the advantages associated with laser light sources, such as intensity and directionality, can be safely utilized for various types of microscopy.

[0040] A laser light modification system 100 for modifying laser light is outlined in FIG. 1 and includes a light conditioning module 104, a light homogenizing module 108, and an output module 112. A first set of conditioning optics forms light conditioning module 104 that receives light from a laser source and adjusts the angular distribution of the laser light. Light conditioning module 104 then directs the light to light homogenizing module 108 at an appropriate angle. Light homogenizing module 108 expands the etendue of the laser beam received from light conditioning module 104. (The etendue of a light beam is how spread out the light is in area and angle. Light from an LED light source, for example, has a very' large etendue, while light from a laser has a low etendue.) The light exiting light homogenizing module 108 is eye-safe and is directed to an intended location, such as a widefield microscope for illumination of a specimen, through output module 112.

[0041] It will be understood that the various optical components may be shared by the different modules and it will further be understood that the order that the laser light encounters the various optical components may be altered so long as the exiting light is eye-safe for use in microscopes and conditioned for illuminating samples in microscopes.

[0042] Light conditioning module 104 may include various optics for altering the angular distribution of the incoming laser beam, such as lensing 120, light guides 124, and additional optics 128. Light homogenizing module 108 may include any appropriate optics for expanding the beam without significantly changing the angular profile of the beam, such as a lens 132, rods 136, lenslet arrays 140, diffusers 144, and holograms 14S. These optics can be used in coordination with the optics of light conditioning module 104 to cause light homogenizing module 108 to irreversibly expand the etendue of the laser beam so that it cannot be focused in a way that could damage the eyes of a user. Therefore, light that passes through the components of light conditioning module 104 and light homogenizing module 108 is unfocused to a degree that allows for the light to be treated under the light source safety guidelines equivalently to light from an incandescent lamp hi other words, the focusability of laser light passing through these modules is attenuated to a level that reduces the laser classification necessary for regulatory approval of the laser. For example, a 0.22 NA laser beam (12 degree half angle) at a diameter of 400 mm, which is a Class 4 laser in the absence of modification by the modules, can have an etendue expanded to a diameter of 3 mm at 12- 15 degrees.

[0043] Once light from a laser source has been modified to be safely used to illuminate a sample for a microscope while retaining the valuable properties of intensity and directionality, that light passes to output module 112. Output module 112 takes the eye-safe light from homogenizing module 108 and collects and directs the conditioned light to a microscope (or to another setting for other uses) and may include any suitable light transporting optic, such as a liquid light guide 152.

[0044] FIG. 2 shows a light conditioning device 160 for modifying laser light as described above that includes a light conditioning module, a light homogenizing module, and an output module (internal to the device, and thus not shown). In addition, device 160 may include an input port 164, which may be a fiber optic connector or other suitable conduit and an output segment 168, such as a liquid light guide or fiber optic tube to carry modified light to the microscope.

[0045] Turning to FIG. 3, a cross sectional view of a laser light modification system 200 is shown that includes a lens 204, a light pipe 208, and a light guide 212. Laser light from a laser (not shown) enters system 200 through an input optic 216 such as a fiber optic or other suitable conduit from a laser source. The light then reaches lens 204, which serves as a conditioning optic. Lens 204 focuses the light on the next optical component, light pipe 208, and thereby effectively controls the angle of entry of the light beam into light pipe 208. By controlling the angle of entry in light pipe 208, the number of internal reflections (or bounces) that happen within light pipe 208 is determined. For example, a tighter focus means that light pipe 208 can be shorter (and still produce the necessary number of internal reflections for homogenizing the light). Thus, lens 204 is selected in view of the parameters of light pipe 208 so that the degree of homogenization needed will occur via light pipe 208. (Laser light that has passed through only lens 204 would not yet be eye safe and would not yet be appropriate for microscopy.)

[0046] Light pipe 208 is selected, as noted, in conjunction with lens 204, to produce a specific light distribution. Light pipe 208 may be any suitable optical component that will homogenize the light. An example is a 2 mm hexagonal light rod or pipe. Light pipe 208 causes an irreversible expansion of the etendue of the entering light beam. This is a result in part of the fact that light going through light pipe 208 exhibits total internal reflections within light pipe 208, which has angled sides (e.g., hexagonal). This configuration causes light pipe 208 to“mash up” and homogenize the light. Thus, light exiting light pipe 208 (if it entered at an appropriate angle from lens 204 such that a substantial portion of the light is internally reflected in light pipe 208) is unfocusable by the retina and so is eye safe.

[0047] In addition to producing eye safe light, lens 204 and light pipe 208 are selected and designe to produce a light distribution that can be used for sample illumination in microscopy and that retains to a sufficient extent the advantages with respect to intensity and directionality of the original laser light source.

[0048] The conditioned light exiting light pipe 208 enters an output coupler such as light guide 212, which can be a liquid light guide or other suitable mechanism for directing the conditioned light toward its intended use, e.g., a sample in a widefield microscope.

[0049] A plan view of an exemplary laser light modification system 300 is shown in FIG. 4A that shows for clarity selected optical components along with examples of light ray paths 303 (e.g., 303a-303f) passing through the optical components. The optical components of system 300 include an input optic 302, an aspheric lens 304, and a hexagonal light pipe 308. Aspheric lens 304 can generally have a diameter in the range of 50 mm to 5 mm and effective focal length of from about 50 mm to 5 mm. hr a preferred embodiment, aspheric lens 304 has a diameter of 12.7 mm and an effective focal length of 8 mm. Alternatively, a combination of lenses may be used to achieve a similar modification of incoming laser light. Thus, a suitable lens or combination of lenses is selected such that incoming laser light converges into the input aperture of the light homogenizing module. Alternatively, concave lenses may be used by being placed close to the light homogenizing module in order to make sure diverging light is captured.

[0050] Tire light homogenizing module is designed so that light rays entering from aspheric lens 304 are internally reflected within the light homogenizing module. In the exemplary

combination of optics shown in FIGS. 4A-4B, hexagonal light pipe 308 has a 2 mm clear aperture and a length of 25 mm. However, the clear aperture can range from about 0.4 mm to about 5 mm and the length can range from about 10 mm to about 200 mm. Generally, the combination of focal lengths of the lens and properties of the light homogenizing optic (e.g., hexagonal rods) are selected so that the light bundle from a laser is completely received into input area 310 of the light homogenizing optic (e.g., hexagonal rod 308) and at an angle such that light rays 303 bounce at least once on the internally reflective surface of the light homogenizing module (e.g., hexagonal rod 308).

[0051] In the exemplary' arrangement of optics shown in FIGS. 4A-4B, the half-angle of the laser light emitted by input optic 302 is approximately 12.7 degrees, in other words, the fiber optic of input optic 302 has an N.A. of 0.22. In general, half-angles ranging from about 5 degrees to 22 degrees can be used for the entering laser light (equating to N.A. ranging from about 0.10 to 0.37). The half-angle of the light exiting from lens 304 is approximately 16 degrees.

[0052] In FIG. 5, system 300 is shown with just two light rays (303a, 303b) passing through for the purpose of illustrating the internal reflections within rod 308. As can be seen, rays 303 enter rod 308 at different angles and therefore strike the interior surface at different angles and locations (e.g., different sides, different distances), which results in an overall dispersion of rays 303 as they are internally reflected hi this way, rays 303 exit rod 308 less coherent than they enter. In other words, rays 303 entering system 300 proximate to each other will exit in a completely different direction, and so cannot be captured to be tightly focused at the same spot, effectively rendering them eye-safe when used for illumination of a sample in a microscope.

[0053] In operation, as shown for example in FIGS. 4A-5, laser light enters optical conditioning system 300 via an input optic 302 such as a fiber optic and then passes through a series of optical components with appropriate properties that are arranged such that the light after passing through is prepared for eye-safe use in a microscope. In particular, after exiting input optic 302, the laser light strikes lens 304, which focuses the light to a light pipe or rod 308, which homogenizes and expands the etendue of the light. The conditioned, homogenized light exits rod 308 and is directed, such as via a liqui light guide or fiber optic, to a microscope for illumination of a sample, for example.

[0054] In an alternative to the use of a hexagonal light pipe for the homogenizing module, a light pipe with an odd number of internally reflecting faces (e.g., 3, 5, or 7) may be used, such as pentagonal light pipe 408 shown in FIG. 6. Light pipes with an odd number of faces can have no longitudinal faces that oppose each other, which can further ensure that light rays do not merely oscillate between parallel faces as they travel down the light pipe. A light pipe with an odd number of faces thereby may provide for an increased homogenizing effect.

[0055] It is noted that there can be rays that enter the homogenizing module at angles small enough so that they do not bounce on any portion of the rod and are therefore not homogenized. In general, this non-reflected light will constitute a very small portion of the output and can therefore be neglected. However, in some circumstances (for example, when the laser source is a single-node laser with a Gaussian output beam at a very low angle) additional optical components to those described above may be necessary to provide enough homogenization, including diffusers (e.g., groimd glass (engineered or holographic) and'dr lens arrays.

[0056] It will be understood that the conditioning optic may be, in addition to a lens, any number of optical elements that can focus and condition the light. Likewise, the light homogenizing module could be any suitable homogenizing optics provided the selected homogenizing optic could be used in conjunction with the preceding optical elements of the conditioning module. Further, there could be another set of optics after the homogenizing optic but before the output optic. In addition to light guides, the output optic could be a wide variety of devices designed for transporting light. All of the optics of the conditioning device could also be embedded in a single, solid-free- form optic that functions to treat the light as above in sequence.

[0057] Exemplary embodiments have been disclosed above and illustrated in the accompanying drawings. It will be understood by those skilled in the art that various changes, omissions and additions may be made to that which is specifically disclosed herein without departing from the spirit and scope of the present invention.

Claims

What is claimed is:

1. A device for preparing laser light for microscopy comprising:

an input conduit designed and configured to receive a light beam from a laser light source: a conditioning optic including a lens having a focal length, the conditioning optic configured to receive the light beam from the input conduit;

a homogenizing optic having a receiving aperture and being designed and configured to

homogenize and to expand an etendue of the light beam when the conditioned light beam passes through the homogenizing optic such that an exiting homogenized light beam is eye-safe for use in microscopy; and

an output optic positioned and configured to guide the homogenized light beam to an external destination.

2. The device for preparing laser light of claim 1, wherein the conditioning optic directs the received light beam to the receiving aperture such that rays of the light beam are internally reflected within the homogenizing optic.

3. The device for preparing laser light of claim 1, wherein the homogenizing optic is a light rod.

4. The device for preparing laser light according to claim 3, wherein the light rod is a hexagonal rod.

5. The device for preparing laser light according to claim 3, wherein the light rod is a

pentagonal rod.

6. The device for preparing laser light according to claim 3, wherein the light rod is a

heptagonal rod.

7. The device for preparing laser light according to claim 3, wherein the light rod has an

aperture between about 0.4 mm and 5 mm and a length between about 10 mm and 200 mm.

8. The device for preparing laser light according to claim 7, wherein the conditioning optic is an aspheric lens, and wherein the focal length is between about 5 mm and 50 nun.

9. The device for preparing laser light according to claim 1, wherein a half-angle of the light beam is between about 5 degrees and 22 degrees when the conditioning optic receives the light beam.

10. The device for preparing laser light according to claim 9, wherein the half-angle of the light beam is decrease upon exiting the conditioning optic.

11. The device for preparing laser light according to claim 1 , wherein the output optic is a liquid light guide.

12. A method of preparing laser light for microscopy, comprising the steps of:

receiving a light beam from a laser light source;

passing the light beam through a conditioning optic to modify an angular distribution of the light beam;

expanding an etendue of the modified light beam by passing the modified light beam through a homogenizing optic;

homogenizing the modified light beam by passing the modified light beam through the homogenizing optic; and

delivering the homogenized light beam to illuminate a sample in a microscope.

13. The method of preparing laser light for microscopy of claim 12, wherein homogenizing the modified light beam includes internally reflecting at least a portion of the light beam within the homogenizing optic.

14. The method of preparing laser light for microscopy of claim 13, wherein passing the light beam through the conditioning optic includes increasing a half-angle of the light beam.

15. The method of preparing laser light for microscopy of claim 14, wherein the homogenizing optic is a light rod with an aperture between about 0.4 mm and 5 mm and a length between about 10 mm and 200 mm.

16. The method of preparing laser light for microscopy of claim 15, wherein the conditioning optic is an aspheric lens having a focal length between about 5 mm and 50 mm.

17. The method of preparing laser light for microscopy of claim 15, wherein the light rod is a hexagonal light rod.

18. The method of preparing laser light for microscopy of claim 15, wherein the light rod is a pentagonal light rod.

19. The method of preparing laser light for microscopy of claim 15, wherein the light rod is a heptagonal light rod.

20. A system for preparing laser light for microscopy comprising:

an input optic for receiving a light beam from a laser light source, the light beam having an etendue;

a conditioning optic with a focal length, the conditioning optic positioned to receive the light beam from the input optic and configured to increase a half-angle of the light beam;

a homogenizing optic positioned to receive the light beam after the light beam passes through the conditioning optic, the homogenizing optic designed and configured to expand the etendue of the light beam when the conditioned light beam passes through the homogenizing optic such that a resulting homogenized light beam is eye-safe for use in microscopy; and

an output optic positioned and configured to deliver the homogenized light beam to a microscope.

21. The system for preparing laser light according to claim 20, wherein the homogenizing optic and conditioning optic are configured such that at least a portion of the light beam is internally reflected within the homogenizing optic.

22. The system for preparing laser light according to claim 21, wherein the homogenizing optic is a light rod.

23. The system for preparing laser light according to claim 22, wherein the light rod is a

hexagonal rod.

24. The system for preparing laser light according to claim 22, wherein the light rod is a

pentagonal rod.

25. The system for preparing laser light according to claim 22, wherein the light rod is a

heptagonal rod.

26. The system for preparing laser light according to claim 22, wherein the light rod has an

27. The system for preparing laser light according to claim 26, wherein the conditioning optic is an aspheric lens, wherein the focal length is between about 5 mm and 50 mm.

28. The system for preparing laser light according to claim 26, wherein the light rod has an odd number of internally reflecting faces.

29. A method of modifying laser light for use in microscopy comprising:

receiving laser light; and

passing the laser light through optical components, the optical components designed and configured to modify the laser light such that tire laser light is eye-safe for use in microscopy.

30. The method of modifying laser light according to claim 29, wherein the laser light is from a Class 4 laser source.