A light source apparatus

Abstract

A light source apparatus 100 for use within an optical microscope or optical inspection system. The light source apparatus contains, mounted within the housing 110, an illumination stage 120 which has

Description

Field of the Invention The present invention relates to a light source apparatus. The invention also relates a microscope comprising the light source apparatus. The invention further relates to methods of optimising the output from the light source apparatus. Background to the Invention Fluorescence microscopy is a specialist technique in which an optical microscope is used to image and analyse specimen that can absorb light from a range of wavelengths and emit light of another range of wavelengths, where typically the emission wavelength is longer than the excitation wavelength. Due to the inefficiencies of fluorescence, the excitation light source must be bright within the appropriate wavelength range. Historically, arc lamps such as mercury and metal halide were used due to their broad spectrum and various spectral peaks within the visible spectrum. However, these technologies had various drawbacks: poor lifetime; lack of spectral tunability; fluctuations in brightness; long warm-up time; inefficiencies with undesired light; and environmental drawbacks. To address these issues, recent developments have focused on the use of LEDs as the source of illumination. However, a significant drawback with the use of LEDs is their low brightness. Due to the inefficiencies of fluorescence, a reduction in the brightness of the light source results in a significant decrease in the performance of the imaging process as a whole. Work in recent years has focused on increasing the brightness of the LEDs to address this issue. Summary of the Invention According to a first aspect of the present invention, there is provided a light source apparatus for use with an optical microscope or optical inspection system, the light source apparatus comprising; a housing; and an illumination stage mounted within the housing, an LED with a light emitting surface mounted on the illumination stage, and an associated collection stage mounted within the housing, a collection optic mounted on the collection stage; wherein the collection stage is configured to, in use, collect light emitted by the LED; wherein the illumination stage is mounted within the housing such that the illumination stage is movable in a first direction and a second direction, the first direction perpendicular to the second direction, and both the first direction and the second direction parallel to the light emitting surface; and wherein the collection stage is mounted within the housing such that the collection stage is movable in a third direction, the third direction perpendicular to the light emitting surface. In this way, there is provided a light source apparatus that optimises the brightness of the LED mounted on the illumination stage. The brightness of light emitted from the light source apparatus is a combination of two factors. The first factor is the brightness of the LED itself, and this has been the focus of technological developments in this area in recent years. The second factor is the efficiency of the light source apparatus itself. The more efficient the light source apparatus, the more of the light emitted by the LED exits the light source apparatus to illuminate a sample within the microscope. Previous approaches to maximising the efficiency of the light source apparatus have focused on the manufacture of components within the light source apparatus. Prior approaches have sought to address this issue by reducing the machine tolerances of components with the light source apparatus, to ensure all components within the light source apparatus are positioned precisely relative to one another. However, there is a natural limit to this approach, as each light source apparatus comprises many components, and the collective impact of many small discrepancies in component position cumulatively have a significant effect on overall efficiency of the light source apparatus. In the present invention, a new approach is taken to improve the efficiency of the light source apparatus. Instead of seeking to address the misalignment of components within the light source apparatus by further refining the machine tolerances specified during the manufacturing process, the natural variations due to existing machine tolerances are accepted. In the present invention, the LED can be moved in two directions on the illumination stage, these directions parallel to the light emitting surface. Additionally, the collection optic can be moved in a third direction perpendicular to the light emitting surface. As such, the position of the key components within the light source apparatus can be adjusted to reduce and / or eliminate any errors in position due to the machine tolerances of individual components, to maximise the efficiency of the light source apparatus. Preferably, the light source apparatus comprises a plurality of illumination stages and a plurality of collection stages, each of the illumination stages within the plurality of illumination stages associated with a separate collection stage within the plurality of collection stages. In this way, where the apparatus comprises a plurality of LEDs, the position, and therefore observed brightness, of each of the LEDs can be optimised individually. Preferably, each LED within the apparatus emits a wavelength of light distinct from the other LEDs within the apparatus. Such a configuration may be preferable where the light source apparatus is required to, in use, illuminate a substrate with many different wavelengths of light in turn, for example where the light source apparatus is used in fluorescence microscopy. Preferably, the light source apparatus further comprises a condenser optic, the condenser optic configured, in use, to condense the light emitted by the LED or plurality of LEDs. Such a feature may be advantageous in coupling the light emitted from the light source apparatus to a fluorescence microscope, in use. Preferably, the light source apparatus further comprises a focusing optic, the focusing optic configured, in use, to focus the light emitted by the LED or the plurality of LEDs. Such a feature may be advantageous in coupling the light emitted from the light source apparatus to a fluorescence microscope, in use. Preferably, the light source apparatus further comprises a magnifying optic, the focusing optic configured, in use, to magnify the light emitted by the LED or the plurality of LEDs. Such a feature may be advantageous in coupling the light emitted from the light source apparatus to a fluorescence microscope, in use. Preferably, the light source apparatus further comprises a dichroic mirror. Dichroic mirrors utilise thin-film coatings to create constructive and destructive interference when they interact with incident light. Therefore, these mirrors manipulate beams of light based upon their wavelength, rather than their geometric properties. As such, the use of dichroic mirrors within the light source apparatus further increases the efficiency of the apparatus. Preferably, the collection stage is positioned between the dichroic mirror and the illumination stage. In this way, the position of the collection lens and the LED may both be optimised to produce, in use, an optimised beam output that is then incident on the dichroic mirror. In this way, the efficiency of the light source apparatus is further increased, as the output of the LED is optimised before it impacts the highly efficiency dichroic mirror. Preferably, the light source apparatus further comprises an excitation filter. Such a feature may be preferable where the light source apparatus is used alongside a fluorescence microscope. Preferably, the illumination stage is movable between 1 pm and 5000 pm inclusive in the first direction. More preferably, the illumination stage is movable between 1 pm and 2000 pm in the first direction. Yet more preferably, the illumination stage is movable between 1 pm and 1000 pm in the first direction. Most preferably, the illumination stage is movable between 1 pm and 500 pm in the first direction. Such a range of position may be preferable, as it allows the LED to be moved in the first direction to optimise the location of the LED within the light source apparatus. The specified range of motion is sufficient to compensate for any expected deviation of position in the first direction due to typical machine tolerance misalignments. Preferably, the illumination stage is movable between 1 pm and 5000 pm inclusive in the second direction. More preferably, the illumination stage is movable between 1 pm and 2000 pm in the second direction. Yet more preferably, the illumination stage is movable between 1 pm and 1000 pm in the second direction. Most preferably, the illumination stage is movable between 1 pm and 500 pm in the second direction. Such a range of position may be preferable, as it allows the LED to be moved in the second direction to optimise the location of the LED within the light source apparatus. The specified range of motion is sufficient to compensate for any expected deviation of position in the second direction due to typical machine tolerance misalignments. Preferably, the collection stage is movable between 1 pm and 30,000 pm inclusive in the third direction. More preferably, the illumination stage is movable between 1 pm and 20,000 pm in the third direction. Yet more preferably, the illumination stage is movable between 1 pm and 10,000 pm in the third direction. Most preferably, the illumination stage is movable between 1 pm and 5,000 pm in the third direction. Such a range of position may be preferable, as it allows the collection optic to be moved in the second direction to optimise the location of the collection optic within the light source apparatus. The specified range of motion is sufficient to compensate for any expected deviation of position in the third direction due to typical machine tolerance misalignments. Preferably, the collection optic comprises a lens, the lens having a focal length smaller than or equal to its diameter. More preferably, the lens has a focal length smaller than or equal to 0.6 times its diameter. The highest irradiance LEDs have an emission area of approximately 1 mm2. To reach the theoretical limits of optical throughput with such a small emission area, the collection optic must have a high numerical aperture. As such, where the collection optic comprises a lens, the ratio between the lens’ focal length and its diameter must be relatively small, preferably <1, more preferably <0.6. Preferably, the LED has a spectral profile where the full width at half maximum is less than or equal to 200 nm. More preferably, the LED has a spectral profile where the full width at half maximum is less than or equal to 30 nm Preferably, the light source apparatus further comprises a fibre optic. More preferably, the light source apparatus is configured such that, in use, light exits the housing through the fibre optic. Such a feature may be advantageous in couple the light source apparatus to a fluorescence microscope, in use. According to a second aspect of the present invention, there is provided a microscope comprising the light source apparatus of the first aspect of the present invention. In this way, there is provided a fluorescence microscope with a light source apparatus with the advantages previously described. Preferably, the microscope is a fluorescence microscope. According to a third aspect of the present invention, there is provided a method of optimising the output of a light source apparatus, the method comprising the steps of: providing the apparatus of the first or second aspect of the invention; powering the LED such that it emits light; measuring the intensity of the emitted light; and moving the illumination stage in the first and second directions, and moving the collection stage in the third direction to maximise the intensity of the emitted light. In this way, there is provided a method that allows the performance of the light source apparatus to be optimised, providing the advantages as previously described herein. According to a fourth aspect of the present invention, there is provided a method of optimising the output of a light source apparatus, the method comprising the steps of: providing the apparatus of the first or second aspect of the invention; powering the LED such that it emits light; measuring the intersection point at which the emitted light intersects a plane, comparing the intersection point to a target intersection point on the plane, moving the illumination stage in the first and second directions, and moving the collection stage in the third direction to minimise the distance between the intersection point and the target intersection point. In this way, there is provided a method that allows the performance of the light source apparatus to be optimised, providing the advantages as previously described herein. Preferably, in the third or fourth aspect of the present invention, the step of moving the illumination stage is caried out before the step of moving the collection stage. Such a method may be advantageous in more precisely optimising the performance of the light source apparatus. Preferably, in the third or fourth aspect of the present invention, the step of moving the collection stage is caried out before the step of moving the illumination stage. Such a method may be advantageous in more precisely optimising the performance of the light source apparatus. Preferably, in the third or fourth aspect of the present invention, the step of moving the collection stage is caried out simultaneously with the step of moving the illumination stage. Such a method may be advantageous in more rapidly optimising the performance of the light source apparatus. Detailed Description Embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which: Figure 1 depicts a light source apparatus according to the present invention; Figure 2 depicts a second light source apparatus according to the present invention; and Figure 3 depicts measurements of the of the output of a light source apparatus according to the present invention after correction by a method according to the invention. Turning first to Figure 1, there is depicted a light source apparatus 100 according to the present invention. The light source apparatus 100 includes a housing 110 and a first illumination stage 120 within the housing. On the first illumination stage 120 a first LED 121 is mounted. The first illumination stage 120 is associated with a first collection stage. The first collection stage includes a first lens 131. The first illumination stage 120 is positioned such that, when lit, light from the first LED 121 is incident on and collected by the first lens 131. The first illumination stage 120 is mounted within the housing 110 such that the illumination stage 120 is movable in a first direction and a second direction. The first and second direction are perpendicular to each other. The first and second direction are parallel to the light emitting surface of the LED 121. When the first illumination stage 120 is moved in the first direction, the first illumination stage is translated horizontally in the configuration and orientation shown in Figure 1. When the first illumination stage 120 is moved in the second direction, the first illumination stage is translated along an axis perpendicular to the plane of the image of Figure 1 in the configuration and orientation as shown in Figure 1. The first collection stage is mounted within the housing 110 such that the collection stage is moveable in a third direction. The third direction is perpendicular to the light emitting surface of the LED 121. When the first collection stage is moved in the third direction, the collection stage is translated vertically in the configuration and orientation shown in Figure 1. The collection stage being movable in a third direction perpendicular to the light emitting surface allows the distance between the LED 121 and the collection lens 131 to be adjusted. In this way, chromatic aberration within the apparatus can be compensated for without the need for doublet achromats such as the flint glass and crown glass sublenses used in apparatuses of the prior art. In this way, the position of both the first illumination stage 120 and the first collection stage can be adjusted to improve the alignment of the first LED 121. This adjustment can overcome tolerance errors in, for example, the position of the dichroic mirror 160, the angle of the dichroic mirror 160, and the position of the condenser lens 170. The light source apparatus 100 includes a second illumination stage 140 within the housing 110. On the second illumination stage 140 a second LED 141 is mounted. The second illumination stage 140 is associated with a second collection stage. The second collection stage includes a second lens 151. The second illumination stage 140 is positioned such that, when lit, light from the first LED 141 is incident on and collected by the second lens 151. The second illumination stage 140 is mounted within the housing 110 such that the illumination stage 140 is movable in a first direction and a second direction. The first and second direction are perpendicular to each other. The first and second direction are parallel to the light emitting surface of the LED 141. When the second illumination stage 140 is moved in the first direction, the second illumination stage 140 is translated vertically in the configuration and orientation as shown in Figure 1. When the second illumination stage 140 is moved in the second direction, the second illumination stage 140 is translated along an axis perpendicular to the plane of the image of Figure 1 in the configuration and orientation as shown in Figure 1. The second collection stage is mounted within the housing 110 such that the collection stage is moveable in a third direction. The third direction is perpendicular to the light emitting surface of the LED 141. When the second collection stage is moved The third direction is horizontal in the configuration and orientation shown in Figure 1. The collection stage being movable in a third direction perpendicular to the light emitting surface allows the distance between the LED 141 and the collection lens 151 to be adjusted. In this way, chromatic aberration within the apparatus can be compensated for without the need for doublet achromats such as the flint glass and crown glass sub-lenses used in apparatuses of the prior art. In this way, simpler, more cost effective piano-spherical lenses may be used. In this way, the position of both the second illumination stage 140 and the second collection stage can be adjusted to improve the alignment of the second LED 141. This adjustment can overcome tolerance errors in, for example, the position of the dichroic mirror 160, the angle of the dichroic mirror 160, and the position of the condenser lens 170. The associated first illumination stage 120 and collection stage are movable independently of the second illumination stage 140 and collection stage. In this way, the position, and therefore observed brightness, of each of the LEDs can be optimised individually. There is a dichroic mirror 160 located within the housing 110. The dichroic mirror 160 is positioned such that, when lit, light from the first LED 121 and lens 131 is incident on the dichroic mirror 160, and light from the second LED 141 and lens 151 is incident on the dichroic mirror 160. The dichroic mirror 160 only allows certain wavelengths to pass through. The dichroic mirror 160 has a first side 161 and a second side 162. When lit, light originating from the first illumination stage 120 is incident on the first side of the dichroic mirror 161 and light originating from the second illumination stage 140 is incident second side of the dichroic mirror 162. In this way, light from the first illumination stage 120 is reflected from on the first side of the dichroic mirror 161, and selected wavelengths from the second illumination stage 140 pass through the dichroic mirror 160. The dichroic mirror couples the light from the first and second illumination stages 120 and 140 to form a single, collimated output from the dichroic mirror 160. The single, collimated output from the dichroic mirror 160 passes to the condenser lens 170. In use, the condenser lens 170 collects and condenses the light, directing the light to the receiver. In Figure 1 the receiver is the liquid light guide 180. The liquid light guide 180 receives the light from the condenser lens 170 and transmits the light to a connected device (not shown). The liquid light guide 180 may be connected to a microscope system. The path of light emitted from the first LED 121 is depicted with solid lines. The path of light emitted from the second LED 151 is depicted with dashed lines. The path of the collimated light from the dichroic mirror 160 is depicted with solid lines. Turning to Figure 2, there is depicted a light source apparatus 200 according to the present invention. Similar reference numerals are used for similar features of Figures 1 and 2. The light source apparatus 200 includes a housing 210, a first illumination stage 220, a first LED 221, a first collection stage, a first collection lens 231, a second illumination stage 240, a second LED 241, a second collection stage, a second collection lens 251, and a dichroic mirror 260. As in the first embodiment, when lit, light emitted from the first LED 221 is collected by the first collection lens 231, and reflected from the first side of the dichroic mirror 261. Light emitted from the second LED 241 is collected by the second collection lens 251, incident on the second side of the dichroic mirror 262 and selected wavelengths pass through the dichroic mirror 260. The first illumination stage 220 and the second illumination stage 240 are each independently movable in two different directions. The first illumination stage 220 is movable in two directions parallel to said first illumination stage. The second illumination stage 240 is movable in two directions parallel to the second illumination stage 240. The collection stages and are each independently movable in a third direction perpendicular to their respective illumination stages 220 and 240. The light source apparatus 200 differs from the light source apparatus 100, in that the light source apparatus 200 includes a magnifying lens 271 and a focusing lens 272, and a microscope 280. When in use, the collimated output from the dichroic mirror is magnified and focused by the magnifying lens 271 and focusing lens 272. The focused light is then received by the microscope 280. The light source apparatus 200 is therefore directly coupled to a microscope without a connecting fibre such as a liquid light guide. Turning to Figure 3, there is shown measurements of the position of the output of a light source apparatus according to the present invention before and after correction by a method according to the invention. The lefthand side graph shows the measurement of the output of a light source apparatus with a displacement due to a 1 ° offset in the dichroic mirror placement and a 100 pm offset of a collection lens relative to the associated LED. The righthand side graph shows the measurement of the output of the light source apparatus after correction by adjustment of the illumination stages and collection stages of the light source apparatus. As can be seen from Figure 3, the present invention provides an apparatus and method for overcoming the tolerance errors in the light source apparatus. The light source apparatus of the present invention is therefore able to compensate for errors in multiple component positions, such as the collection lens and the dichroic mirror. Thus, the apparatus and method of the present invention can compensate for compounding tolerance errors resulting from the positioning of components within the apparatus.

Claims

1. A light source apparatus for use with an optical microscope or optical inspection system, the light source apparatus comprising;a housing; andan illumination stage mounted within the housing, an LED with a light emitting surface mounted on the illumination stage, andan associated collection stage mounted within the housing, a collection optic mounted on the collection stage; wherein the collection stage is configured to, in use, collect light emitted by the LED;wherein the illumination stage is mounted within the housing such that the illumination stage is movable in a first direction and a second direction, the first direction perpendicular to the second direction, and both the first direction and the second direction parallel to the light emitting surface; andwherein the collection stage is mounted within the housing such that the collection stage is movable in a third direction, the third direction perpendicular to the light emitting surface.

2. The light source apparatus of claim 1, wherein the light source apparatus comprises a plurality of illumination stages and a plurality of collection stages, each of the illumination stages within the plurality of illumination stages associated with a separate collection stage within the plurality of collection stages.

3. The light source apparatus of claim 2, wherein each LED within the apparatus emits a wavelength of light distinct from the other LEDs within the apparatus.

4. The light source apparatus of any one preceding claim, wherein the light source apparatus further comprises a condenser optic, the condenser optic configured, in use, to condense the light emitted by the LED or plurality of LEDs.

5. The light source apparatus of any one preceding claim, wherein the light source apparatus further comprises a focusing optic, the focusing optic configured, in use, to focus the light emitted by the LED or the plurality of LEDs.

6. The light source apparatus of any one preceding claim, wherein the light source apparatus further comprises a magnifying optic, the focusing optic configured, in use, to magnify the light emitted by the LED or the plurality of LEDs.

7. The light source apparatus of any one preceding claim, wherein the light source apparatus further comprises a dichroic mirror.

8. The light source apparatus of claim 7, wherein the collection stage is positioned between the dichroic mirror and the illumination stage.

9. The light source apparatus of any one preceding claim, wherein the light source apparatus further comprises an excitation filter.

10. The light source apparatus of any one preceding claim, wherein the illumination stage is movable between 1 pm and 5000 pm inclusive in the first direction.

11. The light source apparatus of any one preceding claim, wherein the illumination stage is movable between 1 pm and 5000 pm inclusive in the second direction.

12. The light source apparatus of any one preceding claim, wherein the collection stage is movable between 1 pm and 30,000 pm inclusive in the third direction.

13. The light source apparatus of any one preceding claim, wherein the collection optic comprises a lens, the lens having a focal length smaller than or equal to its diameter.

14. The light source apparatus of claim 13, wherein the lens has a focal length smaller than or equal to 0.6 times its diameter.

15. The light source apparatus of any one preceding claim, wherein the LED has a spectral profile where the full width at half maximum is less than or equal to 200 nm.

16. The light source apparatus of any one preceding claim, the light source apparatus further comprising a fibre optic, fibre bundle or liquid light guide.

17. The light source apparatus of claim 16, wherein the apparatus is configured such that, in use, light exits the housing through the fibre optic, fibre bundle or liquid light guide.

18. A microscope comprising the light source apparatus of any one preceding claim.

19. A method of optimising the output of a light source apparatus, the method comprising the steps of:providing the apparatus of any one preceding claim;powering the LED such that it emits light;measuring the intensity of the emitted light; andmoving the illumination stage in the first and second directions, and moving the collection stage in the third direction to maximise the intensity of the emitted light.

20. A method of optimising the output of a light source apparatus, the method comprising the steps of:providing the apparatus of any one preceding claim;powering the LED such that it emits light;measuring the intersection point at which the emitted light intersects a plane, comparing the intersection point to a target intersection point on the plane, moving the illumination stage in the first and second directions, and moving the collection stage in the third direction to minimise the distance between the intersection point and the target intersection point.

21. The method of claim 19 or 20, wherein the step of moving the illumination stage is caried out before the step of moving the collection stage.

22. The method of claim 19 or 20, wherein the step of moving the collection stage is caried out before the step of moving the illumination stage.

23. The method of claim 19 or 20, wherein the step of moving the collection stage is caried out simultaneously with the step of moving the illumination stage.