Spectrometer and aperture therefore

Abstract

A module (500) for a spectrometer a first screen (3100A) and a second screen (3100B), the first screen comprises a first slit (3102, 3104, 3106, 3108) and the second screen comprises a second slit (3102, 3104, 3106, 3108), and the first screen and the second screen being movable relative to each other for producing a reconfigurable confocal aperture from the first slit and the second slit wherein the first slit and the second slit are elongate in different directions. Also disclosed is a method of gathering spectral data comprising providing a confocal aperture through a first screen and a second screen by partial alignment of a slit in the first screen and a slit aperture in the second screen wherein the slit in the first screen and the slit in the second screen are elongate in different directions.

Description

[0001] SPECTROMETER AND APERTURE THEREFORE

[0002] The invention of the current application relates to a module comprising a confocal aperture and a spectrometer comprising a confocal aperture, in particular a module comprising a reconfigurable confocal aperture and a spectrometer comprising a reconfigurable confocal aperture.

[0003] Raman spectroscopy is a non-destructive chemical analytical technique often used to analyse chemical or biological samples. The Raman effect is observed when a sample inelastically scatters light incident on the sample, this inelastically scattered light is often called Raman scattered light. Typically, a Raman spectrometer comprises a light source for illuminating a sample. Typically, a monochromatic light source is used, for example a laser. It is known to use lasers having wavelengths of light in the visible, near infrared, near ultraviolet regions. Raman scattered light has a different wavelength to the light used to illuminate the sample. The Raman scattered light is collected and can be analysed.

[0004] Other spectroscopic techniques are known in which a sample is irradiated with monochromatic or polychromatic light, the light is collected and can be analysed. Examples include fluorescent spectrometry and infra-red spectrometry. The present invention is also applicable to such techniques.

[0005] It is possible to use such techniques in a confocal manner in order that only light scattered from a certain plane in the sample is collected. This involves passing the scattered light through a spatial filter exhibiting a pinhole effect. The spatial filter may be a pinhole or a slit which exhibits a pinhole effect in one-dimension.

[0006] WO 92 / 22793 Al discloses a Raman spectrometer having a screen within which extends a slit which has a pinhole effect.

[0007] US 2005 / 0128476 Al discloses an array of different apertures which include a set of pinholes and a slit each of which can act as a confocal aperture.

[0008] According to a first aspect there is provided spectrometer (optionally a Raman spectrometer) comprising a first screen and a second screen, the first screen comprises a first slit and the second screen comprises a second slit, and the first screen and the second screen being movable relative to each other for producing a reconfigurable confocal aperture from the first slit and the second slit (for example by the partial overlap of the first slit and the second slit) wherein the first slit and the second slit are elongate in different directions. Optionally the first screen is movable independently of the second screen. Optionally the first screen is movable relative to other components of the spectrometer. Optionally the second screen is movable relative to other components of the spectrometer. Optionally the second screen is movable independently of the first screen. Optionally the first screen and the second screen are located to so as to produce the reconfigurable confocal aperture at the entrance to a spectrograph of the spectrometer. Optionally the first slit and the second slit are elongate perpendicular directions. The first screen may comprise a plurality of first slits. The second screen may comprise a plurality of second slits. Optionally the plurality of first slits have a common dimension in a first direction, optionally the elongate direction of the slits. Optionally each of the plurality of first slits have a different width (i.e., a different dimension in a direction other than the elongate direction of the slits, for example perpendicular to the elongate direction of the slits). Each of the plurality of first slits may have an elongate axis parallel with the elongate axis of each of the other of the plurality of first slits. The plurality of second slits may have a common dimension in a first direction, optionally the elongate direction of the slits. Each of the plurality of second slits may have a different width (i.e., a different dimension in a direction other than the elongate direction of the slits, for example perpendicular to the elongate direction of the slits). Each of the plurality of second slits may have an elongate axis parallel with the elongate axis of each of the other of the plurality of second slits. Optionally the elongate axis of the first slit (or axes of the plurality of first slits) extends in a different direction (e.g., perpendicular) to the elongate axis of the second slit (or axes of the plurality of second slits). Optionally first screen and second screen are located in parallel planes. Optionally the planes of the first screen and the second screen are orthogonal to the optical axis of the spectrograph. Optionally the planes of the first screen and the second screen are orthogonal to the optical axis of the objective lens. Optionally the planes of the first screen and the second screen are orthogonal to the optical axes of a first lens and a second lens. Optionally the first lens and / or the second lens are for focussing light received from a (particular) plane of a sample to a tight focus at the confocal aperture.

[0009] By providing first and second screens as described above the first screen and second screen can be moved relative to each other in order to overlap a first slit and a second slit and provide a confocal aperture through which light may pass. The confocal aperture through the first screen and the second screen can be reconfigured (i.e., changed in location and / or dimension) by moving the screens relative to each other and / or the spectrograph. This can allow for a compact arrangement for repositioning and / or changing the dimension of the confocal aperture. This can allow for the confocal performance of the spectrometer to be modified. For example, a large number of differently dimensioned confocal apertures can be produced from a relatively small set of slits (or elongate apertures) in the first and second screens. By locating the first and second screens to produce the reconfigurable confocal aperture at the entrance to a spectrograph of the spectrometer it is possible to tune the spectral resolution of the signal that enters the spectrograph. For example, the resolution of the signal in a first dimension could be controlled independently from the resolution of a signal in a second (perpendicular) dimension. The invention allows for a versatile spectrometer where a user can set the dimensions and / or location of a confocal aperture based on considerations including desired confocal resolution, and / or signal strength, and / or acquisition time.

[0010] Optionally the first screen comprises a further slit and where the elongate direction of the first slit(s) (of the first screen) and the elongate direction of the further slit of the first screen are different, optionally perpendicular. The second screen may comprise a further slit and where the elongate direction of the second slit(s) (of the second screen) and the elongate direction of the further slit of the second screen are different, optionally perpendicular. This can allow for faster location of first and or second slit in a desired position by combination of a first slit with the further slit of the second screen (and / or of a second slit with the further slit of the first screen) by allowing a larger area of sample to be assessed in order to find or identify Raman scattered light before carrying out a longer duration scan through a confocal aperture created by the combination of a first slit and a second slit.

[0011] The first and / or second screen may comprise a metal substrate, for example a metal foil. For example, a copper substrate, optionally a copper foil. Optionally the thickness of the screen is 50 pm or less, optionally between 20 and 30 pm, optionally 25 pm.

[0012] Optionally a first face of the first screen is in contact with a first face of the second screen. Optionally contact is maintained between the first screen and the second screen but at least one flexure, optionally a pair of flexures. A first flexure may bias the first screen towards the second screen. A second flexure may bias the second screen towards the first screen. Optionally the first face of the first screen and the first face of the second screen are spaced apart by no more than 25 pm, optionally by 10 pm or less. Optionally the first screen and the second screen are spaced apart by a separator, for example a PTFE separator. Optionally the first face of the first screen and / or the first face of the second screen are coated with a friction reducing layer, for example a Ni comprising layer.

[0013] Optionally at least one motor for moving the first screen and the second screen relative to each other is provided. A first motor may be provided for moving the first screen. A second motor may be provided for moving the second screen.

[0014] According to a second aspect there is provided a module for a spectrometer (optionally a Raman spectrometer) comprising a first screen and a second screen, the first screen comprises a first slit and the second screen comprises a second slit, and the first screen and the second screen being movable relative to each other for producing a reconfigurable confocal aperture from the first slit and the second slit wherein the first slit and the second slit are elongate in different directions. Optionally the first screen is movable relative to other components of the module. Optionally the second screen is movable relative to other components of the module.

[0015] According to a third aspect there is provided a spectrometer (optionally a Raman spectrometer) comprising the module of the second aspect. Optionally the module is located at the entrance to the spectrograph of the spectrometer.

[0016] According to a fourth aspect there is provided a method of gathering spectral data comprising providing a confocal aperture through a first screen and a second screen by partial alignment (or partial overlap) of a slit in the first screen and a slit in the second screen wherein the slit in the first screen and the slit in the second screen are elongate in different directions.

[0017] According to a fifth aspect there is provided a spectrometer comprising a spatial filter for producing a reconfigurable confocal aperture wherein the spatial filter is located at the entrance to a spectrograph of the spectrometer and the reconfigurable confocal aperture can be moved in a plane orthogonal to the optical axis of the spectrograph, wherein the spatial filter comprises a first screen and a second screen, the first screen comprises a first slit and the second screen comprises a second slit, the first screen and the second screen being movable relative to each other for producing the reconfigurable and movable confocal aperture from the first slit and the second slit.

[0018] Also described is a spectrometer which may comprise a first screen and a second screen. Optionally the first screen comprises a first aperture. Optionally the second screen comprises a second aperture. The first screen and the second screen may be movable relative to each other optionally for producing a reconfigurable confocal aperture from the first aperture and the second aperture.

[0019] Features from one aspect may be incorporated into any other aspect.

[0020] The invention will now be described by way of example only and with reference to the following drawings in which:

[0021] Figure l is a schematic representation of an embodiment of a Raman spectrometer;

[0022] Figure 2 is a schematic representation of the reconfigurable confocal aperture in different configurations;

[0023] Figure 3(a) shows a plan view of a screen for forming a reconfigurable aperture;

[0024] Figure 3(b) shows a first screen and a second screen;

[0025] Figure 4 is an alternative view of the screen of Figure 3(a);

[0026] Figure 5 shows a module comprising a reconfigurable confocal aperture; and

[0027] Figure 6 is a plan view of the module of Figure 5.

[0028] Figure 1 shows a first embodiment of a Raman spectrometer according to the invention. An input laser beam 10 is reflected through 90° by a dichroic filter 12 which has been placed at an angle of 45° to the optical path. The laser beam 10 then passes to spatial filter 14 which comprises a first screen 31 A and a second screen 3 IB located between a first lens 32 and a second lens 34. The first screen 31 A comprises a first slit 312 (as shown in Figure 2) extending normal to the plane of the page. The second screen 3 IB comprises a second slit 314 (as shown in Figure 2) extending in the plane of the page and perpendicular to the direction of travel of the laser beam. The second screen 3 IB is shown in phantom because the plane of the page is coincident with the second slit 314. Light may pass through an aperture 30 where the first slit 312 and the second slit 314 coincide (partially overlap). The aperture 30 is a confocal aperture. The second lens 34 focuses the parallel laser beam 10 to a tight focus which allows the laser beam to pass through confocal aperture 30 created by the first screen 31 A and the second screen 3 IB. The first lens 32 collimates the laser beam back into a parallel beam. The laser beam 10 then passes to a microscope objective lens 16, which focuses the laser beam to a spot at a focal point 19 on a sample 18. Light is scattered by the sample at this illuminated spot and is collected by the microscope objective lens 16 and collimated into a parallel beam which passes back to the spatial filter 14. The first lens 32 focuses the parallel beam of scattered light to a tight focus that passes through the aperture 30 formed by the combination of the first slit 312 in the first screen 31 A and the second slit 314 in the second screen 3 IB. The second lens 34 collimates the light into a parallel beam of scattered light. The effect of the aperture 30 is that the microscope objective 16 acts confocally. That is, substantially only the light scattered at the focal point 19 of the lens 16 passes through the aperture 30. Broken lines 36 shown in Figure 1 illustrate a situation for light scattered from a location that is not focal point 19, in this case light being scattered between microscope objective 16 and focal point 19. Figure 1 shows that this light corresponding to broken lines 36 is not brought to focus at the aperture 30 and is therefore substantially blocked by screens 31 A, 3 IB. The same is true for light scattered on the far side of focal point 19 with respect to the microscope objective 16. From the second lens 34, light is passed to dichroic filter 12 which reject Rayleigh scattered light (elastically scattered light having the same wavelength as the input laser beam 10). Dichroic filter 12 transmits Raman scattered light. The Raman scattered light then passes to a Raman analyser 20. The Raman analyser 20 may comprise a tuneable non-dispersive filter for selecting a Raman line of interest. Alternatively, the Raman analyser 20 may comprise a dispersive element such as a diffraction grating. Light from the Raman analyser 20 is focussed by a lens 22 onto a suitable photodetector 24. In the present embodiment a CCD (charge coupled device) 24 is used which comprises a two-dimensional array of pixels, and which is connected to a computer 25 which acquires data from each of the pixels and analyses the data as required. Where the Raman analyser 20 comprises a tuneable non-dispersive filter, light of the selected Raman frequency is focussed at point 26 on CCD 24. Where the Raman analyser 20 comprises a dispersive element (such as a diffraction grating), the analyser 20 produces a spectrum having various bands as indicated by broken lines 28 which are spread out along a line on the CCD 24.

[0029] The first screen 31 A and second screen 3 IB of the embodiment of Figure 1 can be moved relative to each other and the other components of the spectrometer. In the illustrated embodiment first screen 31 A can move forwards and backwards along an axis coincident with the plane of the first screen 31 A and perpendicular to the elongate direction of the first slit 312 in the first screen 31 A. This allows the first slit 312 to move relative to the second screen 3 IB along (forward and backwards) a first direction 202 (shown in Figure 2). Second screen 3 IB can move forwards and backwards along an axis coincident with the plane of the second screen 3 IB and perpendicular to the elongate direction of the second slit 314 in the second screen 3 IB. This allows the second slit 314 to move relative to the first screen 31 A along (forward and backwards) a second direction 204 (shown in Figure 2).

[0030] As shown in Figure 1, first screen 31 A and second screen 3 IB are located in parallel planes. The planes of the first screen 31 A and the second screen 3 IB are orthogonal to the optical axis of the spectrograph. The planes of the first screen 31 A and the second screen 3 IB are orthogonal to the optical axis of the objective lens 16. The planes of the first screen 31 A and the second screen 3 IB are orthogonal to the optical axes of first lens 32 and second lens 34. In the illustrated embodiment it is possible to move the first screen 31 A relative to the other components of the spectrometer including the second screen 3 IB. It is also possible to move the second screed relative to the other components of the spectrometer including the first screen 31 A. This allows movement of each of the first screen 31 A and the second screen 3 IB relative to the other of the first screen 31 A and the second screen 3 IB.

[0031] Figure 2 shows how it is possible to reconfigure the spatial filter 14 by repositioning the first screen 31 A relative to the second screen 3 IB and so move the confocal aperture 30. Figures 2(a) to 2(c) show the first slit 312 moving along a first direction 202 relative to the second slit 314. The second slit 314 is shown in phantom where the second slit 314 is obscured by the first screen 31 A. Where the first slit 312 and the second slit 314 coincide (partially overlap), aperture 30 is formed. Figures 2(a), 2(d), and 2(e) show the second slit 314 moving along a second direction 204 relative to the first slit 312. In the illustrated embodiments the first direction 202 and the second direction 204 are perpendicular. It is possible to set the location of the aperture 30 by changing the positions of the first slit 312 and the second slit 314, for example as shown in Figure 2(f).

[0032] In some embodiments this can allow the aperture 30 to be located in an infinitely variable number of locations where the position of the first slit 312 may be located at any point between the positions illustrated in Figure 2(a) and Figure 2(c), and second slit 314 may be located at any point between the positions illustrated in Figure 2(a) and Figure (e). In other embodiments the locations of the first slit 312 and the location of the second slit 314 may be indexed and so the locations of aperture 30 are dictated by the locations which the first slit 312 may occupy between the positions illustrated in Figure 2(a) and Figure 2(c) and by the locations which the second slit 314 may occupy between the positions illustrated in Figure 2(a) and Figure 2(e).

[0033] Figure 1 also shows an alternative arrangement of parts within the Raman spectrometer. In this alternative embodiment a dichroic filter 12A is positioned between the spatial filter 14 and the microscope objective 16 (instead of in the position of dichroic filter 12). By locating the dichroic filter 12A between the spatial filter 14 and the microscope objective 16, the spatial filter is located directly before the Raman analyser 20 (in other words, the spatial filter is located at the entrance to the spectrograph). Laser beam 10A is input and is reflected through 90° by a dichroic filter 12A which has been placed at an angle of 45° to the optical path. The laser beam 10A then passes to a microscope objective lens 16, which focuses the laser beam to a spot 19 on sample 18. By locating the spatial filter 14 at the entrance to the spectrograph the spatial filter can be used to control the resolution of the signal being passed to the spectrograph / Raman analyser 20. A further advantage of the arrangement having the dichroic filter at position 12A is that the input laser beam 10A does not have to pass through spatial filer 14 and so the risk of the input laser hitting the edges of aperture 30 and scattering is removed. However, in the arrangement where the dichroic filter is located at position 12 (rather than position 12A), the input laser 10 can be used when adjusting the spatial filter 14 during set-up.

[0034] In the current embodiment the first screen 31 A and the second screen 3 IB are held in contact with one another, and contact is maintained while the first screen 31 A and the second screen 3 IB are moved relative to each other in order to move the first slit 312 in the first direction and / or the second slit 314 in the second directions 204. Flexures (not shown) are used to maintain positive contact between the first screen 31 A and the second screen 3 IB. In this embodiment a first flexure biases first screen 31 A towards second screen 3 IB and a second flexure biases second screen 3 IB towards first screen 31 A. The first screen 31 A and the second screen 3 IB are copper foils. The first screen 31 A and the second screen 3 IB both have a face in contact with the other of the first screen 31 A and the second screen 3 IB, for both the first screen 31 A and the second screen 3 IB the contact face has an electro-formed nickel layer, this can reduce friction between the first screen 31 A and the second screen 3 IB. In other embodiments the first screen 31A and second screen 3 IB may be spaced apart, and may be separated by a spacer, for example a PTFE spacer. In embodiments where the first screen 31 A and the second screen 3 IB are spaced apart, the distance between the face of the first screen 31 A facing the second screen 3 IB and the face of the second screen 3 IB facing the first screen 31 A may be 25 pm or less.

[0035] Figure 3(a) shows a plan view of an embodiment of a screen 3100, in this case in the form of a foil 3100. Figure 4 shows an orthographic view of the foil 3100 of Figure 3(a). Foil 3100 is a copper foil comprising a nickel layer on a face, the nickel layer is electro-formed. Foil 3100 shown in Figure 3 extends in a length direction 3120 and in a width direction 3122. The foil 3100 also has a thickness in a direction orthogonal to the length and width directions. In this embodiment, foil 3100 has a thickness of not more than 50 pm, a length in the region of 20 mm (along direction 3120) and a width in the region of 10 mm (along direction 3122). Extending through foil 3100 in a thickness direction are five slits 3102, 3104, 3106, 3108, 3110. Four of the slits 3102, 3104, 3106, 3108 are elongate in the width direction 3122 of the foil 3100 and extend 2 mm in the width direction (in other words the length of each slit 3102, 3104, 3106, 3108 is 2 mm). The slits 3102, 3104, 3106, 3108 have different dimensions in the length direction 3120 of the foil 3100. Slit 3102 extends 10 pm in the length direction 3120 of foil 3100 (in other words the width of the slit 3102 is 10 pm), slit 3104 extends 20 pm in the length direction 3120 of foil 3100 (in other words the width of the slit 3104 is 20 pm), slit 3106 extends 65 pm in the length direction 3120 of foil 3100 (in other words the width of the slit 3106 is 65 pm ), and slit 3108 extends 100 pm in the length direction 3120 of foil 3100 (in other words the width of the slit 3108 is 100 pm). The fifth slit 3110 in foil 3100 has a length of 2 mm in a length direction 3120 of foil 3100 and a width of 1 mm in a width direction 3122 of foil 3100.

[0036] Figure 3(b) shows a first foil 3100A overlayed a second foil 3100B. First foil 3100A and second foil 3100B are both foils 3100.

[0037] Figure 5 illustrates a module 500 for a spectrometer comprising a pair of screens 3100, a first screen 3100A is illustrated in a first carriage 502. The first carriage 502 can be moved in the x-direction by a first motor 506. A first encoder 504 is shown for measuring the position of the first screen 3100 A in the x-direction. The second screen 3100B is located next to the first screen 3100A and rotated 90° in the x-y plane (as shown in Figure 3(b)). In addition, the first screen 3100A and the second screen 3100B are arranged such that the nickel coated face of the first screen 3100 A and the nickel coated face of the second screen 3100B are located facing each other. The second screen 3100B is located in a second carriage which can be moved in the y-direction by motor 508 and a second encoder 510 is shown for measuring the position of the second screen 3100B in the y-direction. Figure 6 shows a plan view of the module 500 shown in Figure 5.

[0038] In use the first slit having a width 10 pm in the x direction of the first screen 3100 A can be combined (partially overlapped) with any of the slits of 3102, 3104, 3106, 3108, 3110 of the second screen3100B. This can be achieved by controlling the relative positions of the first screen3100 A and the second screen3100B by moving the first screen 3100A in the x-direction and / or moving the second screen 3100B in the y-direction. When the first slit having a width 10 pm in the x direction of the first screen 3100A is combined with the slit 3102 of the second screen 3100B an aperture which allows the passage of light through both the first screen 3100A and the second screen 3100B is created having a width of 10 pm in the x-direction and 10 pm in the y-direction. The location of the aperture can further be controlled by moving the first screen 3100 A in the x-direction and the second screen 3100B in the y-direction in a similar manner to that shown in Figure 2.

[0039] When the first slit having a width 10 pm in the x direction of the first screen 3100A is combined with the slit 3104 of the second screen 3100B an aperture which allows the passage of light through both the first screen 3100 A and the second screen 3100B is created having a width of 10 pm is the x-direction and 20 pm in the y-direction. The location of the aperture can further be controlled by moving the first screen 3100 A in the x-direction and the second screen 3100B in the y-direction in a similar manner to that shown in Figure 2.

[0040] When the first slit having a width 10 gm in the x direction of the first screen 3100A is combined with the slit 3106 of the second screen 3100B an aperture which allows the passage of light through both the first screen 3100 A and the second screen 3100B is created having a width of 10 pm is the x-direction and 65 pm in the y-direction. The location of the aperture can further be controlled by moving the first screen 3100 A in the x-direction and the second screen 3100B in the y-direction in a similar manner to that shown in Figure 2.

[0041] When the first slit having a width 10 pm in the x direction of the first screen 3100A is combined with the slit 3108 of the second screen 3100B an aperture which allows the passage of light through both the first screen 3100 A and the second screen 3100B is created having a width of 10 pm is the x-direction and 100 pm in the y-direction. The location of the aperture can further be controlled by moving the first screen 3100 A in the x-direction and the second screen 3100B in the y-direction in a similar manner to that shown in Figure 2.

[0042] When the first slit having a width 10 pm in the x direction of the first screen 3100A is combined with the slit 3110 of the second screen 3100B an aperture which allows the passage of light through both the first screen 3100 A and the second screen 3100B is created having a width of 10 pm is the x-direction and 2 mm in the y-direction. The location of the aperture can further be controlled by moving the first screen 3100 A in the x-direction and the second screen 3100B in the y-direction in a similar manner to that shown in Figure 2.

[0043] The second slit having a width 20 pm pm in the x direction of the first screen 3100 A can be combined with any of the slits of 3102, 3104, 3106, 3108, 3110 of the second screen 3100B. Thus, a repositionable aperture allowing the passage of light therethrough having a 20 pm width in the x-direction and a 10 pm, 20 pm, 65 pm, 100 pm, or 2 mm width in the y-direction when combined with slits 3102, 3104, 3106, 3108, 3110 respectively can be created by the module 500.

[0044] The third slit having a width 65 pm pm in the x direction of the first screen 3100 A can be combined with any of the slits of 3102, 3104, 3106, 3108, 3110 of the second screen 3100B. Thus, a repositionable aperture allowing the passage of light therethrough having a 65 pm width in the x-direction and a 10 pm, 20 pm, 65 pm, 100 pm, or 1 mm width in the y-direction when combined with slits 3102, 3104, 3106, 3108, 3110 respectively can be created by the module 500.

[0045] The fourth slit having a width 100 pm pm in the x direction of the first screen 3100 A can be combined with any of the slits of 3102, 3104, 3106, 3108, 3110 of the second screen 3100B. Thus, a repositionable aperture allowing the passage of light therethrough having a 100 pm width in the x-direction and a 10 pm, 20 pm, 65 pm, 100 pm, or 2 mm width in the y-direction when combined with slits 3102, 3104, 3106, 3108, 3110 respectively can be created by the module 500.

[0046] The fifth slit having a dimension of 2 mm in the x direction of the first screen 3100 A can be combined with any of the slits of 3102, 3104, 3106, 3108 of the second screen 3100B. Thus, a repositionable aperture allowing the passage of light therethrough having a 2 mm width in the x-direction and a 10 pm, 20 pm, 65 pm, or 100 pm width in the y-direction when combined with slits 3102, 3104, 3106, 3108 respectively can be created by the module 500. The fifth slit having a dimension of 2 mm in the x direction of the first screen 3100 A can be combined with the slit of 3110 of the second screen 3100B a repositionable aperture allowing the passage of light therethrough having a maximum 1 mm width in the x-direction and a maximum 1 mm width in the y-direction

[0047] Module 500 can therefore be seen to allow selection of a number of aperture dimensions and aperture positions and can be used as part of a spatial filter within a spectrometer, in particular a Raman spectrometer. In particular the apertures which the module 500 can produce can allow alteration of the confocal performance of the spectrometer. For example, an aperture having a dimension of 10 pm in one direction could be used to provide proof statements of confocality and to achieve high spectral resolution, an aperture having a dimension of 20 pm in one direction could be used for general confocal use, an aperture having a dimension of 100 pm in one direction could be used for high sensitivity confocal use where the amount of Raman scattered light generated by illuminating the sample is low. An aperture having a dimension of 65 pm in one direction could be used for producing a signal intermediate an aperture having a dimension of 20 pm and an aperture having a dimension 100 pm. An aperture having a dimension of 1 mm in one direction could be used to quickly find a location of interest and to align the spectrometer before switching to an aperture having a smaller dimension. An aperture of 2 mm dimension could also be used to for line focus, for example the slit 3110 in one of the first or second screen could be used with one of the apertures 3102, 3104, 3106, 3108 of the other of the first and second screen to produce a confocal slit. Thus, it can be seen that providing a plurality of apertures with differing dimensions can allow the confocallity of a spectrometer to be varied depending on the needs of a user.

[0048] While the embodiment shown in Figure 1 is described as having the dichroic filter 12 (or 12A) at 45° to the input laser beam 10 (10A) in order to reflect the laser beam through a 90° angle so as to be co-axial with the optical axis of lens 16, in other embodiments this need not be the case. In other embodiments the dichroic filter 12 (12A) may be at an angle other than 45° and the input laser beam 10 (10A) may be at a different than shown in Figure 1. In such embodiments the laser beam is reflected by the dichroic filter so as to be co-axial with the optical axis of the lens 16. In such embodiments it may be advantageous to provide further optical features which improve the performance of the filter, for example as disclosed by EP 0543578 Bl. In still further embodiments, the input laser beam may be reflected so as to be co-axial with the optical axis of a lens 16 by reflective elements other than a dichroic filter, for example a mirror. In such embodiments the reflective element may be at 45° to the input laser beam similar to the situation shown in Figure 1, or in other embodiments the reflective element and input laser beam may have a different arrangement (to that shown in Figure 1) and the input laser beam is reflected by the reflective element such that the laser beam is co- axial with the optical axis of a lens 16.

Claims

CLAIMS1. A spectrometer comprising a first screen and a second screen, the first screen comprises a first slit and the second screen comprises a second slit, the first screen and the second screen being movable relative to each other for producing a reconfigurable confocal aperture from the first slit and the second slit wherein the first slit and the second slit are elongate in different directions.

2. A spectrometer according to claim 1 wherein the first screen and the second screen are located to so as to produce the reconfigurable confocal aperture at the entrance to a spectrograph of the spectrometer.

3. A spectrometer according to claim 2 wherein the first slit and the second slit are elongate in perpendicular directions.

4. A spectrometer according to any preceding claim wherein the first screen comprises a plurality of first slits.

5. A spectrometer according to any preceding claim wherein the second screen comprises a plurality of second slits.

6. A spectrometer according to any one of claims 1 to 4 wherein the first screen comprises a further slit and where the elongate direction of the first slit(s) of the first screen and the elongate direction of the further slit of the first screen are different, optionally perpendicular.

7. A spectrometer according to any one of claims 1 to 5 wherein the second screen comprises a further slit and where the elongate direction of the second slit(s) of the second screen and the elongate direction of the further slit of the second screen are different, optionally perpendicular.

8. A spectrometer according to any preceding claim wherein the first and / orsecond screen comprise a copper substrate.

9. A spectrometer according to any preceding claim wherein a first face of the first screen is in contact with a first face of the second screen.

10. A spectrometer according to claim 9 wherein the first face of the first screen and / or the first face of the second screen are coated with a Ni comprising layer.

11. A spectrometer according to any preceding claim comprising at least one motor for moving the first screen and the second screen relative to each other.

12. A module for a spectrometer a first screen and a second screen, the first screen comprises a first slit and the second screen comprises a second slit, and the first screen and the second screen being movable relative to each other for producing a reconfigurable confocal aperture from the first slit and the second slit wherein the first slit and the second slit are elongate in different directions.

13. A module according to claim 12 wherein the first slit and the second slit are elongate in perpendicular directions.

14. A module according to claim 12 or claim 13 wherein the first screen comprises a plurality of first slits and / or the second screen comprises a plurality of second slits.

15. A method of gathering spectral data comprising providing a confocal aperture through a first screen and a second screen by partial alignment of a slit in the first screen and a slit in the second screen wherein the slit in the first screen and the slit in the second screen are elongate in different directions.

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