[0001] This application claims priority to and benefit of UK Patent Application No. 1320733.7 filed on 25 November 2013.

Field of the Invention

[0002] The field of the invention relates to an optical arrangement for imaging a sample Background of the invention

[0003] A microscope is a scientific instrument that is used to image objects, which either are too small themselves or have details that are too small to be visible to the naked eye. There are many types of microscopes available on the market. The most common of these and the first to be invented is the so-called optical microscope, which uses light in a system of lenses to magnify images of the samples. The image from the optical microscope can be either viewed through an eyepiece or, more commonly nowadays, captured by a light- sensitive camera to generate a so-called micrograph. The images were previously captured on photographic film, but modern developments in charge-coupled device (CCD) cameras allow the capture and storage of digital images.

[0004] The illumination sources used in optical microscopes have been developed over the years and wide varieties of illumination sources are currently available, which can emit light or other types of radiation at different wavelengths. Optical filters can be placed between the illumination source and the sample to be imaged in order to restrict the wavelength of the radiation illuminating the sample.

[0005] Modern biological microscopy uses fluorescent probes for imaging specific structures within a cell as the sample. In contrast to normal trans-illuminated light microscopy, the sample in fluorescence microscopy is illuminated through an objective lens with a narrow set of light wavelengths. These narrow set of light wavelengths interact with fluorophores in the sample, which then emit light of a different wavelength. This emitted/fluoresced light is used to construct the image of the sample.

[0006] European Patent EP 1 019 769 (Carl Zeiss Jena) teaches a compact confocal theta microscope which can be used as a microscope with single objective or dual-objective system. The microscope has separate directions of illumination and detection, whereby the direction of detection in the objective is inclined at a set angle in relation to the direction of illumination. The set angle is chosen such that the area of overlap of the illumination cone and detection cone is reduced in comparison with a conventional confocal microscope. In the optical path between the objective and an image plane of the microscope, a beam splitter or reflector is positioned for injecting the illumination light and/or coupling out the detection light. The microscope disclosed in this patent uses point illumination.

[0007] The optical performance of a typical light-sheet microscope is limited by geometrical constraints imposed by physical dimensions of the illumination objective lens and the detection objective lens. The optical performance (contrast, optical resolution and light collection) of the light-sheet microscope depends on the numerical aperture (NA) of the illumination objective lens and the detection objective lens.

[0008] Figs, la and lb show an example of the light-sheet microscope, as known in the art. An illumination objective lens 30 produces an illumination beam 40, which illuminates a sample 20. Radiation 60 is reflected or fluoresced from the sample 20 and enters the detection objective lens 50, where it is measured using a detector (not shown) and images are generated in a computer (not shown). Detectors used are typically CCD detectors.

[0009] The numerical aperture (NA) of the detection objective lens 50 defines the maximum cone of light that can enter the detection lens 50. The numerical aperture is defined as follows: NA = n*sin (Gdet). The refractive index n = 1.33 (water) for most light- sheet microscopes. Bdet is the half angle of the maximum cone of light that can enter or exit the detection objective lens 50. [0010] The illumination light cone 35 of the illumination objective lens 30 and the detection light cone 55 of the detection objective lens 50 may not overlap for perpendicular light-sheets arrangements. In other words, the angle Θ m (half angle of the illumination light cone 35) and Bdet (half angle of the detection light cone 55) must be less than 90°. The mechanical housing of the detection objective lens 50 and the illumination objective lens 30 usually occupy a significantly larger cone than that which is needed for a specific value of the numerical aperture. This results in an arrangement of the illumination objective lens 30 and the detection objective lens 50, which may be sub-optimal.

[0011] International Patent Application No. WO 2014/063764 Al (Karlsruhe Institut fur Technologie) teaches a microscope with an illuminating lens mounted on or above a sample table. The illuminating lens guides at least one illuminating beam in the form of a two-dimensional light sheet to illuminate a sample under examination that is on the sample table. At least one detection objective lens is mounted underneath the sample and detects a detection beam being reflected or emitted from the sample under examination. The optical axis of the illumination lens is arranged at an angle, greater than 90° with respect to the optical axis of the detection objective lens. The illuminating beam is preferably incident upon the illuminating lens outside of the optical axis of the illuminating lens at an incident angle, such that the light sheet lies within the focusing plane of the detection objective.

[0012] The arrangement of this microscope requires a high degree of precision in the arrangement of the sample, source of the illuminating beam and the detection lens to ensure that the images of the sample can be accurately recorded by a camera.

[0013] US Patent Publication No. US 2012/0320438 Al (Knebel et. al. assigned to Leica Microsystems GmbH) also teaches a scanning microscope that includes a light source, illumination optics and a scanning device for moving the illumination focus across a target region and in doing so by varying the direction of incidence in which the illuminating beam enters the entrance pupil of the illumination optics. The illuminating lens and the detection objective lens are mounted at an acute angle (of less than 90°) to each other, above the sample table and lie in a plane perpendicular to the plane of the sample table.

Summary of the invention [0014] The disclosure teaches an optical arrangement for imaging a sample, which is mounted in a sample mount. The optical arrangement comprises an illumination objective lens for producing an illumination and a detection objective lens for imaging radiation from the sample. The illumination objective lens and the detection objective lens are arranged about the sample mount at an obtuse angle (greater than 90°) to each other. In one aspect of the disclosure, the illumination is in the form of a one-dimensional line projected onto the sample.

[0015] The illumination objective lens and the detection objective lens are located in a substantially horizontal plane.

[0016] In one aspect of the disclosure the optical arrangement further comprises a camera positioned in a direction normal to the plane of the illumination objective lens and the detection objective lens which co-operates with a translatable illumination beam generator, located in the back plane of the illumination objective lens to ensure that the sample is illuminated with the illumination light sheet parallel to the optical axis of the detection objective lens. A control processor is connected to both the camera and the translatable illumination beam generator to act as a feedback loop so that the illumination light sheet is in the correct position.

[0017] A further aspect of the disclosure has a further detection lens, which is arranged at a further non-perpendicular angle to the illumination lens. In this further aspect, the further detection lens, the detection objective lens and the illumination objective lens are arranged approximately equiangular angle to each other.

[0018] The objective lenses can be alternatively used as an illumination objective lens or a detection objective lens. Description of the figures

[0019] Fig. 1 shows an optical arrangement, as known in the art. Fig. la is an overview and Fig. lb is an exploded view of the light cones of the detection objective lens and the illumination objective lens.

[0020] Fig. 2 shows an optical arrangement of this disclosure. Fig. 2a is an overview of the optical arrangement. Fig. 2b shows an exploded view of the light cones from the illumination objective lens and the detection objective lens.

[0021] Fig. 3 shows an example of a light source being reflected into the illumination objective lens.

[0022] Fig. 4 shows an example of three objective lenses that can be used as both illumination objective lenses and detection objective lenses.

Detailed description of the invention

[0023] The invention will now be described on the basis of the drawings. It will be understood that the embodiments and aspects of the invention described herein are only examples and do not limit the protective scope of the claims in any way. The invention is defined by the claims and their equivalents. It will be understood that features of one aspect or embodiment of the invention can be combined with a feature of a different aspect or aspects and/or embodiments of the invention.

[0024] Fig. 2a shows an example of an optical arrangement 10 according to one aspect of this disclosure. An illumination objective lens 30 generates an illumination light sheet 40, which illuminates a sample 20 in a sample mount 22. The illumination objective lens 30 has an illumination light cone 35 and a central axis 32. A detection objective lens 50 receives radiated or fluoresced radiation from the sample 20 within a detection light cone 55 and has an axis 52. The illumination objective lens 30 and the detection objective lens 50 are both immersed in the same chamber with the same immersion medium 22 and are arranged around the sample mount 23 (which does not separate the immersion media 22 of the illumination objective lens 30 and the detection objective lens 50). Fig. 2b shows an exploded view of the area about the sample 20. It can be seen that the illumination objective lens 30 is arranged at a non-perpendicular angle to the detection objective lens 50. In particular, the plane of the illumination light-sheet 40 is at a non-perpendicular angle to the central axis 52 of the detection objective lens 50. The non-perpendicular axis is greater than 90°. In another aspect, of the invention, the illumination objective lens 30 generates a line or an array of lines (one-dimensional illumination), which can be scanned across the sample 20 by moving the sample mount 22.

[0025] The sample 20 is immersed in an immersion medium 22 and is mounted on a sample mount 23. The immersion medium 22 and the material from which the sample mount 23 are made have the same refractive index. In one non-limiting example of the optical arrangement 10, the immersion medium 22 is water and the material of the sample mount 23 is fluorinated ethylene propylene (FEP).

[0026] The reflected or fluoresced radiation entering the detection objective lens 50 is imaged on a detector 100 and the images are processed in a processor 110 connected to the detector 100. The detector can be a CCD detector, but this is not limiting of the invention.

[0027] Fig. 3 shows the illumination objective lens 30 in more detail. A radiation source 36 generates a light pattern 62 at the back focal plane 34 of the illumination objective lens 30. This light pattern 62 results in a light-sheet 40 or a scanned line at the sample 20.

[0028] A moveable mirror 70 reflects the light pattern 62 from the radiation source 36 into the rear of the illumination objective lens 30 at an off-centre direction 38, which is off the central axis 32 of the illumination objective lens 30. The moveable mirror 70 can be translated in a direction lying in a plane formed by the illumination path of the light pattern 62 and the reflected light path along the central axis 32 of the illumination objective lens 30 to change the direction at which the light pattern 62 is reflected into the rear of the illumination objective lens 30. The translation of the light pattern 62 in the back focal plane 34 causes the light-sheet (or scanned line) 40 to rotate in object space such that the light sheet 40 at the sample 20 illuminates the sample 20 at an angle substantially perpendicular to the central axis 52 of the detection objective lens 50. This translation of the moveable mirror 70 can be controlled either manually or by use of a motorised stage 90.

[0029] The alignment of the light-sheet 40 (or the scanned line) is monitored by a camera 80 that is positioned perpendicularly to the plane of both of the illumination objective lens 30 and the detection objective lens 50.

[0030] The camera 80 images the illumination beam either by fluorescence emission of a fluorophore solution or by light scattering in the immersion medium 22 (normally water, as noted above, but also, for example, air or oil) of the sample 20. Automatic image analysis run by a control processor 95 connected to the camera 80 and to the motorised stage 90 can be used to determine an angular difference between an illumination plane and a camera object plane. This angular difference can be minimized by a computer control loop 93.

Example 1

[0031] Nikon 25 x (or lOOx) detection objective lenses 30 and illumination objective lenses 50 are used. The angle between the central axis 32 of the illumination objective lens 30 and the central axis 52 of the detection objective lens 50 was 120°. A standard light- sheet setup for illumination had an NA value of 0.3. A tilted light-sheet setup according to the teachings of this disclosure had a numerical aperture of 0.6.

Example 2

[0032] A Nikon 25x (or lOOx) detection objective lens 50 was used with a 16x illumination objective lens 30. The angle between the central axis 32 of the illumination objective lens 30 and the axis 52 of the detection objective lens 50 was 105°. A light sheet using the optical arrangement 10 of this disclosure had a numerical aperture of 0.6, compared to a numerical aperture of point 0.3 for the optical arrangement of the prior art. Example 3

[0033] Nikon 25x (or lOOx) objective lenses were used alternatively as detection objective lenses 50 and illumination objective lenses 30. This yielded in total six views of the same sample 20, without rotating or otherwise moving the sample 20. The six different images can then be processed in a computer to obtain a three-dimensional view of the sample or of the tasks. This is shown in Fig 4 in which a further objective lens 57 is shown and the three objective lenses 30, 50 and 57 are arranged at substantially 120° to each other. The further objective lens 57 is also mounted in the same plane as the detection objective lens 50 and the illumination objective lens 30.

Reference Numerals

Optical arrangement

Sample

Immersion medium

Sample mount

Illumination objective lens

Central axis

Back focal plane

Source

Off-centre direction

Illumination light sheet

Detection objective lens

Axis

Detection light cone

Further objective lens

Radiation source

Light pattern

Moveable mirror

Camera

Motorised stage

Control processor

Detector

Image processor