EP1412796A1

EP1412796A1 - Electron microscope and spectroscopy system

Info

Publication number: EP1412796A1
Application number: EP02753135A
Authority: EP
Inventors: Robert Bennett; Andrew Mark Woolfrey; John Charles Clifford University of Bristol DAY; Angus University of Bristol BEWICK
Original assignee: Renishaw PLC
Current assignee: Renishaw PLC
Priority date: 2001-08-03
Filing date: 2002-08-05
Publication date: 2004-04-28
Also published as: JP5095587B2; JP2009031314A; JP2004538470A; GB0118981D0; WO2003014794A1

Abstract

An electron microscope (10) is adapted to enable spectroscopic analysis of a sample (16). A parabolic mirror (18) has a central aperture (20) through which the electron beam can pass. The mirror (18) focuses laser illumination from a transverse optical path (24) onto the sample, and collects Raman and/or other scattered light, passing it back to an optical system (30). The mirror (18) is retractable (within the vacuum of the electron microscope) by a sliding arm assembly (22). An adjustable kinematic mount (44) defines the inserted position of the parabolic mirror (18). A second parabolic mirror (104) is provided to direct the scattered or generated light towards an optical analyser. The parabolic mirrors are positioned in an aberration cancelling orientation and such that they compensate for inaccuracies in the position of the sliding arm assembly (22).

Description

ELECTRON MICROSCOPE AND SPECTROSCOPY SYSTEM

This invention relates to sample analysis systems. In a preferred embodiment an electron microscope is combined with a spectroscopy system for example a Raman, photoluminescence or cathodoluminescence spectroscopy system.

In our International Patent Application No. 099/58939 an analytical system, for example a scanning electron microscope, projects a beam of electrons along an analytical axis onto a sample. A parabolic mirror is mounted generally in the analytical axis above the sample and an aperture in the mirror allows the electron beam to pass through to the sample. The mirror is mounted on a mirror holder assembly which has an optical axis generally transverse to the analytical axis. The mirror holder assembly may retract the mirror between its operative position and an inoperative position away from the analytical axis.

It is desirable to have precise and repeatable positioning of the mirror with respect to both the analytical axis and an optical system positioned along the optical axis.

Furthermore, as an analysis system such as a scanning electron microscope may operate under ultra high vacuum it is preferable for adjustment of the mirror in both the operative and inoperative positions to be possible external to the vacuum.

A first aspect of the present invention provides an adapter for performing optical analysis of a sample mounted in a sample chamber of another analytical apparatus, said analytical apparatus having an analytical axis and projecting an analysis beam generally along said analytical axis towards a sample; the adaptor comprising an optical element located so as to collect scattered or generated light received from the sample and directing said light generally along an optical axis at an angle to the analytical axis; wherein said optical element is adjustable between an operative position on said analytical axis and an inoperative position away from said analytical axis; characterised in that the operative position is defined by an adjustable mount which restrains movement of the optical element in six degrees of freedom.

Preferably the adjustable mount is kinematic.

Preferably there is reduced pressure inside the sample chamber, wherein said reduced pressure is used to bias the optical element towards the operative position.

Preferably the optical element also receives an input light beam along the optical axis, said optical element directing said input light beam towards the sample.

Preferably the optical element is a mirror. It may alternatively be a fibre optic light collection element .

Preferably the optical axis is generally transverse to the analytical axis.

The inoperative position may be defined by a second mount which restrains movement of the optical element in six degrees of freedom. This second mount may be adjustable.

A second aspect of the present invention provides an adapter for performing optical analysis of a sample mounted in a sample chamber of another analytical apparatus, said analytical apparatus having an analytical axis and projecting an analysis beam generally along said analytical axis towards a sample; the adapter comprising a first optical element having a first focal plane, said first optical element being located so as to collect scattered or generated light received from the sample and directing said light generally along an optical axis at an angle to the analytical axis; wherein said first optical element is adjustable between an operative position on said analytical axis and an inoperative position away from said analytical axis ; wherein a second optical element having a second focal plane is provided in a fixed relationship with the first optical element to direct light directed along the optical axis by the first optical element towards an optical analyser; characterised in that the first and second optical elements are arranged such that when the first optical element is in the operative position, their focal planes are parallel with the direction of movement of the first optical element; such that there is at least part compensation for inaccuracies in the positioning of the first optical element in its operative position. Preferably a location mount is provided to define the position of the first optical element in its operative position; and wherein when the first optical element is in the operative position, the ratio of the focal length of the first optical element to the focal length of the second optical element is inverse to the ratio of the distance along the optical path between the focal point of the first optical element and the location mount to the distance along the optical path between the focal point of the second optical element and the location mount .

Preferably the focal lengths of the first and second optical elements are equal and wherein the distance along the optical path between the focal point of the first optical element and the location mount is equal to the distance along the optical path between the focal point of the second optical element and the location mount when the first optical element is in the operative position.

Preferably the first and second optical elements comprise parabolic mirrors.

A third aspect of the present invention provides an adapter for performing optical analysis of a sample mounted in a sample chamber of another analytical apparatus, said analytical apparatus projecting an analysis beam towards a sample; the adapter comprising an optical element located so as to collect scattered or generated light received from the sample and directing said light generally along an optical axis to an optical analyser; wherein the optical element is a parabolic mirror; characterised in that at least one mirror is provided to align light reflected by the parabolic mirror with the optical analyser, the position of the at least one mirror being adjustable; and wherein distortion at the optical analysis means is corrected using image processing software.

Preferably a second parabolic mirror is located between said parabolic mirror and the optical analyser, wherein the two parabolic mirrors are arranged in an aberration-cancelling orientation. A further two parabolic mirrors may be located between said parabolic mirror and the optical analysis means, wherein the four parabolic mirrors are arranged in an aberration- cancelling orientation.

Reference should be made to US Patent No. 5,446,970 for a discussion of one meaning of the terms "kinematic", "kinematically" and like terms, as used in this specification. These terms encompass not only kinematic supports in which point contacts are provided between the respective pairs of elements on the carrying and receiving members, but also semi- or quasi-kinematic supports, in which there are small areas or lines of contact between the respective elements .

The invention will now be described with reference to the accompanying drawings in which:

Fig 1 is a schematic illustration of a scanning electron microscope coupled with a spectroscopy system;

Fig 2 is a schematic illustration of the retraction mechanism of Fig 1; Fig 3 is an end view of the mechanism flange of the retraction mechanism;

Fig 4 shows an adjustable kinematic mount of the retraction mechanism; Fig 5 is an exploded diagram of part of an adjustable kinematic mount;

Fig 6 is an alternative kinematic mount;

Fig 7 is an end view of the retraction arm of the retraction mechanism; Fig 8 is a schematic illustration of the optical arrangement between the scanning electron microscope and optical system;

Fig 9 shows prior art coupling of parabolic mirrors; Fig 10 shows coupling of parabolic mirrors as used in the present invention;

Fig 11 is an illustration of two lenses in infinite conjugate mode;

Figs 12A and 12B illustrate a simplified version of the optics in the retraction arm; and

Fig 13 illustrates optics within the retraction arm.

Fig 1 shows a scanning electron microscope 10 with a conventional electron beam generation, focusing and scanning system 12. This projects a beam of electrons generally along an analytical axis 14 to a sample 16 in a well-known manner.

In place of a scanning electron microscope the invention may also be used with other types of analytical system including transmission electron microscopes and also with apparatus such as ion beam bombardment systems . A parabolic or other concave mirror 18 is mounted generally on the axis 14 above the sample 16 and has a central aperture 20 so that the electron beam may pass through to the sample 16. The parabolic mirror 18 is mounted on a mirror holder arm 22 having an optical axis 24 which is generally transverse to the analytical axis 14 of the scanning electron microscope. The mirror holder 22 is able to retract the parabolic mirror 18 as shown by double-headed arrow 26 between an operative position (shown by the solid line) and an inoperative position (shown by the dashed line) . In the inoperative position the parabolic mirror 18 does not interfere with other equipment within the scanning electron microscope such as an x-ray detector which can be used to detect x-rays generated by the bombardment of the sample 16 with the electron beam.

An optical system 28 which may for example comprise a spectrometer, is also provided in the system. An input laser beam 27 may be directed via a mirror 25 or other means along the optical axis 24 and focused onto the sample 16 by the parabolic mirror 18 when it is in the operative position. The laser light may be UV, visible or IR, for example. Scattered light from the sample 16 is collected and collimated by the parabolic mirror 18 and fed back in the return direction along the optical axis 24 towards the optical system 28. The collected light may be inelastically scattered light such as Raman, or fluorescence or photoluminescence. It will also include elastically scattered (Rayleigh) light at the laser wavelength. Alternatively, or additionally, the light collected from the sample 16 by the mirror 18 may be cathodoluminescence, generated by the action of the electron beam on the sample 16 without the need for a laser input .

Fig 1 shows a system in which the optical system 28 is fixed rigidly with respect to the scanning electron microscope chamber. In this case the parabolic mirror must locate precisely with respect to both the optical system and the electron beam each time the parabolic mirror is put into the operative position. In an alternative arrangement, the optical system may be fixed rigidly with respect to the parabolic mirror, the whole system retracting together. This arrangement has the advantage that the parabolic mirror only needs to locate precisely with the electron beam but has the disadvantage that the heavy and bulky spectrometer and laser of the optical system, or parts associated with signal collection and laser delivery, must be supported by the mirror holder arm assembly.

The functional elements of the retraction mechanism are shown in Fig 2. The scanning electron microscope is provided with a chamber flange 30 on the wall of the scanning electron microscope chamber 11. The retraction mechanism 32 is mounted to the scanning electron microscope chamber flange 30 via a mechanism flange 34. When the mechanism flange 34 is mounted to the scanning electron microscope chamber 11 it is fixed with respect to the electron beam axis 14, thus all critical optical and mechanical locations are referenced to this mechanism flange 34.

A pair of guide-rails 36 (only one shown) and a retraction screw 38 are mounted on the mechanism flange 34. A retraction arm 40 is mounted on the guide rails 36 and may be wound in or out along the guide-rails 36 by the retraction screw 38, which may be motor-driven. A sliding tube 42 indirectly carries the parabolic mirror 18 and may be mounted concentrically with the retraction arm 40 about the optical axis 24. The position of the sliding tube 42 and thus the parabolic mirror 18 is defined by two sets of mounts, comprising adjustable kinematic mounts, these are the location mount 44 and the retraction mount 46. The retraction arm 40 is wound in or out along the guide-rails 36 to push the sliding tube 42 onto the location mount 44 (i.e. with the parabolic mirror in the inserted position) or onto the retraction mount 46, (i.e. with the parabolic mirror in the retracted position) . A bellows seal 48 is used to create a vacuum seal capable of linear movement. This type of seal has the advantage that it allows tilt, a slight amount of rotation and lateral movement and is a reliable seal down to ultra high vacuum pressures. Alternative seals, such as a sliding o-ring seal could also be used.

The bellows seal has a bellows fixed flange 50 at one end and a bellows travelling flange 52 at the other end. The bellows fixed flange 50 is mounted to the mechanism flange 34 adjacent the scanning electron microscope chamber 10. The bellows travelling flange 52 is mounted to both an optics flange 54 and the distil end of the sliding tube 42 from the scanning electron microscope chamber 10. The optics flange 54 provides a vacuum window 56 for light extraction and also holds a mirror holder arm 22 which supports the parabolic mirror 18 in the scanning electron microscope chamber 10. The retraction arm 40 may be used to push the sliding tube 42 towards the scanning electron microscope chamber 10 where its position is defined by a location mount 44. The retraction arm may also push the sliding tube 42 away from the scanning electron microscope chamber 10 such that its position with respect to the retraction arm 40 is defined by a retraction mount 46 both during retraction and in the retracted position. The position of the sliding tube 42, and thus the parabolic mirror 18, is always defined by either the location or retraction mounts 44,46.

The kinematic mount at the location mount 44 comprises three v-shaped grooves spaced at 120° apart on a circle concentric with the optical axis 24 on the mechanism flange 34 of the retraction mechanism 32. These are provided on a face of the mechanism flange 34 adjacent the sliding tube 42. Each v-shaped groove may be provided by a pair of parallel cylindrical rollers 60, as shown in Fig 3. Three similarly spaced ball-ended bearings are provided on a face of the sliding tube adjacent the mechanism flange 34. As the sliding tube 42 is carried towards the mechanism flange 34 the ball bearings interact with the v-shaped groove to accurately define the position of the sliding tube 42 against the mechanism flange 34 and hence the position of the parabolic mirror 18.

The vacuum in the scanning electron microscope chamber holds the sliding tube in position against the mechanism flange and thus other methods of holding the kinematic elements together, such as by magnetic attraction or springs, are not required. It is desirable for the kinematic mount to be adjustable and for that adjustment to be possible ex- vacuo. In this example the position of each ball-ended bearing is adjustable parallel with the optical axis 5 24. As shown in Figs 4 and 5 each ball-ended bearing is provided by a cylindrical rod 62 with a rounded end 64. Each cylindrical rod 62 is housed in a housing 66 located in the sliding tube 42. The housing 66 has a central aperture 68 running along its longitudinal

10 axis. This aperture is stepped having a wider portion 70 and a narrower portion 72. The cylindrical rod 62 fits into the wider portion 70 with the step 74 into the narrower portion 72 acting as a stop. The cylindrical rod 62 is held in position in the housing

15 66 by a screw 76 inserted through an aperture 78 in the side of the housing 66 which pushes against a flattened portion 80 on one side of the cylindrical rod 62. The rounded end 64 of the cylindrical rod 62 extends out of the central aperture of the housing 66.

20

The exterior of the housing 66 also has a stepped cylindrical profile. The external surface of the - — narrower portion 82—of-the- housing is threaded and is screwed into a threaded aperture 84 in the sliding tube

25 42 and held in position by a bolt 85. The narrower portion 72 of the internal surface of the housing 66 is also threaded and receives an adjustment screw 86 which allows the position of the housing 66 to be adjusted along its longitudinal axis with respect to the sliding

30 tube 42.

The ball -ended bearings are individually adjustable in position parallel to the optical axis 24. The mirror holder arm 22 can thus be tilted about each of three axes at 60° to each other by individual adjustment of the ball bearing positions. The optic arm 58 can also be translated parallel to the retraction axis by collective adjustment of the ball-ended bearing positions. These alignments are sufficient to position the parabolic mirror 18 in three dimensions with respect to the scanning electron microscope axis 14.

The rounded end of the cylinder 64 has two points of contact with the v-shaped groove. Another shape also having two points of contact with the vee-shaped groove may be used, for example the wedge shape shown in Fig 6. The wedge may, for example, have an angle of 60°.

To retract the parabolic mirror 18, the retraction arm 40 is wound into contact with the far end of the sliding tube 42 from the scanning electron microscope chamber 10 and the whole mechanism is withdrawn away from the mechanism flange 34. The contacts at the location mount 44 are broken and the position of the parabolic mirror 18 during retraction is defined by the retraction mount 46. Retraction of the parabolic mirror is limited by an adjustable stop (not shown) on the retraction screw.

The contact between the retraction arm 40 and the sliding tube 42 is by an adjustable kinematic mount similar to that of the location mount 44 in which the ball-ended bearings are located on the retraction arm 40 and are in contact with v-shaped grooves on the sliding tube 42.

Fig 7 shows an end view of the retraction arm. Apertures 92 are provided for the guide rails and a threaded aperture 94 is provided for the retraction screw. Four elongate apertures 90 are provided into which the housings for the ball-ended bearings are located. These elongate slits allow lateral adjustment of each housing individually.

The position of the sliding tube 42 and therefore the parabolic mirror 18 is thus always defined by either the location mount 44 (i.e. with respect to the mechanism flange 34) or by the retraction mount 46 (i.e. with respect to the retraction arm 40) .

After the alignment of the parabolic mirror 18 has been set by adjustment of the kinematic mount at the location mount 44, the kinematic mount of the retraction mount 46 is adjusted so that the plane of its ball bearings is parallel to that of the location mounts. It is also adjusted laterally to ensure that the ball bearings align with the v-shaped grooves, thus compensating for any lateral displacement of the sliding tube 42 with respect to the retraction arm caused by the tilt adjustment of the location mount 44. These adjustments serve to minimise any movement of the parabolic mirror 18 during the transition from engagement of the location mount 44 to engagement of the retraction mount 46 and are only required after changes to the alignment of the parabolic mirror 18 by adjustment of the location mount 44.

The adjustable kinematic mount of this invention is suitable for use in other applications. For example, a fibre optic light collection element, such as described in International Patent Application No. PCT/GB01/00170 may be positioned precisely between a sample and an objective lens of a defect review tool (DRT) , a type of electron microscope for detecting defects in semi- conductor wafers. A defect in the wafer can be accurately positioned in the DRT to be at the electron optical centre and thus the fibre optic light collection element must also be moved precisely to the electron optical centre at a known distance from the sample surface. Thus the fibre optic light collection element must be accurately positioned in X,Y or Z which is achievable by use of the above described adjustable kinematic mounts.

This invention is not restricted to an adjustable kinematic location mount. Other adjustable mounts which constrain the position of the parabolic mirror 18 in six degrees of freedom are also suitable. Such mounts may comprise for example, a combination of balls abutting a plate to constrain some movement and a planar spring to constrain other movement, as disclosed in US Patent No. 4,451,987 and in US Patent No. 4,473,955.

Fig 8 illustrates the optical arrangement which couples the light collected by the parabolic mirror 18 to an optical system, such as a spectrometer. The same reference numbers are used for identical parts seen in previous Figures.

Light collected from the sample by the parabolic mirror 18 is reflected to a second parabolic mirror 104 via adjustable mirrors 100,102. The two parabolic mirrors 18,104 are in a fixed relation to each other and their relative alignment can be adjusted in six axes by the two adjustable mirrors 100,102.

A microscope objective 106 is provided in a fixed position relative to the mechanism flange 34 of the retraction mechanism 32 (and hence the sample chamber) . The microscope objective 106 is positioned at the focus of the second parabolic mirror 104 and collimates the light into a parallel beam suitable to be directed into a spectrometer. It is desirable for the microscope objective 106 to be adjustable to allow it to be accurately positioned at the focus of the second parabolic mirror 104.

Parabolic mirrors are used in preference to plane mirrors because they offer better light collection efficiency. They are used in preference to ellipsoids because these have twin foci which significantly complicates and sensitises the alignment.

An inevitable consequence of using a parabolic mirror is that the off-axis image is distorted. This is improved by using two parabolic mirrors. An even greater improvement is possible by using four parabolic mirrors, however this is at the expense of ease of alignment .

Although Fig 8 shows a pair of parabolic mirrors 18,104 coupling light from the sample to the microscope objective 106 in conjunction with alignment mirrors 100,102, systems using one or four parabolic mirrors in conjunction with alignment mirrors may also be used.

Use of parabolic mirrors for coupling a Raman laser probe to an electron microscope has been previously disclosed in "Raman Microscopy, Developments & Applications" by George Turrel & Jacques Corset. In this system a pair of parabolic mirrors 110,112 are arranged such that their foci 114,116 are in different horizontal planes, as shown in Fig 9. This arrangement has the disadvantage that it does not cancel all aberrations.

In the present invention, the parabolic mirrors are arranged with their foci in the same horizontal plane, as shown in Fig 10. This configuration of the parabolic mirrors cancels the aberrations, in particular it corrects aberrations from paraxial rays.

Image processing techniques, such as image warping, are used to correct for residual distortion (such as pincushion or barrel distortion) .

It is desirable to position the laser spot on the sample repeatably to an accuracy of better than 1 micron. However, if a non-kinematic location mount is used (for example an end stop or sliding bearing) or if the kinematic location mount is contaminated, by dirt for example, the accuracy of the spot position is reduced. Inaccuracies for the position of the laser spot on the sample may be compensated for by arrangement of the optics as described below.

Fig 11 illustrates two identical lenses 120,122 of focal length f working in infinite conjugate mode. If the object 0 is moved upwards, the image I is inverted by the same amount. This property is used for compensation of small inaccuracies in position of the retraction arm.

Fig 12A illustrates a simplified version of the optics used in the retraction arm. Each set of optics may comprise a plane mirror 124,126 and lens 128,130. Alternatively, the optics may comprise a pair of parabolic mirrors as illustrated in fig 8. The optics are rigidly mounted with respect to one another within the retraction arm, with the result that insertion / retraction of the retraction arm moves the whole optic assembly. In addition the optics are a matched pair, so that for a small area about the image/object planes the object will be imaged with a magnification factor of 1, be in focus and inverted.

Fig 12A shows the two mirror and lens assemblies 124,128 and 126,130 having equal focal lengths f and being spaced equidistantly about a pivot point P (i.e. the location mount) .

If, as shown in Fig 12B the whole assembly is translated in the X direction whilst the position of the object O remains fixed, an image I' will be generated which is translated by -X with respect to the retraction arm. The position of the laser spot on the sample thus remains in the same position and is not effected by the slight movement of the retraction arm. The compensation as described above applies for translation of the retraction arm in X,-X,Y and -Y.

This system does not compensate for translation of the retraction arm in the Z direction in the same manner. However small changes of the retraction arm in the Z direction within the depth of field of the optical system do not cause a problem. The depth of field of a parabolic mirror used in this optical system is, for example, approximately 20 microns. As the aim is to position the spot within 1 micron, small movements of the parabolic mirror to this order are accommodated.

The symmetric arrangement of the optics also compensates for small rocking movements of the retraction arm. Fig 11 shows two lenses 120,122 which are rigidly mounted with respect to one another, for example by a housing 132. If the object 0 is fixed and the housing is rocked about the pivot point P, then for small angles within the depth of field, the image I does not move. This is for the same reason as described above. However, this is only true if the pivot is at the centre of the two optics. The location mount of the retraction arm (kinematic or otherwise) acts as the pivot between the optics.

If the focal lengths of the lenses are not equal then the pivot point must be moved to a position closer to the lens with the longer focal length. For example, if the ratio of object lens focal length fl : image lens focal length f2 is 1:2, then the distance ratio of object to pivot point : pivot point to image must be 2:1.

Rocking of the retraction arm also causes movement in z but if the rocking angle is small and the distance from the pivot point to the object is large, then this will not effect the image.

Fig 13 illustrates an optical arrangement of the retraction similar to that shown in fig 8. This arrangement includes two mirrors 134,136 to fold the light path. The location mount forms a pivot P and, if the lenses 128,130 have equal focal lengths, is positioned equidistant from each mirror and lens assembly 124,128 and 126,130 along the light path.

The use of symmetry in the optics therefore provides correction for an inaccurate motion system. This optics arrangement allows a less accurate location mount to be used for stable and repeatable positioning of the retraction arm as small inaccuracies in the position of the retraction arm are compensated for.

In the case where the optics comprise a pair of parabolic mirrors, the degree of correction is a function of image quality across the image field and requires that these parabolic mirrors are identical, as discussed with reference to fig 10. Use of parabolic mirrors has the advantage that they provide better light collection and thus faster optics then the plane mirror and lens arrangement. In addition parabolic mirrors take up less space in the retraction arm and have a greater depth of field which allows for greater movement in z of the retraction arm.

Claims

1. An adapter for performing optical analysis of a sample mounted in a sample chamber of another analytical apparatus, said analytical apparatus having an analytical axis and projecting an analysis beam generally along said analytical axis towards a sample; the adapter comprising a first optical element having a first focal plane, the first optical element being located so as to collect scattered or generated light received from the sample and directing said light generally along an optical axis at an angle to the analytical axis; wherein said first optical element is adjustable between an operative position on said analytical axis and an inoperative position away from said analytical axis ; wherein a second optical element having a second focal plane is provided in a fixed relationship with the first optical element to direct light directed along the optical axis by the first optical element towards an optical analyser; characterised in that the first and second optical elements are arranged such that when the first optical element is in the operative position, their focal planes are parallel with the direction of movement of the first optical element; such that there is at least part compensation for inaccuracies in the positioning of the first optical element in its operative position.

2. An adapter according to claim 1 wherein: a location mount is provided to define the position of the first optical element in its operative position; and wherein when the first optical element is in the operative position, the ratio of the focal length of the first optical element to the focal length of the second optical element is inverse to the ratio of the distance along the optical path between the focal point of the first optical element and the location mount to the distance along the optical path between the focal point of the second optical element and the location mount .

3. An adapter according to claim 2 wherein the focal lengths of the first and second optical elements are equal and wherein the distance along the optical path between the focal point of the first optical element and the location mount is equal to the distance along the optical path between the focal point of the second optical element and the location mount when the first optical element is in the operative position.

4. An adapter according to any of claims 1-3 wherein the first and second optical elements comprise parabolic mirrors.

5. An adapter according to any of claims 2-4 wherein the location mount comprises an adjustable mount which restrains movement of the optical element in six degrees of freedom.

6. An adapter according to claim 5 wherein the location mount is a kinematic mount.

7. An adapter for performing optical analysis of a sample mounted in a sample chamber of another analytical apparatus, said analytical apparatus having an analytical axis and projecting an analysis beam generally along said analytical axis towards a sample; the adapter comprising an optical element located so as to collect scattered or generated light received from the sample and directing said light generally along an optical axis at an angle to the analytical axis; wherein said optical element is adjustable between an operative position on said analytical axis and an inoperative position away from said analytical axis; characterised in that the operative position is defined by an adjustable mount which restrains movement of the optical element in six degrees of freedom.

8. An adapter according to claim 7 wherein the adjustable mount is kinematic.

9. An adapter according to any of claims 7 or 8 wherein the optical element is biased towards the operative position.

10. An adapter according to claim 9 wherein there is reduced pressure inside the sample chamber, and wherein the reduced pressure is used to bias the optical element towards the operative position.

11. An adapter according to any of claims 7-10 wherein the optical element also receives an input light beam along the optical axis, said optical element directing said input light beam towards the sample.

12. An adapter according to any of claims 7-11 wherein the optical element is a mirror.

13. An adapter according to any of claims 7-11 wherein the optical element is a fibre optic light collection element .

14. An adapter according to any of claims 7-13 wherein the optical axis is generally transverse to the analytical axis.

15. An adapter according to any of claims 7-14 wherein the inoperative position is defined by a second mount which restrains movement of the optical element in six degrees of freedom.

16. An adapter according to claim 15 wherein the second mount is adjustable.

17. An adapter for performing optical analysis of a sample mounted in a sample chamber of another analytical apparatus, said analytical apparatus projecting an analysis beam towards a sample; the adapter comprising an optical element located so as to collect scattered or generated light received from the sample and directing said light generally along an optical axis and to an optical analyser; wherein the optical element is a parabolic mirror; characterised in least one mirror is provided to align light reflected by the parabolic mirror with the optical analysis means, the position of the at least one mirror being adjustable; and wherein distortion at the optical analysis means is corrected using image processing software.

18. An adapter according to claim 17 wherein a second parabolic mirror is located between said parabolic mirror and the optical analysis means, wherein the two parabolic mirrors are arranged in an aberration- cancelling orientation.

19. An adapter according to claim 18 wherein a further two parabolic mirrors are located between said parabolic mirror and the optical analysis means, and wherein the four parabolic mirrors are arranged in an aberration-cancelling orientation.