GB2173666A

GB2173666A - Scanning optical microscopes

Info

Publication number: GB2173666A
Application number: GB08605963A
Authority: GB
Inventors: William James Stewart
Original assignee: Plessey Co Ltd
Current assignee: Plessey Co Ltd
Priority date: 1985-04-12
Filing date: 1986-03-11
Publication date: 1986-10-15
Also published as: GB8605963D0; GB8509493D0

Abstract

A scanning microscope has a light source 9 illuminating an object 5 such that the resulting image 3 is incident upon a detector 1 having a plurality of discrete elements arranged in a particular manner such that each element provides a distinct output signal indicative of any one part of the image 3 allowing an improved representation of the image to be achieved. The output signals of the detector elements can be processed together, eg. by weighting and assuming to further optimise the image representation. Figure 1 shows a for-field arrangement of the microscope optics, but a near-field configuration is possible if an additional lens is placed between the object and detector planes (13, Figure 2). A special arrangement of the for-field embodiment (Figure 3) permits its operation as a refracted near-field profiler. <IMAGE>

Description

SPECIFICATION Scanning microscopes The present invention relates to scanning microscopes and more particularly to increasing the quality and variety of information available from a scanning microscope.

Previously, scanning microscopes have comprised a source providing illumination of the object while a single detector has received all the transmitted or reflected light from each scanned position and then this information is either displayed or stored. The effect of the detector is thus to average the results across the whole solid angle of an image beam.

This conventional configuration of a scanning microscope is adequate for thin objects where the effects of variations in scattering and adsorption lengths are limited but with thicker objects the variations between normal and diagonal ray paths are sufficient to cause great variations in the resolution within the image beam which are subsequently transferred to the single detector.

It is an object of the present invention to provide a scanning microscope configuration that is adaptable to a wider range of object structure and giving greater information about the object.

According to the present invention there is provided a scanning microscope comprising:-a light source for illuminating an object; focussing means arranged adjacent to the source for focussing the light from the source onto a limited area of the object to produce an image beam; scanning means for providing relative movement between the object and light from the source; holding means for retaining the object; and, a detector including a plurality of discrete elements each arranged to receive light from a common illuminated area of the object.

Preferably, the light source and detector are arranged on opposite sides of the holding means.

A lens may be used to project the image beam onto at least one discrete element of the detector.

Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which; Figure 1 illustrates an embodiment of the present invention in a far-field configuration; Figure 2 shows an embodiment of the present invention in a near-field configuration; Figure 3 illustrates a profiler embodiment of the present invention.

Referring to Figure 1, this far-field configuration of the present invention is similar to the conventionai configuration but has the single detector replaced by an array of detectors 1 which collects an image beam 3 produced by illumination of object 5 by source beam 7 from source 9. The detectors in the array 1 are substantially the same and the distribution of the detectors in the array 1 is determined by consideration of the Nyquist rate and the maximum expected spatial extent of light in 3. Each detector is also independent of the others and thus only gives information with respect to its own section of the image beam 3 solid angle.

The output signal of each detector can be recorded for subsequent processing or processed on-line for example by a parallel processor to optimise a particular aspect of the image. A simple algorithm which may be used for processing is, (Z) = E Aj(z)Wi where O(z) = Output value for a particular scan position Z = scan position i = detector number A = detector output signal W = detector weighting (or correction) factor ie. -1 < W < +1 if dO and if do were maximised then O.dO dAi I OddzO = E d Wi.EAi(z)Wi so boundary features can be amplified.

A near-field configuration of the scanning microscope is illustrated in Figure 2. Here the image beam 3 passes through a lens 13 before the resultant projected beam 15 is collected by a detector array 11. If only the centre detector 10 of array 11 is used then this configuration is equivalent to that conventionally known. If the detectors in array 1 and 11 of Figures 1 and 2 respectively operated for phase and amplitude then the two configurations would be equivalent. However, most detectors omit phase measurement, thus these configuration differ. It is possible to detect phase by the addition of a reference beam but the effect in each configuration is quite different. The addition of a reference beam to the far-field configuration of Figure 1 would be most convenient as this configuration is less sensitive to disturbance.

Phase contrast could be found by combining detector outputs in figure 1 (far-field).

A special arrangement of a far-field configuration is shown in Figure 3 as a "RNF" (refracted near field) profiler. It comprises concentric detectors 19 and the ideal method of operation wouid be to take the differences between these detectors 19 so cancelling the unwanted average term leaving just the index signal, but usually the inner detector signal is unavailable due in part to capture by the fibre although in the absence of loss this produces no serious effect.

The profiler configuration of Figure 3 gives a response similar to phase contrast for thin objects but for thicker objects the combination of resolution and sensitivity is far better than can be achieved by a conventional microscope.

Claims

1. A scanning microscope comprising a light source for illuminating an object; focusing means arranged adjacent to the source for focussing the light from the source onto a limited area of the object to produce an image beam; scanning means for providing relative movement between the object and light from the source; holding means for retaining the object; and, a detector including a plurality of discrete elements each arranged to receive light from a common illuminated area of the object.

2. A scanning microscope as claimed in claim 1 wherein the light source and detector are arranged on opposite sides of the holding means.

3. A scanning microscope as claimed in claim 1 or claim 2 wherein a lens is used to project the image beam onto at least one discrete element of the detector.

4. A scanning microscope as claimed in claim 1, claim 2 or claim 3 wherein the plurality of discrete detector elements are arranged dependent on the Nyquist rate of imformation pulses from these elements and the maximum spatial extent to light

5. A scanning microscope as claimed in any preceeding claim wherein recording means record the respective output signal of each detector element.

6. A scanning microscope as claimed in any preceeding claim wherein each detector element output signal is processed to enhance a particular aspect of the image.

7. A scanning microscope as claimed in any preceeding claim wherein the illuminating source, object and detector are configured in a near-field configuration.

8. A scanning microscope as claimed in any one of claims 1 to 6 wherein the illuminating source, object and detector are configured in a far-field configuration.

9. A scanning microscope substantially as hereinbefore described with reference to the accompanying drawings.