GB1605265A

GB1605265A - Optical scanning system

Info

Publication number: GB1605265A
Application number: GB337076A
Authority: GB
Inventors: F R Loy
Original assignee: Telecommunications Radioelectriques et Telephoniques SA TRT
Current assignee: Telecommunications Radioelectriques et Telephoniques SA TRT
Priority date: 1975-02-07
Filing date: 1976-01-28
Publication date: 1987-02-04
Also published as: NL184443B; FR2585204A1; NL184443C; DE2604700C1; NL7601301A; FR2585204B1; IT1178451B

Abstract

The present invention relates to a device for optico-mechanical scanning of a field of view in two perpendicular directions, which can be produced solely by means of mirrors and is therefore usable whatever the wavelength of the radiation. The line scanning is carried out by means of a drum rotating about a fixed axis provided with plane reflecting faces and with a fixed optic ensuring the detector's image conveying at a point of the said axis. The frame scanning is ensured by means of a flat mirror which can move about an axis parallel to the direction of line scanning. A so-called field mirror ensures that the beam leaving the objective and the frame scanning device is turned back towards the line scanning system and the detector. It permits exact focusing of the field with the line surface analysed. The device can moreover include a system for direct display of the image of the field using all or part of the scanning optic and a light-emitting diode controlled by the video signal. Application: television. <IMAGE>

Description

(54) AN OPTICAL SCANNING SYSTEM (71) We, TELECOMMUNICATIONS RADIOELECTRIQUES ET TELEPHONIQUES T.R.T., of 88, rue Brillat Savarin, 75013 Paris, France, a limited liability Company organised and established under the laws of the Republic of France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a device for optically scanning a field of vision divided into different regions and for displaying the field.

More particularly, it relates to a device for scanning a field in two directions along beams coming from the different regions and converging on an element sensitive to the radiation in the beams, the scanning device being optically designed to be of use irrespective of the radiation wavelength.

Devices of this kind are used inter aiia in apparatus for displaying a landscape viewed in infrared radiation having a wavelength greater than a micron (1 im). French Patent Specification No. 2245 970 describes such a device in which the objective is a spherical mirror and scanning is by means of mirrors only. The known device has the advantage of being usable with a wide field of vision, up to 180 . On the other hand, it is unsuited for analyzing a small field with a high resolution, as is necessary when recognizing objects at a distance in the field of vision and viewed at a reduced angle. In such cases, it is necessary to pick up a sufficient quantity of the flux radiated by the distant objects. This flux depends on the area of the entry pupil of the device or, strictly speaking in this Specification, on the radius of the analysis circle and on the numerical aperture of the convergence optical system, since the focal length of the objective is in principle equal to the analysis radius.

One possible method of increasing the amount of flux picked up would be to increase the aperture of the optical system for causing the beams to converge on the detector; since, however, there are a number of duplicates of the system disposed side by side around one axis of rotation of the scanning system, the number of duplicates will become smaller, thus increasing the speed of rotation of the convergence optical system for a given rate of scanning, which will result in difficulties in the mechanics of the construction. Another possibility is to make a uniform increase in all the dimensions of the device, but in that case there may be an excessive increase in the bulk and in the moment of inertia of the rotating part.

Some of these disadvantages are obviated in a previous proposal disclosed in French Patent Specification No. 2 245 970 in the name of the Applicants. In order to ensure that the diameter of the entry pupil of the device is at a maximum and that the analysis is small, a system is constructed in which the focal length is not related to the radius of the analysis circle. To this end, an optical element (a lens or mirror depending on the case) is introduced into the focal plane of the objective so as optically to conjugate the centre of the exit pupil of the objective with the detector disposed at the centre of rotation of the analysis system, the element having the advantage of correcting the curvature of the field of the assembly comprising the objective and the analytical device.

In the device according to the last-mentioned proposal, the field is scanned in one direction by the mirror objective oscillating around one of its diameters. One of the difficulties with regard to the aperture, when the objective has a large diameter, is to cause a heavy objective to oscillate at a frequency which, for television images, is of the order of 20 cycles per second.

Furthermore, even if the mirror objective is parabolic, its field is limited by aberrations to a few degrees.

Furthermore, the field of vision of the detector must be sufficiently wide to receive the flux travelling through the optical systems during rotation thereof. Consequently, the detector views the interior of the analytical device which bears the optical systems and which, owing to friction, is usually at a higher temperature than the landscape being analysed. Consequently, in the case of infrared analysis, there is an interfering modulation of the flux falling on the detector in phase with line scanning.

Furthermore, since the image of the field is not in a free position, it is practically impossible to position the detector and the electrominescent diode in the visible region in order directly to display the field image by using the analytical system in the reverse path.

Furthermore, in the aforementioned proposal, the optical systems do not consist entirely of mirrors, so that display is impossible unless the optical system is transparent to visible light, which is difficult to bring about when analysis is performed in the distant infrared (10 yam).

The device according to the invention does not have the same disadvantages. For reasons of convenience, it is constructed so that, although it is compact and of limited bulk, the objective and the detector are separately accessible so that they can be used for a variety of purposes so that they can be changed in accordance with the applications, whereas the system of analysis in two directions remains unmoved and is adapted to all kinds of objectives and detectors and can be made up of mirrors only.

Thus, the device according to the invention is constructed so that the detector and electroluminescent diode can be positioned for directly displaying the image of the field. In order to avoid interfering modulation due to the rotation of components other than optical systems, the line-scanning optical system is constructed in two parts, i.e. a rotating drum having a large number of reflecting plane surfaces and rotating around a fixed axis, and a single stationary convergence optical system for concentrating the flux on the detector; the convergence optical system forms an image of the detector on the axis of rotation of the drum, which operates in a convergent beam.

In order to obtain accurate focusing in the entire field in the direction of line analysis, thus giving constant resolution over the entire line of analysis, a concave "field" mirror optically conjugates the focal surface of the objective with the analysed line surface.

According to the invention, optical conjugation is obtained in that the objective has a curved focal surface with its centre of curvature at the centre of the exit pupil of the objective, and the apex of the surface of the "field" mirror is near the apex of the focal surface of the objective, or, strictly speaking, the point symmetrical with the apex with respect to the axis of rotation of the drum, and optically conjugates the centre of the exit pupil of the objective with a particular point on the axis of rotation of the drum, the beams being directed on to the line-scanning convergence optical system after being reflected on the drum surfaces.

When large-diameter objectives are used in order to avoid oscillation of very heavy masses in a second direction for raster scanning, scanning in the second direction is performed by means of a mobile plane mirror or "raster analysis" mirror around an axis perpendicular to the axis of rotation of the drum, the mirror usually being placed in a convergent beam near the focus of the objective, between the objective and its focus.

The oscillation of the raster analysis mirror in a convergent beam produces additional curvature of the field in the direction of raster analysis. According to the invention, this is compensated by slight reciprocation in translation of the "field" mirror in synchronism with the motion of the raster analysis mirror, the motion in translation being perpendicular to the axis of rotation of the drum.

In order to compensate the deflection of the beams introduced into the line analysis system by the raster scanning mirror and in order to ensure that the conjugate point remains stationary on the axis of rotation of line scanning of the centre of the exit pupil of the objective by the field mirror, the mirror is also reciprocated in rotation in synchronism with the motion of the raster mirror around an axis parallel to the axis of rotation of the raster mirror, so that the central ray of any beam from the field is at a constant angle of incidence to the line-scanning angle of rotation, in dependence on the raster scanning.

The invention provides a device for optically scanning a field of vision divided into different regions and for displaying the field, scanning being made in two perpendicular directions, i.e. "line" scanning in a direction x and "raster" or "image" scanning in a directiony, the device scanning along beams coming from different regions of the field and causing the beams to converge on to a detector sensitive to the radiation in the beams, the device comprising the following components in order, in the direction of the path of the central incident beam from the field of vision; an objective, means for raster scanning in the direction y, a system for deflecting the beams bounded by the detector and the aperture of the objective towards means for line scanning of the image field of the objective in the direction x, the display part of the device having optical means similar to the field of vision scanning means and comprising, instead of the detector, an electro-luminescent diode actuated by a signal coming from the detector, the device being characterised in that: the optical axis of the objective is in a plane P containing they direction and perpendicular to the x direction, the focal surface of said objective being curved and such that its centre of curvature is at the centre of the exit pupil of the objective, the raster scanning means comprise a plane mirror rotating in reciprocation around an axis parallel to the x direction and disposed in a convergent beam behind the objective near the field image in the objective, the line scanning means comprise, firstly, a drum rotating uniformly around a stationary axis YY' contained in the plane P and bearing a large number of flat reflecting surfaces regularly distributed around the drum periphery and, secondly, an image-conveying means symmetrical with respect to the plane P and forming an image of the detector at a fixed point A' along the drum rotation axis YY', the drum being placed in a convergent beam in the path of the image-conveying means on the image side of the detector element, the point symmetrical with the point A' with respect to each surface of the drum, when the surface is perpendicular to the plane P, being in the neighbourhood of the point D which is symmetrical with the focus of the objective with respect to the raster mirror in a position parallel to the YY' axis, and the optical beam-deflecting system comprises a concave or field mirror having the plane P as the plane of symmetry, the apex of the mirror being near D on the ZZ' axis extending through D and perpendicular to the YY' axis, the mirror being so disposed that it conjugates the centre 0 of the exit pupil of the objective with a fixed point 0' on the YY' axis, point 0' being symmetrical with respect to the ZZ' axis with the point where the optical axis of the objective intersects the YY' axis; in order, if required, to ensure that the idle scanning time between two consecutive lines is zero, the field mirror also has a width in the x direction which is slightly less than the length of the analyzed line, which in turn is equal to the distance between the images of the detector in two consecutive surfaces of the rotating drum, the mirror being moved if required for small distances in phase with the movement of the raster scanning means, the small motion comprising reciprocation in translation along the ZZ' axis in the neighbourhood of D and reciprocating rotation around an axis parallel to the x direction, which is symmetrical with respect to the ZZ' axis, the amplitude of the motion in translation being such as to correct the defocusing introduced by the raster scanning means and the amplitude of the rotation being such as to ensure that the field mirror holds 0', the conjugate of the centre 0 of the exit pupil of the objective, in a constant position during the reciprocating rotation of the raster scanning means.

The invention will be more clearly understood from the following description of some embodiments of the device given by way of example with reference to the drawings in which: Fig. 1 shows a first embodiment of the device according to the invention, Fig. 2 is a view of a line analysis device made up of mirrors only, in section through a plane extending through its axis of rotation, Fig. 3 is a view of the same line analysis device in projection on to a plane perpendicular to the aforementioned axis, Fig. 4 is a view of a line analysis device comprising lenses, in section along its plane of symmetry, Fig. 5 is a view of the same device in projection on to a plane perpendicular to its plane of symmetry, Fig. 6 illustrates the function of the "field" mirror, Fig. 7 is the projection of Fig. 6 on to a plane perpendicular to the axis of rotation of the line analysis device, Fig. 8 illustrates the motion of the raster (or image) analysis mirror, Fig. 9 illustrates the motion of the field mirror, Fig. 10 shows a second embodiment of the device according to the invention, comprising mirrors only, Fig. 11 shows a third embodiment of the device according to the invention, comprising mirrors only, in section along its plane of symmetry, Fig. 12 is a view of the last mentioned third embodiment in projection on to a plane perpendicular to its plane of symmetry, Fig. 13 shows an embodiment comprising a first system for directly displaying the image, Fig. 14 shows an embodiment comprising a second direct-display system, Fig. 15 shows a component of the invention for two-colour vivion, Fig. 16 is a view of component 151 in Fig.

15, rotated around the plane of the page, Fig. 17 shows an embodiment of the invention for thermal imaging with pyrometry, Fig. 18 shows an "in parallel" arrangement of the detectors in the device according to the invention, Fig. 19 shows an "in series" arrangement of the detectors in the device according to the invention Fig. 20 shows a "series-parallel" arrangement of the detectors in the device according to the invention.

Fig. 1 diagrammatically shows an embodiment of the invention in section along the plane of symmetry of the device: hereinafter, this plane is referred to as plane P. Reference 11 denotes a fixed objective having an optical axis 12 and a focus F. The optical axis intersects the YY' axis at point E.

The YY' axis is the axis of rotation of a system comprising a drive device 13 and a drum 13' bearing a number of lateral reflecting surfaces.

As shown hereinafter, the drum can have a number of shapes. For simplicity, we assume at present that it is prismatic and its reflecting surfaces are uniformly distributed around the YY' axis. At 17, one of these surfaces is represented in a position perpendicular to the plane of symmetry. A plane mirror 14 can move around an axis perpendicular to the page and extending through E. Actually, according to the invention, the axis does not necessarily extend through E. The feature represented in Fig. 1 is preferred only in the case where, as described hereinafter, the device is provided with additional means for directly displaying the field by means of electro-luminescent diodes. Miros 14 reflects every beam which comes from a region in the field and travels via objective 11 to a concave mirror 16 where it forms an image of the field substantially at mirror 16. In Fig. 1, a particular beam 15 is shown, having a central ray identical with the optical axis 12, the image forming at point D on the ZZ' axis perpendicular to the YY' axis, corresponding to the centre of the field.

Mirror 14 scans the field in a direction which is perpendicular to axis 12 and in the plane of the drawing; this direction will be called the 'y' direction in this specification. Hereinafter, the mirror 14 will be called the "image analysis" or "raster analysis" mirror.

The system also comprises a stationary concave mirror 18 having a reflecting surface which is a surface of revolution around axis YY'. Mirror 18 forms an image at A' of a detector 19, which is disposed at point A on the YY' axis, the image A' being situated on the same axis and symmetrical with D with respect to surface 17.

When drum 13' rotates, the system comprising the drum, mirror 18 and detector 19 is adapted for line-by-line analysis in a direction perpendicular to the plane of the page, of the image of the field given by objective 11 and mirror 14 in the neighbourhood of point D. Hereinafter, this system will be called the "line analysis or "x analysis" system. Mirror 16, which is symmetrical with respect to the plane (ZZ', YY') optically conjugates the centre of the exit pupil 0 of objective 11 which with the fixed point 0' on YY' axis which is symmetrical with E with respect to ZZ', so that any beam reaching the exit pupil of objective 11 is made to converge on to the detector.

Mirror 16 is called the "field mirror" since it limits the analyzed field.

In Fig. 1, objective 11 is made up of lenses.

According to the invention, as described hereinafter, the objective may equally well be made up of mirrors. Since, however, the invention relates not only to the assembly, an embodiment of which has been described, but also and particularly to the choice, arrangement and combination of the constituent elements, these elements will first be described as follows: 1. The line (orx) analysis system A first embodiment of this system is shown diagrammatically in- Figs. 2 and 3 which are projections respectively in the plane (ZZ', YY') and on to a plane perpendicular to the YY' axis. The embodiment comprises a drum 13' rotatable around the YY' axis and having a number of plane reflecting surfaces, and also comprises and image-conveying mirror 18.

Mirror 18 conveys the image of a detector 19 disposed at a point A on the axis of rotation YY' to a point A', which is also on the YY' axis.

The surfaces of drum 13' are placed in the convergent beam in the image-conveyance path of mirror 18.

Consequently points A"1, '2,--- s which are symmetrical with A' with respect respectively to each of the n surfaces of the drum, describe arcs of a circle centred on the axis of rotation YY' and contained in planes perpendicular to the YY' axis, the arcs subtending the scanned lines.

The drum according to the invention can have various shapes. It can be prismatic, all its surfaces being parallel to the YY' axis and at a slight distance therefrom, in which case the points A"1, A"2,...., A", describe a single circle extending through D. This case is shown in Figs. 2 and 3, where A", and A" represent the points symmetrical with A' with respect to two consecutive surfaces 21 and 22 of the drum 13'.

The same applies if the drum is pyramidal and if the reflecting surfaces are equally inclined to the YY' axis, as shown in Figs. 4 and 5. Alternatively, the drum surfaces can be inclined at different angles, in which case points A"1, A"2..., A", describe arcs of different circles centred on the YY' axis and contained in planes parallel to one another and perpendicular to YY'. In that case, the line analysis system, from one surface to another, scans the different lines extending near point D.

The image-conveying mirror 18 may e.g. be toric and have the axis YY'. The cross-section of the mirror is e.g. elliptic and belongs to a portion of an ellipsoid of revolution having the foci A and A'.

It is not essential, however, for the torus to have an elliptical cross-section; the elliptical shape is simply the best theoretical one. In certain cases, depending on the applications.

the elliptical cross-section may be closely approximated by a slightly different crosssection which is easier to construct, e.g. a circular cross-section.

In a variant similar to this embodiment, the torus does not consist entirely of mirrors but is catadioptric. In that case, the scanning device loses the advantage of operating at all wavelengths since it is not made up exclusively of mirrors, but has the advantage of providing new parameters for correcting aberrations.

In a second embodiment, the image of the detector on the axis is transferred by an objective comprising lenses. This embodiment is shown in Figures 4 and 5, which are projections respectively on to a plane containing the yyr axis and on to a plane perpendicular to the aforementioned axis.

The detector 19 is at A, outside the axis of rotation YY'. The objective 41 gives an image of the detector at A' on the axis of rotation YY'. As before, drum 13' can be a prism or a regular or irregular pyramid around the YY' axis. Point A", which is symmetrical with A' with respect to one surface 42 of the drum describes, as before, an arc of a circle 43 centred on the YY' axis and extending through or near D, and the arcs for different surfaces may or may not be identical, as previously described.

The last-mentioned system has the disadvantage of not being a system of revolution around the YY' axis, so that image A' or A" does not have a constant quality in dependence on the rotation of the drum.

Furthermore, objective 41 must have a very large aperture, depending on the length of the analyzed line. The second embodiment may be useful in certain applications, but it is generally preferable to use the toric mirror system since it has the following advantages: The light is used at all wave-lengths and the focusing can be checked and adjusted in visible light since the system is made up entirely of mirrors, thereby simplifying the construction; and an image of constant quality is given by the torus, irrespective of the angle of rotation of the drum, since the YY' axis is an axis of symmetry of the line analysis device.

On the horizontal projection of the line scanning system in Figure 3, 21 and 22 represent two consecutive reflecting surfaces of drum 13', 33 and 34 are the normals to each of the aforementioned surfaces (or the projections of the two normals on to a plane perpendicular to the YY' axis when the drum is pyramidal). The normals make an angle a.

A"1 and A"2 are points symmetrical with the image A' of detector 19 at A with respect to surfaces 21 and 22 respectively. The angle at which mirror 21 or 22 is viewed fromA' is likewise a. Angle a determines the maximum length of the analyzed line subtended by the arc A"1, A"2 during rotation of drum 13 ' and also determines the required aperture of mirror 18. The reason is, that the detector must not simultaneously receive the flux coming from two different points on the line.

Consequently the analyzed line must contain only one image of the detector; assuming that the drum 13' rotates in the direction of arrow 35 and that mirror 22 begins scanning the line at A"1, scanning must terminate at A"2 at the moment when mirror 21 begins scanning the next line at A"l. The aperture of the toric mirror should be sufficient in the plane perpendicular to the YY' axis for the rays from A"1 or A"2 to reflect towards A.

Consequently, as can be seen directly from Figure 3, the aperture must be greater than or equal to 2 a.

Consequently, the idle time between the scanning of two consecutive lines is zero.

The length of the analyzed line is determined by the number of surfaces on the rotating drum, which determines the angle a, i.e. the length A"l, A"2 in Figure 3.

Furthermore, as described hereinafter, the "field" mirror 16 in Figure 1 prevents the detector receiving flux coming from a number of points on the line A"1, A"2 in Figure 3.

2. The field mirror The function and shape of the field mirror (mirror 16 in Figure 1) will be explained with reference to Figures 6 and 7.

In figure 6, the entry optical system is shown in projection on to the plane of symmetry of the device through the YY' axis. The image analysis mirror has been omitted so as to not overload the drawing, and consequently the objective 11 is represented in a position symmetrical with its real position with respect to the YY' axis; this does not in any way limit the following remarks. 0" denotes the centre of the exit pupil of the objective placed in the aforementioned symmetrical position.

Figure 6 also shows a number of crosssections, i.e. the cross-section 61 of the field mirror 16, the cross-section 62 of the focal surface of the objective 11 having the centre O", and the cross-section 63 of the analyzed surface having the centre 0' situated on the YY' axis at the intersection of a ray OG reflected at G on the cross-section 61 of mirror 16. These cross-sections intersect at a point D situated on the optical axis of objective 11 and corresponding to the centre of the field.

Mirror 16 has a number of functions. It is designed to reflect every ray from 0", e.g.

O" G, in a direction 0' Extending through the fixed point 0' on the YY' axis, the point 0' being symmetrical with E, with respect to the intersection of the optical axis and the YY' axis. The first function of mirror 16, therefore, is to conjugate the centre 0" of the exit pupil of objective 11 (i.e. O in reality) with the fixed point 0' on the axis of rotation, which is the condition ensuring that any beam coming from one of the field regions associated with any ray passing through 0 and reflected by the line analysis mirrors can converge on the detector 19 placed at A on the axis of rotation YY'.

A priori, the introduction of this mirror has the disadvantage of introducing its field curvature. Actually this is not so, and we thus find that the field mirror has a second function; according to the invention, its curvature is used to correct the effects of aberrations due to the curvature of objective 11 and of the line analysis system. Mirror 16 gives an image of the focal surface of objective 11 (cross-section 62) the image coinciding with the analyzed surface (crosssection 63) centred at 0', due to the fact that the focal surface (cross-section 62) is centred on the exit pupil of objective 11 and the field mirror optically conjugates 0" (i.e.

0) and 0'.

In its most theoretical form, the field mirror is a portion of an ellipsoid of revolution having the foci 0" and 0' and containing point D and other points such as G.

In practice, according to the invention, use is made of a shape which is near an ellipsoid but easier to obtain, i.e. a portion of a sphere extending through D and centred at the point C at the intersection between the line 0" 0' and the ZZ' axis, perpendicular to YY' and extending through D.

Its radius of curvature is such that, in projection on to the plane perpendicular to YY' and passing through D, the mirror, as shown in Figure 7, conjugates H and H', which are the projections of 0" and 0' respectively on to the last-mentioned plane.

The analyzed line is an arc of a circle 73 having the centre H', being the intersection between the last-mentioned plane and the sphere having the centre 0' and the radius O' D, whereas the cross-sections of the focal surface of objective 11 and of the mirror 16 are arcs of circles 72 and 71 respectively.

According to the invention, mirror 16 can be limited, in the plane perpendicular to YY' and containing ZZ', to an arc of a circle which is infinitely small in the YY' direction and has the centre H', the circle giving an image B' on the arc 73 of a point B of 72 corresponding to a radius of projection HB.

In certain cases, the arc of a circle may be approximated by the tangent surface. In that case, according to the invention, mirror 16 may more particularly be a cylindrical mirror having an axis parallel to YY'and extending through C.

A third function of the field mirror 16 is to determine the dimensions of the analyzed field, for example the length of the line whose maximum value, as already explained, is determined by the number of faces of the rotating drum and corresponds to arc A"1, A"2 centred at A' and shown in Figure 3 A"1and A"2 being the images of the detector 19 given by the line analysis system, by means of two consecutive surfaces of drum 13'.

The width of mirror 16 is less than arc A", A"2, to an extent such that the flux falling on the detector 19 at A comes from only one point on the line.

One edge of the mirror may e.g. coincide with A"2, thus being slightly recessed with respect to A", as shown in Figure 3.

In order to obtain an image of the field having a consistent quality in dependence on the direction of the field analyzed in the y direction, and in order to reduce the bulk of the l A = L2(M2 = I) + R2 R a = 2 1) + arc sin [( - 1) + sin ]] 2 r R = OD, r = ED where i denotes the angle between ED and ZZ'.

According to the invention, this defocusing is corrected by causing mirror 16 to make slight movements such that the tangent 83 to the apex of the mirror is always the midperpendicular of DD". These movements are as follows; reciprocation in translation having the amplitude H2 cos y in the direction ZZ' from Z' to Z, and reciprocating rotation having the amplitude y around an aixs parallel to x and symmetrical with respect to ZZ', the aforementioned translation and rotation being in phase with the motion of the raster analysis mirror 14.

The position of mirror 16 is indicated in Figure 8 for the field angle ss, by means of the tangent 83 to the mirror at its apex, which is initially perpendicular to ZZ' at D for the centre of the field, i.e. when a and ss are zero. The distance between this tangent and D is 1/2 in the direction of DD", and the angle between it and YY' is a - '3 so that 2 the ray OD'3 intersects the ZZ' axis at D after being successively reflected at mirror 14 and mirror 16, and extends through the point 0' which is the conjugate of O by mirror 16 in its initial position.

Consequently, irrespective of the value of ss, D is the image of D" in the field mirror and the centre ray of the beam, after being reflected at a mirror, has a constant inclination i to the ZZ' axis, so that the centre 0 of the exit pupil is constantly conjugated with the same fixed point 0' of the YY" axis.

Consequently, irrespective of the direction of angle ss of the field, the focal image of objective 11 in the field mirror is identical with the surface analyzed by the line analysis device.

The complex motion of the field mirror is produced e.g. as indicated in Figure 9.

Mirror 16 is mounted perpendicular to a rectilinear holder AB such that A moves in translation along the ZZ' axis whereas B describes an arc of a circle 91 centred on the ZZ' axis and contained in the plane (ZZ', YY'). In Figure 9, M denotes the position of the mirror extending through D and corresponding to the centre of the field and M' denotes the position of the mirror when the direction of the field is the angle ss. In that case, the holder occupies the position A'B' and has rotated through the angle a - ith with respect to AB in the direction of 2 arrow 92.

Thus, defocusing is caused or produced by the image analysis mirror 14, and ensures that the limit of resolution in the entire field scanned in the x and y directions is as high as at the centre of the field. Furthermore, the limit of resolution given by the objective is not adversely affected by the system of analysis in the x and y directions.

We shall now, by way of example, describe two other embodiments of an optical scanning device containing in combination the elements which have been described in detail previously.

One embodiment is shown in Figure 10, along the plane of symmetry of the system.

It has the special feature of being made up completely of mirrors. The entry objective comprises a plane mirror 101 formed with an orifice 102, and a telescope mirror 103 having a parabolic cross-section. The optical axis of the objective has the reference 104.

The focus is at F. The beam coming from a point at infinity, after being reflected by the stationary mirrors 101 and 103, travels through orifice 102 and then through the analytical system proper, i.e. the image analysis mirror 14, the field mirror 16, the rotating drum 13' and the image-conveying mirror 18, and converges on detector 19.

Figure 10 shows a beam 105 having a central ray wich is identical with the optical axis 104: the telescopic mirror 103 provides a field of the order of e.g. 0.5 to 3 .

The other embodiment is shown in Figures 11 and 12, which are cross-sections respectively in the plane of symmetry of the device and in projection on to a plane perpendicular to the axis YY' of rotation of the line analysis system.

The special feature of this embodiment is that the image analysis mirror 14 is disposed upstream of the objective in a parallel beam, the mirror being movable around an axis perpendicular to the plane of Figure 11 and extending through point E on the YY' axis, on which axis the detector 19 is disposed at A.

Mirror 14 bounds the beam entering the system and can be regarded as the entry pupil of the analysis system, which has symmetry of revolution around the YY' axis and thus has identical optical properties in all directions of the field.

The objective used is a toric mirror 114 having the axis YY' and a parabolic crosssection through every plane extending through the YY' axis. The focus of the crosssection in the plane of the page is at point D, the centre of the field on the ZZ' axis extending through A', which is the image of the detector made by the line analysis toric mirror 18. The focal length of mirror 114 is made equal to the radius of the analysis circle so that A'D = DS, S being the apex of the torus cross-section and situated on the ZZ' axis. The toric mirror 114 is limited to its surface above the ZZ' axis.

The locus of the foci such as D is a circle 121 having the radius A'D in the plane perpendicular to the W' axis extending through D. These foci are successively identical with the image of the detector in the line analysis system.

The arc described by the image is limited by points A"1A"2 corresponding to the images of the detector in two successive surfaces respectively of the rotating drum In this system, the central ray of the analyzed beam of parallel rays is as before reflected at mirrors 14 and 114 and extends through a point in the arc A"1 A"2, the latter points being the conjugates of detector A by the line analysis system. Thus objective 114 acts as if it were a field mirror, in conjunction with the fact that the YY' axis is an axis of symmetry for the entire optical system.

In order to ensure that the detector 19 does not receive flux from two points in space simultaneously, the field is limited by a diaphragm 125 external to the arc A" A"2.

Thus the analysed field is equal to the angle a from which a surface of the drum is viewed from D (Figure 12), i.e. an angle of the order of e.g. 20 - 60 , depending on the number of drum surfaces.

Some embodiments of the device have been described in which the analysed field is at infinity. Of course, the invention is not limited to these cases and the field may equally well be at a finite distance. The line and raster scanning systems are compatible with the use of any objectives having a small or large field and adjusted to a finite or infinite distance, e.g. microscope objectives or objectives having a variable focal length (Zoom lenses). The resolution obtained is always very high since the detector image is exactly focused on to the image surface of the objective. The resolution may reach the limit due to diffraction, in the entire field of the apparatus.

Note also that the invention may easily be used to provide assemblies which are compact but which, owing to the oblique angle of the beams on to the field mirror and the line scanning elements, still have a structure such that the detector is in a position outside the optical analysis system proper.

In addition to the optical analysis system which has been described in detail, the invention comprises devices for directly displaying the analysed objects, and also comprises the application of the device to obtaining images of certain objects in the infra-red or in other wavelength ranges.

For the purpose of direct display, the video signal from the detector is applied, after suitable amplification, to an electroluminescent diode in the visible spectrum, the luminescence of which is proportional to the signal which it receives.

The analysis system, in the embodiment comprising mirrors only, can be used equally well at all wavelengths. Thus, the analysed object can be directly displayed, using the same system for analysis and restoration.

A first embodiment of the invention relating to the aforementioned display is represented, by way of example, in Figure 13. The analysis and display beams 15, 131 respectively travel along different paths, which are symmetrical with respect to a plane containing the YY' axis. The analysis device is as described in Figure 1. The display device comprises a field mirror 132 and a toroidal mirror 18' symmetrical with mirrors 16, 18 respectively with respect to the YY' axis. Mirror 132 need not be mobile, since the display beam can have a smaller aperture than for analysis and the eye can easily make adjustments to compensate slight curvature in the field.

The image analysis mirror 14 reflects on both surfaces, one surface being used for analysis and the other for display. A mirror 134 is disposed so that the point symmetrical with an electroluminescent diode 133 is identical with the detector 19. An amplification circuit 140 amplifies the video signal coming from detector 19 and applies it to diode 133. The image of the anlysed field, restored by the electroluminescent diode and the display system, is observed by the eye 137 behind a magnifying telescope diagrammatically represented by optical elements 135, 136 behind a collimator 139: the magnifying telescope may be omitted.

Use of the telescope has the advantage of rectifying the image. It can be combined with an intensifying tube 138 for increasing the luminance of the image and providing a time constant, due to the afterglow of the screen, for convenience of display.

A second embodiment of the invention for display purposes is represented in Figure 14.

In this embodiment, which is particularly suitable for obtaining images in a restricted spectrum range, the analysis and display beams 15 and 141 respectively travel along mainly identical paths, owing to the use of two dichroic mirrors 142, 143. These mirrors have the property of being transparent to light in the analysis spectrum but of reflecting all the rest of the spectrum. Mirror 142 is disposed so that the point symmetrical with an electroluminescent diode 144 in the mirror is identical with detector 19. The video signal from detector 19 is amplified by an amplification circuit 145 in the direction of diode 144. Mirrors 142 and 143 reflect light emitted by diode 144, if the light is not in the analysis spectrum, towards the telescope (optical elements 135 and 136) and the eye 137.

When analysis is in the infra-red, the two mirrors 142, 143 each advantageously comprise a strip of germanium which is transparent to infra-red and reflects the visible beam from the electroluminscent diode 144.

In another kind of display of the field image, a cathode-ray tube is used and is fed with a video signal supplied by the detector, the line and raster scanning of the cathode-ray tube being synchronised with the line and raster scanning of the optical device.

When the entry objective is a mirror objective (as in the Figure 10 embodiment), the device according to the invention comprises mirrors only, and may then be used for forming images at any wavelength.

It can provide "two-colour" or "multi-colour" images and be used in the ultraviolet, visible or infra-red spectrum.

According to the invention, analysis can be carried out simultaneously in different colours or in each colour in succession.

For the purpose of simultaneous analysis in different colours, the device may e.g.

comprise n detectors Dl, D2 Dn in a singel Dewar flask, the detectors being sensitive respectively to wavelengths Al, 22--------- Xn and disposed in a single row in the line analysis direction. These detecors supply a sequence of signals Si, S2 Sn which are phase-shifted with respect to one another. The signals are put back into phase by delay lines, whereupon the images at the wavelengths 21, A2 #n can be exactly superposed. It is then possible, by prior-art electronic processing, to show the difference between images at different wavelengths by adding or subtracting signals (e.g. (Sl + S3) - (S2 + Sn)). In another embodiment for simultaneous analysis in several colours, the detectors can be in different Dewar flasks.

For the purpose, for example of "two-colour" analysis at wavelengths Al and 22, the two detectors Dl and D2 in different Dewar flasks can be disposed symmetrically with respect to a dichroic mirror, in the same manner as detector 19 and diode 144 are placed with respect to dichroic mirror 142 in Figure 14, the dichroic mirror being transparent e.g. to wavelength Bl and reflecting wavelength 112.

Figure 15 shows an embodiment of the invention suitable for sequential colour analysis, e.g. in two colours. Two detectors D1 and D2, which are sensitive to wavelengths 21 and 22 respectively, are symmetrical with respect to a rotating disc 151 which forms the dichroic mirror referred to above, the plane of which is shown perpendicular to the page and parallel to the axis of rotation YY'. The disc rotates around an axis 152. The disc surfaces are reflecting and formed with slots.

The disc is shown in plan view in Figure 16.

The reflecting part of the surface is shown hatched, whereas the slots 161 and 162 are shown as un-hatched portions of the Figure.

The rotation of the disc is synchronised with the image scanning rotation. During rotation, D, and D2 alternately receive the flux through the imaging system, for the purpose of "two-colour" analysis. In this embodiment, the device can also comprise a source of radiation 153 disposed so that its central emitting ray is at an angle to disc 151 which is symmetrical with the central ray of the line analysis beam coming from mirror 18, the ray from source 153 travelling through Dl or D2. The source is viewed alternately by Dl and D2 and is used as a reference flux for the flux coming from the analytical system.

The device according to the invention is particularly suited for taking thermal images and measuring absolute temperature. A sample application of the device according to the invention for this purpose is shown in Figure 17, which represents scanning along a line, in projection on to a plane perpendicular to the YY' axis. During scanning, the image of the detector in the analytical system describes and arc of a circle 171 centred on the axis of rotation of the analysis drum, projected at H' in Figure 17. The ends of the arc are A' and B' and respectively correspond to points A and B on the image field situated on the cross-section 173 of the focal surface of the objective. It will be remembered that the special function of the field mirror having the cross-section 172 is to conjugate A and A' and B and B'. At A' the detector receives the flux corresponding to point A of the field, whereas at B' the field mirror is made discontinuous so that the detector receives flux not from point B but from a small reference source 174 at a place corresponding to the field mirror. As we have already seen, the total length of the field mirror and of the reference source should be slightly less than the length of the analysis line. Consequently, at the beginning or end of each analysis line, we have a reference signal which can be calibrated in temperature and compared with the signal given by the objective.

The advantage of the last-mentioned system is that the reference source is viewed at each line of the image. The duration of the reference signal is equal only to a few analyzed points and does not interfere with analysis of the field. The reference source is small, e.g. a black body having an emitting area of less than a square millimetre. Its temperature can be rapidly varied and checked at every instant by conventional measuring means such as a thermocouple.

The device according to the invention can be used with any kind of detector, whether cooled or not.

The detection system can comprise a single detector or alternatively n detectors disposed parallel to one another in a column (an arrangement hereinafter called in parallel).

This arrangement is shown in Figure 18, where the rectangles represent detectors and arrow 181 shows the direction of line scanning, which is perpendicular to the column of detectors.

The image of the detectors in the line analysis system simultaneously scans n lines of the field. During the subsequent line scanning, the image analysis system shifts the line scanning by n lines, so that the speed of rotation of the drum can be reduced. If the number of lines per second is equal, the speed of rotation is n 'times as small as for a single detector. This system requires n channels for amplifying the deflected signal, each channel being associated with one of the detectors. The detection system may also comprise n detectors disposed in sequence in the line scanning direction (an arrangement hereinafter called in series). This arrangement shown in Figure 19, where arrow 191 indicates the direction of scanning. In the line scanning system, each detector image scans the same line and, for each point on the line, gives a signal which is time-shifted with respect to the signal given for the same point by the other detectors. The signals are put back into phase by delay lines so as to obtain a single signal, delivered to a single amplification channel, in which case the procedure is exactly the same as if a single detector were used having sensitivity improved in a ratio of Of course, the detection system may also be of the series-parallel kind, i.e. as shown in Figure 20, comprising n1 columns of detectors placed in n2 lines, line scanning being in the direction of arrow 201. In this manner the rotation speed of the drum (13' in Figure 17) can be divided by n2, the sensitivity being improved in the ratio VW In the case where the image is restored by electroluminescent diodes, use can be made of an assembly of n diodes identical with the assembly of n detectors. Likewise, colour restoration can be directly obtained by supplying different colours with video signals from detectors sensitive to different wavelengths.

In the case of multicolour analysis, a single series, parallel or series-parallel arrangement can be adopted for detectors sensitive to different wavelengths.

Owing to its wide field, the scanning system according to the invention is compatible with conventional high-definition television standards, e.g. 625 lines per image. This standard corresponds to the scanning of 625 lines 25 times per second, i.e. to an actual scanning of 15,625 lines per second. In that case, a device according to the invention can comprise e.g. a rotating drum having 12 surfaces and a detector comprising 5 elements in parallel. 60 (5 x 12) lines are analysed at each revolution of the drum. If the drum rotates at 15,625 r.p.m. the lines of the image are scanned at the same frequency as for 625line television.

WHAT WE CLAIM IS: 1. A device for optically scanning a field of vision divided into different regions and for displaying the field, scanning being made in two perpendicular directions, i.e. "line" scanning in a direction x and "raster" or "image" scanning in a directiony, the device scanning along beams coming from different regions of the field and causing the beams to converge on to a detector sensitive to the radiation in the beams, the device comprising the following components in order, in the direction of the path of the central incident beam from the field of vision: an objective, means for raster scanning in the directiony, a system for deflecting the beams bounded by the detector and the aperture of the objective towards means for line scanning of the image field of the objective in the direction x, the display part of the device having optical means similar to the field of vision scanning means and comprising, instead of the detector, an electro-luminescent diode actuated by a signal coming from the detector, the device being characterised in that: the optical axis of the objective is in a plane P containing they direction and perpendicular to the x direction, the focal surface of said objective being curved and such that its centre of curvature is at the centre of the exit pupil of the objective, the raster scanning means comprise a plane mirror rotating in reciprocation around an axis parallel to the x direction and disposed in a convergent beam behind the objective near the field image in the objective.

the line scanning means comprise, firstly, a drum rotating uniformly around a stationary axis YY' contained in the plane P and bearing a number of flat reflecting surfaces regularly distributed around the drum periphery and, secondly, an image-conveying means symmetrical with respect to the plane P and forming an image of the detector at a fixed point A' along the drum rotation axis YY', the drum being placed in a convergent beam in the path of the image-conveying means on the image side of the detector, the point symmetrical with the point A' with respect to each surface of the drum, when the surface is perpendicular to the plane P, being in the neighbourhood of the point D which is symmetrical with the focus of the objective with respect to the raster mirror in a position parallel to the YY' axis. and the optical beam-deflecting system comprises a concave or field mirror having the plane P as the plane of symmetry, the apex of the mirror being near D on the ZZ' axis extending through D and perpendicular to the YY' axis, the mirror being so disposed that it conjugates the centre 0 of the exit pupil of the objective with a fixed point 0' on the YY'

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

detector or alternatively n detectors disposed parallel to one another in a column (an arrangement hereinafter called in parallel).

This arrangement is shown in Figure 18, where the rectangles represent detectors and arrow

181 shows the direction of line scanning, which is perpendicular to the column of detectors.

The image of the detectors in the line analysis system simultaneously scans n lines of the field. During the subsequent line scanning, the image analysis system shifts the line scanning by n lines, so that the speed of rotation of the drum can be reduced. If the number of lines per second is equal, the speed of rotation is n 'times as small as for a single detector. This system requires n channels for amplifying the deflected signal, each channel being associated with one of the detectors. The detection system may also comprise n detectors disposed in sequence in the line scanning direction (an arrangement hereinafter called in series). This arrangement shown in Figure 19, where arrow

191 indicates the direction of scanning. In the line scanning system, each detector image scans the same line and, for each point on the line, gives a signal which is time-shifted with respect to the signal given for the same point by the other detectors. The signals are put back into phase by delay lines so as to obtain a single signal, delivered to a single amplification channel, in which case the procedure is exactly the same as if a single detector were used having sensitivity improved in a ratio of ç Of course, the detection system may also be of the series-parallel kind, i.e. as shown in Figure 20, comprising n1 columns of detectors placed in n2 lines, line scanning being in the direction of arrow 201. In this manner the rotation speed of the drum (13' in Figure 17) can be divided by n2, the sensitivity being improved in the ratio VW In the case where the image is restored by electroluminescent diodes, use can be made of an assembly of n diodes identical with the assembly of n detectors. Likewise, colour restoration can be directly obtained by supplying different colours with video signals from detectors sensitive to different wavelengths.

In the case of multicolour analysis, a single series, parallel or series-parallel arrangement can be adopted for detectors sensitive to different wavelengths.

Owing to its wide field, the scanning system according to the invention is compatible with conventional high-definition television standards, e.g. 625 lines per image. This standard corresponds to the scanning of 625 lines 25 times per second, i.e. to an actual scanning of 15,625 lines per second. In that case, a device according to the invention can comprise e.g. a rotating drum having 12 surfaces and a detector comprising 5 elements in parallel. 60 (5 x 12) lines are analysed at each revolution of the drum. If the drum rotates at 15,625 r.p.m. the lines of the image are scanned at the same frequency as for 625line television.

WHAT WE CLAIM IS: 1. A device for optically scanning a field of vision divided into different regions and for displaying the field, scanning being made in two perpendicular directions, i.e. "line" scanning in a direction x and "raster" or "image" scanning in a directiony, the device scanning along beams coming from different regions of the field and causing the beams to converge on to a detector sensitive to the radiation in the beams, the device comprising the following components in order, in the direction of the path of the central incident beam from the field of vision: an objective, means for raster scanning in the directiony, a system for deflecting the beams bounded by the detector and the aperture of the objective towards means for line scanning of the image field of the objective in the direction x, the display part of the device having optical means similar to the field of vision scanning means and comprising, instead of the detector, an electro-luminescent diode actuated by a signal coming from the detector, the device being characterised in that: the optical axis of the objective is in a plane P containing they direction and perpendicular to the x direction, the focal surface of said objective being curved and such that its centre of curvature is at the centre of the exit pupil of the objective, the raster scanning means comprise a plane mirror rotating in reciprocation around an axis parallel to the x direction and disposed in a convergent beam behind the objective near the field image in the objective.

the line scanning means comprise, firstly, a drum rotating uniformly around a stationary axis YY' contained in the plane P and bearing a number of flat reflecting surfaces regularly distributed around the drum periphery and, secondly, an image-conveying means symmetrical with respect to the plane P and forming an image of the detector at a fixed point A' along the drum rotation axis YY', the drum being placed in a convergent beam in the path of the image-conveying means on the image side of the detector, the point symmetrical with the point A' with respect to each surface of the drum, when the surface is perpendicular to the plane P, being in the neighbourhood of the point D which is symmetrical with the focus of the objective with respect to the raster mirror in a position parallel to the YY' axis. and the optical beam-deflecting system comprises a concave or field mirror having the plane P as the plane of symmetry, the apex of the mirror being near D on the ZZ' axis extending through D and perpendicular to the YY' axis, the mirror being so disposed that it conjugates the centre 0 of the exit pupil of the objective with a fixed point 0' on the YY'

axis, point 0' being symmetrical with respect to the ZZ' axis with the point where the optical axis of the objective intersects the YY' axis; in order, if required, to ensure that the idle scanning time between two consecutive lines is zero, the field mirror also has a width in the x direction which is slightly less than the length of the analysed line, which in turn is equal to the distance between the images of the detector in two consecutive surfaces of the rotating drum, the mirror being moved if required for small distances in phase with the movement of the raster scanning means, the small motion comprising reciprocation in translation along the ZZ' axis in the neighbourhood of D and reciprocating rotation around an axis parallel to the x direction, which is symmetrical with respect to the ZZ' axis, the amplitude of the motion in translation being such as to correct the defocusing introduced by the raster scanning means and the amplitude of the rotation being such as to ensure that the field mirror holds 0', the conjugate of the centre 0 of the exit pupil of the objective, in a constant position during the reciprocating rotation of the raster scanning means.
2. A device according to Claim 1, characterised in that the rotating drum is a prism having reflecting surfaces which are equidistant from the YY' axis, or is a pyramid having surfaces at an equal inclination with respect to the YY' axis and A' and D are strictly symmetrical with respect to each of the surfaces which are successively placed perpendicular to the plane P.
3. A device according to Claim 1, characterised in that the rotating drum is a pyramid having reflecting surfaces which are inclined at different angles with respect to the YY' axis.
4. A device according to any of Claims 1 to 3, characterised in that the image-conveying means of the line scanning means comprises a toric concave mirror having the YY' axis, the plane of symmetry of the mirror being a plane perpendicular to the YY' axis, and the detector and its image A' in the mirror being situated on the YY' axis.
5. A device according to claim 4, characterised in that the cross-section of the toric mirror in a plane containing the YY' axis is an ellipse, the major axis of which is identical with the YY' axis and one focus of which is occupied by the detector.
6. A device according to Claim 5, characterised in that the cross-section is substantially a circle.
7. A device according to any of Claims 1 to 3, characterised in that the image-conveying means the line scanning means is a toric catadioptre on the YY' axis, the plane of symmetry of the catadioptre being perpendicular to the YY' axis, and the detector and its image being situated on the YY' axis.
8. A device accordingto any of Claims 1 to 3, characterised in that the image-conveying means the line scanning means is an objective comprising lenses, the sensitive element being outside the YY' axis, and the focal length of the lens objective being such that it forms the image A' of the detector on the YY' axis.
9. A device according to any of Claims 1 to 8, characterised in that the field mirror is a portion of an ellipsoid having the foci 0' and 0", 0" being the point symmetrical with 0 with respect to the raster mirror when said mirror is disposed parallel to the YY' axis, the ellipsoid p extending through b or in the immediate neighbourhood thereof.
10. A device according to any of claims 1 to 8, characterised in that the field mirror is a portion of a sphere centred at the point C at the intersection of the ZZ' axis and the straight line joining the aforementioned points 0', 0", the sphere extending through D or in the immediate neighbourhood thereof.
11. A device as claimed in any one of claims 1 to 8, wherein the field mirror is a cylindrical surface.
12. A device according to any one of claims 1 to 11, characterised in that the amplitude of the reciprocation in translation of the field mirror along the ZZ' axis and of the rotation around the x direction, evaluated from the reference position corresponding to the case where the apex of the mirror is at D whereas the raster mirror is parallel to the YY' axis and the field angle is zero, is respectively cos b and = a - - where a 2 represents the angle between the raster mirror and the YY' axis and ss is the angle at which the edge of the field is viewed from the centre of the exit pupil of the objective, I, a and B being related as follows: I = - LM + sin 2α with l = r sin ss M= cos (a + i - 2ss) A = L2(M2 = I) + R2 a = 1 [ss + arcsin [(R - 1) + sin '3j] 2 r R = OD1 r = ED D, being the point symmetrical with D with respect to the YY' axis, E being the intersection of the optical axis of the objective with the YY' axis, and i being the angle between ED and the ZZ' axis.
13. A device according to any of Claims 1 to 3, characterised in that it is constructed according to any of the claims comprising any one of Claims 4 to 6 and any one of Claims 9 to 12.
14. A device according to Claim 13, characterised in that the objective comprises lenses.
15. A device according to Claim 13, characterised in that the objective comprises mirrors only.
16. A device comprising mirrors only and analogous to the device according to Claim 15, characterised in that the raster scanning mirror is placed in a parallel beam in front of the objective, its axis of rotation being perpendicular to the YY' axis and intersecting it, the objective also serving as a field mirror and comprising a stationary concave mirror having a toric shape around the YY' axis and a parabolic cross-section through every plane extending through the axis, the foci of the cross-sections being the conjugates of the detector by the line analysis means, the stationary concave mirror being of dimensions in the raster direction limited to that part disposed above the plane perpendicular to the YY' axis and extending through the locus of the foci, and a field diaphragm being disposed on the focal surface of the mirror and limiting the length of the analysed line.
17. A device according to any of Claims 13 to 16, characterised in that the system for directly displaying the field image comprises optical elements symmetrical with respect to the YY' axis to the elements forming the image analysis system and also comprises a plane mirror giving a virtual image, identical with the detector, of a diode which is electroluminescent in the visible spectrum, and means for applying the signal from the detector to the electroluminescent diode, the field image being observed by the eye, via a telescope if required.
18. A device according to any of Claims 13 to 16, characterised in that the optical elements of the image analysis system are common with the optical elements of the display system, which also comprises two plane dichroic mirrors, i.e. a first dichroic mirror disposed so that it forms a virtual image, identical with the detector, of the electroluminescent diode, and a second dichroic mirror disposed upstream of the line and image analysis systems, the dichroic mirrors being transparent to the analysis light and reflecting the electroluminescence light, the field image being observed by the eye, via a telescope if required.
19. A device according to any one of Claims 1 to 18, characterised in that the detector, like the electroluminscent diode, comprises n elements, the detector elements being sensitive to different wavelengths and the diode elements emitting in different colours, the geometrical assembly of the detector elements being identical with the geometrical assembly of the diode elements, the assemblies being symmetrical with one another with respect to the plane mirror optically conjugating the electroluminscent diode and detector referred to in Claim 17 or 18, and the device comprises means for applying the video signal from a detector element to a diode element, optical elements acting as a light filter if required.
20. A device according to any one of Claims 1 to 18, characterised in that it also comprises a source of reference radiation disposed on the line path of the detector image at the end of an analysis line.
21. A device according to Claim 19, characterised in that the detector comprises two elements D,, D2 sensitive to a wavelength region centred at wavelength Al and wavelength A. respectively, the element Dl being disposed on the YY' axis and the element D2 being symmetrical with D1 with respect to a dichroic mirror, the dichroic mirror being transparent to wavelength A, and reflecting wavelength A2.
22. A device according to Claim 19, characterised in that the detector comprises two elements Dl, D. sensitive to a wavelength region centred at wavelength Al and A2 respectively and in that the two elements are symmetrical with respect to a rotating disc, the disc surface reflecting on both sides and being formed with apertures, the device also comprising, if required, a source of reference radiation emitting in a mean direction having the same inclination to the disc as the central ray of the analysis beam.
23. A device according to any of Claims 1 to 18, characterised in that the detector comprises a number of sensitive elements disposed in a column perpendicular to the direction of line scanning.
24. A device according to any of Claims 1 to 18, characterised in that the detector comprises a number of sensitive elements disposed sequentially in a row parallel to the direction of line scanning.
25. A device according to any of Claims 1 to 18, characterised in that the detector comprises a number of columns of sensitive elements disposed in a number of rows perpendicular to the columns which extend perpendicualr to the direction of line scanning.
26. A device according to any of Claims 1 to 20, comprising detectors which are each sensitive to a certain range of wavelengths, each detector having one of the structures specified in Claims 23 to 25.
27. A device for optically scanning a field of vision, the device being substantially as herein described, with reference to, and as shown in the accompanying drawings.