EP0533538A1 - Image intensifier tube with brightness correction - Google Patents

Image intensifier tube with brightness correction Download PDF

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Publication number
EP0533538A1
EP0533538A1 EP92402488A EP92402488A EP0533538A1 EP 0533538 A1 EP0533538 A1 EP 0533538A1 EP 92402488 A EP92402488 A EP 92402488A EP 92402488 A EP92402488 A EP 92402488A EP 0533538 A1 EP0533538 A1 EP 0533538A1
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EP
European Patent Office
Prior art keywords
intensifier tube
tube according
attenuating
attenuating element
window
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Granted
Application number
EP92402488A
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German (de)
French (fr)
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EP0533538B1 (en
Inventor
Yvan Raverdy
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Thales Electron Devices SA
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Thomson Tubes Electroniques
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J31/00—Cathode ray tubes; Electron beam tubes
    • H01J31/08—Cathode ray tubes; Electron beam tubes having a screen on or from which an image or pattern is formed, picked up, converted, or stored
    • H01J31/50—Image-conversion or image-amplification tubes, i.e. having optical, X-ray, or analogous input, and optical output
    • H01J31/501—Image-conversion or image-amplification tubes, i.e. having optical, X-ray, or analogous input, and optical output with an electrostatic electron optic system
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
    • H01J29/86—Vessels; Containers; Vacuum locks
    • H01J29/89—Optical or photographic arrangements structurally combined or co-operating with the vessel

Definitions

  • the invention relates to image intensifier tubes, in particular of the radiological type. It particularly relates to optical means making it possible to correct the distribution of the light intensity at the output of the image intensifier tube.
  • Image intensifier tubes are vacuum tubes comprising an input screen, located at the front of the tube, an electronic optical system, and a visible image observation screen located at the rear of the tube. tube, on the side of an exit window of the latter.
  • the input screen further includes a scintillator screen which converts the incident x photons into visible photons.
  • Visible photons excite a photocathode which in response generates a flow of electrons.
  • This flow of electrons is then transmitted by the electronic optical system which focuses the electrons, and directs them on the observation screen, more precisely on a cathodoluminescent screen generally constituted by one or more layers ofuciminophoric grains; the cathodoluminescent screen then emits visible light.
  • FIG. 1 schematically shows such an image intensifier tube of the radiological type.
  • the intensifier tube 1 comprises a glass envelope 2, one end of which, at the front of the tube, is closed by an entry window 3 exposed to x-ray photon radiation.
  • the second end of the envelope forming the rear of the tube is closed by an exit window 4 transparent to light.
  • the x-rays are converted into light rays by a scintillator screen 5.
  • the light rays excite a photocathode 6 which in response produces electrons.
  • These electrons are extracted from photocathode 5 accelerated towards the exit window 4 using different electrodes 7, and an anode 8 arranged along a longitudinal axis 9 of the tube and which form the electronic optics system.
  • the exit window 4 is formed by a transparent piece of glass attached in a sealed manner to the envelope 2.
  • This piece of glass furthermore constitutes, in the example shown, a support which carries a cathodoluminescent screen 10, made of phosphors for example.
  • the impact of the electrons on the cathodoluminescent screen 10 makes it possible to reconstitute an image (amplified in luminance) which at the start was formed on the surface of the photocathode 6.
  • the exit window 4 made of glass forms part of the envelope 2, in such a way that an external face 13 of this window, opposite the phosphor layer 10, constitutes an external part of the tube 1.
  • the image displayed by the lumiminophore layer 10 is visible through the glass piece which constitutes the exit window 4.
  • optical sensor devices (not shown) are arranged outside the tube near the exit window 4 to capture this image through it and allow its observation.
  • the intensifier tube 1 may further comprise, as in the example shown, a transparent blade 14 secured by a layer of adhesive 15 to the outer face 13 of the outlet window 4.
  • the function of the transparent blade 14 is to improve the contrast, and for this purpose it includes a significant thickness E 10 mm for example.
  • the surface of the input screen that is to say the surfaces of the input window 3 as well as of the scintillator and of the photocathode 5, 6 are not flat but curved.
  • the electronic density generated by the entry screen is not uniform, and this is reflected at the exit of the tube on the brightness curve, along a diameter D of the exit window 4: the brightness curve represents the light intensity at each point of the diameter D of the exit window 4.
  • this curve is generally in the shape of an arc of a circle: the brightness is maximum towards the center, and decreases markedly as one approaches the edges.
  • the decrease in gloss on the edges relative to the center is commonly between 25% and 30%, and can reach 35% for intensifier tubes having large entry windows.
  • One of the aims of the invention is to improve the brightness curve of an image intensifier tube by reducing the difference between the center and the edges, in a simpler manner and more compatible with industrial requirements, without degrade the other features.
  • the correction of the brightness curve is accomplished at the exit window, using a light attenuator interposed on the path of the light rays emitted by the cathodoluminescent screen in the direction from the outside of the intensifier tube, and by giving this attenuator a non-uniform opacity which achieves the desired compensation.
  • an image intensifier tube comprising an outlet window, a cathodoluminescent screen providing a visible image outside said intensifier tube through the outlet window, is characterized in that it further comprises a light attenuation device disposed facing the exit window and, have a greater opacity to light facing a central area of the exit window than towards the edges of the latter.
  • FIG. 2 is an enlarged view of a box 19 in FIG. 1, in order to more particularly represent the outlet window 4 of an image intensifier tube.
  • the tube 1 has an outlet window 4 carrying, inside the tube, the cathodoluminescent layer 10, in the same manner as in the example of FIG. 1.
  • the exit window 4 carries on its face 13, opposite the cathodoluminescent screen 10, a light attenuating device 20 whose opacity to light varies between its edges 21 and its center O; the center O being located on the longitudinal axis 9 of the tube, it also corresponds to the center of the outlet window 4.
  • the attenuating device comprises an attenuating element 25 made of a semi-transparent material.
  • the thickness of the attenuating element 25 varies from a large thickness EF in the region of the center O, to a reduced thickness ER on the edges 21 of this attenuating element.
  • the attenuating element 25 is produced, for example, from mass-tinted glass (neutral tint for example), a material which is commonly found on the market with different light transmission values which can be for example between 50% and 80%.
  • the attenuating element 25 has the general shape of a lens of the plano-convex type.
  • the compensation provided on the brightness curve by the attenuating element 25 is all the greater when the thickness is large at the center O and small at the edges 21.
  • the edges 21 can have a non-negligible thickness ER compared to the large thickness EF of the center O, as shown in the example of FIG. 2.
  • FIG. 3 shows a brightness curve 40 in solid lines obtained at the output of an image intensifier tube, along the diameter of the outlet window 4 and more precisely along the diameter D1 of the attenuating element 25, with the conditions above mentioned.
  • the diameter D1 is plotted on the abscissa and the brightness, of course measured with the attenuating device 25 interposed, is plotted on the ordinate.
  • the curve 40 shows a maximum of brightness towards the center O and a fairly pronounced decrease towards the edges 21; with a zero value before the edges 21, which shows that the diameter D1 of the attenuating element 25 is a little larger than the diameter of the useful field at the outlet of the tube 1.
  • the curve has the shape of an arc of a circle flattened towards the center O.
  • the attenuating element the attenuation coefficient and the profile which would make it possible to obtain a substantially straight curve and horizontal, or even overcompensation to take into account in some cases the requirements of optical sensor devices intended to observe the image.
  • the attenuation device constitutes an optical doublet with parallel faces 28, 29: it consists of two complementary parts 25, 27 of which the first is the element attenuator 25, in the form of plano-convex lenses, and the second of which is complementary to the first, that is to say of plano-concave shape, and constitutes a cradle 27 at the convex part 30 of the attenuating element 25 ; of course the cradle 27 is transparent to light.
  • the two faces 28, 29 are mutually parallel and parallel to the planes of the outlet window 4 and of the cathodoluminescent screen 10.
  • the attenuating element 25 can also be directly secured to the outlet window 4 by gluing for example.
  • the simplest and most natural way of attaching the attenuating element 25 to the exit window is not the most suitable. Indeed, the simplest way to fix the attenuating element 25 to the window 4 is to place it on the latter with the flat face 28 of this attenuating element 25 resting on the outlet window, that is to say say oriented towards the cathodoluminescent screen 10.
  • the attenuating element 4 is fixed with the opposite orientation, that is to say with its convex part 30 oriented towards the exit window 4 and therefore towards the cathodoluminescent screen 10, for reasons explained below, this as well in the case where the attenuating element 25 is mounted in an optical doublet as in the case where it is mounted directly on the outlet window 4.
  • the space occupied by the cradle 27 shown in Figure 2 is filled with glue; commercially available glues that are transparent to light and have various indices of refraction which can therefore be chosen to be very close to the indices of the transparent materials used.
  • the attenuating element 25 corrects the gloss curve at the outlet of the tube in the same way for one or the other of the two possible orientations defined above.
  • the presence of the attenuating element 25 brings an additional advantageous effect, which is manifested by a strong improvement in contrast.
  • This improvement in contrast results from the fact that, by mounting an element on the exit window 4 which reduces light transmission, the rays parallel to the plane of the exit window are attenuated less, that is to say parallel to the longitudinal axis 9, and the inclined rays are more attenuated because they cross a greater absorbent length; the inclined rays being those which degrade the contrast.
  • the attenuating element is mounted with its convex part 30 oriented towards the outlet window 4, as shown in FIG. 2, and as it is recommended to do, the attenuation due to the absorbent length passed through L a (in the the attenuating element) is the same for radii r1, r2 inclined by the same angle value a1 and penetrating into the attenuating element 25 at the same point B, but with different directions.
  • the attenuating element 25 is mounted with the opposite orientation (not shown), that is to say with its planar face 26 bearing on the outlet window 4, for inclined radii such as r1, r2 penetrating into the attenuator 25 at the same point on its flat face 26, the absorbent lengths are different ; which leads to a variable attenuation of the inclined rays as a function of their direction.
  • the correction of the brightness curve in accordance with the invention can be applied in substantially the same way to all types of image intensifier tubes, with scintillator screen or not, because the attenuating element 25 which achieves this correction, can be mounted outside the intensifier tube. Therefore, another important advantage is that the intensifier tube and the attenuating element 25 can be constructed independently of each other. An attenuating element 25 already mounted can thus possibly be replaced by another carrying out a different correction, and this without damage to the intensifier tube.

Abstract

The invention relates to image intensifier tubes, the brightness curve of which it makes it possible to correct very simply. …<??>The image intensifier tube of the invention comprises an entrance window (3), and an exit window (4) in the vicinity of which the brightness is measured. According to the invention, the exit window (4) carries a light-attenuating device (20), the opacity of which is greater in a central zone (O) than towards the edges (21). …<IMAGE>…

Description

L'invention concerne les tubes intensificateurs d'image, notamment du type radiologique. Elle concerne particulièrement des moyens optiques permettant de corriger la distribution de l'intensité lumineuse en sortie du tube intensificateur d'image.The invention relates to image intensifier tubes, in particular of the radiological type. It particularly relates to optical means making it possible to correct the distribution of the light intensity at the output of the image intensifier tube.

Les tubes intensificateurs d'image sont des tubes à vide comprenant un écran d'entrée, situé à l'avant du tube, un système d'optique électronique, et un écran d'observation de l'image visible situé à l'arrière du tube, du côté d'une fenêtre de sortie de ce dernier.Image intensifier tubes are vacuum tubes comprising an input screen, located at the front of the tube, an electronic optical system, and a visible image observation screen located at the rear of the tube. tube, on the side of an exit window of the latter.

Dans les tubes intensificateurs d'image radiologiques, l'écran d'entrée comporte en outre un écran scintillateur qui convertit les photons x incidents en photons visibles.In X-ray image intensifier tubes, the input screen further includes a scintillator screen which converts the incident x photons into visible photons.

Les photons visibles excitent une photocathode qui en réponse génère un flux d'électrons. Ce flux d'électrons est ensuite transmis par le système d'optique électronique qui focalise les électrons, et les dirige sur l'écran d'observation, plus précisément sur un écran cathodoluminescent constitué généralement par une ou plusieurs couches de grains luiminophores ; l'écran cathodoluminescent émet alors une lumière visible.Visible photons excite a photocathode which in response generates a flow of electrons. This flow of electrons is then transmitted by the electronic optical system which focuses the electrons, and directs them on the observation screen, more precisely on a cathodoluminescent screen generally constituted by one or more layers of luiminophoric grains; the cathodoluminescent screen then emits visible light.

La figure 1 montre schématiquement un tel tube intensificateur d'image du type radiologique.FIG. 1 schematically shows such an image intensifier tube of the radiological type.

Le tube intensificateur 1 comprend une enveloppe 2 en verre dont une extrémité, à l'avant du tube, est fermée par une fenêtre d'entrée 3 exposée à un rayonnement de photons x.The intensifier tube 1 comprises a glass envelope 2, one end of which, at the front of the tube, is closed by an entry window 3 exposed to x-ray photon radiation.

La seconde extrémité de l'enveloppe formant l'arrière du tube est fermée par une fenêtre de sortie 4 transparente à la lumière.The second end of the envelope forming the rear of the tube is closed by an exit window 4 transparent to light.

Les rayons x sont convertis en rayons lumineux par un écran scintillateur 5. Les rayons lumineux excitent une photocathode 6 qui en réponse produit des électrons. Ces électrons sont extraits de la photocathode 5 accélérés vers la fenêtre de sortie 4 à l'aide de différentess électrodes 7, et d'une anode 8 disposées le long d'un axe longitudinale 9 du tube et qui forment le système d'optique électronique.The x-rays are converted into light rays by a scintillator screen 5. The light rays excite a photocathode 6 which in response produces electrons. These electrons are extracted from photocathode 5 accelerated towards the exit window 4 using different electrodes 7, and an anode 8 arranged along a longitudinal axis 9 of the tube and which form the electronic optics system.

Dans l'exemple représenté ; la fenêtre de sortie 4 est formée par une pièce transparente en verre rapportée de façon étanche à l'enveloppe 2. Cette pièce de verre constitue en outre dans l'exemple montré un support qui porte un écran cathodoluminescent 10, fait de luminophores par exemple.In the example shown; the exit window 4 is formed by a transparent piece of glass attached in a sealed manner to the envelope 2. This piece of glass furthermore constitutes, in the example shown, a support which carries a cathodoluminescent screen 10, made of phosphors for example.

L'impact des électrons sur l'écran cathodoluminescent 10 permet de reconstituer une image (amplifiée en luminance) qui au départ était formée sur la surface de la photocathode 6. La fenêtre de sortie 4 en verre forme une partie de l'enveloppe 2, de telle manière qu'une face extérieur 13 de cette fenêtre, opposée à la couche luminophore 10, constitue une partie extérieure du tube 1.The impact of the electrons on the cathodoluminescent screen 10 makes it possible to reconstitute an image (amplified in luminance) which at the start was formed on the surface of the photocathode 6. The exit window 4 made of glass forms part of the envelope 2, in such a way that an external face 13 of this window, opposite the phosphor layer 10, constitutes an external part of the tube 1.

L'image affichée par la couche lumiminophore 10 est visible à travers la pièce en verre qui constitue la fenêtre de sortie 4. Généralement des dispositifs capteurs optiques (non représentés) sont disposés à l'extérieur du tube à proximité de la fenêtre de sortie 4 pour capter cette image au travers de cette dernière et permettre son observation.The image displayed by the lumiminophore layer 10 is visible through the glass piece which constitutes the exit window 4. Generally optical sensor devices (not shown) are arranged outside the tube near the exit window 4 to capture this image through it and allow its observation.

Le tube intensificateur 1 peut comporter en outre, comme dans l'exemple représenté, une lame transparente 14 solidarisée par une couche de colle 15 à la face extérieure 13 de la fenêtre de sortie 4. La lame transparente 14 a pour fonction d'améliorer le contraste, et à cet effet elle comporte une épaisseur E non négligable 10 mm par exemple. Il en résulte que des rayons de lumière 16 émis par la couche luminophore 10 avec des angles importants par rapport à un rayon normal au plan de la lame transparente 14, tendent à émerger de cette lame vers des bords de celle-ci, et tendent ainsi à sortir du champ du dispositif capteur optique (non représenté) ci-dessus mentionné.The intensifier tube 1 may further comprise, as in the example shown, a transparent blade 14 secured by a layer of adhesive 15 to the outer face 13 of the outlet window 4. The function of the transparent blade 14 is to improve the contrast, and for this purpose it includes a significant thickness E 10 mm for example. As a result, rays of light 16 emitted by the phosphor layer 10 with large angles relative to a radius normal to the plane of the transparent strip 14, tend to emerge from this strip towards the edges thereof, and thus tend outside the scope of the above-mentioned optical sensor device (not shown).

Pour des raisons notamment d'optique électronique, la surface de l'écran d'entrée, c'est-à-dire les surfaces de la fenêtre d'entrée 3 ainsi que du scintillateur et de la photocathode 5, 6 ne sont pas planes mais bombées. Il en résulte que si l'on éclaire la fenêtre d'entrée 3 par un faisceau uniforme le rayons x, la densité électronique engendrée par l'écran d'entrée n'est pas uniforme, et ceci se répercute en sortie du tube sur la courbe de brillance, le long d'un diamètre D de la fenêtre de sortie 4 : la courbe de brillance représente l'intensité lumineuse en chaque point du diamètre D de la fenêtre de sortie 4.For reasons notably of electronic optics, the surface of the input screen, that is to say the surfaces of the input window 3 as well as of the scintillator and of the photocathode 5, 6 are not flat but curved. As a result, if the entrance window 3 is illuminated by a uniform x-ray beam, the electronic density generated by the entry screen is not uniform, and this is reflected at the exit of the tube on the brightness curve, along a diameter D of the exit window 4: the brightness curve represents the light intensity at each point of the diameter D of the exit window 4.

On constate que cette courbe est généralement en forme d'arc de cercle : la brillance est maximale vers le centre, et diminue nettement à mesure qu'on s'approche des bords. La diminution de brillance sur les bords par rapport au centre est couramment comprise entre 25% et 30%, et peut atteindre 35% pour les tubes intensificateur ayant des fenêtres d'entrée de grande dimension.It can be seen that this curve is generally in the shape of an arc of a circle: the brightness is maximum towards the center, and decreases markedly as one approaches the edges. The decrease in gloss on the edges relative to the center is commonly between 25% and 30%, and can reach 35% for intensifier tubes having large entry windows.

Dans le cas de tubes intensificateur d'images radiologiques, il a déjà été proposé dans l'art antérieur (document de brevet européen EP 0 239 991) d'améliorer l'homogénéité de la brillance en donnant une répartition non homogène à l'épaisseur de la couche qui constitue le scintillateur 5. Cette méthode procure d'assez bon résultats, mais sa mise en oeuvre est délicate et gênante industriellement, du fait notamment que le rendement d'un scintillateur varie avec son épaisseur.In the case of radiological image intensifier tubes, it has already been proposed in the prior art (European patent document EP 0 239 991) to improve the uniformity of the gloss by giving an inhomogeneous distribution of the thickness. of the layer which constitutes the scintillator 5. This method provides fairly good results, but its implementation is delicate and troublesome industrially, in particular because the yield of a scintillator varies with its thickness.

Un des buts de l'invention est d'améliorer la courbe de brillance d'un tube intensificateur d'image en atténuant l'écart entre le centre et les bords, d'une façon plus simple et plus compatible avec les exigences industrielles, sans dégrader les autres caractéristiques.One of the aims of the invention is to improve the brightness curve of an image intensifier tube by reducing the difference between the center and the edges, in a simpler manner and more compatible with industrial requirements, without degrade the other features.

Conformément à l'invention, la correction de la courbe de brillance est accomplie au niveau de la fenêtre de sortie, à l'aide d'un atténuateur de lumière interposé sur le trajet des rayons lumineux émis par l'écran cathodoluminescent en direction de l'extérieur du tube intensificateur, et en conférant à cet atténuateur une opacité non uniforme qui réalise la compensation recherchée.According to the invention, the correction of the brightness curve is accomplished at the exit window, using a light attenuator interposed on the path of the light rays emitted by the cathodoluminescent screen in the direction from the outside of the intensifier tube, and by giving this attenuator a non-uniform opacity which achieves the desired compensation.

Ainsi la correction de la courbe de brillance s'effectue sans intervenir sur le scintillateur de l'écran primaire, de telle sorte que l'invention peut s'appliquer d'une même manière à tous les tubes intensificateurs d'image, qu'ils soient ou non du type radiologique.Thus the correction of the brightness curve is carried out without intervening on the scintillator of the primary screen, so that the invention can be applied in the same way to all the image intensifier tubes, whether they whether or not they are of the radiological type.

Suivant l'invention, un tube intensificateur d'image, comportant une fenêtre de sortie, un écran cathodoluminescent fournissant une image visible à l'extérieur dudit tube intensificateur à travers la fenêtre de sortie, est caractérisé en ce qu'il comporte en outre un dispositif d'atténuation de lumière disposé en regard de la fenêtre de sortie et, présentent une opacité à la lumière plus grande en regard d'une zone centrale de la fenêtre de sortie que vers les bords de cette dernière.According to the invention, an image intensifier tube, comprising an outlet window, a cathodoluminescent screen providing a visible image outside said intensifier tube through the outlet window, is characterized in that it further comprises a light attenuation device disposed facing the exit window and, have a greater opacity to light facing a central area of the exit window than towards the edges of the latter.

D'autres caractéristiques et avantages de l'invention apparaîtront à la lecture de la description détaillée qui suit et qui est faite en référence aux dessins annexés dans lesquels :

  • la figure 1 déjà décrite représente la structure d'un tube intensificateur d'image radiologique de l'art antérieur ;
  • la figure 2 représente schématiquement une fenêtre de sortie munie d'un atténuateur de lumière conforme à l'invention ;
  • la figure 3 montre une courbe de brillance compensée suivant l'invention ;
Other characteristics and advantages of the invention will appear on reading the detailed description which follows and which is given with reference to the appended drawings in which:
  • FIG. 1 already described represents the structure of a radiological image intensifier tube of the prior art;
  • FIG. 2 schematically represents an exit window provided with a light attenuator according to the invention;
  • Figure 3 shows a compensated brightness curve according to the invention;

La figure 2 est une vue agrandie d'un encadré 19 de la figure 1, afin de représenter plus particulièrement la fenêtre de sortie 4 d'un tube intensificateur d'image.FIG. 2 is an enlarged view of a box 19 in FIG. 1, in order to more particularly represent the outlet window 4 of an image intensifier tube.

Les autres parties de ce tube situées hors de l'encadré n'étant pas modifiées par l'invention, il n'est pas nécessaire de les représenter afin de simplifier la description, et il peut être admis que dans l'exemple l'invention s'applique à un tube 1 intensificateur semblable à celui montré à la figure 1.The other parts of this tube located outside the box not being modified by the invention, it is not necessary to represent them in order to simplify the description, and it can be admitted that in the example the invention applies to a tube 1 intensifier similar to that shown in the figure 1.

Le tube 1 comporte une fenêtre de sortie 4 portant, à l'intérieur du tube, la couche cathodoluminescente 10, d'une même manière que dans l'exemple de la figure 1.The tube 1 has an outlet window 4 carrying, inside the tube, the cathodoluminescent layer 10, in the same manner as in the example of FIG. 1.

Conformément à l'invention, la fenêtre de sortie 4 porte sur sa face 13, opposée à l'écran cathodoluminescent 10, un dispositif atténuateur de lumière 20 dont l'opacité à la lumière varie entre ses bords 21 et son centre O ; le centre O étant situé sur l'axe longitudinal 9 du tube, il correspond également au centre de la fenêtre de sortie 4.According to the invention, the exit window 4 carries on its face 13, opposite the cathodoluminescent screen 10, a light attenuating device 20 whose opacity to light varies between its edges 21 and its center O; the center O being located on the longitudinal axis 9 of the tube, it also corresponds to the center of the outlet window 4.

Suivant un exemple de réalisation préféré, le dispositif atténuateur comporte un élément atténuateur 25 réalisé en un matériau semi-transparent. L'épaisseur de l'élément atténuateur 25 varie, depuis une épaisseur forte EF dans la zone du centre O, jusqu'à une épaisseur réduite ER sur les bords 21 de cet élément atténuateur. L'élément atténuateur 25 est réalisé par example en du verre teinté dans la masse (teinte neutre par exemple), matériau que l'on trouve couramment dans le commerce avec différentes valeurs de transmission de la lumière pouvant être comprises par exemple entre 50 % et 80 %.According to a preferred embodiment, the attenuating device comprises an attenuating element 25 made of a semi-transparent material. The thickness of the attenuating element 25 varies from a large thickness EF in the region of the center O, to a reduced thickness ER on the edges 21 of this attenuating element. The attenuating element 25 is produced, for example, from mass-tinted glass (neutral tint for example), a material which is commonly found on the market with different light transmission values which can be for example between 50% and 80%.

Suivant une forme de réalisation préférée, l'élément atténuateur 25, a la forme générale d'une lentille du type plan-convexe.According to a preferred embodiment, the attenuating element 25, has the general shape of a lens of the plano-convex type.

La compensation apportée sur la courbe de brillance par l'élément atténuateur 25 est d'autant plus forte que l'épaisseur est grande au centre O et faible sur les bords 21. Cependant, pour des questions notamment de robustesse et de facilité de réalisation industrielle, les bords 21 peuvent avoir une épaisseur ER non négligeable par rapport à l'épaisseur forte EF du centre O, comme montré dans l'exemple de la figure 2.The compensation provided on the brightness curve by the attenuating element 25 is all the greater when the thickness is large at the center O and small at the edges 21. However, for questions in particular of robustness and ease of industrial production , the edges 21 can have a non-negligible thickness ER compared to the large thickness EF of the center O, as shown in the example of FIG. 2.

En effet, des résultats très intéressants ont été obtenus dans des conditions qui sont détaillées ci-après à titre d'exemple non limitatif, en utilisant un élément atténuateur 25 ayant la forme générale d'une lentille circulaire du type plan-convexe, et ayant un profil tel qu'illustré à la figure 2 :

  • diamètre D1 de l'élément atténuateur 25 = 30 mm ;
  • rayon de courbure P1 de la partie convexe = 320 mm ;
  • valeur de la plus forte épaisseur EF (au centre O) = 0,7 mm ;
  • valeur de la plus faible épaisseur ER (sur les bords 21) = 0,4 mm ; et en utilisant un verre teinté dans la masse réalisant la transmission de 70 % de la lumière pour une épaisseur de 0,7 mm.
Indeed, very interesting results have been obtained under conditions which are detailed below by way of nonlimiting example, using an attenuating element 25 having the general shape of a circular lens of the type plano-convex, and having a profile as illustrated in FIG. 2:
  • diameter D1 of the attenuating element 25 = 30 mm;
  • radius of curvature P1 of the convex part = 320 mm;
  • value of the greatest thickness EF (in the center O) = 0.7 mm;
  • value of the smallest thickness ER (on the edges 21) = 0.4 mm; and using a mass-tinted glass transmitting 70% of the light for a thickness of 0.7 mm.

La figure 3 montre une courbe de brillance 40 en traits pleins obtenue en sortie d'un tube intensificatuer d'image, suivant le diamètre de la fenêtre de sortie 4 et plus précisément suivant le diamètre D1 de l'élément atténuateur 25, avec les conditions ci-dessus mentionnées.FIG. 3 shows a brightness curve 40 in solid lines obtained at the output of an image intensifier tube, along the diameter of the outlet window 4 and more precisely along the diameter D1 of the attenuating element 25, with the conditions above mentioned.

On a porté en abscisse le diamètre D1 et en ordonnée la brillance mesurée bien entendu avec le dispositif atténuateur 25 interposé.The diameter D1 is plotted on the abscissa and the brightness, of course measured with the attenuating device 25 interposed, is plotted on the ordinate.

La courbe 40 montre un maximum de brillance vers le centre O et une diminution assez prononcée vers les bords 21 ; avec une valeur nulle avant les bords 21, ce qui montre que le diamètre D1 de l'élément atténuateur 25 est un peu plus grand que le diamètre du champ utile en sortie du tube 1. La courbe a la forme d'un arc de cercle aplati vers le centre O.The curve 40 shows a maximum of brightness towards the center O and a fairly pronounced decrease towards the edges 21; with a zero value before the edges 21, which shows that the diameter D1 of the attenuating element 25 is a little larger than the diameter of the useful field at the outlet of the tube 1. The curve has the shape of an arc of a circle flattened towards the center O.

Si l'on confère la valeur 100 % à la brillance maximum affichée dans la zone du centre O, on constate que la différence avec ce maximum juste avant les bords 21 est de l'ordre de 10 %, ce qui correspond à une amélioration de 10 % à 20 % par rapport à l'art antérieur. En effet, ceci est à comparer avec la différence de presque 30 % entre les bords et le centre, dans une courbe 50 (montrée en traits pointillés) qui illustre la brillance en sortie de la fenêtre de sortie en l'absence de la correction accomplie conformément à l'invention.If we give the value 100% to the maximum brightness displayed in the area of the center O, we see that the difference with this maximum just before the edges 21 is of the order of 10%, which corresponds to an improvement in 10% to 20% compared to the prior art. Indeed, this is to be compared with the difference of almost 30% between the edges and the center, in a curve 50 (shown in dotted lines) which illustrates the brightness at the output of the output window in the absence of the correction accomplished. according to the invention.

Bien entendu, il est simple de conférer à l'élément atténuateur le coefficient d'atténuation et le profil qui permettraient d'obtenir une courbe sensiblement droite et horizontale, voir même de réaliser une surcompensation pour tenir compte dans certains cas des exigences des dispositifs capteurs optiques destinés à observer l'image.Of course, it is simple to give the attenuating element the attenuation coefficient and the profile which would make it possible to obtain a substantially straight curve and horizontal, or even overcompensation to take into account in some cases the requirements of optical sensor devices intended to observe the image.

Il est à noter cependant qu'en pratique, une certaine différence de brillance entre le centre O et les bords 21, comme montré par la courbe 40, peut être souhaitable.It should be noted, however, that in practice, a certain difference in gloss between the center O and the edges 21, as shown by curve 40, may be desirable.

En référence à nouveau à la figure 2, dans l'exemple non limitatif représenté, le dispositif d'atténuation constitue un doublet optique à faces 28, 29 parallèles : il est constitué de deux pièces 25, 27 complémentaires dont la première est l'élément atténuateur 25, en forme de lentilles plan-convexe, et dont la seconde est complémentaire de la première, c'est-à-dire de forme plan-concave, et constitue un berceau 27 à la partie convexe 30 de l'élément atténuateur 25 ; bien entendu le berceau 27 est transparent à la lumière. Les deux faces 28, 29 sont parallèles entre elles et parallèles aux plans de la fenêtre de sortie 4 et de l'écran cathodoluminescent 10.Referring again to FIG. 2, in the nonlimiting example shown, the attenuation device constitutes an optical doublet with parallel faces 28, 29: it consists of two complementary parts 25, 27 of which the first is the element attenuator 25, in the form of plano-convex lenses, and the second of which is complementary to the first, that is to say of plano-concave shape, and constitutes a cradle 27 at the convex part 30 of the attenuating element 25 ; of course the cradle 27 is transparent to light. The two faces 28, 29 are mutually parallel and parallel to the planes of the outlet window 4 and of the cathodoluminescent screen 10.

L'avantage d'un tel doublet optique est qu'il peut être réalisé de façon industrielle indépendamment du tube 1, puis rapporté sur ce dernier en le fixant à la fenêtre de sortie 4 à l'aide simplement d'une couche de colle 31 par exemple.The advantage of such an optical doublet is that it can be produced industrially independently of the tube 1, then attached to the latter by fixing it to the outlet window 4 simply using a layer of glue 31 for example.

l'élément atténuateur 25 peut aussi être directement solidarisé à la fenêtre de sortie 4 par collage par exemple.the attenuating element 25 can also be directly secured to the outlet window 4 by gluing for example.

Il est à noter cependant que la façon la plus simple et la plus naturelle de fixer l'élément atténuateur 25 à la fenêtre de sortie n'est pas celle qui convient le mieux. En effet, la façon la plus simple de fixer l'élément atténuateur 25 à la fenêtre 4 consiste à le placer sur cette dernière avec la face plane 28 de cet élément atténuateur 25 en appui sur la fenêtre de sortie, c'est-à-dire orientée vers l'écran cathodoluminescent 10.It should be noted, however, that the simplest and most natural way of attaching the attenuating element 25 to the exit window is not the most suitable. Indeed, the simplest way to fix the attenuating element 25 to the window 4 is to place it on the latter with the flat face 28 of this attenuating element 25 resting on the outlet window, that is to say say oriented towards the cathodoluminescent screen 10.

Mais il est recommandé au contraire de fixer l'élément atténuateur 4 avec l'orientation inverse, c'est-à-dire avec sa partie convexe 30 orientée vers la fenêtre de sortie 4 et donc vers l'écran cathodoluminescent 10, pour des raisons expliquées ci-après, ceci aussi bien dans le cas où l'élément atténuateur 25 est monté dans un doublet optique que dans le cas où il est monté directement sur la fenêtre de sortie 4. Bien entendu dans ce dernier cas, l'espace occupé par le berceau 27 montré à la figure 2 est rempli par la colle ; on trouve dans le commerce de façon courante des colles transparentes à la lumière et présentant divers indices de réfraction qui peuvent donc être choisis pour être très proches des indices des matériaux transparents utilisés.On the contrary, it is recommended to fix the attenuating element 4 with the opposite orientation, that is to say with its convex part 30 oriented towards the exit window 4 and therefore towards the cathodoluminescent screen 10, for reasons explained below, this as well in the case where the attenuating element 25 is mounted in an optical doublet as in the case where it is mounted directly on the outlet window 4. Of course in the latter case, the space occupied by the cradle 27 shown in Figure 2 is filled with glue; commercially available glues that are transparent to light and have various indices of refraction which can therefore be chosen to be very close to the indices of the transparent materials used.

L'élément atténuateur 25 corrige la courbe de brillance en sortie du tube d'une même façon pour l'une ou l'autre des deux orientations possibles ci-dessus définies. Mais la présence de l'élément atténuateur 25 apporte un effet avantageux supplémentaire, qui se manifeste par une forte amélioration du contraste. Cette amélioration du contraste résulte du fait que, en montant sur la fenêtre de sortie 4 un élément qui réduit la transmission de lumière, on atténue moins les rayons parallèles à la normale au plan de la fenêtre de sortie, c'est-à-dire parallèles à l'axe longitudinal 9, et on atténue plus les rayons inclinés du fait qu'il traversent une plus grande longueur absorbante ; les rayons inclinés étant ceux qui dégradent le contraste.The attenuating element 25 corrects the gloss curve at the outlet of the tube in the same way for one or the other of the two possible orientations defined above. However, the presence of the attenuating element 25 brings an additional advantageous effect, which is manifested by a strong improvement in contrast. This improvement in contrast results from the fact that, by mounting an element on the exit window 4 which reduces light transmission, the rays parallel to the plane of the exit window are attenuated less, that is to say parallel to the longitudinal axis 9, and the inclined rays are more attenuated because they cross a greater absorbent length; the inclined rays being those which degrade the contrast.

Si l'élément atténuateur est monté avec sa partie convexe 30 orientée vers la fenêtre de sortie 4, comme représenté à la figure 2, et comme il est recommandé de le faire, l'atténuation due à la longueur absorbante traversée La (dans l'élément atténuateur) est la même pour des rayons r1, r2 inclinés d'une même valeur d'angle a1 et pénétrant dans l'élément atténuateur 25 en un même point B, mais avec des directions différentes.If the attenuating element is mounted with its convex part 30 oriented towards the outlet window 4, as shown in FIG. 2, and as it is recommended to do, the attenuation due to the absorbent length passed through L a (in the the attenuating element) is the same for radii r1, r2 inclined by the same angle value a1 and penetrating into the attenuating element 25 at the same point B, but with different directions.

Au contraire, si l'élément atténuateur 25 est monté avec l'orientation inverse (non représentée), c'est-à-dire avec sa face plane 26 en appui sur la fenêtre de sortie 4, pour des rayons inclinés tels que r1, r2 pénétrant dans l'atténuateur 25 en un même point de sa face plane 26, les longueurs absorbantes sont différentes ; ce qui conduit à réaliser une atténuation variable des rayons inclinés en fonction de leur direction.On the contrary, if the attenuating element 25 is mounted with the opposite orientation (not shown), that is to say with its planar face 26 bearing on the outlet window 4, for inclined radii such as r1, r2 penetrating into the attenuator 25 at the same point on its flat face 26, the absorbent lengths are different ; which leads to a variable attenuation of the inclined rays as a function of their direction.

La correction de la courbe de brillance conformément à l'invention peut s'appliquer sensiblement d'une même manière à tous les types de tubes intensificateurs d'image, avec écran scintillateur ou non, du fait que l'élément atténuateur 25 qui réalise cette correction, peut être monté à l'extérieur du tube intensificateur. De ce fait, un autre avantage important est que le tube intensificateur et l'élément atténuateur 25 peuvent être construits indépendamment l'un de l'autre. Un élément atténuateur 25 déjà monté peut ainsi éventuellement être remplacé par un autre réalisant une correction différente, et ceci sans dommage pour le tube intensificateur.The correction of the brightness curve in accordance with the invention can be applied in substantially the same way to all types of image intensifier tubes, with scintillator screen or not, because the attenuating element 25 which achieves this correction, can be mounted outside the intensifier tube. Therefore, another important advantage is that the intensifier tube and the attenuating element 25 can be constructed independently of each other. An attenuating element 25 already mounted can thus possibly be replaced by another carrying out a different correction, and this without damage to the intensifier tube.

Claims (10)

Tube intensificateur d'image comportant, urne fenêtre de sortie (4), un écran cathodoluminescent (10) fournissant une image visible à l'extérieur dudit tube intensificateur (1) à travers la fenêtre de sortie, caractérisé en ce qu'il comporte en outre un dispositif d'atténuation (20) de l'intensité de la lumière disposé en regard de la fenêtre de sortie (4) et présentant une opacité à la lumière plus grande en regard d'une zone centrale (O) que vers les bords (21) de la fenêtre de sortie (4).Image intensifier tube comprising, at an exit window (4), a cathodoluminescent screen (10) providing a visible image outside said intensifier tube (1) through the exit window, characterized in that it comprises in addition to a device for attenuating (20) the intensity of the light arranged opposite the exit window (4) and having a greater opacity to light facing a central area (O) than towards the edges (21) of the exit window (4). Tube intensificateur suivant la revendication 1, caractérisé en ce que le dispositif atténuateur (20) comporte un élément atténuateur (25) dont l'opacité à la lumière augmente avec son épaisseur (EF, ER).Intensifier tube according to claim 1, characterized in that the attenuating device (20) comprises an attenuating element (25) whose opacity to light increases with its thickness (EF, ER). Tube intensificateur suivant la revendication 2, caractérisé en ce que l'élément atténuater (25) a une épaisseur (EF) plus grande en son centre (O) que vers ses bords (21).Intensifier tube according to claim 2, characterized in that the attenuating element (25) has a thickness (EF) greater in its center (O) than towards its edges (21). Tube intensificateur suivant la revendication 3, caractérisé en ce que l'élément atténuateur (25) a la forme générale d'une lentille du type plan-convexe.Intensifier tube according to claim 3, characterized in that the attenuating element (25) has the general shape of a lens of the plano-convex type. Tube intensificateur suivant l'une quelconque des revendications 2 ou 3 ou 4, caractérisé en ce que l'élément atténuateur (25) comporte une face plane (28) et que son épaisseur (EF, ER) varie par rapport à cette face plane).Intensifier tube according to any one of claims 2 or 3 or 4, characterized in that the attenuating element (25) has a flat face (28) and that its thickness (EF, ER) varies relative to this flat face) . Tube intensificateur suivant la revendication 5, caractérisé en ce que la face plane (28) de l'élément atténuateur (25) est orientée à l'opposé de l'écran cathodoluminescent (10).Intensifier tube according to claim 5, characterized in that the planar face (28) of the attenuating element (25) is oriented opposite the cathodoluminescent screen (10). Tube intensificateur suivant l'une des revendications précédentes, caractérisé er ce que le dispositif atténuateur (20) est fixé à la fenêtre de sortie (4) à l'extérieur dudit tube intensificateur.Intensifier tube according to one of the preceding claims, characterized in that the attenuator device (20) is fixed to the outlet window (4) outside said intensifier tube. Tube intensificateur suivant l'une quelconque des revendications 2 à 6, caractérisé en ce que l'élément atténuateur (25) est fixé par collage à la fenêtre de sortie (4).Intensifier tube according to any one of Claims 2 to 6, characterized in that the element attenuator (25) is fixed by gluing to the outlet window (4). Tube intensificateur suivant l'une quelconque des revendications 2 à 7, caractérisé en ce que le dispositif atténuateur (20) comporte en outre une pièce (27) transparente à la lumière dont la forme est complémentaire de celle de l'élément atténuateur (25) afin de constituer avec ce dernier un doublet optique à faces (28, 29) parallèles.Intensifier tube according to any one of Claims 2 to 7, characterized in that the attenuating device (20) further comprises a part (27) transparent to light whose shape is complementary to that of the attenuating element (25) in order to constitute with the latter an optical doublet with parallel faces (28, 29). Tube intensificateur d'image suivant l'une des revendications précédentes caractérisé en ce qu'il est du type radiologique.Image intensifier tube according to one of the preceding claims, characterized in that it is of the radiological type.
EP92402488A 1991-09-20 1992-09-11 Image intensifier tube with brightness correction Expired - Lifetime EP0533538B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR9111608A FR2681727B1 (en) 1991-09-20 1991-09-20 IMAGE INTENSIFIER TUBE WITH BRIGHTNESS CORRECTION.
FR9111608 1991-09-20

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EP0533538B1 EP0533538B1 (en) 1994-07-13

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EP (1) EP0533538B1 (en)
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DE69200238D1 (en) 1994-08-18
JPH05205693A (en) 1993-08-13
US5248874A (en) 1993-09-28
EP0533538B1 (en) 1994-07-13
DE69200238T2 (en) 1994-11-17
FR2681727B1 (en) 1993-11-05

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