FR2561441A1 - SLOT SCANNING IMAGE CONVERTER TUBE - Google Patents

Abstract

SLOT SCAN IMAGE CONVERTER TUBE. THIS TUBE INCLUDES, BETWEEN A PHOTOCATHODE 2 EQUIPPED WITH A SLOT 34 AND A SCREEN 4, A FIRST ELECTRONIC MEANS TO MAKE THE IMAGE OF THE LARGEST DIMENSION OF THE SLIT ON THE SCREEN AND A SECOND ELECTRONIC MEANS INDEPENDENT OF THE PREVIOUS TO FOCUS AND DEFLECT THE BEAM, IN THE PLAN OF THE SCREEN, IN A DIRECTION PERPENDICULAR TO THE PREVIOUS DIRECTION. THIS SECOND ELECTRONIC MEANS INCLUDES AT LEAST ONE CONVERGENT FLAT LENS 36, 40 AND ONE DEFLECTION ELECTRODE 42, EACH OF THESE TWO MEANS BEING ADJUSTABLE INDEPENDENTLY. APPLICATION TO ULTRARAPID ELECTRONIC CINEMATOGRAPHY.

Description

Slit scan image converter tube The present invention has

for object a tube

  slit scan image converter.

  The recording of images with an extremely short exposure time makes it possible to raise the profile of the evolution over time of luminous phenomena

  very brief. Thus, electronic cinematography

  tra-fast applies to a broad area of research

  and very diversified disciplines: ballistics,

  tonic, study of living cells, experience

around lasers, etc. ..-

  The slit camera allows you to record

  graphically the variation over time of the

  luminous calf of a one-dimensional image of phenomena

  to study. The image of the phenomenon to be studied is made on a photocathode of a converter tube

  conventional type of image including, in addition to

  cathode, a control electrode, acceleration electrodes, a locating electrode, a pair of deflectors and an electroluminescent screen, optionally associated with an electron multiplier device. The number of electrons emitted at each point of the photosensitive layer of the photocathode is

  proportional to the level of local applied light

  is lying. The electrons are accelerated and focused at the location of the phosphor screen, for example, a visible image is made. When the tube is at

  rest, the electrons are blocked at the level of the

  tocathode by a negative potential applied to the control electrode or are deflected by a closing electrode and then intercepted by another electrode. In the slit camera, the image made on the photocathode is delimited by a narrow slit of which the image is made on the screen, the scrolling of the image of the slit being obtained by applying on the

  baffle deflectors a signal of

  layage. On the exit window of the tube, we observe along the scanning axis the evolution of the brightness, as a function of the time of the luminous phenomenon set to

  examination. Along the axis perpendicular to the axis of

  layage, that is to say according to the largest dimension of

  the gap, we note the spatial evolution of the same phenomenon.

  enon. The applicant disclosed in the patent

  No. 74 31136 filed on 13 September 1974 a tube con-

  slit scan image vertifier in which the focusing of the electron beam is independent in the deflection plane, or time plane, and in the spatial plane. The focus of the image of the slot on the screen is thus facilitated. The figures

  la and lb represent respectively

  the shape of the electron beam in the plane

  space and in the plane of deflection in a tube con-

  slit scan image intensifier according to this patent

  vet. FIG. 1a shows the shape of the electron beam in the spatial plane between the photocathode 2 and the screen 4. In this plane, the image of the slot is obtained thanks to a convergent lens made by electrodes 6 and 8, said image

  on screen 4 or on a galette

  10 in an output system with a multi-

  pliers of electrons. Preferably, the lens

  vergente used is a quadrupole lens that has the advantage of not introducing large

  distortions in the spatial plane, since it is de-

  provided with first-order aberrations. The trace of

  electron beam in the spatial plane carries the re-

12.

  In FIG. 1b, the means

  tube deflection and the shape of the electron beam

  in the deflection plane. Between the photocathode 2 and the screen 4 are arranged successively an accelerating electrode 14, the electrodes 16 and 18 of the

  quadrupole lens forming a diverging lens

  in the plane of deflection, a lens of de-

  bending and focusing 20 and possibly a

microcanauz slab 10.

  The deflection and focusing optics is constituted by three pairs of plates 22, 24 and 26. This structure allowed, in the tubes according to the prior art whose length was limited for technological reasons, to physically distance the lens from deflection of the screen, which helps to reduce beam distortion. However, this

  structure leads to the impossibility of optimizing

  irrespective of the focus and deflection of the

beam.

  An object of the invention is to decouple the focusing and the deflection of the beam in the deflection plane. This makes it possible to improve

  compared to the prior art, the sensitivity of

bending of the beam.

  On the other hand, it can be seen that in FIG. 1b, it is necessary to provide a diaphragm 28 at the input of the focusing and deflection optics.

  this so that the electron beam 30 which

  yard at the exit of plates 16 and 18 of the lens

  quadrupole does not come to strike the said optics of

  Calification and deflection. The proportion of current intercepted is important. It is imposed by the size of the diaphragm 28 and by the divergence created by the quadrupole lens set to make, in

  the spatial plane, the image of the slot on the screen.

  The invention proposes to add a lens

  the convergent in the deflection plane, upstream of the quadrupole lens to limit the beam width at the output of said quadrupole lens and thus to limit the magnitude of the intercepted current. The presence of two convergent lenses in the plane of deflection before and after the lens

  Quadrupole also gives an infinite number of combinations

  adjustment sounds of both lenses that allows you to have

  on the screen the image of the slot. These different

  These allow to fix either the collected current, or the thickness of the trace of the beam on the screen, that is to say the resolution, which depends on the width

  the beam at the entrance of the deflector.

  It is thus possible in some

  applications to optimize the current collected at the expense of

  the thickness of the trace. Conversely, it is possible to optimize the number of points along the axis

  space at the expense of the current collected.

  The invention is therefore an improvement to the known slit scan image converter tubes. It allows, while maintaining the temporal resolution of these tubes, to improve the resolution

Space.

  In a precise manner, the object of the invention is

  a slit scan image converter tube of

  designed to observe luminous phenomena of evolution

  fast by scanning on a screen the image of a split

  te, said slot collecting on a photocathode the light sent by the luminous phenomenon to be studied,

  and emitting an electron beam, said tube

  taking said photocathode, a control electrode

  of, an accelerating electrode and an optics of

  bending and focusing of the electron beam

  killed between the accelerating electrode and the screen,

  a focus and focusing optics comprising a first elctronic pattern for imaging the largest size of said slit on the screen and a second electronic means independent of the preceding for focusing and tracking the slice; in the screen, in a direction perpendicular to the direction of the screen. second electronic means 10 ... including .. inter) access to the screen, an I-wafer of Locclat..ion followed by cpune

  tieflxion electrode said let of foca: isa-

  1a-1: 5 -Stretching the slit on the screen and on the screen of the screen in the middle of the screen of the screen. - ': ais: the reflection of the beam of the project is very short.

  independent iL eg: ain;,. szbi e d op 'iriser

  According to one of the embodiments of the invention, one embodiment of the invention and one of the corresponding deflection is provided by one of these two embodiments. Mother and the screen,

  u. :: kentill, pcvn ç "onere; snv-e. a lentil.e qcuadrupo

  li & 2e, unie & ndil.le ndilaï: coe e and Fne :) elecode de f''c 'Sel-on a I;

  electrode. This is a line for propagation.

wave generation.

  This improves the insulin. liity of discussion of the

beam.

  aut rec -ci. act ..... ticks

  The invention will become better after the description.

  yes follow of reisa exemirles given to At-re em-

  plicatit and in no way! iritative, with reference to the

annexes on which:

  FIGS. 1a and 1b, already described, refer to

  show the appearance of the electron beam in the spatial plane and in the plane of deflection of a slot scan image conversion tube according to the known art, - Figure 2 is a perspective diagram of a mode embodiment of the converter tube according to the invention, - Figures 3a and 3b show the shape of the electron beam in the spatial plane and in

  the deflection plane of the converter tube of FIG.

re 2,

  FIGS. 4a and 4b illustrate the modification

  cation of the electron beam due to the electrode

  celery in the spatial plane and in the plane of deflection, - Figures 5a and 5b show two views of the quadrupole lens, respectively in section in Figure 5a and side in Figure 5b,

  - Figure 6 represents a method of

  convergent planar lenses in the plane of deflection,

  FIG. 7 represents a mode of realization

  deflection electrode, and

  - Figure 8 illustrates a mode of

  tion of a means for closing the tube.

  FIG. 2 shows a mode of

  production of a converter tube according to the invention

  tion. The light of the beam 32 is concentrated by an optical system (not shown) on the photocathode 2 in a rectangle 34 constituting the electron emitter slot. The converter tube also comprises an accelerating electrode 14, a convergent planar lens 36, a quadrupole lens 38, another convergent flat lens 40, an electrode

  deflection 42 and a screen 4. In this embodiment,

  did not represent the means of filling the

  tube. These will be described with reference to FIG.

  8. In a conventional manner, the image on the screen is taken up by a brightness intensifier which

  can be either inside the tube (half

  crochannels), or outside the tube. In some cases, the presence of a brightness intensifier in the tube introduces a significant background noise. It is then preferable to use an external brightness intensifier such as a matrix of

  charge transfer devices (in English CCD).

  The accelerating electrode 14 is connected to a positive voltage source 44; the three pairs of plates of the convergent lens 36 are connected to a voltage source 46; the two electrodes 6 and 8 of the quadrupole lens 38 are connected to the same positive voltage supply 48, while the other two facing electrodes 16 and 18 are connected to the same negative voltage supply; the three pairs of plates of the convergence lens 40 are connected to a voltage source 52

  and the deflection electrode 42 to a source of voltage

sion 54.

  In the spatial plane, the plane xOz, the image of the slot 34 is obtained thanks to the convergent lens made by the electrodes 6 and 8 of the quadrupole lens, said image being made on the screen 4. In the plane of deflection, the plane yOz, the electrode 42 deflects in the direction Oy (time axis) the image of the photocathode on

the screen 4.

  FIG. 3a shows the shape of the electron beam in the spatial plane between the photocathode 2 and the screen 4. The potential applied by the power supply 48 of FIG. 2 to the electrodes 6 and 8 is such that, in the xOz spatial plane, the image of the slot of the photocathode is substantially performed on the screen 4. The electron beam is represented

in 56.

  FIG. 3b shows the appearance of the electron beam in the yOz deflection plane. The electron beam 58 is accelerated by the accelerating electrode 10, then it is prefocused by the convergent flat lens 36 before being

  rendering divergent by the electrodes 16 and 18 of the len

  quadrupole. He then enters the len

  convergent flat map 40, after having been

  then diaphragmed by a diaphragm 60, to be

  4. The current stopped by the di-

  60 can be adjusted with the lens of

focusing 36.

  Downstream of the converging lens 40, the beam 58 passes through the deflection electrode 42 which provides the scanning function of the beam on the screen. Preferably, this deflection electrode constitutes a wave propagation line. The deflection voltage signal then propagates on the

  deflection plate (s) at the same speed as the

electron beam.

  FIG. 4a shows the photo-

  cathode 2 and the accelerating electrode 10 as well as the diagram of the beams coming from the photocathode such that

  beams 62 and 64. The point of first conver-

  is located in 66 and the image of the photocathode

  given by the accelerating electrode 10 is

  dotted position in 68. The position of the point of

  The first convergence 66 of the image of the photocathode 68 and the height of the point of first convergence vary according to the ratio e / d, where e is the half-width of the slot of the accelerating electrode 10 and the

  distance between the photocathode and the accelerated electrode

  Empress. In FIG. 4b, there is shown in the spatial plane the photocathode emitting beams of electrons such as 70, 72 and 74, the image 76 of the photocathode given by the accelerating electrode 10

  in this plane being located downstream.

  FIGS. 5a and 5b show the quadrupole lens 38. This lens is formed according to this embodiment of four hyperbola arcs.

  equilaterals, the arches facing 16 and 18 being

  potential + V and arcs 6 and 8 at -V potential.

  In FIG. 4b, the zCme lens is represented

  quadrupole length Ji side view in section se-

the yOz plan.

  The potential within such a long

  is of the form V = A (y - x2); the lens is

  convergent in the plane xOz, âV / x = -2Ax, and di-

  vergente in the plane yOz ,, - V / b y = + 2Ay.

  The convergence property of the quadrupole lens 38 is used to image the slot 34 of the photocathode 2 on the icran. In the spatial plane, the beam from photocathode 2 has

  dimensions which are not negligible in terms of

  port at the inter-electrode distance 2a. It is therefore in the spatial plane that the aberrations of the lens

  quadrupole will alter the quality of the picture.

  In the deflection plane, the height of the

  the slot being, for example, 1 mm, the height of the

  will be weak before 2a, of the order of a centimeter,

  and negligible aberrations. The advantage of the long

  quadrupole lens on the single convergent lens is to not introduce large distortions in

  the spatial plane since it is devoid of aberration

first order.

  The shape of the electrodes making it possible

  the quadrupolar field is, as we have seen, an equilateral hyperbola branch. Since this form is difficult to machine, it is replaced in a variant of

  Invention, by a circular arc oscu

  freezer. FIG. 6 shows an embodiment of a convergent lens in the plane of

  deflection such as lenses 36 and 40. This

  The plate consists of three pairs of plates 78, 80 and 82. The plates 78 and 82 are grounded, and the plate 80 has a negative potential. This potential is

  adjustable and can be adjusted independently for each

  one lens 36 and 40 located on either side of the quadrupole lens 38. This allows, while focusing the beam on the screen, to change its thickness at the entrance of the deflection optics, which conditions the thickness of the trace on the screen. The

  time resolution can thus be adjusted

  each application. The minimum thickness of the trace on the screen is very significantly smaller

  only in the tubes according to the prior art.

  FIG. 7 shows a mode of

  realization of the deflection electrode 42.

  One of the important problems that emerge when deflecting an electron beam is the defocus defocus. When an electron beam is deflected by means of plates,

  positive and negative potentials with respect to a potential

  In the mean, we can see the trace thickening on both sides of the median position. This thickening is

  due to the convergent lens effect created by the

  cation on the plates of the deflection voltages: the electrons close to the positive plates are accelerated

  and being faster are less deviated than electricity.

axial trons.

  On the contrary, the electrons closer to the negative plates are slowed down,

  so that the crossing of trajectories

  closer than desired to the outlet of the deflection plates. We show that the thickness of the trace is proportional to w /(12.L) where v is the beam width at the entrance of the deflection optics, 12 the length of the deflection plates and L the distance

  between the entrance of the deflection plates and the screen.

  The beam thickness can not be reduced

  if one wishes to retain most of the

  transported. In addition, the length of the plates 12 can not be increased without amputating the bandwidth

  of the deflection system. There is therefore interest in increasing

  length L within the limits compatible with the

length of the tube.

  The bandwidth of the deflection system is limited by the transit time of the electrons of the

  beam between the plates. To achieve speed

  high scanning capacity, a system of

  wave-propagated split reflector i.e. a system in which the deflection signal accompanies the beam electrons. This allows to obtain a simple baffle, high sensitivity, so with a low defiexion voltage, and very high bandwidth. The deflection optic 42 shown in FIG. 7 comprises a plate 84 set at a constant potential and a plate 86 forming a zigzag line.

  such that the voltage ramp propagates in the di-

  Oz rection, at the electron velocity of the beam.

  To allow a good propagation of the signal of

  layering, the set of incoming wires, connectors and li-

  zigzag pattern must be impedance matched and

  m on the characteristic impedance. This is achieved by a resistor 87 disposed between the plate 86 and the ground. The adaptation is finally adjusted by means of

  against a plate 88 brought to the potential of the mas-

  is. When the tube is at rest, the electrons can be blocked in known manner at the photocathode by a negative potential applied to a control electrode disposed between the photocathode and the accelerating electrode. An electrical signal of positive rectangular shape is then superimposed on this

  negative polarization potential to obtain the

  opening of the tube. This embodiment is not always

  most suitable day, especially when the distance between the photocathode and the accelerating electrode is of the order of a few millimeters only and that the potential of the accelerating electrode is high, by

example greater than 10 kV.

  FIG. 8 shows another

  embodiment of a shutter system of the

  e-mail. In this figure, representing in section the various elements of the tube, a first shutter lens 90 has been added between the convergent lens 36 and the quadrupole lens 38, and a second shutter lens 92 between the lens

  convergent 40 and the deflection electrode 42. The obturator

  ration is carried out by deflection of the electron beam

  by polarizing one of the electrodes of the lens.

the 90.

  The impact of electrons on the lens 92

  generates secondary electrons of which it would be

  that they can spread in the tube.

  To prevent this, it suffices to confine

  secondary trenches in the space delimited by the

  by applying to said lens a potential

  higher than the potential of the convergent lens 40. A voltage of a few hundred volts is sufficient to ensure the: bturationi

  In conclusion, we will indicate the characteristics

  Geometric and electrical parameters of an embodiment of the invention - photocathode distance at 500 mm, - slot size of the photocathode s 1 12 L mP - magnification in the spatial plane a 2 - dimensions of the slot acc1 2 mm, - quadrupole lens, 1965 mm, a = 14.4.mm - deflection electrode 2 12 = 59 m L = 223 r cu = 2.8 mm, sensitivity f, 08 mmi / V - useful range of the screen 24x32 mm, acceleration potential: 15000 V, - potential of the quadrupole cell: + 219 V, - blocking potential of the closing electrode

- 500 V,

  - potential of flat plane lances: 500 V, - deflection sensitivity: 0.08 mm / V, - deflection defocus: = 25 IMn spatial resolution in the direction of the slot z 25 ft / mm, - distortion less than 2%, - thickness of the trace in the deflection plane: im, temporal resolution along the slot:

1 picosecond.

Claims (8)

  A slit scanning image converter tube for observing rapidly changing light phenomena by scanning on a screen (4) the image of a slit (34), said slot collecting on   a photocathode (2) the light sent by the phenomenon   leads bright to study, and emitting an electron beam (12, 30, 58), said tube comprising said photocathode (2), a shutter means (90, 92), a   accelerating electrode (14) and an optics for   bending and focusing of the electron beam   killed between the accelerating electrode and the screen,   a deflection and focusing optics comprising a first electronic means for imaging the largest dimension of said slot on the screen and a second electronic means independent of the previous one for focusing and deflecting the beam, in the plane of the screen, in a direction perpendicular to the previous direction, said tube being characterized in that said second electronic means comprises, between the accelerating electrode and the screen, a lens of   focusing followed by a deflection   The focusing optics image the smallest dimension of the slot on the screen and limiting the width of the beam at the input of the deflection electrode.   2. Tube image converter according to the re-   claim 1, characterized in that the optics of   and the electrodedeflexion comprises, an accelerating electrode (14) and the screen (4), a converging flat lens (36), a quadrupole lens (38), another convergent flat lens (40) and an electrode deflection (42).   3. Tube image converter according to one   any of claims 1 and 2, characterized in that   the deflection electrode (42) forms a line wave propagation.   4. Converter tube according to any one   than claims 2 and 3, characterized in that   the slot of the photocathode (2) has a rectangular shape, with perpendicular axes Ox and Oy, the axis Ox being parallel to the long side of the center rectangle O, and in that the accelerating electrode (14) is provided with a slot parallel to the axis Ox, the beam   created by the impact of light on the   the tocathode being accelerated along the perpendicular axis Oz   Ox and Oy, with positive applied potential   on the accelerating electrode (14), in that the   quadrupole shell (38) converging in the plane xOz, said spatial plane, is divergent in the plane yOz, said plane of deflection, and in that each plane lens (36, 40) converges in the deflection plane yOz and in this that a power supply applies a variable voltage between the deflection electrodes (42) to deflect in the direction Oy the   electron beam as a function of time.   5. Converter tube according to any one   as in claims 1 to 4, characterized in that the photocathode (32) is flat.   6. Converter tube according to any one   claims 1 to 5, characterized in that the   quadrupole lens (38) is constituted by four cylindrical electrodes (6, 8, 16, 18) generatrices parallel to the axis Oz, and whose cross sections in a plane parallel to the plane zOy are substantially   equilateral hyperbola portions, two electro-   vis-à-vis being brought to a positive potential   and the other two electrodes vis-à-vis a potential negative.   7. Converter tube according to any one   claims 1 to 5, characterized in that the   quadrupole lens (38) is constituted by four cylindrical electrodes and generator parallel to the axis Oz, and whose straight sections in a plane parallel to the plane xOy are arcs of circle, two electrodes vis-à-vis being brought to a positive potential and the other two electrodes at a negative potential. 8. Tube image converter according to one   any of claims 1 to 7, characterized in that   that the convergent flat lenses (36, 40)   try three pairs of plates, the extreme plates being to the mass.