JPH0824037B2 - Image conversion tube by slit scanning - Google Patents

Description

The present invention relates to an image conversion tube by slit scanning.

The recording of images with extremely short exposure times allows plotting of the developed appearance over a period of very short light events. Therefore, high-speed electronic cinematography is applicable to a wide range of research and in various fields such as ballistics, biological cell research, and laser-related experiments.

The slit camera is capable of photographic recording the temporal change in light level of a one-dimensional image of the phenomenon to be investigated. The image of the phenomenon to be investigated is separated from the photocathode, on the photocathode of a conventional image conversion tube having a light emitting screen associated with a control electrode, an accelerating electrode, a focusing electrode, a pair of deflectors and an electron multiplier. Is formed.

The number of electrons emitted at each point of the photosensitive layer of the photocathode is proportional to the locally applied light level. The electrons are accelerated and focused, for example, at the location of the phosphor screen where a visible image is formed. When the converter tube is not in use, the electrons are blocked at the photocathode by the negative potential applied to the control electrode or deflected by the closing electrode and then blocked by the other electrode.

In a slit camera, the image generated on the photocathode is defined by a narrow slit, the image is formed on the screen, and the movement of the image of the slit is obtained by applying a scanning signal to the deflector of the deflection optical system. . The change in brightness along the scan axis on the exit window of the converter tube is observed as a function of the light phenomenon to be examined. Spatial variations of the same phenomenon are recorded along an axis perpendicular to the scan axis, ie along the length of the slit.

French Patent No. 743113, filed September 13, 1974
In No. 6, Applicant disclosed an image conversion tube with slit scanning in which the electron beam is independently focused in the deflection plane or the time plane and in the spatial plane. Therefore, the change of the slit image on the screen is promoted.
1a and 1b show, in a schematic way, the shape of the electron beam in the plane space (parallel to the maximum dimension of the slit) and the deflection plane (orthogonal to the slit) in the slit scanning image conversion tube according to the present invention.

FIG. 1a shows the shape of the electron beam in the space plane between the photocathode 2 and the screen 4. In the plane,
The slit image is obtained by a converging lens realized by electrodes 6 and 8 and is formed on the image screen 4 or on the microchannel wafer 10 in an exit device with an electron multiplier. Preferably, the converging lens used is a quadrupole lens, which has the advantage that it does not introduce a major distortion in the spatial plane, since it has no first order aberrations. The electron beam path in the spatial plane has the reference number 12.

FIG. 1b shows the converter tube deflection means and the electron beam path in the deflection plane. An accelerating electrode 14, a quadrupole lens electrodes 16 and 18 forming a diverging lens in a deflecting plane, a deflecting and converging lens 20, and optionally a microchannel wafer 10 are continuously arranged between the photocathode 2 and the screen 4. To be done.

The deflecting and focusing optics consist of three pairs of plates 22, 24 and 2
It consists of 6. In conventional conversion tubes, whose length is limited for technical reasons, this structure allowed the physical movement of the deflection electrodes away from the screen, which helps reduce the distortion of the electron beam. However, it is inferred that this structure does not allow independent optimization of beam focusing and deflection.

The object of the invention is to separate the focusing and the deflection of the beam in the plane of deflection. Compared to the prior art, this allows an improved beam deflection sensitivity.

In FIG. 1b, it is necessary to provide a diaphragm 28 at the entrance of the focusing and deflecting optical system 20 so that the electron beam 30 diverging at the exit of the quadrupole lens plates 16 and 18 does not collide with the focusing and deflecting optical system. is there. As a result, the widened portion of the electron beam 30 is blocked. The widening depends on the size of the diaphragm 28 and the divergence produced by the quadrupole lens tuned to produce the image of the slit on the screen in the spatial plane.

The present invention provides for the addition of a converging plane lens upstream of the quadrupole lens, in the plane of deflection, to control the width of the beam exiting the quadrupole lens and thus limit the size of the widened portion that is blocked. suggest.

2 in the deflection plane upstream and downstream of the quadrupole lens
The presence of one converging plane lens leads to many possible setting combinations of the two lenses so that a slit image can be shown on the screen. These various settings determine the thickness of the electron beam to be collected or the beam path on the screen,
That is, the resolution that depends on the beam width entering the deflector is fixed.

Therefore, in some applications, the deflection current for adjusting the passage thickness can be optimized. vice versa,
The number of positions along the spatial axis can be optimized to adjust the collected electron beam.

Thus, the present invention is an improvement of the known slit scanning image conversion tube and enables improved spatial resolution while preserving the temporal resolution of the conversion tube.

Therefore, the present invention is particularly suitable for observing a rapid emission phenomenon by scanning on a screen an image of a slit which collects light supplied by a phenomenon to be detected on a photocathode and emits an electron beam. An image conversion tube by slit scanning, comprising a photocathode, a control electrode for closing an electron beam, an accelerating electrode, and an electron beam deflecting and converging optical system arranged between the accelerating electrode and the screen. The deflecting and focusing optics directs an electron beam in the plane of the screen independent of the first electronic means and the first electronic means for producing an image of the maximum dimension of the slit on the screen. And comprises a second electronic means for converging and deflecting in a direction orthogonal to the maximum dimension of the slit, the first electronic means comprising:
A quadrupole lens and a first focusing arranged in the deflection plane upstream of the quadrupole lens so as to limit the width of the electron beam emerging from the quadrupole lens to limit the size of the blocked electron beam. A second converging plane lens having a plane lens, wherein the second electronic means has a second converging plane lens having a deflection electrode provided downstream between the quadrupole lens and the screen; A slit-scan image converter tube, characterized in that a planar lens forms an image of the smallest dimension of the slit on the screen and limits the width of the beam entering the deflection electrode.

Therefore, the focusing and the deflection of the electron beam in the deflection plane are independent. Therefore, each of these two effects can be optimized.

According to a preferred embodiment of the invention, the deflection electrodes constitute propagation lines which improve the deflection sensitivity to the beam.

The present invention will now be described in detail with reference to non-limiting examples and the accompanying drawings.

FIG. 2 shows an embodiment of the image conversion tube according to the present invention. The light beam 32 incident on the photocathode 2 is converted into an electron beam,
The electron beam has a slit 34 which constitutes an electron emission slit.
The light is focused on the photocathode 2 by an optical system (not shown). The image conversion tube includes an accelerating electrode 14, a first converging plane lens 36, a quadrupole lens 38, a second converging plane lens 40,
It consists of the deflection electrode 42 and the screen 4. In this embodiment, the tube closing means with control electrodes for closing the electron beam are not specifically shown, but they will be explained in connection with FIG.

In the usual way, the image on the screen is processed by a brightness intensifier which can be positioned inside the conversion tube (microchannel wafer) or outside the conversion tube. In some cases, the intensity multiplier in the converter tube introduces significant background noise. Therefore, it is preferable to use an external brightness multiplying device such as a cell matrix having a charge coupled device.

The acceleration electrode 14 is connected to the positive power source 44. A first converging plane lens 36 consisting of three pairs of plates is connected to a power supply 46. The two electrodes 6 and 8 of the quadrupole lens 38 are the positive power source 48.
While the other two counter electrodes 16 and 18 are connected to the negative power source 5
Connected to 0. The second converging plane lens 40 consisting of three pairs of plates is connected to a power supply 52 and the deflection electrode 42 is connected to a power supply 54.

In the spatial plane xOz, the image of the slit is obtained by the converging lens formed by the electrodes 6 and 8 of the quadrupole lens,
The image is formed on the screen 4. In the deflection plane yOz, the deflection electrode 42 deflects the photocathode image on the screen 4 in the time axis Oy direction.

FIG. 3a shows the shape of the electron beam in the space plane between the photocathode 2 and the screen 4. Second on electrodes 6 and 8
The potential applied by the power supply 48 in the figure is such that, in the spatial plane xOz, the image of the photocathode slit is substantially realized on the screen 4 and the electron beam is indicated by 56.

FIG. 3b shows the electron beam path in the deflection plane yOz. The electron beam 58 is accelerated by the accelerating electrode 10 and then focused by the first focusing planar lens 36 before being diverged by the electrodes 16, 18 of the quadrupole lens. The electron beam then enters the second converging plane lens 40, after being limited as much as possible by the diaphragm 60 to converge on the screen 4. The electron beam limited by the diaphragm 60 can be adjusted by the first converging plane lens 36.

Downstream of the second converging plane lens 40, the beam 58 passes through a deflection electrode 42 which ensures a beam scanning effect on the screen. Preferably, the deflection electrode constitutes a propagation line.
The deflection voltage signal is then 1 at the same speed as the electron beam.
It is propagated to one or more deflection plates.

FIG. 4a shows the photocathode 2 and the accelerating electrode 10 and the diaphragm of the beam from the photocathode such as beams 62,64. The first convergence point is located at 66 and the accelerating electrode 10
The image of the photocathode given by is shown in dotted line form at 68. The first converging point 66 and the height of the first converging point of the image 68 of the photocathode are such that e is the half width of the slit of the accelerating electrode 10 and d is the distance between the photocathode and the accelerating electrode. Varies as a function of / d.

FIG. 4b shows in the spatial plane the photocathode emitting electron beams such as 70, 72 and 74, in which the image 76 of the photocathode provided by the accelerating electrode 10 is located downstream.

5a and 5b show a quadrupole lens 38. In this example, the lens is formed by four equilateral hyperbolic arcs with opposing arcs 16 and 18 raised to potential + V and arcs 6 and 8 raised to potential -V. FIG. 5b is a sectional side view along the plane yOz showing the same quadrupole lens of length l ₁ .

The potential in such a lens consists of the formula V = A (y ² −x ² ), the lens converges at ∂V / ∂x = −2Ax in the plane xOz and ∂V / ∂y = at the plane yOz. Diversify at +2 Ay.

The convergence property of the quadrupole lens 38 is used to form an image of the slit 34 of the photocathode 2 on the screen. In the space plane, the electron beam from the photocathode 2 has dimensions which are never negligible in relation to the inner electrode space 2a. Therefore, it is in the spatial plane such that the quadrupole lens aberrations lead to a deterioration of the image quality.

In the plane of deflection, if the height of the slit is, for example, 1 mm, the height of the beam is about 1 cm, which is smaller than 2a,
And the aberration can be ignored. 4 for normal converging lenses
The advantage of the polar lens is that it does not introduce significant distortion in the spatial plane because it has no first order aberrations.

The shape of the electrode that enables the generation of the quadrupole region is, as described, the shape of an equilateral hyperbolic branch. Since this shape is difficult to machine, it is replaced according to the invention by a contact arc.

FIG. 6 shows an example of a convergent plane lens in the plane of deflection, such as the first converging plane lens 36 and the second converging plane lens 40. This converging plane lens consists of three pairs of plates7
Formed from 8,80,82. Plates 78 and 82 are at ground and plate 80 is at a negative potential. This potential is adjustable and can be adjusted independently on each side of quadrupole lens 38 for each of lenses 36, 40. Thus, it allows deflection of the thickness of the beam as it enters the deflection optics which influences the thickness of the passages on the screen while the beam is still focused on the screen. As a result, the set time resolution can be selected for each application. The minimum thickness of the passages on the screen is much smaller than in conventional conversion tubes.

FIG. 7 shows an embodiment of the deflection electrode 42. One of the major problems that occur during electron beam deflection is deflection convergence deviation.
When the electron beam is deflected by the plates raised to a positive and negative potential with respect to the average potential, the passages or lines thicken on either side of the average position. This is due to the action of the converging lens generated by applying the deflection voltage to the plate.
When the electrons in the vicinity of the positive plate are accelerated to a high speed, they are deflected in a state along the axis.

However, electrons in the vicinity of the negative plate are slowed down, ie deflected more, resulting in an orbital crossing closer than desired at the exit of the deflection plate. It is known that the thickness of the passage is proportional to ω / (l ₂ · L), where ω is the width of the beam entering the deflection optics, l ₂
Is the length of the deflection plate and L is the distance between the entrance to the deflection plate and the screen.

The beam thickness cannot be reduced if it is desired to maintain most of the transmitted current. Moreover, the plate thickness l ₂ cannot be increased without cutting the passages of the deflection system. It is therefore expedient to increase the length L within limits that do not affect the length of the conversion tube.

The pass band of the deflection system is limited by the transit time of the electrons in the beam between the plates. To achieve high scanning speeds, a propagating split deflection system, i.e. a system in which the deflection signals are associated with electron beam electrons, is used. This makes it possible to obtain simple and sensitive deflectors, ie deflectors with low deflection voltages and very large passbands.

The deflection optics 42 shown in FIG. 7 comprises a plate 84 of constant potential and a plate 86 forming a zigzag line so that the voltage gradient propagates in the direction Oz at the beam electron velocity. In order to allow good propagation of the scanning signal, the leads, connectors and zigzags must be impedance matched and reclosed with the characteristic impedance.
This is a resistor positioned between plate 86 and ground.
Caused by 87. Matching is adjusted by a counter plate 88 raised to ground potential.

When the converter tube is not operating, the electrons can be blocked in the photocathode in a known manner by the negative potential applied to the accelerating electrode positioned between the photocathode and the accelerating electrode. A positive square wave signal is then superimposed on this negative potential to cause the converter tube to open. In this embodiment, in particular, the distance between the photocathode and the accelerating electrode is only a few millimeters and the potential of the accelerating electrode is high.
When it is more than kV, it is not always suitable.

FIG. 8 shows another embodiment of the device for closing the electron beam. FIG. 8 shows various elements of the converter tube in cross section and, in addition thereto, a first converging plane lens 36 and a quadrupole lens 38.
And a second closing lens 92 between the second converging plane lens 40 and the deflection electrode 42 is added. By imparting a polarity to one of the electrodes of the first closing lens 90, the electron beam is deflected to cause interruption. The first closing lens 90 and the second closing lens 92 form a control electrode.

The impact of electrons on the second closing lens 92 produces secondary electrons that are harmful if they are allowed to propagate in the conversion tube. In order to prevent this, a second converging plane lens
By applying a position above the potential of 40 to the second closing lens 92, it is necessary to simply confine the secondary electrons in the space defined by the second closing lens 92. A voltage of a few hundred volts is sufficient to ensure a shutoff or closure.

In conclusion, details regarding the geometric and electrical properties of the embodiments of the present invention are given below.

(1) Distance between photocathode and screen: 500 mm (2) Dimension of photocathode slit: 1 x 12 mm (3) Magnification in space plane: 2 (4) Dimension of acceleration slit: 2 x 12 mm (5) Quadrupole lens: l ₁ = 96.5mm, a = 14.4mm (6) Deflection electrode: l ₂ = 69mm, L = 223mm, ω = 2.8mm, sensitivity 0.08mm / V (7) Useful screen limit: 24 × 32mm ( 8) Acceleration potential: 15000V (9) Quadrupole lens potential: ± 219V (10) Closing electrode cutoff potential: -500V (11) Converging flat lens potential: 500V (12) Deflection sensitivity: 0.08mm / V (13) Deflection Convergence deviation: 25 μm (14) Spatial resolution in slit direction: 25 pl / mm (15) Distortion: 2% or less (16) Thickness of passage or line in deflection plane: 40 μ
m (17) Time resolution along slit: 1 picosecond

[Brief description of drawings]

1a and 1b are schematic diagrams showing electron beam passages in a spatial plane and a deflection plane of a slit image conversion tube according to the prior art, and FIG. 2 is a perspective block diagram showing an embodiment of the image conversion tube according to the present invention. FIGS. 3a and 3b are schematic views showing the shape of the electron beam in the space plane and the deflection plane of the image conversion tube of FIG. 2, and FIGS. 4a and 4b are the electron beams by the acceleration electrodes in the space plane and the deflection plane. 5a and 5b are sectional views and a side view showing a quadrupole lens, FIG. 6 is a schematic view showing an embodiment of a converging plane lens in a deflection plane, and FIG. 7 is a deflection diagram. FIG. 8 is a schematic view showing an embodiment of the electrode, and FIG. 8 is a schematic view showing an embodiment of the conversion tube closing means. In the figure, reference numeral 2 is a photocathode, 4 is a screen, 6 and 8 are electrodes, 10 and 14 are acceleration electrodes, 34 is a slit, 36 is a first converging plane lens, 38 is a quadrupole lens, and 40 is a second Convergent plane lens, 42 deflection electrode, 44, 48 positive power supply, 50 negative power supply, 56,
58 is an electron beam, 60 is a diaphragm, 78, 80 and 82 are plates, 84 and 86 are plates, 87 is a resistance, and 90 and 92 are closing lenses.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Alain Girard France, 94100 Saint-Mall, Avnil Banjyu 8 (72) Inventor Syaruru Rotay France, 77330 Luzany, Riu de Copiyucin 19 (72) ) Inventor Jean-Pierre Roux, France, 94370 Scythe-Brie, Rouille de Vouarene 5 (56) References JP-A-59-35344 (JP, A) JP-A-51-54360 (JP, A) )

Claims (7)

[Claims] 1. A slit scanning method for observing a rapid emission phenomenon by converging light supplied by a test light phenomenon on a photocathode and scanning an image of a slit emitting an electron beam on a screen. An image conversion tube comprising a photocathode, a control electrode for closing an electron beam, an accelerating electrode, and an electron beam deflecting and converging optical system arranged between the accelerating electrode and the screen. And focusing optics for directing an electron beam in the plane of the screen independent of the first electronic means and the first electronic means for producing an image of the maximum dimension of the slit on the screen. It comprises a second electronic means for converging and deflecting in a direction orthogonal to the maximum dimension of the slit, wherein the first electronic means is a quadrupole lens and the quadrupole lens. A first converging plane lens arranged in the deflection plane upstream of the quadrupole lens so as to limit the width of the emitted electron beam and limit the size of the blocked electron beam; The electronic means has a second converging plane lens having a deflection electrode attached downstream between the quadrupole lens and the screen, and the second converging plane lens is provided on the screen. An image conversion tube by slit scanning for forming an image of a minimum size of a slit and limiting a width of a beam entering the deflection electrode. 2. The image conversion tube according to claim 1, wherein the deflection electrode forms a propagation line. 3. The slit of the photocathode is a rectangle having a vertical axis Ox and a time axis Oy, the vertical axis Ox is parallel to a long side of the rectangle with a center O, and the acceleration electrode is Equipped with a slit parallel to the vertical axis Ox, the electron beam generated by the collision of light on the photocathode is the vertical axis due to the positive potential applied to the accelerating electrode.
A spatial plane defined by the vertical axis Ox and the axis Oz, which is accelerated along the axis Oz perpendicular to the Ox and the time axis Oy.
The converging quadrupole lens in xOz has the time axis Oy and the axis O
for diverging in a deflection plane yOz defined by z, the first and second converging plane lenses converging in the deflection plane yOz, and the power supply deflecting the electron beam in the time axis Oy direction as a function of time. An image conversion tube by slit scanning according to claim 1, wherein a variable voltage is applied between the deflection electrodes. 4. The image conversion tube by slit scanning according to claim 1, wherein the photocathode is a flat surface. 5. The quadrupole lens has a vertical axis Ox and a time axis.
A cross section in a plane parallel to a plane xOy defined by the vertical axis Ox and the time axis Oy is substantially constituted by four cylindrical electrodes having generatrices parallel to an axis Oz perpendicular to Oy. 2. An image conversion tube by slit scanning according to claim 1, wherein it is an upper isosceles portion, and two counter electrodes are raised to a positive potential and the other two counter electrodes are raised to a negative potential. . 6. The quadrupole lens has a vertical axis Ox and a time axis.
The cross section of the plane parallel to the plane xOy defined by the vertical axis Ox and the time axis Oy is composed of four cylindrical electrodes having generatrices parallel to the axis Oz perpendicular to Oy. The image conversion tube by slit scanning according to claim 1, wherein the two opposite electrodes are raised to a positive potential and the other two opposite electrodes are raised to a negative potential. 7. The first and second converging plane lenses each have three pairs of plates, and one end of each of the two pairs of plates is grounded. An image conversion tube by slit scanning according to item.