JPH0425727A - Streak tube - Google Patents

Abstract

PURPOSE:To accurately measure the time correlation of variation in intensity with time by setting the thickness of an incidence window so that the optical path difference between two wavelengths to be measured exerts no adverse influence upon a streak image formed on an output surface. CONSTITUTION:The incidence window 1 is provided on the front end surface of a vacuum airtight container 3 and an output window 2 is provided on the rear end surface. A photoelectric surface 4 is formed on the internal surface of the incidence window 1 and connected to a flange 7 by a metallic film 10. Further, a fluorescent surface 9 is formed on the internal surface of the output window 2. A mesh electrode 5 is provided in front of the photoelectric surface 4 opposite and photoelectrons which are accelerated by it are converged by a converging coil 6 and deflected up and down by a deflecting electrode 8. Further, a surface plate made of covar glass to about 1 mm thickness is used for the incidence window 1. Further, the interval between the photoelectric surface 4 and mesh electrode 5 is set to 1.6 mm and when -10KV is impressed to the photoelectric surface 4 and the mesh accelerating electrode 5 is held at 0V, the photoelectrons are accelerated with a large electric field of about 6.3 KV/mm. Consequently, high time resolution is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a streak tube that can measure temporal brightness changes of light that change at high speed on the order of several tens of femtoseconds (f s).

[Conventional technology]

The streak device is a device that converts the temporal intensity distribution of the light to be measured into a spatial intensity distribution on the output surface, and because it can obtain a temporal resolution on the order of picoseconds (ps), it is suitable for analysis of ultra-high stray light development. It is used.

First, the configuration and operation of a conventional streak device will be briefly described.

Figure 8 shows the configuration of a conventional streak tube, and Figure 8 (a)
The right figure is a sectional view taken along a plane that includes the tube axis and is parallel to the deflection electrode, and the left figure is a schematic diagram showing the relationship between the photocathode and the optical image. The right figure in FIG. 8(b) is a cross-sectional view taken along a plane that includes the tube axis of the streak tube and is perpendicular to the deflection electrode, and the left figure is a schematic diagram showing the relationship between the photocathode and the optical image. . An incident light transmitting window (hereinafter referred to as the "incident window") 1 is provided on one end surface of the vacuum-tight container 3 of the streak tube, on which an optical image to be analyzed is formed, and a processed optical window is provided on the other end surface. An image-forming output window 2 is provided. Along the tube axis of this vacuum-tight container 3, between the entrance window 1 and the output window 2, a photocathode 4, a Me-Sauche-shaped accelerating electrode 5, and a focusing electrode 6 are arranged in order.
, an annular electrode 7, a deflection electrode 8, and a fluorescent surface 9 are provided. Then, a focusing electrode 6, a mesh electrode 5,
A higher voltage is applied to the photocathode 4 in this order to the a, <-cha electrodes 7, and the same potential as that of the a/z-cha electrodes 7 is applied to the fluorescent surface 9.

Suppose now that an optical image 4a is projected onto the photocathode 4 through the entrance window 1 on a line passing through its center. The photocathode 4 emits an electron image corresponding to the optical image, and the emitted electrons are accelerated by the mesh electrode 5, focused by the focusing electrode 6, passed through the aperture electrode 7, and made to enter the gap between the deflection electrodes 8. . A gradient deflection voltage is applied to the deflection electrode 8 during the period when this linear electron image passes through the gap between the deflection electrodes 8 . The direction of the electric field generated by this voltage is perpendicular to the tube axis and the linear electron image (perpendicular to the plane of the paper in the cross-sectional view of Fig. 8(a), parallel to the plane of the paper in Fig. 8(b)), and its strength is The height is proportional to the deflection voltage. The light beam is then deflected by the deflection electric field of the deflection electrode 8 and made incident on the fluorescent surface 9 .

The direction of deflection is shown by an arrow 120 in FIG. 8(b).

By scanning a linear electron beam on the fluorescent surface 9 perpendicular to the linear direction, a linear optical image projected onto the photocathode 4 is finally displayed on the fluorescent surface 9. Optical images arranged sequentially in time perpendicular to the direction of the line, a so-called streak image, are formed.

Therefore, the sweep direction on the output surface can be regarded as a time axis, and the change in brightness of the streak image in the sweep direction represents the time change in the intensity of the optical image incident on the photocathode 4. In addition, the streak device not only produces one light, but also
Changes in intensity of multiple lights can be measured. That is, although the optical image 4a in FIG. 8 is represented as a linear image, such measurement becomes possible by arranging a plurality of lights along this direction instead. For example, by using a spectrometer as the light to be measured and arranging two lights of wavelengths λ and λ2 on the photocathode as described in (2) above, it is possible to simultaneously observe changes in the intensity of the two lights. In this case, Fig. 9(a)
As shown in , the time axis is common, and the temporal correlation of intensity changes of multiple lights can also be seen.

[Problem to be solved by the invention]

In the streak tube described above, there is no problem when the temporal resolution is low, but when the streak tube is operated to obtain a high temporal resolution, the following problem occurs. In other words, when operating with high temporal resolution, the sweep speed is increased, so that the streak image obtained on the output surface of the streak tube is further stretched in the sweep direction (corresponding to the time axis). In other words, streak images are observed on a shorter time scale. At this time, for example, the wavelength λ1.
When two negligible optical pulses with a time width of λ2 are simultaneously incident, streak images must appear at the same position in the sweep direction corresponding to the time axis on the output surface, but they appear at different positions in the time axis direction. It appears in Figure 9(b)
shows a streak image in such a case.

When we investigated the cause, we found that it was the difference in transit time between the two lights within the entrance window 1 that was caused by the wavelength. That is, if the refractive index of the material forming the entrance window is n, the speed of light within the face plate is expressed as v-c/n (c is the speed of light in vacuum).

Here, the refractive index n varies depending on the wavelength, for example, the entrance window 1
When the material of is Kovar glass and its thickness is d m + w, the wavelengths of the two lights are each 350 nIIs.
850 na+, the speed of the two lights within the entrance window 1 is 1.9 x 108 m/s, respectively.

2. Ox108 m/s, so the travel time difference Δt between the two lights within the entrance window 1 is expressed by the following equation.

, ()x 1og ) (s) - (1) In the conventional streak tube, the thickness d in equation (1) is 3 to 5 degrees. For example, if d is 4.5 mm, the travel time difference between the two lights will be Δ1−1.18 picoseconds (pS) from equation (1). This shows that even if two pulsed lights are incident on the streak tube at the same time, a streak image does not appear at the same position on the output surface in the sweep direction.

By the way, in a conventional streak tube, the thickness of the entrance window 1 is 4~
The reason why it is as thick as 5II11 is to provide mechanical strength that can withstand atmospheric pressure, and also because the distance between the photocathode 4 and the mesh accelerating electrode 5 is as small as about 1 mm, as shown in FIG.
It is necessary to strengthen the electric field in this part, and in order to improve the electrical breakdown voltage by separating both electrodes as much as possible except for the necessary parts, the shape of the entrance window 1 is made convex toward the vacuum side. be. The connection between the photocathode 4 and the flange 7 is as follows:
This is achieved by a metal film 10 formed on the entrance window 1.

Furthermore, in addition to the above problems, there is another problem when the entrance window 1 is thick.
There are two problems. In other words, recently there has been a demand for streak tubes with a time resolution of 100 fs or several tens of fs, but when we investigated the time spread that occurs in each part of the streak tube in such cases, we found that it was ignored in conventional streak tubes. It was also found that the spread of the leading pulse within the entrance window l cannot be ignored.

- When fishing on a boat, pulsed light with a time width ΔT is accompanied by a wavelength wave length Δλ expressed by the following equation.

Here, λ is the center wavelength of the light to be measured, and C is the speed of light. Due to such wavelength dispersion, in a conventional streak tube, the thickness of the entrance window 1 is about 3 to 5 mm, so the short pulse light spreads over time while traveling through the thickness of the glass, and the The resolution is degraded. In Fig. 11, an entrance window 1 made of Kovar glass with a thickness of 4.5 m+* is shown.
The wavelengths are λ-350■, 600 ni, and 850 ni, respectively.
When measured light of nm is incident, the horizontal axis represents the pulse width at the input surface, and the vertical axis represents the pulse spread after passing through. With this, for example, the wavelength is 600n.
It can be seen that the 20 fs pulsed light of 1 spreads to about 96 fs, which significantly deteriorates the time resolution of the streak tube.

An object of the present invention is to provide a streak tube that solves the above-mentioned problems.

[Means to solve the problem]

The streak tube according to the present invention generates an output image on a predetermined output surface by a photoelectron beam emitted from a photocathode formed in an entrance window, and the thickness of the entrance window is determined by the measurement occurring at the entrance window. The optical path difference between the two wavelengths of light is such that it does not adversely affect the streak image generated on the output surface.

[Effect]

In the present invention, since the entrance window is made thin, the following effects are achieved. First, the first problem is 2.
The traveling time of the two different wavelengths of light within the incident window is different, so even if the two lights enter the streak tube at the same time, they will exit at different positions on the time axis on the output surface. (1 ) As can be seen from the equation, it can be improved by reducing the window thickness. In other words, if we use the example given above and explain that the material of the entrance window is Kovar glass and the wavelengths of the two lights are 350nm and 850t++n, then from equation (1), if the thickness of the entrance window is 4.5+am as before, then For example, the travel time difference between the two lights within the incident window is 1.1
8 ps, but if the thickness of the entrance window is set to 0.5 ps, it can be seen that the travel time difference can be significantly improved to 0.131 ps.

Also, when a very short pulse of light is input into a streak tube, the pulse width expands due to wavelength dispersion within the input window, so by reducing the thickness of the window,
Its spread can be suppressed. That is, the material of the entrance window is Kovar glass, and the wavelength is 350r+m.
Figures 12 and 12 show the calculation results for the pulse spread generated within the entrance window when measured light of , 600 nm, or 850 nm is incident, when the thickness of the entrance window is thinner than the conventional 4.5 m11. It is shown in Figure 13. Figure 12 is 1
Figure 13 shows the thickness of the dragon using an entrance window with a thickness of 0.5 mm.The horizontal axis is the pulse width at the input surface, and the vertical axis is the pulse after passing through the thickness of the entrance window. Indicates width. 11th
As can be seen by comparing with the figure, for example, the wavelength is 600 t.
The incident light with a pulse width of 20 fs at ++n has a thickness of 4.5 mm.
It spreads to about 96 fs at the entrance window of
+om entrance window, each about 24. f s s
It can be seen that the spread is very small at about 21 fs.

The present invention also proposes a structure for increasing the mechanical strength and selection of materials as a specific method for using such a thin face plate as an entrance window of a streak tube.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows the overall configuration of a streak tube according to a first embodiment. As shown in the figure, an entrance window 1 is provided on the front end surface of the vacuum-tight container 3, and an output window 2 is provided on the rear end surface. A photocathode 4 is formed on the inner surface of the entrance window, and the photocathode 4 and the flange 7 are connected by a metal film 10. Furthermore, a fluorescent surface 9 is formed on the inner surface of the output window 2. A mesh electrode 5 is provided in front of the photocathode 4 to face it, and photoelectrons accelerated thereby are focused by a focusing coil 6 and deflected upward and downward in the figure by a deflection electrode 8. In the streak tube in this embodiment, a face plate made of Kovar glass is used for the entrance window 1, and its thickness is about 1 inch.

In the streak tube, the photocathode 4 and the mesh electrode 5
Assuming that the interval is 1.6 mm, -IOKV is applied to the photocathode 4, and the mesh accelerating electrode 5 is set to OV, the photoelectrons are approximately 6 mm.
．． It is accelerated by a strong electric field of 3KV/mu. Therefore, if a gradient deflection voltage is applied to the deflection electrode 8 so that the streak speed is 2×10”rn/s, approximately 400f
A time resolution of s is obtained. In this case, the thickness of the entrance window 1 is changed from the conventional 4.5+n+* to 1 mm, so
Even if multiple individuals receive light of different wavelengths, the travel time difference of each wavelength of light within the entrance window 1 is 1/4.5 compared to the conventional 4.5 mm thickness, and the intensity of the mutual light is reduced. The temporal correlation can be determined more accurately on the fluorescent surface 9 of the output window 2.

For example, when two lights with wavelengths of 350nIIs and 850ni are incident on a streak tube, the conventional 4.5
In the case where the entrance window 1 with a thickness of m is used, the travel time difference within the entrance window 1 was 1184 fs;
/4.5, which is 262 fs.

Therefore, under the operating conditions of a sweep speed of 2 x 108 m/s, which provides a time resolution of about 400 fs, even if the pulsed light of the aforementioned two wavelengths with negligible time widths simultaneously enters the streak tube, the output window 2 A streak image appears at approximately the same position in the sweep direction, and the above-mentioned problem is improved. This example shows the case where the window thickness is 1 mm, but even if the window is about 2 mm thick, compared to the conventional 4.5 mm thickness, the difference in travel time of each wavelength of light is 2/4 compared to the conventional one. .5, so it can be said that there is a significant improvement.

Further, if the thickness of the entrance window 1 is further reduced, the problem can be further improved, but in that case, one difficulty is the mechanical strength against atmospheric pressure. One way to improve this is to use sapphire as the material for the entrance window 1. By using sapphire, even if the thickness of the entrance window 1 is 0.2 mm, it can withstand atmospheric pressure. By changing the entrance window of the embodiment shown in FIG. 1 to a 0.2-inch thick sapphire window, the transit time difference due to the wavelength difference within the entrance window 1 can be further reduced. For example, the same wavelength 3 as explained earlier
It can be seen that for the two lights of 50 ni and 850 nm, the travel time difference within this sapphire window is 74 fs, which is further improved. Another material that has great strength even when made thin is quartz.

Another embodiment of a streak tube using a thin entrance window 1 projecting toward the vacuum side in consideration of electrical withstand voltage is shown in FIGS. 2 and 3, the main parts of which are shown in FIG. In the case shown in FIG. 2, an entrance window 1 is constructed by welding a thin face plate 12 to the top of a glass cylinder 11 extending toward the vacuum side. In this case, the connection between the photocathode 4 formed on the face plate 12 and the flange 7 is realized by a metal HID formed on the glass cylinder 11. In the case shown in FIG. 3, an entrance window 1 is constructed by welding a thin face plate 14 to the top of a conical glass pipe 13 that is convex toward the vacuum side.

FIGS. 4 and 5 show another embodiment of a streak tube using a thin entrance window 1 that is convex toward the vacuum side and maintains mechanical strength.

In the streak tube shown in FIG. 4, a hole is made only in a part of the thick glass material 15 that is convex on the vacuum side.
m, and a thin film 16 with a thickness of 0.5 mm is formed. In this case, since the area of the thin portion 16 is small, the mechanical strength is increased. Figure 5 shows relatively thick glass or metal (3~
5) A hole with a diameter of, for example, 1 mm is made in the center of the plate 17, and a thin window material 18 is airtightly adhered to the vacuum side surface of the plate 17 using an entrance window 1. Showing the tube.

Also in this case, since the area of the thin portion 18 is reduced, mechanical strength can be increased. In this case, the through hole is not limited to a circular shape, but can also be formed into a slit shape to form a linear image of the light to be measured in this direction.

The streak tube of the embodiment shown in FIG. 6 has increased mechanical strength by forming an entrance window 1 by bonding a thin face plate 19 onto a mesoche-like metal structure 51. In this case, the mesh-like metal structure 51 is connected to the flange 7, and since the metal structure 51 and the photocathode 4 are connected by the metal film 10, the photocathode 4 is connected to the flange 7 after all.

Next, FIG. 7 shows an embodiment of a streak tube that achieves extremely high time resolution by using a thin entrance window 1. In this case, the streak tube electron optical system is described in detail in previously filed Japanese Patent Application No. 1-290345.

As shown in the figure, the transmission type photocathode 4 is formed inside the entrance window 1 in the vacuum-tight container 3, whereas the first reflective electrode 43 has its surface tilted downward by about 20 degrees in the figure. It is arranged opposite to the photocathode 4. This photocathode 4
An accelerating electrode (mesh electrode) 5 is arranged between the first reflecting electrode 43 and the second reflecting electrode 43 . The second reflective electrode 44 is arranged parallel to the charging surface 4 and diagonally opposed to the first reflective electrode 43 with the accelerating electrode 5 in between. Further, a shielding electrode 72 is arranged in the vacuum-tight container 3 so as to recess the first reflective electrode 43 . A deflection electrode 8 is arranged adjacent to the acceleration electrode 5 on the opposite side of the second reflection electrode 44 and adjacent to the first reflection electrode 43 with the shielding electrode 72 in between. Further, a focusing coil 6 is arranged outside the vacuum-tight container 3 at a position adjacent to the deflecting electrode 8 on the opposite side of the accelerating electrode 5 . A wall anode 90 is formed on the inner peripheral surface of the vacuum-tight container 3 at a position between the fluorescent surface 9 formed inside the output window 2 and the deflection electrode 8.

The factor that limits the time resolution after photoelectrons are emitted into the vacuum by the streak tube is the variation in the initial velocity of the photoelectrons emitted from the charging surface 4, and the time wave length for these photoelectrons to reach the deflection electrode 8. dominant. Therefore, in the streak tube shown in this embodiment, the first reflective electrode 43 and the second reflective electrode 44 are used so that photoelectrons having a high emission rate can travel a long distance as shown in the figure. Therefore, it is possible to correct the travel time of photoelectrons, and it is possible to achieve a small spread during travel, for example, 20 fs.

However, if the entrance window 1 of this streak tube has the same thickness as the conventional one, as mentioned above, for example, 4.5
For an entrance window made of mm-thick Kovar glass, the wavelength is 60
The 20 fs pulsed light at 0 r+m spreads to 96 fs within the window. For this reason, the time resolution of 20 fs, which is the time resolution of the electron optical system of the streak tube, cannot be utilized.

Therefore, in this embodiment, the entrance window 1 is made of a part of the Kovar glass face plate thinned to 0.5 mm, so that the pulsed light with a wavelength of 600 rv and a width of 20 fs will be transmitted within the entrance window 1 by 21 fsL. Since the time resolution of the electron optical system is 20 fs, the total V 212
+202''-29 (f S ), making it possible to realize a streak tube with extremely high time resolution.

〔Effect of the invention〕

As explained above in detail, according to the streak tube according to the present invention, even if many lights of different wavelengths are incident in parallel, the difference in transit time within the incidence window of the streak tube can be made very small. , it is possible to accurately measure the temporal correlation of the temporal changes in their intensities. Also, streak tubes with very high temporal resolution are possible.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram of a streak tube according to an embodiment of the present invention, and FIGS. 2, 3, 4, 5, and 6 are main parts of streak tubes according to different embodiments. 7 is an overall configuration diagram of a streak tube according to yet another embodiment of the present invention, FIG. 8 is an overall configuration diagram of a conventional streak tube, FIG. 9 is an explanatory diagram of a streak image, and FIG. 1], FIG. 12, and FIG. 13 are characteristic diagrams showing pulse width and pulse spread. DESCRIPTION OF SYMBOLS 1...Incidence window 12...Output window, 3...Vacuum-tight container, 4...Photocathode, 5...Mesh electrode (acceleration electrode)
, 6. Focusing coil, 7. Flange, 8. Deflection electrode, 9. Fluorescent surface, 10. Metal film.

Claims (1)

[Claims] 1. In a streak tube that generates an output image on a predetermined output surface by a photoelectron beam emitted from a photocathode formed on an incident light transmitting window, the thickness of the incident light transmitting window is determined by the thickness of the incident light transmitting window. A streak tube, characterized in that the optical path difference between the two wavelengths of light to be measured that occurs in the incident light transmission window is such that it does not adversely affect the streak image generated on the output surface. 2. The streak tube according to claim 1, wherein the incident light transmission window is made of sapphire or quartz. 3. The streak tube according to claim 1, wherein the incident light transmitting window is formed by forming a thin part of a single face plate. 4. The streak tube according to claim 1, wherein the incident light transmitting window is formed by having a thin face plate on the top of a cylindrical body that is convex toward the photocathode. 5. The streak tube according to claim 1, wherein the incident light transmitting window is formed by providing a plate material having a through hole with a thin face plate that closes the through hole. 6. The streak tube according to claim 1, wherein the incident light transmitting window is formed by fixing a thin face plate to a mesh-like metal structure.