JPH0140938B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an observation device for high-speed repetitive pulsed light that uses a streak device to observe a pulsed light train that is repeatedly generated at high speed.

A streak device is used to observe high-speed pulsed light. First, the general configuration of this streak device will be briefly explained. The streak device is mainly composed of a streak tube having a photocathode, a deflection electrode, and a fluorescent surface. A deflection voltage for deflecting photoelectrons directed from the photocathode toward the fluorescent surface is supplied to the deflection electrode from a deflection power source. The pulsed light from the light source is split by an optical system, and one part is guided to the photocathode of the streak tube, and the other part is guided to the light receiving element of the trigger device for starting the deflection power source.

Photoelectrons traveling from the photocathode to the fluorescent surface are deflected by a deflection electrode. The difference in the generation time of photoelectrons is converted into the distance on the fluorescent surface, and the density of photoelectrons is converted into the magnitude of the brightness of the fluorescent surface and displayed.

Using such a streak device, high speed,
There is a desire to display and observe two or more consecutive light emissions in a repeatedly generated pulsed light train on one screen. This is because if two or more pulsed lights can be displayed on one screen, changes between those pulsed lights can be compared.

The duration of the output pulse light of the dye laser and each light pulse of the light emission phenomenon caused by excitation by the output pulse light of the dye laser is extremely short, 1 to 1000 picoseconds. On the other hand, the repetition period of the output pulse light of the dye laser and the return period of the light emission phenomenon excited by this period are 5 to 12 nanoseconds. Therefore, the proportion of the light emitting part during the repeated cycle is
It will be about 1/5 to 1/12000. If the time axis on the fluorescent surface is set so that two or more light emissions in such a pulsed light train appear consecutively on the fluorescent surface, the length on the fluorescent surface allotted to one light pulse will be extremely short. Become. The pulsed light train duty ratio is 1/
100 and the effective length of the streak tube is 10 mm, and when two light pulses appear on the fluorescent surface, the length on the fluorescent surface assigned to one light pulse is 0.1.
It becomes no more than mm. In other words, only two light emissions are displayed at the expense of the temporal resolution of the streak image, and a detailed comparison between the light pulses is not possible. An object of the present invention is to provide a high-speed repeating pulsed light observation device that can display streak images of two or more consecutive pulsed lights as described above without any interval or adjacently with a small interval. In order to achieve the above object, a high-speed repetition pulse light observation device according to the present invention includes a streak tube including a photocathode, a gate electrode, a deflection electrode, and a fluorescent surface, and a high-speed repetition pulse light input to the photocathode of the streak tube. a first sine wave oscillator that generates a first sine wave that is synchronized with the pulsed light; a second sine wave oscillator that generates a second sine wave that has a slightly different frequency from the pulsed light; and the first sine wave. a phase detector that detects a point in time when a certain phase relationship occurs between the first sine wave and the second sine wave and generates a detection output; a gate pulse generator that outputs a gate pulse that lasts for a period of , and connecting means that connects the gate pulse to the gate electrode of the streak tube and the output of the second sine wave oscillator to the deflection electrode.

According to the above configuration, a plurality of consecutive pulsed lights are transmitted by eliminating the interval between the parts where no pulsed light exists, and
Since it can be displayed continuously, the object of the present invention can be fully achieved.

Hereinafter, the operating principle of the apparatus of the present invention will be explained first, and then the embodiments will be explained in detail.

The sine wave output from the first sine wave oscillator that generates the first sine wave that is synchronized with the high-speed repetitive pulse light input to the photocathode of the streak tube is ₁ =
Assinωat, a second sine wave output from a second sine wave oscillator that generates a sine wave with a frequency slightly different from that of the pulsed light is ₂ =Bsinωbt.

The phase detector detects a point in time when a certain positional relationship occurs between the first sine wave ₁ =Asinωat and the second sine wave ₂ =Bsinωbt, and sends out a detection output.

This phase detector detects the first sine wave and the second sine wave.
a mixer for mixing a sine wave with a sine wave; a low-pass filter for extracting the low frequency component from the output of the mixer;
It can be comprised of a level detector that detects the output level of the low-pass filter.

The output of the mixer which mixes the first sine wave and _{the second} sine wave is given by the following equation.

′=A×Bsinωat・sinωbt=(A×B/2) [cos(ωa−ωb)t −cos(ωa+ωb)t] Since ωa and ωb are only slightly different, ωa−ωb is small, and it is good to set ωa+ωb≒2ωa . The composite wave′ is ωa
Since the signal is passed through a low-pass filter with a cutoff frequency between +ωb and ωa-ωb, only '=(A×B/2)cos(ωa-ωb)t passes through. This is a so-called beat wave. By detecting with a level detector that the output of this low-pass filter ′=(A×B/2)cos(ωa−ωb)t has reached a predetermined level, a constant phase is established between ωa and ωb. It is possible to detect when a relationship occurs. The constant phase (ωa-ωb)t to be detected will be described in detail later using an example. In short, ₁ = Asinωat represents the phase of the optical pulse and the photoelectron flow in the streak tube caused by this, so in order to make this photoelectron flow correspond sequentially to the deflection electric field, the second This means that the phase of the sine wave Bsinωbt at the start of the sweep corresponds in a certain manner to the phase of ₁ = Asinωat.

The gate pulse generator receives the detection output of the phase detector and outputs a gate pulse that lasts for a period longer than a plurality of cycles of the output of the first sine wave oscillator.
This gate pulse is applied to the gate electrode of the streak tube via the connection means.

The pulse width of this gate pulse corresponds to the entire period including a plurality of pulsed lights intended to appear as a streak image on the fluorescent surface of the streak tube.

The gate electrode of the streak tube allows the photoelectron flow to pass toward the phosphor surface only while this gate pulse is applied.

The output sine wave Bsinωbt of the second sine wave oscillator is connected to the deflection electrode of the streak tube by a connecting means. Then, during the period when the gate pulse is applied to the gate electrode of the streak tube, the vicinity where the sine wave Bsinωbt becomes zero is used to generate a deflection electric field.

Each time this deflection electric field is generated, a photoelectron flow caused by the optical pulse portion passes through the deflection electrode portion and appears sequentially on the fluorescent surface.

Pulse light period 2π/ωa and deflection electric field period 2π/
Since it is slightly different from ωb, the streak images of each pulsed light appear on the fluorescent surface with slight shifts in sequence, so they do not overlap. Note that the difference in period is 2π(1/ωa−1/
ωb) is equal to or slightly larger than the width of the pulsed light. Furthermore, a streak image appears on the fluorescent surface only during the period when the output pulse of the phase detector is applied to the gate electrode.

It is desirable that the streak image of the optical pulse that first appears after the gate electrode of the streak tube is in a state of allowing passage of the photoelectron flow is located at one end of the fluorescent surface of the streak tube on the sweep start side. This condition is
The second waveform determines the phase of the pulsed light (actually, it is necessary to consider the delay time until it reaches the deflection electrode, but it can be considered to have a certain correspondence with the phase of the first sine wave) and the deflection position. It is determined by the relationship with the phase of the second sine wave which is the output of the sine wave oscillator.

Since these phase differences appear as the output of the low-pass filter, it is sufficient to determine the detection level of a level detector that detects the output level of the low-pass filter of the phase detector. The detection level at which this phase should be detected can be calculated from any delay time, deflection sensitivity of the streak tube, and amplitude of the second sine wave applied to the deflection electrode. However, in reality (or ultimately) it is easier to adjust the detection level of the level detector included in the phase detector while observing the streak image.

Next, a more detailed explanation will be given with reference to examples.

FIG. 1 is a block diagram showing an embodiment of a pulsed light observation device according to the present invention.

The dye laser oscillator 1 is a light source that repeatedly emits light at high speed. This dye laser oscillator 1 is capable of emitting laser light with a pulse width of 5 picoseconds at an arbitrary repetition period within a frequency range of 80 to 200 MHz.

An anti-transparent mirror 2 forming a beam splitter splits the output light from the dye laser oscillator 1 into two streams. One side of the branched pulsed laser beam is a reflecting mirror,
The light is made incident on the photocathode 31 of the streak tube 3 through an optical system consisting of a slit lens, an optical path length variable device 20, and the like. A first pulsed light synchronized with the high-speed repetitive pulse light input to the photocathode 31 of the streak tube 3.
A first sine wave oscillator that generates a sine wave is composed of the beam splitter, a PIN photodiode 4, and a tuned amplifier 5.

The other of the branched pulsed laser beams is made incident on the PIN photodiode 4 of the first sine wave oscillator. The PIN photodiode 4 is a photoelectric element with an extremely fast response speed, and outputs a pulsed current in response to the incidence of pulsed laser light. The output of the PIN photodiode 4 is connected to a tuned amplifier 5. The tuned amplifier 5 can operate with any frequency in the range of 80 to 200 MHz as the center frequency. The center frequency is set equal to the oscillation frequency of the dye laser, and the tuned amplifier 5 has a first frequency synchronized with the repetition frequency of the output pulse of the PIN photodiode 4.
Sends out a sine wave. The frequency counter 6 counts and displays the frequency of the first sine wave sent out by the tuned amplifier 5.

The sine wave oscillator 7 forms a second sine wave oscillator that generates a second sine wave having a slightly different frequency from the pulsed light. Sine wave oscillator 7 is 80~200M
It is an oscillator that can send out a sine wave of any frequency within the frequency range of Hz.

A phase detector detects a point in time when a certain phase relationship occurs between the output of the first sine wave oscillator and the output of the second sine wave oscillator, and generates a detection output.

This phase detector includes a mixer 8 that mixes the output of the first sine wave oscillator and the output of the second sine wave oscillator, and a low-pass filter that extracts the low frequency component from the output of the mixer 8. 9 and this low-pass filter 9
It is comprised of a level detector 10 that detects the output level of the.

The following explanation will be given using an example in which the dye laser oscillator 1 emits pulsed light at a frequency of 100 MHz. Since the dye laser oscillator 1 is sending out pulsed light at a frequency of 100MHz, the tuning amplifier 5
A first sine wave of 100 MHz is sent out, and the frequency counter 6 displays 100 MHz.

The operator displays 100MHz on frequency counter 6.
Read the sine wave oscillator 7 to (100+Δ)MHz
It is tuned to send out a second sine wave of (Δ<<100).

The mixer 8 receives the output of the first sine wave oscillator, that is, the first sine wave ₁ (100MHz) sent out by the tuned amplifier 5.
and the second sine wave ₂ sent out by the second sine wave oscillator 7
Mix (100+Δ)MHz and send out a composite wave of = ₁ × ₂ .

= ₁ × ₂ = Asin (2 × 10 ⁸ π) t ×Bsin (2 × 10 ⁸ π + 2πΔ) t = A × B / 2 {cos2πΔt - cos (4 × 10 ⁸ π + 2πΔ) t} An example of the configuration of mixer 8 Shown in Figure 2. The mixer 8 is composed of a ring modulator, and receives a first sine wave ₁ which is the output of the tuned amplifier 5 from a terminal 81, and receives a second sine wave ₂ which is the output of the second sine wave oscillator from a terminal 82. The synthesized wave shown in the above equation is output from the terminal 83.

The low-pass filter 9 is a low-pass filter that passes components in the frequency domain below frequencies slightly higher than the frequency Δ. Therefore, the low-pass filter 9 passes only '=(A×B/2)cos2πΔ·t from the output wave of the mixer 8.

The output terminal of the low-pass filter 9 is connected to one input 101 of a comparator 10 constituting a level detector, and the sine wave' is input to the input terminal 101 of the comparator. The other input end 102 of the comparator 10 is connected to the sliding end of a potentiometer 103. The comparator 10 sends out a pulse when the voltage input to the input terminal 101 becomes greater than the voltage input to the input terminal 102.

The output terminal of the comparator 10 is connected to the input terminal of a monostable multivibrator 11.

The monostable multivibrator 11 has a comparator 11
It starts at the rising edge of the output pulse and falls after a certain period of time. This fixed time will be described later.

The gate pulse generator 12 delivers a gate voltage when the output of the monostable multivalve generator is in the on state.

The output of gate pulse generator 12 is connected to capacitor 1
3 to the photocathode 31 of the streak tube 3 and the output end electrode of the microchannel plate 32.

-800 volts on the photocathode 31 when the gate voltage is generated;
A voltage of +900 volts is applied to the output end side electrodes of the microchannel plate 32, respectively. The second sine wave, which is the output of the sine wave oscillator 7, is amplified by the drive amplifier 14 and transmitted to the deflection electrode 3 of the streak tube 3.
3 is applied. The amplitude of the sine wave applied to this deflection electrode 33 is 1150 volts from -575 volts to +575 volts, and the amplitude from +100 volts to -100 volts is used for sweeping.

A photocathode 31 is formed on the inner wall of the entrance surface of the airtight container 30 of the streak tube 3, and a fluorescent surface 34 is formed on the other inner wall.

A mesh electrode 35, a focusing electrode 36, an aperture electrode 37, a deflection electrode 33, and a microchannel plate 32 are arranged in this order between them. The input end side electrode of the microchannel plate 32 and the aperture electrode 37 are grounded. power supply 2
1 and dividing resistors 22, 23, 24, the photocathode 3
A potential of -4000 volts is applied to 1, -4200 volts to the mesh electrode, and -4500 volts to the focusing electrode.
The fluorescent surface 34 is given a potential 3000 volts higher than the output end side electrode of the microchannel plate 32 by the power source 25.

When no gate voltage is applied by the gate pulse generator 12, photoelectrons cannot pass through the mesh electrode 35. Also at this time, microchannel plate 3
Since no multiplied electrons are emitted from the fluorescent surface 34, the fluorescent surface 34 is kept in a dark state.

When a gate voltage is applied by the gate pulse generator, photoelectrons from the fluorescent surface 31 are transferred to the mesh electrode 3.
It is accelerated by the potential of 5. The accelerated photoelectrons are focused on the aperture of the aperture electrode 37 by the electron lens formed by the focusing electrode 36 and enter the region between the two electrode plates of the deflection electrode 33. Here, when a voltage is applied to the deflection electrode 33, the photoelectrons are deflected. In this embodiment, the incident position of photoelectrons is designed to move from the upper end of the microchannel plate 32 to the lower end when the deflection voltage changes from +100 volts to -100 volts. The photoelectrons incident on the microchannel plate 32 are multiplied and incident on the fluorescent surface 34, forming a streak image. The effective distance of the fluorescent surface 34 in the streak tube sweeping direction is 10 mm.

Next, the conditions for making the first streak image of continuous pulsed light appear near the upper end of the fluorescent surface 34 and the reason why they are successively spaced at appropriate intervals and do not overlap will be explained with reference to the drawings.

In FIG. 3, A indicates the optical output of the dye laser oscillator 1. In FIG. Let this frequency be 100MHz. The first sine wave B tuned to this output is also
It is 100MHz. Figure C shows the output waveform of the second sine wave oscillator 7 with an oscillation frequency of 100.5 MHz. FIG. 1D shows the gate drive voltage waveform sent out by the gate pulse generator 12.

Now, if the point in time when the phases of the first sine wave 1 and the second sine wave completely match is the reference point in time (to), then ′, ₁ , _{and 2} when t seconds have passed from that point are expressed by the following equations. Given.

′=cos10πt ₁ = sin (200×10πt) ₂ = sin (201×10πt) The point in time when a 90 degree phase difference occurs between ₁ and ₂ is detected and the gate pulse is connected to the gate electrode of the streak tube. Then, it is assumed that the gate of the streak tube is opened and the adjustment is made so that the group of photoelectrons that first reach the deflection electrode 33 of the streak tube are brought from the upper end of the fluorescent surface 34. In the vicinity of the optical pulse (0) shown in FIG. 3A,
Assuming that a certain phase difference occurs between ₁ and ₂ ,
From this point (just before that), a gate pulse (D) that lasts 100 ns appears. Then, the second pulse shown in FIG. 3F corresponding to the period of this gate pulse (D)
A portion of the sine wave is made to contribute to the deflection.

The fluorescent surface 34 is swept while the phase of ₂ changes from ^-90 to ⁹⁰ and from ¹⁷¹⁰ to ¹⁸⁹⁰ . In addition
Since the time of change from 171 ⁰ to 189 ⁰ is in the middle of successive photoelectron current pulses and there is no photoelectron current pulse in the region of the deflection electrode 33, no image appears on the fluorescent surface 34 due to this sweeping.

The sweep time of the fluorescent surface is 9.95 nanoseconds per period in ₂ , so it becomes (9950 picoseconds) x (18 ⁰ x 360 ⁰ ) = 500 picoseconds,
The sweep speed is 10 mm/500 picoseconds = 20 mm per nanosecond.

Next, referring to Figure 4, the area near the optical pulse (0)
Explain the relationship between ₁ and ₂ .

This figure shows the time point of phase zero of the first sine wave and the point of phase zero of the first sine wave.
In order to facilitate understanding of the phase relationship between the first sine wave and the first sine wave, the time axes of other waveforms near the zero phase of the first sine wave are exaggerated.

Photoelectron current pulse I caused by light pulse (0)
Assume that the phase of the first sine wave is zero at the moment when (0) enters the deflection region of the deflection electrode 33 (this point in time will be referred to as tr as a second reference point). By adjusting the optical path length from the dye laser oscillator 1 to the photocathode 31 using the optical path variable device ₂₀ , the photoelectrons can be made to reach the deflection electrode 33 at an arbitrary phase point.

At this time, the second sine wave is advanced by a predetermined angle δ (180-9=171) degrees than the first sine wave. The phase detector detects this immediately before and generates the gate pulse G.

The voltage applied to the deflection electrode by the second sine wave at the second reference time tr is +100V. This causes the photoelectron current pulse I(0) to be deflected to correspond to the uppermost side of the fluorescent surface.

At the moment when the next photoelectron current pulse I(1) enters the deflection region of the deflection electrode 33 (after 10 nanoseconds from the reference time tr, the phase of the first sine wave is zero), the second sine wave changes to the first sine wave. The sine wave is advanced by δ(180-9=171)+1.8 degrees. The deflection voltage for I(1) is lower than that for I(0), and the image of I(1) appears below the image of I(0) on the fluorescent surface. 1.8 above
The power is 10ns x (1.8/360) = 0.05ns = 50ps, which corresponds to 1mm on the fluorescent surface.

Similarly, the moment the next photoelectron current pulse I(2) enters the deflection region of the deflection electrode 33 (from the reference time tr)
After 20 ns, the second sine wave (phase zero of the first sine wave)
The sine wave of is δ(180-9=171)+ than the first sine wave.
It will be in a state where it has advanced by 1.8 x 2 degrees. The deflection voltage for I(2) is lower than that for I(1), and the image of I(2) appears below the image of I(1) on the fluorescent surface.

Generally speaking, the i-th photoelectron current pulse I(i)
At the moment when the second sine wave enters the deflection region of the deflection electrode 33 (after i×10 ns from the reference time tr, the phase of the first sine wave is zero), the second sine wave becomes δ smaller than the first sine wave.
It will be in a state where it has advanced by (180-9=171)+1.8×i degrees. And the deflection voltage for I(i) is I(i-1)
The image of I(i) appears below the image of I(i-1) on the fluorescent surface.

I(0) and I(11) are shown in FIG. 3G, and a waveform diagram of the second sine wave corresponding to these is shown in FIG. 3H.

FIG. 5A is a schematic diagram showing a streak image appearing on a fluorescent surface, and FIG. 5B shows the correspondence with the photoelectron current pulse I described earlier.

In the device according to the present invention, a second sine wave oscillator that generates a sine wave having a frequency slightly different from that of the pulsed light is provided, and the second sine wave output from this oscillator is used as a deflection voltage. Streak images corresponding to a large number of pulsed lights can be displayed on a surface at once. That is, in the apparatus according to the present invention, a plurality of streak images of optical pulses of an optical pulse train with a small duty ratio can be brought close to each other and displayed simultaneously on the fluorescent surface of the streak tube without reducing the resolution. Comparisons are now possible.

The duration of the light emission that is the object of observation is expected to vary. However, this problem can be solved by arbitrarily adjusting the distance between the streak images by adjusting the frequency of the second sine wave.

In the device according to the present invention, a gate pulse generator is provided which receives the detection output of the phase detector and outputs a gate pulse that lasts for a period (necessary time) longer than a plurality of periods of the output of the first sine wave oscillator, and Substantial operation is performed only during the period when voltage is being generated. Therefore, the problem that the thermionic current is multiplied and collides with the fluorescent surface 34 to emit light outside this period, raising the background level of the fluorescent surface does not occur. Therefore, the streak image can be observed in extremely good condition.

Various modifications can be made to the embodiments described in detail above within the scope of the present invention.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a waveform observation device for high-speed repetitive pulsed light according to the present invention.
FIG. 2 is a circuit diagram showing an example of the configuration of a mixer used in the device. FIG. 3 is a waveform diagram for explaining the operation of the circuit. FIG. 4 is a waveform diagram for explaining the phase relationship near the second reference time point. FIG. 5 is an explanatory diagram showing the correspondence between the streak image appearing on the fluorescent surface and the photoelectron current pulse I. It is a graph. 1... Dye laser oscillator, 2... Anti-transparent mirror (beam splitter), 3... Streak tube, 30...
... airtight container, 31 ... photocathode, 32 ... microchannel plate, 33 ... deflection electrode, 34 ...
... Fluorescent surface, 35 ... Reticular electrode, 36 ... Focusing electrode, 37 ... Aperture electrode, 4 ... PIN photodiode, 5 ... Tuning amplifier, 6 ... Frequency counter, 7 ... (Second) sine wave oscillator, 8... mixer, 9... low pass filter, 10... comparator, 11
... Monostable multivibrator, 12 ... Gate pulse generator.

Claims (1)

[Claims] 1. A streak tube including a photocathode, a gate electrode, a deflection electrode, and a fluorescent surface, and generating a first sine wave synchronized with high-speed repetitive pulse light input to the photocathode of the streak tube. a first sine wave oscillator;
a second sine wave oscillator that generates a second sine wave having a slightly different frequency from the pulsed light, and detecting a point in time when a certain phase relationship occurs between the first sine wave and the second sine wave; a phase detector that generates a detection output; a gate pulse generator that receives the detection output of the phase detector and outputs a gate pulse that lasts for a period longer than a plurality of cycles of the first sine wave; An observation device for high-speed repetitive pulsed light comprising a gate electrode of a streak tube and connection means for connecting the output of the second sine wave oscillator to the deflection electrode. 2. The first sine wave oscillator that generates the first sine wave synchronized with the high-speed repetitive pulse light input to the photocathode of the streak tube branches the high-speed repetitive pulse light input to the photocathode of the streak tube. 1. The beam splitter according to claim 1, further comprising: a beam splitter for taking out a part of the beam, a light receiving element for converting the branched output of the beam splitter, and a tuned amplifier synchronized with the output of the light receiving element. Observation device for high-speed repetitive pulsed light. 3. The phase detector includes a mixer that mixes the first sine wave and the second sine wave, a low-pass filter that extracts the low-frequency component from the output of the mixer, and 2. An observation device for high-speed repetitive pulsed light according to claim 1, which comprises a level detector for detecting the output level of a filter.