JP4567229B2 - Optical waveform measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is an optical waveform measurement applied to a streak camera or the like that measures how the intensity of light (ultra-fast light) generated within an extremely short time changes in time or space (position or wavelength). It relates to the device.
[0002]
[Prior art]
Conventionally, in a streak camera (synchronous scan streak camera) that measures the intensity of high repetition pulse laser light, a streak tube that is a component of the streak camera is usually provided with a pair of parallel plate type vertical deflection plates (hereinafter referred to as deflection plates). The streak sweep described later is performed using a change in the high voltage applied to the deflecting plate (electrode).
[0003]
In the streak tube, a group of electrons photoelectrically converted according to the light intensity on the photocathode on which the pulse laser beam is incident is accelerated by the acceleration electrode. When the accelerated electron group passes between the deflection plates, a streak sweep is performed in which the high voltage applied to the deflection plates, that is, the sweep voltage, is swung from the upper side to the lower side (in the time axis direction). By this sweeping, the electron group is deflected at slightly different angles in the vertical direction, collides with the fluorescent screen via the MCP (microchannel plate), and is converted into light again here.
[0004]
[Problems to be solved by the invention]
In the streak camera as the conventional optical waveform measuring device, in order to measure the change in light intensity more accurately, in other words, to obtain a higher time resolution, a larger sweep voltage amplitude is required. . In order to increase the amplitude of the sweep voltage, either the Q value of the resonance circuit having a coil that resonates with the capacitance of the deflection plate is increased or the input power is increased. Since the former Q value is limited by the residual inductance and stray capacitance of the coil and wiring, it is practically difficult to make it more than the current resonance circuit.
[0005]
As for the latter, since power consumption is mostly performed in the resonance circuit, heat is generated from the deflecting plate, and resonance frequency drift occurs. Furthermore, although the heat generation of the deflecting plate in the streak tube is in a vacuum, there is no escape of heat, and even with a small amount of power, a temperature rise of several hundred degrees Celsius or more occurs, and the streak tube is permanently destroyed. May cause damage. In addition, it is difficult to cool the resonance circuit so as not to vibrate while maintaining a large Q value.
[0006]
Accordingly, an object of the present invention is to provide an optical waveform measuring apparatus capable of measuring a change in light intensity with higher accuracy so as not to generate heat that permanently damages the streak tube.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, an optical waveform measuring device of the present invention is an optical waveform measuring device that measures a waveform by sweeping an electron group after photoelectric conversion of incident light on the photoelectric surface in a time axis direction. Disposed in a vacuum tube having A set of flat plate electrodes are vertically separated from each other in a plane parallel state for a predetermined period. Sweep the electron group in the time axis direction 1's A deflection electrode; In a vacuum tube having a photocathode, it is arranged rearward along the incident optical axis with respect to the first deflection electrode, and a set of flat plate electrodes are vertically separated in a plane-parallel state for a predetermined interval, and the electron group is separated by time. A second deflection electrode that sweeps in an axial direction; The first harmonic signal to which the incident light is synchronized and the first harmonic signal n times the frequency nth harmonic signal (Where n is an order of 1 or more) Output means, and an application means for applying the first harmonic signal to the first deflection electrode and applying the nth harmonic signal to the second deflection electrode.
[0008]
Since the electron group after photoelectric conversion of incident light is swept with the voltage of the first-order harmonic signal by the first deflection electrode, and then swept with the voltage of the n-th-order harmonic signal with the second deflection electrode, The movement of the group becomes the same movement as when swept by the voltage of the synthesized wave signal of the first harmonic signal and the nth harmonic signal. Since the slope of the synthesized wave signal is steeper than that of the first-order harmonic signal, the electron group can be shaken more in the time axis direction, and thereby high time resolution can be obtained.
[0009]
In addition to the first and second deflection electrodes, the optical waveform measurement apparatus of the present invention includes one or a plurality of deflection electrodes arranged along the axis of the incident light. And outputting a harmonic signal of an arbitrary multiple as many as the number of one or a plurality of deflection electrodes, and applying the output harmonic signal to one or a plurality of deflection electrodes via an applying means. It is preferable to have a feature.
[0010]
Since the movement of the electron group is the same as that swept by the voltage of the combined wave signal having a steep slope that combines the harmonic signals, the electron group can be swung more greatly in the time axis direction. High temporal resolution can be obtained.
[0011]
In the optical waveform measuring apparatus of the present invention, it is preferable that the applying means has a resonance circuit configuration including first and second deflection electrodes.
[0012]
Since the deflection electrode is included in the resonance circuit, a higher voltage gain can be obtained compared to the case where a traveling wave type is used for the deflection electrode. Further, when using at a fixed frequency, a high slew rate can be obtained with less power by using a resonant circuit. This is because the traveling wave type deflection electrode has a transmission line structure with a fixed impedance, so it has a wide frequency characteristic, and a rectangular wave having higher harmonics is applied to it. In this case, it is possible to increase the slew rate, but it is physically difficult to increase the impedance while maintaining the broadband characteristics due to stray capacitance and residual inductance. For this reason, since the impedance is limited, the voltage gain is also lowered.
[0013]
In the optical waveform measuring apparatus of the present invention, the phase difference between the first harmonic signal applied to the first deflection electrode from the applying unit and the first harmonic signal input to the applying unit is constant or The phase of the first-order harmonic signal input to the applying means is controlled so as to be 0, the n-order harmonic signal applied from the applying means to the second deflection electrode, and the n-th order harmonic signal input to the applying means It is preferable that phase control means for controlling the phase of the nth-order harmonic signal input to the applying means so that the phase difference from the harmonic signal is constant or zero is preferably provided.
[0014]
Since the phase of the sweep voltage by the first harmonic signal and the nth harmonic signal applied to the first and second deflection electrodes can be made constant, the application means includes the first and second deflection electrodes. It is possible to correct a thermal drift caused by a configured resonance circuit or the like.
[0015]
In the optical waveform measuring apparatus of the present invention, the phase difference between the first harmonic signal applied to the first deflection electrode from the applying unit and the first harmonic signal input to the applying unit is constant or A first-order harmonic signal having a frequency of 0 is oscillated and output to the applying means, and an n-order harmonic signal applied from the applying means to the second deflection electrode and n input to the applying means. It is preferable that an oscillation unit that oscillates an n-order harmonic signal having a frequency such that the phase difference from the second-order harmonic signal is constant or zero and outputs the signal to the applying unit is preferable.
[0016]
Since the phase of the sweep voltage by the first harmonic signal and the nth harmonic signal applied to the first and second deflection electrodes can be made constant, the application means includes the first and second deflection electrodes. It is possible to correct a thermal drift caused by a configured resonance circuit or the like.
[0017]
In the optical waveform measuring apparatus of the present invention, the phase of the nth-order harmonic signal applied to the second deflection electrode via the applying means is set to the opposite phase, and the nth-order harmonic signal having the opposite phase and Phase inversion means for adjusting the amplitude of the nth-order harmonic signal having an opposite phase so that the average slope portion corresponding to the sweep range in the synthesized wave becomes as large as possible when the first-order harmonic signal is synthesized. It is preferable to include
[0018]
Since the sweep range when the electron group after photoelectric conversion of the incident light is swept by the first and second deflection electrodes becomes larger, more electron groups can be swept.
[0019]
In order to solve the above problems, an optical waveform measuring apparatus of the present invention is an optical waveform measuring apparatus that measures a waveform by sweeping an electron group after photoelectric conversion of incident light on a photoelectric surface in a time axis direction. Placed in a vacuum tube with a photocathode, A set of flat plate electrodes are vertically separated from each other in a plane parallel state for a predetermined period. Sweep the electron group in the time axis direction 1's A deflection electrode; In a vacuum tube having a photocathode, it is arranged rearward along the incident optical axis with respect to the first deflection electrode, and a set of flat plate electrodes are vertically separated in a plane-parallel state for a predetermined interval, and the electron group is separated by time. A second deflection electrode that sweeps in an axial direction; The incident light is branched, one branched light is incident on the photocathode, the other branched light is output to the converting means, and the first harmonic from the electric signal converted by the converting means. Wave signal and , N times the frequency nth harmonic signal (Where n is an order of 1 or more) And an application means for applying a first harmonic signal to the first deflection electrode and applying an n order harmonic signal to the second deflection electrode.
[0020]
Since the first harmonic signal and the nth harmonic signal are extracted from the light incident on the photocathode and are finally used as the sweep voltage, synchronization between the incident light and the sweep voltage can be established with higher accuracy. it can. The optical waveform measuring apparatus of the present invention may include a light source (exiting means) that emits incident light.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
A streak camera which is an optical waveform measuring apparatus according to an embodiment of the present invention will be described with reference to the drawings.
[0022]
FIG. 1 is a configuration diagram of a streak camera according to the first embodiment. The streak camera 10 shown in FIG. 1 includes a high repetition pulse laser 12, a streak tube 18 having first and second deflecting plates 14, 16, synthesizers 20, 22, phase shifters 24, 26, and a power amplifier. 28, 30 and matching circuits 32, 34. Hereinafter, each component will be described in detail.
[0023]
The high repetition type pulse laser 12 has a PLL (Phase Locked Loop) circuit built therein, and the f1 signal is obtained by synchronizing with a signal of frequency f1 (hereinafter referred to as f1 signal) output from the synthesizer 20 by the PLL circuit. Is emitted to the streak tube 18.
[0024]
As described in the conventional example, the streak tube 18 basically converts pulsed laser light into an electron group on the photocathode, accelerates it with an accelerating electrode, and performs a streak sweep of the accelerated electron group with a deflector plate. The light is converted again into light on the phosphor screen via the MCP, but the point that the first and second deflecting plates 14 and 16 are used as the deflecting plates is different from the conventional example.
[0025]
The first deflecting plate 14 is composed of a pair of flat plate-like electrodes vertically separated from each other by a predetermined distance, and the second deflecting plate 16 has the same configuration as the first deflecting plate 14 and has the first configuration. The deflecting plate 14 is arranged behind the incident optical axis. That is, the electron group accelerated by the accelerating electrode passes through the first and second deflecting plates 14 and 16 in this order, and is streak-swept by both the deflecting plates 14 and 16 during this passage. The opposing ends of the voltage application ends of the deflection plates 14 and 16 are grounded.
[0026]
The synthesizer 20 outputs the fn signal to the synthesizer 22 and the phase shifter 24 in addition to the high repetition pulse laser 12. The synthesizer 22 operates in synchronization with the f1 signal, and outputs a harmonic of the frequency f1 of the f1 signal, that is, a signal having a frequency n times (hereinafter referred to as fn signal) to the phase shifter 26. However, n times includes 1 time.
[0027]
The phase shifter 24 sets the phase of the f1 signal to a predetermined phase and then outputs it to the power amplifier 28. The phase shifter 26 sets the phase of the fn signal to a predetermined phase and then outputs it to the power amplifier 30. It is.
[0028]
The power amplifier 28 amplifies the f1 signal from the phase shifter 24 to a predetermined power and then outputs it to the matching circuit 32. The power amplifier 30 amplifies the fn signal from the phase shifter 26 to a predetermined power. Thereafter, the data is output to the matching circuit 34.
[0029]
The matching circuit 32 effectively transmits the power of the f1 signal amplified by the power amplifier 28 to the first deflector plate 14, and is therefore configured as a resonance circuit. For example, the series resonance circuit 36 shown in FIG. It is configured. The series resonance circuit 36 includes a capacitor C1, a coil L1, a resistor R, a coil L2, and a capacitor C2. The elements of the capacitor C1, the coil R1, the resistor R, the coil L2, and the capacitor C2 are connected in series between the + input terminal of the signal and the ground. The capacitor C3 is connected between the ground and the ground, and the negative input terminal is grounded. The matching circuit 34 has the same configuration as the matching circuit 32, and effectively transmits the power of the fn signal amplified by the power amplifier 30 to the second deflection plate 16.
[0030]
Further, when the phases of the f1 signal and the fn signal are adjusted by the phase shifters 24 and 26, the electron groups after the photoelectric conversion of the pulsed laser light incident on the streak tube 18 are converted into the first and second deflecting plates 14, When the streak sweep is performed at 16, the adjustment is performed so that the steep portion of each sweep voltage waveform by the f1 signal and the fn signal is optimally captured.
[0031]
The operation of the streak camera 10 having such a configuration will be described. However, the f1 signal output from the synthesizer 20 is a fundamental wave (first harmonic) indicated by a solid curve 38 in FIG. 3, and the fn signal output from the synthesizer 22 is a dashed curve 40 in FIG. It is assumed that the third harmonic shown in FIG. In FIG. 3, the vertical axis is the amplitude (V) axis, the horizontal axis is the time (ns) axis, the amplitude of the fundamental wave 38 is 1, the amplitude of the third harmonic 40 is 0.5, and the fundamental wave 38. Is assumed to be 80 MHz.
[0032]
First, the pulse laser beam emitted from the high repetition pulse laser 12 in synchronization with the fundamental wave 38 from the synthesizer 20 is incident on the streak tube 18. On the other hand, the phase of the fundamental wave 38 from the synthesizer 20 is adjusted by the phase shifter 24. This adjustment is performed so that the electron group after the photoelectric conversion of the pulse laser beam is optimally captured at the steep portion of the amplitude of the fundamental wave 38 when the first deflector plate 14 performs the streak sweep. The phase-adjusted fundamental wave 38 is amplified to a predetermined power by the power amplifier 28 and then applied as a sweep voltage to the first deflection plate 14 via the matching circuit 32. At this time, the voltage is applied so as to resonate with the capacitance of the first deflection plate 14 by the matching circuit 32.
[0033]
Similarly, the phase shifter 26 adjusts the phase of the third harmonic 40 from the synthesizer 22 that operates in synchronization with the synthesizer 20. This adjustment is performed so that the electron group after the photoelectric conversion of the pulse laser beam is optimally captured at the steep portion of the amplitude of the third harmonic 40 when the second deflector plate 16 performs the streak sweep. The phase-adjusted third harmonic 40 is amplified to a predetermined power by the power amplifier 30 and then applied as a sweep voltage from the matching circuit 34 to the second deflection plate 16. At this time, the voltage is applied so as to resonate with the capacitance of the second deflection plate 16 by the matching circuit 34.
[0034]
By applying these, first, when the electron group after the pulse laser beam is photoelectrically converted by the photocathode passes through the first deflecting plate 14, the time axis direction is the steep portion of the amplitude of the fundamental wave 38 shown in FIG. The streak is swept. By this sweeping, the electron group is deflected at slightly different angles in the vertical direction. The deflected electron group moves to the second deflection plate 16 and is swung from the upper side to the lower side at the steep portion of the amplitude of the third harmonic 40 shown in FIG. 3 when passing through the second deflection plate 16. That is, the streak sweep is performed in the time axis direction. By this sweeping, the electron group is deflected at a different angle in the vertical direction further than the previous stage deflection. This deflected electron group collides with the phosphor screen via the MCP, and is converted into light again here.
[0035]
According to the streak camera 10 of the first embodiment described above, the sweep voltage by the fundamental wave 38 that is the first harmonic is applied to the first deflecting plate 14 and the rear of the first deflecting plate 14 along the incident optical axis. A sweep voltage by the third harmonic 40 synchronized with the fundamental wave 38 is applied to the arranged second deflecting plate 16.
[0036]
As a result, the electron group after the incident pulse laser beam is photoelectrically converted on the photocathode is subjected to streak sweeping with the voltage of the fundamental wave 38 by the first deflection plate 14 and then the third harmonic 40 by the second deflection plate 16. Therefore, the movement of the electron group is the same as when the streak sweep is performed with the voltage of the combined wave of the fundamental wave 38 and the third harmonic 40 indicated by a curve 42 in FIG. The slope of the synthesized wave 42 shown by a straight line 44 in FIG. 4 is steeper than the slope 46 of the fundamental wave 38, which is improved about 2.5 times. By this improvement, the electron group can be shaken more in the time axis direction, so that a high time resolution can be obtained.
[0037]
Here, if it is attempted to obtain the slope of the composite wave 42 using only the fundamental wave 38, power that is five times that of the composite wave 42 is required. As described in the section of the problem to be solved, this electric power is almost consumed in the resonance circuit including the streak tube, and thus affects the temperature rise and phase drift due to the heat. In other words, the streak camera 10 according to the first embodiment does not affect the temperature rise and phase drift due to the heat. Therefore, it is possible to measure the change in light intensity with higher accuracy so that heat that causes permanent damage in the streak tube 18 is not generated.
[0038]
Further, when applying the sweep voltage to the first and second deflecting plates 14 and 16, it is performed via matching circuits 32 and 34 having a resonance circuit configuration together with the deflecting plates 14 and 16, and this is performed as follows. Depending on the reason. A traveling wave type can be used as the deflection plate. However, in the case of a traveling wave type deflection plate, for example, a transmission line structure having a fixed impedance such as 100Ω or 200Ω is used. Has frequency characteristics. If a rectangular wave having higher harmonics is applied thereto, the slew rate can be increased. However, it is physically difficult to increase the impedance while maintaining the broadband characteristics due to stray capacitance and residual inductance. At present, since the impedance is about 200Ω, the gain of the sweep voltage is doubled. In contrast, in the resonance circuit, a gain of about 23 dB (about 14 times) can be obtained as in the sweep voltage waveform indicated by the curve 48 in FIG. 5, and therefore, the resonance circuit is used for use at a fixed frequency. The one can obtain a high slew rate with less power. In FIG. 5, the vertical axis is the amplitude (dB) axis, and the horizontal axis is the frequency (MHz) axis.
[0039]
However, although the first embodiment has been described on the assumption that the deflecting plate has two stages, ie, the first and second deflecting plates 14 and 16, the above-described effect can be obtained even if there are three or more stages. Can do. Even in the case of three or more stages, the matching circuit forms a resonance circuit configuration including each deflection plate.
[0040]
Next, a second embodiment will be described.
[0041]
FIG. 6 is a configuration diagram of a streak camera according to the second embodiment. However, in the second embodiment shown in FIG. 6, parts corresponding to those in the first embodiment shown in FIG.
[0042]
The streak camera 50 of the second embodiment shown in FIG. 6 is different from the streak camera 10 of the first embodiment shown in FIG. 1 in that one of the two synthesizers 20 and 22 is one synthesizer 20 and the other synthesizer. The third harmonic generator 52 is provided instead of the second harmonic generator 52. The third harmonic generator 52 generates a frequency signal (hereinafter referred to as a third harmonic signal) that is three times the f1 signal output from the synthesizer 20 whose phase has been adjusted by the phase shifter 24, and supplies this to the phase shifter 26. Output.
[0043]
The operation of the streak camera 50 having such a configuration will be described only with respect to differences from the first embodiment. However, it is assumed that the f1 signal is the fundamental wave 38 shown in FIG. 3 and the third harmonic signal is the third harmonic 40. The fundamental wave 38 whose phase has been adjusted by the phase shifter 24 is input to the power amplifier 28 and the third harmonic generator 52, and the third harmonic generator 52 generates the third harmonic 40 based on the fundamental wave 38. The The third harmonic 40 is input to the power amplifier 30.
[0044]
According to the streak camera 50 of the second embodiment described above, the same effect as that of the first embodiment can be obtained. Note that the third harmonic generator 52 may be replaced with an n harmonic generator to generate an n harmonic signal (nth harmonic).
[0045]
Next, a third embodiment will be described.
[0046]
FIG. 7 is a configuration diagram of a streak camera according to the third embodiment. However, in the third embodiment shown in FIG. 7, parts corresponding to those in the second embodiment shown in FIG. 6 are denoted by the same reference numerals, and the description thereof is omitted.
[0047]
The streak camera 60 of the third embodiment shown in FIG. 7 is different from the streak camera 50 of the second embodiment shown in FIG. 6 in that in addition to the components of the streak camera 50, phase comparators 62 and 64, and a loop Filters 66 and 68 and voltage control phase shifters 70 and 72 are provided.
[0048]
The phase comparator 62 compares the phase of the sweep voltage (f1 signal) applied to the first deflecting plate 14 with the phase of the f1 signal output from the phase shifter 24, thereby calculating the phase difference between the two signals. This is obtained and output to the loop filter 66. The loop filter 66 outputs a voltage corresponding to the phase difference to the voltage control phase shifter 70. The voltage control phase shifter 70 adjusts the phase of the f1 signal from the phase shifter 24 so that the phase difference is constant or 0 (zero) according to the voltage from the loop filter 66, and the adjusted f1 The signal is output to the power amplifier 28.
[0049]
The phase comparator 64 compares the phase of the sweep voltage (third harmonic signal) applied to the second deflection plate 16 with the phase of the third harmonic signal output from the phase shifter 26, thereby comparing both signals. The phase difference is obtained and output to the loop filter 68. The loop filter 68 outputs a voltage corresponding to the phase difference to the voltage control phase shifter 72. The voltage control phase shifter 72 adjusts the phase of the third harmonic signal from the phase shifter 26 so that the above phase difference becomes constant or 0 (zero) according to the voltage from the loop filter 68. The third harmonic signal is output to the power amplifier 30.
[0050]
The operation of the streak camera 60 having such a configuration will be described only with respect to differences from the second embodiment. However, it is assumed that the f1 signal is the fundamental wave 38 shown in FIG. 3 and the third harmonic signal is the third harmonic 40.
[0051]
When the fundamental wave 38 whose phase has been adjusted by the phase shifter 24 and the fundamental wave 38 from the matching circuit 32 applied as the sweep voltage to the first deflector 14 are input to the phase comparator 62, the phase comparator 62 The phase difference between the two fundamental waves 38 is obtained by comparing the phases of the two fundamental waves 38. The obtained phase difference is input to the loop filter 66, where a voltage corresponding to the phase difference is generated and output to the voltage control phase shifter 70. In the voltage control phase shifter 70, the phase of the fundamental wave 38 from the phase shifter 24 is adjusted so that the phase difference is constant or zero according to the voltage, and the adjusted fundamental wave 38 is supplied to the power amplifier 28. Is output.
[0052]
Similarly, the third harmonic 40 whose phase is adjusted by the phase shifter 26 and the third harmonic 40 from the matching circuit 34 applied as a sweep voltage to the second deflector 16 are input to the phase comparator 64. In the phase comparator 64, the phase difference between both the third harmonics 40 is obtained by comparing the phases of both the third harmonics 40. The obtained phase difference is input to the loop filter 68, where a voltage corresponding to the phase difference is generated and output to the voltage control phase shifter 72. In the voltage control phase shifter 72, the phase of the third harmonic 40 from the phase shifter 26 is adjusted so that the phase difference is constant or zero according to the voltage, and the third harmonic 40 after the adjustment is adjusted. Is output to the power amplifier 30.
[0053]
According to the streak camera 50 of the third embodiment described above, the same effect as that of the second embodiment can be obtained, and the phase of the sweep voltage applied to the first and second deflecting plates 14 and 16 is constant. Therefore, it is possible to correct the thermal drift caused by the resonance circuit including the first and second deflecting plates 14 and 16 and the power amplifiers 28 and 30 by the matching circuits 32 and 34. .
[0054]
Next, a fourth embodiment will be described.
[0055]
FIG. 8 is a configuration diagram of a streak camera according to the fourth embodiment. However, in the fourth embodiment shown in FIG. 8, parts corresponding to those in the third embodiment shown in FIG.
[0056]
The streak camera 80 of the fourth embodiment shown in FIG. 8 is different from the streak camera 60 of the third embodiment shown in FIG. 7 in place of the high repetition type pulse laser 12 that is a component of the streak camera 60. Other types of high repetition rate pulse laser 12a, streak tube 18 having first and second deflecting plates 14 and 16, phase shifters 24 and 26, power amplifiers 28 and 30, and matching circuits 32 and 34 In addition to the phase comparators 62 and 64, the loop filters 66 and 68, and the voltage control phase shifters 70 and 72, the half mirror 82, the photodetector 84, and the band pass filters 86 and 88 are provided. is there.
[0057]
The high repetition type pulse laser 12a autonomously emits a pulse laser beam having a frequency f1. The half mirror 82 transmits the emitted pulsed laser light and outputs it to the streak tube 18, and reflects and outputs it to the photodetector 84. The photodetector 84 converts the pulsed laser light from the half mirror 82 into a pulsed electric signal and outputs it to the bandpass filters 86 and 88. The band-pass filter 86 passes only the signal of the frequency f1 that is the fundamental wave among the electrical signals output from the photodetector 84 and outputs the signal to the phase shifter 24. The band-pass filter 88 passes only a frequency signal (n-order harmonic signal) n times the frequency f 1 out of the electric signal output from the photodetector 84 and outputs the signal to the phase shifter 26.
[0058]
The operation of the streak camera 80 having such a configuration will be described only with respect to differences from the third embodiment. However, it is assumed that the signal passing through the bandpass filter 86 is the fundamental wave 38 shown in FIG. 3 and the signal passing through the bandpass filter 88 is the third harmonic 40.
[0059]
The pulse laser beam having the frequency f1 emitted from the high repetition pulse laser 12a passes through the half mirror 82 and is output to the streak tube 18, and is reflected and output to the photodetector 84. In the photodetector 84, the pulsed laser light is converted into a pulsed electric signal, and this electric signal is output to the bandpass filters 86 and 88. In the band pass filter 86, only the fundamental wave 38 of the electric signal is passed and output to the phase shifter 24. In the band pass filter 88, only the third harmonic 40 of the electric signal is passed and output to the phase shifter 26.
[0060]
According to the streak camera 80 of the fourth embodiment described above, the same effect as that of the third embodiment can be obtained. In addition, since the fundamental wave 38 and the third harmonic 40 are extracted from the pulse laser beam itself emitted from the autonomous operation type high repetition rate pulse laser 12a and finally used as the sweep voltage, the synthesizer 20, A device for generating a reference signal such as 22 becomes unnecessary. Further, since it is not necessary to synchronize the high repetition pulse laser 12a with the reference signal, the configuration can be simplified correspondingly.
[0061]
Next, a fifth embodiment will be described.
[0062]
FIG. 9 is a configuration diagram of a streak camera according to the fifth embodiment. However, in the fifth embodiment shown in FIG. 9, parts corresponding to those in the third embodiment shown in FIG.
[0063]
The streak camera 90 of the fifth embodiment shown in FIG. 9 is different from the streak camera 60 of the third embodiment shown in FIG. 7 in that voltage controlled oscillators 92 and 94 are provided instead of the voltage control phase shifters 70 and 72. That is.
[0064]
The voltage controlled oscillator 92 is connected between the loop filter 66 and the power amplifier 28, and has a frequency f1 at which the phase difference obtained by the phase comparator 62 is constant or zero according to the voltage from the loop filter 66. , Ie, the f1 signal is output to the power amplifier 28. The voltage controlled oscillator 94 is connected between the loop filter 68 and the power amplifier 30, and has a frequency f1 at which the phase difference obtained by the phase comparator 64 is constant or zero according to the voltage from the loop filter 68. 3 times a frequency signal, that is, a third harmonic signal is output to the power amplifier 30.
[0065]
The operation of the streak camera 90 having such a configuration will be described only with respect to differences from the third embodiment. However, it is assumed that the f1 signal is the fundamental wave 38 shown in FIG. 3 and the third harmonic signal is the third harmonic 40.
[0066]
The voltage controlled oscillator 92 oscillates a fundamental wave 38 having a frequency such that the phase difference obtained by the phase comparator 62 is constant or zero according to the voltage from the loop filter 66, and this fundamental wave 38 is generated by the power amplifier 28. Is output. The voltage controlled oscillator 94 oscillates the third harmonic 40 having a frequency such that the phase difference obtained by the phase comparator 64 is constant or zero according to the voltage from the loop filter 68. Is output to the power amplifier 30.
[0067]
According to the streak camera 90 of the fifth embodiment described above, the same effect as that of the third embodiment can be obtained.
[0068]
Next, a sixth embodiment will be described.
[0069]
FIG. 10 is a configuration diagram of a streak camera according to the sixth embodiment. However, in the sixth embodiment shown in FIG. 10, portions corresponding to the respective portions of the third embodiment of FIG.
[0070]
The streak camera 100 of the sixth embodiment shown in FIG. 10 is different from the streak camera 60 of the third embodiment shown in FIG. 7 in that a phase inverter 102 is provided between the third harmonic generator 52 and the phase shifter 26. Is connected. The phase inverter 102 reverses the phase of the third harmonic signal generated from the third harmonic generator 52 (0 / π) to obtain an opposite phase and then outputs it to the phase shifter 26 with an arbitrary amplitude. .
[0071]
The operation of the streak camera 100 having such a configuration will be described only with respect to differences from the fifth embodiment. Here, it is assumed that the f1 signal whose phase is adjusted by the phase shifter 24 is the fundamental wave 38 shown in FIG. The fundamental wave 38 is output to the phase inverter 102 after the frequency f1 is tripled by the triple wave generator 52. In the phase inverter 102, the phase of the third harmonic signal is inverted so that the phase is reversed and then an arbitrary amplitude is obtained. An example of a third harmonic signal (hereinafter referred to as a third harmonic antiphase signal) having an arbitrary amplitude in the opposite phase is shown by a curve 110 in FIG. It is assumed that the amplitude of the third harmonic antiphase signal 110 is 0.13. The amplitude of the fundamental wave 38 is 1.
[0072]
The amplitude of the third harmonic anti-phase signal 110 is such that when the fundamental wave 38 and the third harmonic anti-phase signal 110 are synthesized, the time window (sweep range) corresponding to the average slope portion of this synthesized wave is as much as possible. Determine to be larger. In this example, the composite wave has an amplitude of 1.13 as indicated by a curve 112 in FIG. 12 and an average slope longer than that of the fundamental wave 38 as indicated by a straight line 114. However, the straight line 114 shows the average inclination when the time window is set to 5.5 ns / full scale. A broken line portion overlapping the straight line 114 is a sweep voltage.
[0073]
According to the streak camera 100 of the sixth embodiment described above, the same effect as that of the third embodiment can be obtained. In addition to this, when the phase inverter 102 sets the phase of the third harmonic generated from the third harmonic generator 52 to an opposite phase, and the third harmonic and the fundamental wave 38 that have been reversed are synthesized. The amplitude of the third-order harmonic having the opposite phase is adjusted so that the average slope portion 114 corresponding to the sweep range in the synthesized wave 112 is as large as possible. As a result, the sweep range when the electron group after photoelectric conversion of the pulse laser beam is subjected to the streak sweep by the first and second deflecting plates 14 and 16 is increased, so that more electron groups can be swept. Thus, it becomes possible to measure the change in light intensity with higher accuracy.
[0074]
Further, the integral linearity of the synthesized wave 112 is shown in FIG. The straight lines parallel to the horizontal line shown by broken lines in FIG. 13 indicate the first harmonic signals of + 3% and −3%, respectively. These values are values used as guaranteed values as a product of the streak camera 100, and the sweep range must be within the range of those values. FIG. 13 shows that in the streak camera 100, the sweep range is within the range. FIG. 14 shows a differential waveform of the synthesized wave 112 with a curve 116.
[0075]
Further, in order to compare the effect with the streak sweep using only the conventional fundamental wave 38, FIG. 15 shows the average slope 120 of the fundamental wave 38, FIG. 16 shows the integral linearity of the fundamental wave 38, and FIG. 38 differential waveforms 122 are shown. From a comparison between FIG. 15 and FIG. 12, it can be determined that the sweep range is larger in this embodiment. In addition, from the comparison between FIG. 16 and FIG. 13, in this embodiment, the integral linearity is within the guaranteed range, but the integral linearity has deteriorated to 7% or more in the past, and the integral linearity is also improved. I can judge.
[0076]
The above embodiment relates to a type of streak camera that repeatedly sweeps, but can also be applied to a single sweep type streak camera. That is, when a streak image is observed using a pulse laser light source with few repetitions, a ramp voltage is used as the sweep voltage.
[0077]
FIG. 18 is a diagram showing a basic configuration of the system, and FIG. 19 is a waveform diagram of a sweep signal. As shown in FIG. 18, Ti: S fs (titanium / sapphire femtosecond) -pulse laser light source 201 emits pulsed light in synchronization with the trigger signal from the trigger circuit 202. The timing signal from the trigger circuit 200 is branched into two branches, delayed by separate delay circuits 210 and 220, and supplied to the sweep voltage generation circuits 310 and 320. Then, the sweep voltage generation circuits 310 and 320 respectively generate the sweep voltage shown in FIG. 19 and apply it to the first deflection plate 410 and the second deflection plate 420 of the streak tube.
[0078]
As a result, the substantial sweep voltage waveform is the sum of the waveforms applied to the first deflection plate 410 and the second deflection plate 420. Therefore, it is possible to substantially increase the voltage amplitude and extend the pulse width, and the selection range of the device for generating the sweep voltage is expanded. There are advantages and disadvantages depending on the pulse generation method, and there are voltage amplitudes but narrow pulse widths, and voltage amplitudes that are small but high slew rates. The width can be further expanded.
[0079]
【The invention's effect】
According to the optical waveform measuring apparatus of the present invention, when the electron group after photoelectric conversion of incident light is swept in the time axis direction, the first deflection electrode sweeps with the voltage of the first harmonic signal, and then the second Since the deflection electrode sweeps with the voltage of the nth harmonic signal synchronized with the first harmonic signal, the movement of the electron group is the voltage of the combined wave signal of the first harmonic signal and the nth harmonic signal. It will be the same movement as it was swept in. Since the slope of the synthesized wave signal is steeper than that of the first-order harmonic signal, the electron group can be shaken more in the time axis direction, and high time resolution can be obtained. Further, unlike the prior art, there is no influence on temperature rise and phase drift due to heat in the tube. As a result, it is possible to measure the change in light intensity with higher accuracy so that heat that permanently damages the tube is not generated.
[0080]
Further, when the application means for applying the sweep voltage to the first and second deflection electrodes has a resonance circuit configuration including the first and second deflection electrodes, a traveling wave type is used for the deflection electrode. Compared to the case, a higher voltage gain can be obtained. In addition, when using at a fixed frequency, a high slew rate can be obtained with less power by using a resonant circuit.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a streak camera according to a first embodiment.
FIG. 2 is a configuration diagram of a resonance circuit.
FIG. 3 is a waveform diagram of a fundamental wave and a third harmonic.
FIG. 4 is a diagram illustrating waveforms of a fundamental wave and a synthesized wave and an average inclination of the waveforms.
FIG. 5 is a waveform diagram of a sweep voltage.
FIG. 6 is a configuration diagram of a streak camera according to a second embodiment.
FIG. 7 is a configuration diagram of a streak camera according to a third embodiment.
FIG. 8 is a configuration diagram of a streak camera according to a fourth embodiment.
FIG. 9 is a configuration diagram of a streak camera according to a fifth embodiment.
FIG. 10 is a configuration diagram of a streak camera according to a sixth embodiment.
FIG. 11 is a waveform diagram of a third harmonic (third harmonic antiphase signal) obtained by inverting the fundamental wave and the third harmonic.
FIG. 12 is a diagram showing a waveform of a composite wave and an average slope of the waveform.
FIG. 13 is a waveform diagram showing the integrated linearity of a synthesized wave.
FIG. 14 is a diagram showing a differential waveform of a composite wave.
FIG. 15 is a diagram illustrating a waveform of a fundamental wave and an average slope of the waveform.
FIG. 16 is a waveform diagram showing integral linearity of a fundamental wave.
FIG. 17 is a diagram showing a differential waveform of a fundamental wave.
FIG. 18 is a configuration diagram of a streak camera according to another embodiment (single sweep).
FIG. 19 is a waveform diagram showing synthesis of a ramp voltage waveform.
[Explanation of symbols]
10, 50, 60, 80, 90, 100 ... streak camera, 12, 12a ... high repetition pulse laser, 14 ... first deflection plate, 16 ... second deflection plate, 18 ... streak tube, 20, 22 ... synthesizer, 32, 34 ... matching circuit, 52 ... third harmonic generator, 62, 64 ... phase comparator, 66, 68 ... loop filter, 70, 72 ... voltage controlled phase shifter, 82 ... half mirror, 84 ... photodetector, 86, 88 ... band pass filter, 92, 94 ... voltage controlled oscillator, 102 ... phase inverter

Claims (10)

In an optical waveform measuring device that measures the waveform by sweeping the electron group after photoelectric conversion of incident light on the photoelectric surface in the time axis direction,
A first deflection electrode disposed in a vacuum tube having the photocathode, wherein a pair of flat plate electrodes are vertically separated in a plane parallel state for a predetermined interval, and sweeps the electron group in a time axis direction;
In the vacuum tube having the photocathode, disposed behind the first deflecting electrode along the incident optical axis, a pair of flat plate electrodes are vertically separated from each other in a plane-parallel state by a predetermined distance, A second deflection electrode that sweeps the electron group in the time axis direction;
Output means for outputting a first harmonic signal synchronized with the incident light, and an nth harmonic signal (n is an order of 1 or more) having a frequency n times synchronized with the first harmonic signal;
An optical waveform measuring apparatus comprising: application means for applying the first-order harmonic signal to the first deflection electrode and applying the n-order harmonic signal to the second deflection electrode. In addition to the first and second deflection electrodes, one or more deflection electrodes arranged along the traveling direction of the electron group from the photocathode,
The output means outputs the harmonic signal of an arbitrary multiple in synchronization with the first harmonic signal by the number of the one or more deflection electrodes, and the output harmonic signal is passed through the applying means. The optical waveform measuring apparatus according to claim 1, wherein the optical waveform measuring apparatus is applied to the one or more deflection electrodes. 3. The optical waveform measuring apparatus according to claim 1, wherein the applying unit forms a resonance circuit configuration including the first and second deflection electrodes. The phase of each of the first harmonic signal applied to the first deflection electrode and the nth harmonic signal applied to the second deflection electrode is detected so that the detected phase becomes constant. The optical waveform measuring apparatus according to claim 3, further comprising phase control means for controlling phases of the first-order harmonic signal and the n-th-order harmonic signal. In the application means, the phase difference between the first harmonic signal applied to the first deflection electrode from the application means and the first harmonic signal input to the application means is constant or zero. The phase of the input first harmonic signal is controlled, and the nth harmonic signal applied from the applying means to the second deflection electrode and the nth harmonic signal input to the applying means 5. The optical waveform measuring apparatus according to claim 4, further comprising phase control means for controlling the phase of the nth harmonic signal input to the applying means so that the phase difference is constant or zero. A primary having a frequency such that the phase difference between the first harmonic signal applied to the first deflection electrode from the applying means and the first harmonic signal input to the applying means is constant or zero. A harmonic signal is oscillated and output to the applying means, and an n-order harmonic signal applied from the applying means to the second deflection electrode and an n-order harmonic signal input to the applying means 5. The optical waveform measuring apparatus according to claim 4, further comprising an oscillating unit that oscillates an n-order harmonic signal having a frequency such that the phase difference is constant or zero and outputs the signal to the applying unit. The phase of the nth-order harmonic signal applied to the second deflection electrode via the applying means is reversed, and the nth-order harmonic signal and the first-order harmonic signal that are reversed in phase are synthesized. In this case, the composite wave further comprises phase inversion means for adjusting the amplitude of the nth-order harmonic signal having the opposite phase so that the average slope corresponding to the sweep range becomes as large as possible. The optical waveform measuring device according to claim 4. 7. The optical waveform measuring apparatus according to claim 1, further comprising an emitting unit that emits the incident light in synchronization with the first harmonic signal. In an optical waveform measuring apparatus for measuring a waveform by sweeping an electron group after photoelectric conversion of incident light on a photoelectric surface in a time axis direction,
A first deflection electrode disposed in a vacuum tube having the photocathode, wherein a pair of flat plate electrodes are vertically separated in a plane parallel state for a predetermined interval, and sweeps the electron group in a time axis direction;
In the vacuum tube having the photocathode, disposed behind the first deflecting electrode along the incident optical axis, a pair of flat plate electrodes are vertically separated from each other in a plane-parallel state by a predetermined distance, A second deflection electrode that sweeps the electron group in the time axis direction;
Branching means for branching the incident light, making one branched light incident on the photocathode, and outputting the other branched light to the conversion means;
Extraction means for extracting a first-order harmonic signal and an n- order harmonic signal having an n-fold frequency (where n is an order of 1 or more) from the electrical signal converted by the conversion means;
An optical waveform measuring apparatus comprising: application means for applying the first-order harmonic signal to the first deflection electrode and applying the n-order harmonic signal to the second deflection electrode. The optical waveform measuring apparatus according to claim 9, further comprising emission means for emitting light incident on the branching means.

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