JPH083442B2 - High repeatability laser light measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention measures fluctuations in the repetition frequency of measured light itself such as laser light without being affected by jitter in a streak camera circuit or a trigger system. The present invention relates to a highly repetitive laser light measuring device suitable for.

[Conventional technology]

By converting incident light into photoelectrons and sweeping at high speed,
The streak camera, which measures the time-varying incident light intensity as a change in brightness with respect to the position on the screen, can obtain time resolution up to the picosecond order, and is therefore particularly used for analysis of ultrafast light phenomena. Among them, the double-sweep streak camera has a vertical sweep that is repeatedly performed in synchronism with an incident pulse, and a horizontal sweep that is slower than the vertical sweep and has two time axes. It is possible to measure the pulse width, light intensity, phase fluctuation, etc. over a time sufficiently longer than the repetition period.

A conventional double-sweep streak camera will be described with reference to FIGS.

FIG. 5 is a schematic diagram of a double-sweep streak camera, and FIG. 6 is a diagram showing a sweep trajectory when a vertical sweep and a horizontal sweep are simultaneously performed.

In the figure, 1 is a streak tube, 2 is a lens, 3 is a photocathode,
4 is a mesh-shaped acceleration electrode, 5 is an input slit, 6 is a deflection electrode, 7 is a microchannel plate (MCP), 8 is a fluorescent surface, 9 is an imaging device, 10 is an analysis device, 11 is a monitor,
12 is a vertical sweep signal generator, 13 is a horizontal sweep signal generator, 15
Is a beam splitter, and 16 is a photodetector.

In the figure, light to be measured such as laser light is incident on the photoelectric surface 3 of the streak tube 1 through the lens 2 of the incident optical system to form an optical image of the input slit 5. The photocathode 3 is a surface that converts light into photoelectrons. The optical image is converted into an electron image here, and the electrons accelerated by the mesh-shaped accelerating electrode 4 and passing through the input slit are microchannel plates (MCP).
7, there are two pairs of deflection electrodes in the middle,
As shown in FIG. 6, horizontal and vertical sweep voltages are applied by the trigger signal. In this case, the vertical direction is swept at a high speed, while the horizontal direction is swept at a slow speed to draw a sweep locus as shown in the figure, and the electron image reaches MCP7. The sweep timing must be adjusted to the timing at which the electron image passes through the deflecting plate.A part of the incident light or excitation light is split by the beam splitter 15, and the photodetector 16 receives it via the mirror, and the vertical sweep is performed. It is led to the signal generator 12 and used as a trigger. On the other hand, the horizontal sweep signal generator also sweeps in the horizontal direction. The electron image multiplied by MCP7 is converted into an optical image again on the light receiving surface. This image is called a streak image and has luminance having time information in the horizontal direction in addition to the vertical direction.
The optical image of the light receiving surface 8 is picked up by the image pickup device 9,
The pulse width, light intensity, phase fluctuation, etc. of the light phenomenon that repeats at high speed in 10 are measured over a time period longer than the repetition period, and the observed waveform is immediately displayed on the cathode ray tube of the monitor 11.

[Problems to be solved by the invention]

However, since a normal trigger signal for controlling the deflection electrode uses a light beam obtained by optically converting a light beam that is a part of the measured light, the sweep frequency of the streak camera is the pulse repetition frequency of the laser light that is the measured light. Therefore, the laser light is observed following the above, and the fluctuation of the repetition frequency of the laser light itself cannot be observed. Further, when the pulse repetition frequency of the laser beam changes abruptly, the streak camera circuit cannot follow the change, and as a result, observation including jitter in the streak camera circuit and the trigger system is performed. Further, when there is a change in intensity of the laser light itself, there is a problem that this change causes jitter in the streak camera circuit and the trigger system.

The present invention has been made in order to solve the above problems, the fluctuation of the repetition frequency of the laser light itself can be observed,
It is an object of the present invention to provide a jitter measuring apparatus for highly repetitive pulsed light that can be accurately measured without being affected by changes in the intensity of laser light.

[Means for solving problems]

Therefore, the high repetition laser light measuring device of the present invention,
In a high-repetition laser light measuring device using a double-sweep streak camera, a high-frequency signal generator that is independent of the laser light to be measured is provided, and the frequency is substantially the same as the repetition frequency of the laser light to be measured from the high-frequency signal generator, and It is characterized in that one axis of the double-sweep streak camera is swept with a steady high-frequency signal independent of the laser light to be measured.

[Action]

The high-repetition laser light measuring device of the present invention performs the sweep of the double-sweep streak camera at a steady high frequency that is substantially the same as the pulse repetition frequency of the measurement laser light that is independent of the laser light to be measured. It is possible to observe fluctuations in the repetitive frequency and to accurately measure jitter without being affected by changes in the intensity of laser light.

〔Example〕

 Hereinafter, embodiments will be described with reference to the drawings.

FIG. 1 is a basic configuration diagram of a double streak camera of the present invention. In the figure, the same numbers as those in FIG. 5 are given the same numbers 1 to 13, and the description thereof is omitted here.

The apparatus of FIG. 1 differs from the apparatus of FIG. 5 in that the sweep signal for controlling the deflection electrode of the double-swept streak tube 1 is
In the conventional example shown in the drawing, a part of the laser light which is the light to be measured is branched and directly used, whereas in the apparatus of the present invention shown in FIG. 1, a high frequency wave independent of the laser light to be measured is provided. A signal generator 14 is provided, and the deflection electrode 6 is controlled by the output of the high frequency signal generator 14 to perform sweeping.

The operation of the apparatus of the present invention shown in FIG. 1 is different only in the formation of the above-mentioned sweep signal, and the other operations are the same as those of the conventional apparatus shown in FIG.

FIG. 2 shows an observation image as a result of the measurement in FIG. 1, and observation images of two time axes t and T in which time information is incorporated in the vertical direction and the horizontal direction are obtained.

Next, the operation of the highly repetitive pulsed light jitter measuring apparatus of the present invention will be analyzed with reference to the observation image of FIG. In FIG. 2, the vertical sweep is performed at a constant frequency f ₀ , and the horizontal sweep is performed at a much slower speed. The broken line is the swept trajectory, and the solid circle is the observed streak image.

Now, assume that the repetition frequency of the laser light at T ₀ is f _0, and it becomes f ₁ at T ₀ + ΔT. If the repetition frequency changes at a constant rate during this period, f = f ₀ + at (a: constant) Generally, a laser emits pulsed light when the condition of cos 2πft = 1 is satisfied.

_{cos2πft = cos2π (f 0 + at} ) t = cos2πf 0 (t + at 2 / f 0) where streak camera is swept by f _0, a second
In the figure, at T ₀ , light emission is observed at the position of t ₀ . After that, since the frequency of the laser light changes at a constant rate, the phase of the emission point with respect to the swept trajectory waveform gradually shifts,
An image as shown is observed. Letting ΔT be the time difference from the uppermost end position to the lowermost end position of this observed image and Δt be the half cycle of the swept trajectory waveform, a ΔT ² / f ₀ = Δt becomes a = f ₀ · Δt / ΔT ² .

Therefore, f ₁ = f ₀ + (f ₀ · Δt / ΔT ² ) ΔT f ₁ −f ₀ = f ₀ · Δt / ΔT [= Δf].

Therefore, in this equation, f ₀ = 100MHz, Δt = 100ps, ΔT = 10m
If s, Δf = 1 Hz is obtained.

Therefore, the pulse repetition frequency gradually increases to 1H within 10ms.
It can be understood that the measurement can be sufficiently performed even if it changes.

In the above example, Δf / f ₀ = 10 ⁻⁸ , and it is shown that sufficient measurement can be performed even with such a change in the basic frequency within 10 ms.

The principle of the present invention has been described above. Specific means for obtaining a high-frequency signal for sweeping a double-sweep streak camera independently of the laser light to be measured is shown in FIGS. 3 and 4 below. And explain.

In FIG. 3, reference numerals 1 to 14 are the same as those in FIG. 1 and perform the same function, and the operation as the entire double-sweep streak camera is the same, so the description of this point will be omitted. Matters relating to the formation of the high frequency signal for the sweep will be described.

In the figure, 15 is a beam splitter, 16 is a fast response photodetector, 17 is a frequency counter, 18 is a control device, 19 is a gate device, and 20 is a signal from a mode rocker.

In the figure, a frequency counter 17 selectively measures the frequency of the signal obtained by photoelectrically converting a part of the laser light to be measured and photoelectrically converting it by the high-speed response photodetector 16 or the frequency of the electric signal 20 obtained from the mode locker. , Convert to voltage.
The streak camera sweep signal is generated from the high frequency signal generator 14 at a frequency corresponding to this voltage. A gate circuit 19 is provided therebetween, and the voltage from the frequency counter 17 is applied to the high frequency signal generator 14 only when the pulse signal from the controller 18 arrives. The pulse signal interval from the controller 18 is sufficiently longer than the measurement time, and the streak camera sweep signal frequency from the high frequency signal generator 14 is held between the pulse signals. In this way, it is possible to obtain a sweeping high-frequency signal that selectively corresponds to the repetition pulse frequency of the laser light to be measured or the frequency of the signal from the mode rocker and is independent of those signals.

 Next, the embodiment shown in FIG. 4 will be described.

FIG. 4 is a modification of the embodiment of FIG. 3, in which the repetitive pulse frequency of the laser light to be measured is directly input to the gate circuit 19. Then, a pulse signal is applied from the control device 18 to the gate circuit 19 at an interval sufficiently longer than the observation time, and the gate circuit 19 passes the electric signal only when the pulse signal arrives. At this time, the pulse signal is simultaneously applied to the high frequency signal generator 14, and the streak camera sweep frequency from the high frequency signal generator is locked to the frequency of the electric signal input to the gate signal 19. By recording the output signal of the counter 17 in FIG. 3 or the output signal frequency from the high frequency signal generator in FIG. 4 at the same time, the entire streak image and the jitter state of the laser can be clarified. Become.

The overall operation of this embodiment is similar to that of the embodiment shown in FIGS. 1 and 3.

〔The invention's effect〕

As described above, according to the present invention, it is possible to observe the fluctuation of the repetition frequency of the laser light to be measured itself, and the jitter of the streak camera circuit or the trigger system even when the repetition pulse frequency of the laser light suddenly changes. It is possible to make observations with the removed. Further, even if the intensity of the laser light itself changes, it is possible to make observations without any influence. And, the time resolution of the streak camera was set to 10 ps, and with respect to the laser beam of 100 MHz, the conventional apparatus could only observe a fluctuation of up to about 10 ⁻³ , but in the apparatus of the present invention, a fluctuation of about 10 ^−8. There is an effect that can be measured with high accuracy.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram of the present invention, FIG. 2 is an observation diagram obtained by the apparatus of the present invention, FIGS. 3 and 4 are diagrams showing respective embodiments of the present invention, and FIG. 5 is a conventional example. FIG. 6 and FIG. 6 are diagrams showing the double sweep locus. 1 ... streak tube, 2 ... lens, 3 ... photocathode, 4
...... Mesh-shaped accelerating electrode, 5 …… Input slit, 6 ……
Deflection electrode, 7 ... Micro channel plate (MC
P), 8 ... Fluorescent surface, 9 ... Imaging device, 10 ... Analysis device, 11 ... Monitor, 12 ... Vertical sweep signal generator, 13 ...
… Horizontal sweep signal generator, 14… High frequency generator, 15 is beam splitter, 16… High-speed response photodetector, 17… Frequency counter, 18… Control device, 19… Gate circuit.

Claims (3)

[Claims] 1. A high-repetition laser beam measuring apparatus using a double-sweep streak camera, wherein a high-frequency signal generator independent of the laser beam to be measured is provided, and the repetition frequency of the laser beam to be measured from the high-frequency signal generator is substantially the same. A high-repetition laser light measuring device which sweeps one axis of a double-sweep streak camera with a constant high-frequency signal independent of the laser light to be measured. 2. A high-frequency signal generator includes a counter for counting a repetition frequency signal of a laser beam to be measured or a mode-lock signal frequency, and an electric signal corresponding to a count value of the counter according to a control signal from a controller. A high-frequency signal generator that is controlled by a gate circuit to be gated, a gate circuit output, and a signal from a control device, receives a signal from the gate circuit according to a signal from the control device, and continues to generate a high-frequency signal according to the signal The high repetition laser beam measuring device according to claim 1, which comprises: 3. A high-frequency signal generator is controlled by a gate circuit that gates a laser beam to be measured or a mode-lock signal according to a control signal from the controller, and a high-frequency signal output from the gate circuit and a signal from the controller. The high repetition laser according to claim 1, further comprising: a high frequency signal generator that receives a signal from the gate circuit according to a signal from the control device and continues to generate a high frequency signal having the same frequency as the high frequency signal. Light measuring device.