JP2609528B2 - Photon correlation measurement device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photon correlation measuring device for measuring time correlation and position correlation of photons.

[Conventional technology]

2. Description of the Related Art Conventionally, there has been known a photon-to-photon phase measuring apparatus that detects a light to be measured as a photon and measures the time phase and the spatial phase of photons.

FIG. 6 is a principle diagram of the photon correlation measurement. Referring to FIG. 6, the photons are split by the translucent mirror 71 and enter the detectors 72 and 73. By changing the time parameters in the detectors 72 and 73, the time correlation of the photons is measured by the correlator 74. The detectors 72 and 73 are photomultiplier tubes or semiconductor detectors.

In FIG. 6, assuming that the distances from the translucent mirror 71 to the detectors 72 and 73 are l ₁ and l ₂ , respectively, the time difference τ reaching the detectors 72 and 73 is τ = (l ₁ −l ₂ ) / c (1) By measuring the simultaneous detection probabilities in the detectors 72 and 73, the time correlation of photons separated by the time τ can be measured.

FIG. 7 is a block diagram of an apparatus for performing time correlation measurement using one detector, that is, a photomultiplier tube 80. Photons that have passed through a neutral density filter 82 and a pinhole 81 are detected by the photomultiplier tube detector. The detection is performed at 80, the signal line after the detection is divided, and one is delayed, and the time correlation can be obtained by the correlator 83.

Further, FIG. 8 shows a structure similar to that shown in FIG. 6, in which the detector 73 is shifted from the detector 72 by a distance d so that the spatial correlation of points spatially separated by a distance d can be measured by a correlator.
74.

[Problems to be solved by the invention]

By the way, in the conventional correlation measuring apparatus as described above, photons to be correlated are directly or temporally sequentially incident on the detectors 72 and 73 or the detector 80. To get the correlation of
Detector 72, 73 or Detector 80, Correlator 74 or Correlator
83 needed to respond fast and have good time resolution.
However, since a photomultiplier tube, a semiconductor detector, etc. are used for the detectors 72, 73 or 80, the response speed cannot be reduced to 10 picoseconds or less at this time. There is a limit to the high-speed response of the circuits constituting the total 83.

Therefore, the conventional correlation measuring apparatus has a problem that there is a limit in obtaining a time correlation of a short time difference and a spatial correlation of a short distance with high time resolution.

SUMMARY OF THE INVENTION An object of the present invention is to provide a photon correlation measurement apparatus capable of obtaining a time correlation of a short time difference and a spatial phase between short distances with high resolution.

A further object of the present invention is to provide a photon correlation measuring apparatus capable of freely obtaining a desired type of correlation.

[Means for solving the problem]

The present invention analyzes a sweeping means for sweeping photons, a fluorescent screen on which the swept photons are incident, an imaging means for imaging an increase in streaks observed on the fluorescent screen, and a streak image captured by the imaging means. Correlation means for obtaining a correlation, wherein the sweeping means, the fluorescent screen, and the measuring means of the imaging means are single photons, and the fluorescent screen has a bright spot corresponding to each photon. A streak image is obtained, and the imaging unit captures a streak image of a luminescent spot corresponding to each such photon, and the correlation unit includes:
Position detecting means for obtaining the position of each bright point from a streak image of a bright point corresponding to each photon, and correlation calculating means for performing a correlation operation based on positional information of each bright point detected by the position detecting means. An object of the present invention is to improve the above-mentioned problems of the related art by using a photon correlation measurement apparatus provided with the apparatus.

[Action]

According to the present invention, photons which are incident sequentially in time are swept by the sweeping means and are incident on the phosphor screen. At this time, photons are time-space converted on the phosphor screen and observed as streak images. This streak image is picked up by the image pickup means and analyzed by the correlation means to obtain a correlation.
In the present invention, since the correlation is obtained after spatial conversion into a streak image, even if the response speed of the imaging means and the correlation means is not so fast, the time correlation of the short time difference and the spatial correlation between the short distances are enhanced. It can be measured with resolution.

〔Example〕

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

FIG. 1 is a configuration diagram of an embodiment of an elementary particle correlation measuring apparatus (that is, a photon correlation measuring apparatus) according to the present invention.

This elementary particle correlation measuring apparatus (that is, a photon correlation measuring apparatus) includes a member 11 having an opening 10 for guiding elementary particles as photons, and elementary particles passing through the opening 10 and passing through the imaging lens system 50. An elementary particle-electron conversion surface 12, an elementary particle image (photon image) from the elementary particle-electron conversion surface 12, that is, an acceleration electrode 13 for accelerating electrons, a focusing electrode 14 for focusing the accelerated elementary particle image, A deflector 15 for sweeping the particle image, an electron multiplier 16 for multiplying the swept elementary particle image, and a fluorescent light for receiving the elementary particle image sufficiently multiplied by the electron multiplier 16 and converting it into light. Light surface
17 and the increase of the elementary particles converted into light on the fluorescent screen 17 are detected by a photodetector 19.
And a correlator 20 for performing an analysis process on the elementary particle image picked up by the photodetector 19.

The deflector 15 generates an electric field according to an applied voltage, and the electron multiplier 16 is formed of a microchannel plate.

In addition, the elementary particle-electron conversion surface 12, the acceleration electrode 13, the focusing electrode 1
4, the deflector 15, the electron multiplier 16, and the fluorescent screen 17 are high gain and high
A streak camera capable of picosecond time-resolved measurement of the phenomenon of a single photon region by S / N is configured, for example, an SIT camera is used as the photodetector 19, and an image processing device is used as the correlator 20. Can be

In addition, since the measurement target of the conventional streak camera is generally in a range where the light amount is large and the light can be regarded as an analog amount,
The analysis processing of the streak image obtained on the fluorescent screen 17 is mainly performed by accumulating the streak image in, for example, a frame memory, providing a predetermined window, obtaining and displaying the intensity distribution in the window, and measuring the analog distribution to be measured. For example, the waveform of a signal was analyzed.

On the other hand, the measurement target of the streak camera of the elementary particle correlation measurement apparatus of the present embodiment is a single elementary particle,
That is, it is a photon, which is a digital quantity. As a result, a streak image of a bright spot corresponding to each of the converted electrons is obtained on the fluorescent screen 17, and after such a streak image is picked up by the photodetector 19, the bright spot is correlated by the correlator 20. And the correlation operation is performed, and its function is significantly different from the function of the above-mentioned general streak camera.

In the elementary correlation measuring apparatus having such a configuration, when a photon passes through the aperture 10 and forms an image on the elementary particle-electron conversion surface 12 by the imaging lens system 50, electrons are emitted from the elementary particle-electron conversion surface 12, The light enters the deflector 15 via the acceleration electrode 13 and the focusing electrode 14. The electrons swept in a predetermined direction by the deflector 15 are multiplied by an electron multiplier 16 and converted into light by a fluorescent screen 17 and input to a photodetector 19 via an output lens system 18 and imaged as a streak image. Is done.

FIG. 2A is a diagram showing a streak image captured in this manner, and FIG. 2B is a diagram showing an intensity distribution of the streak image.

In FIGS. 2 (a) and 2 (b), the horizontal axis is the sweep direction, and in this example, the streak image is one-dimensional, so that the photodetector 19 has an SI as a two-dimensional detector.
It is not necessary to use a T camera, and a one-dimensional detector such as a photodiode array may be used. Each bright spot of the streak image corresponds to one elementary particle image, that is, an electron, and the streak image is analyzed by the correlator 20 to determine the time position of each elementary particle image, thereby obtaining the correlation.

More specifically, the correlation system 20 stores the intensity distribution of the streak image, that is, the luminance distribution (see FIG. 2 (b)) as shown in FIG. 2 (a) in a frame memory (not shown). First, a position detection process such as a peak detection process, a luminance centroid detection process, or a luminance midpoint detection process is performed. The luminance peak detection processing detects a pixel having the highest luminance from the luminance distribution stored in the frame memory and sets this as the position of a luminescent spot.
The luminance of each pixel constituting a certain bright spot is m _i , and the position of each pixel is r
Let _i be the center of gravity r _α, that is, Is the position of the bright spot, and the center of gravity calculation of the equation (1) is performed for each bright spot. Further, the midpoint detection processing binarizes the luminance distribution, detects the horizontal and vertical widths of a certain luminescent point, and determines the coordinates of the midpoint of these horizontal and vertical widths as the position of the luminescent point. Is what you do. There are various types of position detection processing other than those described above.
Since the size is larger than the size of one pixel, there is no great difference in the detected luminance by any method.

The position information of each bright spot detected in this way is
Recorded in a storage device (not shown) in the storage device 20. It is assumed that the storage device records position information for each streak image obtained by one sweep by the deflector 15.

Next, the correlator 20 performs a correlation calculation process based on the recorded position information of each bright spot. As the correlation operation processing,
A method of measuring the correlation by obtaining an interval distribution between elementary element images corresponding to each bright spot, that is, an arrival time interval distribution of elementary particle images, or a probability distribution of the number of elementary particle images observed within a predetermined time The correlation is measured by obtaining the following.

In the correlation calculation process of measuring the correlation by determining the inter-arrival time distribution of particles image is particle image observed at the time t _i + tau separated by time intervals tau when particles image is observed at time t _i The probability distribution P (τ) relating to the event to be performed is obtained as an interval distribution.

In the example of FIG. 2A, when the positional information of each bright spot is x ₁ , x ₂ ,..., X _n , y _{i, j} , that is, y _{i, j} = x _i− x _j (1 ≦ j <i ≦ n)... (2) paying attention to the time interval τ, and is obtained by calculating the interval y _{i, j} between position information.

By the way, a step-like voltage having a period T as shown in FIG. 3A is applied to the deflector 15 (note that the inclination is not limited to a periodic step-like one as long as the inclination is constant), and electrons are emitted. When a single sweep is performed in the vertical direction, electrons actually incident on the fluorescent screen 17 and observed as a streak image are limited to those within a finite observation field of view t.

On the other hand, the probability distribution P (tau) is an event that particles image is observed at a time t _i + tau when particles image at time t _i = 0 is observed, is based on the time t _i = 0 Therefore, as shown in FIG. 3 (b), when the observation field of view t is finite and the observation time t _i ≠ 0 of the elementary particle image observed immediately before is used as a reference, the probability distribution P ( τ) is modulated so that shorter τs are more frequently observed than longer τs. In other words, the observation time of the previous elementary particle image is
It is difficult to observe if t _i is not t _i <t / 2 with respect to the center t / 2 of the observation field of view t (3), but those with a short τ are observed at the observation time t _i of the previous elementary particle image The position is not limited to the position in the visual field t.

To prevent modulation of such probability distribution P (τ), t / 2 ≧ t i (= x i) t / 2 ≧ τ (= y i, j) satisfying the condition of ... (4) only Is evaluated as data.
If the measurement is performed under the condition of equation (4), a finite observation field of view t
However, the obtained probability distribution P (τ) gives a correlation that is not affected by the observation field of view t.

As shown in FIG. 3 (a), when a step-like voltage is applied to the deflector 15 and measurement is performed in a single sweep, the observation field t is 1 nanosecond, and there are 512 observation points in the observation field t. If so, only correlation data with a time interval of about 20 picoseconds to 500 picoseconds can be obtained. However, as shown in FIG. 4, a sinusoidal voltage is applied to the deflector 15 to perform a synchro scan operation in the vertical direction. And perform a double sweep operation to gradually shift the streak image in the horizontal direction, and use both the falling and rising straight lines of the sinusoidal voltage as the observation field of view. Can be measured. Even in this case, it is necessary to evaluate only data satisfying the condition of equation (4) as data.

A second-order intensity correlation <I (t) · I (t + τ)> is obtained from the probability distribution P (τ) obtained as described above. Further, when photoelectrons are observed at time T,
_{t + τ 1, t + τ} 2, ......, t + τ isolated P simultaneously photoelectrons are observed also in the _{n (τ 1, τ 2,} ......, τ n) order of the correlation i.e. n-order intensity correlation by <I (t)・ I (t +
τ ₁ ) · I (t + τ ₂ )... I (t + τ _n )> can be obtained.

Next, in the correlation calculation processing for measuring the correlation by obtaining the probability distribution of the number of elementary particle images observed within a predetermined time, the probability distribution P in which n elementary particle images are observed within a predetermined observation time τ The correlation is obtained based on (n; τ).

This probability distribution P (n; τ) sets an observation window corresponding to the observation time τ on the frame memory of the correlator 20;
It is obtained by counting the number n of elementary particle images in this observation window.

As described above, in this embodiment, the time-sequentially converted elementary particles are converted into elementary particle images, that is, electrons, swept by the deflector 15, and subjected to time-space conversion as a streak image on the fluorescent screen 17. The streak image is converted to a correlator 20 through a photodetector 19.
And the correlation is measured by the photodetector 19,
Even if the response speed of the correlator 20 is not as fast as the difference, the time correlation of the short-time difference can be measured with high time resolution. That is, the time difference for performing the time correlation is determined by the waveform of the applied voltage applied to the deflector 15, the sweep speed, and the observation field of view,
Since it does not depend on the time resolution of the processing system (photodetector 19, correlator 20) after the fluorescent screen 17, the time correlation of a short time difference of about sub-picosecond can be measured with high time resolution. Further, since a spatial streak image can be obtained on the fluorescent screen 17, the correlator 20 can analyze the streak image in a desired format and freely obtain a desired time correlation result. Further, although not described in detail, the opening 10 is a slit having a spatial expansion, and the length direction of the slit is defined by a deflector.
When the streak image is positioned perpendicular to the 15 sweep directions, one of the obtained streak images is a time axis and the other is a space axis, so that the correlator 20 can simultaneously observe not only between time phases but also between spatial phases.

In the above-described embodiment, the member 11 having the opening 10 is provided at the previous stage of the elementary particle-electron conversion surface 12, but if the opening is provided in the acceleration electrode 13, the member 11 becomes unnecessary, and the efficiency due to the aperture ratio of the acceleration electrode is reduced. Does not occur.

Further, referring to FIG. 1, the electron multiplier 16 is housed in the tube of the streak camera. However, as shown in FIG. Face 17
Is positioned directly, and an image intensifier 21 is provided after the fluorescent screen 17,
The output light from the fluorescent screen 17 may be multiplied by the image intensifier 21 and input to the photodetector 19 via the output lens system 18.

Also in the above embodiment, to determine the correlation of the X-rays, particle - electron conversion surface 12 Au, better to use a C _S I like, to determine the correlation of neutrons, particles - electrons Conversion surface
It is preferable to use U ₂ O ₃ , U ₃ O ₈ or the like for 12.

Further, in the above-described embodiment, the elementary particles are converted into elementary particle images by the elementary particle-electron conversion surface 12, and then swept by the deflector 15, but instead of this, an electro-optic crystal is used. The photons may be swept directly by a change in the refractive index due to the applied voltage.

Although the deflector 15 generates an electric field, the deflector 15 may generate a magnetic field.

〔The invention's effect〕

As described above, according to the present invention, a streak camera capable of picosecond time-resolved measurement is used to obtain a streak image and then calculate a correlation. Can be obtained with high resolution, and furthermore, a desired type of correlation can be freely obtained.

[Brief description of the drawings]

FIG. 1 shows an elementary particle correlation measuring apparatus according to the present invention (ie,
FIG. 2 (a) is a diagram showing an imaged streak image, FIG. 2 (b) is a diagram showing an intensity distribution of the streak image, and FIG. 3 (a). Is the deflector 15
FIG. 3 (b) shows an example of an applied voltage applied to
FIG. 4A is a view showing an observation field of view t on the fluorescent screen 17 when the applied voltage shown in FIG. 5A is applied to the deflector 15; FIG. 4 is a view showing a sinusoidal applied voltage applied to the deflector 15; FIG. 5 is a diagram showing a modification of the elementary particle correlation measuring device (that is, a photon correlation measuring device) of FIG. 1, and FIGS. 6, 7, and 8 are configuration diagrams of a conventional elementary particle correlation measuring device, respectively. It is. 10 aperture, 12 elementary-electron conversion surface, 15 deflector, 17 phosphor screen, 19 photodetector, 20 correlator

Continuation of the front page (56) References JP-A-59-145930 (JP, A) Tayuki, Tsujiuchi, Minami, "Optical Measurement Handbook" (Showa 56-7-25), Asakura Shoten, p. 282-289

Claims (1)

(57) [Claims] 1. A sweeping means for sweeping photons, a fluorescent surface on which the swept photons are incident, an imaging means for capturing a streak image observed on the fluorescent surface, and a streak image captured by the imaging means are analyzed. A correlation means for obtaining a correlation, wherein the sweeping means, the fluorescent screen and the imaging means measure a single photon, and the fluorescent screen has a bright spot corresponding to each photon. A streak image is obtained, and the imaging means captures a streak image of a bright spot corresponding to each such photon.
The image processing apparatus includes: position detecting means for obtaining a position of each bright spot from a streak image of a bright point corresponding to each photon; and correlation calculating means for performing a correlation operation based on positional information of each bright point detected by the position detecting means. A photon correlation measurement device, comprising: