JP4867003B2 - Charged particle detection method and charged particle control method using the same - Google Patents

Description

  The present invention relates to a charged particle detection method for detecting the passage and incidence of charged particles including elementary particles and ions, and a charged particle control method using the same.

  In a wide range of technical fields from basic physics to applied engineering, charged particle detection methods that detect the passage and incidence of charged particles including elementary particles and ions, as well as their passing position, trajectory, and energy are required. It has been.

  For example, in the problem of measuring neutrino mass in basic physics, the measurement of the end-point energy of electrons in tritium beta decay, which is shown as a method for directly measuring the neutrino mass, is important, and the viewpoint of directly measuring the residual neutrino Therefore, it is important to increase the resolution of energy measurement.

As a conventional charged particle detection method, a phenomenon that ionizes a medium when the charged particle enters the medium in the detector is used to electrically amplify the amount of ions and electrons generated as a result of the ionization. What is detected is common (Patent Document 1). That is, the conventional charged particle detection method uses a process in which charged particles inelastically excite the detector medium. According to such a conventional method, not only the presence and position of a charged particle is detected, but also its energy is numerically detected by detecting the moving speed or time of the charged particle and the amount of ions and electrons generated as a result of ionization. Can be detected.
JP-A-6-34759 (Publication date: February 10, 1994) YKSemertzidis et al. `` Electro-optical detection of charged particles '' Nucl. Instrum. Meth. A452: 396-400, 2000.

  However, in the conventional charged particle detection method, it is difficult to improve the energy resolution from about 1 electron volt (eV) which is the lowest energy required for ionization in the detector.

  Further, in the above conventional charged particle detection method, since the process of electrically amplifying the ion amount after ionizing the medium in the detector includes temporal fluctuation, the time for measuring the detection time of the particles There is also a limit on the resolution. For example, about 10 ps is the limit of time resolution that is about the limit.

  Furthermore, in the conventional charged particle detection method described above, when charged particles ionize the medium, the energy and momentum of the charged particles inevitably change depending on the ionization process. Repeated measurements could not be made.

On the other hand, as a conventional technique for avoiding the problems caused by the use of such an ionization process, the charged particle energy when passing through the crystal surface is reduced by using the electro-optic effect when the charged particle enters the crystal. A measuring method is known (Non-Patent Document 1). Specifically, a short electron flux of about 10 ⁹ electrons is incident on a crystal having a Pockels effect (LiNbO ₃ ), and a change in refractive index instantaneously generated in the crystal by an electric field generated by this electron flux is expressed as follows: It is disclosed that the measurement is performed as a change in the polarization state of laser light incident on the crystal.

  Here, the electro-optic effect means an effect in which a refractive index change caused by an electric field occurs when an electric field is applied to a transparent solid or liquid, and the refractive index change is proportional to the strength of the electric field. In addition to the Pockels effect, the Kerr effect in which the change in refractive index is proportional to the square of the electric field strength is known. The electro-optic tensor that expresses the Pockels effect is a third-order tensor having the same structure as the piezoelectric constant tensor that expresses the piezoelectric effect. Therefore, the Pockels effect appears only in symmetric crystals that exhibit piezoelectricity, whereas the Kerr effect is Observed in all symmetrical materials.

  In Non-Patent Document 1, the energy of the electron bundle is successfully measured without affecting the energy of the electron bundle. According to the charged particle detection method using such an electro-optic effect, the energy and momentum of the charged particles are hardly changed unlike the ionization process, so that the same detected by each sensor element at different positions. By measuring the charged particle detection time difference, that is, the moving time of the charged particles (time of flight), the speed or energy of the charged particles can be accurately detected. In the time-of-flight measurement method, the time resolution when measuring the time that charged particles pass through each sensor element determines the final energy resolution.

In practice, however, the S / N (Signal / Noise) ratio is remarkably deteriorated when measuring the change in the refractive index that occurs instantaneously in the crystal as the change in the polarization state of the laser light that is incident on the crystal. For example, it is considered that S / N is about 10 ⁻¹⁰ . Depending on the conventional charged particle detection method, it has been difficult to accurately detect, for example, a single charged particle or its energy.

  The present invention has been made in view of the above problems, and its purpose is to detect charged particles with a high S / N ratio without greatly changing the energy and momentum of the charged particles. It is to provide a detection method and a charged particle control method using the same.

  A charged particle detection method according to the present invention is a charged particle detection method for detecting charged particles by detecting a refractive index change that occurs electro-optically inside a crystal due to an electric field generated by charged particles passing outside. A light irradiation stage for irradiating light inside the crystal; a light component that is irradiated in the light irradiation stage and passes through the crystal; a light component in which an optical phase change based on the refractive index change occurs; and the refraction An optical component separation stage that separates the optical component that has not undergone an optical phase change based on a rate change; and an optical component that has undergone an optical phase change that has been separated in the separation stage. And a charged particle detection stage for detecting particles.

  The form of the charged particle in the present specification is not particularly limited, and means any charged particle such as various ion atoms and ionic molecules regardless of the size of elementary particles such as electrons and neutrinos and their atomic weight and molecular weight. ing.

  Further, as the light in the above configuration, it is preferable to use light having a specific profile and having the same phase, that is, coherent light. As such light, laser light is typical, but various kinds of light can be used as long as the phase changes according to the change in the refractive index in the substance.

  According to the above configuration, only when charged particles pass through the outside of the tetragonal crystal, a refractive index change that occurs electro-optically inside the tetragonal crystal occurs, while the tetragonal crystal is generated in the light irradiation stage. The optical phase of a part of the light irradiated on the inside changes due to the change in refractive index.

  Then, in the light component separation stage, the light passing through the tetragonal crystal is separated into a light component having an optical phase change and a light component having no optical phase change, and in the charged particle detection stage. A light component in which an optical phase change occurs is detected. Note that the separation of the light components in the light component separation stage does not have to be complete, and the separated at least one light component has a higher rate of optical phase change than the light before separation. What is necessary is just separation.

  According to the charged particle detection method having the above-described configuration, the refractive index change occurring inside the tetragonal crystal can be accurately captured without directly affecting the movement of the charged particle. In this state, charged particles can be detected. Therefore, it is possible to repeatedly measure the same charged particle without changing its motion state.

  According to the charged particle detection method having the above-described configuration, an optical phase change is separated from light passing through the tetragonal crystal by separating a light component that does not cause an optical phase change that becomes a detection background noise. Therefore, the charged particle can be detected with a high S / N ratio.

  Furthermore, according to the above-described configuration, in addition to the above-described effects, the charged particles are detected based on detecting the electro-optical change inside the tetragonal crystal, and thus based on the ionization phenomenon of the medium. Compared with the conventional method for detecting charged particles, faster detection of charged particles can be realized.

  Further, in the charged particle detection method according to the present invention, in the configuration described above, in the light component separation stage, by using a lens having a diffraction function, the light irradiated through the light irradiation stage and passing through the crystal is It is preferable to spatially separate a light component in which an optical phase change has occurred and a light component in which the optical phase change has not occurred.

  According to the above configuration, for example, by using a convex lens provided with a rectangular diffraction grating, light passing through a tetragonal crystal can have an optical component in which an optical phase change occurs in the focal plane of the convex lens, and optical Is spatially separated into light components that have not undergone a dynamic phase change.

  Therefore, in addition to the above-described effects, it is easy to detect a light component in which an optical phase change occurs in the charged particle detection stage. For example, a detector is provided only at a position where an optical component in which an optical phase change has occurred is separated, or an optical component in which an optical phase change has not occurred is blocked by a mask or the like so as not to be detected. Becomes easy.

  The charged particle detection method according to the present invention is a charged particle detection method for detecting charged particles by detecting a refractive index change that occurs electro-optically inside a crystal due to an electric field generated by charged particles passing outside. The crystals are a plurality of tetragonal crystals arranged at different positions, a light irradiation stage for irradiating light inside the plurality of crystals, and a light irradiation stage that is irradiated to the light irradiation stage and passes through each crystal. Separating a light component into a light component in which an optical phase change based on the refractive index change is generated and a light component in which an optical phase change based on the refractive index change is not generated, and the separation By detecting the light component in which the optical phase change based on the refractive index change of each crystal separated in stages is detected, the time information when the charged particles pass through each crystal is specified, and these Based on the information during the velocity of the charged particles, momentum, energy, and characterized by comprising a charged particle detection step of detecting at least one of spin information.

  The charged particles and the form of light and the significance of the separation of light components in the above configuration are the same as described above.

  According to the above configuration, only when charged particles pass outside each tetragonal crystal, a refractive index change that occurs electro-optically inside each tetragonal crystal occurs, while each square in the light irradiation stage. The optical phase of a part of the light irradiated to the inside of the crystal system crystal changes due to this refractive index change.

  Then, in the light component separation stage, the light passing through each tetragonal crystal is separated into a light component that has undergone optical phase change and a light component that has not undergone optical phase change. Then, the light component in which the optical phase change has occurred is detected, and the charged component in each tetragonal crystal is detected by detecting the separated light component in which the optical phase change has occurred in the charged particle detection stage. Time information when the particle passes is specified. Furthermore, at least one of the speed, momentum, and energy of the charged particles is detected based on the time information.

  According to the charged particle detection method having the above configuration, in addition to the above-described effects, the charged particle can be charged based on time information when the charged particle passes through a plurality of locations without directly affecting the movement of the charged particle. Since the velocity, momentum, and energy of the particles can be detected, these detection values can be made highly accurate with few errors.

  In the charged particle detection method according to the present invention, in the above configuration, the crystal is preferably a tetragonal crystal. Further, the tetragonal crystal is preferably a uniaxial crystal belonging to the point group 4-bar2m.

Examples of uniaxial tetragonal crystals belonging to 4-bar2m include KHP (KH ₂ PO ₄ ), DKDP (KD ₂ PO ₄ ), EKDP, and the like.

  The first advantage of adopting a uniaxial crystal belonging to 4-bar2m is that it has an xy plane that does not rotate the polarization at all in the absence of an external field, whereas the external field acting perpendicularly to this xy plane. Since the refractive index ellipsoid has a surface that turns 45 degrees, the amount of light leaking from only the phase change portion can be extracted greatly while passing through the linear polarizer and minimizing the leak light from the portion without the phase change. It is.

  The second advantage of adopting a uniaxial crystal belonging to 4-bar2m is that a crystal whose electro-optic coefficient is improved by about three orders of magnitude at a structural phase transition temperature close to room temperature is known, and such a crystal is adopted. Thus, the detection sensitivity can be improved.

  The charged particle control method according to the present invention is a charged particle control method for controlling a movement state of the charged particle using the charged particle detection method, wherein the velocity of the charged particle detected in the charged particle detection step, The control amount of the motion state of the charged particle is determined based on at least one of momentum, energy, and spin information.

  In the above configuration, determining the control amount of the motion state of the charged particle not only determines the control amount of the motion state of the charged particle itself to be detected by the charged particle detection method, but also a plurality of charged particles. (For example, generation of a charged particle beam), based on the detection result of the velocity, momentum, and energy of one of the charged particles, the control state (external) And so on).

  According to said structure, since the movement state of the said charged particle can be controlled based on the highly accurate detection result using the said charged particle detection method, movement, such as the speed of a charged particle, momentum, energy, etc. It becomes possible to control the state with high accuracy.

  According to the charged particle detection method of the present invention, charged particles can be detected with a high S / N ratio while maintaining a non-contact or non-destructive state.

  Further, according to the charged particle control method of the present invention, it is possible to control the movement state of the charged particle with high accuracy based on the detection result of the velocity, momentum, and energy of the charged particle with high accuracy.

[Embodiment 1]
Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a conceptual diagram showing a schematic configuration of a charged particle detection system 1 according to an embodiment of the present invention. As shown in the figure, the charged particle detection system 1 includes a front stage prism 11, a tetragonal crystal 12, a rear stage prism 13, a convex lens 14, a lens focal plane 15, an optical fiber bundle 16, a mask 17, and a light receiving element 18.

  The pre-stage prism 11 and the post-stage prism 13 are arranged so that the polarization directions of the pre-stage prism 11 and the post-stage prism 13 are substantially orthogonal so that the polarization direction of the post-stage prism 13 is the x-axis direction. Here, the angle formed by both polarization directions is set to about 89 degrees so that the extinction ratio of the front-stage prism 11 and the rear-stage prism 13 does not become zero.

The tetragonal crystal 12 serves as an electric field sensor, and among the uniaxial crystals having an electro-optic effect, a tetragonal crystal of a point group 4-bar2m, such as KHP (KH ₂ PO ₄ ), It consists of DKDP (KD ₂ PO ₄ ), EKDP, and the like.

The tetragonal crystal 12 is a tetragonal crystal of the point group 4-bar2m arranged so as to have a uniform refractive index in the xy plane. The tetragonal crystal 12 is preferably used in a state in which the electro-optic coefficient is increased by cooling to a temperature in the vicinity of the structural phase transition point so that the optical phase change described later becomes large. Here, DKDP (KD ₂ PO ₄ ) is adopted as the best crystal candidate. This is because the DKDP crystal has an exceptionally high electro-optic tensor and is easy to handle at a temperature just above the structural phase transition point of −64 ° C. DKDP crystals are widely available as commercial products, and large-size crystals can be obtained at low cost.
As the light receiving element 18, an arbitrary light receiving device such as a photodiode, a photomultiplier tube, or a CCD can be adopted depending on its sensitivity and characteristics.

  The flow of the charged particle detection operation of the charged particle detection system 1 in FIG. 1 is as follows.

  First, in FIG. 1, a laser beam 10 having a cross-sectional light intensity having a standard distribution is incident on the pre-stage prism 11 along the z-axis direction while scanning in the xy plane. The wavelength of the laser beam 10 is preferably set according to the wavelength dependence of the electro-optic coefficient in the tetragonal crystal selected as the tetragonal crystal 12. For example, when DKDP is adopted as the tetragonal crystal 12, the wavelength of the laser light 10 is preferably about 546 nm.

  When the laser beam 10 passes through the front stage prism 11, the laser beam 10 is linearly polarized in the y-axis direction. The laser beam 10 that is linearly polarized in the y-axis direction is incident on the tetragonal crystal 12. As described above, the tetragonal crystal 12 is arranged so as to have a uniform refractive index in the xy plane. Therefore, in the state where the charged particles are not incident on the tetragonal crystal 12, the tetragonal crystal 12 is present. The polarization state of the laser beam 10 emitted from the system crystal 12 is uniform regardless of the scanning position of the laser beam 10.

  On the other hand, when charged particles enter the vicinity of the tetragonal crystal 12 from an arbitrary direction, an electro-optic effect is generated due to an electric field in the crystal caused by the movement of the charged particles. As a result, the two principal refractive indexes consisting of the ordinary ray refractive index and the extraordinary ray refractive index in the tetragonal crystal 12 partially change, and the refractive index in the xy plane of the tetragonal crystal 12 is It is not uniform. For example, as shown in FIG. 2, when an electric field generated by charged particles moving along the x-axis is applied to the z-axis direction of the tetragonal crystal 12, the x-axis direction and the y-axis direction of the tetragonal crystal 12 are A difference in refractive index is generated between them, and a refractive index ellipsoid rotated 45 degrees around the z axis is embedded.

  In the tetragonal crystal 12 in which such a refractive index change has occurred, the laser beam 10 incident in the vicinity of the charged particle passing therethrough is rotated in its polarization direction by the occurrence of an optical phase difference, while from the charged particle. Since the laser beam 10 incident on a distant position is not affected by the electric field generated by the charged particles, an optical phase difference does not occur and its polarization direction does not rotate. In addition, about how much phase difference changes with passage of a charged particle, description is described at the end of this specification.

  Then, among the laser light 10 emitted from the tetragonal crystal 12, the laser light 10 that passes through the post-stage prism 13 passes through the vicinity of the charged particles in the tetragonal crystal 12 and whose polarization direction is rotated. It is.

  That is, the laser beam 10 emitted from the vicinity of the charged particle passage position in the tetragonal crystal 12 includes a light component whose polarization direction is rotated and a leakage light component whose rotation direction is not rotated. 13 is substantially separated. In this way, the mechanism or principle for separating different polarization components by the substantially orthogonal polarizer (front-stage prism 11) and analyzer (rear-stage prism 13) is the same as that of a liquid crystal panel such as the TN system.

  Actually, there is a slight amount of leaked light from other than the vicinity of the locus of the charged particles from the rear stage prism. That is, since the extinction ratio of the front-stage prism 11 and the rear-stage prism 13 is not zero, the laser beam 10 whose polarization direction has not changed by passing through a position away from the charged particle in the tetragonal crystal 12 is also slightly “ It passes through the rear stage prism 13 as “leakage light”.

  The charged particle detection system 1 positively uses this leakage light, and causes the light component whose polarization direction is rotated and the leakage light component whose polarization direction is not rotated to interfere with each other by the convex lens 14. Are spatially separated. Specifically, the charged particle detection system 1 transmits the light passing through the rear prism 13 through a rectangular slit as shown in FIG. 3A in order to separate the leaked light other than the vicinity of the locus of the charged particles. The diffracted light is diffracted by the convex lens 14, and the Fourier transform function in the focal plane is used. Here, the rectangular slit means that the portion where the influence of the electric field remains in the crystal, that is, the shape of the phase change portion is represented by a rectangle as an approximation in the crystal. The Fourier transform function in the focal plane is used.

  FIG. 3B shows an image (light intensity distribution) formed on the lens focal plane 15 after diffracting transmitted light including a rectangular phase change as shown in FIG. 3A by the convex lens 14. Is simulated. That is, FIGS. 3A and 3B analytically show the characteristics of a Fourier transform image of a rectangular aperture qualitatively.

  The convex lens 14 transmits the amplitude of the input light to a lens focal plane 15 that is separated by a predetermined focal length. It is preferable that the diameter of the convex lens 14 is sufficiently large compared to the size of the entire diffraction pattern. This is because it is inconvenient if the lens edge itself is an opening, and therefore it is preferable to make the laser diameter sufficiently smaller than the lens diameter.

  Of the light passing through the rear prism 13, the laser light 10 that has passed through the vicinity of the charged particles in the tetragonal crystal 12 and whose polarization direction has been rotated is a spherical wave, and has a rectangular shape as shown in FIG. When the light transmitted through the phase change portion is diffracted by the convex lens 14, the image is separated from the center of the optical axis so as to be inversely proportional to the slit width. Therefore, in FIG. 3B, on the lens focal plane 15, the laser light 10 that has passed through the vicinity of the charged particle in the tetragonal crystal 12 and whose polarization direction has been rotated is the rectangular aperture in FIG. The image is formed in an area where the slit is rotated 90 degrees.

  On the other hand, the laser light 10 that passes through the tetragonal crystal 12 other than the vicinity of the charged particles and whose polarization direction is not rotated out of the light passing through the rear stage prism 13 is a uniform plane wave. When passing through the convex lens 14 having the rectangular aperture slit of FIG. 3A, the lens converges to the center of the optical axis at the focal plane 15, and the convergence width is proportional to the focal length. Therefore, in FIG. 3B, the laser light 10 (leakage light) whose polarization direction does not rotate through the tetragonal crystal 12 other than the vicinity of the charged particles in the lens focal plane 15 is shown in FIG. An image is formed by localization near the center of (a).

  Therefore, charged particles are incident on the tetragonal crystal 12 by determining the case where imaging light having a predetermined level or higher intensity is obtained in a region other than the portion converging to the optical axis center on the lens focal plane 15. This can be detected effectively.

  Therefore, in FIG. 1, the light passing through the convex lens 14 is detected by the optical fiber bundle 16 provided on the lens focal plane 15 and the light receiving element 18 connected thereto, and between these optical fiber bundle 16 and the light receiving element 18. Further, a mask 17 having a shape that blocks the vicinity of the optical axis center of the convex lens 14 on the lens focal plane 15 is provided.

  In addition, by appropriately designing the focal length of the convex lens 14 and the diameter of the optical fiber constituting the optical fiber bundle 16, the light to be blocked that converges at the center of the optical axis is confined within one optical fiber constituting the optical fiber bundle 16. Above, it is good also as a structure interrupted | blocked by the metal mask 17 provided in the output end of this one optical fiber, and if a fiber is a flexible thing, only the fiber part containing the high intensity light will be another space. You may miss it.

  As a result, of the light that passes through the convex lens 14 and enters the optical fiber bundle 16, the light near the center of the optical axis of the lens focal plane 15, that is, the plane wave that has passed through other than the vicinity of the charged particle locus in the tetragonal crystal 12. In the light receiving element 18, only the slit-shaped light away from the optical axis of the lens focal plane 15, that is, the laser light as a spherical wave that has passed in the vicinity of the charged particle locus in the tetragonal crystal 12, is blocked. Light can be received.

  FIG. 4 shows a simulation of an image (light intensity distribution) formed on the lens focal plane 15. As a plane wave that passes through the vicinity of the charged particle locus in the tetragonal crystal 12 shown in FIG. 4A and as a spherical wave that has passed through the vicinity of the charged particle locus in the tetragonal crystal 12. Intensity distribution of the laser beam 10 (leakage light) as a plane wave that has passed through other than the vicinity of the charged particle locus in the tetragonal crystal 12 shown in FIG. As background noise, it is possible to effectively extract laser light as a spherical wave that has passed through the vicinity of the charged particle locus as shown in FIG. FIG. 4D shows a state where a signal only in a region having a high S / N can be extracted by the mask 17 that blocks the vicinity of the optical axis center.

  With such a configuration, the charged particles pass through the vicinity of the tetragonal crystal 12 by determining the case where imaging light of a predetermined level or more is obtained in a region other than the portion that converges at the center of the optical axis. This can be detected effectively.

  In other words, according to the charged particle detection system 1, the laser beam 10 that passes through the tetragonal crystal 12 is not related to the locus of the charged particles and blocks the light that is the background noise of the detection while blocking the charged particles. Since light originating from the locus can be detected effectively, charged particles that have passed near the tetragonal crystal 12 can be detected with a high S / N ratio. According to the charged particle detection system 1, it is not difficult to detect a single charged particle with high accuracy by using an existing element technology.

  Further, the charged particle detection system 1 identifies the projection of the charged particle locus on the tetragonal crystal 12 onto the xy plane by two-dimensionally analyzing the intensity distribution of light from each optical fiber in the optical fiber bundle 16. can do. This is because when the charged particles pass through the vicinity of the surface of the tetragonal crystal 12, the trajectory is considered to draw a straight line in the xy plane with almost no trajectory being bent. This is because the above-described interference pattern on the lens focal plane 15 is generated in the orthogonal direction.

  Furthermore, the charged particle detection system 1 has a configuration for recording the detection time of charged particles, and can continuously record the presence and detection time of charged particles.

  The charged particle detection system 1 can also be used for Sterngellach type spin measurement. For example, if electrons are inelastically scattered in a material, the spin information of high-energy electrons usually has to be observed only in order to measure the spin information of incident electrons.

  However, if the electron spin and the momentum direction are orthogonal to each other and passed through a non-uniform magnetic field, the charged particle orbits will be spatially discretized and shifted depending on the direction of the spin. Become. A feature of this type of spin measurement is that the spin identification rate is almost 100%. That is, if the charged particle detection system 1 is used, since it is nondestructive measurement, it becomes possible to connect the above-mentioned spin measurement while observing the velocity of a single electron. Can be measured simultaneously. This spin measurement method is also effective for electrons with very low speed.

  As a final description in the present embodiment, an example of typical design parameters in the charged particle detection system 1 of the present embodiment is shown for reference.

a, Standard deviation of light intensity distribution in cross section of laser beam 10: σ = 500 [μm]
b, the total intensity of the laser beam 10: about I ₀ ² = 1 [mW] (corresponding to about 10 ¹⁶ photons)
c, Peak intensity of the laser beam 10: A ₀ ² = I ₀ / (2πσ ² )
d, pulse duration of laser beam 10 per second: τ _d = 1.0 (for example, CW laser)
e, wavelength of the laser beam 10: λ = 0.532 [μm]
f, Focal length of convex lens 14: f = 5 [mm]
g, Extinction ratio of the front prism 11 and the rear prism 13: ε ² = 10 ⁻⁶
h, distance between the surface of the tetragonal crystal 12 and the passing electrons (charged particles): R = 400λ
i, kinetic energy of electrons (charged particles): E _k = 10 [eV]
j, relativistic electron velocity (ratio to the speed of light): β = 0.625
Electron optical tensor of tetragonal crystal 12 (DKDP) at k, −64 ° C .: r ₆₃ = 2.4 × 10 ⁴ [pm / V]
l, phase delay of the laser beam 10 in the tetragonal crystal 12 caused by the passage of electrons (charged particles): δΓ = 5.97 × 10 ⁻⁴
m, electric field action time (impact time) due to passage of electrons (charged particles): τ _i = 113 [ps]
n, slit size in the case where the phase change portion in the crystal which is effectively expected by the velocity of electrons in the convex lens 14 before incidence is approximated to a rectangle: 2 μ × 2ν = 2 × 106 [μm] × 2 × 163 [Μm].

[Embodiment 2]
Next, a system construction example is proposed in which a large number of charged particle detection systems 1 of Embodiment 1 are arranged in an array to detect the speed or energy of charged particles with high accuracy. FIG. 5 shows a conceptual diagram thereof.

  FIG. 5 is a system configuration example for measuring the end point energy of electrons in beta decay of nuclides such as tritium. The electrons emitted from the beta decay nuclide draw an orbit in the right direction in the figure while being restrained by the solenoid magnetic field. When electrons are detected by the first charged particle detection system 1 using continuous laser light as the laser light 10, a trigger signal for generating a short pulse is generated from the charged particle detection system 1. Based on this trigger signal for generating a short pulse, a single short pulse laser is spatially multiplexed and arranged in a number of detector element arrays with different time differences depending on the optical distance. It enters into the charged particle detection system 1 group. Note that the time difference between the pulse lasers that are branched in multiple is set based on an approximate estimated electron velocity in advance.

  According to such a configuration, it becomes possible to detect the position and trajectory of electrons, and based on the distance between the charged particle detection systems 1 and the detection time of the electrons in each charged particle detection system 1, It is possible to accurately measure the velocity or energy of the charged particles by measuring the travel time (time of flight). As described above, according to the charged particle detection system 1, information on the passage time and position can be acquired without affecting the movement of the charged particle, so that the same physical quantity of the charged particle can be repeatedly measured with high accuracy. Because it is.

  Note that the time resolution of the velocity measurement of electrons (charged particles) in the configuration example of FIG. 5 is not the time resolution of the light receiving element 18 (see FIG. 1), but the time width of the pulsed laser beam that is scanned and the tetragonal crystal 12. It is determined by the electric field response time of (see FIG. 1). This is because each charged particle detection system 1 obtains an electron (charged particle) detection signal only when a pulse laser is incident and the effect of the electric field is maintained on the incident electron (charged particle). Because. Therefore, the time resolution of the velocity measurement of electrons (charged particles) is improved by shortening the pulse width of the pulse laser or shortening the electric field response time (rise time and relaxation time) of the tetragonal crystal 12. be able to. It is not difficult to obtain time resolution on the order of femtoseconds by using existing elemental technology. For example, when charged particles flying at almost the speed of light are observed with a laser diameter of about 30 mm, it is considered that a limit time resolution of at least about 100 fs can be obtained.

  As a final description in the present embodiment, a typical design parameter example in the system construction example of the present embodiment is shown for reference.

a, Standard deviation of light intensity distribution in cross section of pulse laser: σ = 100 [μm]
b, Total intensity of pulse laser: I ₀ ² = 1 [mW] or so (corresponding to about 10 ¹⁶ photons)
c, Peak intensity of pulse laser: A ₀ ² = I ₀ / (2πσ ² )
d, pulse duration per second of pulsed laser: τ _d = 10 ⁻⁸ (10 ns)
e, Laser wavelength of pulse laser: λ = 0.532 [μm]
f, Focal length of convex lens 14: f = 5 [mm]
g, Extinction ratio of the front prism 11 and the rear prism 13: ε ² = 10 ⁻⁶
h, distance between the surface of the tetragonal crystal 12 and the passing electrons (charged particles): R = 10λ
i, kinetic energy of electrons: E _k = 10 [eV]
j, relativistic electron velocity (ratio to the speed of light): β = 0.625
Electron optical tensor of tetragonal crystal 12 (DKDP) at k, −64 ° C .: r ₆₃ = 2.4 × 10 ⁴ [pm / V]
l, the phase delay of the pulse laser in the tetragonal crystal 12 caused by the passage of electrons: δΓ = 0.0239 × 10 ⁻⁴
m, electric field action time (impact time) due to passage of electrons (charged particles): τ _i = 2.8 [ps]
n, slit size in the case where the phase change portion in the crystal which is effectively expected by the velocity of electrons in the convex lens 14 before incidence is approximated to a rectangle: 2 μ × 2ν = 2 × 2.7 [μm] × 2 × 4.1 [μm]
[Application example of the present invention]
Hereinafter, application or application examples of the charged particle detection method and charged particle control method of the present invention will be described.

  FIG. 6 shows that the ion beam with high accuracy is controlled on the DNA by detecting or controlling the energy of the ion beam with energy resolution of less than eV by the charged particle detection system 1 simultaneously with the generation of ions by thin film irradiation. The conceptual diagram of the ion beam irradiation apparatus which irradiates and cut | disconnects a specific molecular chain is shown. If such a configuration is adopted, when it is desired to cleave only a specific molecular chain in order to study DNA research, for example, DNA repair function, in addition to the size of the ion beam, its energy state is changed to the quantum energy level. It will be possible to specify precisely with.

  Of course, the target to which the ion beam irradiation apparatus of FIG. 6 irradiates the ion beam is not limited to DNA. Such an ion beam irradiation apparatus can be used, for example, as an ion doping apparatus in the manufacture of semiconductor devices. According to the ion doping apparatus using the charged particle detection method of the present invention, a device having a three-dimensional structure can be formed in a semiconductor substrate by controlling the energy of the irradiated ions and the penetration depth thereof with high accuracy. It will be possible.

  FIG. 7 shows an application example of the second embodiment. The nondestructive mass of a protein that measures the energy of a protein ion beam with high accuracy using the light receiving element array of the charged particle detection system 1. It is an example of composition of a mass spectrometry system which realizes analysis. In this mass spectrometry system, after protein is desorbed or ionized by an ultrashort pulse laser, the momentum and velocity of the protein ion beam are obtained nondestructively based on the trajectory, and the mass can be measured. it can. According to the mass spectrometry system, the protein after the mass analysis can be taken out intact, so that the protein after the mass analysis can be used for various subsequent measurements. In the field of proteomics, it is important to specify the mass with high accuracy in order to identify the protein. Therefore, it is considered that such a mass spectrometry system is extremely useful.

  In recent years, the use and detection of charged particles has been applied to medical treatment (eg, ion therapy for cancer), physics (eg, space / particle physics), life science (DNA analysis, post-genome planning, proteomics or functional units) Analysis of protein groups), semiconductor production (ion doping), and the like, and the charged particle detection method of the present invention can be widely applied to these technical fields.

The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.
[Theoretical explanation of phase difference change]
Finally, the electro-optic effect in the tetragonal crystal due to the electric field generated by the charged particles, that is, the phase difference change of the scanning light, plays an essential role in the charged particle detection method of the present invention. Explain the contents.

  Between two components xy components of an electric field orthogonal to the optical axis of scanning light (referred to as the Z-axis direction) generated by an external electric field of charged particles when a point group 4-bar2m uniaxial crystal is used The change δΓ in the phase difference is as follows.

  If the refractive index difference between the xy components generated by the external electric field is δn, the length in the optical axis direction where the refractive index change is generated is δl, and the wavelength of the scanning light is λ, the change in the phase difference is δΓ = (2π / Λ) δnδl.

When a charged particle of a single charge e is running at a relativistic velocity β = ν / C (C is the speed of light) and Lorentz factor γ = 1 / (1-β ² ) ^0.5 , Assuming that the electric field generated at a distance R from the orbit in the vertical plane is E _r (R), the refractive index in the optical axis direction of the crystal is n, and E _r (R) = γe [4πε ₀ (n ) ^0.5 R ² ].

When charged particles pass through the crystal surface, the effective time δt that can be affected by the electric field strength is R / (γβc). During this effective time, the refractive index changes in the range δl in which the scanning light propagates through the crystal, and can be expressed as δl = c (δt) / n = R / (nγβ). Refractive index ellipsoid of the points 4-bar2m is in a state where not applied external electric ^field, and _{^{(x 2 / n o 2)}} + (y 2 / n o 2) + (z 2 / n e 2) = 1 expressed. The refractive index of n _o is the ordinary ray axis, n _e is the refractive index of the extraordinary optical axis.

When acting external electric field _{(E x, E y, E} z) within the crystal, the refractive index ^{_{ellipsoid, (x 2 / n o 2}} ) + (y 2 / n o 2) + (z 2 / n e 2 ) + 2r ₄₁ E _x yz + 2r ₄₁ E _y xz + 2r ₆₃ E _z xy = 1. Here, r ₄₁ and r ₆₃ correspond to a conversion coefficient when converting the magnitude of the electric field into a refractive index change, and are called electro-optic coefficients.

At this _time, if you choose the arrangement such that _E x ₌ E y ₌ 0 and _{E z = E r (R)} , the refractive index ^{_{ellipsoid, (x 2 / n o 2}} ) + (y 2 / n o 2 _{^{) + (x 2 / n e}} 2) + become 2r ₆₃ E z xy = 1. This refractive index ellipsoid is expressed as follows when a new axis obtained by rotating the xy axis around the z axis by π / 4 is the x′-y ′ axis.
^{_{[1 / (n o) 2 -r}} 63 E z ] x ^'2 + ^{_{[1 / (n o) 2 -r}} 63 E z ] y' ² + [1 _{/ (n} ^{e) 2]} z ^'2 = 1
Therefore, in the range covered by the external electric field (E _x , E _y , E _z ), the refractive index ellipse locally rotated by π / 4 around the z axis with respect to the refractive index ellipsoid without the external electric field. It is considered that the body is inserted.

At this time, if the optical axis of the scanning light is taken as the z-axis, the refractive index difference between x′-y′2 components newly generated by the external electric field applied in the z-axis direction is δn = 1 / [1 / (n _o) ² -r ₆₃ E _z] ^0.5 -1 / ^{_{[1 / (n o) 2 +}} r 63 E z ] ^0.5 is approximately ^{_{(n o) 3 r 63 E}} z.

  Accordingly, when the optical axis of the scanning light is taken as the z-axis and the trajectory of the charged particle is made parallel to the x′-y ′ plane, the phase difference δΓ generated when the charged particle passes is expressed as follows. .

_{δΓ = (2π / λ) (} n o) 3 r 63 E T (R) [R / _{(n e} γβ)]
= E / (2ε _o ) × (n _o / (n _e ) ^0.5 ) ³ r ₆₃ [1 / (mλ ² β)]
However, in the above equation, the distance R from the charged particle is expressed as a length in units of the wavelength of the scanning light, where R = mλ.

  The present invention includes medical treatment (for example, cancer treatment by ion beam), physics (for example, space / particle physics), life science (analysis of DNA, post-genome planning, proteomics, or analysis of protein groups as functional units). It can be widely applied to detection and motion control of charged particles in various technical fields such as semiconductor manufacturing (ion doping).

It is a figure showing a schematic structure of a charged particle detection system concerning one embodiment of the present invention. It is a figure which shows a mode that the electric field produced by a charged particle produces the change of a refractive index in a tetragonal crystal. (A) shows the shape of the rectangular aperture slit, and (b) is a diagram showing the result of simulating the state of the image (light intensity distribution) connected to the lens focal plane by the convex lens having the rectangular aperture slit. . FIG. 4 is a diagram showing a simulation result showing that a high S / N region is extracted by subtracting background noise in an image (light intensity distribution) connected to the lens focal plane. It is a figure which shows the example of a system construction which detects the speed | rate thru | or energy of a charged particle with high precision by arrange | positioning many charged particle detection systems in an array form. It is a figure which shows the structural example of an ion beam irradiation apparatus. It is a figure which shows the structural example of the mass spectrometry system of protein.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Charged particle detection system 10 Laser beam 11 Front stage prism 12 Tetragonal crystal 13 Back stage prism 14 Convex lens 15 Lens focal plane 16 Optical fiber bundle 17 Mask 18 Light receiving element

Claims (6)

A charged particle detection method for detecting charged particles by detecting a refractive index change generated electro-optically inside a crystal by an electric field generated by charged particles passing outside,
A light irradiation step of irradiating light inside the crystal;
The light irradiated through the light irradiation stage and passing through the crystal is divided into a light component that has undergone an optical phase change based on the refractive index change, and a light component that has not undergone an optical phase change based on the refractive index change. A light component separation stage that separates into
A charged particle detection method comprising: a charged particle detection step of detecting the charged particle by detecting a light component that has undergone an optical phase change separated in the separation step.   In the light component separation step, by using a lens having a diffractive function, the light that has been irradiated in the light irradiation step and passes through the crystal is changed into a light component in which the optical phase change occurs and the optical phase change. The charged particle detection method according to claim 2, wherein the charged particle detection method spatially separates the light component from the light component that has not been generated. A charged particle detection method for detecting charged particles by detecting a refractive index change generated electro-optically inside a crystal by an electric field generated by charged particles passing outside,
The crystals are a plurality of tetragonal crystals arranged at different positions;
A light irradiation step of irradiating light inside the plurality of crystals;
The light component irradiated with the light irradiation stage and passing through each crystal has a light component in which an optical phase change based on the refractive index change occurs and a light component in which an optical phase change based on the refractive index change does not occur A light component separation stage that separates into
By detecting the light component in which the optical phase change based on the refractive index change of each crystal separated in the separation step is detected, the time information when the charged particles in each crystal pass is specified, and these A charged particle detection method comprising: a charged particle detection step of detecting at least one of velocity, momentum, energy, and spin information of the charged particle based on time information.   The charged particle detection method according to claim 1, wherein the crystal is a tetragonal crystal.   The charged particle detection method according to claim 4, wherein the tetragonal crystal is a uniaxial crystal belonging to the point group 4-bar2m. A charged particle control method for controlling a movement state of the charged particles using the charged particle detection method according to claim 3,
A charged particle control method comprising: determining a control amount of a motion state of the charged particle based on at least one of velocity, momentum, energy, and spin information of the charged particle detected in the charged particle detection step.

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