JPH0612720B2 - Polarization generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention utilizes high-speed electrons accelerated by a linear accelerator and high-speed electrons such as an electron storage ring to produce clockwise and counterclockwise circularly polarized light The relationship between two circularly polarized light beams is said to be orthogonal to each other), either of two linearly polarized light beams whose polarization planes are orthogonal to each other can be used, and the invention relates to a polarized light generation device that can be easily switched to another polarized light beam.

[Conventional technology]

As is well known, in order to investigate the dichroism, circular dichroism, magnetic circular dichroism, etc. of a substance, two orthogonal linear polarizations or two orthogonal circular polarizations (clockwise and counterclockwise circular polarizations) It is necessary to provide a polarized light generating device that generates a polarized light. Further, if the polarized light is switched alternately and quickly, the measurement becomes easy.

In a conventional device, in order to produce linearly polarized light, a polarizer is placed in front of a light source, and by rotating this polarizer by 90 °, orthogonal linearly polarized light having different 90 ° polarization is obtained. Moreover, recently, the synchrotron radiation from the electron storage ring is linearly polarized, and there are examples of applying this linearly polarized light. In the case of this synchrotron radiation, there is currently no device that alternately obtains two linearly polarized light beams that are orthogonal to each other.

The method of the prior art relating to the generation of circularly polarized light is mainly the one using an optical element, and the method using a quarter wave plate,
A method utilizing the electro-optic effect of the crystal and a method utilizing the stress strain of the crystal have been adopted as the operation principle. Therefore, the lithium fluoride (L
Even if iF) was used, circularly polarized light having a wavelength shorter than 1050Å could not be produced.

On the other hand, in principle, as a device with no wavelength limit, a double spiral coil is placed in the orbit of high-speed electrons, and the currents in opposite directions are given to each coil, so that the center of this double spiral coil is On the axis has a magnetic field transverse to the axis,
There was a so-called helical wiggler that has a magnetic field distribution in which the magnetic field direction rotates spirally along the axis. When a high-speed electron is run along the central axis of this double spiral coil, the electron also advances while drawing a spiral by Lorentz force, and thus circularly polarized dipole radiation is emitted in the forward direction. In addition, this emitted light interferes with a specific wavelength depending on the length of one cycle of the coil, so that strong light can be obtained (BM Kincaid, "A Sh
ort Period Helical Wiiggler as an Improved Source
of Synchrotron Radiation '' Journal of Applied Physic
s, vol.48, No.7, July 1977, p.2684 ~ 2691, LRElias et al., `` Observation of Stimulated Emission of Radiation
by Relativistic Electrons in a Spatially Periodic
Transverce Magnetic Field ”Physical Review Letters
Vol.36, No.13 March 1976, p.717-720, Hideo Kitamura "New Radiation Source" Mathematical Science No.243, September 1983, p22
See ~ 30. Of these, the literature demonstrates that circularly polarized light is emitted from the helical wiggler. Also, the literature describes the generation of interfering linearly polarized light from a device called an undulator, which has a magnetic field distribution in which the magnetic field direction alternates in the same plane).

In such a conventional device, the rotation direction of the spiral motion of electrons is uniquely determined by the winding method of the double spiral coil, and therefore, only clockwise or counterclockwise circularly polarized light can be obtained. On the other hand, although similar to the present invention, one magnet row is composed of electromagnets, and right and left are alternately generated by periodically reversing the direction of the magnetic field obtained by the electromagnets. Circularly polarized light generator (Japanese Patent Publication 4-76
No. 00) has recently been proposed. On the other hand, the present invention is based on a method which is different in principle from the one of the above-mentioned application, and it is possible to generate the magnetic field only by the permanent magnet.

[Outline of Invention]

The present invention has been made in view of the above-mentioned drawbacks of the conventional device, and uses a high-speed electron beam such as a linear accelerator or an electron storage ring to make two orthogonal circular polarizations (clockwise and counterclockwise circular polarizations) and orthogonal polarizations. (EN) A polarization generation device capable of generating any one of the two linearly polarized lights, and easily switching to another polarization. Less than,
The present invention will be described.

Example of Invention

FIG. 1 is a configuration diagram showing an embodiment of the present invention. A pair of upper and lower magnets A ₁ creates a magnetic field in one direction, and a pair of upper and lower magnets A ₂ similarly creates a magnetic field in the opposite direction. Next to each other. In this manner, the magnets A ₁ and A ₂ are alternately changed and repeated to be arranged along the central axis M in the traveling direction of the electron beam trajectory E _b to form one set of magnet rows A. The magnets A ₁ and A ₂ need to always maintain the same magnetic field strength, and may be made of permanent magnets. Two adjacent magnets A ₁ , A ₂
The intervals are all equal. With this series of magnets (along with A ₁ , A ₂ , A ₁ , A ₂ , ... A ₁ , A ₂ ), the direction of the magnetic field is periodically reversed along the central axis M, and Form an orthogonal magnetic field distribution.

Next, a series to is perpendicular to the magnet array A of the magnet _A 1, _{A 2,} the magnet having the same effect as the magnet _{A 1} and _{A 2} set _{B 1} and B
₂ (thus, the magnets B ₁ and B ₂ have the opposite magnetic field directions) are arranged in the same number as the series of magnet rows A, and another set of magnet rows B is formed. Therefore, the direction of the magnetic field generated by the magnet array B is orthogonal to both the direction of the magnetic field of the magnet array A and the direction of the central axis M. Then, the polarized light generation device of the present invention is configured by providing a driving unit (not shown) that moves either the magnet array A or the magnet array B along the longitudinal direction of the central axis M to change the relative position. It

Next, the operation will be described.

When the magnets B ₁ and B ₂ are arranged between the magnets A ₁ and A ₂ , respectively, the directional distribution of the magnetic field along the central axis M is spirally rotated as shown in FIGS. 2 (a) and 2 (b). (The arrow indicates the direction of the magnetic field on the central axis M). In the case of FIG. 2A, the spiral rotation is clockwise. With respect to the arrangement of the magnet rows A and B shown in FIG. 2 (a), the magnet row B is moved along the central axis M by λ.
_0/2: by moving forward only (lambda ₀ one cycle length of the magnetic field), changes to the sequence of Figure 2 (b), the direction of the magnetic field is counterclockwise. That is, by changing the relative position of the set of magnets B to the set of magnets A, the rotation direction of the magnetic field can be switched.

Next, when moving the magnet array B along the central axis M so that the positions of the pair of magnet arrays A and B coincide with each other, there are two arrangements so that the magnets A ₁ and B ₁ coincide with each other. There are a magnet arrangement (which will be referred to as C ₁ ) and a magnet arrangement (which will be referred to as C ₂ ) that allows the magnets A ₂ and B ₁ to coincide with each other. If the magnet A ₁ produces a vertically downward magnetic field and the magnet B ₁ has a horizontal leftward magnetic field (the magnet A ₂ faces upward) (the magnet B ₂ has a horizontal rightward direction), then the magnet array A ₁ in the magnet arrangement C ₁ By the combined magnetic field of the magnet array B and on the central axis M, it becomes as shown in FIG. That is, as shown in FIG. 3 (b), the magnetic fields are aligned in the direction of the solid line arrow inclined at 45 ° with respect to the horizontal axis (x-axis), and the directions are alternately opposite. In the magnet arrangement C ₂ , the composite magnetic field of the magnet array A and the magnet array B results in the state of FIG. 3C on the central axis M. That is, as shown in FIG. 3B, it is inclined by 135 ° with respect to the horizontal axis (x axis). Therefore, the directions of the magnetic fields are orthogonal to each other in FIGS. 3 (a) and 3 (c). The y-axis is the vertical axis.

When high-speed electrons are incident along the central axis M of the space having the spiral magnetic field distribution of FIGS. 2 (a) and 2 (b), the high-speed electrons receive Lorentz force, and in the case of FIG. 2 (a). Running while drawing a clockwise spiral, in the case of FIG. 2 (b), a spiral spiral is made counterclockwise. Circularly polarized light is emitted from high-speed electrons that perform spiral motion (the above-mentioned reference p. 2658, reference p.
718). The counterclockwise circular polarized light is emitted from the counterclockwise spiral electron, and the clockwise circular polarized light is emitted from the clockwise spiral electron (where the circular polarized light rotates in the direction of the emitted light). Observed from the direction opposite to the direction of the synchrotron radiation is defined as clockwise circularly polarized light that is clockwise. In the case of the magnetic field distribution shown in FIG. 3, fast electrons passing through the central axis M are subjected to Lorentz force and move in a meandering motion in a plane perpendicular to the direction of the magnetic field. Therefore, in the magnetic field distribution of FIG. 3 (a), linearly polarized light having a polarization plane in the direction of the dotted arrow in FIG. 3 (b) is used, and in the magnetic field distribution of FIG. 3 (c), FIG. It emits linearly polarized light polarized in the direction of the dotted arrow in (see References). However, in the case of FIG. 3 (c), the light generated in the independent magnet portions at both ends has different planes of polarization, but the light amount is small, so it was ignored. In FIGS. 3A and 3C, the polarization planes are orthogonal to each other.

Whether the circularly polarized light is generated or the linearly polarized light is generated, the light is strongly concentrated in the forward direction due to the relativistic effect when the electron velocity is close to the high speed. Further, the lights emitted in the respective magnetic fields of the magnet array A (as well as the magnet array B) interfere with each other, and when observing the traveling light on the central axis M, in the case of the circular polarization arrangement, the following (1) )
Complement each other at the wavelength λ ₁₀ (Å) shown in the formula (see the above-mentioned references) λ ₁₀ = λ ₀ (1 + K ² ) / 2γ ² (1) where K = 0.093 × B ₀ × λ ₀ , Γ = E / 0.5
Given by 1. Here, λ ₀ is one cycle length (cm) of the magnetic field shown in FIGS. 2 and 3, and B ₀ is the magnetic field strength (KGa).
uss) and E represent electron energy (MeV), respectively.

As a specific example, B ₀ = 2KGauss, λ ₀ = 6 cm, E = 6
At 00 MeV, λ ₁₀ was 470 Å. When circularly polarized light is generated in the arrangement shown in FIG. 2, the radius of gyration of relativistic electrons that make a spiral motion is about 10 μm, and the pitch angle (central axis M
The angle formed by the spiral orbit with respect to is found to be about 1 mradian. Further, as is clear from the above equation (1), when the electron energy E and the magnetic field strength B ₀ change, the interfering wavelength λ ₁₀ changes (this has already been proved. Therefore, if the energy of the electron or the strength of the magnetic field is continuously changed, tunable circularly polarized light and orthogonally polarized linearly polarized light can be obtained.

A concrete example of the generation of the magnetic field is shown in FIG. Fourth
For the sake of clarity, the figure is a schematic view of a magnet array that creates a vertical magnetic field. Permanent magnets of the same size (material SmC
O ₅ and residual magnetic field of 9000 Gauss) are arranged as arrows (indicate the direction of the magnetic field inside the magnet) (thick arrows indicate the direction of the magnetic field created in the space), the cycle length λ ₀ is 6 cm, and one side of the magnet Length (shorter) d is 1.5 cm, gap G between upper and lower magnets
And the depth l of the magnet are equal to G = 1 and 5 cm, the magnetic field strength B ₀ obtained at the central axis M is about 1 KGau.
When ss and the gap G are 3.5 cm, a magnetic field strength B ₀ of about 2 KGauss is obtained (see the above reference). By placing a magnet array having a similar structure on a horizontal plane, it is possible to obtain a horizontal magnetic field of similar strength.

〔The invention's effect〕

As described in detail above, according to the present invention, a plurality of magnets A having magnetic fields of constant strength in which magnetic field directions are opposite to each other are provided.
₁ and a magnet A ₂ are arranged alternately along the traveling direction of the electron beam at equal intervals, and the magnetic field direction is orthogonal to the electron beam direction. A plurality of magnets having magnets A ₁ and A ₂ of A, which are perpendicular to the magnetic field directions of the magnets A ₁ and A ₂ and have the same magnetic field strength as the magnets A ₁ and A ₂ , respectively. Of magnets ₁ and B ₂ are alternately arranged at equal intervals along the traveling direction of the electron beam, and the magnetic field direction is orthogonal to the electron beam direction. Since a means for changing the relative position of the electron beam direction between the magnet A and the magnet array B is provided, clockwise and counterclockwise circularly polarized light or linearly polarized light can be easily generated, and the existing electron storage ring can be easily generated. It can also be installed in the linear part of It is also possible to use these high-speed electrons, and it is possible to use two circularly polarized light and two linearly polarized light that are orthogonal to each other in the short wavelength region of 1000 Å or less, which has been impossible in the past. It is possible to measure dichroism, circular dichroism and magnetic circular dichroism of a substance over a range, and there is an advantage that a polarization generator having a wide range of applications and a high degree of freedom can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention, FIGS. 2 (a) and 2 (b) are schematic diagrams showing a magnetic field direction distribution and an electron beam trajectory, and FIGS. 3 (a) and 3 (c) are Schematic diagrams showing the direction distribution of the synthetic magnetic field, FIGS. 3 (b) and 3 (d) showing the direction of the synthetic magnetic field and the polarization direction of the linearly polarized light, and FIG. 4 showing the magnet array relating to the generation of the vertical magnetic field. It is a perspective view which shows the specific example of. In the figure, A and B are magnet arrays, A ₁ , A ₂ , B ₁ and B ₂ are magnets, M is a central axis, and E _b is an electron beam orbit.

Claims (1)

[Claims] 1. A polarization generator for generating right-handed circularly polarized light, left-handed circularly polarized light, and two orthogonal linearly polarized light from a high-speed electron beam, the magnetic field having a constant magnetic field in which the directions of the magnetic fields are opposite to each other. A set of a plurality of magnets A ₁ and magnets A ₂ which are alternately arranged at equal intervals along the traveling direction of the electron beam and in which the directions of the magnetic fields are orthogonal to the direction of the electron beam. Of the magnet array A and the magnets A ₁ and A ₂ of the magnet array A, which are orthogonal to the magnetic field directions of the magnets A ₁ and A ₂ and have the magnetic field directions reversed from each other. A plurality of magnets B ₁ and B ₂ having a constant magnetic field are alternately arranged at equal intervals along the traveling direction of the electron beam, and the directions of the magnetic fields are orthogonal to the direction of the electron beam. A set of magnets B arranged in a row , Polarized light generator being characterized in that a means for changing the relative position of the electron beam direction between the magnet array A and the magnet row B.