JP2010002846A - Multiple image polarization element group - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multiple image polarization element which has a polarization characteristic suitable for an optical apparatus. <P>SOLUTION: Two or more multiple image polarization elements are produced by choosing two or more different birefringence crystals among LiNbO<SB>3</SB>, calcite, YVO<SB>4</SB>or the like and wavelength dependency of an isolating angle or isolating breadth can be adjusted by combination of the multiple image polarization elements. Since the isolating angle at a short wavelength side can be made small or the isolating angle or the isolating breadth can be linearly changed from a short wavelength region toward a long wavelength region, when the multiple image polarization element is used for a polarization imaging apparatus, a polarization spectroscope and a multi-channel Fourier spectroscope, a wide wavelength range can be simultaneously measured. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a double-image polarizing element group combining a Wollaston prism, which is a birefringent polarizing device using a birefringent crystal used in an optical instrument, and a Savart plate.

  When unpolarized light (for example, natural light) is incident on an optically anisotropic crystal (birefringent crystal) such as calcite, quartz, lithium niobate, or titanium oxide, two refracted rays are observed. This phenomenon is called birefringence. Among the two refracted light rays, a light ray that follows Snell's law is called an ordinary ray, and a light ray that does not follow Snell's law is called an extraordinary ray. A birefringent crystal in which the speed of ordinary light in the crystal is faster than the speed of extraordinary light is called a positive crystal, and crystal and titanium oxide belong to this. Conversely, a birefringent crystal in which the speed of extraordinary rays in the crystal is higher than that of ordinary rays is called a negative crystal, and calcite and lithium niobate belong to this.

  Examples of a double image polarizing element using a birefringent crystal include a Wollaston prism and a Savart plate. These double-image polarizing elements are used in various optical equipment such as optical pickups for optical disks, as well as observation and measurement devices such as polarization interferometers used in differential interference microscopes, astronomical observation devices, polarization spectrometers, and Fourier spectrometers. It is used.

  The Wollaston prism is a kind of double-image polarizing element. As shown in FIG. 18, a birefringent crystal prism having the same apex angle α is arranged so that the optical axes of the birefringent crystal are orthogonal to each other. The two are generally bonded together. The optical axis of the first prism 51 is an arrow direction parallel to the paper surface as shown in FIG. 18, and the optical axis of the second prism 52 is a direction perpendicular to the paper surface. As shown in FIG. 18, when the Wollaston prism 41 is installed so that the optical axis is perpendicular to the optical axis of the optical system (Optical axis), the polarization in the direction of the arrow parallel to the paper surface (S-polarized light) is Polarized light in the direction perpendicular to the paper surface (P-polarized light) becomes an extraordinary ray and travels straight through the first prism 51 and is separated by refraction at the interface between the first prism 51 and the second prism 52, and The S-polarized light that was an ordinary ray in one prism becomes an extraordinary ray, and the P-polarized light that was an extraordinary ray in the first prism becomes an ordinary ray. FIG. 18 shows a case where a Wollaston prism made of a negative crystal is installed. O means an ordinary ray and E means an extraordinary ray. The angle θ shown in FIG. 18 is called a separation angle.

  The Savart plate is a kind of double-image polarizing element, and as shown in FIG. 19, is parallel with the same shape and the same thickness t cut so as to form an angle of approximately φ = 45 ° with respect to the optical axis of the birefringent crystal. Two flat birefringent plates are bonded together so that the optical axis and the plane (main cross section) including the optical axis are orthogonal to each other. As shown in FIG. 19, when the Savart plate 42 is installed so that the joint surface is perpendicular to the optical axis of the optical system and an unpolarized light beam is incident, an extraordinary ray E is incident on the incident surface of the first polarizing plate 53. Refracts and advances, and the ordinary ray O goes straight. In the second polarizing plate 54, the ordinary ray O in the first polarizing plate 53 is refracted and proceeds as an extraordinary ray E, and the extraordinary ray E in the first polarizing plate 53 goes straight as an ordinary ray O. As a result, as shown in FIG. 19, polarized lights orthogonal to each other are separated in a azimuth of 45 ° with respect to the main cross section of the two birefringent plates with a separation width a.

  Since the required polarization separation characteristics differ depending on the type and application of the optical device, a birefringent crystal is selected so as to satisfy this, and the shape of the double-image polarizing element is designed. The separation angle or separation width of the double-image polarizing element can be adjusted to some extent depending on the birefringent crystal used, the shape of the double-image polarizing element, and the manner of installation. The larger the birefringence Δn, which is the difference between the refractive index of ordinary light (ordinary light refractive index) and the extraordinary light refractive index (abnormal light refractive index) of a birefringent crystal, the greater the separation angle θ between ordinary and extraordinary rays. Alternatively, the separation width a becomes larger. In the case of the Wollaston prism, the separation angle θ is increased by increasing the apex angle α shown in FIG. In the case of a Savart plate, the separation width a is increased by increasing the thickness S (S = 2t) in the optical axis direction shown in FIG.

For example, in Patent Document 1, it is necessary to obtain a separation angle required by a magneto-optical head by using lithium niobate having a larger birefringence Δn as a birefringent crystal instead of a conventionally used crystal. The apex angle of the Wollaston prism is reduced to shorten the effective length of the magneto-optical head. Further, in Patent Document 2, by adjusting the installation interval of two Wollaston prisms that are manufactured using the same birefringent crystal and have the same apex angle, the interval at which the two light beams separated by polarization are separated. Therefore, the present invention provides a double-image polarizing element group that can cope with the case where the interval between two required light beams is changed to some extent depending on the measurement conditions of the Fourier spectrometer.
JP-A-8-22647 Japanese Patent No. 2514756

  However, since the separation angle of the Wollaston prism and the separation width of the Savart plate depend on the wavelength dependence of the birefringence Δn, which is a material characteristic of the birefringent crystal, the technique described in the above-mentioned document has a separation angle or separation width of It is not enough to adjust the wavelength dependence. For example, in a Wollaston prism using lithium niobate as a birefringent crystal, the birefringence Δn of lithium niobate increases as the wavelength decreases in the near-ultraviolet to near-infrared region, and the amount of change also increases. The separation angle also shows the same tendency, and the shorter the wavelength, the larger the variation. That is, the change in the separation angle is small in the region where the wavelength is 700 nm or more, but the separation angle tends to be large in the region where the wavelength is 700 nm or less. However, for example, when used as a polarization interferometer of a multi-channel Fourier spectrometer, the wavelength resolution becomes finer for shorter wavelengths and becomes coarser for longer wavelengths. It is necessary to reduce the side separation angle and increase the long wavelength side separation angle. Since there is no birefringent crystal that is transparent from ultraviolet to visible light and has a birefringence Δn that is smaller on the shorter wavelength side and larger on the longer wavelength side, the technique described in the above document has such a double-image polarization having such wavelength dependence. An element cannot be obtained.

  There has been a demand for time-resolved spectroscopic measurement in the past in chemical reactions, biological reactions, and physical processes, and time-resolved spectroscopic measurements have been performed using a multichannel analyzer in a dispersive spectroscope that performs wavelength resolution using a diffraction grating or prism. It was. However, a dispersive spectrometer cannot measure beyond the limit of the wavelength range of about one octave. When measuring in a wide wavelength range, it is necessary to change the wavelength range and perform measurement several times. . For this reason, time-resolved spectroscopic measurement is expected in a wide wavelength range using a multi-channel Fourier spectrometer. However, with the technique described in the above document, the wavelength dependence of the birefringent crystal used in the Wollaston prism is expected. Thus, it is impossible to obtain a double-image polarizing element having the wavelength dependency of the separation angle required as a polarization interferometer of a multichannel Fourier spectrometer.

Further, there may be a case where a double-image polarization element having a separation angle that is substantially constant regardless of the wavelength, such as a polarization imaging measurement device. Artificial crystals such as barium borate (BaB ₂ O ₄ , BBO) have been developed as such birefringent crystals having the wavelength dependence of the separation angle, but there are not many methods for producing large crystals. The current situation is that it has not been established and uses are limited.

Therefore, the present invention relates to calcite (CaCO ₃ ), barium borate (BaB ₂ O ₄ ), lithium yttrium fluoride (LiYF ₄ ), crystal (SiO ₂ ), lithium niobate (LiNbO ₃ ), yttrium vanadate (YVO). ₄ ) The first double-image polarizing element using any one of titanium oxide (TiO ₂ ) and lead molybdate (PbMoO ₄ ) as a birefringent crystal is different from the first double-image polarizing element. Provided is a double image polarizing element group in which a second double image polarizing element using a birefringent crystal is combined. Examples of the birefringent crystal used for the second double-image polarizing element include calcite, barium borate, lithium yttrium fluoride, quartz, lithium niobate, yttrium vanadate, titanium oxide, or lead molybdate. A material different from the polarizing element is selected and used.

  The first and second double image polarizing elements constituting the double image polarizing element group are arranged to share the optical axis of the light beam to be transmitted, and both of the first and second double image polarizing elements are Wollaston. Either a prism or both are Savart plates. The Wollaston prism and the Savart plate are both double-image polarization elements made by laminating cut-out birefringent crystals, and are common in that they are separated into mutually orthogonal polarized light when unpolarized light is incident. To do. Further, the separation angle of the Wollaston prism, the separation width of the Savart plate, and the wavelength dependence are common in that they depend on the magnitude and wavelength dependence of the birefringence Δn of the birefringent crystal used as the material.

  When there is a light source on the first Wollaston prism side, the light beam passing through the first Wollaston prism is given to the light beam passing through the opposite angle to the angle given to the light beam. A second Wollaston prism is installed. When there is a light source on the second Wollaston prism side, the first Wollaston prism is given an angle opposite to that given to the light beam by passing through the second Wollaston prism. Installed. That is, when the light beam passes through the first and second Wollaston prisms, the angle given to the light beam by the first Wollaston prism and the angle given to the light beam by the second Wollaston prism are mutually The first and second Wollaston prisms are installed so as to be in opposite directions.

  When there is a light source on the first sabal plate side, the first sabal plate is separated from the separation width given to the light beam by passing through the first savar plate so as to cancel the separation width of the first savar plate. Two savar boards are installed. When there is a light source on the second sabal plate side, the first savar so as to cancel the separation width given to the light beam by passing through the second savar plate and the separation width of the second savar plate. The board is installed. That is, when a light beam is passed through the first and second sabal plates, the separation width imparted to the light beam by the first savar plate and the separation width imparted to the light beam by the second savar plate are mutually beaten. The first and second savar boards are installed so as to be turned off.

  According to the present invention, by combining conventional birefringent crystals, it is possible to obtain a double-image polarizing element group having a wavelength dependency of a desired separation angle or separation width. Furthermore, the separation angle or separation width is small on the short wavelength side and large on the long wavelength side, which cannot be realized by designing and installing a double image polarizing element using only one type of birefringent crystal. Alternatively, it is possible to provide even a double image polarizing element group having a wavelength dependency of the separation width. For example, when such a double-image polarization element group is used in a polarization interferometer of a multichannel Fourier spectrometer capable of time-resolved measurement, almost constant wavelength resolution can be obtained regardless of the wavelength. This makes it possible to perform time-resolved measurement for a wide range of wavelengths at once, which conventionally required several measurements with a limited wavelength range.

  In addition, according to the present invention, a double-image polarizing element that can be adjusted to have an appropriate separation angle or separation width corresponding to the operating conditions of the optical apparatus by exchanging one of the two double-image polarizing elements. A group can be provided.

The main features of the embodiments described below are listed below.
(Feature 1) In the double-image polarizing element group, the interval at which the double-image polarizing elements are installed does not affect the wavelength dependence of the separation angle or the separation width.
(Characteristic 2) In the double-image polarizing element group, each double-image polarizing element is installed sharing the optical axis of the optical system.
(Characteristic 3) In the double-image polarizing element group, the same separation angle is obtained even if the intermediate point of each double-image polarizing element is on the optical axis of the optical system and rotated in the longitudinal direction of the optical axis around the intermediate point. Comb can obtain the wavelength dependence of the separation width.
(Characteristic 4) When the light beam is passed through the first and second double-image polarizing elements, the separation angle or the separation width given to the light beam by the first double-image polarizing element, and the second double-image polarizing element The first and second double-image polarizing elements are installed so that the separation angle or separation width imparted to the light beam is in a direction that cancels each other (opposite directions).

Example 1
Embodiment 1 of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram in which a double-image polarizing element group 1 using two Wollaston prisms used in Example 1 of the present invention is used in a polarization interferometer of a Fourier spectrometer. The polarization interferometer 2 includes a light source 3, an entrance hole 4, a first lens 5, a polarizer 6, a double image polarization element group 1, an analyzer 7, a second lens 8, and a multichannel detector 9 in this order. The optical axis 10 is shared. The light beam that has passed through the incident hole passes through the first lens 5 and the polarizer 6 to become two polarized lights having wavefronts perpendicular to each other. By passing through the double-image polarizing element group 1, the two polarized lights are converted. They are separated with a separation angle θ. The polarization directions of the two separated polarizations are adjusted by the analyzer 7, pass through the second lens 8, form an image, and form interference fringes in the multichannel detector 9. The broken line indicates the localized surface 15 of the interference fringes.

In the first embodiment, as shown in FIG. 2, it is constituted by two Wollaston prisms that share the optical axis 10. On the light source side, a first Wollaston prism 11 made of lithium niobate and designed with an apex angle α ₁ = 16.5 ° is installed. A second Wollaston prism 12 made of calcite and designed to have an apex angle β ₁ = 20 ° is installed in a direction opposite to the light source with respect to the first Wollaston prism. The apex angle α ₁ and the apex angle β ₁ are almost the same as the separation angle obtained for a wavelength of 700 nm when a Wollaston prism made of lithium niobate having an apex angle α ₀ = 14 ° is used alone. Have been adjusted so that. In the first Wollaston prism 11, the optical axis of the central prism piece is perpendicular to the paper surface, and the optical axes of the prism pieces bonded to both sides thereof are parallel to the paper surface. This is the direction. In the second Wollaston prism 12, the direction of the optical axis is reversed, the optical axis of the central prism piece forms the direction of the arrow parallel to the paper surface, and the optical axis of the prism piece bonded to both sides. Is perpendicular to the page.

In this example, the separation angle was calculated using Snell's law in each Wollaston prism. The outline of the calculation method will be described below with reference to FIG. In FIG. 14, a Wollaston prism 43 (ordinary refractive index n _1o , extraordinary refractive index n _1e ) made of a negative birefringent crystal and having an apex angle α is installed on the light source side, The Wollaston prism 44 (ordinary refractive index n _2o , extraordinary refractive index n _2e ) having an apex angle β made of a birefringent crystal is provided. The light beam includes two polarizations orthogonal to each other, that is, S-polarized light in the direction of an arrow parallel to the paper surface and P-polarized light in a direction perpendicular to the paper surface. Of the two Wollaston prisms, the optical axis of the prism piece on the light source side is in the direction of the arrow parallel to the same plane as the S-polarized light, and the optical axis of the prism piece on the lower side of the light source is the same as that of the P-polarized light The orientation is perpendicular to the page. The two Wollaston prisms are installed so that the inclinations of the joint surfaces face each other.

The two polarized light beams enter the Wollaston prism 43 having the apex angle α, the S polarized light travels straight as an ordinary ray, and the P polarized light travels straight as an extraordinary ray, and enters the joint surface AA ′ at an incident angle α. When the refraction angle of S-polarized light at the joint surface AA ′ is θ _S1 , the refraction angle of P-polarized light is θ _P1, and Snell's law is used, the S-polarized light changes from ordinary light to extraordinary light at the joint surface AA ′. Since polarized light changes from an extraordinary ray to an ordinary ray, the following equation is established.
n _1o sin (α) = n _1e sin (θ _S1 ) (1)
n _1e sin (α) = n _1o sin (θ _P1 ) (2)
Here, since the Wollaston prism 43 having the apex angle α is a negative crystal and n _1o > n _1e , θ _P1 <α <θ _{S1 is} satisfied, and the S-polarized light is upward in FIG. In FIG. 14, it is separated in the downward direction on the paper surface.

S-polarized light travels in the crystal as an extraordinary ray, and P-polarized light travels in the crystal as an ordinary ray, reaches the interface BB ′, is refracted, and exits from the Wollaston prism 43 having an apex angle α. When the refraction angle of S-polarized light at the interface BB ′ is θ _S2 and the refraction angle of P-polarized light is θ _P2 , the following equation is established according to Snell's law.
n _1e sin (α−θ _S1 ) = n _m sin (θ _S2 ) (3)
n _1o sin (α−θ _P1 ) = n _m sin (θ _P2 ) (4)
Here, _nm is the refractive index of the medium around the Wollaston prism, and is 1 in the case of a vacuum. The difference between θ _S2 and θ _P2 represents the separation angle given to the light beam by the Wollaston prism 43 having the apex angle α installed on the light source side.

When the refraction angle of S-polarized light at the interface CC ′ incident on the Wollaston prism 44 having the apex angle β is θ _S3 and the refraction angle of P-polarized light is θ _P3 , the S-polarized light is an ordinary ray, and the P-polarized light is an extraordinary ray. Similarly, the following equation is established.
n _m sin (θ _S2 ) = n _2o sin (θ _S3 ) (5)
n _m sin (θ _P2 ) = n _2e sin (θ _P3 ) (6)

Similarly, if the refraction angle of the S-polarized light at the joint surface DD ′ is θ _S4 and the refraction angle of the P-polarized light is θ _P4 , the S-polarized light changes from an ordinary ray to an extraordinary ray at the joint surface AA ′. Since the extraordinary ray is changed to the ordinary ray, the following equation is established.
n _2o sin (β−θ _S3 ) = n _2e sin (θ _S4 ) (7)
n _2e sin (β−θ _P3 ) = n _2o sin (θ _P4 ) (8)
Here, the Wollaston prism 44 having the apex angle β is a negative crystal, and n _2o > n _2e .

S-polarized light travels through the crystal as an extraordinary ray, and P-polarized light travels through the crystal as an ordinary ray to interface EE.
'Is reached, refracts and exits from the Wollaston prism 44 with apex angle β. When the refraction angle of S-polarized light at the interface EE ′ is θ _S5 and the refraction angle of P-polarized light is θ _P5 , the following equation is similarly established.
n _2e sin (β−θ _S4 ) = n _m sin (θ _S5 ) (9)
n ₂ sin (β−θ _P4 ) = n _m sin (θ _P5 ) (10)

Here, θ _S5 is an angle formed by S-polarized light and the optical axis, and θ _P5 is an angle formed by P-polarized light and the optical axis. _Therefore , the difference between θ _S5 and θ _P5 is the double-image polarizing element shown in FIG. The group separation angle θ. When used in a polarization interferometer as in this embodiment, it is desirable that the optical path difference between the P-polarized light and the S-polarized light incident in parallel to the optical axis is the same, so that the double Wollaston prism is used when the apex angle is increased. Is used. The calculation method using the above formulas (1) to (10) can be similarly used in the double Wollaston prism.

FIG. 3 is a diagram showing the results of examining the wavelength dependence of the separation angle by applying the calculation method described using the equations (1) to (10) to the double-image polarizing element group in the present embodiment. Yes, the result of this example is indicated by a one-dot chain line. The angle of the vertical axis indicates the angle at which each polarized light is separated, and the two polarized lights are separated by being given angles in opposite directions with 0 ° being parallel to the optical axis. Show. The difference between the curve having a positive angle and the curve having a negative angle represents the separation angle θ. As a comparative example, the separation angle of a Wollaston prism using lithium niobate with an apex angle α ₀ = 14 ° at which the separation angle at a wavelength of 700 nm is substantially the same is also shown as a solid line in FIG.

  As shown in FIG. 3, the separation angle in the long wavelength region is almost the same in both the present example and the comparative example and is almost constant with respect to the wavelength. However, in the short wavelength region, the wavelength in the comparative example is In contrast, in the double-image polarizing element group of this example, the separation angle becomes smaller as the wavelength becomes shorter as the length becomes shorter.

In the present invention, whether a double Wollaston prism or a Wollaston prism composed of two prism pieces as shown in FIG. It can be installed so that the wavelength dependency is almost the same. In FIG. 4, a Wollaston prism made of lithium niobate and having an apex angle α ₂ = 2.0 ° is used as the first Wollaston prism 11 and is made of calcite and has an apex angle β ₂ = 1.9 °. A Wollaston prism is used as the second Wollaston prism 12. The apex angle α ₁ and the apex angle β ₁ are substantially the same as the separation angle obtained for a wavelength of 900 nm when a Wollaston prism made of lithium niobate having an apex angle α ₀ = 2 ° is used alone. Have been adjusted so that. The first and second Wollaston prisms are installed so as to share the optical axis. The direction of the optical axis of the prism piece on the light source side is parallel to the paper surface indicated by the arrow in FIG. The direction of the axis is a direction perpendicular to the paper surface. The inclination of the joint surface of the first Wollaston prism is low on the light source side and increases in the traveling direction of the light source. The inclination of the joint surface of the second Wollaston prism is opposite to that of the first Wollaston prism.

By applying the calculation method described in the formulas (1) to (10) to the double-image polarizing element group installed as shown in FIG. 4, the result of calculating the wavelength dependence of the separation angle θ of the double-image polarizing element group is shown. This is indicated by a broken line in FIG. As a comparative example, the solid line in FIG. 5 also shows the separation angle of a Wollaston prism using a single piece of lithium niobate with an apex angle α ₀ = 2 ° at which the separation angle at wavelengths of 700 nm or more is substantially the same. In the double-image polarizing element group of the example, as in the case of FIG. 3, the separation angle on the short wavelength side is smaller than that on the long wavelength side.

FIG. 6 is a diagram showing wavelength resolution in a Wollaston prism using a single image of the lithium niobate having the apex angle α ₀ = 2 ° used in the double-image polarizing element group of this example and the comparative example. Waves on the vertical axis represents an optical path difference between an ordinary ray and an extraordinary ray generated by a Wollaston prism having a diameter of 10 mm, that is, an optical path difference between an ordinary ray and an extraordinary ray corresponding to 10 mm in a localized plane of interference fringes on the detector. Is a dimensionless number normalized by the wavelength, and the horizontal axis is the wavelength. The fact that the curve in FIG. 6 approaches linearity indicates that the wavelength resolution (Δλ) is constant regardless of the wavelength. As shown in FIG. 6, compared with the comparative example, in this example, the wavelength is closer to linear at a wavelength of 400 to 1000 nm, and if this is used for a Fourier spectrometer, wavelength decomposition is not dependent on the wavelength in a specific wavelength range. It can be almost constant.

(Example 2)
In the double-image polarizing element group of this example, as in Example 1, the birefringent crystal used for the first Wollaston prism 11 is lithium niobate and the birefringent crystal used for the second Wollaston prism 12 is calcite. As shown in FIG. When a Wollaston prism made of lithium niobate with apex angle α ₁ = 4.5 °, apex angle β ₁ = 9 ° and apex angle α ₀ = 14 ° is used alone, a wavelength of 700 nm is obtained. It is adjusted so as to be almost the same as the separation angle.

  Also in this example, the wavelength dependence of the separation angle was calculated in the same manner as in Example 1, and the result is shown by a two-dot chain line in FIG. As shown in FIG. 3, when a Wollaston prism is combined as in this embodiment, a double-image polarizing element group having a separation angle θ of about 0 to 5 ° regardless of the wavelength can be obtained. Thus, the double-image polarization element group having almost no wavelength dependency of the separation angle is suitable for performing polarization imaging measurement.

An artificially manufactured barium borate (BaB ₂ O ₄ , BBO) is a birefringent crystal having almost no wavelength dependency of the separation angle. However, barium borate has a drawback that it is difficult to obtain large crystals. Lithium niobate and calcite used in this example are birefringent crystals that can obtain large crystals, and combinations thereof can provide characteristics comparable to barium borate. Expanding.

(Example 3)
In the double-image polarizing element group of this example, as in Example 1, the birefringent crystal used for the first Wollaston prism 11 is lithium niobate and the birefringent crystal used for the second Wollaston prism 12 is calcite. As shown in FIG. When a Wollaston prism made of lithium niobate with apex angle α ₁ = 30 °, apex angle β ₁ = 8.95 °, and apex angle α ₀ = 14 ° is used alone, a wavelength of 700 nm is obtained. It is adjusted so as to be almost the same as the separation angle.

  Also in this example, the wavelength dependence of the separation angle was calculated in the same manner as in Example 1, and the result is shown by the broken line in FIG. As shown in FIG. 3, in the region where the wavelength is 700 nm or more, the present embodiment and the comparative example have the same separation angle. However, in the region where the wavelength is shorter than 700 nm, the separation of the present embodiment is performed. The corner is larger than the separation angle of the comparative example. In order to reduce the separation angle in a wide wavelength region, the vertex angle of the Wollaston prism may be adjusted, but the separation angle in the short wavelength region is also reduced. However, if the Wollaston prism is combined to cancel the separation angle as in this embodiment, the separation angle in a wide wavelength region is reduced, but the separation angle in a short wavelength region is not so small. That is, it is possible to obtain a multi-image polarizing element group in which the ratio of the separation angle in the short wavelength region to the separation angle in the long wavelength region is larger than that of a single Wollaston prism.

  Since Wollaston prisms can acquire both vertical and horizontal polarization at the same time, they have been used for polarization spectroscopy observations. However, the separation angle in the short wavelength region is smaller than the separation angle in the wide wavelength region, and chromatic dispersion is achieved. Because of its small size, a Wollaston prism was combined with a dispersive element to compensate for this. According to the double-image polarizing element group in which the Wollaston prism of this embodiment is combined, the ratio of the separation angle in the short wavelength region to the separation angle in the long wavelength region is larger than that of the single Wollaston prism. Therefore, the chromatic dispersion can be increased with respect to the separation angle, and when used for deflection spectroscopy observation, a dispersive element can be dispensed with.

In the first to third embodiments, the first Wollaston prism using lithium niobate as a birefringent crystal and the second Wollaston prism using calcite as a birefringent crystal are combined to form a double image. They are the same in that they constitute a polarizing element group, and differ in the ratio tanβ ₁ / tanα ₁ of the magnitude of the tangent of the apex angles of the two Wollaston prisms. When the apex angle tangent ratio tanβ ₁ / tan α ₁ is combined so as to be 0.46 or less, the wavelength dependency of the separation angle as in Example 3 is obtained, and the apex angle tangent ratio is increased to increase tan β ₁ When / tan α ₁ is about 0.57 to 0.8, the wavelength dependence of the separation angle as in Example 1 is obtained, and when the ratio of the tangent of the apex angle tan β ₁ / tan α ₁ is about 2, This is the wavelength dependency of the separation angle. That is, for example, the first Wollaston prism made of lithium niobate is fixed, and several types of second Wollaston prisms made of calcite having different apex angles are prepared, and are replaced as appropriate to obtain the wavelength dependence of a desired separation angle. It is also possible to adjust so that the wavelength dependency of an appropriate separation angle is obtained according to the operating conditions of the optical apparatus.

  In Examples 1 to 3, the double-image polarizing element group is configured by using lithium niobate as the first Wollaston prism and calcite as the second Wollaston prism as the birefringent crystal. Calcite, barium borate, lithium yttrium fluoride, quartz, lithium niobate, yttrium vanadate, titanium oxide, or molybdenum, depending on what optical device the image polarizing element group is used in and in what wavelength range Two birefringent crystals having different (not similar to) the wavelength dependence of birefringence Δn may be selected from lead acid, and one of them may be a first Wollaston prism and the other may be a second Wollaston prism. For example, as in Examples 1 to 3, birefringent crystals are formed from lithium niobate, yttrium vanadate, titanium oxide, or lead molybdate in which the wavelength dependence of birefringence Δn is relatively large in the region of wavelength 400 nm or more. The first Wollaston prism is selected, and the second Wollaston prism is selected by selecting a birefringent crystal from calcite, barium borate, lithium yttrium fluoride, and quartz whose wavelength dependence of the birefringence Δn is relatively small. Is preferred.

  On the other hand, lithium niobate, yttrium vanadate, titanium oxide, or lead molybdate, whose wavelength dependence of birefringence Δn is relatively large, cannot be suitably used because light absorption increases in the region of 400 nm or less. In such a case, it is necessary to use calcite, barium borate, lithium yttrium fluoride, or quartz crystal that transmits light to a region where the wavelength in the ultraviolet region is near 200 nm as the birefringent crystal. In this case, for example, a calcite having a relatively large wavelength dependency of birefringence Δn in the ultraviolet region is used as the first Wollaston prism, and barium borate, lithium yttrium fluoride having a relatively small wavelength dependency of birefringence Δn, It is preferable to use quartz as the second Wollaston prism.

Example 4
In this embodiment, the double-image polarizing element group 1 is composed of two double Wollaston prisms that share the optical axis 10 as shown in FIG. On the light source side, a first Wollaston prism 11 made of lithium niobate and designed with an apex angle α ₃ = 40 ° is installed. In the direction opposite to the light source with respect to the first Wollaston prism, A second Wollaston prism 12 made of yttrium vanadate and designed with an apex angle β ₃ = 15.8 ° is provided.

  As shown in FIG. 7, in the first and second Wollaston prisms 11 and 12, the optical axis of the central prism piece is perpendicular to the paper surface, and the prism pieces are bonded to both sides thereof. These optical axes are in the direction of arrows parallel to the paper surface. The first and second Wollaston prisms 11 and 12 are installed such that the apex angles of the central prisms are upward.

  Also in this example, the wavelength dependence of the separation angle was calculated in the same manner as in Example 1, and the results are shown in FIG. From FIG. 8, when the Wollaston prism is installed as in this embodiment, the wavelength dependence of the separation angle approaches linear in the wavelength range of 800 nm to 3000 nm, and the separation angle is small in the short wavelength region and large in the long wavelength region. A double-image polarizing element group can be obtained. If this is used for polarization spectroscopy measurement, it is possible to overcome the disadvantage that the wavelength resolution becomes finer as the short wavelength and becomes coarser as the long wavelength. In the wide wavelength range of wavelengths from 800 nm to 3000 nm, almost constant wavelength resolution can be achieved. Obtainable.

In the present embodiment, a third Wollaston prism may be added further to the lower side of the light source than the second Wollaston prism. FIG. 9 is a diagram in which a titanium oxide double Wollaston prism is installed as the third Wollaston prism 13. The first to third Wollaston prisms 11, 12, and 13 share the optical axis 10 of the optical system, and the apex angles are upward in the first, second, and third order from the light source side. It is installed as follows. The optical axis of the third Wollaston prism 13 is the same as that of the first and second Wollaston prisms 11 and 12, and the optical axis of the central prism piece is perpendicular to the paper surface, and both sides thereof. The optical axis of the prism piece bonded to the head is in the direction of an arrow parallel to the paper surface. Designed with the first Wollaston prism apex angle α ₃ = 40 °, the second Wollaston prism apex angle β ₃ = 9.3 °, and the third Wollaston prism apex angle γ ₁ = 5 ° Yes.

  Also in this example, the wavelength dependence of the separation angle was calculated in the same manner as in Example 1, and the results are shown in FIG. Compared with the result without the third Wollaston prism shown in FIG. 8, the wavelength dependence of the separation angle is linear even in a shorter wavelength region.

  Based on the result of FIG. 10, as in the first embodiment, the dimension of the vertical axis Waves is a dimensionless number obtained by normalizing the optical path difference between the ordinary ray and the extraordinary ray generated by the Wollaston prism having a diameter of 10 mm by the wavelength. FIG. 11 shows the wavelength. From FIG. 11, the wavelength is closer to linear at a wavelength of 500 to 3000 nm, and the wavelength resolution is constant regardless of the wavelength. When this is used for a Fourier spectrometer, the wavelength resolution is almost constant in a specific wavelength range. can do.

  In this embodiment, it is possible to provide a double-image polarizing element group having the wavelength dependency of the separation angle or separation width which has not been obtained conventionally. If such a double-image polarizing element group is used as a polarization spectroscopic measurement or a polarization interferometer of a multichannel Fourier spectrometer, it is possible to obtain almost constant wavelength resolution regardless of wavelength, and time-resolved measurement at a wide wavelength at a time. Will be able to do.

  In Example 4 and its modifications, yttrium vanadate, titanium oxide, and lead molybdate can be used as the birefringent crystal instead of lithium niobate. These birefringent crystals have a wavelength dependency of birefringence Δn similar to that of lithium niobate in a region of wavelength of 400 nm or more, and are larger than calcite and quartz. Similarly, in Example 4 and the modification, lithium niobate, titanium oxide, and lead molybdate can be used as a birefringent crystal instead of yttrium vanadate. In the modification of Example 4, titanium oxide Alternatively, lithium niobate, yttrium vanadate, or lead molybdate can be used as the birefringent crystal. However, in any case, the first to third Wollaston prisms are composed of different birefringent crystals.

  In Example 4, when two birefringent crystals are selected from lithium niobate, yttrium vanadate, titanium oxide, and lead molybdate having similar wavelength dependence of birefringence Δn, among the above four substances, In comparison, it is preferable to combine birefringent crystals having relatively different wavelength dependencies of birefringence Δn.

  In the first to fourth embodiments and the modifications thereof, the distance between the first to third Wollaston prisms does not affect the wavelength dependence of the separation angle of the double-image polarizing element group. Whether the Wollaston prisms are installed in contact with each other or separated from each other, a double-image polarizing element group having the same wavelength dependency of the separation angle can be obtained.

  Further, in the above-described first to fourth embodiments and the modifications thereof, when the direction of the light source is reversed, that is, the intermediate point of the first to third Wollaston prisms is set on the optical axis, and this is the center. Even when rotated 180 ° in the longitudinal direction of the optical axis, the same wavelength dependence of the separation angle can be obtained.

  In addition, since the birefringent crystal to be used is a positive crystal or a negative crystal, the directions of the angles given to the two polarized lights are reversed, so the angles given by the first Wollaston prism for each polarized light, It is necessary to change the direction of the optical axis and the direction of the inclination of the joint surface so that the angles given by the second Wollaston prism are opposite to each other. Since lead molybdate is the same negative crystal as lithium niobate, a Wollaston prism may be installed in the same direction as lithium niobate. Since yttrium vanadate and titanium oxide are positive crystals, when used in place of lithium niobate, the optical axis of the prism constituting the double-image polarizing element is rotated by 90 ° around the optical axis, or the double-image polarizing element Needs to be adjusted by a method such as rotating 180 ° around the optical axis.

(Example 5)
FIG. 12 is a diagram in which a double-image polarization element group 21 using two Savart plates used in Example 5 of the present invention is used in a polarization interferometer of a Fourier spectrometer. In the polarization interferometer 22, a light source 23, a polarizer 26, a double-image polarization element group 21, an analyzer 27, a lens 28, and a multichannel detector 29 are installed in this order while sharing the optical axis 10. The light beam emitted from the light source 23 passes through the polarizer 26, thereby having two wave polarizations having a wavefront perpendicular to each other and forming an angle of 45 ° with the paper surface in FIG. The two polarized light beams are separated with a separation width a by passing through the double-image polarizing element group 21. The polarization directions of the two separated polarizations are adjusted by the analyzer 27, pass through the lens 28, and form interference fringes in the multichannel detector 9.

  In the fifth embodiment, the double-image polarizing element group 21 includes a first sabal plate 31 made of lithium niobate and a second savar plate 32 made of calcite as shown in FIG. As shown in FIG. 13, the optical axis of the first savar plate 31 and the optical axis of the second savar plate 32 are installed so as to be opposite to each other.

  As in the first to third embodiments, the ratio M / L of the width L of the first sabal plate 31 made of lithium niobate and the width M of the second savar plate 32 made of calcite is changed. By doing so, the wavelength dependence of the separation width obtained by the double-image polarizing element group 21 can be adjusted.

The separation width of the Savart plate can be calculated as described below. When the angle between the incident surface and the optical axis is φ (= 45 °), the thickness of one birefringent plate in the optical axis direction is t, and the separation width is δ, the separation width a of the Savart plate is given by Can be represented.
_{^{δ = t (n e 2 -n}} o 2) sin 2 φ / (n e 2 sin 2 φ + n o 2 cos 2 φ) ...... (11)
If φ = 45 °,
_{^{δ = t (n e 2 -n}} o 2) / (n e 2 + n o 2)
_{≒ 2t (n e -n o)} / (n e + n o) ...... (12)
Since the separation width a of the 2t-thick Savart plate is a = √2δ, the separation width can be calculated from Equation (12).

When the separation width is calculated for the double-image polarizing element group shown in FIG. 13 using Equation (12), the separation width a ₁ obtained by the first Savart plate is a ₁ = √2L (n _1e −n _1o ) / (N _1e + n _1o ). Similarly, the separation width a ₂ obtained by the second Savart plate is a ₂ = √2M (n _2e −n _2o ) / (n _2e + n _2o ). As shown in FIG. 13, when the separation width a _{1 provided} by the first savar plate is arranged in such a direction that the separation width a _{2 provided} by the second savar plate cancels, the entire double-image polarizing element group Since the separation width x obtained in ( ₁₎ is x = a ₁ −a ₂ , it is expressed by the following equation.
x = √2L (n _1e −n _1o ) / (n _1e + n _1o )
−√2M (n _2e −n _2o ) / (n _2e + n _2o ) (13)

  In this embodiment, since the birefringent crystal used for the first savar plate and the birefringent crystal used for the second savar plate are different, the first savar plate 31 is based on the equation (13). The wavelength dependency of the separation width obtained by the double-image polarizing element group 21 can be adjusted by changing the ratio M / L of the width L of the second sabal plate 32 and the width M of the second Savart plate 32.

In this embodiment, the calculation of the separation width when the ratio M / L of the width L of the first savar plate 31 and the width M of the second savar plate 32 is changed using the above equation (13). went. As Example 5-1, when the width L of the first Savar plate is 40 mm and the width of the second Savar plate is M = 20.157 mm, the width L of the first Savar plate is as Example 5-2. When the width M of the second sabal plate is 10 mm and the width M of the second savar plate is 10.8 mm, the width L of the first savar plate is 60 mm and the width M of the second savar plate is 13.438 mm as Example 5-3. FIG. 15 shows the calculation results of the respective separation widths. In FIG. 15, the vertical axis represents the separation width obtained by the double image polarizing element composed of two Savart plates according to this embodiment, and the horizontal axis represents the wavelength. In this example, the directions of the first and second savar plates are as shown in FIG. 13, and when a savar plate made of lithium niobate having a width L ₀ = 20 mm is used alone, the wavelength is 900 nm. The separation width is adjusted so as to be almost the same. As a comparative example, a Savart plate made of lithium niobate having a width L ₀ = 20 mm is also shown in FIG.

  From FIG. 15, in Example 5-2 with a large M / L, the wavelength dependence of the separation width can be canceled as in Example 2. In Example 5-1, in which M / L is smaller than that in Example 5-2, the separation width can be reduced on the short wavelength side as in Example 1. Further, in Example 5-3 in which M / L is further reduced, as in Example 3, the separation width in a wide range can be reduced without excessively reducing the separation width on the short wavelength side.

  As shown in FIG. 15, in this embodiment, lithium niobate is used as a birefringent crystal as in Embodiments 1 to 3 related to the double-image polarizing element group including two Wollaston prisms. The wavelength dependence of the separation width can be adjusted by adjusting the ratio M / L of the width L of the first savar plate and the width M of the second savar plate using calcite as a birefringent crystal. In addition, a double-image polarizing element group suitable for optical instruments such as polarization imaging measurement, a polarization interferometer of a Fourier spectrometer, and polarization spectroscopy observation can be provided. Similarly, the first Savart plate made of, for example, lithium niobate is fixed, and several types of second Wollaston prisms made of calcite having different widths M are prepared. It is also possible to adjust so that the wavelength dependency of the appropriate separation width is obtained according to the operating conditions of the optical apparatus.

Also in this example, as in Examples 1 to 3, depending on what optical device the double-image polarizing element group is used and in what wavelength range, calcite, barium borate, Two birefringent crystals with different (not similar) wavelength dependence of birefringence Δn are selected from lithium yttrium fluoride, crystal, lithium niobate, yttrium vanadate, titanium oxide, or lead molybdate, and one of them is the first savar. A plate may be used and the other may be a second Savart plate. For example, as in Examples 1 to 3, birefringent crystals are formed from lithium niobate, yttrium vanadate, titanium oxide, or lead molybdate in which the wavelength dependence of birefringence Δn is relatively large in the region of wavelength 400 nm or more. It is preferable to select a birefringent crystal from calcite, barium borate, lithium yttrium fluoride, and quartz that have a relatively small wavelength dependence of birefringence Δn, and to make a second savar plate. .
In a region where the wavelength in the ultraviolet region is near 400 nm, a calcite having a relatively large wavelength dependence of the birefringence Δn in the ultraviolet region is used as the first Wollaston prism, and a borolith having a relatively small wavelength dependence of the birefringence Δn. It is preferable to use barium acid, lithium yttrium fluoride, or quartz as the second Wollaston prism.

(Example 6)
In this example, the first savar plate is a savar plate having a width L = 20 mm using lithium niobate as a birefringent crystal. In Example 6-1, the second savar plate has a width M = In Example 6-2, the second Savart plate was yttrium vanadate having a width L = 7.08 mm. The installation directions of the first and second Savart plates are the same as in FIG. Also in this example, the wavelength dependence of the separation width was calculated using the equation (13) in the same manner as in Example 5 and is shown in FIG. In FIG. 16, the absolute value of the scale on the vertical axis is the separation width of the two polarized lights to be separated.

  As shown in FIG. 16, also in this example, as in Example 4, the wavelength dependence of the separation angle approaches linear in the wavelength region of 800 nm to 3000 nm, the separation angle is small in the short wavelength region, and the long wavelength region. It is possible to obtain a double-image polarizing element group that becomes larger at As in Example 4, if this is used for polarization spectroscopy measurement, the wavelength resolution can be overcome as the shorter wavelength becomes finer, and the longer wavelength becomes rougher. In a wide wavelength range of wavelengths from 800 nm to 3000 nm. A substantially constant wavelength resolution can be obtained.

(Example 7)
In this example, the first savar plate was a savar plate made of lithium niobate, the second savar plate was titanium oxide, and the third savar plate was yttrium vanadate. Regarding the width L of the first savar plate, the width M of the second savar plate, and the width N of the third savar plate, in Example 7-1, L = 20 mm, M = 9.08 mm, N = 2 mm It was. In Example 7-2, L = 20 mm, M = 6 mm, and N = 1.08 mm. In Example 7-3, L = 20 mm, M = 4 mm, and N = 3.08 mm. The installation directions of the first and second Savart plates are the same as in FIG. In the installation direction of the third sabal plate of Example 7-1, the separation width given to the light beam by the second savar plate and the separation width given to the light beam by the third savar plate are struck together. It is installed so that the direction of the optical axis is opposite to that of the second Savart plate. The installation direction of the third sabal plate of Example 7-2 and Example 7-3 is given to the light beam by the separation width given to the light beam by the first savar plate and the third savar plate. It is installed so as to be in the same optical axis direction as the second Savart plate so that the separation widths cancel each other. Also in this example, the wavelength dependence of the separation width was calculated using the equation (13) in the same manner as in Example 5 and is shown in FIG. In FIG. 17, the absolute value of the scale on the vertical axis is the separation width of the two polarized lights to be separated.

  Compared to Example 6-2 shown in FIG. 16 in which the first sabal plate is sodium niobate and the second savar plate is yttrium vanadate, titanium oxide is further added as the third savar plate shown in FIG. In Examples 7-1 to 7-3 according to the present example arranged below the light source, the wavelength dependence of the separation width is close to linear even in a region where the wavelength is shorter than 800 nm. The result is the same as that of the modified example of Example 4 in which the prism is used as the double image polarizing element.

  In Example 6 and Example 7 as well, as in Example 4 and the modification described above, lithium niobate, yttrium vanadate, titanium oxide, and lead molybdate used as the birefringent crystals can be exchanged with each other. is there. However, in any case, the first to third Savart plates are made of different materials. In addition, when exchanging the positive crystal sabal plate and the negative crystal savar plate, for example, they are installed in a direction rotated by 180 ° around the optical axis so that the angles given to the two polarized lights do not change. The points that are necessary are the same as in the fourth embodiment and the modified example. Also in Example 6, as in Example 4, when selecting two birefringent crystals from lithium niobate, yttrium vanadate, titanium oxide, and lead molybdate having similar wavelength dependence of birefringence Δn, It is preferable to combine birefringent crystals having relatively different wavelength dependences of the birefringence Δn among the four substances.

  Also in the fifth to seventh embodiments, as in the first to fourth embodiments and the modified example, the interval between the respective Savart plates forming the double-image polarizing element group may or may not be present. Further, the same wavelength dependence of the separation width can be obtained even if the intermediate point of each Savart plate is taken on the optical axis of the optical system and rotated 180 ° in the longitudinal direction of the optical axis around the intermediate point. .

The block diagram of the multichannel Fourier spectrometer using the double-image polarizing element group which consists of a Wollaston prism of an Example. FIG. 6 is a side view of a double-image polarizing element group according to Embodiments 1 to 3. The figure which shows the wavelength dependence of the separation angle which concerns on the double image polarizing element group of Example 1 thru | or Example 3, and the double image polarizing element of a comparative example. FIG. 3 is a side view of the double-image polarizing element group of Example 1. FIG. 4 is a diagram showing the wavelength dependence of the separation angle according to the double-image polarizing element group of Example 1. FIG. 3 is a diagram illustrating wavelength decomposition related to a double-image polarizing element group of Example 1 and a double-image polarizing element of a comparative example. FIG. 6 is a side view of a double-image polarizing element group of Example 4. FIG. 10 is a diagram showing the wavelength dependence of the separation angle according to the double-image polarizing element group of Example 4. The side view of the double image polarizing element group of a modification. The figure which shows the wavelength dependence of the separation angle which concerns on the double-image polarizing element group of a modification. The figure showing the wavelength decomposition which concerns on the double image polarizing element group of a modification. FIG. 6 is a configuration diagram of a multichannel Fourier spectrometer using a double-image polarizing element group composed of a Savart plate of Example 5. FIG. 13A is a plan view of the double-image polarizing element group of Example 5, and FIG. 13B is a side view of the double-image polarizing element group of Example 5. The figure explaining the refraction of the light beam in two Wollaston prisms. FIG. 10 is a diagram showing the wavelength dependence of the separation width according to the double-image polarizing element group of Example 5. FIG. 10 is a diagram showing the wavelength dependence of the separation width according to the double-image polarizing element group of Example 6. FIG. 10 is a diagram showing the wavelength dependence of the separation width according to the double-image polarizing element group of Example 7. The figure explaining a Wollaston prism. The figure explaining a Savart board.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Double image polarization element group comprised by Wollaston prism 2 Polarization interferometers 3, 23 Light source 4 Entrance hole 5 First lens 6, 26 Polarizer 7, 27 Analyzer 8 Second lens 9, 29 Multichannel detection Device 10 Optical axis 11 First Wollaston prism 12 Second Wollaston prism 13 Third Wollaston prism 15 Local surface 21 of interference fringes Double-image polarizing element group 28 composed of a Savart plate Lens 31 First Savart plate 32 Second Savart plate 41 Wollaston prism 42 Savart plate 43 Wollaston prism 44 installed on the light source side Wollaston prism 51 installed on the lower side of the light source 51 First prism 52 Second prism 53 First polarizing plate 54 2 polarizing plates

Claims (4)

A first Wollaston prism using calcite, barium borate, lithium yttrium fluoride, quartz, lithium niobate, yttrium vanadate, titanium oxide, or lead molybdate as a birefringent crystal;
A second material using, as a birefringent crystal, a material different from the first Wollaston prism among calcite, barium borate, lithium yttrium fluoride, crystal, lithium niobate, yttrium vanadate, titanium oxide, or lead molybdate. A double-image polarizing element group including a Wollaston prism,
The first Wollaston prism and the second Wollaston prism share an optical axis with respect to a light beam passing through the first and second Wollaston prisms, and are formed by the first Wollaston prism. A multi-image polarizing element group installed such that an angle given to the light beam and an angle given to the light beam by the second Wollaston prism are opposite to each other. Of the calcite, barium borate, lithium yttrium fluoride, crystal, lithium niobate, yttrium vanadate, titanium oxide, or lead molybdate, a material different from the first and second Wollaston prisms is used as the birefringent crystal. A third Wollaston prism is added,
The first to third Wollaston prisms share an optical axis with respect to light beams that pass through the first to third Wollaston prisms, and are converted into light beams by the first or second Wollaston prisms. 2. The double-image polarizing element according to claim 1, wherein the imparted angle and the angle imparted to the light beam by the third Wollaston prism are opposite to each other. group. A first Savart plate using calcite, barium borate, lithium yttrium fluoride, crystal, lithium niobate, yttrium vanadate, titanium oxide, or lead molybdate as a birefringent crystal;
A second material using, as a birefringent crystal, a material different from the first Savart plate among calcite, barium borate, lithium yttrium fluoride, crystal, lithium niobate, yttrium vanadate, titanium oxide, or lead molybdate A double-image polarizing element group comprising a Savart plate,
The first sabal plate and the second savar plate share an optical axis with respect to the light beam passing through the first and second savar plates, and are applied to the light beam by the first savar plate. The double-image polarizing element group in which the first and second savar plates are installed so that the separation width and the separation width given to the light beam by the second savar plate cancel each other. Of calcite, barium borate, lithium yttrium fluoride, crystal, lithium niobate, yttrium vanadate, titanium oxide, or lead molybdate, a material different from the first and second Savart plates is used as a birefringent crystal. A third sabal plate is added,
The first to third savart plates share an optical axis with respect to the light beams passing through the first to third savart plates, and are given to the light beams by the first or second savart plate. The said 2nd and 3rd saval board is installed so that the separation width and the separation width provided to a light beam by the said 3rd savar board may mutually cancel. Double image polarizing element group.

Images