Broadband circular polarizer and measurement device equipped with the broadband circular polarizer

Abstract

To provide an optical element that can be used in wavelength regions from vacuum ultraviolet to near-infrared light and can create precise circularly polarized light.SOLUTION: A wide-band circular polarizer 1 includes: a λ / 2 part H for giving a phase difference of approximately 180 degrees between a p-wave and an s-wave by total reflection; and a λ / 4 part Q for giving a phase difference of approximately 90 degrees between the p-wave and the s-wave by the total reflection. The incident surface of the λ / 4 part Q is rotated with respect to the incident surface of the λ / 2 part H by approximately 60 degrees with an incidence light beam axis as an axis of rotation. The λ / 2 part H and the λ / 4 part Q are formed of Fresnel rhomb and convert straight polarization into circular polarization.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a circular polarizer, and more particularly to a broadband circular polarizer that can be used in a broad band and a measurement device equipped with the broadband circular polarizer. [Background technology]

[0002] A wave plate is an optical element that changes the state of incident polarization by giving a specific phase difference (optical path difference) to two orthogonal polarized components. Generally, two types of wave plates are commonly used: 1 / 2 wave plates (λ / 2 plates) and 1 / 4 wave plates (λ / 4 plates).

[0003] A half-wave plate (HWP) is a wave plate that gives a phase difference of 1 / 2 to the incident light beam, specifically, it is an optical element that gives a phase difference of λ / 2 (180°) to the electric field vibration direction (polarization plane) of the incident light beam. A half-wave plate gives a phase difference of λ / 2 (180°) to the incident light beam and is used to rotate linearly polarized light for emission.

[0004] A quarter-wave plate (QWP) is a wave plate that gives a quarter phase difference to the incident light beam, specifically, it is an optical element that gives a phase difference of λ / 4 (90°) to the electric field vibration direction (polarization plane) of the incident light beam. A quarter-wave plate gives a phase difference of λ / 4 (90°) to the incident light beam, and is used to change linearly polarized light into circularly polarized light, or circularly polarized light into linearly polarized light.

[0005] Patent Document 1 describes a technique that uses a phase difference plate in which a quarter-wave plate and a half-wave plate are bonded together at a pre-designed angle to control the wavelength dispersion of retardation, and in particular, makes the ratio of retardation to the wavelength (λ) of incident light (Δnd / λ) almost constant.

[0006] Patent Document 2 describes a stacked wave plate in which two wave plates are stacked so that their optical axes intersect at an angle of 60°, and the whole functions as a quarter-wave plate at wavelengths of 400 nm, 650 nm, and 785 nm. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 10-68816 [Patent Document 2] Patent No. 4825951 Summary of the Invention [Problem to be solved by the invention]

[0008] In recent years, light sources that emit circularly polarized light have been developed, but currently there are very few light sources that emit circularly polarized light. Therefore, in order to create a circularly polarized state, specific optical elements are required.

[0009] By using circularly polarized light, optical systems are less susceptible to the effects of instrument polarization, and in polarization analysis, it is also useful for improving the accuracy of analysis. Circularly polarized light is also necessary for circular dichroism spectroscopy, which is useful for analyzing organic materials and liquid crystals. Therefore, there has been a demand for optical elements that can produce a circularly polarized state over a wide wavelength range.

[0010] The present invention has been made in consideration of the above problems, and an object of the present invention is to provide an optical element that can be used in the wavelength range from vacuum ultraviolet to near infrared and is capable of producing highly accurate circularly polarized light, and a measurement instrument equipped with said optical element. [Means for solving the problem]

[0011] As a result of intensive research into solving the above problems, the inventors discovered a combination of a broadband waveplate, which is a combination of a conventionally known birefringent λ / 2 plate and a λ / 4 plate, with a Fresnel rhomb, which is known as a broadband phase shifter, and thus completed the present invention.

[0012] The above problem is solved by the broadband circular polarizer of the present invention, which provides a phase difference of approximately 180°±10% between p-waves and s-waves having wavelengths of at least 200 to 2000 nm by total reflection. Made up of Fresnel roms The λ / 2 section and total reflection provide a phase difference of approximately 90°±10% between p-waves and s-waves having wavelengths of at least 200 to 2000 nm. Made up of Fresnel roms a λ / 4 section, the incident surface of the λ / 4 section being rotated by approximately 60°±10% with respect to the incident surface of the λ / 2 section with the incident light axis as the rotation axis, Small This problem is solved by converting linearly polarized light having a wavelength of at least 200 to 2000 nm into circularly polarized light.

[0013] In this way, by combining a broadband Fresnel Rhomb phase shifter with an even broadband structure, it is possible to provide a broadband circular polarizer that has a phase difference of λ / 4 (90°), has ultra-broadband characteristics that can be used in the wavelength range from vacuum ultraviolet to near infrared, and is capable of producing highly accurate circularly polarized light.

[0014] In this case, the Fresnel rhombs constituting the λ / 2 portion and the λ / 4 portion are preferably made of at least one material selected from the group consisting of quartz, CaF2, and LiF. In this case, it is preferable that the Fresnel rhombs constituting the λ / 2 portion and the λ / 4 portion have a multilayer film formed on at least one total reflection surface. At this time, the λ / 2 portion is reflected by total reflection. , having a wavelength of at least 200 to 2000 nm Between p and s waves 9 to 0° ±10% The first and second Fresnel rhombs provide a phase difference of , having a wavelength of at least 200 to 2000 nm Between p and s waves 9 to 0° ±10% a third Fresnel rhomb that gives a phase difference of One The incident surface of the third Fresnel rom is arranged to rotate about the incident light axis with respect to the incident surfaces of the first Fresnel rom and the second Fresnel rom. 6 0° ±10%It is preferable that they are arranged in a rotated manner. At this time, the Fresnel rhomb is , having a wavelength of at least 200 to 2000 nm Between p and s waves 9 to 0° ±10% It is preferable that the phase difference be given by At this time, the Fresnel rhomb is reflected three times by total reflection. , having a wavelength of at least 200 to 2000 nm Between p and s waves 9 to 0° ±10% It is preferable that the phase difference be given by

[0015] Moreover, the above-mentioned problems can be solved by the measurement device of the present invention by including the above-mentioned broadband circular polarizer. Effect of the Invention

[0016] The broadband circular polarizer of the present invention has a phase difference of λ / 4 (90°) and can be used in the wavelength range from vacuum ultraviolet to near infrared (e.g., 200 to 2600 nm), making it possible to produce highly accurate circularly polarized light.

[0017] Furthermore, since the broadband circular polarizer of the present invention has the above-mentioned properties, by applying it to measurement devices including various measuring devices, analytical devices, inspection devices, and observation devices, it becomes possible to inspect and observe minute areas, and perform various polarization measurements. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic diagram of an H+Q structure broadband waveplate. [Figure 2A] 1 is a graph showing the phase difference characteristics of a λ / 4 plate (QWP) constituting an H+Q structure wideband waveplate. [Figure 2B] 1 is a graph showing the phase difference characteristics of a λ / 2 plate (HWP) constituting an H+Q structure wideband waveplate. [Figure 2C] 1 is a graph showing the phase difference characteristics of an H+Q structure broadband waveplate. [Figure 2D] 1 is a graph showing the ellipticity characteristics of an H+Q structure broadband wave plate. [Figure 2E]1 is a graph showing the polarization axis direction of an H+Q structure broadband wave plate. [Figure 3A] This is a schematic diagram of a standard λ / 4 Fresnel rommer (made by BK-7). [Figure 3B] This is a schematic diagram of a standard λ / 2 Fresnel rommer (made by BK-7). [Figure 4A] 1 is a graph showing the relationship between the angle of incidence from BK-7 to air and the phase difference. [Figure 4B] 1 is a graph showing the relationship between the angle of incidence from quartz to air and the phase difference. [Figure 5A] 1 is a graph showing the wavelength dependence of the phase difference of a BK-7 Fresnel rhomb (λ / 4). [Figure 5B] 1 is a graph showing the wavelength dependence of the phase difference of a BK-7 Fresnel rhomb (λ / 2). [Figure 6A] 1 is a graph showing the wavelength dependence of the phase difference of a quartz Fresnel rhomb (λ / 4). [Figure 6B] 1 is a graph showing the wavelength dependence of the phase difference of a quartz Fresnel rhomb (λ / 2). [Figure 7] FIG. 1 is a schematic diagram showing the structure of an H+Q type Fresnel rhomb according to one embodiment of the present invention. [Figure 8A] 1 is a graph showing the phase difference characteristics of an H+Q type quartz Fresnel rhomb. [Figure 8B] 1 is a graph showing the ellipticity characteristics of an H+Q type quartz Fresnel rhomb. [Figure 8C] 1 is a graph showing the polarization axis direction of an H+Q type quartz Fresnel rhomb. [Figure 9A] 1 is a graph showing the phase difference characteristics (fine adjustment of combination angle) of an H+Q type quartz Fresnel rhomb. [Figure 9B] 1 is a graph showing the ellipticity characteristics (fine adjustment of combination angle) of an H+Q type quartz Fresnel rhomb. [Figure 9C] 1 is a graph showing the direction of polarization axes of an H+Q type quartz Fresnel rhombic reflector (fine adjustment of combination angle). [Figure 10] 1 is a graph showing a comparison between an example of the present invention and a King-type Fresnel rhomb with an optical film. [Figure 11]FIG. 1 is a schematic diagram showing the structure of a King-type Fresnel rhombohedron with an H+Q type optical film. [Figure 12A] 1 is a graph showing the phase difference characteristics of a King-type quartz Fresnel rhombohedron with an H+Q type optical film. [Figure 12B] 1 is a graph showing the ellipticity characteristics of a King-type quartz Fresnel rhomb with an H+Q type optical film. [Figure 12C] 1 is a graph showing the polarization axis direction of a King-type quartz Fresnel rhomboid with an H+Q type optical film. [Figure 13] FIG. 2 is a schematic diagram showing the structure of a quartz Fresnel prism. [Figure 14] 1 is a graph showing an example of the circular polarization separation angle of a quartz Fresnel prism. [Figure 15] FIG. 2 is a schematic diagram showing the structure of an H+Q type quartz Fresnel rhomb (Example 1). [Figure 16A] 4 is a graph showing the phase difference characteristics of the element of Example 1. [Figure 16B] 4 is a graph showing the ellipticity characteristics of the element of Example 1. [Figure 16C] 4 is a graph showing the polarization axis direction of the element of Example 1. [Figure 17A] 13 is a graph showing the phase difference characteristics of the element of Example 1-2. [Figure 17B] 13 is a graph showing the ellipticity characteristics of the element of Example 1-2. [Figure 17C] 13 is a graph showing the polarization axis direction of the element of Example 1-2. [Figure 18A] 13 is a graph showing the phase difference characteristics of the element of Example 2. [Figure 18B] 13 is a graph showing the ellipticity characteristics of the element of Example 2. [Figure 18C] 13 is a graph showing the polarization axis direction of the element of Example 2. [Figure 19] FIG. 1 is a schematic diagram showing the structure of an H+Q type LiF Fresnel rhombohm (Example 3). [Figure 20A] 13 is a graph showing the phase difference characteristics of the element of Example 3. [Figure 20B] 13 is a graph showing the ellipticity characteristics of the element of Example 3. [Figure 20C] 13 is a graph showing the polarization axis direction of the element of Example 3. [Figure 21] FIG. 1 is a schematic diagram showing the structure of a multilayer-coated H+Q type quartz Fresnel rhombohedron (Example 4). [Figure 22A] 13 is a graph showing the phase difference characteristics of the element of Example 4. [Figure 22B] 13 is a graph showing the ellipticity characteristics of the element of Example 4. [Figure 22C] 13 is a graph showing the polarization axis direction of the element of Example 4. [Diagram 23] FIG. 1 is a schematic diagram showing the structure of a King-type H+Q quartz Fresnel rhombohm with an optical film (Example 5). [Figure 24A] 13 is a graph showing the phase difference characteristics of the element of Example 5. [Figure 24B] 13 is a graph showing the ellipticity characteristics of the element of Example 5. [Figure 24C] 13 is a graph showing the polarization axis direction of the element of Example 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] 1 to 24C, a broadband circular polarizer according to one embodiment of the present invention (hereinafter, this embodiment) will be described. The broadband circular polarizer according to this embodiment is a broadband circular polarizer in which the wavelength dependency of the retardation is small in the wavelength region from vacuum ultraviolet to near infrared.

[0020] In this specification, O nm to Δ nm means not less than O nm and not more than Δ nm. In this specification, "approximately" means a numerical range of ±10%, preferably ±5%, more preferably ±3%, even more preferably ±2%, and particularly preferably ±1%. In this specification, "contact" refers to a pair of adjacent Fresnel rhombs (prism elements, rhombohedrons) that are arranged in contact with each other, and includes optical contact in which the rhombs are directly bonded as well as bonding by adhesive. In addition, in this specification, when Fresnel rhombs (prism elements, rhombohedrons) are "facing" this includes cases where they are directly bonded together through optical contact, cases where they are bonded together through an intermediary material such as an adhesive, and cases where there is an air layer between them.

[0021] [1. Basic idea] The broadband circular polarizer according to this embodiment is a combination of a broadband waveplate that combines a conventionally known birefringent λ / 2 plate and a λ / 4 plate, and a Fresnel rhombic plate known as a broadband retarder. First, a description will be given of a broadband waveplate that combines a conventionally known birefringent λ / 2 plate and a λ / 4 plate.

[0022] (1) Wideband wave plate combining birefringent λ / 2 plate and λ / 4 plate (H+Q structure wave plate) Figure 1 shows the structure (layout) of the H+Q structure wave plate HQP. As shown in Figure 1, first, a λ / 2 plate (HWP) is placed with its optical axis Ha rotated 15° with respect to the incident linearly polarized light, and then a λ / 4 plate (QWP) is placed with its optical axis Qa rotated 75° with respect to the incident linearly polarized light. In this element, the incident side must be an HWP and the exit side must be a QWP. The HWP and QWP may be a single birefringent plate or a wave plate combining multiple birefringent plates.

[0023] Figures 2A and 2B show the wavelength dependence of the phase difference of a λ / 2 plate (HWP) and a λ / 4 plate (QWP) made by combining quartz and MgF2 crystals to form an H+Q structure wideband waveplate. The optical characteristics of the H+Q structure wideband waveplate made by combining these are shown in Figures 2C to 2E. It can be seen from FIG. 2C that the wavelength band in which the phase difference is within 90°±5% is λ=350 to 1500 nm.

[0024] (2) Fresnel rom The shapes of standard Fresnel rhombs are shown in Figures 3A and 3B. Figure 3A is a schematic diagram of a λ / 4 Fresnel rhomb (manufactured by BK-7), and Figure 3B is a schematic diagram of a λ / 2 Fresnel rhomb (manufactured by BK-7).

[0025] As shown in FIG. 3A , first rhombohedron 10 constituting the λ / 4 Fresnel rhomb has first incident end face 11, first exit end face 12 arranged parallel to first incident end face 11, first total reflection surface 13 intersecting first incident end face 11 and first exit end face 12, and second total reflection surface 14 arranged parallel to first total reflection surface 13.

[0026] In the first rhombohedron 10, the first incident end face 11 and the first exit end face 12 are parallel to each other, and the first total reflection surface 13 and the second total reflection surface 14 are parallel to each other. In the first rhombohedron 10, the first incident end face 11 and the first total reflection surface 13, and the first exit end face 12 and the second total reflection surface 14 intersect with each other at an angle (wedge angle α) smaller than 90 degrees. In the first rhombohedron 10, the first incident end face 11 and the second total reflection surface 14, and the first exit end face 12 and the first total reflection surface 13 intersect with each other at an angle larger than 90 degrees.

[0027] As shown in Fig. 3B, the λ / 2 Fresnel rhomb has a structure in which two parallelogram-shaped prism elements are combined (roof-shaped Fresnel rhomb). Specifically, the λ / 2 Fresnel rhomb has a first rhomb 10 and a second rhomb 20, each of which has a parallelogram-shaped cross section (a cross section parallel to the plane of Fig. 3B, i.e., a cross section perpendicular to each of the entrance end face, exit end face, and total reflection surface described below). The first rhomb 10 and the second rhomb 20 have the same shape and are made of an isotropic material.

[0028] The second rhombohedron 20 has a second incident end face 21, a second exit end face 22 arranged parallel to the second incident end face 21, a third total reflection surface 23 intersecting the second incident end face 21 and the second exit end face 22, and a fourth total reflection surface 24 arranged parallel to the third total reflection surface 23.

[0029] In the second rhombohedron 20, the second incident end face 21 and the second exit end face 22 are parallel to each other, and the third total reflection surface 23 and the fourth total reflection surface 24 are parallel to each other. In the second rhombohedron 20, the second incident end face 21 and the third total reflection surface 23, and the second exit end face 22 and the fourth total reflection surface 24 intersect at an angle smaller than 90 degrees (wedge angle α). In the second rhombohedron 20, the second incident end face 21 and the fourth total reflection surface 24, and the second exit end face 22 and the third total reflection surface 23 intersect at an angle larger than 90 degrees.

[0030] The first rhombohedron 10 and the second rhombohedron 20 are disposed facing each other so that the first emission end face 12 of the first rhombohedron 10 and the second incidence end face 21 of the second rhombohedron 20 are parallel to each other. The first emission end face 12 and the second incidence end face 21 are preferably directly bonded by optical contact, but it is also possible to bond them together using an ultraviolet-transmitting adhesive, or to arrange them with a gap between them without bonding them.

[0031] As described above, the first incident end face 11 and the first total reflection surface 13 (the first exit end face 12 and the second total reflection surface 14) of the first rhombohedron 10 form a wedge angle α, and similarly, the second incident end face 21 and the third total reflection surface 23 (the second exit end face 22 and the fourth total reflection surface 24) of the second rhombohedron 20 also form a wedge angle α. Here, the wedge angle α can be appropriately set according to the type of isotropic material constituting the first rhombohedron 10 and the second rhombohedron 20; when the isotropic material is BK-7, the wedge angle α may be set to 55°, when the isotropic material is quartz, the wedge angle α may be set to 54°, and when the isotropic material is CaF2, the wedge angle α may be set to 54°.

[0032] As mentioned above, Fresnel rhombs are made of isotropic materials that do not have birefringence, but they are phase shifters that utilize the phase difference between p-waves and s-waves that occurs during total reflection. Total reflection is a phenomenon that occurs when light is incident from a high refractive index material to a low refractive index material at an angle equal to or greater than the critical angle. Figures 4A and 4B show the relationship between the angle of incidence on the reflecting surface and the phase difference that occurs when the materials are BK-7 and quartz, which are typical optical glasses.

[0033] From Figures 4A and 4B, we can see that no phase difference occurs with normal reflection below the critical angle. We can also see that the phase difference that occurs varies depending on the angle, even above the critical angle. We can also see that the maximum value of the phase difference that occurs varies depending on the refractive index of the ROM material (the difference in refractive index between the entrance and exit media).

[0034] When the ROM material is BK-7, the phase difference is about 45° when the angle of incidence is about 55°. Therefore, by total reflecting twice, it is possible to achieve a phase difference of 90°, and by total reflecting four times, it is possible to achieve a phase difference of 180°.

[0035] Figures 5A and 5B show the wavelength dependence of the phase difference of a BK-7 Fresnel rhomb. Figures 6A and 6B show the wavelength dependence of the phase difference of a quartz Fresnel rhomb. Figures 5A and 5B and 6A and 6B show that the wavelength dependence of the phase difference of the Fresnel rhomb is small. However, it can be seen that the phase difference of the quartz Fresnel rhomb is greater than that of the BK7 Fresnel rhomb.

[0036] (3) H+Q type Fresnel rhombohedron (the broadband circular polarizer of this embodiment) The broadband circular polarizer according to this embodiment has a structure in which the above-mentioned two broadband phase shifters are combined. By configuring the broadband Fresnel-Rohm phase shifter with an even broader structure, it is possible to obtain ultra-broadband characteristics that have not been available in the past.

[0037] As an example of the wideband circular polarizer 1 according to this embodiment, Fig. 7 shows a quartz H+Q type Fresnel rhomb. Figs. 8A to 8C show output polarization parameters such as phase difference. The wideband circular polarizer according to this embodiment, like a wave plate with an H+Q structure, exhibits performance as an element that converts linearly polarized light into circularly polarized light due to its characteristics as a general λ / 4 plate (QWP).

[0038] The basic structure is as shown in Figure 7, in which a phase shifter (λ / 2 part: H part) that imparts a phase difference of 180° between the p-wave and s-wave by total reflection, and a phase shifter (λ / 4 part: Q part) that imparts a phase difference of 90° between the p-wave and s-wave by total reflection are rotated by approximately 60° (θ2-θ1=75°-15°) around the light axis (incident light axis).

[0039] There is no need to generate a phase difference of approximately 180° or approximately 90° between the p-wave and the s-wave in one total reflection. In the example of Figure 7, the phase difference generated by one total reflection is approximately 45°. Total reflection is repeated four times to generate a phase difference of approximately 180°, and total reflection is repeated two times to generate a phase difference of approximately 90°.

[0040] In Figure 7, each ROM (rectangular block) is bonded, but it is not necessary to do so. When bonding each ROM, an adhesive may be used as long as it is transparent in the wavelength range used. However, since there are few adhesives that are transparent in the deep ultraviolet range, it is preferable to bond them using optical contact. When bonding, care must be taken to avoid applying stress to the isotropic material of the ROM, which can cause anisotropy.

[0041] An AR film (anti-reflection film) may be applied to the end face, and it is preferable to improve the transmittance over the entire band of use. However, for example, in the case of the element of the present invention, when the material is quartz, the wavelength band of use is λ=180 to 2600 nm, and generally, since it is difficult to apply an effective anti-reflection film over this entire band, the reflectance cannot be significantly reduced, but there is a method of using a single layer of MgF2. There is also a method of applying a special anti-reflection film with a moth-eye structure. Of course, it is not necessary to apply an anti-reflection film. In this case, there is no significant effect on the output polarization. The end face refers not only to the input and output surfaces, but also to the input and output surfaces of each ROM when the ROMs are not joined.

[0042] In Figure 7, the three ROMs have the same shape, but they do not necessarily have to be the same, and as long as they combine phase shifters with phase differences of approximately 180° and approximately 90° (λ / 2 part H and λ / 4 part Q), the effect of broadening the bandwidth can be achieved. In addition, the number of reflections does not have to be a combination of 4 and 2. By applying an optical multilayer coating to the total reflection surface and using a ROM with a broadband, the bandwidth can be further broadened and the accuracy of the output circular polarization can be improved.

[0043] As shown in Figures 8C and 9C, the phase shifter of this structure changes the direction of the polarization axis of the emitted light depending on the wavelength. This is the same as the H+Q structure using birefringent materials. However, since the emitted polarized light is circularly polarized, this does not pose any particular problem. However, in order to obtain linearly polarized light from circularly polarized light, the optical axis of the incident circularly polarized light must be changed for each wavelength as shown in Figures 8C and 9C, and the light must be incident from the ROM side with a phase difference of 90° (the λ / 4 part Q side), which is not realistic. Therefore, this element is mainly effective in creating circularly polarized light from linearly polarized light, and the light must be incident from the ROM side with a phase difference of 180° (the λ / 2 part H side).

[0044] From Figure 8B, we can see that the ellipticity is close to 1 and the emitted polarization is almost circularly polarized. However, it deviates from 1 in the infrared region. By finely adjusting the angle between the two ROMs in Figure 7 from 60° to 59.6°, the characteristics in Figures 8A to 8C can be adjusted to those in Figures 9A to 9C.

[0045] (4) Advantages and disadvantages of the broadband circular polarizer according to this embodiment The advantages of the broadband circular polarizer according to this embodiment include that it can convert linearly polarized light into circularly polarized light in a wide wavelength range, and that it is easy to manufacture. The disadvantages of the broadband circular polarizer according to this embodiment include that the incident light and the outgoing light are not on the same axis, that the direction of linear polarization differs depending on the wavelength when converting circularly polarized light into linearly polarized light, that it is not suitable for use in changing the polarization state from linearly polarized light to elliptical polarization or circular polarization like a general λ / 4 plate, and that it is relatively large in size. Thus, the broadband circular polarizer according to this embodiment has many disadvantages compared to its advantages, but it is an element that excels in its ability to convert linearly polarized light into highly accurate circularly polarized light in a wide wavelength range, which is its advantage.

[0046] [2. Prior Art] Below, a wideband λ / 4 phase shifter and a circular polarizer are shown as conventional techniques. As described above, the H+Q structure is a structure that can create a phase shifter with better broadband characteristics than the original λ / 2 phase shifter and λ / 4 phase shifter, and with an ellipticity close to 1. Therefore, if the original phase shifter has little wavelength dependency and an ellipticity close to 1 (close to circular polarization), a circular polarizer with even less wavelength dependency and an ellipticity close to 1 can be created.

[0047] As is conventionally known, Fresnel rhombic plates have less wavelength dependence than λ / 2 and λ / 4 plates made of birefringent materials, so it is clear that the product of the present invention is a circular polarizer with a wider bandwidth than circular polarizers combined with birefringent materials.

[0048] Furthermore, even in the case of a circular polarizer with an H+Q structure that uses a birefringent film to expand the wavelength band, since it is made using organic matter, it is not transparent in the ultraviolet range and has characteristic absorption lines in the infrared range, so it is not a circular polarizer that covers the entire range from ultraviolet to infrared.

[0049] Next, a comparison is made with a King-type Fresnel rhomb with an optical thin film, which is an element with the widest wavelength band and an ellipticity close to 1 among conventional Fresnel rhombs. FIG. 10 shows a comparison of the ellipticity between the King-type Fresnel rhomb with an optical film and the Fresnel rhomb shown in FIG. 7 (broadband circular polarizer according to this embodiment). From FIG. 10, it can be seen that the broadband and ellipticity characteristics are almost the same. Here, the King-type Fresnel rhomb with an optical thin film compared here is a λ / 4 retarder, so by arranging two of them in series, it becomes a λ / 2 retarder, and by arranging another one in a direction rotated by about 60°, the King-type Fresnel rhomb with an optical thin film can be arranged in an H+Q type. By arranging in this way, it is possible to further approach the ellipticity to 1.

[0050] Figure 11 and Figures 12A to 12C show the structure and optical characteristics of a King-type H+Q Fresnel rhomb with an optical film. Therefore, it is meaningless to compare the present invention with a conventional Fresnel rhomb. Figure 12C shows that in this example, the polarization axis has little wavelength dependency, and therefore it is possible to change circularly polarized light to linearly polarized light.

[0051] A completely different structure and wideband circular polarizer is the Fresnel prism, which is a circular polarizer that separates left- and right-handed circularly polarized light at the joint surface by combining, for example, right-handed and left-handed quartz crystals.

[0052] Figure 13 shows a schematic diagram of a quartz Fresnel prism. Figure 14 shows an example of the wavelength dependency of the separation angle of right-handed and left-handed circularly polarized light. A Fresnel prism is an element that can obtain almost perfect circular polarization over a wide band, but as no material that can obtain a large separation angle has been found, it is an element with little practical use. The present invention is a practical circular polarizer because it can be used with any isotropic material with a wide transmission band.

[0053] [3. Detailed Description of the Structure of the Broadband Circular Polarizer 1 of the Present Embodiment] The broadband circular polarizer 1 of this embodiment has a structure in which a λ / 4 Fresnel rhomb (FIG. 3A, λ / 4 part Q) and a λ / 2 Fresnel rhomb (FIG. 3B, λ / 2 part H) are combined, and is an optical element that converts linearly polarized light into circularly polarized light. Specifically, as shown in FIG. 15, the broadband circular polarizer 1 creates a substantially 180° polarization between the p-wave and the s-wave due to total reflection. (Specifically, 180°±10%) The λ / 2 part H gives a phase difference of about 90° between the p-wave and the s-wave due to total reflection. (Specifically, 90°±10%) and a λ / 4 portion Q which gives a phase difference of about 60° with respect to the incident surface of the λ / 2 portion H, with the incident light axis as the rotation axis. (Specifically, 60°±10%) They are rotated (θ2-θ1) and positioned.

[0054] Each Fresnel rhomb constituting the λ / 2 part H and the λ / 4 part Q is formed from an isotropic material, and FIG. 7 shows a case where quartz is used as the isotropic material (wedge angle α=54°). The isotropic material may be any material that transmits wavelengths from vacuum ultraviolet to near infrared, and from the viewpoint of availability, it is preferable to use at least one material selected from the group consisting of quartz (fused quartz: refractive index n=1.46@550nm), calcium fluoride (CaF2: refractive index n=1.44@546nm) and lithium fluoride (LiF: refractive index n=1.39@600nm). It is also important that the isotropic material used does not have defects or distortions that may deteriorate the phase difference, and it is preferable to use quartz (fused quartz) rather than CaF2.

[0055] As shown in FIG. 7, the λ / 2 portion H is separated by approximately 90° between the p-wave and the s-wave due to total reflection. (Specifically, 90°±10%) The first Fresnel rhomb FR1 and the second Fresnel rhomb FR2 provide a phase difference of about 90° between the p-wave and the s-wave by total reflection. (Specifically, 90°±10%) The incident surface of the first Fresnel rom FR1 is rotated about the incident light axis relative to the incident surface of the second Fresnel rom FR2. One The incident surface of the third Fresnel rom FR3 is arranged to rotate at an angle of approximately 60° with respect to the incident surfaces of the first Fresnel rom FR1 and the second Fresnel rom FR2. (Specifically, 60°±10%) They are rotated and positioned.

[0056] An incident light ray I incident on the first entrance end surface 11 of the first Fresnel rhomb FR1 (first rhomb 10) constituting the λ / 2 portion H is totally reflected four times (reflected light ray R) and is emitted as an output light ray E from the third Fresnel rhomb FR3 constituting the λ / 4 portion Q. In the broadband circular polarizer 1, the incident light ray I is inclined at an angle of approximately 90° (specifically, 90°±5°) with respect to the incident light ray I in the wavelength region from vacuum ultraviolet to near infrared. % , preferably 90°±3 % , more preferably 90°±2 % , more preferably 90°±1 % ) is given to the output light beam E.

[0057] When the broadband circular polarizer 1 is used, an incident light ray I that is incident substantially perpendicularly from the outside on the first entrance end surface 11 of the first Fresnel rhomb FR1 (first rhomb 10) proceeds as follows: The incident light ray I is internally reflected at the first total reflection surface 13 and the second total reflection surface 14 of the first Fresnel rhomb FR1 (first rhomb 10), and the reflected light ray R exits from the first exit end surface 12 of the first Fresnel rhomb FR1 (first rhomb 10) to the second entrance end surface 21 of the second rhomb 20. Then, the reflected light ray R that is incident from the first exit end face 12 of the first Fresnel rhomb FR1 (first rhomb 10) to the second entrance end face 21 of the second Fresnel rhomb FR2 (second rhomb 20) is internally reflected at the third total reflection surface 23 and the fourth total reflection surface 24, and the reflected light ray R is incident on the third Fresnel rhomb FR3 from the second exit end face 22 of the second Fresnel rhomb FR2 (second rhomb 20), is internally reflected twice, and is emitted as an exit light ray E.

[0058] (Multilayer film M) It is preferable that the Fresnel rhombs constituting the λ / 2 portion H and the λ / 4 portion Q have a multilayer film M formed on at least one or more total reflection surfaces. Specifically, it is preferable that the first total reflection surface 13 and the second total reflection surface 14 of the first rhomb 10, which are the Fresnel rhombs constituting the λ / 2 portion H and the λ / 4 portion Q, and the third total reflection surface 23 and the fourth total reflection surface 24 of the second rhomb 20 are coated with a multilayer film M having a refractive index different from that of the isotropic material constituting the first rhomb 10 and the second rhomb 20.

[0059] Here, the multilayer film M is a high refractive index film M formed of a high refractive index material having a refractive index higher than that of the isotropic material constituting the first rhombohedron 10 and the second rhombohedron 20. H and a low refractive index film M formed of a low refractive index material having a refractive index smaller than that of the isotropic material constituting the first rhombohedron 10 and the second rhombohedron 20. L and are laminated alternately. High refractive index film M H and low refractive index film M L The layering order is as follows: on the isotropic material that serves as the substrate, a high refractive index film M H , low refractive index film M LAlternatively, a low refractive index film M may be laminated on an isotropic material serving as a substrate. L , high refractive index film M H The layers may be laminated in this order.

[0060] The incident light I is totally reflected by each total reflection surface, and at the same time, a phase difference occurs between the p-polarized light and the s-polarized light. Usually, the phase difference caused by total reflection increases as the wavelength becomes shorter. Therefore, in each Fresnel rhomb, a high refractive index film M with a refractive index higher than that of the isotropic material (quartz or CaF2) constituting the first rhombohedron 10 and the second rhombohedron 20 is provided. H and a low refractive index film M L It is advisable to provide a multilayer film M on the total reflection surface, in which two types of film materials consisting of the above are alternately laminated.

[0061] High refractive index film M H Examples of high refractive index materials constituting the low refractive index film M include gadolinium fluoride (GdF3: refractive index n=1.59@550 nm), lanthanum fluoride (LaF3: refractive index n=1.59@550 nm) and neodymium fluoride (NdF3: 1.61@550 nm), but are not limited to these materials. L An example of a low refractive index material constituting the layer 10 is magnesium fluoride (MgF2: refractive index n=1.38 to 1.40@550 nm), but the present invention is not limited to this.

[0062] High refractive index film M H and low refractive index film M L The high refractive index film M can be formed by a method such as vacuum deposition, CVD, or sputtering. H and low refractive index film M L The thickness of the film depends on the type of material and may be, for example, 100 Å to 650 Å, but is not limited to this range.

[0063] In the broadband circular polarizer 1 of this embodiment, the λ / 4 part Q and the λ / 2 part H are not limited to the configuration shown in Fig. 7. For example, as shown in Fig. 19, it is possible to perform eight reflections at the λ / 2 part H to provide a phase difference of 180° and four reflections at the λ / 4 part Q to provide a phase difference of 90°, that is, a structure in which three roof-type Fresnel rhombs are arranged. In this structure, two roof-type Fresnel rhombs with a phase difference of 180° and one roof-type Fresnel rhomb with a phase difference of 90° are arranged by rotating the incident light axis by 59.5° (θ2-θ1=74.5°-15°).

[0064] Furthermore, as shown in FIG. 23, it is also possible to arrange three King type Fresnel rhombs with a phase difference of 90° in the direction of the light axis, with two on the incident side regarded as Fresnel rhombs with a phase difference of 180° (λ / 2 part H) and one on the exit side regarded as a Fresnel rhomb with a phase difference of 90° (λ / 4 part Q), and to arrange the Fresnel rhombs with a phase difference of 180° and the Fresnel rhombs with a phase difference of 90° rotated by 60° (θ2-θ1=75°-15°) around the incident light axis as the rotation axis.

[0065] [4. Application Examples of the Broadband Circular Polarizer of the Present Embodiment] The application examples of the broadband circular polarizer of the present embodiment are shown below. The broadband circular polarizer of the present embodiment can be applied to a measurement device. Here, the term "measurement device" includes various measurement devices, analysis devices, inspection devices, and observation devices.

[0066] A semiconductor inspection device is a device that inspects minute areas and actively uses ultraviolet light, so it is suitable to use the broadband circular polarizer of this embodiment, which can be used in the wavelength range from vacuum ultraviolet to near infrared. The broadband circular polarizer of this embodiment can be used in any semiconductor inspection device that uses polarized white light.

[0067] A spectroscopic ellipsometer is an example of a specific target device to which the broadband circular polarizer of the present embodiment can be applied. Specifically, the broadband circular polarizer can be used as a compensation element for the spectroscopic ellipsometer.

[0068] The broadband circular polarizer of this embodiment can also be applied to an observation device for observing a minute region. There are cases where contrast can be improved by controlling polarization. In order to perform finer observation, observation using short wavelengths is also required, so there is an advantage in using the broadband circular polarizer of this embodiment.

[0069] Furthermore, in order to detect foreign objects, the broadband circular polarizer of this embodiment can be applied to observation devices and inspection devices that utilize the characteristic that the polarization state of scattered light from foreign objects differs from that of normal parts, specifically, devices that observe the polarization state of wiring patterns on semiconductor wafers to find foreign objects. Although the way in which polarization is used varies depending on the device, when detecting abnormalities (defects) that occur in each semiconductor process from polarization information, various polarization measurements become possible by combining the broadband circular polarizer of this embodiment with a retarder with a phase difference of 180° (λ / 2).

[0070] The broadband circular polarizer of this embodiment can also be applied to a film thickness gauge. Film thickness gauges are mainly used for inspection during semiconductor processes, but are also used to inspect other film-like objects, such as to measure film thickness and coating thickness. There are various measurement principles for film thickness gauges, but some devices measure film thickness using polarization analysis similar to an ellipsometer.

[0071] In addition, the broadband circular polarizer of this embodiment can be used in place of a depolarizing element to reduce instrument polarization. In a reflective optical system, the reflectance of p-polarized light and s-polarized light is different, so when the polarization state of the incident light differs or varies, the transmittance differs or varies. To prevent this, the polarization state of the incident light may be kept constant, or the polarization state of the light emitted from the optical system may be kept constant. In the case of a device that performs precise measurements, it is necessary to keep the polarization states of the incident light and the emitted light constant. By combining the broadband circular polarizer of this embodiment with a retarder with a phase difference of 180° (λ / 2), any polarization state can be created, making it possible to keep the polarization states of the incident light and the emitted light constant.

[0072] Methods for analyzing the three-dimensional structure of polymers such as proteins, pharmaceuticals, and foods include optical rotatory dispersion measurement (ORD) and circular dichroism (CD) spectroscopy, which examine the optical isomers of polymers. These measurements measure the difference in refractive index and absorption between left and right circularly polarized light, and require a highly accurate circular polarizer with a wide wavelength band. The broadband circular polarizer of this embodiment meets such demands and can improve the accuracy of optical rotatory dispersion measurement and circular dichroism spectroscopy measurement. EXAMPLES

[0073] The broadband circular polarizer of the present invention will be described in more detail below based on examples, but the present invention is not limited to the following examples.

[0074] <Example 1: H+Q type quartz Fresnel rhomb> The H+Q type quartz Fresnel rhomb of Example 1 has a structure in which a typical quartz roof-type Fresnel rhomb (λ / 2 part: H part) with a phase difference of 180° and a parallelogram-shaped Fresnel rhomb (λ / 4 part: Q part) with a phase difference of 90° are rotated by 60° (θ2-θ1=75°-15°) around the incident light axis (FIG. 15, Table 1).

[0075] [Table 1]

[0076] The roof-type Fresnel rhomb with a phase difference of 180° (part λ / 2: part H) is composed of two parallelogram Fresnel rhombs with a phase difference of 90° arranged side by side, so it can also be considered as a structure in which three parallelogram Fresnel rhombs with a phase difference of 90° are arranged rotated by 15°, 15°, and 75° with respect to the incident polarized light.

[0077] The parallelogram Fresnel rhombs may be spaced apart from each other or may be joined together. Since the wavelength band used is wide, it is preferable to use optical contact for the joining, but as long as no phase difference due to stress occurs in the parallelogram Fresnel rhombs and no light absorption occurs, it is also possible to use methods such as adhesion or fusion. It is preferable to apply an anti-reflection film to the surface of each parallelogram Fresnel rhomb through which light passes, but it is not necessary to apply an anti-reflection film. Figures 16A to 16C show the optical characteristics of the H+Q type quartz Fresnel rhomb of Example 1. 16A shows that the phase difference is 90° in the wavelength range of λ=200 nm to 2600 nm, and FIG 16B shows that the ellipticity is close to 1 in the above wavelength band, and circularly polarized light is emitted.

[0078] <Example 1-2: H+Q type quartz Fresnel rhomb optimized type> Example 1-2 has a structure in which the rotation angle of the 180° phase difference Fresnel rhomb and the 90° phase difference Fresnel rhomb of Example 1 is set to 59.6° (θ2-θ1=74.6°-15°) (Table 2). As can be seen from a comparison between Figs. 16A to 16C and Figs. 17A to 17C, the ellipticity can be made closer to 1 in the entire wavelength band used (200 nm to 2600 nm) by adjusting the rotation angle of the λ / 2 part (H part) and the λ / 4 part (Q part) to be optimal. The bonding method and anti-reflection film are the same as those of Example 1.

[0079] [Table 2]

[0080] <Example 2: H+Q type CaF2 Fresnel rhomb optimized type> CaF2 crystal is an isotropic material that is transparent from λ=130 to 6000 nm. Although the Fresnel rhomb using CaF2 is also a wideband retarder, a Fresnel rhomb with a phase difference of 180° and a Fresnel rhomb with a phase difference of 90° made of CaF2 are rotated by 59° (θ2-θ1=74°-15°) to form a structure in which they are arranged, resulting in an element with a wider band and an ellipticity characteristic close to 1 (Table 3, Figs. 18A to 18C). The bonding method and anti-reflection film are the same as those in Example 1. The H+Q type CaF2 Fresnel rhomb optimized type (Example 2) whose ellipticity characteristic is shown in Fig. 18B is better than the H+Q type quartz Fresnel rhomb optimized type (Example 1) whose ellipticity characteristic is shown in Fig. 17B. Wavelength λ = 130nm to 6000nm It can be seen that circularly polarized light with an ellipticity close to 1 can be obtained over a wide wavelength band.

[0081] [Table 3]

[0082] <Example 3: H+Q type LiF Fresnel rhomb optimized type> LiF crystals are isotropic crystals that are transparent in the wavelength range of approximately λ = 110 to 9000 nm. Therefore, if a Fresnel rhomb is made with LiF, it may be possible to manufacture a phase shifter with a very wide band. However, the refractive index is relatively small, and the difference in refractive index is large between the vacuum ultraviolet region and the mid-infrared region, making it difficult to manufacture a phase shifter that makes use of the transparent band.

[0083] The following shows Example 3 of the H+Q type LiF Fresnel rom using LiF as a material. Since the refractive index is relatively small and it is difficult to obtain a large phase difference by one total reflection, the phase difference by one reflection is set to about 22.5°, and 8 reflections are performed at the λ / 2 part (H part) to obtain a phase difference of 180°, and 4 reflections are performed at the λ / 4 part (Q part) to obtain a phase difference of 90° (FIG. 19, Table 4). In other words, it is a structure in which three roof-type Fresnel roms are arranged side by side. Two roof-type Fresnel roms with a phase difference of 180° and one roof-type Fresnel rom with a phase difference of 90° are arranged with the incident light axis rotated by 59.5° (θ2-θ1=74.5°-15°). The bonding method and anti-reflection film are the same as those in Example 1.

[0084] [Table 4]

[0085] 20A to 20C show the optical characteristics of the H+Q type LiF Fresnel rhomb optimized type of retarder of Example 3. From Fig. 20B and Fig. 20C, it can be seen that although the performance deteriorates to some extent on the long wavelength side, it is still sufficiently high performance compared to the conventional retarder. It can be seen from Fig. 20A that the phase difference is 90° in the wavelength range λ=110 nm to 6000 nm, and from Fig. 20B that the ellipticity is close to 1 in the above wavelength band, and circularly polarized light is emitted.

[0086] <Example 4: Small-sized H+Q-type quartz Fresnel rhombohedron with multilayer film> Example 4 has a structure in which three small Fresnel rhombs with multilayer film and a phase difference of 90° are arranged in the light direction, two on the incident side are regarded as Fresnel rhombs with a phase difference of 180° (λ / 2 part: H part), and one on the exit side is regarded as a Fresnel rhomb with a phase difference of 90° (λ / 4 part: Q part), and the Fresnel rhombs with a phase difference of 180° and 90° are rotated by 59.8° (θ2-θ1=74.8°-15°) around the incident light axis (FIG. 21 and Table 5).

[0087] [Table 5]

[0088] Since the original compact Fresnel rhomb with multilayer film has incident and outgoing light on the same axis, the outgoing light and the incident light are also collinear in this embodiment. The bonding method and anti-reflection film are the same as those in embodiment 1. Figs. 22A to 22C show the optical characteristics of the compact H+Q quartz Fresnel rhomb with multilayer film of embodiment 4. Fig. 22B shows that it emits highly accurate circularly polarized light with an ellipticity close to 1, especially at λ=200 to 2000 nm. 22A also shows that the phase difference is 90° at the above wavelength. Among the examples, the inventive product having the configuration of this embodiment has the narrowest wavelength range, but it can be seen that the wavelength band is wider than that of the conventional product.

[0089] <Example 5: King type H+Q quartz Fresnel ROM with optical coating> This structure has the widest wavelength band of any known structure, is made of quartz with an ellipticity close to 1, has a total reflection angle of 72°, and has an optical thin film applied to the slope used. Three King-type Fresnel rhombs with a phase difference of 90° are arranged in the direction of the light axis, two on the incident side are considered to be Fresnel rhombs with a phase difference of 180° (λ / 2 part: H part), and one on the exit side is considered to be a Fresnel rhomb with a phase difference of 90° (λ / 4 part: Q part). The 180° phase difference Fresnel rhomb and the 90° phase difference Fresnel rhomb are rotated 60° (θ2-θ1=75°-15°) around the incident light axis (Fig. 23 and Table 6).

[0090] Each King type Fresnel rom may or may not be bonded, as in Example 1. If they are bonded, the bonding method is not important as long as they do not cause distortion that generates optical anisotropy in the Fresnel rom and do not absorb light. It is preferable to apply an anti-reflection film to the surface through which light passes, but it is not necessary to apply an anti-reflection film.

[0091] [Table 6]

[0092] 24A to 24C show the optical characteristics of the King type H+Q quartz Fresnel rhomb with optical film of Example 5. As shown in Fig. 24A to 24C, the output polarization characteristics are superior to any of the conventional Fresnel rhombs, and also superior to any of the phase shifters. Since this structure is a structure that enhances the performance of the phase shifter, which is a component, it can be seen that when the performance of the component is high, higher characteristics are exhibited.

[0093] In this embodiment, as the phase difference and ellipticity characteristics increase, the wavelength dependency of the polarization axis also decreases, so that, like a general λ / 4 plate, it is possible to freely change the incident polarized light from linearly polarized light to elliptically polarized light or circularly polarized light. Also, good polarization characteristics can be obtained even when a light beam is incident from the phase difference 90° side (λ / 4 side). However, better performance is obtained when a light beam is incident from the phase difference 180° side (λ / 2 side). [Explanation of symbols]

[0094] 1 Broadband circular polarizer H λ / 2 part (H part) Q λ / 4 part (Q part) FR1 Fresnel ROM No. 1 FR2 2nd Fresnel ROM FR3 3rd Fresnel ROM 10 First rhombohedron 11 First entrance end face 12 First output end face 13 First total reflection surface 14 Second total reflection surface 20 Second rhombohedron 21 Second incident end face 22 Second exit end face 23 Third total reflection surface 24 Fourth total reflection surface M Multilayer film θ Incident angle α Wedge angle α1 Total reflection angle HQP H+Q structure wavelength plate HWP λ / 2 plate Ha Optical axis of λ / 2 plate QWP λ / 4 plate Qa Optical axis of λ / 2 plate I Incident ray Ia Incident polarization direction R Reflected ray E Exit ray X Optical axis

Claims

1. A λ / 2 section constituted by a Fresnel rhomb that provides a phase difference of 180°±10% between p waves and s waves having wavelengths of at least 200 to 2000 nm by total reflection; A λ / 4 section formed of a Fresnel rhomb that provides a phase difference of 90°±10% between p waves and s waves having wavelengths of at least 200 to 2000 nm by total reflection; The incident surface of the λ / 4 portion is rotated by 60°±10% relative to the incident surface of the λ / 2 portion with the incident light axis as the rotation axis, A broadband circular polarizer that converts linearly polarized light having a wavelength of at least 200 to 2000 nm into circularly polarized light.

2. 2. The broadband circular polarizer according to claim 1, wherein the Fresnel rhombs constituting the λ / 2 portion and the λ / 4 portion are formed of at least one material selected from the group consisting of quartz, CaF2, and LiF.

3. 3. The broadband circular polarizer according to claim 1, wherein the Fresnel rhombs constituting the .lambda. / 2 portion and the .lambda. / 4 portion have a multilayer film formed on at least one total reflection surface.

4. The λ / 2 portion has a first Fresnel rhomb and a second Fresnel rhomb that provide a phase difference of 90°±10% between a p wave and an s wave having a wavelength of at least 200 to 2000 nm by total reflection, The λ / 4 section has a third Fresnel rhomb that imparts a phase difference of 90°±10% between a p wave and an s wave having a wavelength of at least 200 to 2000 nm by total reflection, an incidence surface of the first Fresnel rhomb is arranged to coincide with an incidence surface of the second Fresnel rhomb with the incidence light axis as a rotation axis; 4. The wideband circular polarizer according to claim 1, wherein the incident surface of the third Fresnel rhomb is rotated by 60°±10% relative to the incident surfaces of the first Fresnel rhomb and the second Fresnel rhomb, with the incident light axis as a rotation axis.

5. The Fresnel rhomb provides a phase difference of 90°±10% between a p wave and an s wave having a wavelength of at least 200 to 2000 nm by two total reflections.

6. The Fresnel rhomb provides a phase difference of 90°±10% between p-waves and s-waves having wavelengths of at least 200 to 2000 nm by three total reflections.

7. A measuring device comprising the broadband circular polarizer according to claim 1 .

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