JP4480653B2 - Polarization state measuring device, circular dichroism measuring device and method thereof - Google Patents

Description

  The present invention relates to a polarization state measuring device, a circular dichroism measuring device, and a method for measuring the optical rotation and circular dichroism of an optically active substance.

  Conventionally, an optical rotation measuring device for measuring the optical rotation and concentration of optically active substances having optical activity such as sugars and amino acids is known.

  As a typical optical rotation measuring apparatus, an apparatus using a rotating analyzer method and an apparatus using a Faraday cell or a Pockels cell are known. However, the rotation analyzer method requires a measurement time because the analyzer is mechanically rotated, and it is difficult to reduce the size of the device because a space is required for the rotation mechanism of the analyzer. There was a problem. The apparatus using the Faraday cell has a problem that a very high voltage must be applied to the Faraday cell, and that lead is used in the Faraday cell, which is not preferable in terms of environment. In addition, the apparatus using the Pockels cell has a problem that the cost is high because the Pockels cell is expensive.

  As an optical rotation measuring apparatus that solves these problems, there is an apparatus that rotates a polarization plane of linearly polarized light incident on a sample using a liquid crystal element and a quarter-wave plate (see Patent Document 1). In this apparatus, in order to detect the optical rotation with high accuracy, the birefringence phase difference of the quarter-wave plate is required to be exactly 90 °. In addition, the quarter wave plates are designed for specific wavelengths, respectively, and do not function correctly at other wavelengths. Therefore, in this apparatus, unless the quarter-wave plate is replaced, the optical rotation cannot be measured by changing the wavelength, and thus the wavelength dependency (optical rotation dispersion) of the optical rotation cannot be obtained.

By the way, the optically active substance has a property of circular dichroism with different degrees of absorption with respect to left and right circularly polarized light. There is a close relationship between optical rotation and circular dichroism, and both the optical rotatory dispersion and circular dichroic dispersion, which are wavelength dependence thereof, are used for analysis of the three-dimensional structure of optically active substances. Therefore, an apparatus capable of measuring both optical rotation and circular dichroism is desired.
JP 2004-69452 A

  An object of the present invention is to provide a polarization state measuring device and a circular dichroism measuring device that solve the above problems.

  A polarization state measuring apparatus according to the present invention includes a first polarizer that transmits a predetermined polarization component of light including a predetermined band component, and a polarization modulator that modulates light transmitted through the first polarizer into desired polarization. A second polarizer that transmits a predetermined polarization component of the light transmitted through the measurement object via the polarization modulator, a detection unit that detects the light intensity of the light transmitted through the second polarizer, and a detection unit Measuring means for measuring the polarization state of the object to be measured based on the Fourier coefficient when the light intensity detected in (4) is represented by a Fourier series, and the polarization modulating means includes first and second liquid crystal elements, and liquid crystal Voltage control means for controlling the voltage applied to the element.

  It is preferable that the polarization state includes the optical rotation or circular dichroism of the measurement target.

  The first liquid crystal element has a fast axis inclined at an odd multiple of 45 ° with respect to the transmission axis of the first polarizer, and the second liquid crystal element has a transmission axis of the first polarizer. It is preferable to have a fast axis inclined at an even multiple of 45 °.

  The birefringence phase difference of the first liquid crystal element is variable in the range of 0 ° to 360 °, and the birefringence phase difference of the second liquid crystal element is 90 ° different from the birefringence phase difference of the first liquid crystal element. preferable.

  Assuming that the birefringence phase difference of the first liquid crystal element is δ and the birefringence phase difference of the second liquid crystal element is δ + 90 °, the measurement means uses the basis functions cos δ and sin 2 δ in the Fourier series of the light intensity detected by the detection means. It is preferable to measure the polarization state of the measurement object based on the coefficient.

  The first and second liquid crystal elements preferably include nematic liquid crystal cells.

  It is preferable that the polarization modulation means further includes a temperature control means for controlling the temperatures of the first and second liquid crystal elements.

  A polarization state measuring method according to the present invention includes a step of transmitting a predetermined polarization component of light including a predetermined band component, a polarization modulation step of modulating the transmitted light into a desired polarization, and performing polarization modulation and transmitting the measurement target Transmitting a predetermined polarization component of the transmitted light, detecting the light intensity of the transmitted light, and measuring the polarization state of the measurement object based on a Fourier coefficient when the detected light intensity is represented by a Fourier series And the polarization modulation step includes a step of modulating transmitted light by the first and second liquid crystal elements and a step of controlling a voltage applied to the liquid crystal element.

  A circular dichroism measuring apparatus according to the present invention includes a polarizer that transmits a predetermined polarization component of light including a predetermined band component, a polarization modulator that modulates light transmitted through the polarizer into a desired polarization, and polarization modulation. A detecting means for detecting the light intensity of the light transmitted through the measuring object via the means, and a measuring means for measuring the circular dichroism of the measuring object based on the light intensity detected by the detecting means, and polarization modulation The means includes first and second liquid crystal elements, and voltage control means for controlling a voltage applied to the liquid crystal elements.

  The circular dichroism measurement method according to the present invention is a method of transmitting a predetermined polarization component of light including a predetermined band component, a polarization modulation step of modulating the transmitted light into a desired polarization, and performing polarization modulation and measuring. A step of detecting light intensity of light transmitted through the object; and a step of measuring circular dichroism of the measurement object based on the detected light intensity, wherein the polarization modulation step includes the first and second liquid crystals. Modulating the transmitted light by the element, and controlling a voltage applied to the liquid crystal element.

  According to the present invention, it is possible to provide a polarization state measuring device and a circular dichroism measuring device that improve measurement accuracy and measurement speed, are small and inexpensive, and are environmentally friendly.

  FIG. 1 is a schematic configuration diagram showing an embodiment of a polarization state measuring apparatus 10 according to the present invention.

  As shown in FIG. 1, the apparatus 10 includes a light source 12 that emits white light, a wavelength selection unit 14 that selects monochromatic light having a predetermined wavelength from the white light from the light source 12, and a wavelength selection unit 14. A polarizer 22 that converts the monochromatic light into linearly polarized light, a polarization modulator 24 that modulates the linearly polarized light from the polarizer 22 to a desired polarization, and a predetermined light of the light modulated by the polarization modulator 24 and transmitted through the sample S. Analyzer 48 that transmits the polarization component of light, detection means 50 that detects the intensity of light transmitted through the analyzer 48, and measurement means that measures the optical rotation of the sample S based on the light intensity detected by the detection means 50. 52.

  More details are as follows.

  The light source 12 is a white light source such as a halogen lamp, and emits white light including a wide range of wavelength components.

  The wavelength selection unit 14 is arranged at a predetermined position with respect to the reflection type diffraction grating 16 and the reflection type diffraction grating 16 that reflects each wavelength component of the white light emitted from the light source 12 in different directions according to the wavelength. And a slit 18 through which the wavelength component of the light reflected in a predetermined direction by the reflective diffraction grating 16 passes. More specifically, the reflective diffraction grating 16 emits monochromatic light, which is each wavelength component of incident natural light, in different directions depending on the wavelength by diffraction. The slit 18 transmits monochromatic light emitted from the reflective diffraction grating 16 toward the opening of the slit 18.

  The wavelength selecting unit 14 further includes a driving unit 20 that rotates the reflective diffraction grating 16. The wavelength of the monochromatic light passing through the slit 18 can be changed by the rotation of the reflective diffraction grating 16. With such a configuration, monochromatic light having a predetermined wavelength can be selected from white light including a wide range of wavelength components.

  The polarizer 22 is made of, for example, a polaroid plate, and transmits linearly polarized light having a polarization plane in the direction of the transmission axis a (FIG. 1). Hereinafter, the traveling direction of light is referred to as the z direction, and the direction of the transmission axis a of the polarizer 22 is referred to as the x direction.

The polarizer 22 uses a Mueller matrix when the direction of the transmission axis a (x direction) is the horizontal direction.

It is expressed. On the other hand, the incident monochromatic light uses Stokes vector,

Therefore, the light emitted from the polarizer 22 is

X-direction linearly polarized light expressed as follows.

The polarization state of this linearly polarized light is represented by a point P ₁ on the S ₁ axis in the Poincare sphere of FIG. 2 having Stokes parameters (S ₁ , S ₂ , S ₃ ) as orthogonal coordinates.

Referring to FIG. 1 again, the polarization modulation means 24 controls the voltages applied to the first and second liquid crystal elements 26 and 28 made of parallel nematic liquid crystal cells and the first and second liquid crystal elements 26 and 28, respectively. , And first and second voltage control means 30 and 32 for changing the birefringence phase differences δ ₁ and δ ₂ of the liquid crystal elements 26 and 28.

More specifically, the first liquid crystal element 26 on the near side of the light traveling direction is a direction rotated 45 ° counterclockwise toward the light traveling direction with respect to the transmission axis a (x direction) of the polarizer 22. Has a main axis (phase advance axis) b. Accordingly, when the birefringence phase difference of the first liquid crystal element 26 is δ ₁ , the first liquid crystal element 26 uses the Mueller matrix.

It is expressed. Therefore, the light emitted from the first liquid crystal element 26 is

It is expressed.

In the Poincare sphere of FIG. 2, the polarization state of the light emitted from the first liquid crystal element 26 is represented by the point P _2. Therefore, the change in the polarization state by the first liquid crystal element 26 corresponds to moving the point P ₁ by an angle δ ₁ around the S ₂ axis in the direction of the arrow A.

The birefringence phase difference δ ₁ is variable by controlling the voltage applied to the first liquid crystal element 26. Therefore, the point P ₂ can be an arbitrary point on the circle B that is the intersection of the spherical surface of the Poincare sphere and the S ₁ S ₃ surface. More specifically, the outgoing light from the first liquid crystal element 26 becomes left elliptically polarized light having a major axis in the x direction in FIG. 1 when 0 ° <δ ₁ <90 °, and the left circle when δ ₁ = 90 °. It becomes polarized light, when it is 90 ° <δ ₁ <180 °, it becomes left elliptically polarized light having a major axis in the y direction (vertical direction), and when it is δ ₁ = 180 °, it becomes linearly polarized light in the y direction. Also, when 180 ° <δ ₁ <270 °, right elliptically polarized light having a major axis in the y direction is obtained, when δ ₁ = 270 °, right circularly polarized light is obtained, and when 270 ° <δ ₁ <360 °, it is long in the x direction. It becomes right elliptically polarized light having an axis, and becomes linearly polarized light in the x direction when δ ₁ = 0 ° or 360 °.

The second liquid crystal element 28 in the second light traveling direction has a principal axis (fast axis) c parallel to the transmission axis a (x direction) of the polarizer 22. Therefore, if the birefringence phase difference of the second liquid crystal element 28 is δ ₂ , the second liquid crystal element 28 uses the Mueller matrix,

It is expressed. Therefore, the light emitted from the second liquid crystal element 28 is

It is expressed.

In the Poincare sphere shown in FIG. 2, the polarization state of the outgoing light from the second liquid crystal element 28 is represented by a point P ₃ . Therefore, the change in the polarization state by the second liquid crystal element 28 corresponds to moving the point P ₂ on the circle B by an angle δ ₂ around the S ₁ axis in the direction of the arrow C.

The birefringence phase difference δ ₂ is variable by controlling the voltage applied to the second liquid crystal element 28. Therefore, since the point P ₂ can be an arbitrary point on the circle B, the point P ₃ can be an arbitrary point on the spherical surface of the Poincare sphere. That is, the outgoing light from the second liquid crystal element 28 can be polarized in an arbitrary polarization state.

As described above, the two liquid crystal elements 26 and 28 in which the inclinations of the fast axis with respect to the transmission axis a of the polarizer 22 are 45 ° and 0 ° and the birefringence phase differences δ ₁ and δ ₂ are variable are used. Thus, the predetermined linearly polarized light emitted from the polarizer 22 can be changed into arbitrary linearly polarized light, elliptically polarized light, or circularly polarized light.

Referring to FIG. 1 again, the sample S is accommodated in a measurement cell 46 disposed between the polarization modulation means 24 and the analyzer 48. When the optical rotation of the sample S is θ, the sample S uses a Mueller matrix,

It is expressed. Therefore, the polarization plane of the light incident on the sample S from the polarization modulator 24 is rotated by the optical rotation of the sample S,

Is emitted as elliptically polarized light expressed as follows.

  The analyzer 48 has a transmission axis d perpendicular to the transmission axis a (x direction) of the polarizer 22 and transmits linearly polarized light having a polarization plane in the direction of the transmission axis d (y direction). The analyzer 48 is made of a polaroid plate, for example, like the polarizer 22.

The analyzer 48 uses a Mueller matrix,

It is expressed. Therefore, the light transmitted through the sample S and emitted from the analyzer 48 is

The linearly polarized light expressed as

The detection means 50 is composed of, for example, a photoelectric sensor, detects the light intensity of the outgoing light from the analyzer 48, converts it into a voltage, and outputs it. Since the light intensity detected by the detection means 50 is S ₀ of the Stokes parameter of the light emitted from the analyzer 48, from the equation (11),

It becomes.

  The measuring unit 52 measures the optical rotation of the sample S based on the output from the detecting unit 50.

  For example, the optical rotation of the sample S is obtained as follows by measuring the light intensity of the light transmitted through the sample S while changing the polarization state of the incident light on the sample S.

For example, the birefringence phase differences δ ₁ and δ ₂ of the first and second liquid crystal elements 26 and 28 are set to δ ₁ = δ and δ ₂ = δ + 90 °, and δ is continuously changed from 0 ° to 360 °. . At this time, the light emitted from the second liquid crystal element 28 of the polarization modulator 24 is expressed by the following equation (7):

It is expressed.

FIG. 3 is a Poincare sphere showing the polarization state of the light emitted from the polarization modulator 24. As shown in the figure, the polarization state of the emitted light represented by the point P ₃ changes according to δ, and the change is two points on the equator (S ₁ , S ₂ , S 2) that are the intersections of the S ₁ axis and the spherical surface. ₃ ) = (1,0,0), (-1,0,0) and the northern hemisphere 8-shaped trajectory D passing through the north pole (0,0,1). Therefore, the outgoing light from the polarization modulator 24 continues from the horizontal linearly polarized light to the left circularly polarized light, the vertical linearly polarized light, the left circularly polarized light, and again to the horizontal linearly polarized light while rotating the polarization plane. The left-handed polarization changes.

When the light whose polarization state changes in this way is incident on the sample S, the light intensity detected by the detection means 50 is expressed by the equation (12):

It becomes. Here, a ₀ (= 1/4), a ₁ (= −1 / 4 cos 2θ) and b ₂ (= 1/8 sin 2θ) indicate the coefficients of the Fourier functions cos 0, cos δ and sin 2 δ, respectively. From equation (14), it can be seen that when δ is continuously modulated in the range of 0 ° to 360 °, the light intensity I _θ (δ) periodically changes. Therefore, by performing a Fourier analysis on the periodic change of the light intensity I _θ (δ) measured by the detection means 50 and obtaining the coefficients a ₁ and b ₂ , the optical rotation θ of the sample S is

Can be calculated.

  Referring again to FIG. 1, the polarization modulation unit 24 further includes temperature control units 34 and 36 that control the temperatures of the liquid crystal elements 26 and 28. As shown in FIG. 4, each temperature control means 34, 36 includes a temperature adjustment element 38, 40 made of a thermo module such as a Peltier element provided on the inner side, that is, the liquid crystal element side, and a heat made of a copper plate provided on the outer side. Transmission plates 42 and 44. The temperature adjusting elements 38, 40 and the heat transfer plates 42, 44 have openings 38a, 40a, 42a, 44a through which light incident on the liquid crystal elements 26, 28 or light emitted from the liquid crystal elements 26, 28 passes, respectively.

  By keeping the temperature of the liquid crystal elements 26 and 28 uniform and constant by using the temperature control means 34 and 36, the incident light on the sample S can be accurately set in a desired polarization state, and the optical rotation can be detected with high accuracy. can do.

  FIG. 5 shows the relationship between the voltage applied to the liquid crystal element and the birefringence phase difference of the liquid crystal element for each temperature. More specifically, the birefringence phase difference of the liquid crystal element when a voltage of 800 mV to 3800 mV is applied with the temperature of the liquid crystal element maintained at 26 ° C., 30 ° C., 35 ° C., and 40 ° C., respectively. As shown in the figure, the relationship between the applied voltage and the birefringence phase difference of the liquid crystal element depends on the temperature. Therefore, if the temperature of the liquid crystal element is not constant, an error (difference between the set value and the actual value) occurs in the birefringence phase difference with respect to the same applied voltage.

  FIG. 6 shows the optical rotation error due to the birefringence phase difference error of the liquid crystal element. Curves a, b, c, d, e, and f show the optical rotation when the error of the birefringence phase difference of the liquid crystal element is 0 °, 2 °, 4 °, 6 °, 8 °, and 10 °, respectively. The error is obtained by analysis. As shown by the curve f, when the error of the birefringence phase difference of the liquid crystal element is 10 °, the measured error of the optical rotation becomes a maximum of 0.6 ° or more. Therefore, in order to accurately measure the optical rotation, it is necessary to keep the temperature of the liquid crystal elements 26 and 28 constant by the temperature control means 34 and 36.

  According to the configuration of the polarization state measuring apparatus 10, the optical rotation can be measured by changing the measurement wavelength according to the sample S by providing the wavelength selection unit 14. Moreover, optical rotation dispersion can be easily obtained by measuring the optical rotation at various measurement wavelengths.

  A predetermined linearly polarized light from the polarizer 22 is provided by including the polarization modulation means 24 including two liquid crystal elements 26 and 28 whose inclinations of the main axes b and c with respect to the transmission axis a of the polarizer 22 are 45 ° and 0 °, respectively. Can be made incident on the sample S with the desired polarization changed, and the optical rotation can be detected by various methods.

  By using the polarization modulation means 24 including the two liquid crystal elements 26 and 28 instead of the analyzer rotating mechanism, the apparatus can be miniaturized. In addition, since the birefringence phase difference of the liquid crystal elements 22 and 24 can be changed at a high speed on the order of milliseconds (msec), the polarization state of the incident light on the sample S can be changed at a high speed, thereby shortening the time required for measurement. can do. Furthermore, since the voltage applied to the liquid crystal elements 22 and 24 is generally in the range of 0 to 5 V, the device can be driven at a lower voltage than when a conventional Faraday cell is used. Also, the apparatus can be manufactured at a lower cost than when a Pockels cell is used.

  By providing the temperature control means for keeping the temperature of the liquid crystal element uniform and constant, the optical rotation can be detected with high accuracy.

  Since the polarization state measuring apparatus 10 can change the incident light to the sample S into an arbitrary polarization state, it may be possible to measure not only the optical rotation but also circular dichroism. Moreover, it can also be set as a circular dichroism measuring apparatus.

When the circular dichroism is measured by the polarization state measuring device 10 or the circular dichroism measuring device, the polarization modulation unit 24 uses, for example, the first liquid crystal element 26 in order to change the incident light on the sample S to right circularly polarized light. of the birefringent phase difference [delta] ₁ and 90 °, the birefringence phase difference [delta] ₂ of the second liquid crystal element 28 to 0 °.

Similarly, the polarization modulation unit 24 sets the birefringence phase difference δ ₁ of the first liquid crystal element 26 to 90 °, for example, so that the incident light on the sample S is left circularly polarized light. The refractive phase difference δ _{2 is set} to 180 °.

The measuring means 52 calculates the extinction coefficient α _{R for} right circularly polarized light and the extinction coefficient α _L for left circularly polarized light, respectively.

Calculate by Here, I _SR and I _SL are the light intensities of right circularly polarized light and left circularly polarized light transmitted through the sample S, respectively, measured by the detection means 50. I _NR and I _NL are the light intensities of right circularly polarized light and left circularly polarized light measured by the detection means 50 without placing the sample S, respectively. The I _NR and I _NL are preferably measured and stored in advance.

Since circular dichroism is the difference between the extinction coefficients of left and right circularly polarized light, the measuring means 52 calculates the circular dichroism Δα of the sample S from the extinction coefficients α _R and α _{L of} right circularly polarized light and left circularly polarized light.

Calculate according to

  According to the polarization state measuring apparatus 10 or the circular dichroism measuring apparatus, the circular dichroism dispersion can be easily obtained by measuring the circular dichroism at various measurement wavelengths by providing the wavelength selecting means 14. it can.

  Note that the analyzer 48 is not necessary when measuring circular dichroism. The analyzer 48 may be detachably installed in the apparatus, and the analyzer 48 may be configured to be removed when the circular dichroism is measured, or the optical rotation and the circular dichroism can be maintained with the analyzer 48 placed. You may comprise so that both measurements may be performed.

Example 1
FIG. 7 shows the result of measuring the optical rotation angle with respect to the rotation of the half-wave plate using the embodiment of the polarization state measuring device according to the present invention.

  The measurement was performed by omitting the wavelength selection means in the configuration of FIG. More specifically, the half-wave plate as the sample is rotated by 5 ° in a range where the inclination of the optical axis of the half-wave plate with respect to the transmission axis of the polarizer 22 is −45 ° to 45 °. The optical rotation was measured.

  The measured optical rotation was twice the rotation angle of the half-wave plate, that is, twice the angle of the optical axis of the half-wave plate with respect to the transmission axis of the polarizer 22. Therefore, it can be understood that the optical rotation angle with respect to the rotation of the half-wave plate was accurately measured by the polarization state measuring apparatus according to the present invention.

Example 2
FIG. 8 shows the results of measuring the optical rotation of a standard quartz plate using an embodiment of the polarization state measuring device according to the present invention.

  In the configuration of FIG. 1, a halogen lamp was used as a light source in the configuration of FIG. 1, light having a wavelength of 589.3 nm obtained using an interference filter as a wavelength selection means, and a wavelength selection means were omitted, and a He—Ne laser was obtained as a light source. The measurement was performed using light having a wavelength of 632.8 nm. For sample S, standard quartz plates with specific rotations of 8 ° and 34 ° were used.

  In FIG. 8, the solid line shows the measurement result at a wavelength of 589.3 nm, and the broken line shows the measurement result at a wavelength of 632.8 nm. At a wavelength of 589.3 nm, the measured optical rotation shown on the vertical axis is approximately equal to the specific optical rotation shown on the horizontal axis. Therefore, it can be seen that the optical rotation of the sample S can be measured with high accuracy by the polarization state measuring apparatus according to the present invention. At a wavelength of 632.8 nm, the optical rotation is measured to be smaller than that at the wavelength of 589.3 nm. This is considered to be due to the influence of optical rotation dispersion.

  In short, the embodiment of the polarization state measuring device according to the present invention has the following characteristics.

1. The polarization state measuring device (10)
A first polarizer (22) that transmits a predetermined polarization component of light including a predetermined band component;
Polarization modulation means (24) for modulating the light transmitted through the first polarizer into a desired polarization;
A second polarizer (48) that transmits a predetermined polarization component of the light transmitted through the measurement object (S) via the polarization modulator;
Detection means (50) for detecting the light intensity of the light transmitted through the second polarizer;
Measurement means (52) for measuring the polarization state of the measurement object based on the Fourier coefficient when the light intensity detected by the detection means is represented by a Fourier series;
Have
The polarization modulation means includes first and second liquid crystal elements (26, 28) and voltage control means (30, 32) for controlling a voltage applied to the liquid crystal elements.

2. The polarization state includes the optical rotation or circular dichroism of the measurement target.

3. The first liquid crystal element (26) has a fast axis (b) inclined at an odd multiple of 45 ° with respect to the transmission axis of the first polarizer (22);
The second liquid crystal element (28) has a fast axis (c) inclined at an even multiple of 45 ° with respect to the transmission axis of the first polarizer (22).

4). The birefringence phase difference (δ ₁ ) of the first liquid crystal element is variable in the range of 0 ° to 360 °, and the birefringence phase difference (δ ₂ ) of the _second liquid crystal element is birefringence of the first liquid crystal element. It is 90 ° different from the phase difference.

5. Assuming that the birefringence phase difference of the first liquid crystal element is δ and the birefringence phase difference of the second liquid crystal element is δ + 90 °, the measurement means uses the basis functions cos δ and sin 2 δ in the Fourier series of the light intensity detected by the detection means. The polarization state of the measurement object is measured based on the coefficient.

6). The first and second liquid crystal elements include nematic liquid crystal cells.

7). The polarization modulation means further includes temperature control means (34, 36) for controlling the temperature of the first and second liquid crystal elements.

  The embodiment of the optical rotation measurement method according to the present invention has the following features.

8). The polarization state measurement method is
Transmitting a predetermined polarization component of light including a predetermined band component;
A polarization modulation step for modulating the transmitted light to a desired polarization;
Transmitting a predetermined polarization component of light that has undergone polarization modulation and transmitted through the measurement object;
Detecting the light intensity of the transmitted light;
Measuring the polarization state of the measurement object based on the Fourier coefficient when the detected light intensity is represented by a Fourier series;
Have
The polarization modulation step includes a step of modulating the transmitted light by the first and second liquid crystal elements and a step of controlling a voltage applied to the liquid crystal element.

  The embodiment of the circular dichroism measuring device according to the present invention has the following features.

9. Circular dichroism measuring device
A polarizer (22) that transmits a predetermined polarization component of light including a predetermined band component;
Polarization modulation means (24) for modulating the light transmitted through the polarizer into a desired polarization;
Detection means (50) for detecting the light intensity of light transmitted through the measurement object via the polarization modulation means;
Measurement means (52) for measuring the circular dichroism of the measurement object based on the light intensity detected by the detection means;
Have
The polarization modulation means includes first and second liquid crystal elements (26, 28) and voltage control means (30, 32) for controlling a voltage applied to the liquid crystal elements.

  The embodiment of the method for measuring optical rotation and circular dichroism according to the present invention has the following features.

10. Circular dichroism measurement method is
Transmitting a predetermined polarization component of light including a predetermined band component;
A polarization modulation step for modulating the transmitted light to a desired polarization;
Performing polarization modulation and detecting the light intensity of the light transmitted through the measurement object;
Measuring the circular dichroism of the measurement object based on the detected light intensity;
Have
The polarization modulation step includes a step of modulating the transmitted light by the first and second liquid crystal elements and a step of controlling a voltage applied to the liquid crystal element.

  Moreover, said measuring apparatus and measuring method have the following effects.

(1) The apparatus can be reduced in size.

(2) The manufacturing cost of the apparatus can be reduced.

(3) The device can be driven at a low voltage.

(4) The measurement time can be shortened.

(5) It can measure with high accuracy.

(6) Optical rotation dispersion and circular dichroism dispersion can be easily obtained.

  In addition, this invention is not limited to the said embodiment, It can implement with other various forms.

For example, regarding the optical rotation calculation method, in order to reduce the number of samplings, the light intensity I _θ (0), I _θ (when the phase modulation amount δ of the liquid crystal element is 0 °, 135 °, 180 °, and 225 °. 135), I _θ (180) and I _θ (225), respectively. In this case, the optical rotation θ is

Can be calculated from

  It can be used not only for measuring the concentration of saccharides and amino acids, but also for structural analysis of proteins, physical properties analysis of organic materials, and optical crystals.

  Moreover, it can utilize as a glucose sensor which measures the glucose level in blood, ie, a blood glucose level, non-invasively. It is possible to make it as small as a wristwatch.

FIG. 1 is a schematic configuration diagram showing an embodiment of a polarization state measuring apparatus according to the present invention. FIG. 2 is a Poincare sphere representing a change in the polarization state of light. FIG. 3 is a Poincare sphere showing an example of the polarization state of the light emitted from the polarization modulation means. FIG. 4 is a perspective view showing the configuration of the temperature control means of FIG. FIG. 5 shows the relationship between the voltage applied to the liquid crystal element and the birefringence phase difference of the liquid crystal element. FIG. 6 shows an optical rotation measurement error due to a birefringence phase difference error of the liquid crystal element. FIG. 7 shows the optical rotation angle with respect to the rotation of the half-wave plate measured using the embodiment of the polarization state measuring device according to the present invention. FIG. 8 shows the optical rotation of a standard quartz plate measured using an embodiment of the polarization state measuring apparatus according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Polarization state measuring apparatus 12 Light source 14 Wavelength selection means 16 Reflection type diffraction grating 18 Slit 20 Driving means 22 Polarizer 24 Polarization modulation means 26 First liquid crystal element 28 Second liquid crystal elements 30, 32 Voltage control means 34, 36 Temperature control means 46 measuring cell 48 analyzer 50 detecting means 52 measuring means

Claims (7)

In a polarization state measuring apparatus for measuring the polarization state of a measurement object having light transmittance,
A first polarizer that transmits a predetermined polarization component of light including a predetermined band component;
Polarization modulation means for modulating the light transmitted through the first polarizer into a desired polarization;
A second polarizer that transmits a predetermined polarization component of light transmitted through the measurement object via the polarization modulator;
Detecting means for detecting the light intensity of the light transmitted through the second polarizer;
Measuring means for measuring the polarization state of the measurement object based on a Fourier coefficient when the light intensity detected by the detection means is represented by a Fourier series;
Have
The polarization modulation means possess first and second liquid crystal element, and a voltage control means for controlling a voltage applied to the liquid crystal element,
The birefringence phase difference of the first liquid crystal element is variable in the range of 0 ° to 360 °, and the birefringence phase difference of the second liquid crystal element is 90 ° different from the birefringence phase difference of the first liquid crystal element. ,
A polarization state measuring device. The polarization state measuring apparatus according to claim 1, wherein the polarization state includes optical rotation or circular dichroism to be measured. The first liquid crystal element has a fast axis inclined at an odd multiple of 45 ° with respect to the transmission axis of the first polarizer;
The polarization state measuring apparatus according to claim 1, wherein the second liquid crystal element has a fast axis inclined at an even multiple of 45 ° with respect to the transmission axis of the first polarizer. Assuming that the birefringence phase difference of the first liquid crystal element is δ and the birefringence phase difference of the second liquid crystal element is δ + 90 °, the measurement means is a basis function in the Fourier series of the light intensity detected by the detection means. The polarization state measuring apparatus according to claim 1, wherein the polarization state of the measurement target is measured based on the coefficients of cos δ and sin 2 δ. The polarization state measuring device according to claim 1 or 3, wherein the first and second liquid crystal elements include nematic liquid crystal cells.   2. The polarization state measuring apparatus according to claim 1, wherein the polarization modulation unit further includes a temperature control unit that controls the temperatures of the first and second liquid crystal elements. In a polarization state measurement method for measuring a polarization state of a measurement object having light transmittance,
Transmitting a predetermined polarization component of light including a predetermined band component;
A polarization modulation step for modulating the transmitted light to a desired polarization;
Transmitting a predetermined polarization component of light that has undergone polarization modulation and transmitted through the measurement object;
Detecting the light intensity of the transmitted light;
Measuring the polarization state of the measurement object based on a Fourier coefficient when the detected light intensity is represented by a Fourier series;
Have
The polarization modulation step, possess the step of modulating transmitted light by the first and second liquid crystal element, and controlling the voltage applied to the liquid crystal element, a,
The birefringence phase difference of the first liquid crystal element is variable in the range of 0 ° to 360 °, and the birefringence phase difference of the second liquid crystal element is 90 ° different from the birefringence phase difference of the first liquid crystal element. ,
A polarization state measuring method characterized by the above.

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