Calibration sample holder, and method for calibrating polarization measuring device employing same

Abstract

A calibration sample holder 10 for a polarization measuring device comprises: a cylindrical holder body 5; fixing means 1, 2, 3 for fixing a calibration sample 4 that exhibits optical anisotropy on a central axis inside the holder body 5; and the calibration sample 4. At least one part 5A, 5B of the outer periphery of the holder body 5 has an outer diameter larger than that of other parts, and has an axisymmetric regular polygonal cross-sectional shape. The holder body 5 is configured to be capable of being installed on a V-shaped block provided in the polarization measuring device, such that the center of the optical path of polarized light in the polarization measuring device coincides with the central axis of the holder body 5. The V-shaped block has the same opening angle as the angle formed by two sides of the axisymmetric regular polygon, and the holder body 5 is configured to be capable of being installed on the V-shaped block at a plurality of installation angles. A calibration value is assigned to the calibration sample 4 for each installation angle of the holder body 5.

Description

Calibration sample holder and method for calibrating a polarization measurement device using the same Related Applications

[0001] This application claims priority from Japanese Patent Application No. 2024-002570, filed January 11, 2024, which is incorporated herein by reference.

[0002] The present invention relates to the calibration of polarimetry instruments.

[0003] There are various instruments for measuring the polarization properties of samples, but there is a need for a method to properly and easily calibrate such polarimetry instruments.

[0004] Patent Document 1 discloses a cylindrical liquid cell for use in a polarimeter, which is a type of polarization measurement device. Because such cylindrical cells are commonly used in polarimeters, when calibrating a polarimeter, a calibration sample (such as a quartz plate) can be attached to a cylindrical holder with the same external shape as the cylindrical cell, and the cylindrical holder for calibration can be placed in the sample chamber in the same way as the cylindrical cell.

[0005] Furthermore, Patent Document 2 discloses a cylindrical holder incorporating a quartz plate for calibration. The quartz plate inside the holder has its angle of rotation previously determined using a high-precision polarimeter. When calibrating a polarimeter using such a cylindrical holder, it is necessary to accurately reproduce the installation angle of the quartz plate at the time of determination in order to avoid optical defects inherent in the quartz plate. In Patent Document 2, the shape of the cylindrical holder is utilized to enable the cylindrical holder to be installed in the polarimeter's sample chamber at various angles around its axis. Since the angle of rotation for each installation angle can be measured, the installation angle closest to the determined angle is found and calibration is performed at that installation angle.

[0006] JP 2007-33460 A International Publication No. 2017 / 108034

[0007] However, calibration of a polarization measurement device is not a one-time process but is performed periodically or repeatedly as needed. Therefore, when performing calibration by placing a cylindrical holder, such as that described in Patent Document 1, on a V-shaped block in a sample chamber, the installation angle of the cylindrical holder relative to the V-shaped block is not fixed and changes each time it is installed. Furthermore, while the calibration method described in Patent Document 2 utilizes the shape of the cylindrical holder to facilitate measurements at multiple installation angles, it is necessary to perform measurements at multiple installation angles each time calibration is performed to reproduce the installation angle of the quartz plate used for pricing, which is time-consuming. In other words, the contents described in Patent Documents 1 and 2 leave room for improvement in the reproducibility of the installation angle of the calibration sample (quartz plate) fixed to the cylindrical holder.

[0008] An object of the present invention is to provide a calibration sample holder with excellent reproducibility of installation angles. It is also an object of the present invention to provide a calibration sample holder that can be easily changed to a plurality of different installation angles, the polarization characteristic values ​​of the calibration sample measured at each installation angle, and the resulting measurements compared with polarization characteristic values ​​(also referred to here as calibration values) previously assigned for each installation angle. It is also an object of the present invention to provide a method for calibrating a polarimetry device using the same.

[0009] That is, the calibration sample holder of the present invention is a calibration sample holder for a polarization measurement device comprising: a cylindrical holder body; a fixing means for fixing a calibration sample exhibiting optical anisotropy on the central axis of the holder body inside the holder body; and the calibration sample, wherein at least a portion of the outer periphery of the holder body has an outer diameter larger than other portions and has a cross-sectional shape of an axisymmetric regular polygon, the holder body is configured to be installable on a V-block provided on the polarization measurement device so that the center of the polarized light path of the polarization measurement device coincides with the central axis of the holder body, wherein the V-block has an opening angle that is the same as the angle formed by two sides of the axisymmetric regular polygon, and the holder body is configured to be installable on the V-block at a plurality of installation angles, and the calibration sample is assigned a calibration value for each installation angle of the holder body.

[0010] Preferably, the portion having an axisymmetric regular polygonal cross section is formed at two different locations along the central axis of the holder body.

[0011] Next, a method for calibrating a polarization measurement device according to the present invention includes the steps of: using a cylindrical holder body having an outer diameter in at least a portion of its outer periphery that is larger than the remaining portions and having a cross-sectional shape of an axisymmetric regular polygon in that portion; and using a calibration sample exhibiting optical anisotropy that is fixed within the holder body so as to be positioned on the central axis of the holder body; providing a V-shaped block having an opening angle that is the same as the angle formed by two sides of the axisymmetric regular polygon along the optical path of polarized light that is the measurement light of the polarization measurement device; installing the holder body at a predetermined installation angle on the V-shaped block so that the center of the optical path of the polarized light coincides with the central axis of the holder body; measuring the polarization characteristic value of the calibration sample; the holder body being configured to be installable on the V-shaped block at a plurality of installation angles, and the calibration sample being assigned a calibration value for each installation angle of the holder body; and comparing the measured polarization characteristic value with the calibration value corresponding to the predetermined installation angle.

[0012] Furthermore, it is preferable to measure the polarization characteristic values ​​of the calibration sample at a plurality of installation angles by installing the holder body on the V-block at an installation angle different from the predetermined installation angle.

[0013] The above-described calibration sample holder configuration provides a calibration sample holder with excellent reproducibility of the installation angle on the V-block, improving the reliability of the analysis results of a polarimetry instrument calibrated using this holder. In addition, by setting the same calibration sample at multiple installation angles with clear angles, detailed calibration using the calibration values ​​for each of the multiple installation angles becomes possible, further improving the reliability of the analysis results of the polarimetry instrument.

[0014] Furthermore, according to the above calibration method, the installation angle of the calibration sample on the V-shaped block can be accurately and reproducibly set, and by performing this calibration method, the reliability of the analysis results of the polarimetry device is improved. In addition, detailed calibration is possible using the calibration values ​​of the calibration sample at multiple installation angles with clear angles, and a polarimetry device with excellent reliability of analysis results can be provided.

[0015] Fig. 1 is an exploded view of a calibration sample holder according to one embodiment of the present invention; Fig. 2 is a cross-sectional view of the calibration sample holder; (A) to (F) are six-view diagrams of the calibration sample holder; Fig. 3 is a perspective view showing an example of use of the calibration sample holder; Fig. 4 is a side view of the incident side showing an example of use of the calibration sample holder; Fig. 5 is a diagram of an apparatus configuration when calibrating a polarimeter using the calibration sample holder;

[0016] An embodiment of a calibration sample holder according to the present invention will be described below with reference to the drawings. As shown in the exploded view of Figure 1, the calibration sample holder 10 comprises a spring retainer 1, a coil spring 2, a spacer 3, a calibration sample 4, and a holder body 5. The spring retainer 1, the coil spring 2, and the spacer 3 constitute a fixing means 8 for fixing the calibration sample 4 to the holder body 5.

[0017] The calibration sample 4 is an optical element having anisotropy, and a scale indicating the anisotropy is defined as a calibration value. For example, the calibration sample 4 for a polarimeter has an optical rotation (α ｔ λ (where λ is wavelength, t is temperature, and the unit is angle.) is assigned as a calibration value. The shape of the calibration sample 4 is not limited, but is generally a disk, square plate, or other regular polygonal plate.

[0018] The calibration sample holder 10 can be used for calibration samples 4 for optical rotation measurements, as well as for calibration samples in circular dichroism measurements, linear dichroism measurements, birefringence measurements, polarized transmission measurements, polarized reflection measurements, polarized Raman measurements (which refers to measurements of the polarization direction dependence of Raman scattering intensity), and polarized light microscopy measurements.

[0019] Specific examples of the calibration sample 4 include standard samples such as a polarizing plate and a wavelength phase plate. A linear polarizing plate, which is one type of polarizing plate, is an optical element in which the vibration direction of linearly polarized light that passes through it is determined. A quarter-wave plate, which is one type of wavelength phase plate, is an optical element that has orthogonal principal axes and generates a phase difference of a quarter wavelength between the polarized light components in the directions of the respective principal axes.

[0020] In addition, polarization measurement devices to which the calibration sample holder 10 can be applied include circular dichroism spectrometers, linear dichroism spectrometers, birefringence measurement devices, infrared spectrophotometers, Raman spectrophotometers, and ultraviolet-visible-near-infrared spectrophotometers.

[0021] The holder body 5 is cylindrical overall and has a through hole 6 along its central axis. One side of the through hole 6 is the incident side, and the other side is the exit side. Specifically, the shape of the holder body 5 along its central axis is as follows: a cylindrical portion is located at the end of the incident side, and a regular octagonal cylindrical portion 5A, with a larger outer diameter than the cylindrical portion, is located on the exit side. A slightly longer cylindrical portion is located on the exit side of the regular octagonal cylindrical portion 5A, with the same outer diameter as the cylindrical portion on the incident side. On the exit side, there is another regular octagonal cylindrical portion 5B, with the same outer diameter as the regular octagonal cylindrical portion 5A on the incident side, forming the end of the exit side. In other words, regular octagonal cylindrical portions 5A and 5B, with an outer shape with eight flat surfaces aligned along the outer periphery, are located at two locations along the central axis of the holder body 5, and both have a regular octagonal cross-sectional shape of the same size perpendicular to the central axis. The cross-sectional shape is not limited to a regular octagon, but may be a regular polygon with an even number of sides of four or more, such as a square, a regular hexagon, a regular dodecagon, or a regular hexagon.

[0022] The cylindrical portion on the incident side has a scale marked every 45 degrees along the outer circumference. The numbers "-90", "0", and "90" are marked next to the scale corresponding to each installation angle. Furthermore, the cylindrical portion between the regular octagonal tube portions 5A and 5B has eight thermometer sockets 7 lined up along the outer circumference. During calibration, a thermometer is inserted into one of the sockets 7 to measure the temperature inside the holder main body 5. A socket 7 is formed for each installation angle so that measurements can be made approximately equally regardless of the installation angle of the holder main body 5.

[0023] The cross-sectional view of Figure 2 shows the calibration sample 4 attached to the calibration sample holder 10. As shown in Figure 2, the through-hole 6 of the holder body 5 has different cross-sectional shapes on the incident side and the exit side. In the example of Figure 2, the cross-sectional shape of the through-hole 6 on both the incident and exit sides is circular, but the inner diameter on the exit side is smaller than that on the incident side. The disk-shaped calibration sample 4, ring-shaped spacer 3, coil spring 2, and spring holder 1 all have outer diameters approximately the same as the inner diameter of the through-hole 6 on the incident side. These are inserted into the through-hole 6 in order from the incident side. The spring holder 1 is cylindrical and is screwed into the through-hole 6 on the incident side. Screwing the spring holder 1 compresses the coil spring 2, and the biasing force of the coil spring 2 acts on the calibration sample 4 via the spacer 3, fixing the calibration sample 4 to the holder 5.

[0024] Here, the cross-sectional shape of the through-hole 6 on the incident side may be determined in accordance with the shape of the calibration sample 4. For example, if the external shape of the calibration sample 4 is not circular but rectangular, the cross-sectional shape of the through-hole 6 on the incident side may also be rectangular.

[0025] The spring holder 1 is not limited to a screw-in type, and may be made of rubber. By fitting the rubber spring holder 1 into the through-hole 6 on the incident side, the coil spring 2 is compressed, and the calibration sample 4 is fixed to the holder 5.

[0026] 3A to 3F show six views (front view, plan view, bottom view, rear view, right side view, and left side view) of the calibration sample holder 10 of this embodiment. A calibration method using the calibration sample holder 10 will be described with reference to FIGS. 4 and 5.

[0027] (1) For example, the calibration sample holder 10 is placed in a V-shaped block 20 provided in the sample chamber of a polarimeter having the configuration shown in FIG. 6 . When the polarimeter has regular octagonal cylindrical sections 5A and 5B, the opening angle of the V-shaped block 20 is set to 90 degrees (see FIG. 5 ). Alternatively, when the polarimeter has regular hexagonal cylindrical sections, the opening angle is set to 60 degrees. Alternatively, a V-shaped block 20 having an opening angle corresponding to the shape of an axisymmetric regular polygon is used. Therefore, regardless of the orientation in which the calibration sample holder 10 is placed, the two inclined surfaces of the V-shaped block 20 come into contact with the two outer peripheries of the regular octagonal cylindrical sections 5A and 5B of the holder body 5 (the two surfaces intersecting at 90 degrees), and the placement angle of the calibration sample 4 in the holder 10 is determined (see FIG. 5 ).

[0028] (2) After placing the calibration sample holder 10 on the V-shaped block 20, read the topmost scale from the scales on the entrance-side cylindrical portion of the holder body 5 and record it as necessary. In this way, the user can confirm the installation angle of the calibration sample 4 held in the calibration sample holder 10 based on the scale readout. In the case of Figure 4, the installation angle is 0 degrees. In addition to the method of the user reading it themselves, a mechanism may be provided in which the polarimeter automatically reads the scale of the calibration sample holder 10 placed in the sample chamber using a known technique such as image recognition, and records the read installation angle of the calibration sample 4 together with the measured value (angle of rotation).

[0029] (3) To avoid variations in the angle of rotation due to the temperature of the calibration sample 4, a temperature control means (e.g., a temperature control device using a Peltier element) installed in the V-shaped block 20 is used to maintain the temperature of the calibration sample 4 in the calibration sample holder 10 at a predetermined temperature, and the polarimeter is operated to measure the angle of rotation of the calibration sample 4. The polarimeter is then calibrated by comparing the measured value of the angle of rotation with a calibration value (angle of rotation) previously assigned to the calibration sample 4. The measured temperature of the calibration sample 4 may be recorded together with the installation angle and the measured value (angle of rotation). In the case of a polarimeter, for example, the emission line (D line) of a sodium lamp is used as the light source, and linearly polarized light extracted from this by a polarizer in front of the sample chamber is guided into the through-hole on the entrance side of the calibration sample holder 10 installed in the sample chamber, thereby measuring the angle of rotation of the calibration sample 4.

[0030] (4) The installation angle of the calibration sample holder 10 is changed and the angle of rotation of the calibration sample 4 is measured at a plurality of installation angles. Then, the measured angle of rotation at each installation angle is compared with the calibration value (angle of rotation) for each installation angle assigned to the calibration sample 4, thereby enabling detailed calibration of the polarimeter. Note that the temperature measurement value, installation angle, and measurement value (angle of rotation) of the calibration sample 4 may also be recorded for each installation angle.

[0031] In the above calibration method, the calibration sample holder 10 is installed on the V-shaped block 20 at different orientations (eight installation angles from −180 degrees to +180 degrees) around its central axis in 45-degree increments. This allows the user to easily reproduce the installation angle of the calibration sample 4 fixed to the holder 10. In other words, when previously calibrating using the same holder 10, the installation angle of the calibration sample 4 can be read and recorded based on the scale (angle) on the holder body 5 (or specified to be a constant angle). This makes it easy to install the calibration sample 4 at the same installation angle during the next calibration. Alternatively, instead of the same installation angle, it is also easy to select a desired orientation from different orientations in 45-degree increments and install the calibration sample 4 at that installation angle.

[0032] With conventional cylindrical holders, the installation angle of the calibration sample 4 during calibration is often unknown. Without a clear orientation of the calibration sample 4, the installation angle of the cylindrical holder is changed in multiple ways, and the average or median of the measurements taken at each installation angle is obtained. Alternatively, if the variation in the measurements at multiple installation angles is within a predetermined range, a representative value is obtained. The value obtained in this manner is compared with the calibration value of the calibration sample 4, which makes it difficult to achieve reproducibility of the installation angle of the calibration sample 4 during the next calibration. In contrast, as described above, the holder 10 of this embodiment allows a predetermined installation angle to be selected from multiple predetermined installation angles, and the optical rotation of the calibration sample 4 at a uniquely identifiable setting angle can be measured even after calibration. This allows the installation angle of the calibration sample 4 to be accurately reproduced during the next calibration. This allows for proper calibration of the polarimeter, improving the reliability of the polarimeter's analysis results. In addition, setting the same calibration sample 4 at multiple installation angles with clear angles enables detailed calibration using calibration values ​​previously assigned to each of the multiple installation angles, further improving the reliability of the analysis results of the polarimeter.

[0033] In particular, in optical rotation measurements, circular dichroism measurements, linear dichroism measurements, birefringence measurements, polarized transmission measurements, polarized reflection measurements, polarized Raman measurements, polarized microscopic measurements, and the like, which measure the polarization state of a sample, the sample installation angle has a significant effect on the measurement results, so the reproducibility of the installation angle of the calibration sample 4 is extremely important, and by using the calibration sample holder 10 of this embodiment, the reliability of the analysis results of these polarization measurement devices is improved.

[0034] Furthermore, in the case of a conventional cylindrical holder, the contact area between the holder and the V-shaped block 20 is small because the holder is in line contact with the V-shaped block 20. In contrast, the holder 10 of this embodiment is in surface contact with the V-shaped block 20, so the contact area between the holder and the V-shaped block 20 is large. This has the advantage of improving the heat transfer efficiency of temperature control and eliminating the effects of vibration, etc.

[0035] For example, if a Peltier element is installed on a V-shaped block 20 and the temperature of the calibration sample 4 in the calibration sample holder is controlled via the V-shaped block 20, surface contact makes it easier to adjust the temperature of the calibration sample holder.

[0036] Furthermore, even when the calibration sample 4 in the holder 10 is subjected to vibrations from outside the device (for example, vibrations caused by a person or object coming into contact with the device, or vibrations transmitted from nearby equipment such as a dehumidifier or circulating thermostatic bath), surface contact makes it less likely that vibrations will occur in the calibration sample holder 10, thereby achieving the effect of suppressing vibration generation.

[0037] In addition, the installation angle of the calibration sample 4 can be easily changed, and the calibration process, which could only be carried out through complex operations with conventional cylindrical holders, can now be carried out with a simple flow, making it possible to carry out more detailed calibration within a realistic work time.

[0038] Furthermore, the calibration sample holder 10 of this embodiment can also be used for measuring the polarization of a sample by placing a sample, which is the object to be measured, in place of a calibration sample.

[0039] Finally, a specific example will be given showing that detailed calibration is possible by setting the calibration sample holder of this embodiment at a plurality of installation angles and calibrating the polarimeter at each installation angle.

[0040] First, the pass criterion is that the measured value of the optical rotation of the standard sample (calibration sample) falls within the following range: Optical rotation of standard sample ± ([instrument accuracy] + [expanded uncertainty of standard sample]). Here, instrument accuracy is a value dependent on the performance of the instrument and is set, for example, to 0.2% of the optical rotation. If the optical rotation of the standard sample is 17,000°, the instrument accuracy is 17,000 x 0.2% = 0.034°. The expanded uncertainty of the standard sample represents the variation in the optical rotation value and is the value listed on the calibration certificate of the standard sample (optical rotatory plate). Here, for simplicity, we will assume the expanded uncertainty of the standard sample to be 0.

[0041] The four items used for calibration are a polarimeter, a thermometer (for measuring the temperature of the standard sample), a valued standard sample, and the calibration sample holder of this embodiment. The standard sample (optical rotatory plate) is always installed in the calibration sample holder and is never removed from the holder. Therefore, the relationship between the installation angle of the standard sample and the holder does not change, and the "installation angle of the holder = angle of the standard sample" is the same. The valued optical rotation at a wavelength of 589 nm and the pass criteria for each installation angle are, for example, as shown in the table below.

[0042]

[0043] The calibration steps (1) to (5) are as follows: (1) Set the calibration sample holder containing the standard sample on the polarimeter at an installation angle of 0°. (2) Insert the thermometer into the thermometer socket. (3) Check the temperature of the standard sample, and when it reaches 20±0.5°C, measure the angle of rotation at a wavelength of 589 nm and record it along with the sample temperature at that time. (4) Correct the measured angle of rotation to the angle of rotation at a temperature of 20°C. (5) If the corrected angle of rotation is within 17.000±0.034°, it is considered a pass.

[0044] When the above calibration procedure is performed using a conventional cylindrical holder, the installation angle of the standard sample (optical rotatory plate) is not fixed, resulting in a certain range of the pre-assigned "optical rotation of the standard sample" among the pass criteria. As a result, the calibration result may fail even if the polarimeter's performance would normally pass. In contrast, using a calibration sample holder with an axisymmetric regular polygonal cross section as in this embodiment, the installation angle of the standard sample is fixed, so the polarimeter's performance is accurately reflected in the calibration result. Furthermore, not only is it accurate, but the ability to assign values ​​to the standard sample at each angle increases the amount of information available for calibration for a single standard sample. For example, with a regular octagonal holder, instrument calibration is possible at an installation angle of 0°, and similarly, eight different instrument calibrations are possible at 45° increments, such as 45°, 90°, 135°, etc. Although the calibration test is performed at only one installation angle, more reliable instrument calibration can be achieved by performing measurements at other installation angles as reference data.

[0045] REFERENCE SIGNS LIST 1 spring holder 2 coil spring 3 spacer 4 calibration sample 5 holder body 5A, 5B regular octagonal cylindrical portion 6 through hole 7 thermometer insertion port 8 fixing means 10 calibration sample holder 20 V-shaped block

Claims

1. A calibration sample holder for a polarization measurement device, comprising: a cylindrical holder body; fixing means for fixing a calibration sample exhibiting optical anisotropy on the central axis of the holder body inside the holder body; and the calibration sample. At least a part of the outer periphery of the holder body has an outer diameter larger than that of other parts and has a cross-sectional shape of an axisymmetric regular polygon. The holder body is configured to be installable on a V-block provided in the polarization measurement device such that the center of the polarization optical path of the polarization measurement device coincides with the central axis of the holder body. Here, the V-block has the same opening angle as the angle formed by two sides of the axisymmetric regular polygon, and the holder body is configured to be installable on the V-block at a plurality of installation angles. A calibration value is assigned to the calibration sample for each of the installation angles of the holder body. A calibration sample holder characterized by the above.

2. The calibration sample holder according to claim 1, wherein the portion having the cross-sectional shape of the axisymmetric regular polygon is formed at two different positions along the central axis of the holder body. A calibration sample holder characterized by the above.

3. A calibration method for a polarization measurement device, using a cylindrical holder body having an outer diameter larger than that of other parts at least in part of the outer periphery and having a cross-sectional shape of an axisymmetric regular polygon, and using a calibration sample exhibiting optical anisotropy fixed inside the holder body so as to be located on the central axis of the holder body. A V-block having the same opening angle as the angle formed by two sides of the axisymmetric regular polygon is provided along the optical path of the polarized light, which is the measurement light of the polarization measurement device. The holder body is installed on the V-block at a predetermined installation angle such that the center of the optical path of the polarized light coincides with the central axis of the holder body. The polarization characteristic value of the calibration sample is measured. The holder body is configured to be installable on the V-block at a plurality of installation angles, and a calibration value is assigned to the calibration sample for each of the installation angles of the holder body. The measured polarization characteristic value is compared with the calibration value corresponding to the predetermined installation angle. A calibration method characterized by the above.

4. In the calibration method according to claim 3, further, by installing the holder body on the V-block at an installation angle different from the predetermined installation angle, the polarization characteristic values of the calibration sample at a plurality of installation angles are measured. A calibration method characterized by this.

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