JPS60244822A - Measuring method of spectral transmissivity of polarizing sample - Google Patents

Abstract

PURPOSE:To obtain the transmissivety of the titled polarizing sample to natural light by making the projection light of a spectroscope incident on the polarizing sample through a linear polarizer, rotating the linear polarizer and polarizing sample by 90 deg. relatively, and averaging transmissivity values before and after the rotation. CONSTITUTION:The projection light of the spectroscope is made incident on the polarizing sample. The linear polarizer and polarizing sample are rotated relatively and an equation I is estimated from measure apparent transmissivity. An equation II is derived from the equation II. This equation II shows the relation between the apparent transmissivity and angular position of rotation of the polarizing sample on the optical axis of a spectrophotometer. When natural light is incident, light only in one polarization direction is reduced in energy to half and denoted as (a/2)+c. Therefore, the average of transmissivity gamma(theta+pi/2) at the time of 90 deg. rotation and transmissivity gamma(theta) at the time of 0 deg. is the transmissivity to the natural light.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a spectral transmittance measuring device for measuring the spectral transmittance of a polarizing sample to natural light.

Mouth Conventional technology Measurement of spectral transmittance 1 A spectrophotometer is used.

However, when attempting to measure the spectral transmittance of a polarizing sample, the polarization characteristics of the spectrometer itself become a problem. Diffraction gratings, which are dispersive elements used in spectrometers, have significant polarization properties, and the polarization properties vary depending on the wavelength, so spectrometers using diffraction gratings also have wavelength-dependent polarization properties. have

Even spectrometers using prisms have polarization characteristics, as is well known, as the surface reflectance of the prism and other optical elements that make up the spectrometer is not as good as that of spectrometers using diffraction gratings. exhibits polarization properties. Moreover, this polarization characteristic differs depending on the spectrometer. Therefore, in the case of a polarizing sample, simply measuring the transmittance using a spectrophotometer will not give a meaningful transmittance value.An example of a polarizing sample is the polarizer itself. ,
These include thin film samples, optical components for oblique incidence, and optical materials. Traditionally, spectrophotometers have been used for spectroscopic analysis, measuring the color of various materials, and measuring the transmittance of isotropic materials, so the polarization characteristics of spectrometers have rarely been an issue; The polarization characteristics themselves had not been clearly determined.

However, in recent years, the use of thin films has increased due to advances in thin film engineering, and technological advances such as the spread of optical fiber applications and increased opportunities to handle polarized light due to the spread of lasers have resulted in accurate spectral transmittance of polarized samples. There is an increasing need to reconsider the polarization characteristics of various materials and devices that have been overlooked in the past.

C. Purpose The present invention allows a spectrophotometer to have arbitrary spectral polarization characteristics, and uses such a spectrophotometer to detect unique natural light, i.e., polarized light in all directions, for a polarized sample. The purpose of the present invention is to provide a method for measuring the spectral transmittance of light containing the same proportions.

Two configurations The present invention makes spectrometer output light incident on a sample through a linear polarizer, and changes the relative angular position of the linear polarizer and the sample in a plane perpendicular to the optical axis of the optical system by 90 degrees. The transmittance in oil immersion is measured, and the average value is calculated and used as the transmittance for natural light. The angular position between the polarizer and the sample here refers to the relationship between the mutual directions when the polarizer and the sample rotate around the optical axis of the optical system that makes the spectrometer output light incident on the sample. It is. In other words, assuming that one mark is placed on each of the polarizer and the sample in the direction perpendicular to the optical axis, it is the angle between the two marks. Also, when I say relative here, I mean fix the sample and set the polarizer at 90°.
This means that it is the same whether the polarizer is rotated or the sample is rotated by 90° with the polarizer fixed, and does not include changing the angular position by 90° by rotating both together. This means that only one of the numbers - 10,000 is turned 90 degrees.

The basis for determining the transmittance of natural light as described above will be explained below. 3A-3D show the spectral polarization characteristics of several spectrometers. This characteristic can be determined by using a polarizer as a measurement sample, rotating the polarizer around the optical axis of the optical system, and measuring and plotting the apparent transmittance. Here, the S component is polarized light whose electric vector is perpendicular to the grating lines of the diffraction grating, and the P component is polarized light whose electric vector is parallel to the grating lines at 0°.

90° is the direction of the linear polarizer, and 90° is defined as the direction in which only the light component having an electric vector parallel to the slit of the spectrometer is extracted. The third diagram is especially for the polarizer lθ
These are the results of measuring the characteristics of the spectrometer by rotating it in degrees. FIG. 4 plots the apparent transmittance at a given wavelength as a function of the polarizer angle in polar coordinate form based on the results of the third plot. In the sample spectrometer, the polarization characteristics are reversed (rotated by 90°) at a wavelength of around 450 nm. In FIG. 4, T1 and T2 are measurement results at two wavelength positions in the wavelength range before and after 450 nm, and the transmittance is expressed as a relative value with the maximum being 100. Figure 5 is a graph showing the relationship between the transmittance of a polarizer and the angle for linearly polarized light.
It is expressed as os θ. Figure 6 shows the relationship between the transmittance of a linear polarizer for natural light and the angle, which is a perfect circle, and is expressed as γ( = c (constant).
It is expected that it can be expressed as aSIn θ+c−[formula for IKTl]. Subtracting a in the above formula from the actual measured values that are the basis for Figure 4, we get -47,8s+n θ+17.8...
...(2) becomes. The difference between the actual measured value and the actual measured value of γ calculated using the above formula is shown in Table 1 at the end.The maximum error is 1.1
(error rate 2%), but in this actual measurement, the polarizer angle T
(θ)=asin CO”r)+c= ・・・=
= (It can be said that it has been proven that it can be expressed in the form of 31.

Using this property, from formula 131 we get γ(θ)+7 (0+-) 7 a+2 c...
...+4] is derived. The relationship holds true regardless of θ. Ill, t2L t3) 2 above represents the polarization characteristics of a spectrometer at an arbitrary wavelength, but if you look at it differently, the angle of the polarizer and the apparent value when measuring the transmittance of a linear polarizer with an arbitrary spectrometer. It represents the relationship between the transmittance and, more generally, the relationship between the angular position of rotation about the optical axis of the spectrophotometer of a sample with polarization characteristics and the apparent transmittance. According to this view, the meaning of equation (4) is that the apparent transmittance γ(at any angular position of the sample) and the apparent transmittance γζθ +
This means that the average of π/2) is the transmittance for natural light. The reason for this is explained below.

A: When the sample is a linear polarizer.

Since generality is not lost even if we discuss based on equation (1) (
Since θ is arbitrary),]1) Based on the formula,
a represents the transmittance of the polarized light component when the electric vector of the open light component of the incident light and the polarizer are parallel (90°), and the total transmittance in this case is a + c.

When the orientation of the polarizer is 0°, the transmittance of the polarized light component is OL, so the total transmittance is C. Now, if we consider natural light of the same wavelength and the same energy as the light emitted from the spectrometer, the polarization component of the light emitted from the spectrometer will equally divide the energy into polarized light in all directions. When light is extracted in only one polarization direction, the energy is halved. Therefore, the energy of the transmitted light is (a/2)+c. That is, the transmittance for natural light is the average of γ( and γ(θ+π/2)).

B. Case of an arbitrary sample An arbitrary sample is equivalent to a mosaic of a non-polarizing part and a polarizer part. In the non-polarizing part, the transmittance does not change even if the sample is rotated, so the value of the constant C in the tl1 equation is simply increased. Regarding the polarizing part, what was said in A can be applied. Therefore, in this case as well, the average transmittance of the arbitrary angular position and the angular position rotated by 90° is the transmittance of the natural light S.

E. Embodiment FIG. 1 shows an embodiment of the present invention. This device is configured as an accessory that is set in the sample chamber of a spectrophotometer. l is the base block through hole 1al socket z
, 2' are inserted, and the socket 2°2' is fixed with the screw lb. Sockets 2 and 2I are 90°+X in the circumferential direction
It has notches 2a and 2'a in the range. 3 is the sample hole)
It consists of an insertion part 3a that fits into the socket 2', a face plate 3b, and a leaf spring 3c. S is a sample that is pushed between the face plate 3b and the leaf spring 3c, and is held in the holder 3 by being pressed against the face plate 3bl by the leaf spring 3cl. The insertion portion 3a of the socket 3 has a pin 3d. Sample ho JL
When the pin 3d is held in the socket 2' by inserting the insertion part 3a into the socket 2', the pin 3d is inserted into the notch 2'a.
The sample holder can rotate about the central axis of the socket 2' within a range that corresponds to both ends of the socket 2'. Since the angle of 90°+X of the notch 2'a corresponds to the thickness of the pin 3d, the specimen holder 3
can be rotated through an angular range of 90°. 4 is a polarizer holder, which has an insertion part 4a that fits into the socket 2, and a partial hook pin 4b of 4a stands up, and like the sample holder, the socket 2
When the pin 4b is inserted in the
It can be rotated by 0°. The optical axis in the sample chamber of the spectrophotometer is X.

When a diffraction grating is used as the dispersive element, the output light from the spectrometer has a wavelength range in which the polarization component (S component) with an electric vector parallel to the grating of the diffraction grating is at its maximum, and polarized light with an electric vector perpendicular to the grating. There is a wavelength range in which the component (P component) is maximum (see the third diagram).Therefore, the output light of such a spectrometer is naturally polarized by polarizer P at +45° and -45° with respect to the output slit of the spectrometer. When the socket 2 is fixed to the base block 1 so that it can take an angle of The intensity of the light transmitted through the polarizer is the same at the and -45° positions, but the direction of polarization differs by 90°.This means that if the polarizer P is fixed at the +45° or -45° positions, The polarization directions of sample S are θ and θ+9.
It is equivalent to switch to two ◇ positions of 0°. In other words, if the sample S is fixed and the transmittance of the sample S is measured both when the polarizer P is set at 145 degrees and when the polarizer P is set at 145 degrees and averaged, the transmittance of the sample to natural light can be calculated. circle. second at the end
The table shows an example in which a commercially available, inexpensive thin-film polarizer was taken as sample S, and its transmittance to natural light was measured. Polarizer P
A Glan-Thompson linear polarizer was used, and the measurement wavelength was 510 nm. In this measurement method, the sample S is not rotated, but in order to prove the correctness of the measurement method, the set angle of the sample S was changed from 08 to 900 in 5 steps at 22.5° intervals. did. The correctness of this measuring method is proved by the fact that the average transmittances in each case are mutually equal.

The measurement operation using the apparatus 1 described above involves fixing the polarizer P and moving the sample S at an arbitrary set angle θ and θ-90°.
Alternatively, the average apparent transmittance at each position may be calculated. In this case, it is most desirable to set the polarizer P at 45° with respect to the exit slit of the spectroscope. Polarizer P is set ±4 to the output slit of the spectrometer.
The benefit of rotating by 5 degrees or fixing at 45 degrees (-45 degrees is also acceptable) is clear when referring to the third diagram. Although it is almost constant regardless of the wavelength, the polarization component changes greatly depending on the wavelength in the direction parallel to the exit slit or at 90 degrees, and in the wavelength range where the polarization component in that direction is large, the sensitivity is high and the S/N ratio is low. Good measurements can be made, but in the wavelength range where the component in that direction is minimum, the amount of light is small, resulting in low sensitivity and low S/N ratio measurements.When measuring spectral transmittance, uniform sensitivity and S/N ratio N
This means that the ratio cannot be measured. Furthermore, when the polarizer is at 90°, the S component of the spectrometer output light exhibits the maximum in a wide wavelength range, so high sensitivity and high S/N ratio measurements can be made. Since the anomaly reflection of the grating is strong, there is a possibility that a shock due to this anomaly reflection may appear in the measurement output during the wavelength scanning process.

FIG. 2 shows the configuration of a spectrophotometer for carrying out the method of the invention. FIG. 2A shows a single beam configuration, L is a light source, M is a spectrometer, D is a photodetector, SC is a sample chamber, and PA is an accessory shown in FIG. Figure 2B shows a double beam configuration. A mirror C that divides the luminous flux into the sample luminous flux S and the reference luminous flux γ.
It is set between H. This configuration is inexpensive because only one polarizer P is required, but since a reflective element is included after the polarizer, the polarization states of the sample light and the reference light are not strictly the same. Figure 2C also has a double beam configuration, with the accessories shown in Figure 1 set on the sample beam S side and 1'! on the reference beam γ side. Set only the polarizer P. This polarizer is attached to the sample holder 3. with the accessory shown in Figure 1. It can be attached to an accessory other than the socket 2' (the same applies to Figure 2B). The configuration shown in Figure 2C uses two polarizers, so it is expensive, but
Since there is a polarizer just in front of the sample, more accurate measurements can be made than in FIG. 2B.

Effects According to the present invention, it is possible to measure the natural light sensitivity of a polarizing sample by a simple operation of rotating either the polarizer or the sample by 90°, measuring the apparent transmittance twice, and calculating the average. It has the advantage that the spectral transmittance can be measured accurately and that a normal spectrophotometer can be used.

Table 1 Apparent transmittance of Glan-Thompson linear polarizer

[Brief explanation of drawings]

FIG. 1 is an exploded perspective view of an accessory for a spectrophotometer embodying the present invention, FIGS. 2A, B, and C are plan views showing the configuration of a spectrophotometer embodying the present invention, and FIGS. 3A-D are Graphs showing the spectral polarization characteristics of several spectrometers. Figure 4 is a graph showing the polarization characteristics of the output light of the spectrometers in polar coordinates. Figure 5 is a graph showing the transmission characteristics when linear polarizers are stacked on top of each other. polar coordinate graph,
FIG. 6 is a polar coordinate graph of the polarization characteristics of natural light. l...Base block, 2. 2'...Vacquette, 3...Sample holder, 4...Polarizer holder, S...Sample, P...Polarizer, L...Light source, M... ...Spectrometer, D...Optical detector, SC...
・Sample chamber, PA...Accessories for spectrophotometer for carrying out the present invention. Agent Patent Attorney Kosuke

Claims (1)

[Claims] Spectrometer output light is incident on the sample through a linear polarizer, and either the linear polarizer or the sample is rotated 90° around the optical axis of the sample incident light, and the sample is rotated before and after this 90° rotation. Measuring apparent transmittance