JPS6244215B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for measuring the spectral transmittance and spectral reflectance of natural light of an object having polarization characteristics, such as a polarizer or an interference thin film used for oblique incidence.

The light emitted from a diffraction grating spectrometer is highly polarized, so when measuring the spectral transmittance of a sample such as a polarizer, an interference filter used at oblique incidence, or a solid that has polarization, the sample's The measured spectral transmittance differs depending on how it is placed. Therefore, precise measurement of the spectral transmittance of a sample against natural light requires a very troublesome operation such as rotating the sample, measuring both the maximum and minimum transmittance, and averaging them, or using a prism with little polarization. It is necessary to use a spectrometer. However, prism spectrometers are much more expensive than diffraction grating spectrometers, which are commonly used as spectrometers in spectrophotometers, and they exhibit polarization, albeit slightly.

The present invention has been made with the object of providing an apparatus that can obtain spectral transmittance in a single measurement operation by making monochromatic natural light incident on a sample and measuring the spectral transmittance.

The spectral transmittance measuring device of the present invention is characterized in that the light emitted from the spectrometer is made incident on a white diffusely reflecting surface such as a light diffusing plate or the inner surface of an integrating sphere, and the reflected light is made incident on a sample. The present invention will be explained below with reference to Examples.

FIG. 1 shows an embodiment of the invention. M is a spectroscope, L is a light source, MR is a reflecting mirror, and D is a light diffusing plate coated with barium sulfate, etc. The light emitted from the spectroscope M is reflected by the reflecting mirror MR and enters the light diffusing plate D. S denotes a sample, into which a portion of the light diffusely reflected by the light diffusing plate D is incident. A slit-shaped collimator C is arranged in front of the sample S, so that only the light beam in the direction perpendicular to the diffuser plate D among the light beams diffusely reflected by the light diffuser plate D is incident on the sample S.
In ST, a sample S is placed on a sample stage, and the orientation of the sample can be changed around an axis perpendicular to the plane of the figure, allowing the angle of incidence of light on the sample to be changed. . An angle scale Ag is provided on the stage ST. I is an integrating sphere on which the light that has passed through the sample S is made to enter. DT is a photodetector, into which light emitted from a window different from the sample transmitted light entrance window of the integrating sphere I is made incident. The MS uses a light-shielding mask to define the width of the light beam incident on the sample, and also blocks light that is diffusely reflected in all directions from the light diffusing plate D, thereby preventing an increase in the level of stray light within the apparatus.

Although the light emitted from the spectrometer M is considerably polarized, it becomes almost natural light by being reflected by the light diffusing plate. The slit-shaped collimator C is made by stacking thin plates parallel to each other with a slight distance between them.By blocking oblique light and allowing only light in a direction parallel to the thin plates to pass, only the parallel component is removed from the scattered light. It is for extracting. In this embodiment, the length l of the plates is 10 mm, the interval between the plates is 1 mm, and the aperture angle of the light beam exiting this collimator is ±5.7° (tan ^-1 1/10).

The reason why the light transmitted through the sample S is not made to enter the photodetector DT immediately, but the integrating sphere I is used is as follows.

When the inclination of the sample S with respect to the light transmission direction is changed, the entire sample-transmitted light beam moves in parallel (up and down in the figure). On the other hand, photomultiplier tubes and the like used as photodetectors have local sensitivity unevenness on the photosensitive surface, so if the light incident area on the photosensitive surface moves, the photodetection output will fluctuate even if the same light flux is incident. . When the incident luminous flux is thick and the amount of movement of the incident area (cross section of the luminous flux) is small compared to the thickness, the output change will be small, but
Still, it cannot be ignored for high-precision measurements. When the inclination of the sample S is changed, the transmitted light flux is translated in parallel as described above, so if the sample S is directly incident on the light detector, output fluctuations will occur. In order to prevent this, the integrating sphere I is interposed. Therefore, it is not necessary when measuring the transmission characteristics of an element used in a direction perpendicular to the direction of light incidence, such as a polarizing filter. On the other hand, since something like a thin film interference filter is used with various angles of incidence of light, an integrating sphere I is required to measure characteristics with high precision.

Spectral reflectance can be measured by placing a sample at position A on integrating sphere I.

FIG. 2 shows another embodiment of the invention. In this embodiment, the spectrometer output light is focused onto the light diffusing plate DF by the reflecting mirror MR, so the light irradiation point on the light diffusing plate becomes like a small-area light source, and the light is reflected in all directions. Therefore, the reflected light is focused onto the sample S using a condenser lens LC, or is made incident on the sample as a parallel beam of light, thereby eliminating the slit collimator C of the previous embodiment. Although the integrating sphere is omitted in the figure, it can of course be installed in front of the photodetector DT if necessary.

FIG. 3 shows an embodiment in which a two-beam system is introduced into the present invention. The light emitted from the spectrometer M is time-divisionally split into two beams by the sector mirror BS, and the sample beam S
The light is made incident on the sample S through the reflecting mirror MR, the light diffusing plate D, and the slit collimator C, as in the embodiment shown in FIG. 1, and the sample transmitted light is made incident on the integrating sphere I. The reference light r divided by the sector mirror is made incident on the integrating sphere I through a reflecting mirror MR', a light diffusion D' and a slit collimator C'. Integrating sphere I has a light extraction window on the opposite side in the diagram, and a photodetector is installed on the other side.
DT is installed. The output of the photodetector DT is subjected to signal separation and signal processing in synchronization with the rotation of the sector mirror BS.

The embodiment shown in FIG. 4 differs from the embodiment shown in FIG. 1 in that the locations of the reflecting mirror MR and the light diffusing plate D are swapped. In this configuration, the light that is reflected by the light diffusing plate D and turned into natural light is reflected by the reflector MR and becomes polarized again, albeit slightly, so it is not suitable for high-precision measurement, but it is similar to the collimator slit. It is easy to configure and does not require anything.

It goes without saying that if there is no restriction on the space occupied by the apparatus, the reflecting mirror MR may be omitted in the embodiment shown in FIG. 1, and the light emitted from the spectrometer M may be made to directly enter the light diffusing plate. Also, light diffuser plate D
You can also use an integrating sphere instead. The inner surface of the integrating sphere is also a white diffusely reflecting surface of the same quality as the light diffusing plate, so it functions in the same way as the light diffusing plate.

Figure 5 shows the spectral transmission characteristics of a dichrome filter (commercially available polarizing filter) when only a diffraction grating spectrometer is used.The solid line Tv is the dashed line Tp, which is the data when the plane of polarization of the polarizing filter is rotated at right angles. .
There is an average difference of about 1% in the wavelength range of 400 to 760 nm, but the range where the polarization of the emitted light becomes particularly significant with a diffraction grating spectrometer (range where anomaly characteristics appear: in this example, around 500 nm and 700 nm) nearby) is 2
The difference in transmittance in the two directions becomes large and varies irregularly with respect to wavelength. Figure 6 shows data obtained by measuring the same sample using the device of the present invention, with solid lines and
The dashed line is a curve with the same meaning as in Fig. 5, and even in the wavelength range where anomaly characteristics of the spectrometer appear, the difference depending on the direction of the polarization plane of the polarizer is about 1.5% at most.

The device of the present invention has the above-mentioned configuration and uses a light diffusing plate to convert polarized light into natural light, thereby producing light that is much closer to natural light than using a prism spectrometer without using an expensive device such as a prism spectrometer. Therefore, the spectral characteristics of the sample can be measured, and the measurement operation does not require the troublesome operation of taking the average of the spectral transmittance at two positions on the sample, and is the same as simply measuring the spectral transmittance. It has the advantage of being able to measure the spectral transmittance of a polarized sample to natural light.

[Brief explanation of the drawing]

FIG. 1 is a plan view of an apparatus according to an embodiment of the present invention, and FIG.
The figure is a plan view of another embodiment of the present invention, FIG. 3 is a plan view of still another embodiment, FIG. 4 is a plan view of still another embodiment, and FIG. 5 is a typical diffraction grating spectrometer. FIG. 6 is a graph of the spectral transmittance measurement results of a polarizing filter using the apparatus of the present invention. M...Spectroscope, D...Light diffusion plate, S...Sample, I...Integrating sphere, DT...Photodetector.

Claims (1)

[Claims] 1. Inject the emitted light from the spectrometer onto a white diffusely reflecting surface such as a light diffusing plate or the inner surface of an integrating sphere, make the reflected light from this white diffusely reflective surface enter the sample, and measure the transmitted light or reflected light from the sample. A device for measuring spectral transmittance and spectral reflectance of polarized samples.