JPH0213832A - Refractive index measurement for sample liquid - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for measuring the refractive index of a test liquid, and in particular, to a refractive index suitable for measuring the refractive index of a test liquid such as a matching liquid used in an interferometer. Regarding measurement methods.

[Prior Art] To measure the refractive index of a liquid, a refractometer such as an Atsube refractometer is generally used. However, in measurements using a refractometer, for example, it is not possible to measure the refractive index of the sample liquid used in the interferometer while it is still in the interferometer, and therefore the refractive index changes depending on various conditions such as temperature. It is not possible to measure the refractive index of a sample liquid in real time while the interferometer is in use, and the refractive index of the matching liquid, which finely adjusts the refractive index by mixing multiple liquids, cannot be measured while it is inside the interferometer. cannot be measured in this condition.

Conventionally, the following method, for example, has been used to measure the refractive index of a test solution such as a matching solution used in an interferometer.

The device used as a whole is, for example, a Pine Zehnder interferometer, in which a light beam is used as a plane wave reference and illumination light, and a glass with a known refractive index is inserted into the light beam for reference of the refractive index. Set the sample by immersing it in the matching solution. N
The difference in the thickness of the sample during which the interference fringes of the wood were observed was measured, and the refractive index of the matching liquid was determined from the measured value.

[Problems to be Solved by the Invention] However, in the conventional measurement method described above, if the refractive index of the matching liquid changes, the range in which the N-tree interference fringes occur also changes.
The thickness of the sample must be measured at that part each time, which makes the measurement work extremely complicated. However, it is extremely difficult to make measurements, and it is also difficult to automate the measurements.

The present invention eliminates such conventional drawbacks and provides a test solution that can easily measure the refractive index of a test solution such as a matching solution used in an interferometer in real time, and can easily automate the measurement. The purpose of the present invention is to provide a refractive index measurement method.

[Means for Solving the Problems] In order to achieve the above object, the method for measuring the refractive index of a reagent solution of the present invention involves immersing a wedge-shaped transparent sample with a known refractive index and shape in the reagent solution, and then applying a coherent By transmitting light and superimposing the transmitted light wave with a reference light wave to generate interference fringes, measuring the brightness intensity distribution of the interference fringes and determining the spatial frequency of the interference fringes from the intensity distribution, The present invention is characterized in that the refractive index of the sample liquid is determined from the known refractive index and shape and the spatial frequency of the interference fringes.

[Operation] As shown in Figure 4, when the wavelength of coherent light is input,
The shape of the wedge-shaped glass sample 9 is θ.

L, the refractive index of the glass sample 9 and the refractive index of the test solution 8 are each n
Let g*nm.

The interference fringes 30 produced by the light waves transmitted through the wedge-shaped glass sample 9 immersed in the test liquid 8 are straight, parallel, and equally spaced fringes. Then, by measuring the intensity distribution of the stripes, the spatial frequency aF of the stripes can be found, and once the spatial frequency F is found, F = /L (nu - ng) Letan θ = λ, so from the following formula, the test solution can be calculated. The refractive index of can be determined.

nfi"ng+in*F/lanθ [Example] FIG. 1 shows a measuring device used in the present invention,
This device is basically a Matsuha-Zehnder interferometer. 1 is a coherent light source that emits coherent light (wavelength λ); for example, a He-Me laser light source is used. The light beam emitted from the coherent light source 1 is expanded by the beam expander lens 2,
The collimator lens 3 creates a parallel light beam. 4 is the first
The light beam reflected by the half mirror 4 is further reflected by the movable mirror 5 and transmitted through the transparent container 6. The angle of the movable mirror 5 can be moved (tilted) as desired.

The transparent container 6 is made of undistorted glass. 7
is a lid that can be opened and closed. Inside the transparent container 6, the material of the test lens 10 is polymethyl methacrylate (acrylic).
In this case, a matching liquid 8 containing, for example, a mixture of dimethyl silicone oil and phenylmethyl silicone oil is contained.

In the matching liquid 8, as shown in FIG. The lens 10 to be measured is placed in parallel and perpendicular to the transmitted light. In addition, glass sample 9
The material of the sample does not necessarily need to be glass, and may be plastic or other materials as long as it is an optically homogeneous and non-deformable transparent sample, and its shape does not necessarily have to be entirely wedge-shaped. , it may be partially wedge-shaped.

The light beam transmitted through the first half mirror 4 is reflected by the first fixed mirror 11, and then further reflected by the second half mirror.
! 2 and is superimposed on the light wave that has passed through the test lens 10 or the glass sample 9. Interference fringes generated by the overlap of the two light waves are then reflected by the first imaging lens 13 onto the surface of the image sensor 14. image is formed.

The first imaging lens 13 and the image sensor 14 are provided so as to be able to move in the vertical direction in the figure as a unit. Therefore, in FIG. 1, the first imaging lens 13 faces the test lens lO, but the first imaging lens 13 may also face the glass sample 9 as shown in FIG. can.

Returning to FIG. 1, the image sensor 14 is formed of, for example, 50×50 independent photoelectric elements. An AD converter 15 and a digital arithmetic circuit 16 are connected to the output terminal.
and a display device 17 are sequentially connected. The arithmetic circuit 16 also includes a memory 18 that stores data necessary for the arithmetic operation.
and an input circuit 19 for inputting known data are sequentially connected. Note that as the arithmetic circuit 16, a microcomputer or other arithmetic device can be used.

Reference numeral 20 denotes an observation device for observing the state inside the transparent container 6, which includes a second fixed mirror 21 provided opposite to the second half mirror 12, a second imaging lens 22, and the like. Imaging device 23 and television monitor 2 provided at the imaging position
4.

In order to measure the refractive index of the matching solution 8 (test solution) using the measurement method of the present invention, first, known data is input to the input circuit 1.
Enter from 9. The known data (ng, θ, L) regarding the glass sample 9 are input into the memory 18 and stored therein.

Next, as shown in FIG. 3, the first imaging lens 13
to face the glass sample 9. Then, as shown in FIG. 4, interference fringes 30 generated by the overlap of the light wave transmitted through the glass sample 9 and the reference light wave are imaged on the image sensor 14. and.

A calculation circuit 16 calculates the spatial frequency F of the stripe based on the output from the image sensor 14 at that time. This can be done by a well-known discrete Fourier transform (DFT), but preferably by a faster fast Fourier transform (FFT).

In this case, first, the intensity distribution on a line segment 31 as shown in FIG. 5, which is perpendicular to the interference fringes 30 on the image sensor 14, is measured. FIG. 6 shows an example of the intensity distribution on the line segment 31, which is a sine wave-like curve.

The intensity distribution data measured in this way is the line segment 3
It is of a finite range above 1. Therefore, assuming that such intensity distribution continues indefinitely, FFT
Fourier analysis is performed to find the spatial frequency F. In that case, if the starting point A and the ending point B of the waveform of the intensity distribution on the line segment 31 exactly match as shown in Figure 6, the curves will be continuously connected when expanded infinitely. This is convenient, but if the starting point A and the ending point B do not match, the part where these curves are connected becomes discontinuous, and when this is subjected to Fourier analysis using FFT, a high frequency component is generated and an error occurs. Therefore, when calculating the frequency, it is recommended to remove high frequency components using a so-called window function.Also, if a discrete Fourier transform is performed, a quantization error will inevitably occur, and the number of manuscripts will inevitably be 0. The occurrence of an error equivalent to five lines is unavoidable, so if the amplitude peak position is detected by quadratic function approximation in the frequency range, the error can be reduced to about half.

With such correction, the frequency F of the interference fringes is determined in the arithmetic circuit 16. Then, from the memory 18, ng, θ
, L is read out, and the arithmetic circuit 16 continues to calculate the refractive index nm of the matching liquid 8 as nfi=ng+λeF.
/lanθ and outputs the result to the display device 17 for display.

Then, when performing optical measurement of the test lens lO,
As shown in FIG. 1, the first imaging lens 13 is moved to a position facing the test lens 10. .

[Effects of the Invention] According to the method for measuring the refractive index of a reagent solution of the present invention, the refractive index of the reagent solution is determined from the spatial frequency of interference fringes generated by irradiating the test solution with coherent light, so quantitative measurement is possible. Automation is now possible and the refractive index of a test solution can be easily measured. Moreover, since the refractive index can be measured in real time while using the test in an interferometer, optical measurements using an interferometer can be performed with high precision.

[Brief explanation of the drawing]

Figures 1 to 3 are schematic diagrams showing an example of a measuring device for carrying out measurements according to the present invention, and Figures 4 to 6 are schematic diagrams showing the procedure for determining the refractive index of a matching solution (test solution). . Agent Patent Attorney Kazuhiko Mitsui Go to Figure 4 Figure 5 @ Figure 6

Claims (1)

[Claims] A wedge-shaped transparent sample with a known refractive index and shape is immersed in a test solution, coherent light is transmitted through it, and the transmitted light wave is superimposed on a reference light wave to generate interference fringes, and the brightness intensity of the interference fringes is measured. distribution is measured and the spatial frequency of the interference fringes is determined from the intensity distribution, and the refractive index of the test solution is determined from the known refractive index and shape of the transparent sample and the spatial frequency of the interference fringes. A method for measuring the refractive index of a test solution.