JPH05240786A - Temperature coefficient measuring device for refractive index - Google Patents

Abstract

PURPOSE:To improve measurement accuracy and work efficiency by measuring in one-time of heating/cooling process the linear expansion coefficient of a sample to be inspected and simultaneously the temperature coefficient of the refractive index to the light of each wavelength for a light having multiple wavelengths. CONSTITUTION:A temperature coefficient measuring device for a refraction factor is provided with the first polychromatic diffraction grating spectroscope P-1 to collect the light from plural number of spectral light sources 2, 3 and 4 having different wave length values in prescribed slit positions, a collimator which transforms the light from the slit positions into a parallel light flux and converges the reflected light from a Fizeou's interferometer F and the Fizeou's interferometer F having a heating/cooling means for a sample to be inspected, and is also provided with the second polychromatic diffraction grating spectroscope P-2 which divides the light to give Fizeou's interference fringes obtained by a temperature change in the sample to be inspected into respective spectral light and introduces them to the respective prescribed slit positions and a light detecting/measuring device which detects the light from the respective slit positions synchronously and measures those outputs.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical glass used in the field of cameras, optical devices for semiconductor manufacturing, etc., or a transparent material used in the field of communication devices, substrates for optical recording media, etc. The present invention relates to an apparatus for measuring the temperature coefficient of refractive index for light in the infrared and infrared regions.

[0002]

2. Description of the Related Art Conventionally, in measuring the temperature coefficient of refractive index (hereinafter, represented by dn / dT) of a transparent material such as glass, a spectrometer or a Fizeau interferometer is used to measure a plurality of wavelengths (for example, visible light). (5 wavelengths in the region, 1 wavelength in the near-ultraviolet and near-infrared regions), and the sample is repeatedly heated and cooled for each wavelength for measurement. Since these materials generally have poor thermal conductivity, for example, a glass sample is tested at −50 ° C. to +8.
Usually, it takes about 3 to 5 hours per wavelength to measure while changing the temperature in the range of 0 ° C, and as a measurement factor, the temperature change of the linear thermal expansion coefficient of the sample must be measured separately. It takes a long time of 24 to 40 hours to measure dn / dT per sample. In recent years, as the fields of use of these materials have expanded, the required measurement temperature range has expanded from the liquid nitrogen temperature to a high temperature range of several hundreds of degrees Celsius, and it takes longer and longer for measurement. In addition, the whole measurement operation is very complicated, and the measurement accuracy for each wavelength is likely to vary due to chromatic aberration of the optical system.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to improve the above-mentioned drawbacks of the conventional dn / dT measurement technique.
An object of the present invention is to provide a dn / dT measuring device which has a simple operation in measuring dn / dT with respect to a large number of wavelengths of light, can significantly reduce the measuring time, and can improve the measuring accuracy.

[0004]

The features of the structure of the temperature coefficient measuring device for the refractive index of the present invention which achieves the above objects are that a plurality of spectral light sources having different wavelength values are provided, and the light from the light sources is provided at predetermined slit positions. A first polychromatic diffraction grating spectroscope for converging the light on the sample, a collimator for collimating the light from the slit position and converging the reflected light from the Fizeau interferometer, and a heating / cooling means for the sample to be tested, A Fizeau interferometer for interfering parallel light beams from the collimator, and light for forming Fizeau interference fringes obtained by the temperature change of the sample to be analyzed is split into each spectrum light of the light source and guided to each predetermined slit position. 2 equipped with a polychromatic diffraction grating spectroscope and a light detection / measurement device that simultaneously detects the light from each slit position and measures the output. .

In the above measuring apparatus of the present invention, if the coefficient of linear expansion of the sample to be tested is previously known by a separate measurement, it is possible to simultaneously measure dn / dT for each light of multiple wavelengths. However, performing the two measurements separately in this way is similarly inefficient and tends to cause deterioration in measurement accuracy. Therefore, in the measuring apparatus of the present invention, the parallel luminous flux is separated into two fields of view so that the linear expansion coefficient of the sample to be measured and the dn / dT using this data are measured in the same heating and cooling process. The field diaphragm and d between the facing parallel planes of the test sample corresponding to the above two fields of view
It is preferable to provide a Fizeau interferometer in which the optical interference part for measuring n / dT is provided and the optical interference part for measuring linear expansion coefficient is provided in the space formed by the two substrates sandwiching the test sample.

Further, when the dn / dT value is calculated by the Fizeau interferometer, it is necessary to previously obtain the movement number (ΔN) of the interference fringes in the predetermined temperature range (Ti to Tj). I) -The temperature width of ΔN for one cycle including the temperatures Ti and Tj in the interference fringe waveform drawn on the temperature (T) coordinate axis is read, and Ti and Tj are read.
For each intensity (I) in (1), the deviation from the maximum value (or minimum value) of the intensity in the vicinity of each temperature was adjusted. Since this measuring means reads the fringe movement with only a few data points, various accidental errors are included, and the measurement accuracy is likely to deteriorate. In order to improve this drawback, in the measuring apparatus of the present invention, the function of storing the interference fringe waveform for each wavelength light represented on the Fizeau interference light intensity (I) -observation temperature (T) coordinate, this interference Read the m (many) observation temperatures corresponding to the maximum and minimum values of the fringe waveform, plot this data on the interference fringe movement number (N) -temperature (T) coordinate, and observe these m observations. A function of obtaining m high-order observation equations by the least squares method for points, and the interference fringe movement number (ΔN) in a predetermined temperature range is calculated based on the above observation equations to calculate the temperature coefficient of the refractive index. It is preferable to provide a measuring device having a function.

[0007]

Next, preferred embodiments of the temperature coefficient measuring device for the refractive index of the present invention will be described with reference to the drawings. That is, FIG. 1 is a layout explanatory diagram of the optical system and the measurement system of the entire apparatus of the present embodiment. 2 is an enlarged side sectional view showing the positional relationship between the Fizeau interferometer F and the field stop 49 in FIG. 1, and FIG. 3 is a plan view of the main part of the Fizeau interferometer of FIG. As shown in FIG. 1, a near-infrared spectrum laser light source 1 and visible / ultraviolet spectrum light sources 2, 3 and 4 are respectively prepared as a plurality of spectrum light sources having different wavelength values. A first polychromatic diffraction grating spectroscope P-1 is provided in the vicinity of these light sources, and 16 to 22 and a concave diffraction grating 8 are arranged on a Rowland circle 27 of this spectroscope. Near infrared spectrum light source 1
The light from is reflected by the concave mirror 6, passes through the slit 15,
The plane mirror 7, the concave diffraction grating 8 and the plane mirror 9 are reflected, but since the concave diffraction grating 8 is for visible light and ultraviolet light, it is converged on the slit 23 as zero-order light. The light of each wavelength from the visible and ultraviolet spectrum light sources is directly or through the plane mirror 10.
14 is reflected, passes through slits 16 to 22, respectively, and is reflected by the concave diffraction grating 8 and the plane mirror 9, and converges on the slit 23. Slit 2 at the focal position of the light from each light source
After being bent by the semi-transparent mirror 28, the polychromatic light from 3 is reflected by the concave mirror 29, which is a collimator, into a parallel light flux, which is bent vertically upward by the plane mirror 30 and then the field stop 3
Pass 1.

As shown in FIGS. 2 and 3, in the Fizeau interferometer F, the test sample 34 having parallel planes between the three points (C, C ') on the opposing planes of the glass substrates 32, 33 is provided. It has a structure of sandwiching. In addition, the field stop 3
1, the aperture windows A and B are provided, and the glass substrate 32 has an opening A ′ for directly introducing the light from the aperture window A into the test sample 34, and the light from the opening A ′ is The light passes through the optical interference portion A ″ provided on the test sample and reflects the inner upper surface in the original direction. The glass substrate 33 corresponding to this opening portion A ′.
Is a non-reflective surface. A light interference portion B ′ is provided in the space between the glass substrates 32 and 33 sandwiching the sample 34 to be inspected. Reflect to. The glass substrate and the test sample are housed in a metal case 37 provided with a heating element 35 and a cooling pipe 36, and the tip of a thermocouple 38 for measuring the temperature of the test sample is fitted into the sample to provide a thermoelectric control for temperature control. The pair 38 ′ is embedded in the metal case 37. These are surrounded by a vacuum / heat retaining tank (not shown).
Although not shown, a heat conductive paint is appropriately applied to the surfaces of the glass substrate and the test sample in order to heat them more quickly. It is connected with a flexible copper wire.

The light that gives the interference fringes generated in the Fizeau interferometer F returns to the original optical path, and is reflected by the plane mirror 30 and the collimator 2.
9 is reflected and it passes through the semi-transparent mirror 28. A second polychromatic diffraction grating P-2 is provided behind the semi-transparent mirror 28, and a concave diffraction grating 41 with slits 46 to 52 and a field stop 42 is arranged on a Rowland circle 39 of this diffraction grating. ing. The light transmitted through the semi-transparent mirror 28 is focused on the slit 40, and the light passing through the slit position is reflected by the plane mirror 43 and then dispersed by the concave diffraction grating 41 into the light of each original wavelength. At this time, the light from the field stop B is removed by the field stop 42. These dispersed lights pass through the slits 45 and 46 to 52 placed on the focal points thereof, respectively, and then the plane mirrors 53 to 5 provided in the vicinity of these slits.
8 is reflected, and it injects into the photomultiplier tubes 59-65, and is detected. The near-infrared light and light of all other wavelengths converge as a zero-order light on the slit 45, but the short-wavelength cut filter 6
Other than near infrared light is absorbed by 6, and only the near infrared light is detected by the photodiode 67. Light from the visible light laser light source 5 passes through the light guide 68 and passes through the slit 23.
After passing through the slit 26 after being bent by the small prism 25 placed in the vicinity of, the light enters the Fizeau interferometer F in the same manner as described above, and light that gives interference fringes is generated. This light is a semi-transparent mirror 28
After passing through, the light is bent by the small prism 69 and converges on the slit 70. Each half of this convergent light is a semi-transparent mirror 7.
1, the light enters the photomultiplier tubes 75 and 76 via the plane mirror 72 and the field diaphragms 73 and 74, respectively, and is detected. Here, the light from the field stop A produces light which gives Fizeau interference fringes in the light interference part A ″, but this light is limited by the slit 40 and the field stop 73, and enters only the detector 75, and the concave surface. It is used to measure the interference fringe movement number (ΔN) due to temperature change for the wavelength light that cannot be separated by the diffraction grating 41. Further, the light from the field stop B is the light interference portion B ′.
At, a light which gives Fizeau interference fringes is generated, and this light is limited by the field stop 74 and enters only the detector 76, and is used for measuring the interference fringe movement number (ΔN ′) related to the linear expansion coefficient.

For a given wavelength λ and dn / dT of the sample to be tested, dn / dT = λdn / 2LΔT-nλΔN '/ 2
LΔT (relational expression 1) is established, and n · λΔN ′ / 2LΔT = n · α (relational expression 2) for the two terms of this relational expression.
Is known to be. The second term is a correction term due to the thermal expansion of the test sample. Where ΔN and ΔN ′ are
The change in the number of movements of the Fizeau interference fringes caused by the temperature change of the object in the interference portions A ″ and B ′, respectively, L
Is the thickness of the test sample. The optical path length in the interference part A ″ is nL, the optical path length in the interference part B ′ is L in the case of vacuum,
In the atmosphere, it is na · L (na; refractive index of air). Further, α is a coefficient of linear expansion of the test sample. Photomultiplier tubes 59 to 65, 75 and photodiode 67
Is the measurement detector of the above-mentioned relational expression 1 for each wavelength, and the photomultiplier tube 76 is the measurement detector of the above-mentioned item 2, and dn of the test sample for each wavelength in a predetermined temperature range. / DT and α can be measured simultaneously. An amplifier 77, a measuring device 78, and a printer 79 are sequentially provided in order to measure the temperature coefficient of the refractive index based on the output signals from the above detectors.

FIG. 4 is an example in which the intensity change of Fizeau interference fringes with respect to temperature is recorded. The vertical axis shows the light intensity (I) of the interference fringes, and the horizontal axis shows the temperature (T). The change curve of FIG. 4 shows that it becomes a sine wave, and the temperature T ₁
The change of one cycle from the minimum intensity (Imin) at T _{2 to} the maximum intensity (Imax) at T ₂ to Imin at T ₃ is the change in the number of stripes (ΔN) = 1 in the above item 1.
Equivalent to. In FIG. 1, the amplifier 77 includes light of each wavelength from the detector (wavelengths of light passing through the field stop A are λ ₁ and λ ₂
... and the wavelength of the light passing through the field stop B is λ ')
Amplifies the output signal for. As shown in the system diagram of FIG. 6, the measuring device 78 provided at the rear of the amplifier 77 is
A function of storing the interference fringe waveform on the interference light intensity (I) -temperature (T) coordinate shown in FIG. 4 based on the data 1, 2, ... have. After smoothing this waveform, the maximum value and the minimum value of this waveform are read, and this data is converted into the interference fringe movement number (N) − as shown in FIG.
Plotted on the temperature (T) coordinates, and for these m observation points, m high-order observation equations N by the least square method.
(T) (for example, in the case of the third order, N (T) = aT ³ + bT ² +
cT + d (a, b, c, d are coefficients)), a function to obtain the interference fringe movement numbers ΔN and ΔN 'in a predetermined temperature range based on this observation equation, from the interference fringe movement number (ΔN') It has a function of calculating α of the test sample and a function of calculating dn / dT of the test sample from the relational expressions 1 and 2. The interference fringe waveform, the observation equation N (T) curve and the calculation result are displayed on the printer 79.

Since the apparatus of the present embodiment has the above-mentioned configuration, it is possible to simultaneously measure dn / dT for all required wavelengths of light using the same sample under the same heating and cooling conditions. The linear thermal expansion coefficient of the sample can be measured at the same time. Therefore, it is possible to prevent the intervention of the measurement error, so that it is possible to significantly improve the measurement accuracy while improving the efficiency of the measurement work as compared with the conventional technique. Further, in the apparatus of the embodiment, since the optical system does not include any lens and is configured by the mirror system, there is no difference in aberration for each wavelength, and it is possible to perform measurement with the same accuracy for all wavelength light. There are advantages.

[0013]

As described above, the temperature coefficient measuring device for the refractive index of the present invention comprises a plurality of spectral light sources, a first polychromatic diffraction grating spectroscope, a collimator, a Fizeau interferometer, and a second polychromatic diffraction. Since the grating spectroscope and the light detecting / measuring device are provided, the temperature coefficient of the refractive index can be measured synchronously in the same heating and cooling process for each wavelength light of multi-wavelength light. Therefore, not only the measurement work efficiency but also the measurement accuracy can be significantly improved. In addition, the Fizeau interferometer is equipped with an interferometer for measuring the linear expansion coefficient of the sample to be tested, or a number of higher-order observation equations are obtained based on the interference intensity detection data, and the number of movements of the interference fringes is obtained from this. , Dn / dT is provided, it is possible to further improve the signal / noise ratio of the measured value and improve the accuracy.

[Brief description of drawings]

FIG. 1 is an overall explanatory view of an embodiment of a temperature coefficient measuring device for refractive index of the present invention.

FIG. 2 is a vertical sectional view of the Fizeau interferometer in FIG.

FIG. 3 is a plan view of a main part of the Fizeau interferometer of FIG.

FIG. 4 is an explanatory diagram of an interference fringe detection waveform at an interference light intensity (I) -observed temperature (T) coordinate.

FIG. 5 is a dot plot of the maximum and minimum values of the interference fringe waveform in the interference fringe movement number (N) -observed temperature (T) coordinate.

FIG. 6 is a functional system diagram of the measuring device in FIG.

[Explanation of symbols]

1-5 ... Light source 27,39 ... Roland circle 6,7,9,10-14,30,43,44,53-5
8, 72 ... Planar mirror 28, 71 ... Semi-transparent mirror 8, 41 ... Concave diffraction grating 15, 16-22, 23, 26, 40, 45, 46-5
2, 70 ... Slit 31, 42, 73, 74 ... Field stop 66 ... Short wavelength cut filter 59-65, 75, 76 ... Photomultiplier tube 67 ... Photodiode 32, 33 ... Substrate glass 34 ... Specimen sample 38, 38 '... Thermocouple F ... Fizeau interferometer A, B ... Aperture window A ", B' ... Optical interference part C, C '... Subject sample support part

Claims (3)

[Claims] 1. A plurality of spectral light sources having different wavelength values,
A first polychromatic diffraction grating spectroscope for converging light from the light source at a predetermined slit position, a collimator for collimating the light from the slit position into a parallel beam, and converging the reflected light from the Fizeau interferometer, A Fizeau interferometer having a heating / cooling means for the test sample, a light which gives a change in Fizeau interference fringes obtained by a temperature change of the test sample is split into each spectrum light of the light source and is guided to each predetermined slit position. 2 polychromatic grating spectrometer,
A temperature coefficient measuring device for a refractive index, comprising a light detecting / measuring device for simultaneously detecting light from each of the slit positions and measuring the output thereof. 2. A field stop for separating a parallel light flux into two fields of view, and a space formed between two parallel planes of a sample to be tested and two substrates sandwiching the sample to be tested corresponding to the two fields of view. The temperature coefficient measuring device for the refractive index according to claim 1, further comprising a Fizeau interferometer each provided with an optical interference section. 3. A function of storing an interference fringe waveform for each wavelength light represented on the Fizeau interference light intensity (I) -observation temperature (T) coordinate, corresponding to the maximum value and the minimum value of the interference fringe waveform. The observation temperature of a large number (m) is read and plotted on the interference fringe movement number (N) -temperature (T) coordinate, and for these m observation points, the m higher order 2. A measuring device having a function of obtaining an observation equation and a function of obtaining a movement number of interference fringes in a predetermined temperature range and calculating a temperature coefficient of a refractive index based on the observation equation. The refractive index temperature coefficient measuring device according to claim 2.