JP2013024825A - Measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a measuring device of a refractive index and a refractive index temperature coefficient usable in a wide wavelength band and capable of improving measuring accuracy with a simple configuration.SOLUTION: The measuring device includes: a measuring light detector 11 for receiving a light flux reflected on a mirror surface 501a of a mirror slit 501 after a parallel light flux entered into a constant temperature bath 6 via a window 601, reflected on a first surface 701 of a wedge prism type sample 7, and then discharged out of the constant temperature bath 6 via the window 601 or a parallel light flux entered into the constant temperature bath 6 via the window 601, entered from the first surface 701 into the sample 7, reflected on the rear surface of a second surface 702, then discharged out of the sample 7 via the first surface 701, and discharged out of the constant temperature bath 6 via the window 601 returns to a collimator 5 to be condensed by a collimator mirror 502; and an analysis control unit 15 for carrying out rotational control of a sample rotation stage 8, and calculating the refractive index of the sample 7 on the basis of a relation between an output from the measuring light detector 11 and the rotational angle of the sample rotation stage 8 detected by a rotational angle detection unit 8a.

Description

The present invention relates to an apparatus for measuring the refractive index and refractive index temperature coefficient of an optical material in the infrared region.

Conventionally, a measuring apparatus using a Littrow method is known for measuring the refractive index and refractive index temperature coefficient of an optical material in the infrared region (see, for example, Non-Patent Documents 1 and 2).

Rapid and Accurate Measurements of Refractive Index in the Infrared E. D. McAlister et al. JOURNAL OF THE OPTICAL SOCIETY OF AMERICA Vol.46, No.7 The Thermal Change in the Nondispersive Infrared Refractive Index of Optical Materials A. Ray Hilton and Charlie E. Jones APPLIED OPTICS Vol.6 No.9

There is a demand for a device that can be used in a wide wavelength band and has high measurement accuracy while having a simpler configuration than conventional measurement devices.

The present invention has been made in view of such a problem, and provides a measurement apparatus for refractive index and refractive index temperature coefficient that can be used in a wide wavelength band and can improve measurement accuracy with a simple configuration. For the purpose.

In order to achieve such an object, according to an embodiment of the present invention, a light source unit that emits a predetermined single wavelength light beam, a collimator mirror having a positive power, and a plate-like member in which a small opening is formed are provided. The surface is a mirror surface, the opening coincides with the focal position of the collimator mirror,
The mirror surface is directed to the collimator mirror side, and includes an aperture plate installed to be inclined with respect to the optical axis so as not to return to the collimator mirror when the light beam collected by the collimator mirror is reflected. A collimator that converts a light beam incident from the opening of the aperture plate from the light source unit into a parallel light beam by the collimator mirror, and a window that can transmit the parallel light beam from the collimator unit. And a ridge line formed by a first surface and a second surface sandwiching the apex angle of the sample in a state in which the wedge prism type sample is placed, and the temperature chamber is capable of variable temperature control. A rotation stage rotatable around a rotation axis parallel to the
A rotation angle detection unit that detects a rotation angle of the rotation stage, and enters the thermostatic chamber through the window, reflects off the first surface of the sample, and then exits the thermostatic chamber through the window. Either the parallel light flux or the inside of the thermostatic chamber through the window is incident on the sample from the first surface and reflected by the back surface of the second surface, and then passes through the first surface to the outside of the sample. Measurement light for receiving the light beam reflected by the mirror surface of the aperture plate after the parallel light beam emitted and emitted to the outside of the thermostatic chamber through the window returns to the collimator unit and is collected by the collimator mirror Analysis that controls the rotation of the detector and the rotation stage, and calculates the refractive index of the sample based on the relationship between the output from the measurement light detector and the rotation angle of the stage detected by the rotation angle detector. Measuring device characterized in that it comprises a control unit is provided.

ADVANTAGE OF THE INVENTION According to this invention, although it is a simple structure, it can be used by a wide wavelength band and the measuring apparatus of the refractive index and refractive index temperature coefficient which can improve a measurement precision is realizable.

It is the schematic of the refractive index measuring apparatus which concerns on this embodiment. It is explanatory drawing of a Hartmann plate It is explanatory drawing of the wedge prism type | mold sample used by this embodiment, (a) is a top view, (b) is a side view. It is a figure explaining the measuring method of the incident angle of the measurement light beam to a sample. It is explanatory drawing of the minimum deflection angle method as a sample transmission system. It is the schematic of the conventional thermostat used by the minimum deflection angle method. It is a corresponding explanatory view of angle parameters in the minimum deflection angle method and the Littrow method. It is explanatory drawing of the prior art using the Littrow method. It is the schematic of the measuring device of the Littrow method comprised with the refraction type optical system.

  Hereinafter, this embodiment is described based on an accompanying drawing.

Various methods for measuring the refractive index have been known, but the least deviation method is often used. As shown schematically in FIG. 5, the minimum declination method searches for a minimum declination position with respect to a single wavelength parallel light beam used for refractive index measurement in a wedge prism type sample 7 made of a medium to be measured. The angle value ε is measured, and the refractive index n of the sample 7 is calculated by the equation (1) from the measured minimum declination value ε and the apex angle τ formed by the entrance surface and the exit surface of the sample 7. is there.

By the way, in measuring the temperature coefficient of the refractive index, first, the refractive index of the sample 7 is measured at the reference temperature, then the temperature of the sample 7 is changed by a predetermined amount, and then the refractive index of the sample 7 is measured again. However, it is difficult to change the temperature of the entire measurement system uniformly. Therefore, when the refractive index temperature coefficient is measured using the minimum deviation method shown in FIG. 5, only the sample 7 is placed in the thermostat 6 as shown in FIG. In general, the minimum deviation value ε is measured. Although the minimum declination value ε depends on the refractive index of the measurement medium, the positions of the entrance window 602 and the exit window 603 of the thermostat 6 are fixed with respect to the thermostat 6, so that the sample 7 is approximately the predetermined minimum deviation. In order to show the angle value ε, it is necessary to change the apex angle τ of the sample 7 in accordance with the refractive index of the sample 7. However, when the refractive index of the sample 7 is unknown, first, the refractive index of the sample 7 at the reference temperature is measured without the thermostatic chamber 6, and the sample 7 that is adapted to the thermostatic chamber 6 is again based on the measurement result. It takes two steps to rework and measure the temperature characteristics.

In order to save such trouble, it is conceivable to adopt a Littrow method in which only one window of the thermostatic chamber 6 is required. The Littrow method is a form of the minimum deflection method, and a wedge prism having a first surface 701 and a second surface 702 sandwiching the apex angle τ as shown in FIGS. 3A and 3B is used as a sample. 7 is used. In such a wedge prism type sample 7, the parallel light beam incident from the first surface 701 is refracted by the first surface 701, reflected by the second surface 702, and again the first surface 70.
Returning to 1, it undergoes a refraction action and is ejected out of the sample 7.

Here, when the measurement light beam is incident on the second surface 702 of the sample 7 perpendicularly, the two refraction angles on the first surface 701 are exactly the same, which is equivalent to the refraction condition at the minimum deflection angle. .
Therefore, it can be seen that the refractive index n of the sample 7 is obtained by the equation (2) by comparing the geometrical relationship shown in FIG. 7 with the equation (1). The angle i is an angle with respect to the normal line of the first surface 701 of the measurement light beam.

An apparatus for measuring a refractive index in the infrared region by the Littrow method is introduced, for example, in Non-Patent Documents 1 and 2 described above. In these prior arts, an emission line light source or a monochromator light source whose wavelength is known is used as a light source, and an optical system that is composed entirely of a reflection system is used. Then, in order to separate the optical path between the incident light beam to the collimator and the reflected light beam collected from the sample back to the collimator, the collimator slits of the respective light paths are tilted by tilting the parallel light beam of the measurement light incident on the sample. The passing position in the longitudinal direction is characterized by being shifted so as to be symmetric with respect to the collimator optical axis.

The prior art of this Littrow method will be described with reference to the schematic diagram of FIG. In FIG. 8, the collimator mirror 502 is expressed by a thin lens. As shown in FIG. 8, when the passing positions of the incident light beam and the reflected light beam in the slit 504 are shifted with respect to the longitudinal direction of the slit 504, the parallel light beam incident on the sample 7 has an inclination angle α with respect to the sample main section 704. become. The sample main section 704 is the ridge line 7 formed by the first surface 701 and the second surface 702 of the sample 7.
It is a plane perpendicular to 03. The minimum declination value measured under these conditions is larger than the minimum declination value ε for the incident light beam parallel to the sample main section 704 (for example, Akira Shoten edited by Hiroshi Yoshinaga, Applied Spectroscopy Handbook (1973)). P.399). That is, the refractive index n is
Although it should be obtained from the minimum declination value ε for the incident light beam parallel to the sample main cross section 704, in principle, a value deviated from the original value ε is calculated by the method according to this prior art.

As a general method for solving this problem, as shown in FIG. 9, there is a method of separating the optical paths of the incident light beam and the reflected light beam to the sample 7 using a beam splitter prism 505. The optical system used in this method is an optical system often used for an autocollimator used in the visible range, and can be set so that the incident light beam on the sample 7 does not tilt with respect to the sample main section 704. Specifically, a part of the reflected light beam from the sample 7 is branched by the beam splitter prism 505 and passes through a slit 507 conjugate with the slit 504 through which the incident light beam to the sample 7 passes.
The rotation stage 8 on which the sample 7 is placed is rotated to adjust the incident angle of the parallel light beam on the sample 7. However, in this method, a non-parallel light beam passes through the beam splitter prism 505, and axial chromatic aberration, spherical aberration, and the like are generated by the beam splitter prism 505. Therefore, in order to correct these aberrations, the entire optical system or In many cases, a refractive lens is used. FIG. 9 shows an example in which a doublet lens 506 is used as a collimator. In such an optical system, the wavelength band that can be measured is limited by the spectral transmission characteristics of the transmission material used. Therefore, in order to ensure the wide wavelength band of the apparatus as much as possible, it is necessary to avoid the use of a transmissive material and to configure the optical system with a reflection mirror.

In addition, when the infrared region is used as the measurement light beam, there are few bright line light sources in the infrared region, and in order to create a single wavelength light beam, a continuous light source can be used to cut out a light beam that can be regarded as a single wavelength. It is normal. A monochromator is often used as a bandpass filter, but the wavelength accuracy of the single wavelength light beam output from the monochromator depends on the wavelength display accuracy of the monochromator. Calibration was essential.

In order to solve the problems of the prior art as described above, the present embodiment employs a Littrow method that allows easy measurement of the refractive index and the refractive index temperature coefficient because there is only one constant temperature chamber window. It can be used in a wide wavelength band using the optical system configured with the above, and an accurate minimum declination value can be obtained by preventing the incident (measurement) light beam on the sample from tilting with respect to the main cross section of the sample. Provided is a measuring device for refractive index and refractive index temperature coefficient configured so that an accurate wavelength value of a measurement light beam can be easily grasped in a small infrared region.

Hereinafter, the measuring apparatus for refractive index and refractive index temperature coefficient according to the present embodiment will be described with reference to FIG. The light source unit 1 shown in FIG. 1 uses an electrothermal infrared light source 101 such as a nichrome wire or a ceramic heater as a measurement light source. The measurement light beam emitted from the infrared light source 101 is
After passing through the rotary chopper 102, reflected and collected by the light source unit concave mirror 103 and reflected by the light source unit dichroic mirror 104, a light source image of the infrared light source 101 is formed on the entrance slit 201 of the monochromator unit 2. . The light source unit dichroic mirror 104 uses a glass parallel plane plate that is transparent in the visible region as a substrate, and an ITO film is formed on the reflection surface. The ITO film has a property of reflecting infrared light and transmitting visible light. The visible region bright line light source 105 is a light source that emits visible region bright line light for calibrating the wavelength of the measurement light beam, and a visible region laser, a bright line lamp, or the like is used. In the present embodiment, the He − having a wavelength of 632.82 nm is used. A Ne laser is used. The laser beam emitted from the visible range bright line light source 105 is condensed by the condensing optical system 106, passes through the light source unit dichroic mirror 104, and enters the entrance slit 20 of the monochromator unit 2.
Concentrate on 1.

As the monochromator unit 2, an optical element in which all optical elements are configured by a mirror or a reflective diffraction grating is used. In the present embodiment, the Zernsey-Turner type is adopted. In such a monochromator unit 2, the measurement light beam incident from the entrance slit 201 is converted into the plane mirror 20.
2, the optical path is bent, collimated into a parallel light beam by the collimator mirror 203, subjected to spectral action by the planar reflection grating 204, and reflected and diffracted at different diffraction angles depending on the wavelength. Thereafter, the measurement light beam is condensed by the condensing mirror 205, and the flat mirror 206
However, only the light beam reflected by the planar reflection grating 204 at a predetermined diffraction angle is condensed on the exit slit 207 and emitted outside the monochromator unit 2. The planar reflection grating 204 is installed on the rotary stage 208 and rotates together with the rotary stage 208. By rotating the plane reflection grating 204 and changing the wavelength of the light beam emitted from the exit slit 207, a desired single wavelength light beam is extracted. Exit slit 2
Immediately after 07, a Hartmann plate 209 is installed. Hartmann plate 20
2 has two light shielding plates as shown in FIG. 2, which are held by a holding mechanism (not shown) and move along the longitudinal direction of the slit 207 (vertical direction in the drawing). And
It functions to change the size of the outlet slit 207 in the longitudinal direction of the opening. A Hartmann plate similar to the above may be installed just before the entrance slit 201 of the monochromator unit 2.
Many monochromators have such a configuration.

The luminous flux emitted from the exit slit 207 is the monochromator dichroic mirror 3.
It hits. The monochromator dichroic mirror 3 is a light source dichroic mirror 1.
With the same mirror as 04, an ITO film is formed on the reflection surface, reflects infrared light (measurement light beam), and transmits visible light. The measurement light beam reflected by the monochromator dichroic mirror 3 is
The first concave mirror 4 is reflected and focused on the opening of the mirror slit 501, and the mirror slit 5
The light passes through 01 and enters the collimator unit 5. The wavelength calibration light beam from the visible region bright line light source 105 that has passed through the monochromator unit dichroic mirror 3 is condensed on the wavelength calibration light detector 14 by the relay lens 13 and received by the detector 14.

The collimator unit 5 includes a mirror slit 501, a collimator mirror 502, and a plane mirror 503. The mirror slit 501 is composed of two slit blades, and the surface of the two slit blades on the collimator mirror 502 side is flat-polished to form a mirror surface 501a coated with aluminum or gold. The slit mirror surfaces 501a are held on the same plane so that the opening width can be adjusted. The opening width of the mirror slit 501 is variable in this embodiment, but may be fixed if there is no problem in the specification. Such a holding mechanism for the mirror slit 501 is not shown. The measurement light beam that has passed through the mirror slit 501 is reflected by the collimator mirror 502 while diverging to become a parallel light beam. The collimator mirror 502 is a concave off-axis parabolic mirror having positive power, and the parabolic focus is set to the mirror slit 501.
It is installed according to the opening center. After being reflected by the collimator mirror 502, the measurement light beam that has become a parallel light beam is reflected by the flat mirror 503, the optical path is bent, and enters the interior of the thermostatic chamber 6 from the window 601.

The thermostat 6 has a structure in which the inside is sealed, and the temperature can be raised and lowered with respect to the outside. However, since the mechanism is outside the scope of the present invention, it will not be described in detail here.
The window 601 is a parallel plane plate made of a material (for example, silicon crystal, germanium crystal, zinc sulfide crystal, etc.) that is transparent to the measurement light beam that is infrared light, and is fitted into the side wall of the thermostatic chamber 6. Both surfaces of the window 601 are provided with anti-reflection coatings having spectral characteristics adapted to the refractive index measurement wavelength range. However, if the window 601 is orthogonal to the incident measurement light beam, the reflected light from the window 601 returns in the same direction as the incident light beam, and is mixed with the refractive index measurement light beam and becomes measurement noise. In order to avoid this, the window 601 is inclined with respect to the measurement light beam, and the sample 7
So that the reflected light beam does not return to the same optical path as the measurement light beam. The measurement light beam that has passed through the window 601 is incident on the sample 7 installed on the sample rotation stage 8 inside the thermostat 6.

As shown in FIGS. 3A and 3B, the sample 7 is a wedge prism made of an optical material whose refractive index is to be measured. The sample 7 has a first surface (incident surface) 701 and a first surface that have been polished. It has two surfaces (reflection surfaces) 702. In the present embodiment, the apex angle formed by the first surface 701 and the second surface 702 is τ. An antireflection coat is applied to the first surface 701, which is the incident surface of the measurement light beam, as necessary. In addition, the second surface 702 on which the measurement light beam incident on the sample 7 is reflected is mirror-coated as necessary to form a rear surface mirror. Both are treatments when it is desired to improve the measured S / N ratio. A plane orthogonal to a ridge line 703 that is an intersection line between the first surface 701 and the second surface 702 is defined as a sample main cross section 704. The measurement light beam incident from the first surface 701 into the sample 7 while being refracted is
The light is reflected by the second surface 702, returns to the first surface 701, is refracted again, and is emitted to the outside of the sample 7. The sample rotation stage 8 on which the sample 7 is placed rotates the sample 7 about the rotation axis parallel to the ridge line 703. Further, the sample rotation stage 8 is provided with a rotation angle detector 8a, and has a function of reading the rotation angle of the stage 8 with reference to a predetermined initial position. The rotation angle of the sample rotation stage 8 read by the rotation angle detection unit 8a is transmitted to the analysis control unit 15.

The reflected light beam on the first surface 701 or the reflected light beam on the second surface 702 of the sample 7 goes out of the thermostatic chamber 6 through the window 601. Incident light beam (measurement light beam) to the thermostat 6 and the thermostat 6
If the angle formed with the reflected light beam returned from the light beam is within a predetermined angle range, the light beam emitted from the thermostatic bath 6 enters the collimator unit 5, and the opening image of the mirror slit 501 is converted into the mirror slit 50.
1 is formed at a projection magnification of 1 ×. The mirror surface 501a of the mirror slit 501 is installed so as to be inclined with respect to the optical axis, and the light beam reflected by the mirror surface 501a of the mirror slit 501 is reflected and collected by the second concave mirror 9, and is measured by the measurement light detector 11. And is received by the detector 11. If the aperture image of the mirror slit 501 is formed so as to coincide with the aperture of the mirror slit 501, most of the light energy is (without being reflected) the mirror slit 5.
01 passes through and does not reach the measurement light detector 11.

In order to increase the reception S / N ratio of the measurement light detector 11, the present embodiment adopts an AC photometry method often used for infrared photometry. That is, the measurement light beam emitted from the infrared light source 101 is chopped at a predetermined frequency by the mechanical chopper 102. The mechanical chopper 102 and the measurement light detector 11 are synchronously controlled by the lock-in amplifier 12 to perform AC photometry of the measurement light beam.

The analysis control unit 15 controls the rotation of the sample rotation stage 8 and also measures the measurement light detector 1.
The refractive index of the sample 7 is calculated based on the relationship between the output from 1 and the rotation angle of the sample rotation stage 8 detected by the rotation angle detection unit 8a. Further, the refractive index temperature coefficient of the sample 7 is calculated based on the relationship between the calculated refractive index and the internal temperature of the thermostatic chamber 6. The procedure is shown below.

First, the refractive index measurement procedure will be described. The sample 7 is placed on the sample rotation stage 8 in the thermostat 6 so that the first surface 701 of the sample 7 is orthogonal to the incident measurement light beam. While the sample rotation stage 8 is rotated, the reflected light from the first surface 701 is monitored by the measurement light detector 11. The time when the reflected light beam from the first surface 701 passes through the mirror slit 501 is the first.
When the surface 701 is orthogonal to the incident light beam, the output of the measuring light detector 11 is minimized. In the rotation angle detection unit 8a, the position of the sample rotation stage 8 at this time is set as a “reference position”, and the rotation-side scale position that coincides with the fixed cursor 801 of the sample rotation stage 8 as shown in FIG. The scale is 802. At this time, the measurement light beam does not necessarily have to be the measurement wavelength light. In order to increase the measurement S / N ratio, the 0th-order diffracted light that provides a strong intensity can be output from the monochromator unit 2, and this can be used as the light source. .

After reading the reference scale 802 via the rotation angle detection unit 8a, the sample rotation stage 8 is rotated in a state where the wavelength of the light beam emitted from the monochromator unit 2 is the measurement wavelength.
The reflected light beam from the second surface 702 can be monitored by the measurement light detector 11. Next, the rotation angle of the sample rotation stage 8 is adjusted to search for a position where the output of the measurement light detector 11 is minimized. The position where the output of the measurement light detector 11 is minimum is the minimum deflection angle state, and this is the minimum deflection angle position. The scale that matches the cursor 801 at the minimum deflection angle position is set as the minimum deflection scale 803. The angle between the reference scale 802 and the minimum declination scale 803 is
As shown in FIG. 7, the incident angle i of the measurement light beam on the first surface 701 of the sample 7 at the minimum deviation angle.
become. The analysis control unit 15 substitutes the actually measured values of the apex angle τ and the incident angle i of the sample 7 in the above-described equation (2), and calculates the refractive index n of the sample 7 at the measurement wavelength.

Subsequently, a procedure for measuring the refractive index temperature coefficient will be described. First, the refractive index of the sample 7 at the reference temperature is measured as described above. Next, the temperature inside the thermostat 6 is changed by a predetermined temperature,
Stabilize in this state. And the refractive index measurement of the above-mentioned sample 7 is performed again. The temperature to be changed is set such that the value obtained by dividing the refractive index change amount obtained by these measurements by the temperature change amount can be approximately regarded as a differential value with respect to the temperature of the refractive index of the sample 7 near the reference temperature. The value thus obtained is the refractive index temperature coefficient of the sample 7 in the vicinity of the reference temperature for the measurement wavelength.

In addition, if the temperature inside the thermostat 6 is changed, a difference will arise in the refractive index of the air inside and outside the thermostat 6. Since the window 601 of the thermostatic chamber 6 is installed inclined with respect to the optical axis as described above, the window 601 is installed.
There is a difference between the refraction angle of the measurement light beam on the outer surface side of the window and the refraction angle of the measurement light beam on the inner surface side of the window 601, and the measurement light beam is deviated when passing through the window 601. In the state, the reciprocal optical path of the window 601 coincides in principle, and does not affect the measured value.

Next, a method for accurately grasping the wavelength value of the measurement light beam will be described. Both the light beams from the infrared region light source 101 and the visible region bright line light source 105 pass through the entrance slit 201 of the monochromator unit 2. The lattice constant of the planar reflection grating 204 is set so that the light beam having a wavelength of 632.82 nm of the He—Ne laser used as the visible range bright line light source 105 is reflected by a predetermined high-order diffraction. In the present embodiment, the lattice constant of the planar reflection grating 204 is 0.01 m.
m. Table 1 below shows the measurement light beam wavelength from the infrared light source 101 output from the exit slit 207 of the monochromator unit 2 together with the high-order diffraction light beam having a wavelength of 632.82 nm.
The diffraction order of a 32.82 nm light beam is shown up to 10. Note that the measurement light beams are all in the case of first-order diffracted light.

(Table 1)
Wavelength 632.82nm Light diffraction order Measurement light flux (nm)
2 1265.64
3 1898.46
4 2531.28
5 3164.10
6 3796.92
7 4429.74
8 5062.56
9 5695.38
10 6328.20

While rotating the rotating stage 208 of the monochromator unit 2, the wavelength calibration light detector 14 monitors the light beam having a wavelength of 632.82 nm output from the exit slit 207. Wavelength 6
After the 32.82 nm light beam is output from the exit slit 207, it is transmitted through the monochromator dichroic mirror 3 while being diverged, is collected by the relay lens 13, and reaches the wavelength calibration light detector 14.

The diffraction order of a light beam with a wavelength of 632.82 nm is a wavelength of 632.82 nm and a lattice constant of 0.01 m.
m, the rotation angle of the rotation stage 208 from the 0th-order diffraction position, and the incident angle and diffraction angle of the light beam with respect to the planar reflection grating 204. The correspondence between the rotation angle of the rotation stage 208 and the diffraction order can be determined in advance. There is no need to calculate each time. Further, since the monochromator unit 2 is entirely composed of reflective optical elements, there is no wavelength dependency. Therefore, the wavelength of the measurement light beam is not affected by the chromatic aberration of the optical system, and the wavelength of 632.82n.
It is accurately determined based on m luminous flux.

For example, in Table 1, when a light beam having a wavelength of 6328.20 nm, which is a measurement light beam, is output, second-order diffracted light having a light beam of 3164.10 nm is also output together. In order to remove high-order diffracted light having a short wavelength that is output at the same time, the order selection filter turret 10 is installed immediately before the measurement light detector 11. In this case, a filter having spectral characteristics that transmits a light beam having a wavelength of 6328.20 nm and blocks a light beam having a wavelength of 3164.10 nm is inserted into the optical path.
In this way, a plurality of filters having predetermined spectral characteristics different from each other are installed in the turret,
By selecting an appropriate filter according to the measurement wavelength and inserting it in the optical path, it is possible to prevent unnecessary high-order diffracted light from entering the measurement light detector 11.

Subsequently, a measurement light beam in the middle of the higher-order diffraction position of the light beam having a wavelength of 632.82 nm, for example, Table 1
A method for outputting wavelengths such as 3000 nm, 4000 nm, and 5000 nm will be described. First, the rotation angle of the rotary stage 208 of the monochromator unit 2 corresponding to the measured light beam wavelength in Table 1 is measured before, after, or in the middle of the measurement, and the rotation of the rotary stage 208 corresponding to the intermediate wavelength is determined from these values. The angle is calculated by interpolation. By adjusting the rotation stage 208 to the calculated rotation angle, a measurement light beam having a desired intermediate wavelength can be output with high accuracy.

Needless to say, the opening width of the entrance slit 201 and the slit opening width of the exit slit 207 of the monochromator unit 2 directly affect the wavelength purity of the measurement light beam. In addition, the longitudinal dimension of the opening of the exit slit 207 also affects the wavelength purity of the measurement light beam. The optical system is set so that the measurement light beam output from the exit slit 207 and the light beam having a wavelength of 632.82 nm for calibration of the wavelength of the measurement light beam overlap each other over the entire opening of the exit slit 207. Since the image of the possible entrance slit 201 is curved so as to be concave toward the long wavelength side (see, for example, Applied Spectroscopy Handbook edited by Hiroshi Yoshinaga, Asakura Shobo (1973) P.409), the longitudinal direction of the opening of the exit slit 207 Is too long, there is a shift in the passing wavelength between the opening center and the end of the exit slit 207, and the wavelength purity of the measurement light beam is lowered.

Further, as described in the description of the prior art, when the incident light beam on the sample 7 has an angle with respect to the sample main cross section 704, the minimum deviation value is shifted in the direction of increasing with respect to the correct value. The longer the exit slit 207, the greater this effect and lowers the refractive index measurement accuracy.

As described above, the size in the opening longitudinal direction of the exit slit 207 of the monochromator unit 2 affects the measurement accuracy of the wavelength purity of the measurement light beam and the minimum deviation angle. . On the other hand, the larger the opening widths of the entrance slit 201 and the exit slit 207, the larger the light energy of the measurement light beam. Therefore, while looking at the S / N ratio of the output of the measurement light detector 11, the entrance slit 201 and The slit opening width of the exit slit 207 and the length in the longitudinal direction are determined. The slit width in the opening longitudinal direction of the exit slit 207 is determined by adjusting the interval between the Hartmann plates 209. In the present embodiment, since the measurement light beam passing through the central portion of the exit slit 207 in the longitudinal direction of the opening is used, the dimension of the exit slit 207 in the longitudinal direction of the opening is minimized. When it is known that the accuracy and light intensity necessary for measurement can be obtained, the entrance slit 201 and the exit slit 20
The opening of 7 may be fixed.

As described above, in the measuring apparatus according to the present embodiment, (1) since the refractive index measuring apparatus using the Littrow method requires only one constant temperature chamber window, the refractive index and the refractive index temperature coefficient. (2) Since an optical system mainly composed of a reflecting mirror is used, it can be used in a wide wavelength band. (3) The incident light flux on the sample is adjusted by adjusting the rotation angle of the rotary stage. The tilt component with respect to the main cross section of the sample can be minimized, so that the error is small and a more accurate minimum declination value can be obtained. (4) The exact wavelength value of the measured light beam, particularly in the infrared region where there are few bright lines Can be easily grasped. (5) Since the temperature chamber window is inclined with respect to the incident light beam, the measurement light beam reflected by the temperature chamber window does not reach the measurement light detector, and is reflected by the mirror surface of the mirror slit. Because the mirror slit is tilted with respect to the optical axis at an angle where the return beam from the tank and the measurement beam coming out of the mirror slit do not overlap,
Since only the returning light beam from the thermostat reflected by the mirror surface of the mirror slit enters the measurement light detector, the refractive index and the refractive index temperature coefficient can be measured with a high S / N ratio.

In this embodiment, the Czerny-Turner type is adopted as the monochromator unit 2, but the present invention is not limited to this. For example, it is also possible to employ a Seya / Namioka type monochromator composed of one concave diffraction grating.

DESCRIPTION OF SYMBOLS 1 Light source part 101 Infrared region light source 102 Chopper 103 Light source part concave mirror
104 Dichroic mirror (first dichroic mirror)
105 Visible Line Light Source 106 Condensing Optical System 2 Monochromator Unit 201 Entrance Slit 202 Planar Mirror 203 Collimator Mirror 204 Planar Reflection Grating 205 Condensing Mirror 206 Plane Mirror 207 Exit Slit 208 Rotation Stage (Rotation Drive Unit)
209 Hartmann plate 3 Monochromator dichroic mirror (second dichroic mirror)
4 First concave mirror 5 Collimator section 501 Mirror slit 501a Mirror surface 502 Collimator mirror 503 Flat mirror 6 Constant temperature bath 601 Window 7 Sample 701 Incident surface 702 Reflecting surface 703 Ridge line 704 Sample main section 8 Sample rotation stage (rotation stage)
8a Rotation angle detector 801 Cursor 802 Reference scale 803 Minimum declination scale 9 Second concave mirror 10 Order selection filter turret 11 Measurement light detector 12 Lock-in amplifier 13 Relay lens 14 Wavelength calibration light detector 15 Analysis control section

Claims (6)

A light source unit that emits a predetermined single wavelength light beam;
One surface of a collimator mirror having a positive power and a plate-like member formed with a small opening is a mirror surface, the opening coincides with the focal position of the collimator mirror, and the mirror surface faces the collimator mirror side. And an aperture plate that is inclined with respect to the optical axis so that it does not return to the collimator mirror when the light beam collected by the collimator mirror is reflected, and the aperture of the aperture plate A collimator unit that converts the light beam incident from the light source unit into a parallel light beam by the collimator mirror;
A constant temperature bath provided with a window capable of transmitting a parallel light beam from the collimator unit, the inside of which is sealed and the temperature can be variably controlled;
Rotation that can be rotated around a rotation axis parallel to the ridge line formed by the first surface and the second surface sandwiching the apex angle of the sample in a state where the wedge prism type sample is placed in the thermostatic chamber. Stage,
A rotation angle detector that detects a rotation angle of the rotation stage;
The parallel light flux that is incident on the inside of the thermostatic chamber through the window and is reflected by the first surface of the sample and then exits the thermostatic chamber through the window, or the thermostatic chamber through the window The light enters the inside of the sample from the first surface, is reflected by the back surface of the second surface, is then emitted to the outside of the sample through the first surface, and is emitted to the outside of the thermostatic chamber through the window. A measuring light detector for receiving the light beam reflected by the mirror surface of the aperture plate after the parallel light beam returns to the collimator unit and is collected by the collimator mirror;
An analysis control unit that performs rotation control of the rotation stage and calculates a refractive index of the sample based on a relationship between an output from the measurement light detector and a rotation angle of the stage detected by the rotation angle detection unit; A measuring apparatus comprising: The analysis control unit performs rotation control of the rotary stage, and the parallel light beam reflected by the first surface passes through the opening, and the amount of light incident on the measurement light detector is minimized.
When the rotation angle of the rotation stage detected by the rotation angle detector and the parallel light beam reflected from the back surface of the second surface pass through the opening and the amount of light incident on the measurement light detector is minimized. The measurement apparatus according to claim 1, wherein the refractive index of the sample is calculated based on a relationship with a rotation angle of the rotation stage detected by the rotation angle detection unit. The light source unit is
A measurement light source that emits continuous spectrum light in a predetermined measurement wavelength band in the infrared region;
The monochromator unit for extracting the predetermined single wavelength light used for measuring the refractive index of the sample from the continuous spectrum light emitted from the measurement light source. Measuring device. A wavelength calibration light source that emits visible line light;
A first dichroic mirror that superimposes the light beam from the measurement light source and the light beam from the wavelength calibration light source so as to pass through the same optical path;
It has an entrance slit, a reflection type diffraction grating, and an exit slit, and all other optical elements are composed of reflection elements, and the diffraction grating is rotated to change the wavelength of the light beam emitted from the exit slit. The monochromator unit having a rotation drive unit;
A second dichroic mirror that separates a light beam from the measurement light source and a light beam from the wavelength calibration light source from the light beam emitted from the exit slit;
A wavelength calibration light detector for receiving a light beam from the wavelength calibration light source separated by the second dichroic mirror;
The rotation control unit that controls the rotation drive unit based on an output result of the wavelength calibration light detector so that the light beam emitted from the exit slit has a predetermined wavelength. Measuring device. 2. The thermostatic chamber, wherein the window is installed to be inclined with respect to the parallel light beam from the collimator unit so that a light beam reflected by the window does not enter the measurement light detector. The measuring apparatus as described in any one of -4. The said analysis control part calculates the refractive index temperature coefficient of the said sample based on the relationship between the refractive index of the said sample, and the temperature change amount inside the said thermostat. A measuring device according to claim 1.

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