JP5380889B2 - Refractive index measuring method, dispersion measuring method, refractive index measuring device, and dispersion measuring device - Google Patents

Description

  The present invention relates to a refractive index measurement method, a dispersion measurement method, a refractive index measurement device, and a dispersion measurement device for optical materials and the like.

A typical method for measuring the refractive index of an optical material is a minimum deviation method (see Patent Document 1). In this method, measurement light having a specific wavelength is projected onto a prism-shaped optical material to measure the minimum deflection angle and the apex angle, respectively, and a predetermined calculation formula (refer to Formula (1) in Patent Document 1). ). According to this method, an absolute refractive index of the order of 10 ⁻⁶ can be measured.
JP-A-6-267420

  However, this method mainly has the following problems.

  (1) Usually, in the minimum deflection angle measurement, it is necessary to search for the rotation position (minimum deflection angle position) of the optical material that minimizes the deflection angle of the measurement light before and after passing through the optical material. Requires systems and mechanisms.

  (2) The search for the minimum declination position requires skillful techniques and is difficult to automate.

  Therefore, an object of the present invention is to provide a refractive index measurement method and a dispersion measurement method capable of performing highly accurate measurement with a simple configuration and a simple procedure.

  Another object of the present invention is to provide a refractive index measurement device and a dispersion measurement device that can automatically perform high-precision measurement with a simple configuration.

One aspect of the refractive index measurement method of the present invention includes a projection optical system that projects measurement light onto a prism-shaped measurement object, a turntable that changes an arrangement angle of the measurement object with respect to the measurement light, and A refractive index measurement method using a return optical beam returning from a measurement object and a detection optical system for detecting an angular relationship between the measurement light and projecting the measurement light to one inclined surface of the measurement object. , A procedure for detecting the rotational position θ ₁ of the turntable so that the angular deviation between the return light reflected on the back surface on the other slope after passing through the slope and the measurement light becomes zero, and the measurement object while projecting the measurement light the to one slope, and procedures for detecting the turntable rotational position theta _2, such as angle deviation between the measurement light and return light surface reflection at the slope becomes zero, The measurement light to the other slope of the measurement object While projecting light, the rotational position and the procedure angular deviation between the return light and the measurement light surface reflection at the slope detecting the turntable of the rotational position theta ₃ such that zero, the rotational position theta ₁ and and a procedure for calculating the refractive index n of the measurement object based on θ ₂ , the rotational position θ ₃ and the following formula .

  Further, one aspect of the dispersion measuring method of the present invention is characterized in that the refractive index measuring method according to any one of the above aspects is used.

An aspect of the refractive index measuring apparatus of the present invention includes a light projecting optical system that projects measurement light onto a prism-shaped measurement object, and a turntable that changes an arrangement angle of the measurement object with respect to the measurement light. A detection optical system for detecting an angular relationship between the return light returning from the measurement object and the measurement light, and a control means for controlling the light projecting optical system, the turntable, and the detection optical system. The means projects the measurement light onto one slope of the measurement object, and the angle deviation between the return light reflected on the back surface on the other slope after passing through the slope and the measurement light becomes zero. angular deviation Do means the detecting the turntable of the rotational position theta _1, wherein while projecting said measurement light to one of the slopes of the measurement object, the returning light and the measurement light surface reflection at the inclined surface rotational position theta ₂ but of the turntable such that zero Means for detecting, with for projecting said measurement light to the other inclined surface of the object to be measured, the angle deviation between the measurement light and return light surface reflection at the inclined surface of the rotary table such that zero further comprising means for detecting a rotational position theta _3, and means for calculating a refractive index n of the rotational position theta ₁ and the rotational position theta ₂ and the rotational position theta ₃ or less of the measurement object based on the formula It is characterized by.

  Moreover, one aspect of the dispersion measuring apparatus of the present invention is characterized by including the refractive index measuring apparatus according to any one of the above aspects.

  According to the present invention, a refractive index measurement method and a dispersion measurement method capable of performing highly accurate measurement with a simple configuration and a simple procedure are realized.

  Further, according to the present invention, a refractive index measurement device and a dispersion measurement device that can automatically perform high-accuracy measurement with a simple configuration are realized.

  Embodiments of the present invention will be described below. The present embodiment is an embodiment of a refractive index / dispersion measuring apparatus.

  First, the configuration of the refractive index / dispersion measuring apparatus will be described.

  FIG. 1 is a schematic configuration diagram of a refractive index / dispersion measuring apparatus. As shown in FIG. 1, the refractive index / dispersion measurement apparatus includes a plurality of types of light sources 6, a light source switching mechanism 5, a wavelength selection plate 7, a selection wavelength switching mechanism 17, a pinhole plate 8, and a collimator. A mirror 9, a diaphragm 10, a beam splitter 11, an image sensor 14, a plane reflection mirror 12, a shutter 13, and a stage 15 are provided. Although not shown, the refractive index / dispersion measuring apparatus is also provided with a control unit. This control unit has a control function for controlling each element in the refractive index / dispersion measurement apparatus, and an information processing function for capturing and processing an image output from the image sensor 14.

A sample 16 such as an optical material is placed on the table 15 a of the stage 15. The sample 16 is processed into a prism shape in advance, and the apex angle α has an arbitrary value within a range of 30 ° to 45 °. It is assumed that the _two inclined surfaces s ₁ and s ₂ sandwiching the apex angle are polished with sufficient accuracy and the bottom surface is not polished. Thereby, it can be considered that the reflectance of the slopes s ₁ and s ₂ is sufficiently higher than the reflectance of the bottom surface.

In FIG. 1, in order to easily distinguish the _two slopes s ₁ and s ₂ , the slope s ₁ is represented by a thick line and the slope s ₂ is represented by a thin line (the same applies to other drawings). The posture of the sample 16 on the table 15a is such that the slopes s ₁ and s ₂ are substantially parallel to the normal line of the table 15a, as shown in FIG.

  The table 15a is attached to the base of the stage 15 via a rotation mechanism (not shown), and a motor is connected to the rotation mechanism. When the motor is driven, the table 15a rotates around the normal line.

  Also, an angle sensor such as a rotary encoder is built in the stage 15 between the rotation mechanism and the base. The rotational position θ of the table 15a is detected by the output signal of the angle sensor.

  A tilt mechanism (not shown) is also interposed between the table 15a and the rotation mechanism, and a motor is connected to the tilt mechanism. When the motor is driven, the table 15a tilts around two axes orthogonal to each other on the table 15a. Note that the tilt range around these two axes is, for example, about ± 3 °.

  The light source 6, the light source switching mechanism 5, the wavelength selection plate 7, and the selection wavelength switching mechanism 17 are all surrounded by the light shielding wall 4, and a pinhole plate 8 is provided in the opening of the light shielding wall 4. .

  Light emitted from the light source 6 enters the pinhole plate 8 via the wavelength selection plate 7. Of the light, only the light that has passed through the pinhole of the pinhole plate 8 is emitted to the outside of the light shielding wall 4. The wavelength of the light emitted from the light shielding wall 4 is switched by driving the light source switching mechanism 5 and the selection wavelength switching mechanism 17.

  The light emitted from the light shielding wall 4 is shaped into parallel light by the collimator mirror 9, given an arbitrary opening from the diaphragm 10, and then enters the beam splitter 11. The light branches on the separation surface of the beam splitter 11 into the measurement light LM traveling toward the stage 15 and the reference light LR traveling toward the planar reflection mirror 12.

The measurement light LM goes to the sample 16. Incidentally, when one of the slopes s ₁ of as a sample 16 shown in Figure 1 was directly opposite the measuring light LM is incident to the slope s _1. A part of the measurement light LM is reflected (surface reflection) by the inclined surface s ₁ , and the other part is incident on the inside of the sample 16. Part of the measurement light LM incident on the inside of the sample 16 is reflected (back surface reflection) on the slope s ₂ , and the other part passes through the slope s ₂ . Therefore, there are two types of light (return light) returning from the sample 16 to the beam splitter 11 side, that is, return light reflected on the surface by the slope s ₁ and return light reflected on the back surface by the slope s ₂ .

Incidentally, as shown in FIG. 1, the measurement light LM may incident from front to slope s _1, return light surface reflection at the slope s ₁ is folded optical path incident on the beam splitter 11. The return light is deflected in the direction of the image sensor 14 by the separation surface of the beam splitter 11 to form a spot (measurement spot) on the image sensor 14. Note that the size of the measurement spot changes according to the diameter of the diaphragm 10, and the measurement spot does not appear on the image sensor 14 when the sample 16 is not placed on the stage 15.

  On the other hand, the reference light LR is incident on the planar reflection mirror 12 from substantially the front. When the reference light LR is reflected by the plane reflection mirror 12, the optical path is turned back, passes through the beam splitter 11, enters the image sensor 14, and forms a spot (reference spot) on the image sensor 14.

  Note that the size of the reference spot changes according to the diameter of the diaphragm 10, and when the shutter 13 disposed between the beam splitter 11 and the plane reflection mirror 12 is closed, the reference spot is placed on the image sensor 14. Does not appear.

  The image output from the image sensor 14 is sent to the control unit. The control unit performs processing on the image as necessary.

  Here, in the refractive index / dispersion measurement apparatus of the present embodiment, even if the plane reflection mirror 12 is slightly inclined, the orientation of the reference light LR reflected by the plane reflection mirror 12 and the measurement light LM toward the sample 16 are measured. The angular relationship with the azimuth is unchanged.

Therefore, the refractive index and dispersion measuring apparatus of this embodiment, the orientation of the reference light LR reflected by the plane reflecting mirror 12, i.e. the center coordinates P _R of the reference spot formed on the imaging device 14, the measurement light LM orientation Use as a reference.

Therefore, the control unit, prior to the measurement of refractive index and dispersion, when the specimen 16 is not placed on the table 15a, to measure the center coordinates P _R of the reference spot. In the measurement of the centroid coordinates P _R, the control unit opens the shutter 13, suitable aperture diameter of the aperture 10, to light any light source 6. As a result, a reference spot having a sufficiently small size (a size that can be completely accommodated on the imaging surface) appears on the imaging surface of the imaging element 14. Then, the control unit performs a profile extraction processing to an image capturing device 14 outputs, upon obtaining the outer shape of the reference spot, the center of gravity coordinates of the contour is calculated as the centroid coordinates P _R of the reference spot.

  Next, the operation of the control unit relating to the measurement of refractive index / dispersion will be described.

  FIG. 2 is an operation flow of the control unit. Hereinafter, each step will be described in order.

  Step S11: The control unit closes the shutter 13, opens the diameter of the diaphragm 10, sets the wavelength of the measurement light LM to an initial value, and turns on the necessary light source 6. When the diameter of the diaphragm 10 is opened, the diameter of the measurement light LM becomes a sufficiently large size (a size that can completely cover the imaging surface).

Step S12: The control unit sets the rotational position θ of the table 15a as a reference position. Here, the reference position is assumed to be a rotational position as shown in FIG. In this state, the measurement light LM is not incident on any of the polished slopes s ₁ and s ₂ , so that almost no return light is generated.

  Subsequently, the control unit monitors the luminance I of the image output from the image sensor 14 while rotating the table 15a in the direction of the arrow in FIG. Thereby, the control unit can acquire a θ-I curve as shown in FIG. Peaks A, B, C, and D appear in the θ-I curve.

Of these, the first peak A appears, as shown in FIG. 5 (A), a when the rotational position theta stage 15a is in the theta _A, in this state, the return was back surface reflection at the slope s ₂ Since the angular deviation between the light and the measurement light LM is substantially zero, the return light enters the image sensor 14 via the beam splitter 11.

Further, the next peak B appears when the rotational position θ of the stage 15a is at θ _B as shown in FIG. 5B, and in this state, the return light reflected from the inclined surface s ₁ is obtained. And the measurement light LM are substantially zero, the return light enters the image sensor 14 via the beam splitter 11.

Further, the next peak C appears when the rotational position θ of the stage 15a is at θ _C as shown in FIG. 5C. In this state, the return light reflected from the inclined surface s ₂ is reflected. And the measurement light LM are substantially zero, the return light enters the image sensor 14 via the beam splitter 11.

Also, the next peak D appears, as shown in FIG. 5 (D), a when the rotational position theta stage 15a is in the theta _D, in this state, return light back reflection at the slope s ₁ And the measurement light LM are substantially zero, the return light enters the image sensor 14 via the beam splitter 11.

Subsequently, the control unit recognizes three rotation positions θ _A , θ _B , and θ _C that give three peaks A, B, and C from such a θ-I curve.

Note that the control unit in this step recognizes the rotational positions θ _A , θ _B , and θ _C after acquiring the θ-I curve, but it may be performed during the acquisition of the θ-I curve. In that case, the control unit compares the luminance I with the threshold value in real time during the rotation of the table 15a, and considers the rotational positions at the time when the threshold value is exceeded as the rotational positions θ _A , θ _B , θ _C, θ _D in order. Good.

Incidentally, among the rotational positions θ _A , θ _B , θ _C , and θ _D , the rotational positions θ _A and θ _D (FIGS. 5A and 5D) indicate that they are incident on the inside of the sample 16. The rotation positions θ _B and θ _C (FIGS. 5B and 5C) show the return light reflected from the surface of the sample 16 while the direction of the return light reflected from the back surface. This is the direction. Therefore, the luminance I of the peaks B and C is higher than the luminance I of the peaks A and D (see FIG. 4).

Of the rotational positions θ _A , θ _B , θ _C , and θ _D , the rotational positions θ _A and θ _D (FIGS. 5A and 5D) indicate that they are incident on the inside of the sample 16. In contrast to the direction of the return light, the rotational positions θ _B and θ _C (FIGS. 5B and 5C) show the direction of the return light that did not enter the sample 16. . Therefore, when the wavelength of the measurement light LM changes, the rotation positions θ _A and θ _D are slightly shifted, but the rotation positions θ _B and θ _C do not change even if the wavelength of the measurement light LM changes.

Step S13: The control unit sets the rotational position θ of the table 15a to the rotational position θ _B , and in this state, monitors the luminance I while tilting the table 15a around the two axes, and the monitored luminance I is When the maximum value is reached, the tilt angle of the table 15a is fixed. Next, the control unit sets the rotational position θ of the table 15a to the rotational position θ _C , and in this state, monitors the luminance I while tilting the table 15a around the two axes, and the monitored luminance I is When the maximum value is reached, the tilt angle of the table 15a is fixed. Then, the control unit repeats the above procedure a predetermined number of times (for example, several times). Thereby, the tilt adjustment of the table 15a is completed.

  Step S14: The control unit appropriately stops the diaphragm 10. As a result, the diameter of the measurement light LM becomes a sufficiently small size (a size that can be completely accommodated on the imaging surface).

Subsequently, the control unit sets the rotational position theta table 15a in the rotational position theta _B. At this time, a measurement spot is formed at any location within the imaging surface of the imaging device 14. The control unit calculates the barycentric coordinate P _B of the measurement spot based on the image output from the imaging element 14 in this state. The calculation method of the barycentric coordinates is as described above. Then, the control unit calculates the barycentric coordinates P _B, reference spots were previously measured deviation [Delta] P _B between the center of gravity coordinates P _R. When the deviation ΔP _B is zero, the control unit sets the rotational position θ _B as the rotational position θ _{B (TRUE),} and when the deviation ΔP _B is not zero, the control unit deviates from the optical path length from the table 15a to the image element 14. By correcting the rotational position θ _B with the angle correction amount Δθ _B determined according to ΔP _B , the rotational position of the table 15a when the deviation ΔP _B becomes zero is calculated, and the rotational position θ _{B (TRUE)} is calculated. And In this rotational position θ _{B (TRUE)} , the angular deviation between the return light that is reflected from the inclined surface s ₁ of the sample 16 and then travels toward the image sensor 14 and the reference light LR reflected by the planar reflection mirror 12 is completely zero. Is the rotational position of the table 15a.

Subsequently, the control unit sets the rotational position theta table 15a in the rotational position theta _C. At this time, a measurement spot is formed at any location within the imaging surface of the imaging device 14. Control unit on the basis of the image output by the image sensor 14 in this state, calculates the barycentric coordinates P _C of the measurement spot. The calculation method of the barycentric coordinates is as described above. Then, the control unit calculates the barycentric coordinates P _C, reference spots were previously measured deviation [Delta] P _C between the center of gravity coordinates P _R. If the deviation [Delta] P _C is zero, the control unit, the rotational position theta _C as the rotation position θ _{C (TRUE),} if the deviation [Delta] P _C is not zero, the optical path length and the deviation from the table 15a to the image element 14 by correcting the rotational position theta _C at an angle correction amount [Delta] [theta] _C determined in accordance with the [Delta] P _C, and calculates the rotational position of the table 15a when the deviation [Delta] P _C is zero, the rotational position theta _C it _(TRUE) And At this rotational position θ _{C (TRUE)} , the angular deviation between the return light that is reflected from the inclined surface s ₂ of the sample 16 and then travels toward the image sensor 14 and the reference light LR that is reflected by the planar reflection mirror 12 is completely zero. Is the rotational position of the table 15a.

Step S15: The control unit calculates the apex angle α of the sample 16 by fitting the rotational positions θ _{A (TRUE)} , θ _{B (TRUE)} , and θ _{C (TRUE)} acquired in Step S14 to the equation (1). .

Step S16: The control unit sets the rotational position theta table 15a in the rotational position theta _A. At this time, a measurement spot is formed at any location within the imaging surface of the imaging device 14. Note that the measurement spot formation position slightly deviates depending on the wavelength of the measurement light LM, but in any case, the measurement spot is sufficiently small so that it does not deviate from the imaging surface.

Subsequently, the control unit on the basis of the image output by the image sensor 14 in this state, calculates the barycentric coordinates P _A of the measurement spot. The calculation method of the barycentric coordinates is as described above. Then, the control unit calculates the barycentric coordinates P _A, reference spots were previously measured deviation [Delta] P _A between the center of gravity coordinates P _R. When the deviation ΔP _A is zero, the control unit sets the rotational position θ _A as the rotational position θ _{A (TRUE),} and when the deviation ΔP _A is not zero, the control unit deviates from the optical path length from the table 15 a to the image element 14. By correcting the rotational position θ _A with the angle correction amount Δθ _A determined according to ΔP _A , the rotational position when the deviation ΔP _A becomes zero is calculated, and is set as the rotational position θ _{A (TRUE)} . In this rotational position θ _{A (TRUE)} , the angular deviation between the return light reflected from the back surface of the sample 16 on the inclined surface s ₂ and then toward the image sensor 14 and the reference light LR reflected by the planar reflection mirror 12 is completely zero. Is the rotational position of the table 15a.

Step S17: The control unit obtains the rotational position θ _{A (TRUE)} measured in the previous step S16 and θ _{B (TRUE)} and θ _{C (TRUE)} measured in the previous step S14 to Equation (2). By applying, the minimum deviation angle θ _min of the sample 16 is calculated.

Step S18: The control unit applies the refractive index n of the sample 16 by applying the minimum deviation angle θ _min calculated in the previous step S17 and the apex angle α calculated in the previous step S15 to the equation (3). Is calculated.

  Step S19: The control unit determines whether or not the processing of steps S16 to S18 (refractive index measurement processing) has been performed for all the predetermined wavelengths, and if it has been performed, proceeds to step S21. If not executed, the process proceeds to step S20.

  Step S20: The control unit changes the wavelength of the measurement light LM and then returns to step S16. Therefore, the refractive index n is measured in order for each wavelength.

  Step S21: The control unit calculates the dispersion of the sample 16 based on the refractive index of each wavelength measured in order, and ends the flow.

Next, the above-described calculation formula (2) (calculation formula of the minimum deviation angle θ _min ) will be described in detail.

FIG. 6 shows a state when the rotational position θ of the sample 16 is at the minimum declination position. The rotational position corresponds to a rotational position between the rotational position theta _B shown in rotational position theta _A and FIG. 5 (B) shown in FIG. 5 (A).

In FIG. 6, a line segment that starts from the vertex X of the sample 16 and bisects the apex angle α is denoted by XY, and an intersection point of the optical path of the measurement light LM passing through the sample 16 and the line segment XY is denoted by W. When a line segment starting from the point W and perpendicular to the optical path of the measurement light LM before entering the sample 16 is denoted by WZ, the minimum deviation angle θ _min of the sample 16 is equal to 2 × ∠YWZ.

The angle formed by the line segment XY with respect to the optical path of the measurement light LM before being incident on the sample 16 is (θ _{B (TRUE)} −θ _{A according} to the rotational positions θ _{B (TRUE)} and θ _{A (TRUE). (TRUE)} ).

The angle formed by the line segment WZ with respect to the optical path of the measurement light LM before entering the sample 16 is (θ _{B (TRUE)} −α based on the rotation position θ _{B (TRUE)} and the vertex angle α described above. / 2).

Therefore, the minimum deflection angle θ _min of the sample 16 is expressed by the following formula (4).

Therefore, it is clear that the minimum deviation angle θ _min can be calculated by the calculation formula (2).

As described above, the refractive index / dispersion measurement apparatus according to the present embodiment, instead of searching for the minimum deflection angle position when measuring the minimum deflection angle θ _min , returns light reflected from the back surface of the sample 16 to the image sensor 14, The rotational position θ _{A (TRUE)} of the table 15a is measured such that the angular deviation with respect to the reference light LR reflected by the plane reflection mirror 12 becomes zero. Therefore, the refractive index / dispersion measuring apparatus according to the present embodiment can automate all procedures relating to the measurement of the refractive index (and dispersion).

Further, since the measurement of the rotational position θ _{A (TRUE)} does not require a special optical system or mechanism as in the search for the minimum deviation angle position, the rotational position θ _{B (TRUE)} necessary for calculating the apex angle α. , Θ _{C (TRUE)} can be used as it is (the beam splitter 11 in FIG. 1 and its upstream optical system).

Therefore, the refractive index / dispersion measurement apparatus of the present embodiment can obtain the relationship between the rotational positions θ _{A (TRUE)} , θ _{B (TRUE)} , and θ _{C (TRUE)} with high accuracy with a common optical system. Therefore, the measurement accuracy of the refractive index (and dispersion) is also high.

Incidentally, when the rotational positions θ _{A (TRUE)} , θ _{B (TRUE)} , and θ _{C (TRUE)} are measured with a common optical system, the light projection position of the measurement light LM on the sample 16 also substantially matches between the measurements. It is considered that the surface accuracy of the slopes s ₁ and s ₂ has little influence on the measurement accuracy of the refractive index (and dispersion).

  In addition, the refractive index / dispersion measurement apparatus according to the present embodiment does not require a special optical system or mechanism as described above, and therefore has an advantage that error factors in the apparatus can be suppressed.

  In addition, since the refractive index / dispersion measuring apparatus according to the present embodiment does not require a special optical system or mechanism as described above, even if the refractive index (and dispersion) in the VUV wavelength region is measured, the N2 purge is performed. Measurement error due to N2 fluctuation can be suppressed while suppressing the volume.

  Next, the supplement of this embodiment is described.

  In the refractive index / dispersion measuring apparatus of the present embodiment described above, the pinhole plate 8 is provided at the opening of the light shielding wall 4, but a slit plate may be provided instead of the pinhole plate 8.

  Further, the refractive index / dispersion measuring apparatus of the present embodiment is a type of measuring apparatus with a built-in light source, but may be a type of measuring apparatus without a built-in light source. In that case, the light emitted from the light source may be introduced into the measuring device from a light source disposed outside the measuring device by a light guide means such as a fiber.

  In addition, the refractive index / dispersion measuring apparatus of the present embodiment uses the correction calculation according to the deviation ΔP to rotate the table 15a so that the deviation ΔP between the center of gravity coordinates of the measurement spot and the center of gravity of the reference spot becomes zero. Although calculated, it goes without saying that such a rotational position may be actually searched.

In that case, the control unit in step S14 described above monitors the shift ΔP _B while rotating the table 15a by a minute angle in the vicinity of the rotational position θ _B , and the rotational position of the table 15a when the shift ΔP _B becomes zero. May be the rotational position θ _{B (TRUE)} . The control unit in step S14 described above, a table 15a in the vicinity of the rotational position theta _C monitor [Delta] P _C shift while rotating by a small angle, the rotational position of the table 15a at the time when the deviation [Delta] P _C is zero The rotation position θ _{C (TRUE)} may be used. The control unit in step S16 described above, a table 15a in the vicinity of the rotational position theta _A monitor [Delta] P _A shift while rotating by a small angle, the rotational position of the table 15a at the time when the deviation [Delta] P _A is zero The rotation position θ _{A (TRUE)} may be used.

  Further, the refractive index / dispersion measurement apparatus according to the present embodiment uses the image sensor 14 to detect the angular relationship between the return light from the sample 16 and the reference light LR reflected by the plane reflection mirror 12. Other light detection elements such as sensors and split photometry elements may be used.

  Further, for example, instead of the image sensor 14, as shown in FIG. 7, a detection optical system including a combination of an imaging optical system 141, a slit plate 142, and a light detection element 143 may be used. In this detection optical system, the reference light LR reflected by the plane reflection mirror 12 enters the imaging optical system 141 via the beam splitter 11, and is condensed near the slit of the slit plate 142 by the imaging optical system 141. To do. Then, after passing through the slit, it enters the light detection element 143.

  Here, the slits of the slit plate 142 face the vertical direction (note that the vertical direction is a direction perpendicular to the plane on which the optical path of the measurement light LM is formed). The lateral position of the slit plate 142 is adjusted in advance before measuring the refractive index and dispersion so that the slit is disposed at the condensing point of the imaging optical system 141. During this adjustment, the shutter 13 is opened and the sample 16 is removed from the table 15a. When the adjustment is completed, the shutter 13 is closed.

  Therefore, the light detection element 143 of this optical system has a constant intensity only when the lateral deviation on the slit plate 142 between the return light from the sample 16 and the reference light LR reflected by the plane reflection mirror 12 becomes zero. Output a signal. When this optical system is used, the object searched by the control unit is the rotational position of the table 15a when the lateral deviation becomes zero.

FIG. 1 is a schematic configuration diagram of a refractive index / dispersion measuring apparatus. FIG. 2 is an operation flow of the control unit relating to the measurement of refractive index / dispersion. FIG. 3 is a diagram illustrating the state of the sample 16 at the start of the flow. FIG. 4 is a diagram illustrating an example of the θ-I curve. FIG. 5 is a diagram for explaining the rotational positions θ _A , θ _B , θ _C , and θ _D. FIG. 6 shows a state when the rotational position θ of the sample 16 is at the minimum declination position. FIG. 7 is an example of an optical system that detects the presence or absence of an angle shift between the return light from the sample 16 and the reference light LR.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 6 ... Light source, 5 ... Light source switching mechanism, 7 ... Wavelength selection plate, 17 ... Selection wavelength switching mechanism, 8 ... Pinhole plate, 9 ... Collimator mirror, 10 ... Aperture, 11 ... Beam splitter, 14 ... Image sensor, 12 ... Planar reflection mirror, 13 ... Shutter, 15 ... Stage, 15a ... Table

Claims (4)

A projection optical system for projecting measurement light onto a prism-shaped measurement object;
A turntable for changing an arrangement angle of the measurement object with respect to the measurement light;
A refractive index measurement method using a detection optical system that detects an angular relationship between return light returning from the measurement object and the measurement light,
The rotation so that the measurement light is projected onto one slope of the measurement object, and the angular deviation between the return light reflected by the back surface on the other slope after passing through the slope and the measurement light becomes zero A procedure for detecting the rotational position θ _{1 of the} table;
The rotation position θ ₂ of the turntable is set so that the measurement light is projected onto the one slope of the measurement object, and the angular deviation between the return light reflected on the slope and the measurement light is zero. Steps to detect,
The rotation position θ ₃ of the turntable is set so that the measurement light is projected onto the other slope of the measurement object, and the angular deviation between the return light reflected on the slope and the measurement light is zero. Steps to detect,
And a procedure of calculating a refractive index n of the object to be measured based on the following equation the rotational position theta ₁ and the rotational position theta ₂ and the rotational position theta ₃

A method for measuring a refractive index. Dispersion measurement method characterized by utilizing the refractive index measuring method according to claim 1. A projection optical system for projecting measurement light onto a prism-shaped measurement object;
A turntable for changing an arrangement angle of the measurement object with respect to the measurement light;
A detection optical system for detecting an angular relationship between the return light returning from the measurement object and the measurement light;
Control means for controlling the projection optical system, the turntable, and the detection optical system,
The control means includes
The rotation so that the measurement light is projected onto one slope of the measurement object, and the angular deviation between the return light reflected by the back surface on the other slope after passing through the slope and the measurement light becomes zero Means for detecting the rotational position θ _{1 of the} table;
The rotation position θ ₂ of the turntable is set so that the measurement light is projected onto the one slope of the measurement object, and the angular deviation between the return light reflected on the slope and the measurement light is zero. Means for detecting;
The rotation position θ ₃ of the turntable is set so that the measurement light is projected onto the other slope of the measurement object, and the angular deviation between the return light reflected on the slope and the measurement light is zero. Means for detecting;
And means for calculating the refractive index n of the object to be measured based on the following equation the rotational position theta ₁ and the rotational position theta ₂ and the rotational position theta ₃

A refractive index measuring apparatus characterized by the above. A dispersion measuring apparatus comprising the refractive index measuring apparatus according to claim 3 .

Images