JP2012052997A - Optical measurement method and optical measurement device for measuring apparent refraction factor of rough surface of solid body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical measurement method and optical measurement device capable of measuring an apparent refraction factor of a rough surface of a solid body.SOLUTION: The optical measurement device includes a light radiation unit (a light source 10 and a polarizer 20) for making p-polarized light in which electric field component of linear polarization vibrates in an incidence plane incident on the rough surface 32 of a sample 30, a light detection unit 40 for detecting light intensity of reflection light reflected on the rough surface 32 of the sample 30 according to the principle of reflection, a rotation driving unit for changing an incidence angle φ of the linear polarization light by rotating the sample 30, and a calculation processing unit 72 for calculating the apparent refraction index nof the rough surface 32 of the sample 30 based on an incidence angle φwhere the intensity of the reflection light is minimum and a refractive factor nof a gas being contact with the rough surface 32 of the sample 30.

Description

  The present invention relates to an optical measurement method and an optical measurement apparatus for measuring an apparent refractive index of a solid rough surface.

  Conventionally, as a typical refractive index measurement method, a minimum deviation method, a critical angle method, an ellipsometry (an ellipsometry), an immersion method, and the like are known. The minimum deviation method (see Non-Patent Document 1) is a method for obtaining the refractive index by measuring the apex angle and the minimum deviation angle of a sample processed into a prism, and can measure the refractive index most precisely. The critical angle method (see Non-Patent Document 2) is suitable for measuring the refractive index of a liquid. The refractive index of the sample liquid is obtained as a relative value with respect to the reference prism. Ellipsometry (see Non-Patent Document 3) is a method in which p-polarized light and s-polarized light are incident on a sample thin film on a substrate having a known refractive index, and the thickness, refractive index, and extinction of the thin film are determined from changes in the polarization state due to reflection. This is a method for obtaining a coefficient. The immersion method (see Non-Patent Document 4) uses a powdered sample and a large number of transparent liquids whose refractive index changes stepwise, and mixes the powder sample with these liquids to produce a liquid that is most difficult to see the outline of the sample. This is a method for obtaining the refractive index by selecting. In this method, the refractive index can be measured without mirror-treating the sample.

Everitt Charles, "Refraction." The Encyclopedia Britannica, 11th Ed. Vol. 23, The Encyclopedia Britannica Company, New York (1911) 26-27. Tilton, Leroy W., and John K. Taylor, "Refractive Index Measurement," in Physical Methods in Chemical Analysis Vol. 1, 2nd ed .; Walter G. Berl, editor (1961) 411-62. (E ABBE, " Carl's Repertorium der Physik ", Vol. 15, 643 (1879). C. PULFRICH," Zeitschrift fuer Instrumentenkunde ", Vol. 18, 107 (1898)) Hiroyuki Fujiwara, Spectroscopic Ellipsometry, Maruzen Co., Ltd. 2003, 7-124. Miyakonojo Akiho, Hisagi Ikuo, “Iwagaku I”, Kyoritsu Shuppan 2000, pp.90-93.

  The apparent refractive index of a solid rough surface is determined by the refractive index of the solid and the gas surrounding it, and is the refractive index actually felt when light incident on the rough surface is reflected by the rough surface. is there. The apparent refractive index is used in various fields such as image quality evaluation, spectral image processing, computer graphics, and quantitative evaluation of cosmetics because it is connected to human sensitivity such as material texture and gloss.

  Since the sample is processed into a prism, the minimum deviation method is not suitable for measuring the apparent refractive index of a rough surface, which is premised on nondestructive measurement. The critical angle method is a refractive index measurement method suitable for measuring the refractive index of a transparent liquid, and the apparent refractive index of a rough solid cannot be measured as in the minimum deflection angle method. Ellipsometry is suitable for measuring a solid or transparent liquid whose surface has been flattened by optical polishing or vapor deposition, and is not suitable for measuring the apparent refractive index of a rough solid, on which nondestructive measurement is a prerequisite. Furthermore, in the immersion method, a finely pulverized powder is immersed in a liquid with a clear refractive index, and the refractive index of the sample is known by observing the contour of the powder. This method is also premised on nondestructive measurement. This is not suitable for measuring the apparent refractive index of a rough solid.

  The present invention has been made in view of the problems as described above, and the object of the present invention is to measure the apparent refractive index of the solid rough surface without applying any processing to the solid rough surface. It is an object of the present invention to provide an optical measurement method and an optical measurement apparatus.

(1) The present invention relates to an optical measurement method for measuring an apparent refractive index of a solid rough surface.
P-polarized light whose electric field component of linearly polarized light vibrates in the incident plane is incident on the solid rough surface at an incident angle φ ₁ ;
Finding the incident angle φ _{min at} which the intensity of the reflected light reflected at the reflection angle φ ₁ from the solid rough surface according to the law of reflection is minimized,
The apparent refractive index n _cs of the solid rough surface is obtained based on the incident angle φ _min and the refractive index n _{s of the} gas in contact with the solid rough surface.

  Here, the refractive index actually felt when light incident on the solid rough surface is reflected or refracted on the rough surface is referred to as an apparent refractive index. The apparent refractive index is determined from the refractive index of the solid, the refractive index of the atmosphere surrounding it, and the uneven state of the rough surface, unlike the original refractive index of the solid. Of the return light from the interface between two media having different refractive indexes, the light that follows the law of reflection is called reflected light, and the other return light is called scattered light. In addition, among the light transmitted through the interface between two media having different refractive indexes, light complying with Snell's law is called transmitted light, and the other light is called scattered light. Furthermore, the ratio of the electric field of incident light and the electric field of reflected light is defined as electric field reflectance, and the ratio of incident light power and reflected light power is defined as power reflectance.

  According to the present invention, the apparent refractive index of a solid rough surface can be measured nondestructively.

(2) In the present invention,
The apparent refractive index n _cs of the rough surface may be obtained based on

(3) In the present invention,
Based on the refractive index n _m of the refractive index n _cs and the solid apparent the rough surface, the volume ratio of the solid and gas in the mixed layer when the rough surface of the solid was considered a mixed layer of a solid and a gas γ may be obtained.

  According to the present invention, the volume ratio γ can be measured when the refractive index of the solid is known.

(4) In the present invention,
When the volume ratio of the solid volume V _m to the gas volume V _{s in} the mixed layer is γ = V _s / V _m ,
The refractive index n _m of the refractive index n _cs and the solid apparent the rough surface,
Represented by

The volume ratio γ may be obtained based on the above.

(5) The present invention provides an optical measurement apparatus for measuring the apparent refractive index of a solid rough surface.
A light irradiator that causes p-polarized light whose electric field component of linearly polarized light vibrates in an incident plane to be incident on the solid rough surface at an incident angle φ ₁ ;
A light detection unit for detecting the intensity of the reflected light reflected at a reflection angle φ ₁ according to the law of reflection from the solid rough surface;
A rotation drive unit that changes the incident angle φ ₁ of the p-polarized light by rotating the solid;
The apparent refractive index n _cs of the solid rough surface is calculated based on the incident angle φ _{min at} which the intensity of the reflected light is minimized and the refractive index n _{s of the} gas in contact with the solid rough surface. And an arithmetic processing unit that performs arithmetic processing.

  According to the present invention, the apparent refractive index of a solid rough surface can be measured nondestructively.

The figure which shows typically the mode of reflection and scattering of the light in the solid surface. The figure which shows the model which considered the solid rough surface as the mixed layer of a solid and gas. The figure which shows the relationship between the incident angle (phi) _min where the intensity | strength of the reflected light from a rough surface becomes the minimum, and the scattering coefficient (alpha) of a mixed layer. The figure which shows an example of a structure of the optical measuring device of this embodiment. The side view which shows an example of a structure of the 1st rotation mechanism which rotates a sample stand, and the 2nd rotation mechanism which rotates a photodetector stand. The figure which shows the modification of an optical measuring device. The figure which shows the modification of an optical measuring device. The figure which shows the modification of an optical measuring device. 9A is an image obtained by imaging the reflected light reflected by the light rough surface, and FIG. 9B is an image obtained by imaging the reflected light reflected by the heavy rough surface. The figure for demonstrating the initial setting which determines the angle of incident light and a sample surface. The figure for demonstrating the initial setting which determines the angle of incident light and a sample surface. Figure 12 (A) is a diagram showing the relationship between the power reflectivity R _p of mild rough surface of the LiTaO ₃ crystal and the incident angle phi _1, FIG. 12 (B) is the power of severe rough surface of the LiTaO ₃ crystal It is a figure which shows the relationship between reflectance _Rp and incident angle (phi) ₁ .

  Hereinafter, this embodiment will be described. In addition, this embodiment demonstrated below does not unduly limit the content of this invention described in the claim. In addition, all the configurations described in the present embodiment are not necessarily essential configuration requirements of the present invention.

1. Measurement Principle The measurement principle employed by the optical measurement method and the optical measurement apparatus according to this embodiment will be described.

1-1. Measurement of Apparent Refractive Index of Solid Rough Surface FIG. 1A schematically shows how light is reflected and scattered on a solid surface having a rough surface. As shown in FIG. 1, the surface of frosted glass or as-cut crystal is a rough surface having fine irregularities, and has a structure in which a solid and a gas (for example, air) surrounding it are intricately complicated. Yes. When the fine portion of the rough surface structure is smaller than the wavelength of incident light, the solid rough surface is regarded as a mixed layer of solid and gas, as shown in FIG. Can do. This mixed layer exists, for example, between the upper surface and the lower surface when the surface that is in contact with the highest portion of the rough surface is the upper surface and the surface that is in contact with the lowest portion of the rough surface and is parallel to the upper surface is the lower surface. It is a layer which makes the solid (solid which comprises a rough surface) and gas (gas which is in contact with the rough surface) to constitute.

  In this embodiment, the apparent refractive index of the solid rough surface and the volume ratio of the solid to the atmosphere in the mixed layer are measured using a model in which the solid rough surface is regarded as a mixed layer of solid and gas.

As shown in FIG. 2, the angle of incidence of p-polarized light incident on the mixed layer (rough surface of the solid) and phi _1, the refraction angle of the mixed layer and phi _2, the refraction angle of the solid and phi _3, the mixed layer Assuming that the scattering coefficient and the thickness are α and d, respectively, the power reflectivity R _p φ ₁ of the mixed layer with respect to p-polarized incident light is expressed by the following equation.

In equation (1), r ₁ is the amplitude reflectivity (reflectance of the electric field of light) due to Fresnel reflection when light enters the mixed layer from the gas, and r ₂ is the light at the boundary between the mixed layer and the solid. Is the amplitude reflectivity due to Fresnel reflection, and is expressed by the following equations, respectively.

Here, n _s is the refractive index of the gas, n _cs is the apparent refractive index of the mixed layer, and n _m is the refractive index of the solid.

  In Expression (1), L is a physical optical path length when light makes one round trip through the mixed layer, and Ψ is a phase difference between adjacent reflected lights, each represented by the following expression: . Where λ is the wavelength of the incident light.

Here, when the product αL of the scattering coefficient α and the optical path length L in the mixed layer is very small, not only the reflected light on the surface of the mixed layer (light ray 100 shown in FIG. 2) but also the reflection from the inside of the mixed layer according to the law of reflection. Since the presence of reflected light that cannot be ignored is also negligible, the power reflectivity R _p φ ₁ of the reflected light shows a periodic change with the change of φ ₁ according to the equation (1). On the other hand, when the αL is very large, the light incident on the mixed layer is scattered in various directions, and the reflected light from the inside of the mixed layer becomes extremely small. At this time, the reflected light of the mixed layer surface (ray 100 shown in FIG. 2) is, thus dominating the power reflectivity R _p phi ₁ of the reflected light from the mixed layer, the power reflectivity R _p of the reflected light,

It becomes.

Here, the scattered light is radiated in all directions as shown in FIG. 1, whereas the reflected light uses the optical system shown in FIGS. 6 to 10 described later in order to maintain the same reflection angle as the incident angle. For example, most of the scattered light can be blocked and the reflected light can be selectively extracted. If the main component of the light incident on the photodetector 40 shown in FIGS. 6 to 10 is reflected light, the apparent refractive index n _{cs of the} mixed layer (that is, the rough surface) is obtained using Brewster's law. Can be requested.

When the Brewster angle at the interface between the mixed layer and the gas and phi _B, the refractive index n _cs of the mixed layer can be expressed by the following equation.

At this time, since r ₁ = 0 by Brewster's law, the power reflectivity R _p φ _{B at} the Brewster angle φ _B is expressed by the following equation from the equation (1).

In order to find a condition for satisfying the equation (8), the equations (2) to (5) are substituted into the equation (1) to obtain a partial derivative ∂R _p φ ₁ ) / φ ₁ related to the variable φ ₁ , which is zero. Find the angle of incidence when Here, the solid refractive index n _m = 2.5, the gas refractive index n _s = 1, the mixed layer refractive index n _cs = 1.6 to 2.4, and the mixed layer thickness d = 1000 nm. And the calculation was performed under the condition that the wavelength λ of the incident light of p-polarized light was 632.8 nm.

FIG. 3 is a diagram showing an analysis result showing a relationship between the incident angle φ _{min at} which the power reflectivity R _p φ ₁ is the minimum value and the scattering coefficient α of the mixed layer. FIG. 3 shows that the incident angle φ _min becomes a constant value when αd> 2. Table 1 shows the results of calculating the incident angle φ _min by changing the refractive index n _cs of the mixed layer in the range of 1.6 to 2.4.

The incident angle φ _min shown in Table 1 is in agreement with the Brewster angle φ _B expressed by the equation (7). The analysis results in FIG. 3 and Table 1 are examples, and even if n _s , n _cs , n _m , d, and λ are changed, φ _min = φ _B is established as long as the mixed layer satisfies the condition of αd> 2. To do. Therefore, it is clear from this analysis that the refractive index n _cs of the mixed layer satisfying αd> 2 is obtained by the following equation.

Therefore, p-polarized light is incident on a solid rough surface in contact with gas, and the incident angle φ _{min at} which the intensity of reflected light reflected by the rough surface (or power reflectivity R _p φ ₁ ) is minimized is measured. By substituting the measured incident angle φ _min and the refractive index n _{s of the} gas into the equation (9), the refractive index n _cs of the mixed layer when the rough surface of the solid is regarded as a mixed layer of the solid and the gas ( That is, the apparent refractive index of the solid rough surface can be obtained.

  Thus, according to the present embodiment, the apparent refractive index of the rough surface can be measured nondestructively by regarding the solid rough surface as a mixed layer of gas and solid.

1-2. Measurement of volume ratio of solid to gas in mixed layer Next, the principle of measuring the volume ratio γ of solid to gas in the mixed layer satisfying αd> 2 will be described.

If the density of the solid is ρ _m , the density of the gas is ρ _s, and the density of the mixed layer is ρ _cs , the Lorentz-Lorentz (Lorentz-) From the Lorenz formula, the following relationship is established:

  Here, β is the weight (%) of the gas in the mixed layer.

It is also clear that the following equation holds, where V _m is the solid volume in the mixed layer, V _s is the volume of gas in the mixed layer, and V _cs is the volume of the mixed layer.

  From the equations (11) to (13), the following equation is obtained.

Here, as already defined, γ is a ratio of the volume V _m of the solid and the volume V _s of the gas in the mixed layer.

  Rewriting equation (13),

And rewriting equation (12),

It becomes. Substituting equation (17) into equation (16) yields:

  Substituting equation (14) into equation (18) yields:

Here, the functions f _m , f _s , f _cs of the refractive index n _m of the solid, the refractive index n _{s of the} gas, and the refractive index n _cs of the mixed layer are expressed as _follows :

And substituting Expression (20) and Expression (14) into Expression (10), the following expression is obtained.

  Substituting equation (19) into equation (21) yields:

Thus, solid refractive index _{n m} (i.e., the function of the _{n m f m)} and a gas having a refractive index _{n s} (i.e., _{n s} function _{f s)} of the case is obvious, refraction measurements in a mixed layer By substituting the rate n _cs (that is, the function f _{cs of} n _cs ) into the equation (22), the volume ratio γ of the solid and the gas in the mixed layer can be obtained.

That is, by substituting the refractive index n _cs (that is, the apparent refractive index of the solid rough surface) of the mixed layer obtained by the equation (9) into the equation (20), f _cs is obtained, and the obtained f _cs and By substituting f _m and f _s into equation (22), the volume ratio γ of the solid and gas in the mixed layer when the solid rough surface is regarded as a mixed layer of solid and gas can be obtained.

Here, the refractive index n _s of the gas atmosphere is approximately 1 (for example, if air, n _s = 1.000292 under the conditions of 0 ° C. and 1 atm), the function f _{s of the} refractive index n _s is obtained from the equation (20). Will be approximately zero. Therefore, the solid / gas volume ratio γ in the mixed layer may be obtained by substituting f _cs and f _m into the following equation.

  As described above, according to the present embodiment, when the refractive index of the solid is clear, the ratio γ of the volume of the solid constituting the mixed layer and the volume of the gas can be measured from the apparent refractive index of the rough surface. it can. By measuring the volume ratio γ of the mixed layer, it is possible to quantitatively evaluate the unevenness of the rough surface.

2. Configuration FIG. 4 is a diagram illustrating an example of the configuration of the optical measurement apparatus of the present embodiment.

The optical measuring device 1 of the present embodiment is a device that measures the apparent refractive index n _cs of the rough surface 32 of the sample 30 (solid having a rough surface) to be measured, and the volume ratio γ of the solid and gas in the mixed layer. It is. The optical measuring device 1 includes a light source 10 composed of a laser diode, a beam splitter 12, an aperture 14 having a circular aperture, a polarizer 20 and an analyzer 22 that transmit p-polarized light, and a photoelectric sensor (photo detector). First and second photodetectors 40 and 42, a chopper 50 for chopping continuous light, a chopper controller 52, a lock-in amplifier 54, a sample stage 60 on which the sample 30 is placed, and a first light A photodetector stage 62 on which the detector 40 is placed, a first rotation mechanism (not shown) for rotating the sample stage 60 around the rotation axis RA, and a photodetector stage 62 around the rotation axis RA. A second rotation mechanism (not shown) that rotates the first rotation mechanism, and an arithmetic unit 70. The rotation axis RA is parallel to the Z axis, exists in or near the rough surface 32 of the sample 30, and is orthogonal to the normal 33 of the rough surface 32.

  The light emitted from the light source 10 passes through the polarizer 20 and becomes p-polarized light that vibrates in a horizontal plane (a plane including the X axis and the Y axis in FIG. 4). That is, the p-polarized electric field vibrates on a horizontal plane including the normal line 33 of the rough surface 32 of the sample 30. The p-polarized light is pulse-modulated by the chopper 50 and is incident on the rough surface 32 of the sample 30. The intersection of the incident light and the reflected light is preferably coincident with the rotation axis RA or at least near the rotation axis RA.

  The p-polarized light reflected by the rough surface 32 travels in the direction of the reflection angle φ equal to the incident angle φ as shown in FIG. On the other hand, scattered light is radiated in all directions from the intersection of incident light and reflected light. In order to measure the intensity of the reflected light and scattered light, an aperture 14, an analyzer 22 and a first light detector 40 having an opening having substantially the same diameter as the beam diameter of the incident light are installed on the light detector table 62. ing.

  The first photodetector 40 (light detector) receives the reflected light and scattered light reflected by the rough surface 32 as the photodetector base 62 rotates, and converts the intensity of the received light into a current or voltage ( Photoelectrically converted) and output to the lock-in amplifier 54 as light intensity information (detection signal).

  The chopper controller 52 outputs a control signal (drive signal) to the chopper 50 to control the drive of the chopper 50 and outputs the control signal to the lock-in amplifier 54 as a reference signal. The lock-in amplifier 54 detects a frequency component equal to the reference signal output from the chopper control unit 52 among the detection signals output from the first photodetector 40, and outputs the detected frequency component to the arithmetic device 70. By using the chopper 50, the chopper controller 52, and the lock-in amplifier 54, the measurement accuracy can be improved.

  The beam splitter 12 reflects a part of the light emitted from the light source 10. The second photodetector 42 receives the light reflected by the beam splitter 12, performs photoelectric conversion, and outputs a detection signal to the arithmetic device 70. The light detected by the first photodetector 40 due to the fluctuation of the emitted light intensity by detecting the fluctuation of the emitted light intensity from the light source 10 using the beam splitter 12 and the second photodetector 42. Variations in intensity can be compensated for and measurement accuracy can be improved.

  Although an example using a semiconductor laser as a light source is shown here, a gas laser, a dye laser, or a solid-state laser can be used instead of the semiconductor laser. A so-called incoherent light source such as a halogen lamp or a xenon lamp can also be used. However, since incoherent light generally has a very wide emission spectrum, it is necessary to insert an optical bandpass filter that narrows the spectrum between the light source 10 and the beam splitter 12.

  FIG. 5A is a side view showing an example of the configuration of the first rotation mechanism 61 that rotates the sample stage 60 and the second rotation mechanism 63 that rotates the photodetector stage 62.

  As shown in FIG. 5A, the sample stage 60 includes a first rotation mechanism 61 that rotates the sample stage 60, an tilt mechanism 64 (gonio) that adjusts the tilt angle of the sample stage 60, and the sample stage 60 as XYZ. It is provided on an XYZ moving mechanism 65 that moves in the axial direction. The XYZ moving mechanism 65 is supported by a first support pole 67.

  The photodetector base 62 is attached to a second rotation mechanism 63 that rotates the photodetector base 62. The photodetector base 62 includes a support pole (not shown) that supports the aperture 14, a second support pole 68 that supports the analyzer 22, and a vertical movement mechanism that vertically moves the first photodetector 40. 66 is provided, and the vertical movement mechanism 66 is provided with a third support pole 69 that supports the first photodetector 40. The first and second rotation mechanisms 61 and 63 can be configured by a manual rotation stage, an automatic rotation stage, or the like.

  The rotation axes RA of the first rotation mechanism 61 and the second rotation mechanism 63 coincide with each other, and the rotation axis RA coincides with the center of the circular sample stage 60. The sample stage 60 is rotated around the rotation axis RA by the first rotation mechanism 61, and the photodetector stage 62, the aperture 14, the analyzer 22, and the first photodetector 40 are rotated by the second rotation mechanism 63. It rotates around the rotation axis RA.

As described above, in this embodiment, the incident angle φ _min (or the incident angle φ _i ) that minimizes the intensity of the reflected light reflected by the rough surface of the sample 30 is obtained. Therefore, by rotating the sample stage 60 by the first rotating mechanism 61, the incident angle φ of p-polarized light (see FIG. 4) is changed, and the second rotating mechanism is changed according to the change of the incident angle φ of p-polarized light. By rotating the photodetector table 62 by 63, the reflected light reflected by the rough surface 32 of the sample 30 enters the first photodetector 40 via the aperture 14 and the analyzer 22. .

  FIG. 5B is a top view and a side view of the sample stage 60. As shown in FIG. 5B, the circular sample stage 60 shows a point indicating the rotation axis RA and a straight line passing therethrough. The sample 30 is placed so that the surface of the straight line and the rough surface 32 are flush with each other (illustration of devices necessary for installation is omitted).

Referring to FIG. 4 again, the arithmetic device 70 includes an arithmetic processing unit 72 and a storage unit 74. Based on the light intensity information output from the lock-in amplifier 60, the arithmetic processing unit 72 obtains the incident angle φ _min of p-polarized light that minimizes the intensity of the reflected light reflected by the rough surface 32 of the sample 30. Based on φ _min and the refractive index n _{s of the} gas atmosphere, a calculation process for calculating the apparent refractive index n _cs of the rough surface of the sample 30 is performed. Further, the arithmetic processing unit 72, based on the refractive index n _m of the refractive index n _cs and sample 30 the apparent rough surface 32 of the sample 30, the rough surface 32 of the sample 30 was considered a mixed layer of a solid and a gas The calculation process which calculates the volume ratio (gamma) of the solid and gas in the said mixed layer at the time is performed.

  When the optical measurement device 1 does not include the chopper 50, the chopper control unit 52, and the lock-in amplifier 54, the arithmetic processing unit 72 is based on the light intensity information output from the first photodetector 40. Perform arithmetic processing.

  The storage unit 74 has a function of temporarily storing various data, and stores, for example, light intensity information output from the lock-in amplifier 60 in association with the incident angle φ of p-polarized light.

  6-8 is a figure which shows the modification of the optical measuring device 1. As shown in FIG.

  In the optical measuring device 1 shown in FIG. 6, the convex lens 16 is provided between the sample stage 60 and the aperture 14. Here, the distance between the convex lens 16 and the aperture 14 coincides with the focal length f of the convex lens 16. Therefore, the reflected light from the sample 30 that is parallel light passes through the opening of the aperture 14 and enters the first photodetector 40. On the other hand, the distance a between the sample 30 and the convex lens 16 is equal to or shorter than the focal length f of the convex lens 16, and scattered light from the sample 30 is blocked by the aperture 14. Further, according to the configuration shown in FIG. 6, the length in the direction along the optical path of the photodetector base 62 can be shortened as compared with the configuration shown in FIG. 4.

  In the optical measurement apparatus 1 shown in FIG. 7, a beam expander 18 is provided between the light source 10 and the sample stage 60 to increase the beam diameter of the p-polarized light emitted from the light source 10. By increasing the beam diameter of the p-polarized light incident on the sample 30, the reflected light from the sample 30 that is parallel light is condensed into a smaller spot by the convex lens 16, and therefore compared with the configuration shown in FIG. The aperture of the aperture 14 can be made smaller, and the influence of scattered light from the sample 30 can be made smaller.

  In the optical measuring apparatus 1 shown in FIG. 8, an optical modulator 51 (for example, a photoelastic modulator) is provided instead of the chopper 50, and a signal generator 53 and an amplifier 55 are used instead of the chopper controller 52. . By using the optical modulator 51, the intensity of light emitted from the light source 10 can be changed not only to a rectangular wave shape but also to a sine wave shape, and the modulation frequency can be freely selected from a low frequency to a high frequency. Can do.

3. Measurement Method Prior to measurement, initial setting is performed to determine the angle between the incident light and the sample surface (rough surface 32 of the sample 30).

  When the sample 30 has a light rough surface, as shown in FIG. 9A, the presence of reflected light (a bright portion near the center of the image shown in FIG. 9A) mixed with scattered light is recognized. It is done. In this case, the optical axis of the incident light and the normal of the sample surface can be matched by a very general method shown in FIG. That is, an aperture having an opening that substantially matches the diameter of the laser beam is provided between the light source 10 and the sample 30, and the angle of the sample stage 60 may be adjusted so that the reflected light from the sample 30 passes through this opening. If this state is set to 0 degree and the sample stage 60 is rotated about the rotation axis RA by the angle φ as shown in FIG. 10B, φ becomes the incident angle. At this time, if the photodetector base 62 is rotated about the rotation axis RA so that the reflected light from the sample 30 enters the first photodetector 40 via the aperture 14 and the analyzer 22, the incident light is incident. The intensity of the reflected light from the sample 30 in the case of the angle φ can be measured.

  Further, when the sample 30 has a severe rough surface, as shown in FIG. 9B, the scattered light and the reflected light cannot be distinguished with the naked eye. In this case, as shown in FIG. 11, convex lenses 101 and 102 are provided between the aperture and the sample 30, and between the beam splitter and the second photodetector 42, respectively, and the reflected light from the sample 30 is converted into a convex lens. The light is reflected by the beam splitter via 101 and the reflected light from the beam splitter is incident on the second photodetector 42 via another convex lens 102. By adjusting the angle of the sample stage 60 so that the light intensity detected by the second photodetector 42 is maximized, the optical axis of the incident light and the normal line of the sample surface can be matched.

When the above initial setting is completed, the initial setting aperture and convex lens are removed from the optical path, and measurement is performed. In other words, the incident angle φ of the p-polarized light is changed by rotating the sample stage 60, and the light detector stage 62 is rotated to reflect the light reflected by the rough surface 32 of the sample 30 by the first photodetector 40. measuring the intensity _{I R} of light. At this time, the intensity I _{i of} the light emitted from the light source 10 is also measured by the second photodetector 42, and a normalized power reflectance R _p of the following equation is calculated.

The reflected light intensity divided by the incident light intensity, it is possible to cancel the variation of the incident light intensity, it is possible to improve the measurement accuracy of the power reflectivity R _p. Then, the incident angle φ _min of the p-polarized light that minimizes the power reflectivity R _p is obtained, and the apparent refractive index n _cs (refractive index of the mixed layer) of the rough surface 32 of the sample 30 is calculated based on the incident angle φ _min. .

4). Measurement Results FIG. 12A, FIG. 12B, and Table 2 show the measurement results of the optical measurement apparatus and the optical measurement method of this embodiment. Here, in the optical measuring apparatus 1 shown in FIG. 4, measurement was performed using an as-cut LiTaO ₃ crystal (LT crystal) as a sample and a 632.8 nm wavelength He—Ne laser as a light source.

FIG. 12 (A) shows the relationship between the power reflectance R _p and incidence angle phi ₁ of LT crystals with mild rough surface, FIG. 12 (B) is the power reflection of the LT crystal having a severe rough surface The relationship between the rate R _p and the incident angle φ ₁ is shown. Based on the incident angle φ _min obtained from these measurement results, the apparent refractive index n _cs (rough surface of the rough surface) is obtained for each of the LT crystal having a light rough surface and the LT crystal having a heavy rough surface. The refractive index of the mixed layer when regarded as a mixed layer of solid (crystal) and gas (air)), and the volume ratio γ of solid and air in the mixed layer were determined. The measurement results are shown in Table 2.

  The technical scope of the present invention is not limited to the above-described embodiment, and appropriate modifications can be made without departing from the spirit of the present invention.

  It can be used for measuring the apparent refractive index of samples that are not allowed to be processed, such as expensive substances, fossils, and art works, and for quantitative optical evaluation of cosmetics (foundations and powders). Further, since the apparent refractive index of the rough surface can be accurately known, it can be used for analysis of a phone model frequently used in spectral image processing. Since this model is connected to computer graphics (CG) technology, it can contribute to high image quality such as CG images and animations.

DESCRIPTION OF SYMBOLS 10 Light source, 12 Beam splitter, 14 Aperture, 16 Convex lens, 18 Beam expander, 20 Polarizer, 22 Analyzer, 30 Sample, 32 Rough surface, 33 Rough surface normal, 40 1st photodetector, 42 1st 2 photodetectors, 50 choppers, 51 optical modulators, 52 chopper controllers, 53 signal generators, 54 lock-in amplifiers, 55 amplifiers, 60 sample stands, 61 first rotation mechanism, 62 photodetector stands, 63 Second rotation mechanism, 70 arithmetic device, 72 arithmetic processing unit, 74 storage unit, 100 first reflected light from mixed layer, 101 convex lens, 102 convex lens

Claims (5)

In an optical measurement method for measuring the apparent refractive index of a solid rough surface,
P-polarized light whose electric field component of linearly polarized light vibrates in the incident plane is incident on the solid rough surface at an incident angle φ ₁ ;
Finding the incident angle φ _{min at} which the intensity of the reflected light reflected at the reflection angle φ ₁ from the solid rough surface according to the law of reflection is minimized,
An optical measurement method for obtaining an apparent refractive index n _cs of the solid rough surface based on the incident angle φ _min and the refractive index n _{s of the} gas in contact with the solid rough surface. In claim 1,
An optical measurement method for obtaining an apparent refractive index n _cs of the rough surface based on the above. In claim 1 or 2,
Based on the refractive index n _m of the refractive index n _cs and the solid apparent the rough surface, the volume ratio of the solid and gas in the mixed layer when the rough surface of the solid was considered a mixed layer of a solid and a gas An optical measurement method for obtaining γ. In claim 3,
When the volume ratio of the solid volume V _m to the gas volume V _{s in} the mixed layer is γ = V _s / V _m ,
The refractive index n _m of the refractive index n _cs and the solid apparent the rough surface,
Represented by
An optical measurement method for obtaining the volume ratio γ based on the above. In an optical measuring device that measures the apparent refractive index of a solid rough surface,
A light irradiator that causes p-polarized light whose electric field component of linearly polarized light vibrates in an incident plane to be incident on the solid rough surface at an incident angle φ ₁ ;
A light detection unit for detecting the intensity of the reflected light reflected at a reflection angle φ ₁ according to the law of reflection from the solid rough surface;
A rotation drive unit that changes the incident angle φ ₁ of the p-polarized light by rotating the solid;
The apparent refractive index n _cs of the solid rough surface is calculated based on the incident angle φ _{min at} which the intensity of the reflected light is minimized and the refractive index n _{s of the} gas in contact with the solid rough surface. An optical measurement device including an arithmetic processing unit that performs arithmetic processing.