JPH073318Y2 - Sensor head using photoexcited surface plasma vibration resonance - Google Patents

Description

TECHNICAL FIELD The present invention relates to a refractometer for measuring the refractive index of a gas or liquid test object, and more particularly to a refractometer for contacting the test object to be detected. More specifically, the present invention relates to the structure of a sensor head that utilizes surface plasma vibration.

(Prior Art) Contrast with a refractometer that utilizes total internal reflection. Use of total internal reflection,
That is, as the refractometer based on the measurement of the critical angle, those using the Kohllausch method, the Pulfrich refractometer, the Abbe refractometer, and the like have been conventionally known.

The reflection type Abbe refractometer measures the dependence of the reflectance on the incident angle to obtain the refractive index of the test object. FIG. 1 shows a principle diagram of this reflection type Abbe refractometer. In this method, the prism (1) having a known refractive index is brought into contact with the sample (2), and the critical angle at the boundary surface (3) is measured. When the incident angle (5) of the incident light (4) is θ and the reflectance is R, FIG. 2 shows an R-θ curve by Abbe's refractive index obtained by computer simulation. Incident light (4) wavelength is 632.8n
m, the refractive index of the prism (1) is 1.805, and three types of samples A, B, and C with different absorption (refractive index is A: 1.362, B: 1.362 + i0.0
01, C: 1.362 + i0.003) is the result of calculation.

In the case of the sample A having no absorption (curve a), the reflectance sharply increases near the critical angle and reaches 1 at the critical angle θc. Therefore, the critical angle can be determined more strictly than the angle at which the reflectance becomes 1. However, in the case of the samples B and C having absorption (curve b, curve c), the reflectance shows a gentle change near the critical angle. Therefore, when there is absorption, it is impossible to measure the critical angle with the angle at which the reflectance is 1. Therefore, another index is required. If, for example, the angle at which the reflectance is 0.9 is the critical angle as this index, a deviation of 0.10 ° occurs in the case of the curve b as compared with the curve a. This is 0 when converted to the refractive index of the measured sample.
The error is 002. Similarly, for curve c, the critical angle is 0.87.
There is a deviation of 0 °, resulting in an error of 0.0018 in refractive index conversion.

(Problems to be Solved by the Invention) As described above, when the sample has absorption, an error occurs between the obtained refractive index and the true value. There is no ideal substance that has no absorption, and even a transparent substance has a small amount of absorption (since the imaginary part of the refractive index always has a value), the conventional refractometer has a problem in terms of measurement accuracy. There is.

In addition, conventional refractometers and the like are generally used for stationary laboratories, are expensive, and are complicated such as requiring sample extraction.

On the other hand, in fields such as chemical processes, environmental surveys, and medical measurement, in-situ measurement has been desired in recent years, and it is not necessary to perform sample extraction (in sit state).
There is a demand for measurement in u), in-vivo measurement for biological samples, small and lightweight equipment that is convenient to carry, and inexpensive equipment.

An object of the present invention is to provide a sensor head capable of measuring the refractive index with high accuracy and satisfying the above-mentioned demand.

(Means for Achieving the Object) A sensor head according to the present invention has a high refractive index having a surface on which a metal thin film capable of exciting surface plasma vibration resonance by light is brought into contact with a gas or liquid test object. A prism, a point light source, a light flux converging means for converging a light flux from the point light source on the metal thin film adhered surface of the prism at an incident angle of a critical angle or more, and total reflection on the metal thin film adhered surface of the prism. Photoexcited surface plasma including a lens that receives a light flux and Fourier transforms its intensity, a one-dimensional photoelectric element array, a dark box body that supports at least the prism, the light flux converging means, and the lens, and that can keep the inside dark The basic feature is that the sensor head uses vibration resonance.

(Operation) The divergent light flux from the point light source is converged by the light flux converging means and is incident on the metal thin film adhered surface of the prism.
In a metal thin film (solid-state plasma) in contact with an object to be inspected, only the light having a specific incident angle among the incident light having the continuous incident angle correlates with the refractive index of the object to be inspected. Excite surface plasma vibrations in the thin film. Light having another incident angle is totally reflected, and enters the lens for Fourier transform together with the reflected light of the light having the specific incident angle. This lens Fourier transforms this incident light flux to
The light intensity distribution information is given to the three-dimensional photoelectric element array. The one-dimensional optoelectronic array is electronically scanned to provide an angular spectrum.

The refractive index of the test object is detected based on the position of the absorption peak of this angular spectrum, as illustrated in FIG.

Since the absorption peak position of this angle spectrum remains unchanged even if the test object has absorption, the refractive index can be obtained with extremely high accuracy.

In addition, since all the constituent elements can be optical elements or photoelectric elements without having a mechanical section for changing the incident angle and a mechanical scanning section for detection, it is possible to reduce the size and weight. is there.

(Embodiment) FIG. 4 is a vertical sectional view of an embodiment of the present invention.

In Fig. 4, (11) is made of optical glass with a high refractive index.
It is a 45 degree right angle prism. A thin film (12) of silver is applied to one surface (11-1) (referred to as the first surface) of the right-angle prism (11) that crosses the right angle, and the other surface (11-2) (the second surface). The surface) is coated with a relatively thick aluminum film (13).

(14) is a light emitting diode as a point light source. In front of the light emitting diode (14), a polarizer (1
5) is provided.

(16) is a semi-cylindrical cylindrical lens that converges the divergent light flux from the light emitting diode (14) that has passed through the polarizer (15). The transmitted light flux of the polarizer (15) is refracted by this cylindrical lens (16), and the right angle prism (1
It is reflected by the aluminum mirror surface formed on the second surface (11-2) of (1), and the first surface (11-1) of the rectangular prism (11) and the silver thin film (1
2) It converges on the interface with. The first surface (11-1) of the rectangular prism (11) coated with the silver thin film (12) forms a sensing surface for contacting a gas or liquid test object.

Reference numeral (17) is a semi-cylindrical cylindrical lens that receives the light beam totally reflected by the first surface (11-1) of the rectangular prism (11) and Fourier transforms the intensity of the light beam. The mounting position of the light emitting diode (14) is selected so that all the converged light beams are totally reflected by the first surface (11-1) of the rectangular prism (11).

The light flux emitted from the cylindrical lens (17) passes through an analyzer (18) that extracts only P-polarized light, and its light-receiving surface is aligned with the rear focal plane of the cylindrical lens (17).
The light is received by the three-dimensional image sensor (19).

The rectangular prism (11), the light emitting diode, the polarizer (15), the cylindrical lenses (16) and (17), the analyzer (18), and the one-dimensional image sensor (19) are in a cylindrical dark box (20). It is supported and fixed in place. The dark box body (20) blocks outside light and keeps the inside dark. In addition, the second surface (11
-2) does not allow external light to enter, but a semi-transparent silver thin film (1
External light may enter from the first surface (11-1), which is the sensing surface of 2), but the one-dimensional image sensor (19)
Then, only the totally reflected light on this surface is received, and the light entering from the sensing surface is not detected by the one-dimensional image sensor (19), and no error occurs in the output.

In the embodiment shown in FIG. 4, a cylindrical lens (16)
And the cylindrical lens (17) are both attached to the third surface (11-3) of the rectangular prism (11).
For example, it is attached using matching oil. A sheet-shaped polarizer (15) is also attached to the front surface of the light emitting diode. In addition, the analyzer (1
8) is also a sheet-shaped one-dimensional image sensor (1
It is attached to the front of the light-receiving surface of 9). In this way, the sensor element has four basic constituent elements, namely, a dark box body, a light emitting portion, a light receiving portion, and a rectangular prism portion.
Only one. As long as the dark box body is processed so as to have the assembling accuracy, the remaining three optical members are simply attached to the dark box body. It is extremely easy to make, and no complicated optical system adjustments are required. However, it is of course possible to individually support the related elements on the dark box without integrating them.

In the embodiment shown in FIG. 4, the second surface (11-
The mirror surface formed in 2) is used. By doing so, the optical axis extending from the light emitting diode (14) and the optical axis of the cylindrical lens (17) for Fourier transform can be made parallel. As a result, the dark box body (20), that is, the entire sensor head can be formed into an elongated cylindrical shape. Moreover, since the light flux emitted from the cylindrical lens (17) is directly received by the light receiving surface of the one-dimensional image sensor (19), the height of this sensor head is approximately the width of the one-dimensional image sensor (19). Determined only by the length. Therefore, this height can be at most 20-30 mm.
The depth of the sensor head is also given by the length of the one-dimensional image sensor (19), but since this is no more than 30-40 mm, the depth of the sensor head can be 40-50 mm. . Therefore, this sensor head has a cylindrical shape, and the cross section of the cylindrical shape can be at most 30 × 50 mm,
It is handheld (it can be held with one hand) and lightweight, and it can be easily applied to any target by field use, field process such as opening a detection window in the plant.

In fact, the sensor head having the structure shown in FIG. 4 has a width, height, and length of 50 mm × 30 mm × 150 mm. Right angle prism (1
1) is 15 mm on a side and made of LaSF08 optical glass (n = 1.878)
5). The cylindrical lens (16) has a radius of curvature of 5 mm and is made of BK7 (n = 1.515). The cylindrical lens (17) has a radius of curvature of 58 mm, is made of BK7 (n = 1.515), and has a focal length of 113 mm.

The one-dimensional image sensor (19) is a 2048-element CCD image sensor (TCD102D; manufactured by Toshiba Corporation), and the size of one element is 14 μm × 14 μm, the pitch is 14 μm, and the width of the entire light-receiving portion is 28.7 mm. . The incident angle range that can be measured by the sensor head of this embodiment is 40 ° to 52 °. The resolution of the peak angle measurement is determined by the pitch between the elements of the one-dimensional image sensor and the focal length of the lens (17), which is about 0.007 ° with this sensor head. Converting these into a refractive index, the measurable range is 1.16 to 1.39, and the resolution is 0.0001.

The light emitting diode (14) as a point light source has a peak wavelength of 66.
0nm light emitting diode, TLRA150, manufactured by Toshiba Corporation.
A semiconductor laser (laser diode) may be used instead of the light emitting diode. In this case, the laser light is
Since it is originally polarized, basically,
5) and (18) can be eliminated. However, in order to eliminate adverse effects such as scattered light, it is preferable to provide a polarizer that gives at least one P-polarized light in the optical path. The position to be provided is preferably in the middle between the semiconductor laser and the collimating lens that converges the laser beam. Since the semiconductor laser has a narrow emission spectrum width, it gives a sharp absorption peak.
In this sense, it is a more suitable light source than a light emitting diode.
However, because of high coherence, optical noise such as speckle noise is generated. Therefore, in order to obtain high detection accuracy, a device for reducing this is required.

The silver thin film (12) deposited on the first surface (11-1) of the rectangular prism (11) is formed by vacuum evaporation. The film thickness is about
It is 60 nm. If this film thickness is thinner than this, the absorption peak becomes broad, whereas if it is too thick, the peak drop becomes shallow. This is because the evanescent wave component to the test object is attenuated. Therefore, the film thickness has an optimum value depending on the system to be designed. The metal species of the metal thin film used to excite the surface plasma vibration resonance include gold, platinum, aluminum and the like, in addition to silver as in the examples. However, it has been confirmed that aluminum does not have a sharp absorption peak. This is due to the size of the ratio of the real part and the imaginary part of the complex dielectric constant, and silver has a small imaginary part.

The silver thin film (12) on the first surface (11-1) of the prism forming the sensing surface is exposed to the outside air and the object to be inspected. In particular, silver is easily sulfurized, which causes a problem in terms of durability of the sensor head. Therefore, in the embodiment, a protective film is provided on the silver thin film (12). It is coated with a dielectric (MgF ₂ etc.) with a thickness of about 10 nm. This solves the problem of durability in application to the process.

The aluminum film (13) on the second surface (11-2) of the prism is formed sufficiently thick by vacuum evaporation.

Next, another embodiment will be described. In particular, the arrangement, arrangement, and shape of the optical elements are different from those of the embodiment shown in FIG.

In FIG. 5, the 45 ° right-angle prism (21) is coated with a metal thin film (22) capable of exciting surface plasma vibration resonance on the first surface (21-1) which is the hypotenuse thereof. The converging lens (26) and the Fourier transform lens (27) are attached to the second surface (21-2) and the third surface (21-3) of the prism (21), respectively. The point light source (24), the polarizer (25) that gives P-polarized light, the rectangular prism (21), the polarizer (28) that takes out P-polarized light, and the one-dimensional image sensor (29) are the dark box (3
It is supported by 0).

In the embodiment shown in FIG. 5, the optical axes of the incoming and outgoing luminous fluxes are orthogonal to each other. With this configuration, compared to the one in FIG.
Although the height of the sensor head becomes slightly higher, the length can be shortened accordingly. Further, since only the sensing surface is exposed to the outside, this embodiment is advantageous in terms of liquid shield and maintenance as compared with the embodiment of FIG.

FIG. 6 shows another embodiment. The feature is that a triangular prism (31) having a curved surface (31-2) is used. A metal thin film (32) capable of exciting surface plasma vibration resonance is deposited on the first surface (31-1) of the prism (31). A mirror surface (33) is formed on the second curved surface (32-2) by vacuum evaporation of aluminum, for example. That is, a concave mirror is formed by the curved mirror surface (33), and the divergent light flux from the point light source (34) is reflected by the concave mirror on the first surface (31-).
It is focused on the interface between 1) and the metal thin film (32). The point light source (34), the polarizer (35), the triangular prism (31), the Fourier transform lens (37), the polarizer (38) and the one-dimensional image sensor (39) are supported by the dark box body (40). Has been done.

In the embodiment shown in FIG. 6, in order to converge the divergent light beam from the point light source (34), the converging lens, which is essential in the embodiments shown in FIGS. 4 and 5, is not used. It is converged by the curved mirror surface (33) of the triangular prism. As a result, a more compact structure than that of the previous embodiment is realized, and it also has a price advantage.

The embodiment shown in FIGS. 7, 8 and 9 is the fourth embodiment, respectively.
It is a modification of the embodiment shown in FIGS. 5, 5 and 6. In either case, the point light source and the one-dimensional photoelectric element array are provided outside the dark box. For this reason, an optical fiber for guiding the divergent light beam from the point light source and an optical fiber for receiving the light beam from the Fourier transform lens and guiding the received light beam to the one-dimensional photoelectric element array are coupled to the dark box. .

In the embodiment shown in FIG. 7, the divergent light flux of the point light source (14) is guided by the single mode optical fiber (14l), and the dark box (2
The light is emitted as a divergent light flux from the exit end face (14le) supported at a predetermined position (0). The light flux from the Fourier transform lens (17) is received by the one-sided end face of a fiber bundle (or taper) (19l) having its uniform end face supported by the dark box body (20), and the one-dimensional image sensor ( It is configured to be guided to 19). The embodiment shown in FIGS. 8 and 9 has substantially the same structure as the embodiment shown in FIG.

As described above, the point light sources (14), (24), (34) and the one-dimensional photoelectric element arrays (19), (29), (39) are placed in the dark box (2
0), (30), and (40) are provided outside, the sensor head can be made non-electric, and in an environment where electric sparks fly, an environment with a lot of electromagnetic induction, or an environment with an explosive atmosphere, There is an advantage that they are not directly affected by these influences, and they are not affected, and moreover, stable sensing can be performed.

In the embodiment shown in FIGS. 4 to 9, basically, the lens used is a cylindrical lens. However, when the cylindrical lens is used for focusing or Fourier transform, the lens moves in the vertical direction (vertical direction in the cross-sectional view). The light is still diverging, and it cannot be said that it is using light effectively. Therefore, as an improvement measure, a method is adopted in which an aspherical lens is used instead of the cylindrical lens, and the point light source and the image sensor are in an image forming relationship in the vertical direction. As a result, the use efficiency of light is significantly increased. Particularly, in the embodiments shown in the seventh, eighth and ninth embodiments, since the optical fiber is used, this method using the aspherical lens is extremely effective.

Finally, a measurement example is shown. This is an example in which the sensor head having the configuration shown in FIG. 4 is used. The sensing surface (12) is brought into contact with the liquid. An angular spectrum signal is generated in the one-dimensional image sensor (19). This signal is taken into the computer (60) through the interface (50) by self-scanning based on a predetermined start command. The computer (60) processes the received signal, displays it on the display monitor (70), and causes the plotter (80) to draw it.

The first measurement example is a case where the test object is pure water. The measured reflection spectrum is shown in FIG. The vertical axis represents the reflectance and the horizontal axis represents the incident angle when the plane wave is incident. An absorption peak due to the excitation of surface plasma vibration resonance is seen at 48.72 °. As a result of repeating measurement 9 times for the same pure water,
The standard deviation of peak position measurement was 0.011 °. Converting this result into the precision of the refractive index measurement, it is about 0.0002.

Next, make a test object by mixing a small amount of ethanol with pure water,
The R- [theta] curve was measured for a test object having an alcohol concentration of 0.1% to 10%. The relationship between the peak position of the obtained R-θ curve and the concentration of the test substance is shown in FIG. The horizontal axis is alcohol concentration,
The vertical axis represents the relative value from the angle of the peak for the test object of 0.1%. Using the curve in Fig. 11 as a calibration curve, R-θ
The concentration can be measured from the peak position of the curve.

Third is the measurement of the test object including the scatterer. FIG. 12 is an R-θ curve of the obtained tomato juice. A sharp absorption peak similar to that when pure water is used as a sample is seen. As a result of performing the measurement three times on the same sample, the measured peak positions were the same for all three times. From this result, it can be said that the present sensor head has sufficiently high measurement accuracy even for the test object including the scatterer.

Finally, this sensor head was used to measure a sample with strong absorption. Blue ink was used as a sample. R obtained
The −θ curve is shown in FIG. An absorption peak about twice as wide as that of pure water as a sample is observed. This is because the absorption of the sample increased the attenuation of surface plasmons. Since the absorption peak was blunted, the accuracy of the absorption peak position measurement was reduced by about 1/2 compared to the measurement of a sample with extremely small absorption such as pure water, but this sensor has a strong absorption like blue ink. It has been shown to be extremely useful for measuring objects.

Incidentally, each of the above-mentioned embodiments is intended for a liquid test object, and LaSF08 is used for the prism, but if the material of the prism is appropriately selected, a gas test object or a test object having a large refractive index is used. Measurements are possible as well. For example, when a gas is used as the test object, the absorption peak is 43 ° when a BK7 prism is used.
Appears in the vicinity.

(Effect) As described above, according to the sensor head of the present invention, the refractive index of the test object can be measured with high accuracy, and since it is small and lightweight, it does not require the conventional sample extraction, It has practical effects that can be applied directly to field use and in-process measurement.

[Brief description of drawings]

FIG. 1 is a principle diagram of the Abbe refractometer, FIG. 2 is a graph showing an R-.theta. Curve by the Abbe refractometer, and FIG. 3 is an R according to the principle of the present invention which has the same object as the graph of FIG. FIG. 4 is a vertical sectional view of an embodiment of the present invention, FIG. 5 is a vertical sectional view of another embodiment of the present invention, and FIG. 6 is a longitudinal sectional view of another embodiment of the present invention. Longitudinal sectional views, FIG. 7, FIG. 8 and FIG. 9 are respectively FIG. 4, FIG.
FIG. 11 is a longitudinal sectional view showing still another embodiment corresponding to the embodiment shown in FIG. 6, FIG. 10 is a graph showing the measurement result of pure water performed using the embodiment shown in FIG. FIG. 12 is a graph showing the results of measuring the ethanol concentration of ethanol-mixed water, FIG. 12 is a graph showing the results of measuring tomato juice, and FIG. 13 is a graph showing the results of measuring blue ink. 11,21,31 …… Prism, 14,24,34 …… Light emitting diode as point light source, 16,26 …… Lens, 17,27,37 …… Fourier transform lens, 19,29,39 …… One-dimensional image sensor.

Claims (11)

[Scope of utility model registration request] 1. A high-refractive-index prism having a surface coated with a metal thin film capable of exciting surface plasma vibration resonance by light, which is brought into contact with a gas or liquid sample, a point light source, and a point light source A light flux converging means for converging a light flux on the metal thin film adhered surface of the prism at an incident angle of a critical angle or more; and a lens for receiving the light flux totally reflected on the metal thin film adhered surface of the prism and Fourier transforming the intensity thereof A photo-excited surface plasma vibration resonance consisting of a one-dimensional photoelectric element array for detecting the distribution of the light flux from this lens, and a dark box body that supports at least the prism, the light flux converging means and the lens, and that can keep the inside in the dark Sensor head using 2. The point light source is a light emitting diode, further comprising a polarizer for converting a light flux from the light emitting diode into a P-polarized light and an analyzer for detecting a polarization of the light flux directed to the one-dimensional photoelectric element array. A sensor head utilizing the photoexcited surface plasma vibration resonance according to claim 1. 3. The point light source is a semiconductor laser.
A sensor head utilizing the photoexcited surface plasma vibrational resonance described. 4. The photoexcited surface plasma vibration resonance according to any one of claims 1 to 3, wherein the metal thin film is provided with a protective film for eliminating adverse effects from outside air or an object to be inspected. Sensor head using 5. The sensor head using photoexcited surface plasma vibration resonance according to claim 1, wherein an optical axis extending from the light source and an optical axis of the lens are parallel to each other. 6. The prism is a triangular prism, the light flux converging means includes a mirror surface formed on the second surface of the triangular prism, the Fourier transform lens is a cylindrical lens, and the cylindrical lens is a cylindrical lens. The sensor head utilizing photoexcited surface plasma vibration resonance according to any one of claims 1 to 5, which is attached to a third surface of the triangular prism. 7. The prism is a triangular prism, the light flux converging means includes a mirror surface formed on the second surface of the triangular prism, and the Fourier transform lens is an aspheric lens. The sensor head using photoexcited surface plasma vibration resonance according to claim 1, wherein a lens is attached to the third surface of the triangular prism. 8. A sensor utilizing photoexcited surface plasma vibration resonance according to claim 6 or 7, wherein said luminous flux converging means includes either a cylindrical lens or an aspherical lens attached to the third surface of said triangular prism. head. 9. The sensor head using photoexcited surface plasma vibration resonance according to claim 6, wherein the triangular prism is a right-angled prism. 10. The sensor utilizing photoexcited surface plasma vibration resonance according to claim 1, wherein at least one of the point light source and the one-dimensional photoelectric element array is provided outside the dark box body. head. 11. The sensor head using photoexcited surface plasma vibration resonance according to claim 1, wherein the dark box is cylindrical and has a length of 200 mm or less.