JP2005249696A - Measuring method and measuring instrument for measuring physical property of measured object by depositing measured object onto tip of optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a measuring method and instrument capable of measuring various kinds of physical properties of a measured object, without being limited to surface tension, viscosity and density, and variation thereof, by depositing the measured object onto a tip of an optical fiber. <P>SOLUTION: This measuring instrument for measuring the physical properties of the measured object S is provided with a light source 1, a Michelson interferometer, the optical fiber 20 arranged in a signal arm of the Michelson interferometer, interference signal detecting means 15, 16, 17 for detecting interference signals by the Michelson interferometer, and an interference signal analytical means 18 for finding a vibration condition of a surface of the measured object S deposited onto the tip of the optical fiber, and an amplitude thereof or a deformation amount thereof, based on the detected interference signals. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a measurement method and a measurement apparatus for measuring a physical property of a measurement object by attaching the measurement object to the tip of an optical fiber, and in particular, physical properties such as surface tension, viscosity, density, etc. using a repron with a small amount of liquid sample. The present invention relates to a measurement method and a measurement apparatus that can measure the above.

  Thermal vibration called ripplon on the surface of the liquid is a ripple having an amplitude of several millimeters caused by thermal excitation on the surface of the liquid. The surface tension and density of the liquid determine the dispersion relationship of the reprons (relationship between the frequency and the wavelength), and the viscosity is the amplitude and coherence (the distance to propagate with the phase of the waves aligned, how long the wave once generated will disappear. Affect). Therefore, the surface tension, density, and viscosity of the liquid can be determined by examining the lipron (Non-Patent Document 1).

  It was first predicted in Non-Patent Document 2 that a wave originating from thermal excitation may be generated on the liquid surface, and was experimentally observed in Non-Patent Document 3. At present, it is observed by the light scattering method using lipron as a traveling diffraction grating. Diffracted light from the repron changes not only in the propagation direction but also in the frequency, and the dispersion relationship of the repron can be obtained.

  This light scattering method includes a method of analyzing reflected light by irradiating a liquid surface with laser light (Non Patent Literatures 4 and 5) and a method of analyzing refracted light (Non Patent Literature 6). Although the method of analyzing the reflected light is highly sensitive, it has a drawback that it is easily affected by the direction of gravity and the vibration of the measurement environment. The method of analyzing refracted light is less sensitive to vibrations in the measurement environment, although the sensitivity is reduced.

On the other hand, the method using the Michelson interferometer is highly sensitive but not used for observing the reprons. Since the Michelson interferometer only measures the displacement of a point on the liquid surface, it cannot acquire information about the spatial propagation of the reprons. For this reason, the dispersion relation cannot be obtained.
"Surface Science" Vol.21, No.10, pp.623-629,2000 Ann.Physik 25,225 (1908) Ann.Physik 41,609 (1913) Phys. Rev. Lett. 19, 64 (1967) Rev. Sci. Instrum. 55 (1984) 716 Rev. Sci. Instrum. 62 (1991) 1192

  The present invention has been made in view of such a situation in the prior art, and the purpose thereof is not limited to the surface tension, viscosity, and density of the object to be measured by attaching a small amount of the object to be measured to the tip of the optical fiber. An object is to provide a measuring method and apparatus capable of measuring various physical properties and changes thereof.

  A measuring method for measuring the physical properties of an object to be measured by attaching the object to be measured to the optical fiber tip of the present invention that achieves the above object is an optical fiber arranged in the optical path of a signal arm of an optical interferometer such as a Michelson interferometer. The vibration state of the surface of the liquid sample and its amplitude or deformation amount are determined from the interference signal obtained by attaching the liquid sample to the tip of the liquid and interfering the signal light reflected from the surface of the liquid sample with the reference light. The method is characterized in that the physical property of the liquid sample is measured by obtaining.

  Here, the liquid sample includes a gel sample and a rubber sample.

  In this case, the vibration of the surface of the liquid sample may be thermal vibration due to thermal excitation of the surface of the liquid.

  Further, vibration or deformation of the surface of the liquid sample may be based on an external force applied.

  The force applied from the outside in that case may be based on excitation light introduced into the optical path of the signal arm from the middle of the optical path of the signal arm, or may be a force caused by a magnetic field, an electric field, or gravity.

  Further, it is desirable to obtain the interference signal of the optical interferometer by differential detection.

  A measuring apparatus for measuring a physical property of a measurement object by attaching the measurement object to the tip of the optical fiber according to the present invention includes a light source, an optical interferometer, an optical fiber disposed in a signal arm of the optical interferometer, and an optical interference. An interference signal detection means for detecting an interference signal by a meter, and an interference signal analysis means for obtaining the vibration state and amplitude or deformation amount of the surface of the liquid sample adhering to the tip of the optical fiber from the detected interference signal. It is characterized by.

  In that case, a light introducing means for introducing light for exciting the liquid sample may be arranged in the optical path of the signal arm.

  Further, at least the optical path from the light source to the reference mirror at the tip of the reference arm of the optical interferometer and the optical path from the light source to the optical fiber in the signal arm of the optical interferometer may be connected by an optical fiber.

  According to the measuring method and measuring apparatus for measuring the physical properties of a measured object by attaching the measured object to the tip of the optical fiber of the present invention, the optical fiber arranged in the optical path of the signal arm of the optical interferometer such as a Michelson interferometer From the interference signal obtained by attaching the liquid sample to the tip and causing the signal light reflected from the surface of the liquid sample to interfere with the reference light, the vibration state and amplitude or deformation amount of the surface of the liquid sample are obtained. Thus, since the physical property of the liquid sample is measured, the physical property can be measured with a small amount of sample. In addition, since the liquid sample is strongly attached to the tip of the optical fiber by intermolecular force, it can be stably measured at any location without being affected by vibration of the measurement environment and gravity. Moreover, since the liquid sample is simply attached to the tip of the cut optical fiber, the price can be easily measured at a low price.

  The basic principle of the measuring method and measuring apparatus for measuring the physical properties of the object to be measured by attaching the object to be measured to the tip of the optical fiber of the present invention is to use a Michelson interferometer to attach a liquid sample droplet to the tip of the optical fiber. By directly observing the displacement and vibration of the droplet surface, it is possible to measure the physical properties of the liquid sample such as surface tension, viscosity, density, spectral characteristics, magnetoelectric characteristics, and changes thereof.

  First, an example in which the repron spectrum of the reprons of the liquid sample attached to the tip of the optical fiber is obtained will be described. FIG. 1 is a schematic view of a measuring apparatus for that purpose. In this apparatus, single wavelength light from a light source 1 passes through an isolator 2, a polarizing beam splitter (PBS) 3, a Faraday rotator 4, a half-wave plate 5 in this order, and then a non-polarizing beam splitter ( NPBS) 6, and is divided into a reflected light component input to the reference arm and a transmitted light component to the signal arm. The reference light reflected by the NPBS 6 enters the reference mirror 8, is inverted, and returns to the NPBS 6 again. A piezoelectric element PZT (piezoelectric transducer) 9 is disposed on the back surface of the reference mirror 8, and the length of the reference arm can be adjusted by adjusting the voltage applied thereto. The light transmitted through the NPBS 6 is adjusted in its polarization plane through the half-wave plate 10, is condensed by the lens 11, and enters the optical fiber 20 from the rear end 21 of the polarization plane-preserving optical fiber. The tip 22 is reached. The tip 22 of the optical fiber 20 is cut, for example, in a plane perpendicular to the axis and is affinity to the liquid sample S, and the liquid sample S adheres in a substantially hemispherical shape due to surface tension. The light that has reached the liquid sample S from the tip 22 of the optical fiber 20 is reflected by the surface thereof, returns through the optical fiber 20, returns to the NPBS 6 again through the lenses 11, 12 and the half-wave plate 10. The rear end 21 of the optical fiber 20 is cut obliquely with respect to the axis in order to prevent unnecessary interference.

  There is a phase difference of 180 ° between the signal light transmitted through the NPBS 6 to the half-wave plate 5 side and the signal light reflected by the NPBS 6, and the signal light and the reference light returning to the half-wave plate 5 side. , Reversely travels through the half-wave plate 5 and the Faraday rotator 4 and is then reflected by the PBS 3 and enters the photodetector 15 to obtain a first interference signal. The signal light and the reference light reflected by the NPBS 6 are incident on another photodetector 16 to obtain a second interference signal. The first interference signal and the second interference signal are signals whose phases are inverted with each other, and by differential detection of both signals by the differential detector 17, the signal intensity is doubled, The amplitude noise of the light from the light source 1 is canceled out. The output of the differential detector 17 passes through an analog / digital converter (not shown) and is taken into a computer 18 where it is subjected to Fourier transform to obtain a spectrum.

  FIG. 2 and FIG. 3 show the repron spectrum specifically obtained in such a configuration. The measurement conditions are a stabilized diode laser with a wavelength of 780 nm and an output of 26 mW as the light source 1, and the voltage applied to the PZT 9 is slowly controlled by negative feedback with a time constant of 1 second, and the Michelson interferometer is always in the state of maximum sensitivity. It was made. The optical fibers 20 had diameters of 80 μm (FIG. 2) and 125 μm (FIG. 3), and a length of 150 mm. The analog-to-digital converter was 16 bit 2 Msample / s. One measurement time was 2 seconds. The spectrum intensities shown in FIGS. 2 and 3 indicate that one fringe of the Michelson interferometer is ½ wavelength, and the signal (repron) being measured is random noise. Using proportionality, it is expressed in pm / √Hz. As the liquid sample S to be attached to the tip 22 of the optical fiber 20, ethanol (ethanol), methanol (water), and water (water) were used, and the temperature was room temperature (18 ° C.). In order to obtain a sufficient amount of reflected light from the tip 22 of the optical fiber 20, the liquid needs to be uniformly attached. Ethanol and methanol adhered evenly without special care. Before adhering water, the optical fiber 20 was ultrasonically cleaned in pure water to remove dirt. Otherwise, the optical fiber 20 partially repels water, so that the surface of the droplet is distorted and there is almost no reflected light. Further, in order to prevent the liquid sample S from evaporating from the optical fiber tip 22, the measurement was performed in a sealed container. The optical fiber end face 22 was measured vertically and horizontally with respect to gravity, but there was no difference that could be detected.

  The first peak value in each graph is a standing wave having a wavelength of about the diameter of the optical fiber 20 formed on the substantially hemispherical surface of the liquid sample S (the arc length of the hemispherical surface is about 1.5 times the diameter). And the observed vibration of the reprons is 1.5 × wavelength on the arc.)

  In the repron, it is known that the density of the liquid is ρ, the viscosity is η, the surface tension is σ, the frequency of the repron is f, the wavelength is λ, and the attenuation coefficient is Γ.

^{η = Γρλ 2 / (8π 2} ) ··· (1)
σ = ρf ² λ ³ / (2π) (2)
Here, Γ is a value proportional to the half-value width of the standing wave peak in FIGS. 2 and 3, f may be the frequency thereof, λ may be the diameter of the optical fiber 20, and if the density ρ of the liquid sample S is known, The viscosity η and surface tension σ can be obtained.

The viscosity η and surface tension σ of ethanol, methanol, and water actually obtained using the results of FIGS. 2 and 3 are in good agreement with the actual values. According to the present invention, a very small amount (10 ⁻⁷ cm It can be seen that measurement is possible with the liquid of ³ ), and because the liquid is strongly attached to the optical fiber by intermolecular force, measurement can be made almost unaffected by vibration in the measurement environment.

  In FIG. 1, two physical properties of the surface tension, viscosity, and density of the liquid sample S are obtained by measuring the frequency and amplitude of the reprons generated on the surface of the liquid sample S by thermal vibration. These physical properties can be obtained not only by vibration but also by external forced vibration. An outline of the measuring device in that case is shown in FIG. In this apparatus, a polarization beam splitter (PBS) 27 is inserted into the signal arm between the NPBS 6 and the half-wave plate 10 with respect to the apparatus of FIG. The repetitive laser light emitted from the excitation laser 25 pulsating at a constant period is reflected by the PBS 27 and combined with the measurement light, and the combined light passes through the half-wave plate 10 and the lens 11 and the rear end 21 of the optical fiber 20. The surface of the liquid sample S attached to the tip 22 of the optical fiber 20 is forcibly vibrated by the heat of the repeated laser light from the excitation laser 25 and the pressure of the light.

  Note that the laser beam from the excitation laser 25 may not be a periodic pulse oscillation. For example, the oscillation intensity may be modulated by a pseudo random sequence.

  In this case, the surface tension, viscosity, density, etc. of the liquid sample S are measured by measuring the amplitude and phase of the surface of the liquid sample S and the state of vibration of the liquid surface after blocking the excitation light. can do.

  Furthermore, when the liquid sample S is irradiated using a wavelength variable laser capable of continuously changing the wavelength of the laser light as the excitation laser 25 in FIG. Since the sample S is deformed, the spectral absorptance of the liquid sample S can be measured by detecting this deformation from the output signal from the differential detector 17. In conventional photo-acoustic spectroscopy, a sample is irradiated with laser light, the sample absorbs the laser beam, and then rapidly expands. The generated elastic wave is detected by a microphone or Michelson interferometer. However, according to this method of the present invention, since surface vibrations of a small amount of liquid are detected, loss of elastic energy is small, and highly sensitive measurement is possible.

  By the way, the above-described measuring apparatus of the present invention uses the optical fiber only for the portion to which the liquid sample S is attached. However, all the optical paths are made into optical fibers so as not to be affected by the measurement environment such as vibration and heat. be able to. Examples thereof are shown in FIGS.

  FIG. 5 shows a configuration in which differential detection is not performed as shown in FIGS. 1 and 4. Single wavelength light from a light source 1 made of a laser is connected to an isolator 2 by an optical fiber 31, and light passing through the isolator 2 is The optical fiber 33 is connected to the optical fiber coupler 34 via the optical fiber 33. The optical fiber coupler 34 is configured such that the cores of two parallel optical fibers are fused, and the light input from one of the four ports is equally divided and output to two opposing ports. On the other hand, the light input from the two ports facing each other is output equally to the two ports facing each other, and the light input to the optical fiber coupler 34 via the optical fiber 33 is opposed to the optical fibers 35 and 37 facing each other. Divided evenly. The optical fiber 35 constitutes a reference arm, and a reflection coat 36 is applied to the output end thereof. The reference light input to the optical fiber 35 is reflected by the reflection coat 36, passes through the optical fiber 35 in the opposite direction, and returns to the optical fiber coupler 34 again. Return. On the other hand, the optical fiber 37 constitutes a signal arm, and its output end is cut into a plane perpendicular to the axis, for example, as in FIGS. 1 and 4, and is compatible with the liquid sample S. The liquid sample S is attached in a substantially hemispherical shape due to surface tension. The light that has reached the liquid sample S from the optical fiber 37 is reflected on the surface thereof, passes through the optical fiber 37 in the opposite direction, and returns to the optical fiber coupler 34 again. The signal light and the reference light that have returned to the optical fiber coupler 34 enter the optical fiber 38 that constitutes yet another port of the optical fiber coupler 34, enter the photodetector 16 connected to the output end thereof, and output an interference signal. Accordingly, the repron spectrum can be obtained in the same manner as in FIGS.

  FIG. 6 shows a configuration for performing differential detection similar to FIGS. 1 and 4. Single wavelength light from a light source 1 made of a laser is connected to an isolator 2 by an optical fiber 31, and light passing through the isolator 2 is optical fiber. It is connected to the directional coupler 32 via 39. The directional coupler 32 may be composed of the PBS 3, the Faraday rotator 4 and the half-wave plate 5 as in the case of FIGS. 1 and 4. It is preferable to use an optical waveguide type or optical fiber type directional coupler. The light that has passed through the directional coupler 32 is connected to the optical fiber coupler 34 via the optical fiber 33, as in FIG. 5, and is equally divided into the optical fibers 35 and 37 facing each other by the optical fiber coupler 34. The reference light input to the optical fiber 35 of the reference arm is reflected by the reflection coating 36 at the output end, returns to the optical fiber coupler 34 through the optical fiber 35 in the opposite direction. On the other hand, the light reaching the liquid sample S from the optical fiber 37 of the signal arm is reflected on the surface thereof, returns to the optical fiber coupler 34 through the optical fiber 37 in the opposite direction. The signal light and reference light that have returned to the optical fiber coupler 34 are equally divided into optical fibers 33 and 38 that constitute two opposing ports of the optical fiber coupler 34, and the signal light and reference light that have passed through the optical fiber 38 are connected to their output ends. The light is incident on the detected photodetector 16 and a second interference signal is output. Further, the signal light and the reference light that have passed through the optical fiber 33 enter the optical fiber 40 constituting another port via the directional coupler 32, enter the optical detector 15 connected to the output end thereof, and enter the first interference signal. Is output. The first interference signal and the second interference signal are signals whose phases are inverted with each other, and by differential detection of both signals by the differential detector 17, the signal intensity is doubled, The amplitude noise of the light from the light source 1 is canceled out. The output of the differential detector 17 passes through an analog / digital converter (not shown) and is taken into the computer 18 where it is Fourier transformed to obtain a spectrum.

  5 and 6 also, the excitation laser light is combined with the measurement light from the middle of the optical fiber 37 so that the surface of the liquid sample S attached to the tip of the optical fiber 37 is forcibly vibrated. Thus, the surface tension, viscosity, density, and the like can be measured, and the spectral absorptance of the liquid sample S can be measured.

  By the way, in the configuration as shown in FIGS. 1 and 4 to 6, the physical properties before and after adding an enzyme or an antibody to the liquid sample S attached to the tips of the optical fibers 20 and 37 are measured, or vice versa. It is possible to selectively detect only various molecules, proteins, and antigens by attaching an enzyme, an antibody, or the like to the tips of 20 and 37 and then immersing them in an unknown solution.

  Further, by measuring the deformation of the liquid sample S attached to the tips of the optical fibers 20 and 37 when a magnetic field, electric field or gravity is applied, the magnetic characteristics, electrical characteristics or density of the liquid sample S is measured. You can also.

  Further, by detecting minute changes in the lipron spectrum, it is possible to detect the presence or absence of a chemical reaction, the force acting on the liquid sample, and the like.

  In addition, various measurements can be performed by processing the tip of the optical fiber into a special shape. If a dent or a hole is made at the tip of the optical fiber, a sample that does not adhere sufficiently by being cut vertically can be attached. Further, if the optical fiber tip is cut obliquely, unnecessary reflection from the fiber end surface can be suppressed and further high-precision measurement can be performed.

  Furthermore, various measurements are possible by processing the tip of the optical fiber into a special state. For example, if the tip of the optical fiber is processed to be hydrophilic, only an aqueous substance can be selectively attached. Similarly, if it is processed to be oleophilic, only oily substances can be selectively attached.

  Further, in the conventional spectroscope, the sample is put in the polished quartz glass cell. However, in the present invention, the sample is only attached to the tip of the cut optical fiber, so that the price is low and simple. Also, if the tip of the optical fiber becomes dirty or deteriorates, it is economical because it is only necessary to cut the tip and expose a new surface.

  The optical interferometer used in the present invention is not limited to the Michelson interferometer, and any other type of interferometer can be used as long as it is an optical interferometer that separates and combines the signal light optical path and the reference light optical path. .

It is the schematic of one Example of the measuring device which attaches a to-be-measured object to the front-end | tip of an optical fiber based on this invention, and measures the physical property of a to-be-measured object. It is a figure which shows one example of the repron spectrum calculated | required specifically using the measuring apparatus of FIG. It is a figure which shows another example of the repron spectrum calculated | required specifically using the measuring apparatus of FIG. It is the schematic of another Example of the measuring device which attaches a to-be-measured object to the front-end | tip of an optical fiber based on this invention, and measures the physical property of a to-be-measured object. It is the schematic of one Example which made all the optical paths into optical fiber. It is the schematic of another Example which made all the optical paths into optical fiber.

Explanation of symbols

S ... Liquid sample 1 ... Light source 2 ... Isolator 3 ... Polarizing beam splitter (PBS)
4 ... Faraday rotator 5 ... Half-wave plate 6 ... Non-polarizing beam splitter (NPBS)
8 ... Reference mirror 9 ... PZT
DESCRIPTION OF SYMBOLS 10 ... Half wavelength plate 11 ... Lens 15 ... Photo detector 16 ... Photo detector 17 ... Differential detector 18 ... Computer 20 ... Optical fiber 21 ... Optical fiber rear end 22 ... Optical fiber front end 25 ... Excitation laser 26 ... periodic power supply 27 ... polarization beam splitter (PBS)
31, 33, 35, 37, 38, 39, 40 ... optical fiber 32 ... directional coupler 34 ... optical fiber coupler 36 ... reflective coating

Claims (9)

From the interference signal obtained by attaching the liquid sample to the tip of the optical fiber arranged in the optical path of the signal arm of the optical interferometer and interfering the signal light reflected from the surface of the liquid sample with the reference light, the liquid sample Measuring method for measuring physical properties of measured object by attaching measured object to optical fiber tip, measuring physical property of liquid sample by determining vibration state and amplitude or deformation amount . 2. The measuring method for measuring physical properties of a measured object by attaching the measured object to the tip of an optical fiber according to claim 1, wherein the vibration of the surface of the liquid sample is thermal vibration caused by thermal excitation of the surface of the liquid. 2. The measuring method for measuring physical properties of a measurement object by attaching the measurement object to the tip of an optical fiber according to claim 1, wherein the vibration or deformation of the surface of the liquid sample is based on an externally applied force. 4. The measurement object according to claim 3, wherein the force applied from the outside is based on excitation light introduced into the optical path of the signal arm from the middle of the optical path of the signal arm. A measurement method that measures the physical properties of materials. 4. The measuring method for measuring physical properties of an object to be measured by attaching the object to be measured on an optical fiber tip according to claim 3, wherein the force applied from the outside is a force caused by a magnetic field, an electric field or gravity. 6. The measuring method for measuring physical properties of a measured object by attaching the measured object to the tip of an optical fiber according to claim 1, wherein an interference signal of the optical interferometer is obtained by differential detection. A light source, an optical interferometer, an optical fiber arranged in a signal arm of the optical interferometer, an interference signal detecting means for detecting an interference signal by the optical interferometer, and the detected interference signal attached to the tip of the optical fiber Measurement for measuring physical properties of a measurement object by attaching the measurement object to the tip of an optical fiber, characterized by comprising an interference signal analysis means for obtaining a vibration state of the surface of a liquid sample and its amplitude or deformation amount apparatus. 8. A light introducing means for introducing light for exciting the liquid sample is disposed in the optical path of the signal arm, wherein the object to be measured is attached to the tip of the optical fiber to thereby improve the physical properties of the object to be measured. Measuring device to measure. The optical path from at least the light source to the reference mirror at the tip of the reference arm of the optical interferometer and the optical path from the light source to the optical fiber in the signal arm of the optical interferometer are connected by an optical fiber. 8. A measuring apparatus for measuring physical properties of an object to be measured by attaching the object to be measured to an optical fiber tip according to 8.

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