JP2014006173A - Particle characteristic measurement apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a particle characteristic measurement apparatus capable of simultaneously calculating the particle size and the zeta potential of an electrophoretic fine particle.SOLUTION: The particle characteristic measurement apparatus comprises: a laser oscillator having a light source and irradiating an object to be measured that contains a solvent and fine particles dispersed in the solvent with a laser beam output from the light source; a light detection unit for converting a laser output beam which is modulated with a scattered feedback beam from the object to be measured, into a signal; and a signal processor for analyzing the signal converted by the light detection unit. The signal processor obtains frequency characteristics of an intensity fluctuation of the modulated laser output beam by analyzing the signal, determines a diffusion coefficient of a fine particle contained in the object to be measured from the frequency characteristics of the intensity fluctuation, and determines a particle size of the fine particle contained in the object to be measured from the diffusion coefficient. The signal processor also determines a moving velocity of the fine particle contained in the object to be measured from the frequency characteristics of the intensity fluctuation and determines the zeta potential of the fine particle contained in the object to be measured from the moving velocity.

Description

  The present invention relates to a particle property measuring apparatus for measuring the particle size and zeta potential of fine particles such as colloidal particles dispersed in a solvent.

  Conventionally, in the fields of the powder industry, the cosmetics industry, and the color material industry, particle diameter and zeta potential have been widely measured for the evaluation of fine particles in solvents. As a method for measuring the particle size of fine particles dispersed in a solution, a method for evaluating the particle size from observation under a microscope, or a method for measuring the particle size from the scattered light by irradiating the particle with laser light (dynamic light scattering method) It has been known.

  The zeta potential of a particle is the potential difference between the sliding surface of the particle in solution and the bulk solvent. The interface of the fine particles in contact with the solvent is basically charged. The electric field created by the charged fine particles attracts ions of opposite polarity from the solvent and stays near the particle surface. When an electric field is applied to this solvent, the fine particles are electrophoresed toward the electrode in a state where ions are attracted. The surface where this movement occurs is a sliding surface, and the potential difference between the sliding surface and the solvent is called the zeta potential. The zeta potential is evaluated based on the electrophoretic mobility when an electric field is applied to a solution containing fine particles. This electrophoretic mobility is detected using a method of evaluating electrophoretic mobility from observation with a microscope, or the fact that the frequency of scattered light from fine particles is changed by the Doppler effect when irradiated with laser light. A laser Doppler method for detecting electrophoretic mobility is known.

  In such a conventional technique, the particle diameter and the zeta potential are individually measured by different measuring methods, and a measuring device is also required individually. There are devices that assemble each measurement device into one device, but the particle size and zeta potential cannot be measured at once because the particle size and zeta potential are measured separately. Further, a method is disclosed in which the particle diameter and zeta potential are measured by indirectly obtaining the particle diameter by numerical calculation from the mobility obtained by observing an image of the electrophoretic fine particles (for example, Patent Document 1). reference.). However, this method cannot measure fine particles with a nanometer diameter because the fine particle image is observed.

  Conventionally, part of the output light emitted from the light source is incident on the object to be measured, and scattered feedback light from the object to be measured is fed back to the light source and induced by interference between the feedback light and the output light. A laser velocimeter (for example, see Patent Document 2), a particle diameter measuring device (for example, see Non-Patent Document 1), and a flow velocity measuring device (for example, see Patent Document 2) using a technique for measuring the frequency of intensity fluctuation of the output light. , See Non-Patent Document 2.) and the like.

JP 2007-322329 A JP 2004-226093 A

S. Sudo, Y. et al. Miyasaka, K. et al. Otsuka, Y. et al. Takahashi, T .; Oishi, and J.H. -Y. Ko, “Quick and easy measurement of particle size of Brownian particles and plantons in water using a self-mixing laser”, OPTICS EX6, June, 2003. 14, no. 3, p. 1044-1054. S. Sudo, Y. et al. Miyasaka, K. et al. Nemoto, K .; Kamikariya, and K.K. Otsuka, “Detection of small particle in fluid using a self-mixing laser”, OPTICS EXPRESS, June 25, 2007, Vol. 15, no. 13, p. 8135-8145.

  However, in the above-described prior art, it has been impossible to simultaneously calculate the particle size and the zeta potential of nano-sized fine particles to be electrophoresed using a single particle property measuring device.

  The present invention has been made in view of the above problems, and a particle characteristic measuring apparatus capable of calculating the particle diameter of fine particles to be electrophoresed easily and accurately using a single particle characteristic measuring apparatus. The purpose is to provide.

  It is another object of the present invention to provide a particle characteristic measuring apparatus capable of simultaneously calculating the particle size and zeta potential of fine particles to be electrophoresed.

  A particle characteristic measurement apparatus according to an embodiment of the present invention includes a light source, and a laser oscillator that causes a laser beam output from the light source to be incident on a measurement object including a solvent and fine particles dispersed in the solvent; A signal detection unit that converts a laser output light modulated by scattered feedback light from the object to be measured into a signal; and a signal processing unit that analyzes the signal converted by the light detection unit, the signal processing unit Analyzing the signal to obtain a frequency characteristic of intensity fluctuation of the modulated laser output light, obtaining a diffusion coefficient of the fine particles contained in the object to be measured from the frequency characteristic of the intensity fluctuation, and from the diffusion coefficient It includes determining the particle diameter of the fine particles contained in the object to be measured.

  The signal processing unit may obtain a moving speed of the fine particles contained in the measured object from the frequency characteristic of the intensity fluctuation, and obtain a zeta potential of the fine particles contained in the measured object from the moving speed.

但し，Ｆはフーリエ変換を表しており，ｊは虚数単位，ｔは時間，ｖは前記移動速度，Ｄは前記拡散係数，ｗは前記レーザ光のビーム幅，θは前記被測定物の移動方向と前記光源の発振軸のなす角度，ｋは波数を示す。また，波数ｋは次式（ＩＩ）により導出される。

但し，ｎは前記溶媒の屈折率，λは前記レーザ光の波長，φは散乱角を示す。 When the frequency characteristic of the intensity fluctuation, that is, the power spectrum is I (ω), the curve of the object to be measured is obtained by curve fitting to the following formula (I) or the superposition formula of the following formula (I). A diffusion coefficient and the moving speed may be obtained.

Where F is Fourier transform, j is an imaginary unit, t is time, v is the moving speed, D is the diffusion coefficient, w is the beam width of the laser beam, and θ is the moving direction of the object to be measured. And k represents the wave number. The wave number k is derived from the following equation (II).

Where n is the refractive index of the solvent, λ is the wavelength of the laser beam, and φ is the scattering angle.

  A photoacoustic modulation element (AOM) that shifts the frequency of the laser light is further provided, and the signal processing unit causes the laser light frequency-shifted by the photoacoustic modulation element (AOM) to enter the object to be measured. Then, a signal obtained by converting the laser output light modulated by the scattered feedback light from the object to be measured may be analyzed to obtain the frequency characteristic of the intensity fluctuation.

  A program according to an embodiment of the present invention includes a laser output light modulated by scattering feedback light from a measurement object by causing a laser beam to enter the measurement object including a solvent and fine particles dispersed in the solvent. A program for causing a computer to analyze a signal obtained by converting the signal to obtain a characteristic of the fine particles contained in the object to be measured, the computer analyzing the signal and modulating the signal. The frequency characteristic of the intensity fluctuation of the laser output light is obtained, the diffusion coefficient of the fine particles contained in the measured object is obtained from the frequency characteristic of the intensity fluctuation, and the particles of the fine particles contained in the measured object are obtained from the diffusion coefficient. A process for obtaining a diameter is executed.

  Further, the computer is caused to execute a process of obtaining a moving speed of the fine particles contained in the measured object from the frequency characteristic of the intensity fluctuation, and obtaining a zeta potential of the fine particles contained in the measured object from the moving speed. May be.

  According to the particle characteristic measuring apparatus according to one embodiment of the present invention, the particles of the fine particles that are easily and accurately electrophoresed using one particle characteristic measuring apparatus without observing the image of the fine particles with a microscope or the like. The diameter can be calculated.

  Furthermore, according to the particle characteristic measuring apparatus according to an embodiment of the present invention, it is possible to simultaneously calculate the particle diameter and zeta potential of the fine particles to be electrophoresed.

It is a schematic block diagram of the particle characteristic measuring apparatus of this invention. It is the flowchart which showed the process which calculates the particle characteristic by the particle characteristic measuring apparatus of this invention. It is a schematic block diagram of the particle characteristic measuring apparatus which concerns on the Example of this invention. It is a graph which shows the power spectrum of the laser output light measured with the particle | grain characteristic measuring apparatus which concerns on the Example of this invention.

  Hereinafter, the particle characteristic measuring apparatus of the present invention will be described with reference to the drawings. In addition, the particle characteristic measuring apparatus of the present invention is not limited to the following embodiment, and can be implemented with various modifications.

  Hereinafter, the particle characteristic measuring apparatus 1 according to the present invention will be described with reference to FIG. FIG. 1 is a schematic configuration diagram of a particle property measuring apparatus 1 according to the present invention. The particle characteristic measuring apparatus 1 includes fine particles which are a laser oscillator 2, a beam splitter 3, a condensing lens 4, a photodetector 5, a signal processing unit 6, and an object to be measured 7.

  The laser oscillator 2 includes a light source, and laser light output from the light source is incident on the object to be measured 7. The beam splitter 3 transmits a part of the output light and makes it incident on the object 7 to be measured, and reflects the remaining output light at a certain angle and makes it incident on the photodetector 5. The photodetector 5 converts the incident light into an electrical signal, and the signal processing unit 6 analyzes the signal output from the photodetector 5.

When part of the output light emitted from the laser oscillator 2 of a light source (oscillation light) is incident on the object 7 to be measured, the scattered backward light E _S from the object to be measured 7 is fed back to the oscillation axis of the light source. Since modulation is given to the laser output beam by such scattered returned light E _S, the laser output light modulated is converted into an electric signal by the photodetector 5, the signal processing unit 6 analyzes the converted signal By doing so, the particle characteristics of the DUT 7 can be calculated.

Hereinafter, based on the laser output light modulated by the scattered backward light E _S from the object to be measured 7, a method for calculating the particle properties of the object 7 in the signal processing unit 6.

First, scattered returned light E _S from the object to be measured 7 is subjected to Doppler frequency shift f _D, such as the following formula _[Hz].

Here, v [m / s] is the moving speed of the object to be measured, λ [m] is the wavelength of the oscillation light, and θ is the angle [rad] between the moving direction of the object to be measured and the oscillation axis of the light source. Therefore, the the laser oscillator 2 is injected light shifted in frequency by f _D. As a result, scattered returned light E _S is by interfering with the oscillation light E _0, these two field difference frequency, that is, oscillation light E ₀ at f _D is intensity-modulated. At this time, the time change of the oscillation light intensity (S ₀ = E ₀ ² ) is expressed by the following equation.

However, n _p [/ m ³ ] is an inversion distribution density, t ₀ = τ / τ ₀ (τ [s]: time, τ ₀ [s]: inversion distribution lifetime), K = τ ₀ / τ _p (τ _p [S]: Photon lifetime), τ _p = τ ₁ / κ ² (κ: amplitude transmittance of the output mirror of the laser oscillator 2). τ _l (= 2L / c) is the round-trip time of light in the laser oscillator 2, c is the speed of light (2.99 × 10 ⁸ m / s), and L [m] is the laser oscillator length . K is the ratio of the inverted distribution lifetime to the photon lifetime.

As shown in the equation (2), the oscillation light intensity S ₀ is modulated at the frequency f _D , and the modulation degree in this case is proportional to K (= τ ₀ / τ _p ). Therefore, the amplitude of the scattered return light E _S is the sufficiently large degree of modulation by increasing the K be a very weak is obtained. In a laser with a small L, τ _l is short and τ _p is proportional to τ _l , so an extremely large K can be obtained. For example, if a LiNdP ₄ O ₁₂ solid-state laser having a crystal thickness of about 1 mm excited by a semiconductor laser is used as the laser oscillator 2, K = 10 ⁵ to 10 ⁶ can be obtained. Therefore, the more sensitive the measurement is possible, the thinner the solid-state laser is used.

Also as shown in Equation (2), the second term of equation (2) representing the intensity fluctuations of the laser output beam, the ratio of the scattered return light E _S and the oscillation light E _0, i.e. proportional to the feedback of the laser beam To do. Therefore, a sufficiently large degree of modulation can be obtained by increasing the feedback rate of the laser beam.

However, the microparticles that electrophorese in the solvent do not translate at a constant speed, but move while fluctuating due to collision with solvent molecules. At this time, the signal processing unit 6 derives the frequency characteristic of the intensity fluctuation of the laser output light based on the signal obtained by photoelectrically converting the laser output light modulated by the scattered feedback light from the object to be measured by the photodetector 5. . The frequency characteristic (power spectrum) I (ω) of the intensity fluctuation of the laser output light is expressed by the following equation.

  Here, F represents Fourier transform, j is an imaginary unit, t [s] is time, v [m / s] is a moving speed of the object to be measured, D is a diffusion coefficient, and w [m] is irradiated to the fine particles. The beam width of the laser light, θ [rad] is the angle between the moving direction of the object to be measured and the oscillation axis of the light source, and k is the wave number. In addition, the first item of Equation (3) represents the Doppler shift, the second item represents the diffusion of fine particles, and the third item represents the translational movement of the fine particles. Here, the magnitude of the wave number k is k = 4πn / λsin (φ / 2) using the refractive index n of the solvent, the wavelength λ [m] of the oscillation light, and the scattering angle φ [rad]. However, in the particle property measuring apparatus 1 shown in FIG. 1, φ = π.

From the diffusion coefficient D of Expression (3), the particle diameter d [m] of the fine particles can be obtained as follows.

Here, k _B is the Boltzmann constant, T [K] is the temperature of the solvent, and η [Ps · s] is the viscosity of the solvent. On the other hand, the electrophoretic mobility U [m ² / Vs] and the zeta potential ζ [V] of the fine particles to be electrophoresed can be obtained as follows.

  Here, E is the magnitude of the electric field applied to the solvent containing fine particles, and ε is the dielectric constant of the solvent. Therefore, the particle diameter d and the zeta potential ζ of the fine particles can be obtained by analyzing the frequency characteristic I (ω) of the intensity fluctuation of the laser output light based on the equation (3) (curve fitting). Further, when obtaining the particle diameter d and the plurality of zeta potentials ζ of a plurality of fine particles, analysis (curve fitting) may be performed using the superposition equation of equation (3).

According to the particle characteristic measurement apparatus 1 of the present invention, as shown as a flow diagram in Figure 2, first, based on the signal laser output light modulated by the scattered backward light E _S from the measured object is photoelectrically converted The signal processing unit 6 obtains the frequency characteristic I (ω) of the intensity fluctuation of the laser output light (S1 in FIG. 2). Next, the frequency characteristic I (ω) of the obtained intensity fluctuation is curve-fitted using the equation (3), thereby obtaining the diffusion coefficient D of the fine particles contained in the measured object and the moving speed v of the measured object ( S2 in FIG. Next, the obtained diffusion coefficient D can be substituted into the equation (4) to obtain the particle diameter d of the fine particles contained in the object to be measured (S3 in FIG. 2). Further, by substituting the moving velocity v of the object in the formula (1), it is possible to obtain the Doppler frequency shift f _D. Furthermore, the electrophoretic mobility U can be obtained from the moving speed v of the object to be measured based on the equation (5), and the zeta potential ζ can be obtained from the electrophoretic mobility U based on the equation (6). (S4 in FIG. 2). Thus, from the frequency characteristic I (ω) of the same intensity fluctuation, the diffusion coefficient D of the fine particles contained in the object to be measured and the moving speed v of the object to be measured can be simultaneously obtained by curve fitting. And the zeta potential ζ can be determined from the moving speed v.

  As described above, according to the particle characteristic measuring apparatus 1 according to the embodiment of the present invention, the particle diameter d of the fine particles to be electrophoresed can be calculated using the particle characteristic measuring apparatus 1 having a simple configuration.

  Furthermore, according to the particle characteristic measuring apparatus 1 according to the embodiment of the present invention, the zeta potential ζ is calculated simultaneously with the particle diameter d of the electrophoretic fine particles using the above-described equations (3) to (6). It becomes possible to do.

  Hereinafter, a particle characteristic measuring apparatus 10 according to an embodiment of the present invention capable of simultaneously measuring the particle diameter d and the zeta potential ζ of fine particles will be described with reference to FIGS. 3 and 4.

FIG. 3 illustrates a schematic configuration of the particle property measuring apparatus 10 according to the embodiment of the present invention. The particle characteristic measuring apparatus 10 includes a solid-state laser 11, a solid-state laser excitation semiconductor laser unit 12, a beam splitter 13, a condensing lens 14, a photodetector 15, a signal processing unit 16, a sample unit 17, and a light modulation unit 18. The solid-state laser excitation semiconductor laser unit 12 includes a semiconductor laser 22, a laser shape molding unit 23, and a condenser lens 24. As the solid-state laser 11, a LiNdP ₄ O ₁₂ solid-state laser having a crystal thickness of about 1 mm excited by the solid-state laser excitation semiconductor laser unit 12 was used. K is from 10 ⁵ to 10 ⁶ .

The light modulation unit 18 includes a photoacoustic modulation element (AOM) 35 and a modulation element driver 36, and shifts the frequency of the laser light applied to the sample of the sample unit 17 in advance. In solid-state laser oscillation light, there are low frequency components called pedestals and relaxation oscillations inherent to solid-state lasers, so the intensity fluctuation of the output light is observed superimposed on the low frequency components and relaxation oscillations. For this reason, if the spectrum of the modulated light to be observed is analyzed, extraction is difficult because the spectrum of the low vibration frequency component and the relaxation vibration are superimposed on the spectrum having information on the particle diameter d and the zeta potential ζ of the fine particles. Therefore, the center frequency (that is, frequency shift) of the intensity fluctuation of the output light is set to be sufficiently away from these frequencies by using the light modulation unit 18 including the photoacoustic modulation element 35 and the like. In the embodiment shown in FIG. 3, a photoacoustic modulation element (AOM) 35 made of TiO ₂ is used. As the laser beam reciprocates through the optical modulation unit 18, a frequency shift of f _AOM is added to the laser beam.

  The beam splitter 13 is not particularly limited as long as it transmits a part of the incident output light and reflects the remaining output light at a certain angle. The photodetector 15 uses an InGaAs photodiode in the embodiment shown in FIG. 3, but is not limited to this.

  The signal processing unit 16 analyzes the signal output from the photodetector 15. In the embodiment shown in FIG. 3, the signal processing unit 16 acquires a signal using an AD conversion board and performs Fourier transform on the computer, but a spectrum analyzer may be used. This signal includes a signal derived from the intensity modulation of the laser based on the expression (2), and the signal derived from the intensity modulation is extracted by Fourier transform and filter processing. Further, curve fitting is performed on the calculated spectrum by the equation (3) on a computer, and the diffusion coefficient D and the moving speed v are obtained simultaneously. Then, the particle diameter d of the fine particles is obtained from the diffusion coefficient D, and the zeta potential ζ is obtained from the moving speed v.

  The sample unit 17 includes a quartz cell 31 having a pair of electrodes 32 attached therein and a DC power source 33 that applies a voltage to the electrodes. The quartz cell 31 is filled with a sample containing fine particles as a measurement object, and the fine particles are electrophoresed by applying a voltage. The quartz cell is irradiated with the laser beam condensed by the condenser lens 14. Since the electrode 32 contacts the sample, it may corrode. Therefore, although stainless steel is used in the embodiment shown in FIG. 3, gold or platinum electrodes, or metal plated with gold or platinum may be used. The size of the electrodes is not limited, but if the distance between the electrodes is too close, the intensity of the electric field applied to the sample becomes too large.

  FIG. 4 shows the power spectrum of the modulated laser beam measured by the particle characteristic measuring apparatus 10 according to the embodiment of the present invention when a dispersion in which polystyrene latex having a particle diameter d = 200 nm is dispersed in water is used as a sample. It is the graph which illustrated. The solid line is a curve fitting of these measured power spectra using Equation (3).

Referring to FIG. 4, the power spectrum described by Equation (3) was observed on the higher frequency side than f _AOM = 2.0003 MHz. The particle diameter d = 200 nm and the Doppler frequency shift f _D = 85.0 Hz could be obtained by analysis using the equation (3). Further, from the obtained Doppler frequency shift f _D , the electrophoretic mobility U of the fine particles was found to be 130 μm ² / Vs, and the zeta potential ζ was found to be 16.7 mV.

Thus, according to the particle characteristics measurement apparatus 10 according to an embodiment of the present invention, the laser light frequency shift by the light modulation unit 18 is modulated by the scattered backward light E _S from the sample of the sample portion 17 Therefore, the frequency characteristic I (ω) can be obtained with high accuracy. Then, by analyzing this spectrum based on the equation (3), the diffusion coefficient D and the moving speed v of the fine particles contained in the object to be measured can be calculated more accurately. Therefore, based on the equation (4), the particle diameter d of the fine particles contained in the object to be measured can be accurately obtained from the diffusion coefficient D (S3 in FIG. 2), the Doppler frequency shift f _D , Electrophoretic mobility U and zeta potential ζ can be determined accurately (S4 in FIG. 2).

  As described above, according to the particle characteristic measuring apparatuses 1 and 10 according to the present invention, fine particles that are electrophoresed using the particle characteristic measuring apparatuses 1 and 10 having a simple configuration without observing an image of the fine particles with a microscope or the like. Can be detected. In addition, it is possible to calculate the particle characteristics and the like more accurately by shifting the frequency of the laser beam in advance by the light modulator 18.

  In addition, according to the particle characteristic measuring apparatuses 1 and 10 according to an embodiment of the present invention, it is possible to simultaneously detect the particle diameter d and the zeta potential ζ of the electrophoretic fine particles.

  The signal processing units 6 and 16 of the above-described particle property measuring apparatuses 1 and 10 of the present invention are implemented in the form of a computer program that runs on a computer. The computer program is recorded on a computer-readable recording medium (HDD or the like). This computer program may be provided in the form of an optical disc or may be provided in a form that can be downloaded from a server device connected via the Internet. This computer program is loaded into the main memory of the computer and executed.

  The present invention is used to measure the particle size and zeta potential of ceramic nanoparticles, metal nanoparticles, carbon, pharmaceuticals, viruses, paints / pigments, cosmetics, various polymers, foods, CMP (chemical mechanical polisher) slurries, etc. Is possible.

DESCRIPTION OF SYMBOLS 1 Particle characteristic measurement apparatus 2 Laser oscillator 3 Beam splitter 4 Condensing lens 5 Photo detector 6 Signal processing part 7 Object to be measured 10 Particle characteristic measurement apparatus 11 Solid laser 12 Semiconductor laser part for solid laser excitation 13 Beam splitter 14 Condensing lens DESCRIPTION OF SYMBOLS 15 Photodetector 16 Signal processing part 17 Sample part 18 Optical modulation part 22 Semiconductor laser 23 Laser shape shaping part 24 Condensing lens 31 Quartz cell 32 Electrode 33 DC power supply 35 Photoacoustic modulation element 36 Modulation element driver

Claims (6)

A laser oscillator comprising a light source, and causing a laser beam output from the light source to be incident on a measurement object including a solvent and fine particles dispersed in the solvent;
A light detector for converting laser output light modulated by scattered feedback light from the object to be measured into a signal;
A signal processing unit for analyzing the signal converted by the light detection unit,
The signal processing unit analyzes the signal to obtain a frequency characteristic of intensity fluctuation of the modulated laser output light, obtains a diffusion coefficient of the fine particles contained in the object to be measured from the frequency characteristic of the intensity fluctuation, A particle characteristic measuring apparatus comprising: obtaining a particle diameter of the fine particles contained in the object to be measured from the diffusion coefficient.   The signal processing unit obtains a moving speed of the fine particles contained in the measured object from the frequency characteristic of the intensity fluctuation, and obtains a zeta potential of the fine particles contained in the measured object from the moving speed. The particle characteristic measuring apparatus according to claim 1. When the frequency characteristic of the intensity fluctuation is I (ω), the diffusion coefficient and the movement of the object to be measured are obtained by curve fitting to the following formula (I) or a superposition formula of the following formula (I). The particle characteristic measuring device according to claim 2, wherein a velocity is obtained.

Where F is Fourier transform, j is an imaginary unit, t is time, v is the moving speed, D is the diffusion coefficient, w is the beam width of the laser beam, and θ is the moving direction of the object to be measured. And k represents the wave number. The wave number k is derived from the following equation (II).

Where n is the refractive index of the solvent, λ is the wavelength of the laser beam, and φ is the scattering angle. A photoacoustic modulation element (AOM) for shifting the frequency of the laser light;
The signal processing unit causes the laser light frequency-shifted by the photoacoustic modulation element (AOM) to enter the object to be measured, and outputs laser output light modulated by the scattered feedback light from the object to be measured. 4. The particle characteristic measuring apparatus according to claim 1, wherein the converted signal is analyzed to obtain a frequency characteristic of the intensity fluctuation. 5. The computer analyzes the signal obtained by causing the laser beam to enter the object to be measured including the solvent and fine particles dispersed in the solvent, and converting the laser output light modulated by the scattered feedback light from the object to be measured. A program for executing processing for obtaining characteristics of the fine particles contained in the object to be measured,
The computer analyzes the signal to obtain a frequency characteristic of intensity fluctuation of the modulated laser output light, obtains a diffusion coefficient of the fine particles contained in the object to be measured from the frequency characteristic of the intensity fluctuation, and the diffusion The program which performs the process which calculates | requires the particle diameter of the said fine particle contained in the said to-be-measured object from a coefficient.   Causing the computer to determine a moving speed of the fine particles contained in the object to be measured from the frequency characteristic of the intensity fluctuation, and to execute a process for obtaining a zeta potential of the fine particles contained in the object to be measured from the moving speed. The program according to claim 5, wherein the program is characterized by:

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