JP2023178763A - Photoacoustic wave generation device, photoacoustic wave generation method, and composition estimation method - Google Patents

Abstract

To provide a technique for generating a photoacoustic wave with the use of mid-infrared pulse light which can be more easily used than a terahertz free electron laser.SOLUTION: A photoacoustic wave generation device (1) includes an irradiation section (11) for generating a photoacoustic wave to be propagated in a liquid containing water by irradiating a surface of the liquid with mid-infrared pulse light.SELECTED DRAWING: Figure 1

Description

The present invention relates to a photoacoustic wave generation device, a photoacoustic wave generation method, and a composition estimation method.

A known method is to generate photoacoustic waves underwater and measure an object using the photoacoustic waves. For example, it is known to generate photoacoustic waves by irradiating water with pulsed laser light of visible light to near-infrared light. However, since light in the visible to near-infrared wavelengths is not absorbed by water, it is necessary to bring a solid absorber such as black rubber into contact with the water sample, or to mix an absorber such as a dye into the aqueous solution. This method has problems such as limitations due to the shape of the solid absorbent body and deterioration of the absorbent body, as well as problems such as staining and chemical damage caused by these.

Furthermore, Non-Patent Document 1 discloses a technique for generating photoacoustic waves in water using terahertz laser pulses from a terahertz free electron laser. According to this technology, terahertz light is easily absorbed by water, so it is not necessary to place a solid absorber in water to generate photoacoustic waves or to mix absorbers such as dyes into the aqueous solution. .

Masaaki Tsubouchi, Sho Yamazaki et al., Hiromichi Hoshina, Masaya Nagai, Goro Isoyama, Optics, 50, 509-516 (2021).

However, the technique disclosed in Non-Patent Document 1 requires the use of high-intensity pulsed terahertz light to generate photoacoustic waves. Currently, the only light source that directly generates high-intensity pulsed terahertz light is a terahertz free electron laser, but this equipment requires large facilities and is difficult to put into practical use. Furthermore, transmission optical components such as optical fibers have not been sufficiently developed for terahertz light, and it is relatively difficult to handle it when incorporating it into practical equipment.

In view of the above-mentioned problems, one aspect of the present invention aims to provide a technique for generating photoacoustic waves using mid-infrared pulsed light, which is more easily available than a terahertz free electron laser.

In order to solve the above problems, a photoacoustic wave generator according to one aspect of the present invention provides a photoacoustic wave generator that transmits photoacoustic waves that propagate in the liquid by irradiating the surface of a liquid containing water with mid-infrared pulsed light. It is equipped with an irradiation section that generates waves.

In order to solve the above problems, a photoacoustic wave generation method according to one aspect of the present invention provides photoacoustic waves that propagate in the liquid by irradiating the liquid surface of a liquid containing water with mid-infrared pulsed light. It includes an irradiation step that generates waves.

In order to solve the above problems, a composition estimation method according to one aspect of the present invention irradiates the surface of a liquid containing water with mid-infrared pulsed light, thereby estimating photoacoustic waves propagating in the liquid. an irradiation step to generate an image; an acquisition step to obtain an image representing a wavefront of the photoacoustic wave propagating in the liquid; and a determination step to identify the sound speed of the photoacoustic wave in the liquid by referring to the image. and an estimating step of estimating the composition of the liquid by referring to the sound speed of the photoacoustic wave.

According to one aspect of the present invention, it is possible to provide a technique for generating photoacoustic waves using mid-infrared pulsed light, which is more easily available than a terahertz free electron laser.

1 is a block diagram showing the configuration of a photoacoustic wave generator according to Embodiment 1 of the present invention. FIG. 2 is a schematic diagram showing the difference between a spherical wave and a plane wave. FIG. 2 is a schematic diagram showing an example of the configuration of a generation section and an irradiation section according to Embodiment 1. FIG. It is a graph showing an example of a Fourier transform spectrum of mid-infrared light. FIG. 2 is a schematic diagram showing an example of the configuration of an irradiation section according to Embodiment 1. FIG. This is an example of an image obtained by capturing photoacoustic waves using the shadow graph method. This is a shadow graph image when photoacoustic waves are generated while changing the condensing diameter (beam diameter) of mid-infrared pulsed light on the water surface. This is a table summarizing the condensed diameter and energy density, which are conditions for mid-infrared pulsed light, and the divergence angle of the generated photoacoustic waves. FIG. 2 is a flow diagram showing the flow of a photoacoustic wave generation method S1 according to the first embodiment. FIG. 2 is a flow diagram showing the flow of a composition estimation method according to Embodiment 1 of the present invention. It is a graph showing the measurement results of the molar fraction dependence of the photoacoustic wave velocity in a water/ethanol mixed solution.

[Embodiment 1]
(Photoacoustic wave generator 1)
DESCRIPTION OF THE PREFERRED EMBODIMENTS A photoacoustic wave generation device according to an embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a photoacoustic wave generator 1 according to this embodiment. The photoacoustic wave generator 1 is a device that generates photoacoustic waves in a liquid containing water. Further, the photoacoustic wave generator 1 may estimate or analyze the composition of the liquid by measuring the photoacoustic waves generated in the liquid.

As shown in FIG. 1, the photoacoustic wave generator 1 includes an irradiation section 11. The irradiation unit 11 generates photoacoustic waves that propagate in the liquid by irradiating the surface of the liquid containing water with mid-infrared pulsed light. The irradiation unit 11 focuses mid-infrared pulsed light so as to irradiate the surface of the liquid with a predetermined irradiation area. The size of this irradiation area may be appropriately set depending on the directivity of the mid-infrared pulsed light, the pulse intensity of the mid-infrared pulsed light, the type of liquid, etc. Note that the liquid that can be used in this embodiment may be any liquid that contains water. The liquid containing water is preferably a mixture of water and a substance that mixes with water without separating. This is because water absorbs mid-infrared pulsed light well and is easy to handle. Because of these properties of water, it has not been conventionally possible to analyze liquids containing water using mid-infrared light. However, this embodiment utilizes such properties of water inversely. Note that the proportion of water contained in the liquid is not limited. However, it is preferable to use a liquid whose generated photoacoustic waves can be easily measured. For example, a liquid containing as little solid matter as possible is preferable.

Here, photoacoustic waves will be explained. The energy of the irradiated laser pulse is accumulated in the thickness α ⁻¹ (α is the absorption coefficient) near the liquid surface within the time of the laser pulse width. The energy diffuses at the speed of sound from the point where it is stored, but if the energy storage by the laser pulse ends before the energy propagates through the region of thickness α ^-1 where the energy is confined, the subsequent thermoelastic process Because they occur all at once, a strong pulse-like pressure wave is generated. This pressure wave is called a photoacoustic wave.

Note that if the optical energy is too large, implosion will occur and the material that has absorbed the energy will be scattered, and no photoacoustic waves will be generated. In this embodiment, mid-infrared pulsed light having an energy smaller than such energy is used. Conversely, if the light energy is too small, no photoacoustic waves will be generated, or even if they are generated, it will be difficult to measure the photoacoustic waves. Therefore, in this embodiment, mid-infrared pulsed light having enough energy to generate measurable photoacoustic waves is used.

As shown in FIG. 1, the photoacoustic wave generator 1 may include a generator 10 that generates mid-infrared pulsed light. Although there is no clear definition, mid-infrared light refers to light having a wavelength of 3 μm or more and 20 μm or less in this embodiment. Further, the pulse width of the pulsed light is the pulse width necessary to generate a photoacoustic wave in the liquid. Specifically, from the aforementioned photoacoustic wave generation mechanism, the pulse width of mid-infrared pulsed light is smaller than (αν) ^-1 , where α is the absorption coefficient of the liquid and ν is the sound velocity in the liquid. . For example, assuming that the mid-infrared pulsed light has an absorption coefficient of 300 cm ^-1 at a wavelength of 5 μm and an underwater sound velocity of 1500 m/s at room temperature, the required pulse width is approximately 20 ns, and the mid-infrared pulsed light described in the embodiment described later The light pulse width of 100 fs is sufficiently small compared to this.

Further, the energy per pulse of the mid-infrared pulsed light is, as described above, strong enough to generate a measurable photoacoustic wave. However, since the absorption coefficient of the mid-infrared pulsed light differs slightly depending on the type of liquid and the wavelength of the mid-infrared pulsed light, the lower limit of the energy per pulse changes depending on these conditions. For example, the energy of the mid-infrared pulsed light is preferably 10 μJ/pulse or more. Mid-infrared pulsed light having this level of energy can generate a spherical photoacoustic wave in the liquid by focusing it on a small area (focusing point) on the liquid surface. A spherical wave is a wave whose wavefront spreads over a spherical surface centered on a focal point. As mentioned above, the upper limit of the energy per pulse of mid-infrared pulsed light is the upper limit of energy that causes thermoelastic processes in the liquid, and energy exceeding this causes implosion and causes the liquid to scatter. Cannot be measured.

FIG. 2 is a schematic diagram showing the difference between a spherical wave and a plane wave of photoacoustic waves. FIG. 2A shows a spherical wave 230 when the mid-infrared pulsed light 210 is focused by a condensing lens 220 or the like to a converging point 201 on the liquid surface. The spherical wave 230 is generated when the focal diameter of the focal point 201 is approximately the wavelength of the photoacoustic wave. The spherical wave 230 travels in a spherical shape centered on the focal point 201 .

For example, plane photoacoustic waves can be generated in a liquid by irradiating mid-infrared pulsed light in a circular shape with a focused diameter larger than the wavelength of the photoacoustic waves. FIG. 2(b) shows a plane wave 240 when the mid-infrared pulsed light 210 is irradiated onto the irradiation surface 202 of the liquid surface. As shown in the figure, the plane wave 240 has a wavefront parallel to the irradiation surface 202 traveling in a direction perpendicular to the irradiation surface 202 . The photoacoustic wave of the plane wave 240 has higher directivity than the spherical wave 230. The highly directional plane wave 240 can travel a longer distance than the spherical wave 230 generated with the same energy. In order to generate a plane photoacoustic wave, the energy of the mid-infrared pulsed light is preferably 100 μJ/pulse or more. This is because it is necessary to irradiate a wider range than the focal point 201 to generate photoacoustic waves.

FIG. 3 is a schematic diagram showing a configuration example of the generation section 10 and the irradiation section 11. In the example shown in FIG. 3, the generation unit 10 includes a known titanium sapphire laser (for example, wavelength 800 nm, pulse width 50 fs, pulse energy 1.2 mJ) and an optical parametric amplifier (hereinafter referred to as "OPA"). ) to generate mid-infrared pulsed light.

Specifically, as shown in FIG. 3 as an example, pulsed excitation light 50 from a titanium sapphire laser (not shown) is introduced into the OPA 51, and signal light (wavelength 1380 nm) 41 and idler light (wavelength 1900 nm) 42 are generated. generate. After adjusting the delay times of the signal light 41 and the idler light 42 via two multilayer mirrors 52 and 54 and delay stages 53 and 55, they are introduced into an AgGaS ₂ crystal 64. Due to the difference frequency generation process within the AgGaS ₂ crystal 64, mid-infrared pulsed light (wavelength 5 μm) 43 with a pulse width of 100 fs equal to the frequency difference between the signal light 41 and the idler light 42 is generated, and is extracted through the filter 56. , and sent to the irradiation section 11.

The mid-infrared pulsed light 43 is introduced into an interferometer (a combination of a beam splitter 65, a delay stage 59, and a mirror 60) shown on the left side of FIG. After measuring with a photodiode 61 through an ND filter 63 and a pinhole 62, the wavelength can be confirmed by obtaining a spectrum as shown in FIG. 4 by Fourier transformation.

The irradiation unit 11 includes a parabolic mirror 71 that reflects the mid-infrared pulsed light (pulse width 100 fs) 43 sent from the generation unit 10 from above toward the liquid surface. As shown in FIG. 5, the mid-infrared pulsed light 43 reflected by the parabolic mirror 71 is irradiated toward the surface of the liquid 91 placed in the cell 90.

Note that the irradiation unit 11 may be configured using a parabolic mirror 71 so that the mid-infrared pulsed light 43 is focused on the surface of the liquid 91 at a predetermined focusing diameter, as shown in FIG. Alternatively, a plane mirror or the like may be used so that the mid-infrared pulsed light 43 is irradiated onto the liquid surface as parallel light. Alternatively, it may be constructed by combining a lens, a collimator, etc. so as to produce parallel light of a predetermined area.

The irradiated mid-infrared pulsed light 43 is completely absorbed near the liquid surface and is accumulated as thermal energy in a very narrow area in a short time of about 100 fs. The accumulated thermal energy is released into the liquid and into the air as pressure waves (photoacoustic waves) by a thermoelastic process in a time of about 1 ns. Photoacoustic waves emitted into a liquid propagate deep into the liquid.

In the embodiment described above, a titanium sapphire laser and an OPA were used as the generation unit 10 to generate mid-infrared pulsed light. However, the generation device or generation method is not limited to this. The method is not limited as long as it can generate mid-infrared pulsed light having a certain amount of pulse energy. In particular, in recent years, laser devices that can emit mid-infrared pulsed laser light with high pulse energy that can be applied to this embodiment have been developed, and such commercially available laser devices can be used.

The photoacoustic wave generation device 1 may include an image generation section 12, as shown in FIG. The image generation unit 12 converts the photoacoustic waves into an image using, for example, a shadow graph method. The shadowgraph method is a method in which a target medium is irradiated with parallel light, and the light transmitted through the medium is acquired by a sensor as an electrical signal and displayed as an image. Since the difference in the concentration of the medium is detected as a difference in brightness, it is possible to obtain an image of photoacoustic waves as pressure waves.

The image generation unit 12 includes, for example, a laser light source 72, an ND filter 73, a mirror 74, lens groups 75 and 76, and an imaging camera 77. The image generation unit 12 can image the photoacoustic waves by a shadow graph method using incoherent pulsed laser light. For example, as the laser light source 72, a laser device that generates incoherent pulsed laser light (eg, wavelength 645 nm, pulse width 10 ns) can be used. The reason for using incoherent pulsed laser light is that when coherent light is used, interference fringes are likely to occur in the image due to minute dust and diffraction effects, making it difficult to obtain a high-quality shadowgraph image.

Incoherent pulsed laser light 80 emitted from laser light source 72 passes through ND filter 73, is reflected by mirror 74, and passes through liquid 91 placed in the aforementioned cell 90. The incoherent pulsed laser beam 81 that has passed through the liquid 91 forms an image on an image sensor (for example, a CMOS (Complementary Metal-Oxide Semiconductor) device) of an image pickup camera 77 by lens groups 75 and 76 . The electrical signal data of this image sensor can be acquired and displayed as an image. The image transfer magnification was 2x. By analyzing the shadow graph image captured by the imaging camera 77 in this manner, the velocity of the photoacoustic wave can be determined.

By using pulsed light as the irradiation light source, a snapshot image of the photoacoustic wave with the time resolution of the pulse width can be obtained, and observation can be made from the time when the photoacoustic wave is generated at the liquid surface (timing of mid-infrared pulsed light irradiation). By scanning the interval between irradiation times with the pulsed light source, it is possible to observe how photoacoustic waves propagate through water (changes over time).

FIG. 6 is an example of an image obtained by capturing photoacoustic waves using the shadow graph method. Figure 6(a) shows snapshots every 0.5 μs of the underwater propagation of the photoacoustic waves generated when mid-infrared pulsed light with a wavelength of 5.1 μm and pulse energy of 14 μJ is focused on the water surface to a beam diameter of 77 μm. This is the image shown in . The elapsed time is from upper left to lower left: 0 μs, 0.5 μs, 1 μs after irradiation, and from upper right to lower right: 1.5 μs, 2 μs, and 2.5 μs after irradiation. The reason why the liquid surface (black line in the image) is curved is because the surface tension is pulling the water surface against the left and right inner walls of the cell.

FIG. 6(b) is a graph showing a temporal change in the waveform of a vertical cross section of a photoacoustic wave. The vertical axis is the intensity of the wavefront (units are arbitrary). Specifically, it corresponds to the photoacoustic wave image shown in FIG. 6(a), and is a diagram in which the intensity distribution in the direction perpendicular to the mid-infrared pulsed light irradiation position is plotted for each elapsed time. It can be seen from FIG. 6(b) that the photoacoustic wave reaches a depth of 3 mm in 2 μs after irradiation with the mid-infrared pulsed light. From this, the speed of the photoacoustic wave is estimated to be approximately 1500 m/s, which corresponds to the speed of sound in room temperature water.

In the practical application of photoacoustic waves, it is preferable that the photoacoustic waves be made into highly directional waves that approach plane waves. This allows photoacoustic waves to reach long distances by concentrating energy in the direction of a specific target.

FIG. 7 is a shadow graph image when a photoacoustic wave is generated by changing the condensing diameter (beam diameter) of mid-infrared pulsed light on the water surface. The imaging time is 1 μs after the mid-infrared pulsed light irradiation. The locations indicated by dotted circles SP in each image in FIG. 7 are light condensing portions. (a), (b), (c), and (d) of FIG. 7 are shadow graph images when the converging diameters are 0.077 mm, 0.110 mm, 0.142 mm, and 0.177 mm, respectively. Further, FIG. 8 is a table summarizing the condensed diameter and energy density, which are the conditions of the mid-infrared pulsed light, and the divergence angle of the generated photoacoustic waves for each image in FIG. As shown in FIG. 8, in the result (d) with a wide condensing diameter, the beam divergence angle is as small as about 27 degrees, and highly directional photoacoustic waves are generated. This is because according to Huygens' principle, when the wave source becomes larger, the waves in the traveling direction are strengthened due to interference.

By increasing the energy density of the mid-infrared pulsed light, it is possible to generate a plane wave with a smaller divergence angle. This allows photoacoustic waves to reach further distances. For this purpose, for example, a Q-switched nanosecond pulse laser capable of emitting a high-energy laser can be used. Note that the method of imaging photoacoustic waves is not limited to the shadow graph method. Other methods may also be used, including, for example, the Schlieren method.

(Photoacoustic wave generation method)
Next, a photoacoustic wave generation method according to this embodiment will be explained. FIG. 9 is a flow diagram showing the flow of the photoacoustic wave generation method S1. As shown in FIG. 9, the photoacoustic wave generation method S1 includes step S12 of irradiating the surface of a liquid containing water with mid-infrared pulsed light. Thereby, it is possible to generate photoacoustic waves that propagate in the liquid. The conditions for the mid-infrared pulsed light for generating photoacoustic waves are as described in the embodiment of the photoacoustic wave generator 1.

As shown in FIG. 9, the photoacoustic wave generation method S1 may include a step S11 of generating mid-infrared pulsed light before step S12. The method for generating mid-infrared pulsed light is the same as described in the embodiment of the photoacoustic wave generator 1.

As described above, according to the photoacoustic wave generation device 1 and the photoacoustic wave generation method S1 according to the present embodiment, by irradiating the liquid surface of a liquid containing water with mid-infrared pulsed light, the light propagates through the liquid. It is possible to generate photoacoustic waves. Since mid-infrared pulsed light is well absorbed by water, it has not been considered to use mid-infrared pulsed light for measurement. However, the inventor of the present application has taken advantage of this property to generate photoacoustic waves using a device that is cheaper and easier to handle than the method using terahertz light by using mid-infrared pulsed light. We focused on what can be done. This method has made it easy to apply measurement methods using photoacoustic waves to a wide range of fields.

[Embodiment 2]
Next, a second embodiment of the present invention will be described. As a measurement method using photoacoustic waves, for example, the composition of a liquid can be estimated. This embodiment is a method of estimating the composition of a liquid using photoacoustic waves. FIG. 10 is a flow diagram showing the flow of the composition estimation method S2 according to this embodiment.

The composition estimation method S2 includes the following steps. In step S21, a photoacoustic wave that propagates in the liquid is generated by irradiating the surface of the liquid containing water with mid-infrared pulsed light (irradiation step). The method or device for generating mid-infrared pulsed light and the method or device for irradiating the surface of a liquid containing water with the generated mid-infrared pulsed light are as described in Embodiment 1.

Next, in step S22, an image representing the wavefront of the photoacoustic wave propagating in the liquid is acquired (acquisition step). The image acquisition method is as described in the first embodiment.

Next, in step S23, the sound speed of the photoacoustic wave in the liquid is specified by referring to the image (identification step). The method of identifying the sound speed of a photoacoustic wave from an image is as described in the first embodiment.

Next, in step S24, the composition of the liquid is estimated by referring to the sound speed of the photoacoustic wave (estimation step). In this estimation step, the composition of the liquid is estimated based on the relationship between the composition of the liquid and the sound speed of the photoacoustic wave in the liquid, which has been obtained in advance.

According to the above composition estimation method S2, by obtaining the relationship between the composition of a liquid and the sound speed of a photoacoustic wave in the liquid in advance, it is possible to estimate the composition of many types of liquid. This means that the compositions of many types of liquids can be estimated with one photoacoustic wave generation device equipped with an image generation section.

The present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. are also included within the technical scope of the present invention.

An embodiment of the present invention will be described below. Many methods are known for analyzing the composition of liquids. However, the analysis method often differs depending on the component. Therefore, it would be advantageous if a single method could be used to quantitatively analyze the components of a solution or mixed solution whose components are known. In this example, the ethanol concentration in an ethanol aqueous solution (a mixture of water and ethanol) was estimated using photoacoustic waves.

It is known that the physicochemical properties of a mixed solution of water and alcohol exhibit a specific and strong dependence on the molar fraction. For example, the speed of photoacoustic waves in an ethanol solution does not monotonically change with respect to the mole fraction, but has an extreme value around the mole fraction of 0.1, as shown in FIG. Because of this strong dependence, by utilizing the speed of photoacoustic waves, it is possible to achieve higher sensitivity and faster measurement in quantitative analysis (mixing ratio analysis) of mixed solutions.

The measurement results of the mole fraction dependence of the photoacoustic wave velocity in a water/ethanol mixed solution measured using the method described in Embodiment 2 and the literature values (G. D'Arrigo and A. Paparelli, The Journal of Chemical Physics, vol. 88, pages 405-415 (1998)) and results measured using photoacoustic waves generated using terahertz light as a comparative example, are shown in FIG. 11. This measurement was completed within one minute, and as shown in the figure, it also has quantitative properties that show very good agreement with literature values. Since this method uses two-dimensional image observation using the shadow graph method, it is possible to image the two-dimensional spatial distribution of velocity, that is, the mixture ratio distribution, and relatively fast measurement within one minute is possible. be.

Currently, the measurement time is limited by the communication time of the mechanism that sweeps the time from mid-infrared pulsed light irradiation to shadowgraph pulsed light irradiation, and by improving this point, the measurement time can be reduced to 1. It is also possible to shorten it to about /10. This makes it possible to measure in a line, so it is useful for measuring the composition uniformity of transparent (for visible and near-infrared light regions) materials that allow acoustic waves to propagate and to which the shadowgraph method can be applied. Possible applications. For example, it may be applied to measuring the uniformity of mixed solutions (alcohol products, etc.) and the state of mixing. Up until now, measurements of the brewing process of alcoholic beverages have mainly been based on empirical measurements. It is said that photoacoustic waves strongly depend on the solution structure, and each state during the brewing process also strongly depends on the mixed state of water and alcohol molecules (molecule groups). Therefore, it is thought that by quantifying the mixing state as photoacoustic wave velocity and converting it into a two-dimensional image, it will be possible to evaluate the degree of brewing.

Note that the method described in the above example can be applied not only to mid-infrared pulsed light but also to photoacoustic waves generated in the same manner as in the above embodiment using terahertz pulsed light, as shown in FIG. I get the same result. In other words, the composition can also be estimated using the composition estimation method described below.

The composition estimation method includes the steps of irradiating the surface of a liquid containing water with pulsed light with a wavelength ranging from mid-infrared light to terahertz light to generate photoacoustic waves that propagate in the liquid; an acquisition step of acquiring an image representing a wavefront of the photoacoustic wave propagating through the liquid; a specifying step of identifying the sound speed of the photoacoustic wave in the liquid by referring to the image; estimating the composition of the liquid by referring to the method. According to this method, components in a solution or mixed solution containing water can be quantitatively analyzed by using photoacoustic waves. For example, it can be applied to measuring the uniformity of mixed solutions (alcohol products, etc.) and the mixing state.

〔summary〕
A photoacoustic wave generation device according to aspect 1 of the present invention includes an irradiation unit that generates photoacoustic waves that propagate in the liquid by irradiating the surface of a liquid containing water with mid-infrared pulsed light. There is.

A photoacoustic wave generation device according to aspect 2 of the present invention is the photoacoustic wave generation device according to aspect 1, wherein the wavelength of the mid-infrared pulsed light is 3 μm or more and 20 μm or less.

A photoacoustic wave generation device according to aspect 3 of the present invention is the photoacoustic wave generation device according to aspect 1 or 2, in which the pulse width of the mid-infrared pulsed light is such that the absorption coefficient of the liquid is α, is smaller than (αν) ^-1 , where ν is the speed of sound.

A photoacoustic wave generation device according to aspect 4 of the present invention is the photoacoustic wave generation device according to any one of aspects 1 to 3, wherein the energy of the mid-infrared pulsed light is 10 μJ/pulse or more.

A photoacoustic wave generation device according to aspect 5 of the present invention is the photoacoustic wave generation device according to any one of aspects 1 to 4, wherein the energy of the mid-infrared pulsed light is 100 μJ/pulse or more, and the irradiation The part irradiates the liquid surface with the mid-infrared pulsed light in an irradiation area where the photoacoustic wave becomes a plane wave.

A photoacoustic wave generation device according to an aspect 6 of the present invention is the photoacoustic wave generation device according to any one of aspects 1 to 5, further comprising a generation unit that generates the mid-infrared pulsed light.

A photoacoustic wave generation device according to a seventh aspect of the present invention is the photoacoustic wave generation device according to any one of aspects 1 to 6, further comprising an image generation unit that converts the photoacoustic wave into an image.

In the photoacoustic wave generation device according to aspect 8 of the present invention, in the photoacoustic wave generation device according to aspect 7, the image generation unit converts the photoacoustic wave into an image by a shadow graph method using incoherent pulsed laser light. become

The photoacoustic wave generation method according to aspect 9 of the present invention includes an irradiation step of generating a photoacoustic wave that propagates in the liquid by irradiating the surface of the liquid containing water with mid-infrared pulsed light. There is.

A composition estimation method according to aspect 10 of the present invention includes an irradiation step of irradiating the surface of a liquid containing water with mid-infrared pulsed light to generate a photoacoustic wave that propagates in the liquid; an acquisition step of acquiring an image representing a wavefront of the photoacoustic wave propagating through the liquid; a specifying step of identifying the sound speed of the photoacoustic wave in the liquid by referring to the image; estimating the composition of the liquid by referring to the method.

A composition estimation method according to an eleventh aspect of the present invention is the composition estimation method according to the tenth aspect, wherein the liquid is a mixed liquid of water and alcohol.

1... Photoacoustic wave generator 10... Generation section 11... Irradiation section 12... Image generation section 41... Signal light 42... Idler light 43... Mid-infrared pulsed light 50... Pulsed excitation light 51... Optical parametric amplifier (OPA)
52, 54... Multilayer mirror 53, 55, 59... Delay stage 56... Filter 58... Flipper mirror 60, 74... Mirror 61... Photodiode 62... Pinhole 63, 73... ND filter 64... AgGaS ₂ crystal 65... Beam splitter 71... Parabolic mirror 72... Laser light source 75, 76... Lens group 77... Imaging camera 80, 81... Incoherent pulsed laser light

Claims (11)

comprising an irradiation unit that generates photoacoustic waves that propagate in the liquid by irradiating the surface of the liquid containing water with mid-infrared pulsed light;
A photoacoustic wave generator characterized by: The wavelength of the mid-infrared pulsed light is 3 μm or more and 20 μm or less,
The photoacoustic wave generating device according to claim 1, characterized in that: The pulse width of the mid-infrared pulsed light is smaller than (αν) ⁻¹ , where α is the absorption coefficient of the liquid and ν is the sound velocity in the liquid.
The photoacoustic wave generating device according to claim 1, characterized in that: The energy of the mid-infrared pulsed light is 10 μJ/pulse or more,
The photoacoustic wave generating device according to claim 1, characterized in that: The energy of the mid-infrared pulsed light is 100 μJ/pulse or more, and the irradiation unit irradiates the liquid surface with the mid-infrared pulsed light in an irradiation area where the photoacoustic wave becomes a plane wave.
The photoacoustic wave generation device according to any one of claims 1 to 4. further comprising a generation unit that generates the mid-infrared pulsed light;
The photoacoustic wave generation device according to any one of claims 1 to 4. further comprising an image generation unit that images the photoacoustic wave;
The photoacoustic wave generation device according to any one of claims 1 to 4. The image generation unit images the photoacoustic wave by a shadow graph method using incoherent pulsed laser light.
The photoacoustic wave generating device according to claim 7, characterized in that: The method includes an irradiation step of generating a photoacoustic wave that propagates in the liquid by irradiating the surface of the liquid containing water with mid-infrared pulsed light.
A photoacoustic wave generation method characterized by: An irradiation step of generating a photoacoustic wave that propagates in the liquid by irradiating the surface of the liquid containing water with mid-infrared pulsed light;
an acquisition step of acquiring an image representing a wavefront of the photoacoustic wave propagating in the liquid;
identifying the sound speed of the photoacoustic wave in the liquid by referring to the image;
estimating the composition of the liquid by referring to the sound speed of the photoacoustic wave;
A composition estimation method characterized by the following. The liquid is a mixture of water and alcohol.
The composition estimation method according to claim 10.

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