JPH03156362A - Method and apparatus for detecting photo-acoustic signal - Google Patents

Abstract

PURPOSE:To decrease the halation of a photo-acoustic image and to make it possible to perform stable measurement at high resolution by obtaining a reverse filter for restoring the deterioration of the resolution of the photo-acoustic image based on the thermal impulse response of a sample, and making the filter act to the photo-acoustic image. CONSTITUTION:The parallel light emitted from an Ar laser 31 is modulated with intensity in a photo-acoustic modulating element 32. The intermittent light is condensed at a rear focal point position 81 with a lens 34. The luminous flux becomes collimated through a lens 36. The light is reflected from dichroic mirror 37 and condensed at a front focal-point position 82. An ultrasonic wave is generated by a thermal distortion wave generated by the photo-acoustic effect at the condensed spot of a sample 7. At the same time, minute displacement is generated on the surface of the sample 7. A Michelson interference optical system 140 detects the photo-acoustic effect generated in the inside of the sample in the two-dimensional directions of the sample and forms the two-dimensional photo-acoustic image. A computer 68 obtains a reverse filter for restoring the deterioration in resolution of the photo-acoustic image based on the thermal impulse response of the sample 7. The filter is made to act on the photo-acoustic image, and the resolution of the photo-acoustic image is improved. Thus, the internal information in the sample can be detected stably at high resolution.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention is directed to the use of photoacoustic signals.
The present invention relates to a photoacoustic signal detection method and apparatus for detecting surface and internal information of a sample using a photoacoustic signal, and a method for detecting internal defects in a semiconductor element.

[Conventional technology]

The photoacoustic effect was developed by Tyndall in 1881.
, Bell, Rontogen
) was discovered by et al. That is, as shown in FIG. 10, when intensity-modulated light (intermittent light) 19 is focused and irradiated onto the sample 7 through the lens 5, a light absorption region (2) is formed. .

Heat is generated at 21 and periodically diffuses through the thermal diffusion region V, , 23 given by the thermal diffusion length μ, 22, and this thermal strain wave generates a surface acoustic wave (ultrasonic wave).

This ultrasonic wave, or photoacoustic signal, is detected using a microphone (acoustoelectric transducer), piezoelectric element, or optical interferometer, and by determining the signal component synchronized with the modulation frequency of the incident light, information on the surface and interior of the sample is obtained. can be obtained. Regarding the detection method of the photoacoustic signal, for example, see the literature "Nondestructive Testing; Vol. 36, No. io, p. 730-p.
736 (October 1986)" and "IEE, 1986 Ultrasonics Symposium 9.
．． 515-526 (1986) (IEEE; 198
6 ULTRASONIC3S YM P OS I
UM-p, 515-526 (1986)) J.

That is, the photoacoustic signal is detected using, for example, an optical interferometer, and a modulation frequency component synchronized with the modulation frequency of the incident light is extracted.

By changing the modulation frequency, this frequency component contains information about the surface or inside of the sample depending on the frequency.
The thermal diffusion length μ, 21 can be changed, and information in the depth direction of the sample can be obtained. If there is a defect such as a crack in the thermal diffusion region V, 23, a signal change appears in the modulation frequency component in the interference intensity signal, and its existence can be known.

[Problem to be solved by the invention]

However, although the above conventional technology is an extremely effective means for detecting photoacoustic signals in a non-contact and non-destructive manner, it is difficult to detect internal information of a sample having a fine structure of 1 m or less with the above conventional technology. There was a problem with this.

The purpose of the present invention is to provide an optical flF signal detection method and apparatus that reduce blur in photoacoustic images, significantly improve resolution, and stably detect internal information of a sample at a high resolution of 1 m or less. It is about providing.

[Means to solve the problem]

In order to achieve the above object, the present invention includes a light source, a modulator that modulates the intensity of light from the light source at a desired frequency, and a condenser that focuses the intensity-modulated light onto a sample (for example, a semiconductor device). an optical means, a detection means for detecting a photoacoustic effect generated within the sample, an information extraction means for extracting surface and internal information of the sample from the detection signal', and two-dimensional scanning of light from the sample or a light source. In a photoacoustic signal detection device consisting of a scanning means that By determining an inverse filter that restores the resolution degradation of the photoacoustic image using the transfer function (transfer function) and applying the inverse filter to the obtained photoacoustic image, the resolution of the photoacoustic image is improved and the internal information of the sample is captured at high resolution. This enables stable detection.

Similarly, in the photoacoustic signal detection device of the present invention, a pure thermal impulse response in a homogeneous sample (a heat wave generated from an infinitesimal point propagates inside the sample and is converted into a temperature distribution inside the sample) The resolution deterioration of photoacoustic images can be repaired using the transfer function (transfer function until the change in temperature at an infinitesimal point is converted to a minute displacement on the sample surface, that is, a photoacoustic signal) and thermoelastic impulse response By finding an inverse filter for this purpose and applying the inverse filter to the obtained photoacoustic image, the resolution of the photoacoustic image is improved and internal information of the sample can be detected stably with high resolution.

[Effect]

By the way, the lateral resolution and depth resolution of a photoacoustic signal are in the light absorption region■. , 21, that is, when the spot diameter of the laser beam is smaller than the thermal diffusion region V, , 23, it is given by the thermal diffusion length μ, 22. This μ is defined by equation (1).

However, k: Thermal conductivity of the sample ρ: Heavy density: Specific heat f: Laser intensity modulation frequency For example, when f = lOkHz, Si and ^l are μ, ~5
It is 0μI, and Sin is about ~5μ.

That is, as shown in FIG. 11, the thermal impedance distribution 7a inside the sample is now considered as the internal information of the sample 7. Scanning of laser beam 19 for excitation (actually XY
As the sample 7 is moved by the stage), the amplitude and phase of the thermal distortion wave change due to the thermal impedance distribution 7a existing in the thermal diffusion region 23 at each beam position, and this change causes a minute displacement of the surface of the sample 7. Appears at 30. A photoacoustic signal is obtained by detecting this minute displacement as an interference intensity signal using the probe beam 24 of the interferometer. Therefore, the photoacoustic signal obtained at each excitation beam position is the integral of thermal impedance information within the thermal diffusion region 23. A two-dimensional photoacoustic image is constructed using the integrated photoacoustic signals at each point. Therefore, the photoacoustic image obtained becomes a so-called blurred image. The lower graph in FIG. 11 shows the photoacoustic image p(x,y) of the thermal impedance distribution 7a.
It shows the amplitude distribution p (x) in the direction. It can be seen that the signal at the boundary in the X direction of the thermal impedance distribution 7a is greatly smoothed.

This blurring can be improved by making the thermal diffusion region 23 smaller, but as shown in equation (1), the thermal diffusion length μ is determined by the modulation frequency f of the excitation laser beam and the thermal properties of the sample 7. In order to obtain a thermal diffusion length on the order of 1 m or less, some samples require a modulation frequency of several hundred MHz. Therefore, considering the band of the lock-in amplifier, etc., it is currently extremely difficult to detect internal information of a sample having a microstructure on the order of μm or less.

Therefore, according to the photoacoustic signal detection device of the present invention, an inverse filter for repairing the resolution degradation of the photoacoustic image is determined from the pure thermal impulse response and thermoelastic impulse response of the sample, and the detected photoacoustic image is By applying the obtained inverse filter, the resolution of the optical acoustic image can be improved, and the internal information of the sample can be detected stably with high resolution.

〔Example〕

Before explaining the present invention in detail, its basic principle will be explained below.

The photoacoustic image p(x, y) actually detected is given by equation (2).

Thermal impedance information at that point (infinitely small) that is generated and detected (= a collection of infinitely small point heat sources) h (x, y): Thermal impulse response of the sample The heat wave generated from one infinitesimal point For example, the transfer function for propagating inside the sample and converting it into a photoacoustic signal due to minute displacements on the sample surface. However, q(x, y): Ideal photoacoustic image Excited by a point light source on the sample surface μ , :Thermal diffusion length Generally, since a photoacoustic signal is obtained as a complex number having an amplitude and a phase, equation (2) is subjected to two-dimensional complex Fourier transform to obtain equation (4).

P(μ, υ) −F [p(x, y))Q(μ, υ)・
H (μ, υ) (4) However, μ, v: Spatial frequency P (μ, υ) in x and y directions
: Fourier transform image Q(μ, υ) of p(x,y) :
Fourier transform image H(μ, υ) of q(x, y): h(
By using the Fourier transform image 1 /H (μ, υ) of x, y) as an inverse filter, multiplying both sides of equation (4) to obtain equation (5).

(2) If the equation (5) is subjected to a two-dimensional inverse complex Fourier transform, the ideal light g 99 pictures #1 q (x, y) is finally obtained.

q (x, y) = F-' CQ (μ, υ)] In other words, from the thermal impulse response h (x, y) of the sample, find the inverse filter 1/H (μ, υ) and obtain it. Takoon Shunga #p
After multiplying the Fourier transform image P (μ, υ) of (x, y),
By performing inverse Fourier transform, an ideal photoacoustic image without deterioration in resolution can be obtained.

Example 1 A first example of the present invention will be described below with reference to FIGS. 1 to 6. FIG. 1 shows a photoacoustic detection optical system in a first embodiment of the present invention. This optical system uses an Ar laser (wavelength 0.515
A modulated laser irradiation optical system 130 using a light source (μm) 31,
Michelson interference optical system 1 for detecting photoacoustic signals
40, a stage system 150, and a signal processing system 160. In the modulated laser irradiation optical system 130, the parallel light emitted from the Ar laser 31 is intensity-modulated at a desired frequency by the acousto-optic modulator 32, and the intermittent light is expanded to a desired beam diameter by the beam expander 33, and then The lens 34 focuses the light on the rear focal position 8■. A pinhole 35 is installed at the condensing position 81, and as shown in FIG. 2, it blocks higher-order diffracted light components 101a and 101b existing around the peak portion 100 of the condensed spot. As a result, the light intensity distribution immediately after passing through the pinhole 35 has only a peak portion 100, as shown in FIG. Since the focal position 81 is the front focal position of the lens 36, the light beam after passing through the pinhole 35 becomes parallel light after passing through the lens 36. This parallel light is reflected by the dichroic mirror 37
(wavelengths of 0.58 μm or less are reflected, wavelengths of 0.6-m or more are transmitted), and are then reflected by the objective lens 39 at its front focal point i? The light is focused on i82, resulting in a spot with a light intensity distribution similar to that shown in FIG. That is, the front focal position j181 of the lens 36 and the front focal position 82 of the objective lens 39
is a conjugate as well as a confocal relationship.

Focused spot position 2282 on the surface of sample 7 (objective lens 3
Thermal strain waves generated by the photoacoustic effect at the front focal position of 9) generate superstraddling waves, and at the same time, a minute displacement occurs on the surface of the sample 7.

In the Michelson interference optical system 140, He-Ne
After the circularly polarized parallel light emitted from the laser (wavelength: 0.633 μm) 51 is expanded to a desired beam diameter by the beam expander 52, it is expanded to the rear focal position j1 by the lens 53.
The light is focused on 83. A pinhole 54 is installed at the focal point position 83, and high-order diffracted light components around the peak of the focused spot are blocked in the same way as shown in FIG. The focal position F183 is the front focal position of the lens 55, and the light flux after passing through the pinhole 54 is turned into parallel light by the lens 55. This parallel light is separated into P-polarized light and S-polarized light by a polarizing beam splitter 56. The P-polarized light passes through the polarization beam splitter 56, and then passes through the dichroic mirror 37,
After passing through the λ/4 plate 3 and the metal plate 8, it becomes circularly polarized light, and is focused by the objective lens 39 on the 82nd position II (the front focal position of the objective lens 39) on the sample 7, as shown in FIG. The spot will have a light intensity distribution of . On the other hand, the S-polarized light is reflected by the polarizing beam splitter 56 and is reflected by the λ/4 plate 5
After that, it becomes circularly polarized light and enters the reference mirror 59.

The reflected light from the sample 7 has phase information based on minute displacements generated on the surface of the sample 7, and after passing through the objective lens 39, the λ/4 plate 3, and the metal plate 8, it becomes S-polarized light and is reflected by the polarizing beam splitter 56. The reflected light from the reference mirror 59 is λ/
After passing through four plates, five metal plates, and eight, it becomes P-polarized light and passes through the polarization beam splitter 56. In FIG. 4, 110 indicates the polarization direction of the reflected light from the sample 7, and ill indicates the polarization direction of the reflected light from the reference mirror 59.

Since the two are perpendicular to each other, they do not interfere as is. However, by inserting the polarizing plate 60 into the optical path and setting the polarization direction to 45° as shown at 112 in FIG. 4, the reflected lights from both will interfere. do. This interference pattern includes minute displacements occurring on the surface of the sample 7 as light intensity information, which is focused by the lens 61 onto the rear focal position 84 and detected by a photoelectric conversion element 64 such as a photodiode. In addition, by installing the pinhole 63 at the back focal position 84, stray light generated within the objective lens 39 and the sample 7 can be removed.
As described above, in this Michelson interference optical system 140, the lens 61 blocks multiple interference components generated within the transparent thin film constituting the sample 7 or higher-order diffracted light components generated due to minute irregularities on the surface of the sample 7. Front focal position 84, front focal position 1B2 of objective lens 39 and lens 5
There is a conjugate and confocal relationship with the rear focal position 83 of No. 3. The photoelectrically converted interference intensity signal is amplified by a preamplifier 65 and then sent to a lock-in amplifier 67. The lock-in amplifier 67 uses the modulation frequency signal from the oscillator 66 used to drive the acousto-optic modulation element 32 as a reference signal, and extracts the amplitude of the modulation frequency component included in the interference intensity signal and the phase component with respect to the modulation frequency signal. This frequency component and phase component have information in the thermal diffusion region vLb defined by the modulation frequency. Therefore, if there is a defect such as a crack or a region with different thermal impedance in this thermal diffusion region Vtb, the interference intensity signal The amplitude and phase of the modulated frequency component in the signal change, making its presence known.

The computer 68 of the signal processing system 16G processes the detected photoacoustic image p(x, y
) processing is performed. First, the thermal impulse response h(x, y) of the sample is calculated according to equation (3).

Next, the movement signal of the XY stage 42 and the output signal from the lock-in amplifier 67 are input, and the two-dimensional light sound four-picture@p
(x, y) is constructed. Next, h(x, y) and p(x
, y) are subjected to two-dimensional complex Fourier transform to obtain respective Fourier transforms fliRH(μ, υ) and P(μ, υ).

Next, after calculating 1/H (μ, υ), based on equation (5), the spectrum of thermal impedance information inside the sample,
In other words, the Fourier transform of an ideal photoacoustic image @Q(μ
, υ). Finally, based on equation (6), Q(
μ, υ) is subjected to two-dimensional inverse complex Fourier transform, and the ideal 9M
l! Obtain flq(x,y). This q(x,y) is
Displayed on monitor TV 69.

Figure 6 shows how an ideal photoacoustic image q(x,y) of the thermal impedance distribution 7a inside the sample is obtained due to the effect of this inverse filter 1/H(μ, υ). be. The graph below shows the amplitude distribution q (x) of q (x, y) in the X direction.6 Compared to the graph of the conventional method shown in Figure 1O, the thermal impedance distribution7
It can be seen that the signal at the boundary in the X direction of a is clear.

As described above, according to this example, deterioration in the resolution of a photoacoustic image can be repaired by applying an inverse filter determined from the thermal impulse response of the sample to the obtained photoacoustic image. This enables high-resolution detection of internal information of the sample. In addition, by using a confocal optical system as the modulated laser irradiation optical system, it is possible to irradiate the sample with a minute spot light that does not contain higher-order diffraction light components in the periphery, reducing noise components due to stray light, etc. Can be done. In addition, by using a Michelson interferometer as a confocal optical system, it is possible to reduce the effects of stray light, interference components generated within the transparent film on the sample, and higher-order diffracted light components generated by minute irregularities on the sample surface. This improves the detection sensitivity and signal-to-noise ratio of optical acoustic signals, that is, interference intensity signals.

Example 2 A second embodiment of the present invention will be described based on FIG.

FIG. 7 shows a photoacoustic detection optical system according to a second embodiment of the present invention. In this embodiment, a PZT element 73 is used instead of a Michelson interferometer to detect a photoacoustic signal.
is used. Other modulated laser irradiation optical systems 170,
The functions of the stage system 180 and signal processing system 1.90 are as follows:
This embodiment is completely the same as the first embodiment shown in the figure, and its explanation will be omitted.

According to this embodiment, the same effects as in the first embodiment can be obtained, and at the same time, since the interference optical system is not required, the entire optical system becomes compact and stability is improved.

Embodiment 3 A third embodiment of the present invention will be described based on FIGS. 8 and 9. In this embodiment, the optical system for detecting the light 11 is exactly the same as the optical system of the first embodiment shown in FIG. 1, so its explanation will be omitted.

FIG. 8 is a diagram showing the basic principle of the third embodiment. In the previous two examples, the internal information of the sample was mainly assumed to be the thermal impedance distribution, and the modulation frequency of the laser beam for exciting the sample was constant, but in this example, the internal information of the sample was As such, not only the thermal impedance distribution but also the elastic impedance distribution is considered, and the detected photoacoustic image is treated as a function of the modulation frequency f, that is, a function having information in the depth direction of the sample. That is,
As shown in Figure 8, the excitation light incident on the sample becomes a point heat source through a photothermal conversion process, and the heat wave propagates within the heat diffusion region, forming a certain temperature distribution s (x, y, z). be done. This process can be described as a pure thermal impulse response, (x, 3'
+ z), and the thermal impedance distribution in the sample is expressed as q
When expressed as L(XI yt Z), the internal temperature distribution is approximately given by equation (7).

s (x, y, z) = /// q, (x-ξ+ 3
'-'71 z-()μ嘗・h, (ξt'7tζ)dξdηdζ (7) However,
qt (x, y + z): pure thermal impedance distribution = ideal photoacoustic image, (x, y, z): pure thermal impulse response A thermal wave generated from an infinitesimal point propagates inside the sample, The transfer function, for example, ht(XeLZ) until it is converted into the internal temperature distribution, is given by equation (3).

Furthermore, according to FIG. 8, this temperature distribution s (xt ym
z) is the elastic impedance distribution q, (x, y, z)
is modulated, converted into an elastic wave by thermoelastic conversion, and finally converted into a minute displacement of the sample surface, that is, a photoacoustic signal. This process is described as a thermoelastic impulse response.

When expressed as (x+y+z), the photoacoustic signal p(x, y, f)
(8) (8) (9) q, (x, y, z) "Elastic impedance distribution = ideal photoacoustic image, cxtyez): Thermoelastic impulse response infinitesimal point Transfer function until a temperature change is converted into a minute displacement on the sample surface, that is, a photoacoustic signal. Generally, a photoacoustic signal is obtained as a complex number with amplitude and phase, so equations (7), (8), and ( 9) Expression is subjected to three-dimensional complex Fourier transform to obtain expressions (lO) to (12).

S(/A, 1/, ?)=F [s(x, y, z))=
QL(μ, shi, complete)・H, (μ, shi, γ) (10) P(μ, shi, δ)=S, (μ, shi, γ)・H, (μ, ν
, completion) (11) S, (μ, shi, γ) = Q, (μ, shi, γ) ■S(μ, ν
, γ) (12) F[]: Operator representing Fourier transform ■: Operator representing convolution, where μ, ci, γ: X+y+
Spatial frequency δ in the Z direction: Spatial frequency S in the Z direction S (μ, y, γ): Fourier transform image Q of s (x, y, z), (μ, shi, γ): qL (XI yt z) Fourier transform image H, (μ, shi, ri): h, (x, y, z) Fourier transform image P (μ, shi, δ): Fourier transform image 3q (μ , shi, γ): Fourier transform image H, (μ, ν, γ>: h, (x I y e z) of 5a(x, y-z)
Fourier transform image Q, (μ, shi, γ): q, Fourier transform image of (x, y, z) Substituting equations (10) and (12) into equation (11), (
13) Obtain Eq.

P (μ, shi, δ) = Q, (μ, shi, γ)
3) Therefore, by using l/(H, (μ, ν, completion)·H, (μ, shi, completion)) as an inverse filter and multiplying both sides of equation (13), equation (14) is obtained.

Q, (μ, shi, γ) ■Q, (μ, shi, γ) = P (μ, shi, δ)・H, (μ, shi, γ)・Ho (μ, shi, γ) (14) If equation (14) is subjected to a three-dimensional inverse complex Fourier transform, the final result is the product of the thermal impedance distribution and the elastic impedance distribution, that is, the ideal photoacoustic image q, (x, y, z)
・qL(X, y, z) is obtained.

q・(x* 3'e z) "qL(XI yt z)
=F-”(Q, (μ, shi, γ) ■Q, (μ, shi, γ)]
(15) That is, the pure thermal impulse response of the sample, (x.

y, z) and thermoelastic impulse response hs (Xs 'I
t z), the inverse filter 1 / (H, (μ, shi, γ)
・H, (μ.

ν, γ)), and the resulting photoacoustic image p(x
, y + f) Fourier transform image P(μ, shi, δ)
After that, by performing inverse Fourier transform, an ideal photoacoustic image with no deterioration in resolution can be obtained.

In this embodiment, the configuration and function of the photoacoustic detection optical system are exactly the same as those in the first embodiment, so a description thereof will be omitted.

The computer 68 of the signal processing system 16G processes the detected photoacoustic image p(x, y,
Process f) is performed. First, based on the various thermal and elastic property constants of the sample, the thermal impulse response 1 of the sample is
+, (x, y, z) and thermoelastic impulse response, (
x, y, z). Next, while scanning the modulation frequency f, the movement signal of the XY stage 42 and the output signal from the lock-in amplifier 67 are input, and the three-dimensional light g
An IF image p(x, y, f) is constructed. Next, h, (
x, y, z), h, (x, y, z), and p(
x, y, f) are subjected to two-dimensional complex Fourier transform, and the Fourier transform images H, (μ, ci, γ), H, (μ, ν.

γ) and P(μ, shi, 了). Next, inverse filter 1
/(H, (μ, shi, γ)・H, (μ, shi, γ)), and then a composite spectrum of the thermal impedance distribution and elastic impedance distribution information inside the sample based on equation (14). , that is, a Fourier transform image Q, (μ, shi, γ) of an ideal photoacoustic image Q, (μ, shi, γ) is obtained. Finally, based on equation (15), Q, (μ, shi, γ)■Q
, (μ, shi, γ) are subjected to three-dimensional inverse complex Fourier transform, and an ideal photoacoustic image q, (x, y, z)・q+(x, y, z
). This image is displayed on the monitor TV 69.

According to this embodiment, as in the first embodiment, it is possible to obtain the effect of enabling high-resolution detection of internal information of a sample, and at the same time, as internal information, not only thermal impedance distribution but also elastic impedance distribution can be obtained. It becomes possible to detect distribution information. Furthermore, by combining the inverse filter and scanning at the modulation frequency f, it is possible to improve the detection resolution in the depth direction.

〔Effect of the invention〕

According to the present invention, by applying an inverse filter determined from the thermal impulse response and thermoelastic impulse response of the sample to the obtained photoacoustic image, it is possible to repair the deterioration in the resolution of the optical g91 image. This enables high-resolution detection of internal information of the sample.

[Brief Description of the Drawings] Fig. 1 is a diagram showing a photoacoustic detection optical system in a first embodiment of the present invention, and Fig. 2 is a diagram showing how higher-order diffracted light components of a laser spot are blocked by a pinhole. Figure 3 is a diagram showing the light intensity distribution immediately after passing through the pinhole, Figure 4 is a diagram showing the polarization direction of the polarizing plate, and Figure 5 is a flowchart for repairing deterioration in the resolution of a photoacoustic image using an inverse filter. FIG. 6 is a diagram showing the effect of the inverse filter, FIG. 7 is a diagram showing the photoacoustic detection optical system in the second embodiment of the present invention, and FIG. 8 is a diagram showing the photoacoustic detection optical system in the third embodiment of the present invention. FIG. 9, a diagram showing the basic principle, shows the light 11'I! by the inverse filter in the third embodiment. Figure 10 is a diagram showing the principle of the photoacoustic effect; Figure 11 is a diagram showing how the resolution of a photoacoustic image is degraded due to the integral effect in the heat diffusion region. It is a diagram. 1, 8... Laser 31.51--- He-Ne laser 2.32...
... Acousto-optic modulation element 13.64 ... Photoelectric conversion element 73 ... PZT element 16.67 ... Lock-in amplifier 17.68 ... Meter casing 23 ...・・・・・・Thermal diffusion area @ 1 Eye 2 - Figure 5 Kabuto 4 772... Polarization of polarizing plate 15 Note Figure 6 23... - Hot fox scattering 1 +70 +90 Hahishi 12 r゛On police vL sheep modulation element each sample mouth by mouth?・:)tsu9 Fortune Teller Kite PZT Suyo 1st Light Hundred Priest No. P (χ Five 21- Light Absorption Distributor 22-・Heat Paying Chief Z3・-Hi Gozaihoge 433-

Claims (1)

[Claims] 1. Intensity modulation of light obtained from a light source at a desired frequency,
The intensity-modulated light is focused on the sample, and the photoacoustic effect generated inside the sample is detected in two-dimensional directions of the sample,
In a photoacoustic signal detection method that constructs a two-dimensional photoacoustic image and extracts surface and internal information of a sample from the two-dimensional photoacoustic image, an inverse method is used to repair deterioration in resolution of the photoacoustic image from the thermal impulse response of the sample. 1. A photoacoustic signal detection method characterized by determining a filter and applying the inverse filter to the obtained photoacoustic image. 2. Claim 1, characterized in that the thermal impulse response is a transfer function in which a heat wave generated from one point inside the sample propagates inside the sample until it is converted into a minute displacement on the sample surface.
The photoacoustic signal detection method described. 3. A light source, a modulating means for intensity modulating the light from the light source at a desired frequency, a focusing means for focusing the intensity-modulated light onto the sample, and a photoacoustic effect generated inside the sample. a detection means for detecting in two-dimensional directions, a composition means for configuring a two-dimensional photoacoustic image, an information extraction means for extracting surface and internal information of the sample from the two-dimensional photoacoustic image, and light from the sample or a light source. A photoacoustic signal detection device comprising a scanning means for two-dimensionally scanning a sample, and a calculation means for calculating a thermal impulse response of a sample, and an inverse filter for repairing resolution deterioration of a photoacoustic image based on the thermal impulse response. A photoacoustic signal detection device characterized by comprising a calculation means for calculating and a means for applying the inverse filter to the obtained photoacoustic image. 4. The thermal impulse response is characterized in that it is a transfer function in which a heat wave generated from one point inside the sample propagates inside the sample until it is converted into a minute displacement on the sample surface.
The photoacoustic signal detection device described above. 5. Intensity modulation of the light obtained from the light source at a desired frequency,
The intensity-modulated light is focused on the sample, and the photoacoustic effect generated inside the sample is detected in two-dimensional directions of the sample,
In a photoacoustic signal detection method that constructs a two-dimensional photoacoustic image and extracts surface and internal information of a sample from the two-dimensional photoacoustic image, the photoacoustic 1. A photoacoustic signal detection method, comprising: determining an inverse filter for repairing image resolution degradation, and applying the inverse filter to the obtained photoacoustic image. 6. The pure thermal impulse response according to claim 5, characterized in that the pure thermal impulse response is a transfer function of a heat wave generated from one point inside the sample propagating inside the sample until it is converted into a temperature distribution inside the sample. Photoacoustic signal detection method. 7. The photoacoustic signal detection method according to claim 5, wherein the thermoelastic impulse response is a transfer function until a temperature change at an infinitesimal point is converted into a minute displacement on the sample surface. 8. A light source, a modulating means for intensity-modulating the light from the light source at a desired frequency, a focusing means for focusing the intensity-modulated light onto the sample, and a light-acoustic effect generated inside the sample. a detection means for detecting in two-dimensional directions; a composition means for forming a two-dimensional photoacoustic image; an information extraction means for extracting surface and internal information of the sample from the two-dimensional photoacoustic image; In a photoacoustic signal detection device comprising a scanning means for two-dimensionally scanning light of It is characterized by providing a calculation means for calculating an inverse filter for repairing resolution deterioration of a photoacoustic image from a thermal impulse response and a thermoelastic impulse response, and a means for applying the inverse filter to the obtained photoacoustic image. A photoacoustic signal detection device. 9. The thermal impulse response is characterized in that it is a transfer function in which a heat wave generated from one point inside the sample propagates inside the sample and is converted into a temperature distribution inside the sample.
The photoacoustic signal detection device described above. 10. The photoacoustic signal detection device according to claim 8, wherein the thermoelastic impulse response is a transfer function until a temperature change at an infinitesimal point is converted into a minute displacement on the sample surface.