JPS58169056A - Detection of internal information of solid sample by photo-acoustic method - Google Patents

Abstract

PURPOSE:To detect photo-acoustic (PA) signals in all frequency areas at one time by Fourier transformation of PA signal obtained when a mono pulse laser beam irradiates a solid sample. CONSTITUTION:The laser beam 2 from a pulse laser sorce 1 irradiates a solid sample 8 arranged in a cell 7 through lenses 3 and 4, a mirror 5 and a lens 6 and PA signal is detected with a detector 9 such as microphone. This detected PA signal is once recorded in a wave memory 10 and undergoes Fourier transformation with a Fourier transforming device 11 and then a frequency-dependent characteristics of the amplitude and phase of the PA signal are indicated on a display unit 12 such as X-Y plotter. Depthwise optical and thermal distribution inside the sample are obtained from these dependent characteristics to find optical, thermal and physical natures of the sample.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting internal information of a solid sample using the yt, 1t41 method.

The photoacoustic* method uses light (IIr) whose intensity is modulated at a specific frequency.
A solid sample is irradiated with 1. This is a method for detecting internal information of a solid sample from a photoacoustic signal (hereinafter referred to as rPA signal), and it is a method for detecting optical ψ thermal characteristics of a solid sample that could not be obtained by conventional optical measurement. Since it can be detected with high sensitivity, development research is active and VC is being promoted.

When a solid material is irradiated with intermittent light, heat is generated that is proportional to the optical properties (light absorption rate) of the sample. The heat iJ and the thermal and physical properties of the sample It (thermal diffusivity, specific heat, dense axilla) vt are therefore diffused, raising the surface temperature f of the sample. When a sample is sealed in a cell, the pressure inside the cell changes due to the expansion and contraction of the gas on the sample surface due to intermittent changes in surface temperature. By detecting the pressure change iPA@ with a microphone and analyzing the dependence of the amplitude or phase of bP1g on the incident light modulation frequency, it is possible to detect information inside the sample such as minute compositional unevenness and defects in glfIF. can. Father, V:, piezo electrostrictive element (pzv) k
Internal information of the sample can be detected by detecting it as a thermal strain wave tube PA signal within the pasted sample and conducting a similar analysis.

In other words, PA is responsible for the optical, thermal, and physical properties of a solid sample, so by detecting the dependence of the signal amplitude or phase on the incident light modulation frequency, it is possible to detect the dependence of the signal amplitude or phase on the incident light modulation frequency. Optical/thermal distribution obtained 11. From this, it is possible to know the internal vibrations of the sample as described above.

By the way, when detecting the product of the PA signal, Kfi is also effective and the frequency meter is the frequency of the incident light vlITa.

In addition to the conventional optical sound wisdom method, laser light
・One frequency intermittently? Since the method uses a lock-in amplifier to detect the amplitude or phase of the P^2 signal instead of changing it little by little, the lower the frequency VC, the longer the integration time is required, which is difficult to achieve. For example, a field of intermittent laser light of /θHz *, a period of 60 seconds klk'.

In the past, the PA signal product detection process in the frequency range from /Hz to 100Hz had the drawback of requiring several hours.

The present invention has been developed in view of the above, and uses a tube piece 11 in which a single pulsed laser beam is composed of a combination of many frequencies to produce a single pulsed laser beam on a solid sample.
This is a book that detects PA signals in the entire frequency range at once by irradiating the light and then performing a PA signal at once.
You can hate it.

'' (In other words, if the period of time between redeno and rus is sufficiently shorter than the reciprocal of the highest frequency of the PA signal that you want to know (7 Hz
If you get a PA signal at i, /ms is more intelligent), the PA double signal Fourier conversion is as it is! Rus PA
The frequency-dependent characteristic of the amplitude or phase of a signal is shown (therefore, it is a single beam).In the case of a single optical fiber without Rousselet, the pulse time width of several ns to several μS is used. Therefore, there is no problem at all.

L:*') The advantage of the present invention is that a single pulse
Since three lasers are used, the detection time is short, and the rise in the sample temperature is small.On the other hand, since the incident light 1 can only be used within a linear range in which the output PA There is a fee to limit the amount of incident light so that linearity does not occur.Also, even if the incident laser beam is not considered to be an innocent laser beam and has the width of the southern limit, the time change (Hasugi) of the laser beam can be seen. If it is, the correct frequency dependence characteristic km can be obtained by dividing the Fourier transform of the pulsed PA signal by the Fourier transformation of the input signal.

Hereinafter, the present invention will be explained in detail with reference to Examples.

FIG. 7 is a block diagram showing an example of a detection system for implementing the present invention. Jarls laser beam from pulsed radar source 1m lens 8.4. -Mirror 5-cell through lens fl? A PA signal is generated by irradiating a solid sample 8 placed inside the chamber, and is detected by a detector 9 such as a microphone.
This detected PAgI number is once recorded in the wave memory lO, and then transferred to a Fourier transform device such as a microcomputer.
ll'e Fourier, the amplitude or phase of the P^^ number depending on the number of chest movements is displayed on a display device 12 such as an X-Y7'l:I tube. 1 shows the X-Y stage assembly, although not shown.

Direct piezo electrostrictive element (pzv
) When pasting y, the self is not necessary and the PA signal product detection process can be performed using a test W thread like IW1.

Example] / As shown in FIG. 2, an aluminum substrate 22 having grooves 21 with a depth of 51 and a width of 3 cm bonded to an aluminum group 2B' of 0Irn was used as a specimen 24 for the detection shown in FIG. The wave number dependence characteristics of the PA multiplied signal were investigated using the system. A Yag laser beam with a wavelength of s b n'rn was used as the laser source 1, and the sample was irradiated with a single laser beam of /Qns.

3 is a graph showing frequency 1 dependence characteristics of the amplitude or phase of the PA multiplied signal, which was determined according to the third embodiment; ^ is one prisoner without a groove, and one day is a place with a groove, so 1. Samurai II when irradiated
This is a graph. The characteristics of the eight-limbed horse mackerel deteriorate and change at about 70θHz, which can be confirmed. In other words, there are cavities such as bubbles inside the sample,
If there is a defect such as an impurity in the VC, it can be detected as a change in the slope of the M1 wave number dependent characteristic of the PA flaw signal, so it is possible to detect whether there is a defect at the reading power of the network wave number at that time and at which depth. .

Such detection can be performed in an extremely short time because the PA signal generated by irradiation with a single pulse laser light tube is converted into a signal.

EXAMPLE A cubic potassium chloride (Cg) sample of 20 cubes on each side was attached to PZTl, and the detection system shown in FIG. 7 was used. CO with a wavelength of 1006 μm as a nose laser source
Two laser beams were used, and a single dose of msO was used for irradiation.

FIG. 4 is a graph of the wave number dependence characteristic t7r of the amplitude or phase of the obtained PA signal. Since the phase of PA Hakugo is -7,5th power, one frequency is 1/, S
It shows that it is proportional to rice. In the figure.

Point # is J11d of the PA number requested by IT.
If the wave number dependent characteristic is ``f-o'', if there is absorption only in the sample &th, then (8) is the frequency-dependent characteristic of the PA signal obtained when there is absorption only inside the sample. Depending on whether the slope is closer to (A) or father (S), is it a result of absorption on the surface or inside the sample? Can be detected.

Similar to the detection rJ and the application ψ11/, it can be analyzed for an extremely short period of time (f), so it can be used for situations where the conventional method, which involves changing the frequency little by little, would require a long period of time and cause problems. For example, it has the advantage of being able to detect particles whose surface condition changes over time.

[Brief explanation of drawings]

Figure 1 shows the first generation of the detection thread used to carry out the present invention.
Fig. 2 is a side view of the sample used in the embodiment of the present invention. Graph showing the chest wave number dependence characteristics of the phase. Symbols in the figure: l...Pulse laser beam, 2...)9 pulse laser beam, 7...Cell, 8.24...Ell, 9...Detector, 10...Wave memory , 11...Fourier i chivalry i*. 1B...Display device. Patent applicant: RIKEN Electrical Research Institute (Hz) Figure 4 I'l removal (Hz)

Claims (1)

[Claims] +I+ By irradiating a single matrix solid sample and converting the generated phonetic signal,
A method for detecting internal information of a solid sample from the frequency-dependent characteristics of the amplitude or phase of an obtained photoacoustic signal. (2) The method according to claim 01, wherein dividing the Fourier transform of the acoustic signal by the Fourier i of the pulsed laser light is defined as t%. (3) The light A method according to claims 11 and 121, characterized in that the sound signal is recorded and output in a wave memory and then subjected to Fourier transformation. (4) The photoacoustic signal tube microphone or the piezoelectric It is assumed that the t% characteristic is detected by the strain element!