JPH0410024B2 - - Google Patents
Info
- Publication number
- JPH0410024B2 JPH0410024B2 JP57053414A JP5341482A JPH0410024B2 JP H0410024 B2 JPH0410024 B2 JP H0410024B2 JP 57053414 A JP57053414 A JP 57053414A JP 5341482 A JP5341482 A JP 5341482A JP H0410024 B2 JPH0410024 B2 JP H0410024B2
- Authority
- JP
- Japan
- Prior art keywords
- signal
- sample
- frequency
- laser beam
- solid sample
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
- 239000007787 solid Substances 0.000 claims description 12
- 238000000034 method Methods 0.000 claims description 9
- 230000001419 dependent effect Effects 0.000 claims description 7
- 238000010521 absorption reaction Methods 0.000 claims description 4
- 230000001678 irradiating effect Effects 0.000 claims description 4
- 230000001131 transforming effect Effects 0.000 claims description 3
- 238000001514 detection method Methods 0.000 description 8
- 230000003287 optical effect Effects 0.000 description 5
- WCUXLLCKKVVCTQ-UHFFFAOYSA-M Potassium chloride Chemical compound [Cl-].[K+] WCUXLLCKKVVCTQ-UHFFFAOYSA-M 0.000 description 3
- 230000007547 defect Effects 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 2
- 229910052782 aluminium Inorganic materials 0.000 description 2
- 230000000704 physical effect Effects 0.000 description 2
- 238000013459 approach Methods 0.000 description 1
- 230000008602 contraction Effects 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 230000020169 heat generation Effects 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 230000010354 integration Effects 0.000 description 1
- 230000031700 light absorption Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 235000011164 potassium chloride Nutrition 0.000 description 1
- 239000001103 potassium chloride Substances 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/22—Details, e.g. general constructional or apparatus details
- G01N29/24—Probes
- G01N29/2418—Probes using optoacoustic interaction with the material, e.g. laser radiation, photoacoustics
Description
【発明の詳細な説明】
本発明は光音響法による固体試料の内部情報の
検出方法に関する。DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting internal information of a solid sample using a photoacoustic method.
光音響法は、特定の周波数で強度変調された光
（断続光）を固体試料に照射し、得られる光音響
信号（以下、「PA信号」という。）から固体試料
の内部情報を検出する方法であつて、従来の光学
的測定では得られなかつた固体試料の光学的・熱
的性質を高感度で検出できるので、開発研究が盛
んにすすめられている。 The photoacoustic method is a method of irradiating a solid sample with light whose intensity is modulated at a specific frequency (intermittent light) and detecting internal information of the solid sample from the resulting photoacoustic signal (hereinafter referred to as "PA signal"). Since it is possible to detect optical and thermal properties of solid samples with high sensitivity, which cannot be obtained by conventional optical measurements, development research is being actively carried out.
断続光を固体試料に照射すると、試料の光学的
性質（光吸収率）に比例した発熱が起る。その熱
は試料の熱的・物理的性質（熱拡散率、比熱、密
度）にしたがつて拡散し、試料の表面温度を上昇
させる。試料をセル内に密閉しておけば表面温度
の断続変化による試料表面の気体の膨張・収縮に
よつてセル内の圧力が変化する。その圧力変化を
PA信号としてマイクロフオンで検出し、PA信号
の振幅又は位相の入射光変調周波数に対する依存
持性を解析することにより、試料の微細な組成む
らや欠陥など試料内部の情報を検出することがで
きる。又、試料にピエゾ電歪素子（PZT）を貼
りつけ試料内の熱歪波をPA信号として検出して
同様な解析を行うことにより、試料の内部情報を
検出することができる。 When a solid sample is irradiated with intermittent light, heat generation occurs that is proportional to the optical properties (light absorption rate) of the sample. The heat diffuses according to the thermal and physical properties of the sample (thermal diffusivity, specific heat, density), raising the surface temperature of the sample. If a sample is sealed in a cell, the pressure inside the cell will change due to the expansion and contraction of gas on the sample surface due to intermittent changes in surface temperature. That pressure change
By detecting the PA signal with a microphone and analyzing the dependence of the amplitude or phase of the PA signal on the incident light modulation frequency, it is possible to detect information inside the sample, such as minute compositional irregularities and defects in the sample. Furthermore, internal information of the sample can be detected by attaching a piezo electrostrictive element (PZT) to the sample and detecting thermal distortion waves within the sample as a PA signal and performing a similar analysis.
つまり、PA信号は固体試料の光学的・熱的・
物理的性質を担つているので、信号の振幅又は位
相の入射光変調周波数に対する依存特性を検出す
ることにより、試料内部の深さ方向の光学的・熱
的分布が得られ、これから前記したような試料の
内部情報を知ることができる。 In other words, the PA signal is the optical, thermal,
Since it has physical properties, by detecting the dependence of the signal amplitude or phase on the incident light modulation frequency, the optical and thermal distribution in the depth direction inside the sample can be obtained. You can know the internal information of the sample.
ところで、PA信号を検出する際に最も有効な
パラメーターは入射光を断続する周波数である。 By the way, the most effective parameter when detecting a PA signal is the frequency at which the incident light is interrupted.
従来の光音響法は、レーザー光をチヨツパーで
断続させ、周波数を少しづつ変化させながらPA
信号の振幅又は位相をロツクインアンプで検出す
る方法であるため、低周波になるほど、積分時間
を長くする必要があり、又、精度も上らない。例
えば10Hzの断続レーザー光の場合、60秒程度の時
間を要する。したがつて、１Hz〜100Hz程度の周
波数領域のPA信号を検出処理するためには数時
間を要する欠点があつた。 In the conventional photoacoustic method, the laser beam is intermittent with a chopper, and the frequency is changed little by little while the PA is transmitted.
Since this method uses a lock-in amplifier to detect the amplitude or phase of a signal, the lower the frequency, the longer the integration time is required, and the accuracy does not improve. For example, in the case of intermittent laser light of 10Hz, it takes about 60 seconds. Therefore, there is a drawback that it takes several hours to detect and process a PA signal in a frequency range of approximately 1 Hz to 100 Hz.
本発明は上記に鑑みなされたものであつて、単
一のパルスレーザー光が多くの周波数の合成で成
り立つているのを利用して、固体試料に単一のパ
ルスレーザー光を照射し、得られるPA信号をフ
ーリエ変換することにより、全周波領域のPA信
号を一度に検出するものであつて、極めて高能率
に試料内部の情報を検出することができる。 The present invention was made in view of the above, and utilizes the fact that a single pulsed laser beam is composed of a combination of many frequencies to obtain a solid sample by irradiating a single pulsed laser beam onto a solid sample By Fourier transforming the PA signal, the PA signal in the entire frequency range is detected at once, and information inside the sample can be detected with extremely high efficiency.
すなわち、レーザパルスの時間幅が知りたい
PA信号の最高周波数の逆数より十分短かい場合
（1KHzまでのPA信号を得る場合は1msより短か
い）は、PA信号のフーリエ変換はそのままパル
スPA信号の振幅又は位相の周波数依存特性を示
すことになる。したがつて、単一パルスレーザー
光を用いれば、数ns〜数μs程度のパルス時間幅が
得られるので、全く支障がない。 In other words, I want to know the time width of the laser pulse.
If it is sufficiently shorter than the reciprocal of the highest frequency of the PA signal (shorter than 1ms when obtaining a PA signal up to 1KHz), the Fourier transform of the PA signal directly shows the frequency-dependent characteristics of the amplitude or phase of the pulsed PA signal. become. Therefore, if a single pulse laser beam is used, a pulse time width of several nanoseconds to several microseconds can be obtained, so there is no problem at all.
このように本発明の利点は、単一のパルスレー
ザー光を用いるので検出時間が短かいこと、また
試料の温度上昇が小さいことである。その反面、
入射光量を出力PA信号が比例する線型の範囲で
しか使えないため、非線型性が生じないよように
入射光量を制限する必要がある。なお、入射レー
ザー光がインパルスと見なせず有限の幅をもつて
いたとしても、レーザーパルスの時間変化（波
形）がわかつていれば、パルスPA信号のフーリ
エ変換を、入射レーザーパルスのフーリエ変換で
除算することにより正しい周波数依存特性を得る
ことができる。 As described above, the advantages of the present invention are that the detection time is short because a single pulsed laser beam is used, and that the temperature rise of the sample is small. On the other hand,
Since the amount of incident light can only be used within a linear range in which the output PA signal is proportional, it is necessary to limit the amount of incident light to prevent nonlinearity from occurring. Even if the incident laser beam is not regarded as an impulse and has a finite width, if the time change (waveform) of the laser pulse is known, the Fourier transform of the pulsed PA signal can be expressed as the Fourier transform of the incident laser pulse. By dividing, the correct frequency dependent characteristics can be obtained.
以下、実施例により本発明を詳しく説明する。 Hereinafter, the present invention will be explained in detail with reference to Examples.
第１図は本発明を実施するための検出系の一例
を示すブロツク図である。パルスレーザー源１か
らのパルスレーザー光２をレンズ３，４、−ミラ
ー５−レンズ６を介してセル７内に配置した固体
試料８に照射し、発生するPA信号をマイクロフ
オンなどの検出器９で検出して、この検出PA信
号を一旦ウエーブメモリー１０に記録し、マイク
ロコンピユーターなどのフーリエ変換装置１１で
フーリエ変換し、Ｘ−Ｙプロツターなどの表示装
置１２にPA信号の振幅又は位相の周波数依存特
性を表示する。図中１３は窓、１４はＸ−Ｙステ
ージをそれぞれ示す。なお、図示していないが、
試料表面に検出器として直接ピエゾ電歪素子
（PZT）を貼り付ける場合には、セル７は不要と
なり同様な検出系でPA信号を検出処理すること
ができる。 FIG. 1 is a block diagram showing an example of a detection system for carrying out the present invention. A pulsed laser beam 2 from a pulsed laser source 1 is irradiated onto a solid sample 8 placed in a cell 7 through lenses 3, 4, - mirror 5 - lens 6, and the generated PA signal is sent to a detector 9 such as a microphone. This detected PA signal is temporarily recorded in the wave memory 10, and then Fourier transformed by a Fourier transform device 11 such as a microcomputer, and displayed on a display device 12 such as an X-Y plotter to show the frequency dependence of the amplitude or phase of the PA signal. Display characteristics. In the figure, 13 indicates a window, and 14 indicates an XY stage. Although not shown,
When a piezo electrostrictive element (PZT) is attached directly to the sample surface as a detector, the cell 7 becomes unnecessary and the PA signal can be detected and processed using a similar detection system.
実施例 １
第２図に示すように、深さ２mm、幅３mmの溝２
１を設けたアルミニウム基板２２表面に20μmの
アルミニウム膜２３を接合したものを試料２４と
して、第１図の検出系によりPA信号の周波数依
存特性を調べた。パルスレーザー源１には波長
566nmのヤグ・レーザーを用い、10nsの単一パル
スレーザー光を試料に照射して実施した。Example 1 As shown in Figure 2, a groove 2 with a depth of 2 mm and a width of 3 mm
Sample 24 was prepared by bonding a 20 μm aluminum film 23 to the surface of an aluminum substrate 22 provided with 1, and the frequency dependence characteristics of the PA signal were investigated using the detection system shown in FIG. Pulsed laser source 1 has a wavelength
The experiment was carried out by irradiating the sample with a 10 ns single pulse laser beam using a 566 nm Yag laser.
第３図は得られたPA信号の振幅又は位相の周
波数依存特性を示すグラフである。Ａは溝のない
個所を、Ｂは溝のある個所をそれぞれ照射したと
きに得られたグラフである。周波数が約100Hzの
ところで特性が折れ曲り変化しており、溝の存在
を検知することができる。すなわち、試料内部に
あわなどの空洞や、不純物など欠陥がある場合に
は、PA信号の周波数依存特性の傾きの変化とし
て検出できるので、そのときの周波数の読み取り
からどの深さに欠陥があるかを検知することがで
きる。 FIG. 3 is a graph showing the frequency dependence characteristics of the amplitude or phase of the obtained PA signal. A is a graph obtained when a portion without a groove is irradiated, and B is a graph obtained when a portion with a groove is irradiated. At a frequency of approximately 100Hz, the characteristics curve and change, making it possible to detect the presence of grooves. In other words, if there is a defect such as a cavity such as bubbles or an impurity inside the sample, it can be detected as a change in the slope of the frequency dependent characteristic of the PA signal, so it is possible to determine at what depth the defect is located from the frequency reading at that time. can be detected.
このような検知は、単一パルスレーザー光を照
射して発生するPA信号をフーリエ変換して行う
ので、極めて短時間に行うことができる。 Such detection can be performed in an extremely short time because it is performed by Fourier transforming the PA signal generated by irradiation with a single pulse laser beam.
実施例 ２
一辺２mmの立方体の塩化カリウム（kCl）試料
にPZTを貼り付け、第１図の検出系を用いて実
施した。パルスレーザー源１として波長10.6μm
のCO2レーザーを用い、1msの単一パルスレーザ
ー光を照射して行つた。Example 2 PZT was attached to a cubic potassium chloride (kCl) sample with sides of 2 mm, and the detection system shown in FIG. 1 was used. Wavelength 10.6μm as pulse laser source 1
This was done using a CO 2 laser with a single pulse of 1 ms.
第４図は得られたPA信号の振幅又は位相の周
波数依存特性を示すグラフである。PA信号の振
幅又は位相は傾きが−1.5乗であるので、周波数
の−1.5乗に比例していることを示す。図中、点
線は計算によつて求められたPA信号の周波数依
存特性であつて、(A)は試料表面にのみ吸収がある
場合を、(B)は試料内部にのみ吸収がある場合を示
す。得られるPA信号の周波数依存特性の傾きが、
(A)又(B)のどちらに近ずくかによつて試料の表面又
は内部での吸収の度合を検知することができる。 FIG. 4 is a graph showing the frequency dependence characteristics of the amplitude or phase of the obtained PA signal. Since the amplitude or phase of the PA signal has a slope of -1.5, this indicates that it is proportional to the -1.5 power of the frequency. In the figure, the dotted lines are the frequency-dependent characteristics of the PA signal determined by calculation; (A) shows the case where there is absorption only on the sample surface, and (B) shows the case where there is absorption only inside the sample. . The slope of the frequency dependent characteristic of the obtained PA signal is
Depending on whether you approach (A) or (B), you can detect the degree of absorption on the surface or inside the sample.
このような検知は、実施例１と同様に極めて短
時間に行うことができるので、周波数を少しづつ
変化して行う従来法では長時間を要して支障をき
たすような場合、例えば試料の表面状態が時間と
共に変化する場合でも検出できる利点がある。 As in Example 1, this type of detection can be performed in an extremely short period of time, so it can be used in cases where the conventional method of changing the frequency little by little would take a long time and cause problems, for example when detecting the surface of a sample. It has the advantage of being able to detect even when the state changes over time.
第１図は本発明を実施するために用いる検出系
の一例を示すブロツク図、第２図は本発明の実施
例に用いた試料を断面で示す側面図、第３図と第
４図は本発明の実施例で得られたPA信号の振幅
又は位相の周波数依存特性を示すグラフ。
図中の符号：１……パルスレーザー源、２……
パルスレーザー光、７……セル、８，２４……試
料、９……検出器、１０……ウエーブメモリー、
１１……フーリエ変換装置、１２……表示装置。
Fig. 1 is a block diagram showing an example of a detection system used to carry out the present invention, Fig. 2 is a side view showing a cross section of a sample used in an embodiment of the present invention, and Figs. 5 is a graph showing frequency-dependent characteristics of the amplitude or phase of a PA signal obtained in an embodiment of the invention. Codes in the diagram: 1...Pulse laser source, 2...
Pulsed laser beam, 7... Cell, 8, 24... Sample, 9... Detector, 10... Wave memory,
11... Fourier transform device, 12... display device.
Claims (1)
より短い時間幅の単一のパルスレーザー光を固体
試料に照射し、 得られた音響信号をフーリエ変換し、 光音響信号の振幅又は位相の周波数依存特性の
傾きから固体試料の表面及び又は内部での吸収の
度合を検知する ことを特徴とする固体試料の内部情報の検出方
法。 ２ 音響信号のフーリエ変換をパルスレーザー光
のフーリエ変換で除算することを特徴とする特許
請求の範囲第１項に記載の方法。[Claims] 1. Irradiating a solid sample with a single pulsed laser beam having a time width shorter than the reciprocal of the highest frequency of the photoacoustic signal to be obtained, Fourier transforming the obtained acoustic signal, and obtaining a photoacoustic signal. A method for detecting internal information of a solid sample, comprising detecting the degree of absorption on the surface and/or inside the solid sample from the slope of the frequency-dependent characteristic of the amplitude or phase of the solid sample. 2. The method according to claim 1, characterized in that the Fourier transform of the acoustic signal is divided by the Fourier transform of the pulsed laser beam.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP57053414A JPS58169056A (en) | 1982-03-31 | 1982-03-31 | Detection of internal information of solid sample by photo-acoustic method |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP57053414A JPS58169056A (en) | 1982-03-31 | 1982-03-31 | Detection of internal information of solid sample by photo-acoustic method |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS58169056A JPS58169056A (en) | 1983-10-05 |
| JPH0410024B2 true JPH0410024B2 (en) | 1992-02-24 |
Family
ID=12942168
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP57053414A Granted JPS58169056A (en) | 1982-03-31 | 1982-03-31 | Detection of internal information of solid sample by photo-acoustic method |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS58169056A (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0827264B2 (en) * | 1988-09-21 | 1996-03-21 | 工業技術院長 | Photoacoustic imaging method with multiple modulation frequencies |
| KR100679082B1 (en) * | 1999-09-08 | 2007-02-05 | 주식회사 포스코 | Apparatus for inner defect detection using laser-ultrasonic |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5210383B2 (en) * | 1973-02-06 | 1977-03-23 | ||
| JPS53110589A (en) * | 1977-03-05 | 1978-09-27 | Krautkraemer Gmbh | Method and apparatus for generation of supersonic waves in articles |
| JPS55163453A (en) * | 1979-06-06 | 1980-12-19 | Kobe Steel Ltd | Quality discriminating method of cast metal |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5522535Y2 (en) * | 1975-07-10 | 1980-05-29 |
-
1982
- 1982-03-31 JP JP57053414A patent/JPS58169056A/en active Granted
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5210383B2 (en) * | 1973-02-06 | 1977-03-23 | ||
| JPS53110589A (en) * | 1977-03-05 | 1978-09-27 | Krautkraemer Gmbh | Method and apparatus for generation of supersonic waves in articles |
| JPS55163453A (en) * | 1979-06-06 | 1980-12-19 | Kobe Steel Ltd | Quality discriminating method of cast metal |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS58169056A (en) | 1983-10-05 |
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