JP2672758B2 - Sample thermoelasticity evaluation device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for evaluating thermoelasticity of a sample, and more specifically, it irradiates the sample with excitation light whose intensity is modulated periodically and measures the thermal expansion vibration of the sample surface caused by the excitation light to measure the sample. The present invention relates to a thermoelasticity evaluation device for a sample for evaluating thermoelasticity characteristics and the like.

[0002]

2. Description of the Related Art When a sample is irradiated with an excitation light whose intensity is periodically modulated, the sample generates heat due to absorption of the light, thereby expanding thermally. Since the intensity of the irradiation light is periodically modulated, the temperature change of the sample due to heat generation becomes periodic, and the sample causes thermal expansion vibration. A method for evaluating a sample by measuring these thermal responses is known as a photoacoustic method or a photothermal displacement method (Japanese Patent Application No. 2-70967). FIG. 2 is a schematic diagram showing a schematic configuration of an example of a conventional sample thermoelasticity evaluation apparatus A0 by the photothermal displacement method. As shown in FIG. 2, in the conventional sample thermoelasticity evaluation apparatus A0,
The semiconductor laser 1 is used as an excitation laser that gives the sample 4 photothermal displacement. Then, the emitted light is intensity-modulated with the frequency F by the change of the injection current to the semiconductor laser 1. This emitted light is reflected by the dichroic mirror 2, and the lens 3
The sample 4 is focused and irradiated onto the sample 4. The photothermal displacement of the sample 4 in this irradiation part is measured by a laser interferometer. A He-Ne laser 5 is used as a laser for the laser light interferometer, and a beam 1 and a beam 2 having a frequency difference F _B are generated from the emitted light by an optical frequency shifter (acousto-optic modulator) 6. The beam 1 includes a polarization beam splitter 7, a quarter wave plate 8,
It passes through the dichroic mirror 2 and is condensed by the lens 3,
It is incident on the sample 4. The reflected light of the beam 1 from the sample 4 is
By passing through the quarter-wave plate 8 again, the polarization plane becomes 9
Since it changes by 0 degree, it is reflected by the polarization beam splitter 7 this time. Similarly, the beam 2 passes through the polarization beam splitter 7. Since these laser lights are orthogonal to each other, the polarizing plate 9
To penetrate these beams,
The interference light is received by the photoelectric converter 10. Photoelectric converter 1
The output V from 0 is passed through the filter 11 to extract the beat wave signal E ₁ in the interference light. The signal E ₁ is given by the following equation. E ₁ = Acos (2πF _B t + P (t) + φ (t)) (1) where A is a value depending on the sample 4 and the interference optical system, P
(T) is the phase change of the beam 1 due to the photothermal displacement of the sample 4,
φ (t) is the phase difference due to the optical path length difference between the beam 1 and the beam 2 when P (t) is zero (no photothermal displacement). If the amplitude of the photothermal displacement of sample 4 is L and the phase is q, the phase difference P
(T) is represented by the following equation. P (t) = (4π / λ) · Lsin (2πFt + q) (2) Next, the value of the signal E ₁ is compared with the zero level (threshold value),
The waveform conversion is performed by the comparator 12 so that E ₁ = V if the signal E ₁ is at or above the zero level, and E ₁ = −V if the signal E ₁ is at or below the zero level. The signal E ₂ after the waveform conversion is expressed by the following equation. _{E 2 = (4V / π)} · cos (2πF B t + P (t) + φ (t)) + P in the phase term for (high-frequency components) ... (3) signal E ₂ is free from said value A
By detecting (t) with the phase detection circuit 13, the accurate photothermal displacement of the sample 4 could be detected.

[0003]

The photothermal displacement detected by the conventional sample thermoelasticity evaluation apparatus A0 includes thermoelastic characteristic information such as the thermal conductivity of the sample 4, but the excitation light depends on the characteristic of the sample 4. When the reflectance with respect to changes, the so-called excitation light absorption power, which is the absorption capacity of the excitation light in the sample 4, changes, so the measured photothermal displacement also changes. For example, when the sample 4 is a thin film, the reflectance of the sample 4 with respect to the excitation light changes greatly due to the change in the film thickness, and the photothermal displacement also changes.
As described above, when the thermoelastic characteristics of the sample 4 are evaluated by measuring the photothermal displacement, the measured photothermal displacement includes information on the reflectance of the sample 4 with respect to the excitation light. It was not possible to evaluate the sample by extracting only the characteristics. Further, even when the excitation light passes through the sample 4, for the same reason, it was not possible to evaluate the sample 4 by extracting only the thermoelastic characteristic from the measured photothermal displacement. In order to solve the above problems in the conventional technique, the present invention improves the thermoelasticity evaluation device for a sample, and improves the thermoelastic property of the sample without being affected by the change in the reflectance of the excitation light in the sample. It is an object of the present invention to provide a thermoelasticity evaluation apparatus for a sample that can be evaluated accurately.

[0004]

In order to achieve the above object, the present invention provides an irradiation means for irradiating a sample with excitation light, and an optical interference method for measuring the photothermal displacement of the sample by the excitation light irradiated by the irradiation means. In a thermoelasticity evaluation apparatus for a sample, comprising: a measuring means for measuring by using a first measuring means for detecting the irradiation intensity of the excitation light; and a reflected light and / or a transmitted light of the excitation light on the sample. Of the intensity of the excitation light detected by the first detector, and the intensity of the reflected light and / or the transmitted light detected by the second detector. And a correction means for correcting the photothermal displacement of the sample measured by the measuring means by the excitation light absorption power of the sample calculated by the calculation means. Set up It is configured as a thermoelastic evaluation device of the sample and performing thermoelastic evaluation of the sample based on the photothermal displacement of the sample that has been corrected by the correction means.

[0005]

According to the present invention, when the sample is irradiated with the excitation light by the irradiation means and the photothermal displacement of the sample by the excitation light irradiated by the irradiation means is measured by the measuring means using the optical interferometry, The irradiation intensity of the excitation light is detected by the first detection means, and the intensity of the reflected light and / or the transmitted light of the excitation light on the sample is detected by the second detection means. From the intensity of the excitation light detected by the first detection means and the intensity of the reflected light and / or the transmitted light detected by the second detection means, the excitation light absorption power of the sample is calculated by the calculation means. Is calculated. The photothermal displacement of the sample measured by the measuring unit is corrected by the correcting unit by the excitation light absorption power of the sample calculated by the calculating unit. Thermoelasticity evaluation of the sample is performed based on the photothermal displacement of the sample corrected by the correction means. Since the measured photothermal displacement of the sample and the pumping light absorption power affected by the change of the reflectance of the pumping light in the sample are in a proportional relationship, the pumping light absorption power was made constant by the above correction. The photothermal displacement of time is obtained. As a result, it is possible to obtain a thermoelasticity evaluation apparatus for a sample that can accurately evaluate thermoelastic characteristics of the sample without being affected by a change in reflectance of excitation light in the sample.

[0006]

Embodiments of the present invention will be described below with reference to the accompanying drawings to provide an understanding of the present invention. The following embodiments are examples of embodying the present invention and are not of the nature to limit the technical scope of the present invention. here,
FIG. 1 shows a thermoelasticity evaluation apparatus A for samples according to an embodiment of the present invention.
It is a schematic diagram which shows schematic structure of 1. Further, the same reference numerals are used for the elements common to the conventional sample thermoelasticity evaluation apparatus A0 shown in FIG. As shown in FIG. 1, a thermoelasticity evaluation apparatus A1 for a sample according to this embodiment includes an excitation light irradiation system P (corresponding to irradiation means) including a semiconductor laser 1, a dichroic mirror 2 and a lens 3, and a He—Ne laser 5. , An optical frequency shifter 6, a polarization beam splitter 7, a quarter wave plate 8, a polarizing plate 9, a photoelectric converter 10, a filter 11, a comparator 12, and a phase detection circuit 13 as an optical interference system Q.
(Corresponding to measuring means) is the same as the conventional example. However, in this embodiment, the photodetector 15 (corresponding to the first detecting means) for detecting the irradiation intensity of the excitation laser (excitation light).
And photodetectors 14 and 16 (corresponding to second detecting means) for detecting the intensity of reflected light and / or transmitted light of the excitation laser on the sample 4, and the intensity of the excitation laser detected by the photodetector 15. A calculation function for calculating the absorption amount s (corresponding to the excitation light absorption power) of the excitation laser in the sample 4 from i and the intensity r of the reflected light and / or the intensity t of the transmitted light detected by the photodetectors 14 and 16 ( And a calculator 17 having a correction function (corresponding to a correction means) for correcting the photothermal displacement measured using the optical interference system Q with the absorption amount s, and the sample 4 corrected by the calculator 17 This is different from the conventional example in that it is configured to evaluate the thermoelasticity of the sample 4 based on the photothermal displacement of.

In the present embodiment, the operation of the device A1 will be described below mainly with respect to the parts different from the conventional example, and the parts similar to the conventional example have been described above, and detailed description thereof will be omitted. In this apparatus A1, first, similarly to the conventional example, the excitation light irradiation system P is used to irradiate the sample 4 with the excitation laser, and the photothermal displacement of the sample 4 at this irradiation portion is measured using the optical interference system Q. Further, in this device A1, the beam splitter 18 is installed at the emission part of the excitation laser, and the irradiation intensity of the excitation laser is measured by receiving a part of the emitted light by the photodetector 15. The reflected light from the sample 4 is reflected by the same beam splitter 18 and received by the photodetector 14. With this, the intensity of the reflected light from the sample 4 is measured. The photodetector 16 installed on the back side of the sample 4 measures the transmitted light intensity of the excitation laser when the excitation laser passes through the sample 4. These measured values are digitized by the A / D converter 19 and taken into the computer 17. Further, the photothermal displacement of the sample 4 measured using the optical interference system Q is also digitized by the A / D converter 19 and taken into the computer 17. In the computer 17, the excitation laser irradiation intensity signal and the reflected light intensity signal and / or the transmitted light intensity signal are used to determine the transmission efficiency in the excitation light irradiation system P and the optical interference system Q on the sample 4. The irradiation intensity i of the excitation laser and the reflected light intensity r and / or the transmitted light intensity t are calculated to correct the measured photothermal displacement. Specifically, the absorption amount s of the excitation laser in the sample 4 is calculated from s = i−r (−t), and the magnitude of the photothermal displacement is corrected by dividing by the absorption amount s. The thermoelastic characteristics of the sample 4 are evaluated using the photothermal displacement of the sample as the evaluation value. Here, the absorption amount s
Is changed under the influence of the change in the reflectance of the sample 4 with respect to the excitation laser as described above. Further, the measured photothermal displacement of the sample 4 is the displacement amount when the sample 4 absorbs the excitation laser and generates heat to cause thermal expansion.
The photothermal displacement and the absorption amount s are in a proportional relationship. Therefore, by performing the correction as described above, the photothermal displacement standardized by the absorption amount s, that is, the photothermal displacement when the absorption amount s is constant without changing is obtained. As a result, it is possible to obtain a sample thermoelasticity evaluation apparatus capable of accurately evaluating the thermoelastic characteristics of the sample 4 without being affected by the change in the reflectance of the excitation laser in the sample 4.

[0008]

Since the present invention is configured as described above, it is possible to measure the photothermal displacement when the pumping light absorption power that is affected by the change in the reflectance of the pumping light in the sample is constant. As a result, it is possible to obtain a thermoelasticity evaluation apparatus for a sample that can accurately evaluate thermoelastic characteristics of the sample without being affected by a change in reflectance of excitation light in the sample.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a schematic configuration of a sample thermoelasticity evaluation apparatus A1 according to an example of the present invention.

FIG. 2 is a configuration diagram showing a schematic configuration of an example of a conventional sample thermoelasticity evaluation apparatus A0.

[Explanation of symbols]

 A1 ... Thermoelasticity evaluation device for sample P ... Excitation light irradiation system (corresponding to irradiation means) Q ... Optical interference system (corresponding to measurement means) 15 ... Photodetector (corresponding to first detection means) 14, 16 ... Light Detector (corresponding to second detecting means) 17 ... Calculator (corresponding to computing means and correcting means) s ... Absorption amount (corresponding to excitation light absorption power) i ... Excitation intensity of excitation laser r ... Intensity of reflected light t ... Transmitted light intensity

Claims (1)

(57) [Claims] 1. Thermoelasticity of a sample, comprising: irradiation means for irradiating the sample with excitation light; and measurement means for measuring the photothermal displacement of the sample by the excitation light irradiated by the irradiation means using an optical interferometry method. In the evaluation device, first detecting means for detecting the irradiation intensity of the excitation light, second detecting means for detecting the intensity of reflected light and / or transmitted light of the excitation light on the sample, and the first detecting means. Calculation means for calculating the excitation light absorption power of the sample from the intensity of the excitation light detected by the detection means and the intensity of the reflected light and / or the transmitted light detected by the second detection means, A correction means for correcting the photothermal displacement of the sample measured by the measuring means with the excitation light absorption power of the sample calculated by the calculating means is provided, and the photothermal displacement of the sample corrected by the correcting means is provided. Based on A thermoelasticity evaluation apparatus for a sample, wherein the thermoelasticity evaluation of the sample is performed.