JP3949600B2 - Photothermal conversion measuring apparatus and method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a photothermal conversion measuring apparatus and method for measuring a characteristic change based on a refractive index change generated in a sample due to a photothermal effect when an excitation light is irradiated on the sample, and used when analyzing a substance contained in the sample. Is.
[0002]
[Prior art]
In the analysis of substances contained in various samples, improvement of analysis sensitivity is important in order to reduce the amount of reagents, simplify the sample concentration process, increase the efficiency of analysis, and reduce costs.
By the way, when the sample is irradiated with excitation light, the irradiated portion generates heat by absorbing the excitation light, which is called a photothermal effect. Measuring this heat generation is called photothermal conversion measurement.
Conventionally, a method using a thermal lens effect formed on a sample by a photothermal effect (hereinafter referred to as a thermal lens method) is known as a high-sensitivity analysis method for a sample by this photothermal conversion measurement.
An analysis apparatus (photothermal conversion spectroscopic analysis apparatus) using a thermal lens method is disclosed in Patent Document 1, for example.
FIG. 4 is a configuration diagram of a sample analyzer using the thermal lens method disclosed in Patent Document 1 (see FIG. 1 of Patent Document 1).
As shown in FIG. 4, the excitation light A from the excitation light source 10 is converted into intermittent light (that is, intensity modulated periodically) by the chopper 11, and the beam expander 12, position control mirrors 31, 22, and lens 34. The sample 40 is irradiated through the microscope 35. Thereby, the sample 40 absorbs excitation light and generates heat, and its refractive index changes.
This change in refractive index is detected by the detection light B (measurement light) from the detection light source 20.
The detection light B from the detection light source 20 becomes a coaxial path with the excitation light A via the beam expander 22 and is reflected by the position control mirrors 31 and 32, and further irradiated to the sample 40 via the lens 34 and the microscope 35. The Then, the detection light B that has passed through the sample 40 is condensed by the condenser lens 50, passes through the opening 51A (pinhole), and is received by the detector 53, and its light intensity is detected. Here, since the condensing state of the detection light B in the sample 40 changes due to the change in the refractive index of the sample 40, the intensity of the detection light obtained through the pinhole is a change in the refractive index of the sample (that is, the sample The amount of light absorption varies according to the contained material and the like. By measuring the intensity change of the detection light B, the change in the refractive index of the sample can be measured, and the amount of the substance contained in the sample can be evaluated based on the measurement result.
In Patent Document 1, in order to detect an intensity change of the detection light B with a high S / N ratio (signal-to-noise ratio), an intermittent frequency component (frequency component of the intensity modulation period) of the excitation light A by the chopper by the lock-in amplifier 61 is used. ) Only detected.
[0003]
[Patent Document 1]
Japanese Patent Laid-Open No. 10-232210
[Problems to be solved by the invention]
However, the analysis of the sample by the thermal lens method detects the refractive index change due to the heat generation of the sample by the change in the light intensity (detection signal intensity) due to the change in the condensing state of the measurement light (detection light). This change in light intensity (detection signal intensity) depends not only on the change in the refractive index of the sample, but also on the light receiving position of the detector 53 (photoelectric conversion means), the intensity of the measurement light, its intensity distribution, and the like. For this reason, there is a problem that it is difficult to analyze the sample (measure the refractive index change) with good reproducibility (stable).
In order to increase the measurement sensitivity, it is necessary to increase the intensity of the excitation light or to reduce the diameter of the pinhole through which the measurement light after passing through the sample is passed. The increase in the cost and the increase in the cost of the pinhole have also caused problems such as a decrease in the S / N ratio due to a decrease in the amount of light received by the detector and a longer measurement time.
Accordingly, the present invention has been made in view of the above circumstances, and the object of the present invention is to be able to stably and accurately measure changes in characteristics due to the photothermal effect of a sample, and to increase power consumption and cost. An object of the present invention is to provide a photothermal conversion measuring apparatus and method capable of performing high-sensitivity measurement while preventing the increase in the measurement time, the decrease in the S / N ratio, and the increase in the measurement time.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is a photothermal conversion measuring apparatus for measuring a change in characteristics of the sample caused by the photothermal effect of the sample irradiated with excitation light, wherein the sample is irradiated with predetermined measurement light. A light irradiation means, a back surface side light reflection means provided on the opposite side of the measurement light irradiation surface of the sample, a surface side light reflection means provided on the excitation light irradiation surface side of the sample, Phase change measuring means for measuring the phase change of the measurement light after passing through the sample by irradiating the excitation light to the measurement light irradiation section by optical interferometry, the phase change measurement means comprising: , And measuring the phase change of the measurement light after the measurement light has been multiple-reflected between the back-side light reflection means and the front-side light reflection means and passed through the sample. It is configured as a conversion measuring device .
In this way, the refractive index change due to the photothermal effect of the sample (refractive index change caused by the temperature rise of the sample), and the phase change caused by the excitation light irradiation in the measurement light that has passed (transmitted) through the sample are measured using optical interferometry. If it is detected by measuring, that is, by measuring the phase difference between the reference light and the measuring light, for example, the position of the photodetector (photoelectric conversion means), the intensity of the measuring light, its intensity distribution, etc. for each device. Even if they are different, it is possible to measure the refractive index change (characteristic change) of the sample with high reproducibility (stable) and optically high accuracy without depending on these as long as they do not change during measurement. It becomes. This makes it possible to analyze the sample with high accuracy.
[0006]
Also, before Symbol phase change measuring means, the phase change of the measurement light after by multiple reflection through the sample between the measuring light and the rear surface side light reflecting means and the front surface side light reflecting means by measuring, the measuring light passes through a plurality of times an excitation portion of the sample, without a reduction in output increases and the S / N ratio of the excitation light, it is possible to measure the refractive index change with high sensitivity .
[0007]
Further, it is conceivable that the excitation light is light whose intensity is periodically modulated, and the phase change measuring means measures the phase change of the measurement light for the same period component as the intensity modulation period of the excitation light.
In this case, since the refractive index of the sample changes in the same period as the intensity modulation of the excitation light, only the change in the refractive index of the sample can be measured while removing the influence of noise having no frequency component of the excitation light. Thereby, the S / N ratio in the measurement of the phase change is improved.
[0008]
The excitation light is multiplexed light of intensity-modulated light with a different period for each wavelength, and the phase change measuring means changes the phase change of the measurement light with the same period as the intensity modulation period of each wavelength of the excitation light. What is measured about each component can be considered.
The change in the refractive index of the measurement light due to the photothermal effect also varies depending on the wavelength of the excitation light, and the photothermal effect for the excitation light of each wavelength and the change in the refractive index of the sample due to the photothermal effect also differ depending on the type of substance contained in the sample.
Therefore, according to the above-described configuration, the change in the refractive index of the sample with respect to the measurement light having a plurality of wavelengths can be measured by one measurement. Efficient measurement is possible in terms of labor.
[0009]
Further, the phase change measuring means includes photoelectric conversion means for photoelectrically converting the intensity of interference light between the measurement light and a predetermined reference light having a different optical frequency, and the photoelectric conversion means obtained by the photoelectric conversion means. It is conceivable to include phase change calculation means for calculating the phase change of the measurement light based on the intensity signal of the interference light.
The electric signal (interference light intensity signal) obtained in this way becomes a signal whose optical frequency is converted into an electric signal, and its phase component can be extracted by FM demodulation or the like. The extracted phase component includes a signal of refractive index change due to heat generation of the sample. In addition, since the phase change between the reference beam and the measurement beam is measured, it is highly reproducible (stable) without depending on the position of the photodetector (photoelectric conversion means), the intensity of the measurement beam, its intensity distribution, etc. In addition, it is possible to measure the refractive index change of the sample optically with high accuracy.
[0010]
Further, the present invention may be understood as a photothermal conversion measurement method corresponding to measurement using the photothermal conversion measurement device.
That is, in a photothermal conversion measurement method for measuring a change in characteristics of a sample caused by the photothermal effect of the sample irradiated with excitation light, the sample is irradiated with predetermined measurement light, and the excitation light is irradiated on the measurement light irradiation portion. The phase change of the measurement light after passing through the sample by irradiating the sample is measured by optical interferometry , and the back side light reflecting means provided on the opposite side of the measurement light irradiation surface of the sample at that time And a phase change of the measurement light after passing through the sample by multiple reflection between the sample and the surface side light reflecting means provided on the irradiation surface side of the excitation light of the sample, This is a photothermal conversion measurement method.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments and examples of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. It should be noted that the following embodiments and examples are examples embodying the present invention, and do not limit the technical scope of the present invention.
FIG. 1 is a schematic configuration diagram of the photothermal conversion measuring device X according to the embodiment of the present invention, and FIG. 2 is a diagram illustrating the measurement light in the photothermal conversion measuring device according to the embodiment of the present invention between the front surface and the back surface of the sample. FIG. 3 is a schematic cross-sectional view of a configuration for multiple reflection in FIG. 3, FIG. 3 is a schematic configuration diagram of an excitation light output unit using Fourier spectroscopy in a photothermal conversion measurement device according to an embodiment of the present invention, and FIG. It is a schematic block diagram of a conversion spectroscopy analyzer.
[0012]
Hereinafter, the photothermal conversion measuring apparatus X according to the embodiment of the present invention will be described with reference to FIG.
Excitation light output from a predetermined excitation light source 1 (for example, a laser having a wavelength of 533 nm and an output of 100 mW (YAG harmonic)) is converted into intermittent light (intermittent frequency: f) by a chopper 2 (periodically intensity) This is reflected by the dichroic mirror 3, passes through the lens 4, and irradiates the sample 5. Thereby, the sample 5 absorbs excitation light and generates heat (photothermal effect), and the refractive index of the sample 5 changes due to the temperature change (rise).
On the other hand, the measurement light output from the laser light source 7 (for example, He-Ne laser having an output of 1 mW) that outputs measurement light for measuring the refractive index change of the sample 5 is 1 The polarization plane is adjusted by the / 2 wavelength plate 8, and further split into two polarized waves (P1 and P2) orthogonal to each other by the polarization beam splitter (PBS9).
Each polarization P1, P2 is optical frequency shifted (frequency conversion) by the acousto-optic modulator (AOM 10, 11), reflected by the mirrors 12, 13, and then synthesized by the PBS 14. Frequency difference f _b of 2 to these orthogonal polarization P1, P2, for example, a 30MHz or the like.
One polarization P2 of the synthesized measurement light passes (transmits) through the PBS 15 and is reflected by the mirror 18 to return to the PBS 15 again. Here, since the polarization P2 that has returned to the PBS 15 reciprocates through the quarter-wave plate 16 disposed between the PBS 15 and the mirror 18, the polarization plane is rotated by 90 °. Is reflected by the PBS 15 and travels toward the photodetector 20.
[0013]
On the other hand, the other polarization P1 of the synthesized measurement light is reflected by the PBS 15, passes through the quarter-wave plate 17, the dichroic mirror 3, and the lens 4 and enters the sample 5. The excitation light is configured to irradiate an incident part (irradiation part) of the polarization P1 (measurement light).
Further, the polarized light P1 incident on the sample 5 passes through the sample 5 and is reflected by the reflecting mirror 6 provided on the back surface side of the sample 5 (on the opposite side to the irradiation surface of the measurement light (polarized light P1)). , Again passes through the sample 5 (that is, reciprocating), passes through the lens 4, the dichroic mirror 3, the quarter-wave plate 17, and returns to the PBS 15. Here, since the polarization plane of the polarization P1 is rotated 90 ° by reciprocating through the quarter-wave plate 17, this time, it passes through the PBS 15 and merges with the polarization P2. It goes in the direction of the photodetector 20.
A polarizing plate 19 is arranged between the PBS 15 and the photodetector 20, and the polarization P1 and the polarization P2 having a different optical frequency from the polarization P1 are observed light. (Measurement light) interferes with reference light, and the light intensity of the interference light is converted into an electric signal (hereinafter, the signal value of the electric signal is referred to as interference light intensity) by the photodetector 20 (photoelectric conversion means). . This electrical signal (that is, interference light intensity) is input and stored in a signal processing device 21 such as a computer, and the signal processing device 21 performs arithmetic processing (that is, optical interference) of the phase change of the polarization P1 (measurement light). Measurement of phase change). That is, an optical system device that guides the polarizations P1 and P2 in a predetermined direction, the polarizing plate 19 that forms interference light of the polarizations P1 and P2 (measurement light and reference light), and the photodetector 20 The signal processing device 21 constitutes an example of the phase change measuring unit.
[0014]
Here, the interference light intensity S1 is expressed by the following equation (1).
S1 = C1 + C2 · cos (2π · f _b · t + φ) (1)
C1 and C2 are constants determined by the optical system such as PBS and the transmittance of the sample 5, φ is a phase difference due to the optical path length difference between the polarizations P1 and P2, and f _b is a frequency difference between the two polarized waves P1 and P2. From the equation (1), the change in the phase difference φ can be obtained from the change in the interference light intensity S1 (difference between when the excitation light is not irradiated or when the light intensity is low and when the light intensity is high). Recognize. The signal processing device 21 calculates the change in the phase difference φ based on the equation (1).
Further, the endothermic amount (heat generation amount) changes according to the amount of the predetermined contained substance that absorbs the excitation light in the sample 5, the refractive index changes according to the heat generation amount, and the phase difference according to the refractive index. φ (the optical path length of the polarization P1 in the sample 5) changes. That is, the greater the amount of the contained material, the greater the change in the phase difference φ with respect to the change in the excitation light (that is, the phase change in the polarization P1). Therefore, if the phase difference φ is measured, the change in the refractive index caused by the temperature change of the sample 5 can be obtained, and as a result, the amount (concentration) of the substance contained in the sample can be analyzed.
That is, the photothermal conversion measuring device X is used to measure the change in the phase difference φ for a plurality of types of sample samples whose amounts (concentrations) of a predetermined content are known in advance, and the result and the amount of the content Is stored in the signal processing device 21 as a data table. Then, the signal processing device 21 may execute a process of specifying the amount of the contained substance by, for example, performing an interpolation process on the measurement result of the phase difference φ of the sample to be measured based on the data table. .
In this way, the change in refractive index due to the photothermal effect of the sample 5 is measured using the optical interferometry for the phase change caused by the excitation light irradiation in the measurement light (the polarization P1) that has passed (transmitted) through the sample 5. That is, the measurement is performed based on the relative evaluation (phase difference) of the phase of the reference light (the polarization P2) and the measurement light (the polarization P1). Even if the intensity and its intensity distribution differ, it is possible to measure the change in the refractive index of the sample stably and optically with high accuracy without depending on these as long as it does not change during measurement. .
[0015]
In this photothermal conversion measuring apparatus X, the measurement light (polarized wave P1) is reflected on the sample by reflecting the measurement light (polarized wave P1) on the reflection mirror 6 on the back side (an example of the back side light reflecting means). Therefore, the change in the phase difference φ can be measured with a sensitivity twice that of the one-way passage. In addition, there is no increase in the output of pumping light or a decrease in the S / N ratio.
Furthermore, since the excitation light is intensity-modulated at the frequency f, the refractive index of the sample 5 also changes at the frequency f, and the optical path length of the polarization P1 also changes at the frequency f (the optical path length of the polarization P2 is constant). The phase difference φ also changes with the frequency f. Therefore, if the change in the phase difference φ is measured (calculated) with respect to the component of the frequency f (the same period component as the intensity modulation period of the excitation signal), the influence of noise having no component of the frequency f is removed. Only a refractive index change of 5 can be measured.
Thereby, the S / N ratio in the measurement of the phase difference φ is improved.
[0016]
【Example】
In the embodiment, the sensitivity is improved by reciprocating the measurement light (the polarization P1) through the sample 5. However, the sensitivity is further improved by allowing the measurement light to pass through the sample 5 multiple times. It is also possible to plan.
FIG. 2 is a schematic cross-sectional view of a configuration in which the measurement light is subjected to multiple reflection between the front surface and the back surface of the sample.
As shown in FIG. 2, reflection mirrors 31 and 32 (high reflection mirror, front surface side light reflecting means and back surface side light are respectively provided on the front surface side (the measurement light irradiation surface side) and the back surface side of the sample 5. An example of a reflecting means) can be arranged, and the measurement light (the polarization P1) can be subjected to multiple reflection between the reflecting mirrors 31 and 32. Here, in order to schematically show multiple reflection in FIG. 2, for convenience, the measurement light is shown as being obliquely incident on the reflection mirrors 31 and 32. The reflected light should be coaxial. As a result, the measurement light (the polarized wave P1) is reflected by the reflection mirrors 31 and 32, and a part of the measurement light is transmitted through the reflection mirror 31 on the surface side of the sample 5, and the photodetector 20 is transmitted. Head in the direction of Accordingly, since the measurement light that has passed through the sample 5 is superimposed and input to the detector 20, it is possible to perform phase difference measurement with high sensitivity, that is, measurement of refractive index change.
In this case, a drive mechanism 30 (mirror drive mechanism) for controlling the position of one of the reflection mirrors may be provided in order to finely adjust the distance between the reflection mirrors 31 and 32 so as to synchronize the phase of the multiple reflected measurement light. desirable.
[0017]
The change in the refractive index of the measurement light due to the photothermal effect also varies depending on the wavelength of the excitation light, and the photothermal effect for the excitation light of each wavelength and the change in the refractive index of the sample due to the photothermal effect also differ depending on the type of substance contained in the sample.
Therefore, by irradiating a plurality of excitation light beams having different wavelengths and measuring the change of the phase difference φ for each of them, the type and amount of the substance contained in the sample can be specified (evaluated) from the distribution. However, measuring with irradiation of excitation light at different wavelengths is inefficient in terms of time and labor.
Therefore, the excitation light is a multiplexed light of intensity-modulated light with different periods for each wavelength, and the signal processor 21 changes the phase φ of the measurement light to the intensity modulation period of each wavelength of the excitation light. If each of the same periodic components is measured, the change in the refractive index of the sample with respect to the measurement light of a plurality of wavelengths can be measured by one measurement, and efficient measurement becomes possible.
As a light source (irradiation means) of such excitation light, light from a white light source (for example, a tungsten lamp) is dispersed with a spectroscope, and the intensity is modulated via a chopper having a different frequency for each of the dispersed light. It is conceivable that the above-described excitation light is collected (combined) light.
Further, as shown in FIG. 3, the light from the white light source 40 is split into the beam splitter 41 in two directions, reflected by the fixed mirror 42 and the moving mirror 43, and returned to the beam splitter 41 to be merged. It is also conceivable to use an excitation light output unit using well-known Fourier spectroscopy using as the excitation light.
[0018]
【The invention's effect】
As described above, according to the present invention, the refractive index change due to the photothermal effect of the sample is measured, and the phase change due to the excitation light irradiation in the measurement light that has passed (transmitted) through the sample is measured using the optical interferometry. In other words, the phase difference between the reference light and the measurement light is measured. For example, even if the position of the photodetector (photoelectric conversion means), the intensity of the measurement light, and its intensity distribution are different for each apparatus, If there is no change, the refractive index change of the sample can be measured stably and optically with high accuracy without depending on these.
Furthermore, by a simple configuration in which the measurement light is reflected by a light reflecting means (mirror, etc.), the measurement light is passed through the sample back and forth or three times or more, thereby increasing the output of the excitation light (ie, increasing the power consumption or The change in the refractive index of the sample can be measured with high sensitivity without causing an increase in cost) and a decrease in the S / N ratio.
As a result, stable and highly sensitive sample analysis can be performed.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a photothermal conversion measuring device X according to an embodiment of the present invention.
FIG. 2 is a schematic cross-sectional view of a configuration in which measurement light in a photothermal conversion measurement apparatus according to an embodiment of the present invention is subjected to multiple reflection between a front surface and a back surface of a sample.
FIG. 3 is a schematic configuration diagram of an excitation light output unit using Fourier spectroscopy in the photothermal conversion measurement apparatus according to an embodiment of the present invention.
FIG. 4 is a schematic configuration diagram of a conventional photothermal conversion measuring device (photothermal conversion spectroscopic analyzer).
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Excitation light source 2 ... Chopper 3 ... Dichroic mirror 4 ... Lens 5 ... Sample 6, 32 ... Reflection mirror (back surface side light reflection means)
7. Laser light source (measurement light irradiation means)
10, 11 ... Acousto-optic modulator (AOM)
20: Photodetector (photoelectric conversion means)
21 ... Signal processing device (phase change measuring means)
31 ... Reflection mirror (surface side light reflection means)
P1: Polarization (measurement light)
P2: Polarization (reference light)

Claims (5)

A photothermal conversion measuring device for measuring a change in characteristics of a sample caused by a photothermal effect of a sample irradiated with excitation light,
Measurement light irradiation means for irradiating the sample with predetermined measurement light;
Back side light reflecting means provided on the opposite side of the measurement light irradiation surface of the sample;
Surface-side light reflecting means provided on the irradiation surface side of the excitation light of the sample;
Phase change measuring means for measuring the phase change of the measurement light after passing through the sample by irradiating the excitation light to the measurement light irradiating unit by optical interferometry ,
The phase change measurement means measures the phase change of the measurement light after the measurement light has been multiple-reflected between the back-side light reflection means and the front-side light reflection means and passed through the sample. A photothermal conversion measuring device. The excitation light is light whose intensity is periodically modulated;
The photothermal conversion measuring apparatus according to claim 1 , wherein the phase change measuring means measures the phase change of the measurement light with respect to a component having the same period as the intensity modulation period of the excitation light. The excitation light is multiplexed light of intensity-modulated light with different periods for each wavelength,
The photothermal conversion measuring apparatus according to claim 1 , wherein the phase change measuring means measures the phase change of the measurement light for each of the same period components as the intensity modulation period of each wavelength of the excitation light. The phase change measuring means comprises:
Photoelectric conversion means for photoelectrically converting the intensity of the interference light between the measurement light and the predetermined reference light having a different optical frequency from the measurement light;
Phase change calculation means for calculating a phase change of the measurement light based on an intensity signal of the interference light obtained by the photoelectric conversion means;
The photothermal conversion measuring device according to any one of claims 1 to 3 , further comprising: In the photothermal conversion measurement method for measuring the change in characteristics of the sample caused by the photothermal effect of the sample irradiated with excitation light,
Irradiating the sample with a predetermined measurement light,
The phase change of the measurement light after passing through the sample by irradiating the measurement light irradiation unit with the excitation light is measured by optical interferometry , and at that time, the surface opposite to the measurement light irradiation surface of the sample The phase of the measurement light after multiple reflection between the back side light reflecting means provided on the side and the front side light reflecting means provided on the excitation light irradiation surface side of the sample after passing through the sample A photothermal conversion measurement method characterized by measuring changes .

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