JP2005257414A - Photothermal conversion measurement device, method and cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably and precisely measure a characteristic change by photothermal effect of a sample with enhanced sensitivity while preventing increase in power consumption or cost, reduction in S/N ratio or extension of a measuring time; and to obtain a stable measurement result, even in the case that a cell causes a characteristic change by excitation light irradiation in measuring a sample stored in the cell, without being influenced by this. <P>SOLUTION: The refractive index change by photothermal effect of the sample 5 is measured by measuring a phase change by excitation light irradiation of a measuring light P1 passed through (transmitted by) the sample by use of a light interference method, or based on a phase difference between a reference light P2 and the measuring light P1. In this case, the measuring light P1 is passed through both the cell 6 and the sample 5, but the reference light P2 is passed through only the cell 6. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention is a photothermal conversion measuring apparatus that is used when analyzing a substance contained in a sample, and that measures a change in the characteristics of a sample based on a change in refractive index that occurs in the sample due to a photothermal effect when the sample is irradiated with excitation light. The method further relates to a cell containing the sample.

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. This is called the photothermal effect, and measuring this heat generation is called photothermal conversion measurement.
Conventionally, as a high-sensitivity analysis method of a sample by this photothermal conversion measurement, there is a method using a thermal lens effect formed on the sample by the photothermal effect (hereinafter referred to as a thermal lens method), and an analysis apparatus (photothermal conversion) using a thermal lens method. (A spectroscopic analyzer) is known (for example, refer to Patent Document 1).
FIG. 3 is a configuration diagram of a sample analyzer using the thermal lens method disclosed in Patent Document 1. In FIG. (See FIG. 1 of Patent Document 1). As shown in FIG. 3, 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 30, 31, 32, The sample 40 is irradiated through the lens 34 and the microscope 35. As a result, the sample 40 absorbs the excitation light A and generates heat, and its refractive index changes.
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 C that has passed through the sample 40 is condensed by the condenser lens 50, passes through the opening 51A (pinhole), 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 C obtained through the pinhole 51A is a change in the refractive index of the sample 40 ( That is, it varies according to the amount of light absorption according to the amount of substance contained in the sample. By measuring the intensity change of the detection light C, the change in the refractive index of the sample 40 can be measured, and the amount of the substance contained in the sample 40 can be evaluated based on the measurement result.
Japanese Patent Laid-Open No. 10-232210

In the analysis of the sample by the thermal lens method, the refractive index change due to the heat generation of the sample is detected by the change in the light intensity (detection signal intensity) due to the change in the focusing state of the measurement light (detection light). The change in 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 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 S / N ratio and a longer measurement time due to a decrease in the amount of light received by the detector.
The present invention has been made in view of the above circumstances. The purpose of the present invention is, firstly, the characteristic change due to the photothermal effect of the sample can be measured stably and with high accuracy, and further, the power consumption can be increased. An object of the present invention is to provide a photothermal conversion measuring apparatus and method capable of easily measuring with high sensitivity while preventing an increase in cost, a decrease in S / N ratio, and a long measurement time.
Furthermore, in general, the sample is measured in a cell (container) such as glass, and at this time, the excitation light is irradiated to the sample through the cell. When the excitation light is absorbed in the cell, a temperature change occurs in the cell itself due to irradiation of the excitation light, so that the refractive index of the cell changes. Even with this change in the refractive index of the cell, the measurement light passing through the cell is deflected, which may affect the analysis result. Particularly, when the absorption of the excitation light by the sample is very small, there is a problem that the measurement accuracy of the temperature change of the sample is deteriorated due to the strong influence of the temperature change of the cell.
It is a second object of the present invention to provide a photothermal conversion measuring device, a photothermal conversion measuring method, and a cell used for these in order to solve the above problems.

In order to achieve the above object, the present invention relates to a characteristic change of the sample caused by the photothermal effect of a sample housed in a cell and irradiated with excitation light, a measurement light passing through the sample, and a reference not passing through the sample. In a photothermal conversion measuring device for measuring by detecting a phase difference between measurement light after passing through the sample measured by causing interference with light and reference light, the measurement light and reference light in the cell As a photothermal conversion measuring apparatus, the light is passed through the same path, and further passes through the cell after irradiating the sample with the measurement light, and further passes through the cell after bypassing the sample. It is configured.
The measurement light and the reference light have different types of polarization, and are provided on the incident side of the measurement light with respect to the sample, pass through the measurement light and reflect the reference light, and the sample And a second means for reflecting the measurement light after passing through the sample.
It is desirable that the first means comprises a filter portion formed on an inner surface facing or in contact with the measurement light incident side surface of the sample of the cell.
Further, the second means reflects the measurement light after passing through the sample formed on the inner surface facing or in contact with the surface opposite to the measurement light incident side of the sample of the cell by the first means. It is desirable that the measuring light reflecting portion reflects in substantially the same direction as the reference light.
Furthermore, it is desirable that the measurement light and the reference light are incident on the sample from an oblique direction.

The excitation light is light whose intensity is periodically modulated, and the phase change of the measurement light can be measured for the same period component as the intensity modulation period of the excitation light. As a result, the temperature of the measurement part of the sample changes in the same cycle as the intensity modulation cycle, so that the influence of noise that does not have the same periodic component is removed, and the sample characteristic change (temperature Only the refractive index change due to the change) can be measured. Therefore, the S / N ratio of the phase change measurement is improved, and the sample can be analyzed with high accuracy.
It is also possible that the excitation light is multiplexed light of intensity-modulated light with different periods for each wavelength, and the phase change of the measurement light is measured for each of the same period components as the intensity modulation period of each wavelength of the excitation light. . As a result, it is possible to measure the heat generation (absorption characteristics) of the sample with respect to the measurement light of a plurality of wavelengths by a single measurement. This enables efficient measurement.
Further, photoelectric conversion means for photoelectrically converting the intensity of interference light between the measurement light and the reference light having a different optical frequency, and the measurement light based on the intensity signal of the interference light obtained by the photoelectric conversion means It is also conceivable to include a phase change calculating means for calculating the phase change. The electric signal (intensity signal of interference light) obtained thereby becomes a signal whose optical frequency is converted into an electric signal, and the phase component can be extracted by FM modulation. Since the extracted phase component includes a refractive index change signal due to heat generation of the sample, the temperature change of the sample can be measured. In addition, since the phase of the obtained interference signal is measured, it is stable and optically accurate without depending on the position of the photodetector (photoelectric conversion means), the intensity of the measurement light and its intensity distribution, etc. It becomes possible to measure the characteristic change of the sample.

Further, the present invention may be understood as a photothermal conversion measurement method performed by the photothermal conversion measurement device.
That is, the characteristic change of the sample caused by the photothermal effect of the sample contained in the cell and irradiated with the excitation light is measured by causing the measurement light passing through the sample to interfere with the reference light not passing through the sample. In the photothermal conversion measurement method for measuring by detecting the phase difference between the measurement light after passing through the sample and the reference light, the measurement light and the reference light are passed through the same path in the cell and the measurement is performed. The photothermal conversion measurement method is characterized in that after the sample is irradiated with light, the cell is further passed through, and the reference light is further passed through the cell after bypassing the sample.
Furthermore, it may be configured as a sample storage cell used in the photothermal conversion measuring apparatus and method. That is, the change in the characteristics of the sample caused by the photothermal effect of the sample irradiated with the excitation light passes through the sample measured by causing the measurement light passing through the sample to interfere with the reference light not passing through the sample. When measuring by detecting the phase difference between the later measurement light and the reference light, the cell accommodates the sample, provided on the incident side of the measurement light with respect to the sample, passes through the measurement light and passes through the measurement light. A first means for reflecting the reference light; and a second means for reflecting the measurement light after passing through the sample, provided on the opposite side of the measurement light incident on the sample. Cell.

The present invention measures the temperature change that occurs in the sample due to the photothermal effect of the sample irradiated with the excitation light, and the phase change of the measurement light after passing through the sample by the optical interferometry that causes the measurement light and reference light to interfere with each other. It is based on that. Therefore, even if the position of the photodetector (photoelectric conversion means), the intensity of the measurement light, its intensity distribution, etc. are different, if they do not change during the measurement, they do not depend on them and are stable. It becomes possible to measure the optical deflection characteristic of the sample optically with high accuracy.
Further, the measurement light and the reference light are irradiated in a coaxial state, and the reference light is transmitted only through the cell and not through the sample, while the measurement light is transmitted through the cell and the sample. All are transmitted through substantially the same path in the cell. Therefore, the measurement light and the reference light are equally affected by the temperature change due to the absorption of the excitation light in the cell and the influence of the refractive index change. Therefore, the optical path length difference (that is, phase difference) between the measurement light and the reference light is only due to the measurement light passing through the sample, and the characteristic change of the sample can be measured with high accuracy.

Hereinafter, embodiments and examples of the present invention will be described with reference to the accompanying drawings for understanding of the present invention. 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 a photothermal conversion measuring apparatus according to an embodiment of the present invention, and its function will be described.
Excitation light (for example, laser having a wavelength of 532 nm and an output of 100 mW (YAG harmonic)) output from a predetermined excitation light source 1 is reflected by the mirror 3 and passes through the lens 4 and the sample cell 6 to irradiate the sample 5. Is done. As a result, the sample 5 absorbs the excitation light and generates heat, and the refractive index of the sample 5 changes due to the temperature change (rise) (photothermal effect).
On the other hand, the measurement light output from the laser light source 7 that outputs the measurement light (for example, a He—Ne laser having an output of 1 mW) is adjusted in the type of polarization, and further, the laser beam having a different type of polarization by the polarization beam splitter (PBS9). Branches to (P1, P2). Here, in the half-wave plate 8, the laser beam P1 is vertically polarized and the laser beam P2 is horizontally polarized. Of the laser beams having different types of polarization, light that passes through the sample later is measurement light, and light that does not pass is reference light. In this example, laser light P1 is measurement light and P2 is reference light.
The measurement light P1 and the reference light P2 are reflected by the mirrors 12 and 13 and then combined by the polarization beam splitter PBS14.
The synthesized measurement light P1 and reference light P2 are irradiated on the cell 6 in which the measurement sample is contained in a coaxial form. Here, for example, the upper surface (A surface) of the cell 6 is subjected to a non-reflective coating process, and at the interface (B surface) between the cell 6 and the upper surface of the sample 5, the type of polarized light of the measurement light P1 is used. Is applied with a coating process (an example of the first means) for total reflection with respect to the light of the reference light P2 which is non-reflective and has a different polarization type. Therefore, the reference light P2 passes through the cell 6 once, then is reflected by the first means (B surface), and passes through the cell 6 without passing through the sample 5 (bypass).
The interface (C surface) with the cell 6 at the lower part of the sample 5 is coated with a total reflection film (an example of the second means), and the measurement light P1 after passing through the sample 5 is used as the reference light P2. Is reflected in substantially the same direction as the direction reflected by the first means (B surface). Therefore, the measurement light P1 once passes through the cell 6 along the same path as the reference light P2, then passes through the sample 5, and further passes through the cell 6 along the substantially same path as the reference light P2.
As described above, the measurement light P1 transmitted through the cell 6 and the sample 5 and reflected by the C surface and the reference light P2 reflected by the interface B surface between the cell 6 and the sample 5 are obtained. One means comes into contact with the measurement light P1 incident side surface of the sample 5 of the cell 6 (opposite when there is a gap between the cell 6 and the sample 5) from the filter portion formed on the inner side surface (B surface). If this is the case, the measurement light P1 can pass through the cell 6 along substantially the same path as the reference light P2, which is preferable.
In addition, the second means is in contact with the surface of the sample 6 of the cell 6 opposite to the measurement light P1 incident side (facing when there is a gap between the cell 6 and the sample 5). If the reflection direction is substantially the same as the reflection direction of the reference light P2 on the B surface, the measurement light P1 is in the cell 6 along the substantially same path as the reference light P2. , And interferes with the reference light P2 through the polarizing plate 16 described later.
The measurement light P1 and the reference light P2 are incident on the sample 5 from the oblique direction, whereby the first means (surface B) transmits a suitable filter characteristic (the measurement light P1 is transmitted and the reference light P2 is transmitted). It has been confirmed that reflective properties can be obtained.
These reflected lights are reflected by the mirror 19 and interfere through the polarizing plate 16, and the light intensity of the interference light is converted into an electric signal by the photodetector 17 (photoelectric conversion means). This electric signal (interference light intensity) S1 is expressed by the following equation (1).
S1 = C1 + C2 · cos (2π · f _b · t + Φ) (1)
Here, C1, C2 are constants determined by the optical system such as the measurement light laser intensity, AOM, PBS, mirror, and the transmittance and reflectance of the sample 5 and the cell 6, and Φ is the optical path of the measurement light P1 and the reference light P2. phase difference due to the length difference, an optical frequency difference between f _b is the measuring light P1 and the reference light P2. From the equation (1), the change in the phase difference Φ is measured from the change in the interference light intensity signal S1, and thereby the temperature change of the sample can be detected and measured.
Here, the measured phase difference Φ is an optical path length difference between the measurement light P1 and the reference light P2, and the measurement light P1 and the reference light P2 pass through substantially the same path in the cell. It can be understood that this is the optical path length difference caused by the measurement light P1 passing through the sample. Therefore, even if there is a refractive index change due to absorption of the excitation light in the cell 6, they cause almost the same phase change in both the measurement light P <b> 1 and the reference light P <b> 2. (Cell) is not affected by the refractive index change.
This electric signal (interference light intensity) S1 is input to the signal processing device 18, and the change of the phase difference Φ can be calculated 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 changes. That is, the greater the amount of the contained material, the greater the change in the phase difference Φ relative to the change in the excitation light. Therefore, if the phase difference Φ is measured, the refractive index 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, using the photoelectric conversion measuring device, the change in the phase difference Φ is measured for a plurality of types of sample samples whose amounts (concentrations) of the predetermined contained substances are known in advance, and the results and the amounts of the contained substances are determined. Is stored in the symbol processing device 18 as a data table. Then, the amount of the contained substance can be specified by performing an interpolation process or the like on the measurement result of the phase difference Φ for the sample to be measured based on the data table.

  As shown in FIG. 1, the excitation light output from the excitation light source 1 can be converted (periodically intensity modulated) into intermittent light (intermittent frequency: f) with a predetermined period by a chopper 2. In this embodiment, 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 phase difference Φ also changes at the frequency f. Therefore, if the change of 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 change in refractive index due to a temperature change of 5 can be measured. Thereby, the S / N ratio of the measurement of the phase difference Φ is improved.

The characteristic change (refractive index change) of the sample 5 due to the photothermal effect differs depending on the wavelength of the excitation light, and the photothermal effect on the excitation light of each wavelength also differs depending on the type of the substance contained in the sample 5.
Therefore, by irradiating a plurality of different wavelengths of excitation light and measuring the change in the phase difference Φ for each of them, the type and amount of the substance contained in the sample 5 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 a different period for each wavelength, and the signal processor 18 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 light deflection characteristics of the sample with respect to the measurement light of a plurality of wavelengths can be measured by one measurement, and efficient measurement is possible.
As a light source (irradiation means) 1 for such excitation light, the light of 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 light that has collected (merged) them is the excitation light.
Specifically, as shown in FIG. 2, the light from the white light source 40 is split in two directions by a beam split 41, reflected by the fixed mirror 42 and the moving mirror 43, and returned to the beam splitter 41 again to be merged. It is conceivable to use an excitation light output unit using well-known Fourier spectroscopy using this as excitation light.

As shown in FIG. 1, an embodiment in which the measurement light P1 and / or the reference light P2 is optically shifted (frequency converted) by an acousto-optic modulator (AOM 10, 11) is also conceivable. In this case, an optical frequency difference f _b is generated between the measurement light P1 and the reference light P2. For example, the optical frequency difference f _b is about 30 MHz.
Here, when there is no optical frequency difference f _{b in the} equation (1) (that is, f _b = 0), the equation (1) is expressed as follows.
S1 = C1 + C2 · cosΦ (2)
Based on the equation (2), the phase difference Φ is derived from the value S1 obtained by the measurement by the optical interferometry. The value of the phase difference Φ changes according to changes in constants C1 and C2 other than S1. To do. Therefore, it is necessary to always make these constants C1 and C2 the same for measurement, and the optical system such as the measurement light laser intensity, AOM, PBS, mirror, and the transmittance and reflectance of the sample 5 and the cell 6 are measured. Each time, there is an annoyance of adjusting to a predetermined value.
On the other hand, when an optical frequency difference f _b exists between the measurement light P1 and the reference light P2 (for example, f _b = 30 MHz), the electric signal S1 is time (t) as is apparent from the above equation (1). It is a periodic signal that changes in accordance with the change in. The phase difference Φ can be derived by removing the fluctuation of the adjustment state such as the measurement light laser intensity by FM demodulation and the like.

The schematic block diagram of the photothermal conversion measuring apparatus which concerns on embodiment of this invention. The schematic block diagram of the output part of the excitation light using the Fourier spectroscopy in the photothermal conversion measuring apparatus which concerns on the Example of this invention. The schematic block diagram of the conventional photothermal conversion measuring apparatus (photothermal conversion spectroscopy analyzer).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Excitation light source 2 ... Chopper 3,12,13,15,19 ... Mirror 4 ... Lens 5 ... Sample 6 ... Cell 7 ... Laser light source 8 ... 1/2 wavelength plate 9,14 ... Beam splitter 10,11 ... Acoustic optics Modulator 16 ... Polarizing plate 17 ... Photodetector (photoelectric conversion means)
18 ... Signal processing device

Claims (10)

The characteristic change of the sample caused by the photothermal effect of the sample housed in the cell and irradiated with excitation light is measured by causing the measurement light passing through the sample to interfere with the reference light not passing through the sample In a photothermal conversion measurement device that measures by detecting the phase difference between the measurement light after passing through the sample and the reference light,
The measurement light and the reference light are allowed to pass through the same path in the cell, and the measurement light is applied to the sample and then further passed through the cell. After the reference light is bypassed the sample, the cell is further passed through the cell. Let through,
A photothermal conversion measuring device. The measurement light and the reference light are different from each other in the type of polarization,
A first means provided on an incident side of the measurement light with respect to a sample, passing through the measurement light and reflecting the reference light;
A second means for reflecting the measurement light after passing through the sample, provided on the opposite side to the measurement light incident side with respect to the sample;
The photothermal conversion measuring device according to claim 1, further comprising:   3. The photothermal conversion measurement device according to claim 2, wherein the first means includes a filter unit formed on an inner surface facing or in contact with a measurement light incident side surface of the sample of the cell.   The second means is formed on the inner surface facing or in contact with the surface opposite to the measurement light incident side of the sample of the cell, and the measurement light after passing through the sample is reflected by the first means. 4. The photothermal conversion measuring device according to claim 2, further comprising a measuring light reflecting portion that reflects in substantially the same direction as the reference light.   5. The photothermal conversion measurement device according to claim 1, wherein the measurement light and the reference light are incident on the sample from an oblique direction.   The photothermal energy according to any one of claims 1 to 5, wherein the excitation light is light whose intensity is periodically modulated, and the phase change of the measurement light is measured for the same period component as the intensity modulation period of the excitation light. Conversion measuring device.   The excitation light is multiplexed light of intensity-modulated light with different periods for each wavelength, and the phase change of the measurement light is measured for each of the same period components as the intensity modulation period of each wavelength of the excitation light. The photothermal conversion measuring device according to any one of 1 to 6.   Photoelectric conversion means for photoelectrically converting the intensity of interference light between the measurement light and the reference light having a different optical frequency; and a phase 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 7, further comprising a phase change calculating means for calculating a change. The characteristic change of the sample caused by the photothermal effect of the sample housed in the cell and irradiated with excitation light is measured by causing the measurement light passing through the sample to interfere with the reference light not passing through the sample In the photothermal conversion measurement method for measuring by detecting the phase difference between the measurement light after passing through the sample and the reference light,
The measurement light and the reference light are allowed to pass through the same path in the cell, and the measurement light is applied to the sample and then further passed through the cell. After the reference light is bypassed the sample, the cell is further passed through the cell. Passing,
A photothermal conversion measurement method characterized by the above. Changes in the characteristics of the sample caused by the photothermal effect of the sample irradiated with the excitation light are measured by causing the measurement light passing through the sample and the reference light not passing through the sample to interfere with each other after passing through the sample. A cell that accommodates the sample when measuring by detecting the phase difference between the measurement light and the reference light,
A first means provided on an incident side of the measurement light with respect to a sample, passing through the measurement light and reflecting the reference light;
A second means for reflecting the measurement light after passing through the sample, provided on the opposite side to the measurement light incident side with respect to the sample;
A cell comprising:

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