JP4331126B2 - Thermal lens spectrometer - Google Patents

Description

  The present invention relates to a thermal lens spectroscopic analyzer that is suitably used in an analyzer that easily analyzes and detects a trace amount of sample.

  Analysis for bedside diagnosis (POC (point of care) analysis) that performs measurements necessary for medical diagnosis in the vicinity of the patient, and analysis of harmful substances in rivers and wastes at rivers and waste disposal sites (POU (point of use) analysis), and analysis / measurement at or near the site where analysis / measurement is required, such as contamination inspection at food cooking, harvesting, and importing sites The importance of (hereinafter collectively referred to as “POC analysis, etc.”) has attracted attention. In recent years, the development of detection methods and detection apparatuses applied to such POC analysis and the like is being emphasized.

In the detection method and the detection apparatus applied to such POC analysis and the like, it is required that the analysis is performed at a low cost and the apparatus is small. Moreover, in medical diagnosis and environmental analysis, it is generally required that highly sensitive and highly accurate analysis be performed in order to accurately compare with a reference value determined by the country.
As a detection method suitable for such POC analysis or the like, there is a photothermal conversion spectroscopic method in which a substance such as a dye in a solution absorbs light and measures the amount of heat generated in the relaxation process. This photothermal conversion spectroscopic method is known as a highly sensitive concentration measurement method, and in particular, a thermal lens spectroscopic method using a refractive index distribution due to a temperature distribution generated by generated heat is an absorptiometric method for measuring the amount of transmitted light. It is known that the sensitivity is 100 times higher than the method (see Patent Documents 1 to 3 and Non-Patent Documents 1 to 6).

JP 60-174933 A Japanese Patent Laid-Open No. 10-142177 JP-A-4-369467 Manabu Tokeshi et al., J. Lumin. Vol. 83-84, 261-264, 1999 A. C. Boccara et. Al., Appl. Phys. Lett. 36, 130, 1980 J. Liquid Chromatography 12,2575-2585 (1989) M. Harada et. Al. 4,280-284,1997 Anal. Chem. Vol.65,2938-2940,1993 Kawanishi et al., Abstracts of the 44th Annual Meeting of the Analytical Society of Japan, p119, 1995

In POC analysis and the like, since it is necessary to transport the analyzer to the site where analysis is performed, there has been a risk of positional displacement of the components of the analyzer due to vibration during transportation. Therefore, the sensitivity and accuracy of analysis may be reduced. In addition, vibrations and the like are likely to occur in the analyzer at the site where analysis is performed, and the analysis is often adversely affected. Furthermore, since it is preferable that the analysis can be easily performed in the field, it has been demanded that fine adjustment of the analyzer before the analysis is unnecessary.
Therefore, the present invention solves the problems of the conventional thermal lens spectroscopic analyzer as described above, and it is difficult for the sensitivity and accuracy of the analysis to decrease even if the position shift or vibration occurs in the parts, and before the analysis. It is an object of the present invention to provide a thermal lens spectroscopic analyzer that does not require fine adjustment.

In order to solve the above problems, the present invention has the following configuration. That is, the thermal lens spectroscopic analysis apparatus according to claim 1 of the present invention is configured to make the probe light enter the thermal lens generated in the sample by the incidence of the excitation light, and based on the change of the probe light by the thermal lens at that time. A thermal lens spectroscopic analyzer for analyzing the sample, wherein the excitation light condensing optical element condenses the excitation light on the sample, and probe light condensing for condensing the probe light on the thermal lens. An optical element and detection means for receiving and detecting the probe light transmitted through the thermal lens are provided, and the following four conditions are satisfied.

(1) The excitation light condensing optical element condenses the excitation light such that the half sine of the maximum cone angle of the light bundle is 0.15 or less.
(2) The probe light condensing optical element condenses the probe light such that the half sine of the maximum cone angle of the light bundle is 0.15 or less.
(3) The size of the light receiving unit so that the light receiving unit of the detecting unit receives only the portion of the probe light changed by the thermal lens and does not receive the portion not affected by the thermal lens. Is set.
(4) The focal position of the excitation light and the focal position of the probe light can be adjusted independently, and the distance between the two focal positions is 200 μm or more.

  The “half-angle of the maximum cone angle of the light beam” here refers to an image forming portion (ideal focal position) formed when light such as laser is condensed by a condensing optical element such as a lens. Means the half value of the apex angle of the cone of ray bundle. When a lens is used for condensing, NA (numerical aperture) ≡ sin θ (when the medium is air) is established, where θ is the half angle of the maximum cone angle of the light beam.

Here will be described the conditions of the four conditions (1) and (2). The excitation light and the probe light are condensed so that the sine of the maximum cone angle of the light beam is 0.15 or less, and the way of focusing is not so strong. Even if directional vibrations occur in a component (for example, the light receiving portion of the detecting means), the degree of fluctuation of the thermal lens signal is small, and the sensitivity and accuracy of analysis are small. In addition, even if there is misalignment in the above direction due to thermal strain or vibration during transportation, the sensitivity and accuracy of the analysis are small, so the thermal lens spectrometer is finely adjusted before analysis at the analysis site. There is no need to do.

  In order to obtain a preferable degree of narrowing of the excitation light and the probe light, the half sine of the aforementioned maximum cone angle is 0.15 or less, that is, the excitation light condensing optical element and the probe light condensing optical element. The numerical aperture must be 0.15 or less, and the half sine of the maximum cone angle is 0.1 or less, that is, the numerical apertures of the excitation light condensing optical element and the probe light condensing optical element are set to 0. More preferably, it is 1 or less.

Next, the condition (3) will be described. The size of the light receiving unit is set according to the distance between the sample and the light receiving unit, and the light receiving unit receives only the portion of the probe light changed by the thermal lens and is not affected by the thermal lens. Since the portion does not receive light, the thermal lens spectroscopic analyzer of the present invention has sufficient analysis sensitivity.
Next, the condition (4) will be described. By separating the focal position of the excitation light and the focal position of the probe light to some extent, sufficient analysis sensitivity is obtained, and at the same time, even if a positional deviation along the optical path or vibration in the same direction occurs in the part, analysis The decrease in sensitivity and accuracy is realized. If the distance between the focal position of the excitation light and the focal position of the probe light is 100 μm or more, sufficient analysis sensitivity is obtained, and the sensitivity and accuracy of analysis are reduced due to the above-described positional deviation and vibration. Is particularly difficult to occur. If the distance between the focal position of the excitation light and the focal position of the probe light is less than 100 μm, the ratio of the portion changed by the thermal lens in the probe light is too large, so the shape of the portion changed by the thermal lens is distorted. This not only hinders the analysis, but also increases the degree of reduction in resistance to the deviation of the optical axis between excitation light and probe light, which will be described later. In order to make such inconvenience less likely to occur, it is more preferable that the distance between the focal position of the excitation light and the focal position of the probe light be 200 μm or more.

The thermal lens spectroscopic analysis device according to claim 2 of the present invention is the thermal lens spectroscopic analysis device according to claim 1, wherein the distance T between the focal position of the probe light and the light receiving unit, and the The diameter D of the light receiving portion satisfies the following formula.
T ≧ 125000 × (half sine of the maximum cone angle of the light beam of the excitation light or the probe light) × [D + 2 × (allowable displacement of the light receiving portion)] / [250 + 2 × (allowable position of the light receiving portion) Deviation))
Note that the unit of T, D, and the allowable positional deviation amount of the light receiving unit is μm.

Furthermore, the thermal lens spectroscopic analysis apparatus according to claim 3 of the present invention is the thermal lens spectroscopic analysis apparatus according to claim 1, in which the distance T between the focal position of the probe light and the light receiving unit, and the The diameter D of the light receiving portion satisfies the following formula.
T ≧ (half sine of the maximum cone angle of the beam bundle of the excitation light or the probe light) × [D + 40] × 400
The unit of T and D is μm.

  As described above, since the sample and the light receiving portion of the detection means are separated from each other by a predetermined distance (in the present invention, from the “distance between the sample and the light receiving portion of the detection means”, “the focal position of the excitation light and the focus of the probe light” The “distance between the focal position of the probe light and the light receiving unit” minus the “distance between the position”, but since it is substantially synonymous in terms and concept, this expression will be used in the following. However, even if a position shift in the direction orthogonal to the optical path or vibration in the same direction occurs in the component (for example, the light receiving part of the detection means), the degree of fluctuation of the thermal lens signal is small, and the sensitivity and accuracy of analysis are reduced. small. As described above, since it is not easily affected by vibration or the like at the site where analysis is performed, it is suitable for POC analysis. In addition, even if there is misalignment in the above direction due to thermal strain or vibration during transportation, the sensitivity and accuracy of the analysis are small, so the thermal lens spectrometer is finely adjusted before analysis at the analysis site. There is no need to do.

The permissible positional deviation amount of the light receiving unit, that is, the positional deviation amount of the light receiving unit (the positional deviation amount in the direction orthogonal to the optical path) that hardly causes an adverse effect on the analysis is desirably ± 20 μm. Therefore, it is more preferable to satisfy the expression according to claim 3 obtained by substituting 20 into the “allowable positional deviation amount of the light receiving portion” of the expression according to claim 2.
Although the thermal lens signal can be detected regardless of the shape of the light receiving portion, the area of the light receiving portion is the same because the thermal lens can be assumed to have an approximately Gaussian distribution. However, the thermal lens signals detected when the shapes are different are not necessarily the same. The cross-sectional shape of the probe light composed of a laser or the like is circular or elliptical. As a result, the distribution of the thermal lens is basically considered to be circular or elliptical, and therefore the shape of the light receiving part is preferably circular or elliptical. However, other shapes such as a rectangle may be used. In this case, it is necessary to correct the value of “D” in the above formula according to the shape.

Further, thermal lens spectroscopic analyzer according to claim 4 of the present invention, the thermal lens spectrometer according to any one of claims 1 to 3, the focus of the focus position of the pre-Symbol probe light the excitation light It exists in the position near the said light-receiving part rather than a position, It is characterized by the above-mentioned .

Furthermore, the thermal lens spectroscopic analysis device according to claim 5 of the present invention is the thermal lens spectroscopic analysis device according to any one of claims 1 to 4, wherein either one or both of the excitation light and the probe light is used. A beam expander is installed on the optical path, and the focal positions of the excitation light and the probe light can be adjusted independently.

Furthermore, the thermal lens spectroscopic analysis device according to claim 6 of the present invention is the thermal lens spectroscopic analysis device according to any one of claims 1 to 5, wherein the excitation light condensing optical element and the probe light collecting device. The optical optical element is the same optical element.
Such a configuration is preferable in terms of cost and size reduction because the number of parts is reduced.

Furthermore, the thermal lens spectroscopic analyzer according to claim 7 of the present invention is the thermal lens spectroscopic analyzer according to any one of claims 1 to 6, wherein a central portion of the light receiving portion of the detecting means is the excitation. It is located on the extended line of the line which connects the focus position of light and the focus position of the probe light.
The optical axis of the excitation light and the optical axis of the probe light may be misaligned even if they are collected by the same optical element due to the influence of the assembly accuracy at the time of manufacturing the thermal lens spectroscopic analysis device. The portion of the probe light that has changed due to the thermal lens is located on an extension of the line connecting the focal position of the excitation light and the focal position of the probe light. Therefore, the sensitivity of the thermal lens spectroscopic analyzer can be increased by arranging the central portion of the light receiving portion of the detecting means on the extension line.
Furthermore, the thermal lens spectroscopic analysis device according to claim 8 of the present invention is the thermal lens spectroscopic analysis device according to claim 7, wherein the excitation light transmitted through the excitation light condensing optical element and the probe light collecting device. The probe light transmitted through the optical optical element is not coaxial.

  The thermal lens spectroscopic analysis apparatus of the present invention is less likely to cause a decrease in analysis sensitivity or accuracy even if a position shift or vibration occurs in a part. In addition, fine adjustment before analysis is not required.

  FIG. 1 is a configuration diagram illustrating a configuration of a thermal lens spectroscopic analyzer according to an embodiment of the present invention. The thermal lens spectroscopic analysis apparatus of FIG. 1 includes a laser emission means 1 (wavelength is about 635 nm) that is a light source of excitation light E, a laser emission means 2 (wavelength is about 780 nm) that is a light source of probe light P, and excitation light. E and the condensing lens 5 which condenses the probe light P (corresponding to the excitation light condensing optical element and the probe light condensing optical element which are constituent elements of the present invention) and the sample solution S are stored. And a probe light P detecting means 9 having an optical fiber 8 (corresponding to a light receiving portion which is a constituent of the present invention) for receiving the probe light P. Since the end face of the optical fiber 8 receives the probe light P, the diameter of the optical fiber 8 corresponds to a diaphragm.

  In such a thermal lens spectroscopic analysis apparatus, the excitation light E is output from the laser light emitting means 1, the probe light P is output from the laser light emitting means 2, and the probe light P is reflected by the reflector 3 to be a beam splitter. 4 is incident. In the beam splitter 4, the excitation light E and the probe light P are coaxial and guided to the condenser lens 5. The excitation light E focused by the condenser lens 5 is condensed on the sample solution S, thereby forming a thermal lens (not shown). Then, the probe light P focused by the condenser lens 5 is condensed toward the thermal lens and is diverged or condensed by the thermal lens effect.

Only the excitation light E is removed from the excitation light E and the probe light P transmitted through the sample cell 6 by the excitation light cut filter 7, and only the probe light P transmitted through the thermal lens is received by the optical fiber 8 according to the diameter. The Then, the received probe light P is guided to the detecting means 9 by the optical fiber 8 and the laser power thereof is measured.
The measurement may be performed in the case where the sample solution S is stored in the sample cell 6 and in the case where the sample solution S is not stored, and a difference between detection values of the detection means 9 may be used as a thermal lens signal. This thermal lens signal is proportional to the degree of thermal lens, that is, the concentration of the sample solution S. Usually, the excitation light E is modulated, and only the fluctuation of the probe light P corresponding to the modulation frequency is extracted using a lock-in amplifier or the like, so that a more accurate result can be obtained.

  In general, it is known that the sensitivity of the thermal lens signal is improved as the excitation light and the probe light are more strongly reduced. However, if the excitation light and the probe light are stronger, the sensitivity of the light source, the condenser lens, the optical fiber, etc. Not only does the sensitivity and accuracy of the analysis tend to be easily reduced due to the effects of component displacement and vibration, but also adjustment of the alignment of the component to the measurement site becomes more difficult. On the other hand, in the POC analysis or the like, it is necessary to transport the thermal lens spectroscopic analyzer to the site where the analysis is performed, and there is a risk that the components of the thermal lens spectroscopic analyzer may be displaced due to vibration during transport. In addition, there may be vibrations caused by the analysis environment during analysis. Therefore, the thermal lens spectroscopic analyzer is required to have a performance that is less likely to cause adverse effects due to component displacement and vibration.

  In the thermal lens spectroscopic analyzer of the present embodiment, the condensing lens 5 has a numerical aperture of 0.15 or less, and the way in which the excitation light E and the probe light P are reduced is not so strong. Even if vibrations in the same direction occur in components such as the condenser lens 5 and the optical fiber 8, the degree of fluctuation of the thermal lens signal is small, and the sensitivity and accuracy of analysis are small (in the following description, FIG. See also). In addition, even if there is a positional shift in the above direction due to vibration during transportation, etc., the sensitivity and accuracy of the analysis are small, so it is necessary to finely adjust the thermal lens spectrometer before analysis at the analysis site. Absent.

In addition, it can also be set as the structure which provides two condensing lenses and condenses the excitation light E and the probe light P with another condensing lens, respectively. Further, the excitation light E and the probe light P may be narrowed using another type of optical element such as a concave reflector instead of the condenser lens 5.
Further, the size of the light receiving surface 8a (the diameter of the optical fiber 8) is set according to the distance between the sample solution S and the light receiving surface 8a of the optical fiber 8, and the light receiving surface 8a of the optical fiber 8 is connected to the probe. Only the portion P ′ changed by the thermal lens L in the light P is received, and the portion not affected by the thermal lens L is not received (that is, the size of the light receiving surface 8a of the optical fiber 8). However, the thermal lens spectroscopic analyzer has a sufficient analysis sensitivity, which is smaller than or equal to the portion P ′ changed by the thermal lens L in the probe light P). If the light receiving surface 8a of the optical fiber 8 is too large, portions of the probe light P that are not affected by the thermal lens L are also received, so that the intensity of the thermal lens signal is reduced under the influence.

Furthermore, in the thermal lens spectroscopic analyzer of this embodiment, the distance T between the focal position of the probe light P and the light receiving surface 8a of the optical fiber 8 (the end surface of the optical fiber 8) and the diameter D of the optical fiber 8 are as follows. The following formula is satisfied (the unit of T and D is μm).
T ≧ (half sine of the maximum cone angle of the beam bundle of excitation light E and probe light P) × [D + 40] × 400
Therefore, even if a positional deviation in the direction orthogonal to the optical path or vibration in the same direction occurs in the component, the degree of fluctuation of the thermal lens signal is small, and the sensitivity and accuracy of analysis are small. In addition, even if there is a positional shift in the above direction due to vibration during transportation, etc., the sensitivity and accuracy of the analysis are small, so it is necessary to finely adjust the thermal lens spectrometer before analysis at the analysis site. Absent.

  Furthermore, in the thermal lens spectroscopic analyzer of the present embodiment, the distance between the focal position of the excitation light E and the focal position of the probe light P is 200 μm or more (for example, 300 μm or 500 μm), and both focal positions are to some extent. Since they are separated, the maximum cone angle of the beam bundle formed by the portion P ′ changed by the thermal lens L in the probe light P is smaller than the maximum cone angle of the beam bundle formed by the entire probe beam P. As a result, even if a positional deviation in the direction along the optical path or vibration in the same direction occurs in the component, the fluctuation in the cross-sectional area of the portion P ′ changed by the thermal lens L in the probe light P is small, and the sensitivity and accuracy of the analysis The decrease is small. In addition, if the distance between the focal position of the excitation light E and the focal position of the probe light P is within the above range, sufficient analysis sensitivity can be maintained.

In order to adjust the distance between the focal position of the excitation light E and the focal position of the probe light P, the chromatic aberration of the condenser lens 5 can be used. If a beam expander or the like is installed on one or both of the optical paths so that the focal positions can be adjusted independently, the distance between the focal positions can be adjusted with higher accuracy.
Furthermore, in the thermal lens spectroscopic analyzer of the present embodiment, the focal position of the probe light P is located closer to the light receiving surface 8a of the optical fiber 8 than the focal position of the excitation light E. Therefore, the thermal lens signal is stable. If both focal positions exist at the same position, or if the focal position of the excitation light E exists closer to the light receiving surface 8a of the optical fiber 8 than the focal position of the probe light P, contrary to the case described above, Unevenness or distortion may be observed in the lens signal distribution, which may cause problems in analysis.

  Furthermore, in the thermal lens spectroscopic analyzer of this embodiment, the central portion of the light receiving surface 8a of the optical fiber 8 is a line connecting the focal points of the excitation light E and the probe light P collected by the same condenser lens 5. The optical fiber 8 is arranged so as to be located on the extension line. As a result, even if the optical axis shift between the excitation light E and the probe light P occurs due to insufficient adjustment or the like, the portion P ′ changed by the thermal lens L in the probe light P can be received efficiently. The sensitivity of the spectroscopic analyzer is increased.

  With the configuration as described above, the thermal lens spectroscopic analyzer of the present embodiment can detect the thermal lens signal even if a positional deviation or vibration in the same direction along the optical path and in the direction orthogonal to the optical path occurs in the component. The degree of fluctuation is small, and the decrease in sensitivity and accuracy of analysis is small. Moreover, the thermal lens spectroscopic analyzer of this embodiment has the necessary sensitivity. Therefore, it is suitable for POC analysis and the like. The necessary sensitivity mentioned above includes the numerical aperture of the condenser lens 5, the distance between the focal position of the excitation light E and the focal position of the probe light P, the light receiving surface 8a (light of the sample solution S and the optical fiber 8). The thermal lens signal obtained when the distance between the optical fiber 8 and the size of the light receiving surface 8a of the optical fiber 8 is set so that the thermal lens signal becomes the maximum value. Then, it means the sensitivity at which a value of 80% or more of the maximum thermal lens signal value is obtained.

Below, each component other than the condensing lens 5 is demonstrated.
The type of laser used as the laser emission means 1 that is the light source of the excitation light E is not particularly limited, and a gas laser, a solid laser, or the like can be used without any problem. Is desirable. However, in the case of using a semiconductor laser, when reflected light from each optical component is incident on the light source of the excitation light E again, it becomes noise due to output change. Therefore, high frequency superposition is applied to the semiconductor laser or a polarization dependent beam splitter is used. It is desirable to incorporate an optical isolator in combination with a quarter wave plate.

  Although not a laser, a light emitting diode (LED) can be used as the light source of the excitation light E if sufficient sensitivity can be realized in the thermal lens measurement. In particular, by combining a plurality of filters with a white light LED having a wide wavelength range, which has been increasing in output, light of a plurality of wavelengths can be used as excitation light, which is impossible with a conventional single wavelength laser. The absorption spectrum can be measured with a thermal lens.

Further, the type of laser used as the laser emission means 2 that is the light source of the probe light P is not particularly limited, and the same laser as the laser emission means 1 is used as long as the wavelength is different from that of the excitation light E. be able to. A light emitting diode can also be used as a light source for the probe light P.
Further, the reflecting plate 3 is for guiding the probe light P to the beam splitter 4 and can be used without any problem as long as it has a sufficient reflectance at the wavelength of the probe light P. However, it is desirable that the reflectance is close to 100%.

  Further, the beam splitter 4 is for making the excitation light E and the probe light P coaxial, and has a sufficiently high reflectance with respect to the probe light P and a sufficiently high transmittance with respect to the excitation light E. I just need it. However, it is preferable that the probe light P has a reflectance close to 100% and the excitation light E has a transmittance close to 100%. For example, there are those utilizing the fact that the wavelengths of the excitation light and the probe light are different, and those utilizing the fact that the polarization planes of the excitation light and the probe light are different. The arrangement of the laser light emitting means 1 and the laser light emitting means 2 in FIG. 1 may be interchanged. In that case, it is needless to say that the characteristics of the reflector 3 and the beam splitter 4 also need to be changed according to the arrangement of the laser emitting means 1 and 2.

  Furthermore, the sample cell 6 is for storing the sample solution S to be measured. The material of the sample cell 6 is not particularly limited as long as it is transparent to the excitation light E and the probe light P, but it is desirable that the transmittance of the excitation light E and the probe light P is as high as possible. Examples thereof include resin materials such as polymethyl methacrylate (PMMA), polycarbonate (PC), polystyrene (PS), and cycloolefin resin, and glass. The shape of the sample cell 6 is not particularly limited, but it is preferable that a flat surface exists at a position where the excitation light E and the probe light P are incident and transmitted. Note that the portion of the sample cell 6 where the excitation light E and the probe light P are incident and transmitted is only required to be transparent with respect to the excitation light E and the probe light P. It may be configured.

  Further, the excitation light cut filter 7 can be used without any problem as long as it can sufficiently remove the excitation light E, but preferably has an optical density of 5 or more. For example, a color glass filter, an interference filter and the like can be mentioned. In the present embodiment, the excitation light cut filter 7 is integrated with the optical fiber 8, but may be a separate body.

  Further, the type of the optical fiber 8 is not particularly limited as long as it guides laser light having the wavelength of the probe light, and an SI (Step Index) type, a GI (Graded Index) type, or the like is used. Can do. The guided mode may be either single mode or multimode. However, when a tolerance for bending is required, the multimode is preferable because the tolerance is high. The material of the optical fiber 8 is not particularly limited, and any material such as resin or glass can be used without any problem. Considering that the cost can be reduced, a multimode waveguide type plastic optical fiber is most preferable.

  The type of the detection means 9 is not particularly limited as long as it has sufficient sensitivity to the probe light P, and examples thereof include a photodiode. In the present embodiment, the detection means 9 is integrated with the optical fiber 8, but may be a separate body. Further, instead of the optical fiber 8, a diaphragm having a predetermined opening diameter may be attached to the detection means 9 such as a photodiode, and the detection means 9 may directly receive the probe light P from this diaphragm. At this time, the aperture diameter of the diaphragm corresponds to the size of the light receiving surface 8 a of the optical fiber 8.

Next, the distance between the focal position of the excitation light and the focal position of the probe light, the distance between the sample and the light receiving portion of the probe light, and the deviation of the optical axis between the excitation light and the probe light will be further detailed. Explained.
[Distance between the focal position of the excitation light and the focal position of the probe light]
The relationship between the distance between both focal positions and the intensity of the thermal lens signal is shown in the graph of FIG. From this graph, it can be seen that even when the distance between the two focal positions is 200 μm or more, the intensity of the thermal lens signal (the sum of the thermal lens signals) is high and the analysis sensitivity is sufficient. When the distance between both focal positions is less than 200 μm, as described above, the proportion of the probe light changed by the thermal lens is too large, so the shape of the probe light changed by the thermal lens is distorted. As a result, the analysis is hindered, and the degree of decrease in resistance to the deviation of the optical axis between the excitation light and the probe light is increased.

Also, the smaller the distance between the two focal positions, the higher the intensity (sensitivity) of the thermal lens signal. The larger the distance between the two focal positions, the greater the intensity of the thermal lens signal even if the distance between the two focal positions varies. It can be seen that the fluctuation is less likely to occur (because the slope of the curve becomes gentler as the distance between both focal positions increases).
The figure showing the relationship between the distance between the focal position of the excitation light and the focal position of the probe light and the size of the probe light changed by the thermal lens (the average half-value width of the thermal lens signal). As can be seen from the graph in FIG. 4, the smaller the distance between the two focal positions, the larger the portion of the probe light that has been changed by the thermal lens (the average half-value width of the thermal lens signal). Therefore, the smaller the distance between the two focal positions, the greater the tolerance for positional deviation in the direction orthogonal to the optical path of the optical fiber (light receiving unit). However, if the distance between both focal positions is too small, it is easy to be affected by the distortion of the portion of the probe light changed by the thermal lens and the deviation of the optical axis between the excitation light and the probe light as described above. . In addition, the larger the distance between the two focal positions, the larger the diameter of the probe light at the focal position of the excitation light that becomes the central region of the thermal lens formation, and thus the tolerance for the deviation of the optical axes of the two lights tends to increase. There is.

  Further, as can be seen from FIG. 5, as the distance between both focal positions increases, the spread angle of the portion of the probe light changed by the thermal lens (in FIG. (Tan θ) is reduced). Therefore, the greater the distance between the two focal positions, the greater the tolerance for misalignment in the direction along the optical path of the optical fiber (light receiving unit).

  When the distance between the focal position of the excitation light and the focal position of the probe light is shortened to a certain distance or less, a phenomenon that the thermal lens signal is disturbed may be observed. Since this phenomenon seems to be related to the confocal range of the laser, the distance between the focal position of the excitation light and the focal position of the probe light can be set according to the confocal length of the laser used. is necessary. In consideration of obtaining a high signal value, the minimum distance for the above phenomenon not being observed is preferably a distance twice the confocal length, and a distance three times the confocal length. More preferred.

  For example, the laser having a wavelength of about 635 nm used in this embodiment is often used in a thermal lens spectroscopic analyzer, and the confocal length is about 75 μm when the numerical aperture is 0.1. Therefore, if the distance is twice the confocal length, it is about 150 μm, and if it is three times the distance, it is about 225 μm, which is close to the value (200 μm) in this embodiment. When the numerical aperture is 0.15, they are about 60 μm and about 100 μm, respectively.

  Further, in the case of a laser having a wavelength of 350 nm close to the ultraviolet region, which has been developed in recent years, when the numerical aperture is 0.1, the confocal length is about 40 μm. Therefore, the distance between the focal position of the excitation light and the focal position of the probe light may be about 100 μm. As described above, the distance between the focal position of the excitation light and the focal position of the probe light is preferably 100 μm or more, and more preferably 200 μm or more.

[Distance between sample and probe light receiving part]
The relationship between the distance between the sample and the light receiving part of the probe light and the size of the portion of the probe light changed by the thermal lens (the average half-value width of the thermal lens signal) is shown in the graph of FIG. From this graph, it can be seen that the average half-value width of the thermal lens signal is larger when the distance between the sample and the light receiving portion of the probe light is larger. Therefore, when the distance between the sample and the light receiving part of the probe light is large, even if a positional deviation in the direction perpendicular to the optical path occurs in the optical fiber (light receiving part), the decrease in sensitivity and accuracy of analysis is small. I understand.

  More specifically, since it can be seen from FIG. 4 that the average half-value width of the thermal lens signal is proportional to the distance between the sample and the light receiving portion of the probe light, based on the values described in the specific examples described later. Considering that the allowable positional deviation amount of the optical fiber (the positional deviation amount in the direction orthogonal to the optical path) is ± 20 μm that can be sufficiently realized, the diameter of the optical fiber may be 250 μm at a position 12.5 mm away from the sample. I understand that. Even when the distance between the sample and the light receiving part of the probe light is less than this, the allowable positional deviation amount of the optical fiber is a constant value, so it is not proportional, and the distance between the focal position of the probe light and the light receiving part is not. T ≧ (D + 40) × 40 holds between the distance T and the diameter D of the light receiving unit. The numerical aperture is 0.1, and the units of T and D are both μm.

When the numerical aperture is 0.2 or less, the value of tan θ is substantially proportional to the numerical aperture, so the spread angle of the portion of the probe light changed by the thermal lens is also the numerical aperture (that is, the half angle of the maximum cone angle of the light beam). Sine). Therefore, the above formula is as follows.
T ≧ (half sine of maximum cone of ray bundle) × [D + 40] × 400

And more generally: In both formulas, the units of T and D are both μm.
T ≧ 125000 × (half sine of the maximum cone angle of the light beam of the excitation light or the probe light) × [D + 2 × (allowable displacement of the light receiving portion)] / [250 + 2 × (allowable position of the light receiving portion) Deviation))
If it is this range, position shift of light-receiving parts, such as an optical fiber, will be accepted. If the light receiving part is made into a pinhole shape and the size of the light receiving part is further reduced, the distance between the sample and the light receiving part can be reduced, but it goes without saying that the thickness of the sample is actually limited. Yes.

[Displacement of optical axis between excitation light and probe light]
A smaller deviation of the optical axis between the excitation light and the probe light is preferable. As can be seen from the graph of FIG. 6, the smaller the ratio (%) of the deviation amount to the optical diameter of the probe light, the higher the intensity of the thermal lens signal. This is presumably because, if the optical axis shift is large, the portion of the probe light that has been changed by the thermal lens is not circular but distorted.

  However, the focal position of the excitation light and the focal position of the probe light are separated from each other by a predetermined distance, and the central portion of the light receiving unit is disposed on an extension line connecting the focal position of the excitation light and the focal position of the probe light. Thus, it is possible to minimize the adverse effect of the deviation of the optical axis. In addition, when a mirror or the like is arranged on the extension line of the line connecting the focal position of the excitation light and the focal position of the probe light and the optical path of the probe light is bent, the line connecting both focal positions is bent in the same way, It goes without saying that the same effect can be obtained by arranging the central portion of the light receiving portion on the extension line.

〔Concrete example〕
Here, the thermal lens spectroscopic analyzer will be described in more detail with a more specific example. When the numerical aperture of the condenser lens 5 is 0.1 and the positioning rigidity of the optical axis is ± 0.25 μm, the optical axis shift between the probe light and the excitation light that causes the fluctuation amount of the thermal lens signal to be 0.5%. 6 is about 0.35%, the optical diameter of the probe light is 70 μm (0.35% of 70 μm is 0.25 μm). This corresponds to the spot diameter when the distance between the focal position of the excitation light and the focal position of the probe light is about 300 μm.

  At this time, it can be seen from FIG. 4 that a thermal lens signal distribution having a half width of about 1000 μm is obtained on a plane 25 mm away from the sample, and it can be seen from FIG. 5 that the spread angle tan θ is about 0.04. Further, from FIG. 5, the spread angle (tan θ) of the portion of the probe light changed by the thermal lens becomes smaller as the distance between the focal position of the excitation light and the focal position of the probe light becomes larger, and the numerical aperture becomes smaller. In the case of 0.1, it is understood that about 0.04 is the maximum value. However, in the case of FIG. 5, the minimum value of the distance between the focal position of the excitation light and the focal position of the probe light is set to 200 μm so that the thermal lens signal can be stably obtained.

  When detecting a thermal lens signal at a position 25 mm away from the sample with an optical fiber having a diameter of 500 μm, the allowable positional deviation amount of the optical fiber with a sensitivity fluctuation amount of 0.5% (the positional deviation amount in the direction orthogonal to the optical path) ) Is ± 40 μm when the thermal lens signal is Gaussian distributed, which is a sufficiently realizable value. That is, within this range, even if the distance between the sample solution S and the light receiving surface 8a of the optical fiber 8 or the position of the condensing lens 5 has changed by several tens of μm (in the direction along the optical path and perpendicular to the optical path). Even if there is a misalignment in the direction), the sensitivity and accuracy of the analysis are hardly reduced. And even if it changes about +/- 5 mm in the direction along an optical path, the sensitivity which can obtain the value of 80% or more of the maximum thermal lens signal value is maintainable.

  Further, when the confocal length is obtained for the case where the numerical aperture of the condenser lens 5 is 0.1, 0.15, and 0.2, the excitation with a wavelength of 635 nm that is mainly used at present and also used in the present embodiment. For light, they are approximately 74 μm, 33 μm, and 18 μm, respectively. Since the confocal length is proportional to the wavelength of the laser, when a shorter wavelength laser is used, for example, if the wavelength is about 350 nm, the confocal length is a little more than half of the above value. If it is considered that the allowable positional deviation amount due to vibration or the like is about 20 μm that can be realized, it is understood that the numerical aperture of the condenser lens is preferably 0.15 or less.

  Here, a brilliant green solution having a concentration of 5 μM was used as a sample. Strictly speaking, the size of the thermal lens during actual measurement varies depending on the sample concentration, excitation light modulation frequency, cell size (flow channel width and depth), etc. From the standpoint of the extinction coefficient range of the kit or the like, it is considered that a brilliant green solution having a concentration of 5 μM can be adopted as a standard value. Some of the various parameters in the present invention are derived based on this, but are considered to be effective as long as the concentration of the measurement substance and the extinction coefficient do not change drastically. Various parameters may be corrected and used in accordance with the concept of the invention.

It is a block diagram which shows one Embodiment of the thermal lens spectroscopy analyzer of this invention. It is a schematic diagram explaining the principal part of the thermal lens spectroscopy analyzer of embodiment. It is a graph which shows the relationship between the distance between the focus position of excitation light and the focus position of probe light, and the intensity | strength of a thermal lens signal. It is a graph which shows the relationship between the distance between the focus position of excitation light and the focus position of probe light, and the magnitude | size of the part changed with the thermal lens among probe light. It is a graph which shows the relationship between the distance between the focus position of excitation light, and the focus position of probe light, and the spreading angle of the part changed with the thermal lens among probe light. It is a graph which shows the relationship between the shift | offset | difference of the optical axis of excitation light and probe light, and the intensity | strength of a thermal lens signal.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser light emission means 2 Laser light emission means 5 Condensing lens 6 Sample cell 8 Optical fiber 8a Light-receiving surface 9 Detection means E Excitation light P Probe light P 'The part which changed by the thermal lens among probe light L Thermal lens S Sample solution

Claims (8)

A thermal lens spectroscopic analyzer that enters probe light into a thermal lens generated in a sample by incidence of excitation light and analyzes the sample based on a change by the thermal lens of the probe light at that time,
An optical element for condensing the excitation light on the sample, an optical element for condensing the probe light on the thermal lens, and the probe light transmitted through the thermal lens A thermal lens spectroscopic analysis device characterized in that the following four conditions are satisfied.
(1) The excitation light condensing optical element condenses the excitation light such that the half sine of the maximum cone angle of the light bundle is 0.15 or less.
(2) The probe light condensing optical element condenses the probe light such that the half sine of the maximum cone angle of the light bundle is 0.15 or less.
(3) The size of the light receiving unit so that the light receiving unit of the detecting unit receives only the portion of the probe light changed by the thermal lens and does not receive the portion not affected by the thermal lens. Is set.
(4) The focal position of the excitation light and the focal position of the probe light can be adjusted independently, and the distance between the two focal positions is 200 μm or more. The thermal lens spectroscopic analyzer according to claim 1, wherein a distance T between the focal position of the probe light and the light receiving unit and a diameter D of the light receiving unit satisfy the following formula.
T ≧ 125000 × (half sine of the maximum cone angle of the light beam of the excitation light or the probe light) × [D + 2 × (allowable displacement of the light receiving portion)] / [250 + 2 × (allowable position of the light receiving portion) Deviation))
Note that the unit of T, D, and the allowable positional deviation amount of the light receiving unit is μm. The thermal lens spectroscopic analyzer according to claim 1, wherein a distance T between the focal position of the probe light and the light receiving unit and a diameter D of the light receiving unit satisfy the following formula.
T ≧ (half sine of the maximum cone angle of the beam bundle of the excitation light or the probe light) × [D + 40] × 400
The unit of T and D is μm. Thermal lens spectrometer according to any one of claims 1 to 3 focal position before Symbol probe light is characterized by the presence at a position closer to the light receiving portion than the focal position of the exciting light. A beam expander is installed on one or both of the excitation light and the probe light so that the focal positions of the excitation light and the probe light can be independently adjusted. Item 5. The thermal lens spectroscopic analyzer according to any one of Items 1 to 4.   The thermal lens spectroscopic analyzer according to any one of claims 1 to 5, wherein the excitation light condensing optical element and the probe light condensing optical element are the same optical element.   The center part of the said light-receiving part is located on the extension line of the line | wire which connects the focus position of the said excitation light, and the focus position of the said probe light, The heat as described in any one of Claims 1-6 characterized by the above-mentioned. Lens spectroscopic analyzer. The thermal lens spectroscopy according to claim 7, wherein the excitation light transmitted through the excitation light concentrating optical element and the probe light transmitted through the probe light condensing optical element are not coaxial. Analysis equipment.

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