JP2004286578A - Reflective thermal lens spectrometer - Google Patents

Abstract

An object of the present invention is to provide a reflection type thermal lens spectrometer capable of analyzing a sample with high sensitivity and high accuracy without performing precise adjustment of the apparatus.
Kind Code: A1 A thermal lens spectroscopy in which probe light is incident on a thermal lens generated in a sample solution by the incidence of excitation light, and the sample solution is analyzed based on a change of the probe light by the thermal lens at that time. A sample cell 7 containing a sample solution S, a retroreflector 8 that receives a probe light P transmitted through the thermal lens and the sample cell 7 and reflects the probe light P in a direction in which the probe light P is incident; Detecting means 12 for detecting the probe light P reflected by the retroreflector 8.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a reflection type thermal lens spectrometer capable of analyzing a sample with high sensitivity and high accuracy.
[0002]
[Prior art]
Photothermal conversion spectroscopy, in which a substance such as a dye in a solution absorbs light and measures the amount of heat generated during the relaxation process, is known as a highly sensitive concentration measurement method. In particular, thermal lens spectroscopy utilizing the refractive index distribution due to the temperature distribution generated by the generated heat is known to be more than 100 times more sensitive than the absorptiometry which measures the amount of transmitted light. (Eg, Manabu Takeshi et al., J. Lumin. Vol. 83-84, 261-264, 1999).
[0003]
As such thermal lens spectroscopy, there are known a single beam method in which excitation of a sample and detection of a thermal lens are performed with the same laser beam, and a double beam method in which separate laser beams are used. Is more sensitive.
On the other hand, recently, a groove of several tens μm to several hundreds of μm has been cut on the surface of a flat chip made of glass or silicon of about 10 cm to several cm square or less, and all of the necessary reactions, separation and detection in this groove are performed. The research on μ-TAS (micro total analysis system), which performs the reaction in a short time, has been actively conducted (for example, JP-A-2-245655).
[0004]
The use of μ-TAS reduces the amount of a specimen, the amount of a reagent required for detection, the amount of waste such as consumables used for detection, and the amount of waste liquid, and the time required for detection is generally short. There is an advantage. For the purpose of developing a low-cost disposable chip, a method of forming a chip with a resin (RM McCormick et al., Anal. Chem. Vol. 69, 2626-2630, 1997, Japanese Patent Laid-Open No. 2-259557) And Japanese Patent No. 2639087) have also been proposed.
[0005]
However, in μ-TAS, the optical path length is several tens μm to several hundred μm, which is 1/10 to 1/100 as compared with normal conditions. There is a problem of shortage. For this reason, highly sensitive thermal lens spectroscopy has been attracting much attention as a detection method in μ-TAS.
[0006]
In a conventional general thermal lens spectroscopic analysis method, a laser beam is incident on a sample, and analysis is performed using light transmitted through the sample. However, in this case, an optical system (condensing optical system) for condensing and irradiating laser light on the sample and an optical system (condensing optical system) for receiving laser light transmitted through the sample and detecting a thermal lens signal ( It is necessary to precisely adjust the positional relationship with the optical system (light receiving optical system), and the entire optical system is large and complicated.
[0007]
In order to solve such problems, the reflection type thermal lens spectroscopy is to reflect the laser light transmitted through the sample with a reflector, re-enter the condensing optical system, and use the reflected light for analysis. A method has been proposed (JP-A-4-369467). In this method, a single beam method is adopted, in which a laser beam is focused on a reflector by a lens, and the laser beam reflected by the reflector is guided to a photodiode by a beam splitter to measure a thermal lens signal. Has been taken.
[0008]
[Patent Document 1]
JP-A-2-245655 [Patent Document 2]
JP-A-2-259557 [Patent Document 3]
Japanese Patent No. 2639087 [Patent Document 4]
JP-A-4-369467 [Non-Patent Document 1]
Manabu Tokyoshi et al. , J. et al. Lumin. Vol. 83-84, 261-264, 1999
[Non-patent document 2]
R. M. McCormick et al. , Anal. Chem. Vol. 69, 2626-2630, 1997
[0009]
[Problems to be solved by the invention]
However, in the reflection type thermal lens spectroscopy described in the above publication, the angle (reflector plate) between the optical axis of the laser beam and the plate surface of the reflector plate in either the single beam method or the double beam method. The present inventors have found that there is a problem that the analysis sensitivity greatly changes depending on the inclination of the sample) and the analysis accuracy is reduced.
[0010]
In order to solve such problems and perform high-precision analysis, a condensing optical system for condensing and irradiating laser light on the sample and a thermal lens signal by receiving the laser light transmitted through the sample Since it is necessary to precisely adjust the positional relationship with the light receiving optical system for detection, easy adjustment, which is one of the advantages of the reflective thermal lens spectroscopy, cannot be realized.
Therefore, the present invention solves the above-mentioned problems of the prior art, and provides a reflection-type thermal lens spectrometer capable of analyzing a sample with high sensitivity and high accuracy without performing precise adjustment of the apparatus. The task is to provide.
[0011]
[Means for Solving the Problems]
In order to solve the above problem, the present invention has the following configuration. That is, the reflection-type thermal lens spectrometer according to claim 1 of the present invention allows the probe light to be incident on the thermal lens generated on the sample due to the incident excitation light, and the change in the probe light caused by the thermal lens at that time. A thermal lens spectroscopy analyzer that analyzes the sample based on the sample cell that contains the sample, and the probe light that has passed through the thermal lens and the sample cell is incident, and the probe light is incident. It is characterized by comprising: retroreflecting means for reflecting in a direction; and detecting means for detecting the probe light reflected by the retroreflecting means.
[0012]
The retroreflective means has a property that, regardless of the direction from which light is incident, the incident light is always reflected in the direction in which the light is incident. That is, the incident angle and the reflection angle of the light are the same. Therefore, no matter what incident angle the probe light is incident on, the reflected light is always reflected in the direction in which the probe light is incident. Even if the position and orientation are slightly changed, there is no problem in sensitivity and accuracy of the analysis. Therefore, it is possible to perform high-sensitivity and high-precision thermal lens spectroscopic analysis without precisely adjusting the installation state of the retroreflecting means (the relative position and direction of the probe light with respect to the optical axis).
[0013]
According to a second aspect of the present invention, there is provided a reflection type thermal lens spectrometer, wherein the sample cell is made of a resin.
Since the resin sample cell is inexpensive, the analysis can be performed at low cost. Further, the resin sample cell is likely to be warped at the time of production by injection molding or the like, but with the reflection type thermal lens spectroscopic analyzer of the present invention, the relative position of the retroreflective means with respect to the optical axis of the probe light and Even if the direction changes due to the warpage, highly accurate measurement is possible.
[0014]
Further, in the reflection type thermal lens spectrometer according to claim 3 of the present invention, in the reflection type thermal lens spectrometer according to claim 1 or 2, the sample cell and the retroreflection means are separated. It is characterized by having a body.
When the shape of the retroreflective means is a plate shape, a film shape, or the like, the sample cell and the retroreflective means can be integrated. However, the sample cell which is preferably disposable is expensive. turn into. However, if the sample cell and the retroreflective means are separated from each other, that is, if the sample cell and the retroreflective means are separated and installed in the apparatus, the cost of the sample cell becomes low, so that the cost is low. Analysis can be performed.
[0015]
Furthermore, in the reflection type thermal lens spectrometer according to claim 4 of the present invention, in the reflection type thermal lens spectrometer according to any one of claims 1 to 3, the optical path length of the sample cell is 1 mm or less. It is characterized by the following.
When the optical path length of the sample cell is short, it is necessary to highly collect the excitation light and the probe light in order to perform highly sensitive analysis. Then, there is a problem that the divergence of the probe light after passing through the sample or the thermal lens increases, and the loss of the light amount increases. However, since the probe light is always reflected in the incident direction by the retroreflecting means, the loss of the light amount is small, and the analysis can be performed with high sensitivity and high accuracy.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of a reflection type thermal lens spectrometer according to the present invention will be described in detail with reference to the drawings.
FIG. 1 is a configuration diagram illustrating a configuration of a reflection type thermal lens spectroscopic analyzer according to one embodiment of the present invention. Note that the present embodiment is an example of the present invention, and the present invention is not limited to the present embodiment.
[0017]
The reflection type thermal lens spectrometer of FIG. 1 includes a laser light emitting means 1 as a light source of the excitation light E, a laser light emitting means 2 as a light source of the probe light P, and a condenser 1 for condensing the excitation light E and the probe light P. One condenser lens 6, a resin sample cell 7 containing the sample solution S (having an optical path length of 1 mm or less), and a retroreflector 8 for reflecting the excitation light E and the probe light P (a component of the present invention) (Corresponding to a certain retroreflective means) and a detecting means 12 for detecting the probe light P. Note that two condensing lenses may be provided so that the excitation light E and the probe light P are condensed by different condensing lenses.
[0018]
In such a reflection-type thermal lens spectrometer, 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 reflecting plate 3. The light enters the beam splitter 4. Then, the excitation light E and the probe light P are made coaxial in the beam splitter 4 and guided to the condenser lens 6.
[0019]
The excitation light E is condensed on the sample solution S by the condenser lens 6, thereby forming a thermal lens (not shown). The probe light P is condensed on the thermal lens by the condenser lens 6, and is diverged or condensed by the thermal lens effect.
The excitation light E and the probe light P transmitted through the sample cell 7 are reflected by the retroreflector 8. At that time, the excitation light E and the probe light P are reflected in the direction of incidence on the retroreflector 8 (the incident angle and the reflection angle are the same). The reflected excitation light E and probe light P are collected again on the sample cell 7 and partially reflected by the half mirror 5 after passing through the condenser lens 6.
[0020]
The excitation light E and the probe light P reflected and refracted by the half mirror 5 are condensed by the lens 9 and introduced into the excitation light cut filter 10. Only the excitation light E is removed by the excitation light cut filter 10, and only the probe light P is introduced into the stop 11. Then, only the light at the center of the probe light P is introduced into the detection means 12 by the stop 11, and the degree of divergence or light concentration thereof is measured. The measurement may be performed when the sample solution S is stored in the sample cell 7 and when the sample solution S is not stored, and the difference between the detection values of the detection unit 12 may be used as the thermal lens signal. Usually, this thermal lens signal is proportional to the degree of thermal lens, that is, the concentration of the sample solution S.
[0021]
The retroreflective plate 8 has such a property that the incident light is always reflected in the direction in which the light is incident, regardless of the direction from which the light is incident. Therefore, no matter what incident angle the excitation light E and the probe light P are incident on, the reflected light is always reflected in the direction in which the excitation light E and the probe light P are incident. Even if the inclination of the retroreflective plate 8 with respect to the optical axis of P slightly changes, no problem occurs in the sensitivity and accuracy of the analysis.
[0022]
Therefore, the reflection type thermal lens spectrometer according to the present embodiment can perform high-sensitivity and high-precision thermal lens spectroscopy without precisely adjusting the installation state of the retroreflector 8 (inclination of the retroreflector 8). It is possible to do. The inclination of the retroreflective plate 8 means an angle between the plate surface of the retroreflective plate 8 and the optical axes of the excitation light E and the probe light P.
[0023]
Here, each component of such a reflection type thermal lens spectrometer will be described.
The type of laser used as the laser light emitting means 1 as a light source of the excitation light E is not particularly limited, and a gas laser, a solid-state laser, or the like can be used without any problem, but a semiconductor laser is preferable because it is inexpensive. . However, when a semiconductor laser is used, when the reflected light from the retroreflective plate 8 is again incident on the light source of the excitation light E, it becomes a noise due to a change in output. It is desirable to incorporate an optical isolator using a combination of a splitter and a quarter-wave plate. It should be noted that a light emitting diode can be used as a light source of the excitation light E, although it is not a laser, if sufficient sensitivity can be realized in the thermal lens measurement.
[0024]
Further, the type of laser used as the laser light emitting means 2 as a light source of the probe light P is not particularly limited, and a laser similar to the laser light emitting means 1 is used as long as the excitation light E has a different wavelength. be able to. Further, a light emitting diode can be used as a light source of the probe light P.
Further, the reflecting plate 3 guides 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%.
[0025]
Further, the beam splitter 4 is for making the excitation light E and the probe light P coaxial, and has a sufficiently high reflectance for the probe light P and a sufficiently high transmittance for the excitation light E. I just need. However, it is preferable to have a reflectance close to 100% for the probe light P and a transmittance close to 100% for the excitation light E. 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.
[0026]
Further, the condenser lens 6 focuses the excitation light E on the sample solution S stored in the sample cell 7 and focuses the probe light P on the thermal lens generated in the sample solution S by the excitation light E. belongs to. The excitation light E is focused on the sample solution S to form a thermal lens, and the probe light P transmitted coaxially there is diverged or focused by the thermal lens effect. It is known that the sensitivity of the thermal lens signal generally increases as the beam diameter at the focusing position decreases, and therefore it is desirable that the numerical aperture of the focusing lens 6 be high.
[0027]
Further, the sample cell 7 is for storing a sample solution S to be measured. The material of the sample cell 7 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 be as high as possible. For example, resin materials such as polymethyl methacrylate (PMMA), polycarbonate (PC), polystyrene (PS), and cycloolefin-based resin, and glass are exemplified. Although the shape of the sample cell 7 is not particularly limited, it is preferable that a flat surface exists at a position where the excitation light E and the probe light P enter and transmit.
[0028]
Further, the retroreflector 8 receives the excitation light E and the probe light P transmitted through the sample cell 7 and reflects both lights E and P in the direction in which the retroreflector 8 is incident. . It is preferable that the reflectance of both lights E and P is close to 100%. Examples of the retroreflective plate include those in which corner cubes are two-dimensionally arranged, those in which spherical beads are two-dimensionally arranged, and those using a diffraction grating or a hologram. When a retroreflector in which corner cubes and spherical beads are arranged two-dimensionally is used, it is desirable to select the optimal corner cube and bead sizes determined by the numerical aperture of the condenser lens 6 and the required reflectance. .
[0029]
Further, the half mirror 5 is for guiding the reflected light from the retroreflector 8 to the detection system, and preferably has a balance between the transmittance and the reflectance for the excitation light E and the probe light P. . For example, a material having a transmittance of 50% and a reflectance of 50% can be used.
Further, the lens 9 is for condensing the excitation light E and the probe light P on the detecting means 12 and may be any as long as it can converge within the area of the detecting portion of the detecting means 12.
[0030]
Further, as the excitation light cut filter 10, any filter that can sufficiently remove the excitation light E can be used without any problem, but a filter having an optical density of 5 or more is preferable. For example, a color glass filter, an interference filter and the like can be mentioned.
Further, the aperture 11 can be used without any problem as long as it can transmit only the central portion of the probe light P.
[0031]
Further, the type of the detection means 12 is not particularly limited as long as it has sufficient sensitivity to the probe light P, and examples thereof include a photodiode.
(Example)
The measurement using the reflection type thermal lens spectrometer according to the present invention will be described in detail with reference to examples. FIG. 2 is a configuration diagram illustrating the configuration of the reflection type thermal lens spectrometer used in the present embodiment. In this embodiment, several kinds of self-made optical components are used, but it is a matter of course that a commercially available optical component having similar characteristics may be used.
[0032]
As the excitation light source 21, a semiconductor laser light emitting device (LT051PS, manufactured by Sharp Corporation) having a wavelength of 635 nm and a rated output of 30 mW was used. As the light source 22 for the probe light, a semiconductor laser light emitting device (ML60114R, manufactured by Mitsubishi Electric Corporation) having a wavelength of 780 nm and a rated output of 50 mW was used. These semiconductor laser light emitting devices can be controlled in output and current by a commercially available LD driver (ALP-6323CA, manufactured by Asahi Data Systems) not shown.
[0033]
The LD driver is connected to a personal computer via a PCI card (NIPCI 6025E, manufactured by National Instruments), also not shown, and the output, current, and modulation frequency of the semiconductor laser light emitting device can be adjusted by the personal computer. ing. Further, the modulation frequency of the excitation light can be from 0 to 100 kHz. Furthermore, a high frequency of 350 MHz was superimposed on both the excitation light and the probe light to reduce the influence of noise generated by the return light.
[0034]
As the collimator lens 23 for the excitation light, a self-made lens having a numerical aperture of 0.34 and a focal length of 8 mm was used. As the probe light collimator lens 24, a self-made lens having a numerical aperture of 0.39 and a focal length of 7 mm was used. The probe light collimator lens 24 was attached to a not-shown micrometer head (MHT3-5, manufactured by Mitutoyo Corporation) so that it could be displaced in the optical axis direction at a resolution of the order of micrometers. Note that the method of displacement is not limited to this example.
[0035]
Further, as the excitation light prism 25 and the probe light prism 26, two self-made prisms whose inclined surfaces are opposed to each other were used. Note that the angle between the two prisms for the excitation light prism 25 was adjusted so that the enlargement ratio became three times. The angle between the two prisms for the probe light prism 26 was adjusted so that the magnification was 2.6 times.
[0036]
Furthermore, a self-made polarization dependent beam splitter having a transmittance of 100% for p-polarized light and a reflectance of 100% for s-polarized light was used as the beam splitter 27 for coaxializing the excitation light and the probe light. . In this case, since the excitation light is s-polarized and the probe light is p-polarized, the power loss in the beam splitter 27 is almost zero.
[0037]
Further, a glass aspherical lens (CJ350280, manufactured by GELTECH) having a numerical aperture of 0.15 and a focal length of 18.4 mm was used as the condenser lens 30 for condensing the excitation light and the probe light. In order to guide the excitation light and the probe light having passed through the beam splitter 27 to the condenser lens 30, a self-made reflector prism 29 for refracting the two lights by 90 ° was used.
[0038]
Further, as the sample cell 31, a glass cell (AB20, manufactured by GL Sciences Inc.) having an optical path length of 50 μm was used. As a stage (not shown) on which the sample cell 31 is mounted, an automatic positioning stage (MINI-60X MINI-5P, manufactured by Sigma Koki Co., Ltd.) capable of performing alignment in the optical axis direction with a resolution of 1 μm was used. .
[0039]
Further, a prism type retroreflective plate (Scotchlite, diamond grade 3900G series, manufactured by Sumitomo 3M Co., Ltd.) was used as the retroreflective plate 32. The retroreflective plate 32 can adjust the inclination with respect to the optical axis at a resolution of 0.1 ° by a micrometer (not shown).
The excitation light and the reflected light of the probe light reflected by the retroreflector 32 are transmitted through the sample cell 31 again, and then are converted into substantially parallel light by the condenser lens 30. Then, the light is refracted by 90 ° by the mirror prism 29 and is introduced into the non-polarization dependent beam splitter 28. The non-polarization dependent beam splitter 28 is a self-made non-polarization dependent beam splitter set to have a transmittance of 80% and a reflectance of 20% for the excitation light and the probe light.
[0040]
The excitation light and the probe light are reflected by the non-polarization dependent beam splitter 28 with a light amount of 20%, and the light amount of 80% is guided to an optical system for detecting a thermal lens signal. The excitation light and the reflected light of the probe light guided to the optical system are cut off only the excitation light by a laser line interference filter 33 (03FIL250, manufactured by Meles Griot Co., Ltd.) having a center wavelength of 635 nm and a half-value width of 10 nm. Is guided to the diaphragm 34. As the diaphragm 34, a zero aperture iris diaphragm (CJ53906, manufactured by Edmund Optics Japan KK) was used.
[0041]
Only the light at the center of the probe light is transmitted by the stop 34 and guided to the condenser lens 35 and subsequently to the cylindrical lens 36. A self-made lens having a focal length of 45.5 mm was used as the condenser lens 35, and a self-made cylindrical lens having a focal length of 286 mm on a curved surface was used as the cylindrical lens 36.
[0042]
The probe light is condensed by a condensing lens 35 and a cylindrical lens 36 on a four-division photodiode 37 (S6344, manufactured by Hamamatsu Photonics KK), which is a detecting means, and the light intensity of each of the four photodiodes is converted into an electric signal. Is done. It is not always necessary to use a four-division photodiode as the detection means, and a non-division photodiode does not pose a problem.
[0043]
The output from the four-division photodiode 37 was converted from a current to a voltage by a self-made circuit. The conversion ratio from current to voltage was 1000 times. The current-to-voltage conversion circuit may be a commercially available product provided that the conversion magnification is 1000 times.
Further, the converted voltage signal is guided to a low-noise preamplifier (LI-75A, manufactured by NF Circuit Block Co., Ltd.) with a gain of 100 times (not shown), and further a two-phase lock-in amplifier (5610B, NF circuit) not shown. Only the electric signal synchronized with the modulation frequency of the excitation light was extracted and used as the thermal lens signal value (output of the lock-in amplifier).
[0044]
This lock-in amplifier is connected to a connector (CB-50LP, manufactured by National Instruments Co., Ltd.) via a BNC cable, and the output from the connector is connected to a notebook computer by a data acquisition card (DAQCARD-700, manufactured by National Instruments Co., Ltd.). It is taken in. The thermal lens signal value taken into the notebook personal computer is displayed on the display screen of the notebook personal computer by software (LABVIEW 5.0, manufactured by National Instruments), and the thermal lens signal value and the temporal change of the thermal lens signal value are recorded. (Neither is shown).
[0045]
(Example of analysis)
The xylene cyanol aqueous solution having a concentration of 25 μM was analyzed using the reflection-type thermal lens spectrometer of the above-described embodiment. At this time, the angle between the retroreflector and the optical axis of the probe light (the inclination of the retroreflector) is varied in the range of -0.5 ° to + 0.5 ° to change the thermal lens signal. A measurement was made.
[0046]
As a result, the thermal lens signal value when the inclination of the retroreflective plate is −0.5 ° and + 0.5 ° is approximately 1 ° from the thermal lens signal value when the inclination of the retroreflective plate is 0 °. %, And there was almost no difference.
On the other hand, in the reflection type thermal lens spectrometer of the above-described embodiment, when the conventional flat type reflection plate was used instead of the retroreflection plate, a decrease of about 65% was observed. The flat reflector is a flat mirror having a diameter of 25 mm (CJ32945, manufactured by Edmund Optics Japan KK).
[0047]
【The invention's effect】
As described above, the reflection-type thermal lens spectrometer of the present invention can analyze a sample with high sensitivity and high accuracy without performing precise adjustment of the apparatus.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing one embodiment of a reflection type thermal lens spectroscopic analyzer of the present invention.
FIG. 2 is a configuration diagram illustrating a configuration of a reflection type thermal lens spectrometer according to the embodiment.
[Explanation of symbols]
7 Sample Cell 8 Retroreflective Plate 12 Detecting Means E Excitation Light P Probe Light S Sample Solution 31 Sample Cell 32 Retroreflective Plate 37 Quadrant Photodiode

Claims (4)

A thermal lens spectroscopic analyzer that analyzes the sample based on a change in the probe light caused by the thermal lens, wherein the probe light is incident on the thermal lens generated in the sample by the incidence of the excitation light,
A sample cell for storing the sample,
The retroreflective means for receiving the probe light transmitted through the thermal lens and the sample cell and reflecting the probe light in the incident direction,
Detecting means for detecting the probe light reflected by the retroreflecting means,
A reflection-type thermal lens spectrometer comprising: 2. The reflection type thermal lens spectrometer according to claim 1, wherein the sample cell is made of a resin. 3. The reflection type thermal lens spectrometer according to claim 1, wherein the sample cell and the retroreflection means are provided separately. The reflective thermal lens spectrometer according to any one of claims 1 to 3, wherein an optical path length of the sample cell is 1 mm or less.

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