JPH08271336A - Photo-acoustic spectroscopic device - Google Patents

Abstract

PURPOSE: To provide a photo-acoustic spectroscopic device which has a simple structure and a high producing efficiency, minimizes the noise resulted from the reflected light from a sample surface, and is measurable in a bright environment. CONSTITUTION: The photo-sound generated from a sample 17 by absorbing the light emitted to the sample 17 by a measuring substance in the sample is detected by an acoustic detecting means. The spectroscopic measurement of the measuring substance is performed on the basis of the detected PAS signal. A sample chamber 15 for airtightly sealing the gas on the sample surface generated by the photosound has an outer wall part 18 consisting of a light shielding material, and an inner wall part consisting of a light transmitting material having a low heat conductivity provided along the inside of the outer wall part 18. The acoustic detecting means is arranged on the side of the sample chamber 15, and the acoustic detecting means and the sample chamber 15 are allowed to mutually communicate by a waveguide extended along the direction substantially orthogonal to the incident direction of the emitted light.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoacoustic spectroscopic measurement apparatus which minimizes noise caused by reflected light on the surface of a sample.

[0002]

2. Description of the Related Art In a conventional photoacoustic spectroscopic measuring apparatus, measurement is performed using modulated light at a single frequency, and a detected photoacoustic signal (hereinafter referred to as PAS signal) is phase-detected by a lock-in amplifier. There is.

Internal noise such as electric signals is removed by integrating detection signals.

Since the PAS signal is proportional to the incident light intensity, when the incident light intensity fluctuates, it is monitored and the detected PAS signal intensity is normalized by the incident light intensity.

Resonance is also a problem in photoacoustic measuring devices. The photoacoustic cell is classified into a resonance type and a non-resonance type, and the former attempts to obtain a strong signal by positively utilizing resonance.

Other noises include noises caused by the light reflected on the sample surface. As a prior art that takes measures against this noise, there is JP-A-1-191040.

[0007]

A part of the light irradiated on the sample for photoacoustic measurement is reflected on the sample surface, and this hits the metal part of the cell to generate photoacoustic. Such non-measurement target PAS signal is detected together with the measurement target PAS signal, that is, it becomes noise.

In Japanese Patent Laid-Open No. 1-191040, which is a prior art in which measures are taken regarding noise of a PAS signal caused by reflection on the surface of a sample, in the measurement by a resonance type photoacoustic cell, reflection of the surface of the sample is described. In order to remove the noise caused by light, the vicinity of the sample chamber is made of a light transmissive material in order to discharge the reflected light to the outside of the cell.

In this prior art, Japanese Patent Laid-Open No. 1-191040,
Since the vicinity of the sample is made of transparent material only, it is common to measure in a bright place. In this device, light enters from the outside, causing disturbance and disturbing the measurement.

In the case of performing spectroscopic measurement by sequentially using modulated light at different frequencies as in the present invention, and obtaining information on different depths of a sample at a time by this, a plurality of samples can be obtained. It is preferable to sufficiently shift the resonance frequency of the cell with respect to the modulation frequency so that the SN ratio at the frequency does not change.

[0011]

SUMMARY OF THE INVENTION The present invention detects the photoacoustic generated from a sample by absorbing the light irradiated on the sample by a measuring substance in the sample, and detects the photoacoustic from the sample, and based on the detected PAS signal, A photoacoustic spectroscopic measurement device for performing spectroscopic measurement of a measurement substance, in which a sample chamber for hermetically sealing a gas on the sample surface where the photoacoustic is generated has an outer wall made of a light-shielding material and an inner side of the outer wall And an inner wall made of a light-transmissive material having a low thermal conductivity.

The acoustic detecting means is disposed laterally of the sample chamber, and the acoustic detecting means and the sample chamber are extended by a waveguide extending along a direction substantially orthogonal to the incident direction of the irradiation light. Can be communicated.

The inner wall portion is formed of a light transmissive material having a low thermal conductivity as a separate component from the outer wall portion,
It can be arranged in a nested manner on the inner surface of the outer wall portion.

The inner wall portion may be a coating layer formed on the inner surface of the outer wall portion and made of a light transmissive material having a low thermal conductivity.

Further, the outer wall portion may be a coating layer made of a light-shielding material formed on the outer surface of the inner wall portion.

On the other hand, a photoacoustic cell having a sample chamber as a part is composed of a cell outer wall portion made of a light shielding material and a light transmissive material having a low thermal conductivity provided along the inner side of the cell outer wall portion. It is also possible to configure with the cell inner wall portion.

In this case, the cell inner wall portion is formed as a component separate from the cell outer wall portion by a light transmissive material having a low thermal conductivity, and the cell inner wall portion is arranged in a nested manner on the inner side surface of the cell outer wall portion. It is possible.

The cell inner wall portion may be a coating layer formed on the inner surface of the cell outer wall portion and made of a light transmissive material having a low thermal conductivity.

The cell outer wall portion may be a coating layer made of a light-shielding material formed on the outer surface of the cell inner wall portion.

[0020]

The reflected light from the sample surface, which is a noise source, passes through the inner wall made of a light transmissive material and reaches the outer wall, and thermal vibration occurs in the outer wall, but the inner wall has a low thermal conductivity. Therefore, the thermal vibration generated in the outer wall portion is attenuated in the inner wall portion, and as a result, the undesired PAS signal reaching the sample chamber is minimized.

Further, since the acoustic detecting means and the sample chamber are communicated with each other by the waveguide extending along the direction substantially orthogonal to the incident direction of the irradiation light, the reflected light from the sample surface penetrating the inside of the waveguide. Is minimized, and P
Undesired PAS signals that occur in the AS signal propagation path are minimized.

Further, since the outer wall portion is made of the light shielding material,
Even if the measurement is performed in a bright environment, no external light enters the photoacoustic cell, particularly the sample chamber.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 shows the outline of the hardware configuration of the photoacoustic spectroscopic measurement device of the present invention. As shown in the figure, the photoacoustic spectroscopic measurement device 1 of the present invention includes a light source 2 for generating modulated light.
And the modulator 3 and the P generated based on the modulated light.
Microphone 4 and preamplifier 5 for detecting and amplifying the AS signal, and PA amplified by the preamplifier 5
An integrating device 6, a recording device 7, and a signal processing device 8 for obtaining a time average value of the S signal and compensating for an error due to noise.
It is provided with. The modulator 3 is capable of sequentially generating modulated light at different frequencies (preferably 0.05 Hz to 3 kHz: higher frequency can be used if necessary). Performs the spectroscopic measurement using the modulated light, and processes the information of the detected PAS signal by the integrating device 6, the recording device 7, and the signal processing device 8 to obtain the information at different depths of the sample. It is configured so that it can be obtained at one time. It is also understood by those skilled in the art that the optical sensor 9 and the preamplifier 10 may be provided as necessary to compensate for an error due to a change in the light intensity of the light source 2 due to a change in the power supply voltage or the like. See.

The photoacoustic cell of the photoacoustic spectroscopic measurement device 1 has a structure as shown in FIG. That is,
In this photoacoustic cell 11, the upper part of its housing 12 is connected to an optical fiber 13 for propagating light from the light source 1, and a sample chamber 15 is provided below the connection part via a window plate 14. . Further, the housing 12 is provided with a microphone chamber 16 on the side of the sample chamber 15 (in this embodiment, the microphone 4 and the microphone chamber 16 form an acoustic detecting means). 16 and the sample chamber 15 are communicated with each other by a waveguide 18 extending along a direction substantially orthogonal to the incident light on the sample 17.

As shown in FIG. 3, the sample chamber 15 is laterally surrounded by an outer wall portion 19 made of metal (brass or the like) and an inner wall portion 20 arranged inside the outer wall portion 19. With
The window plate 14 has its upper end closed, and its lower end is an open end. Here, the inner wall portion 20
Is made of a light-transmissive material having a low thermal conductivity such as quartz or acrylic. The guide 21 formed on the inner wall 20 of the guide 21 has a hole (not shown) formed through the inner wall 20. (Having a diameter approximately the same as that of the pipe 18) is aligned with the waveguide 18. In addition, the measurement is performed in a state in which external light is blocked by pressing the open end of the sample (and the container or the like) to form a closed space. Therefore, the photoacoustic spectrometer of the present invention is
It can be used in bright places. For example, the photoacoustic spectrometer of the present invention can measure the water content of the skin by pressing the open end against human skin under normal light.
When used for such an application, the photoacoustic cell of the photoacoustic spectroscopic measurement device of the present invention has a bottom surface diameter of about 10 to 50 mm to be pressed against the skin, and a height is preferably operated with one hand of about 20 to 140 mm. It will have a possible size. Furthermore,
The sample chamber should have an outer wall with an inner diameter of preferably about 5 to 10 mm, an inner wall with a thickness of preferably about 0.5 to 2 mm disposed inside, and an upper open end of the inner wall. The window plate has a diameter of preferably about 5 to 10 mm and a thickness of preferably about 0.5 to 2 mm, and is a small one having an extremely simple structure.

In such a structure, when the spectroscopic measurement of the sample is performed, the light source 2 is passed through the optical fiber 13 and the window plate 14.
The light sent from is absorbed by the sample as shown in the right half of FIG. 4, and is reflected by the sample surface, transmitted through the inner wall part 20, and then absorbed by the outer wall part 19. At this time, since the inner wall portion 20 is made of a material having low thermal conductivity (quartz, acrylic, etc.) as described above, thermal vibration generated by the light absorbed in the outer wall portion 19 is generated by the inner wall portion 20. Will be attenuated. Therefore, the PAS signal from the outer wall is also attenuated, ie the noise is reduced. In addition, the left half of FIG. 4 is a PAS of a conventional configuration in which the inner wall portion is not provided.
It shows the generation of a signal.

Further, in the case of this photoacoustic spectrometer 1,
The PAS signal generated in the sample chamber 15 is detected in the microphone chamber 16 via the waveguide 18. As described above, the waveguide 18 is arranged along the direction substantially orthogonal to the incident direction of the light on the sample 17, and therefore, the irradiation light entering the waveguide 18 and the sample surface The reflected light is minimized, that is, undesired PAS signals (noise) generated in the PAS signal detection path due to the incident light are minimized.

Next, a second embodiment of the present invention is shown in FIG.
In the figure, instead of the inner wall portion 20, a coating layer 22 made of a light transmissive material is formed on the inner side surface of the outer wall portion 19 (as an inner wall portion) to form a sample chamber. Based on the principle, the noise reduction effect can be obtained. Also in this case, the light transmissive material used for the coating layer 22 has a low thermal conductivity (polyethylene or the like).

Further, a third embodiment of the present invention is shown in FIG.
In the figure, the sample chamber is constructed by vapor-depositing metal 24 as a light-shielding material on the outer surface of a cylindrical cell 23 (as an inner wall portion) formed of the same light-transmitting material as in the first embodiment. Is. Also in this case, the noise reduction effect similar to that of the first and second embodiments can be obtained.

As described above, the photoacoustic cell that realizes low noise in the present invention is a small type that can be constructed very easily, and the production efficiency of the device can be improved.

A microphone chamber is provided on the side of the sample chamber, and the microphone chamber and the sample chamber are connected by a waveguide extending along a direction substantially orthogonal to the incident direction of the irradiation light. Although the present invention has been described based on a photoacoustic spectrometer equipped with a cell, the noise reduction technique according to the present invention using a light transmissive material having a low thermal conductivity is not limited to such a device. However, it will be understood by those skilled in the art that the present invention is also applicable to a photoacoustic spectroscopic measurement device having a microphone chamber in a direction substantially along the traveling direction of irradiation light as described in the section of the related art.

Further, although the lower end of the sample chamber of the photoacoustic cell is formed as an open end, the present invention can be applied to a photoacoustic spectroscopic measuring device having a closed sample chamber. In that case, so as to cover the entire inner side surface of the sample chamber excluding the window plate, that is, the inner wall portion made of the light transmissive material on the side surface and the bottom surface of the metal outer wall portion forming the inner side surface. Nested, or coated with the light-transmissive material on the inner surface of its outer wall, or
The light-shielding material such as metal is coated on the outer surface of the inner wall made of the light-transmitting material.

The sample chamber is generally formed integrally with the photoacoustic cell as a part of the photoacoustic cell. When the sample chamber according to the present invention is implemented in such a photoacoustic cell, in order to improve the production efficiency of the device, the entire inner wall portion of the photoacoustic cell (cell inner wall portion) including a part of the inner wall portion of the sample chamber is used. 2) is formed of a light transmissive material having a low thermal conductivity, and the entire outer wall portion (cell outer wall portion) of the photoacoustic cell including a part of the outer wall portion of the sample chamber is formed of a light shielding material. Further, even in such a case, the cell inner wall portion and the cell outer wall portion can be embodied in the nesting mode or the coating mode according to the present invention.

[0034]

As described above, according to the present invention, since the sample chamber has the outer wall portion made of the light-shielding material and the inner wall portion made of the light transmissive material having a low thermal conductivity, reflection from the sample surface is caused. Light passes through the inner wall made of a light-transmissive material and reaches the outer wall to generate thermal vibration.The thermal vibration generated in the outer wall is attenuated in the inner wall, and as a result, reaches the sample chamber. The unwanted PAS signal, i.e., noise, is minimized.

Further, since the acoustic detecting means and the sample chamber are communicated with each other by the waveguide extending along the direction substantially orthogonal to the incident direction of the irradiation light, the reflected light from the sample surface penetrating the inside of the waveguide. Is minimized, that is, undesired PA generated in the detection path of the PAS signal due to the entering light.
The S signal, or noise, is minimized.

Further, since the outer wall portion is made of the light shielding material,
Even if the measurement is performed in a bright environment, no external light enters the photoacoustic cell, particularly the sample chamber.

Therefore, according to the present invention, the photoacoustic which has a simple structure and high production efficiency, and which can minimize the noise caused by the reflected light from the sample surface and can perform the measurement in a bright environment. A spectroscopic measurement device can be provided.

[Brief description of drawings]

FIG. 1 is a perspective view showing a photoacoustic cell in a photoacoustic spectrometer of the present invention.

FIG. 2 is a block diagram showing a hardware configuration of a photoacoustic spectroscopic measurement device of the present invention.

FIG. 3 is an enlarged perspective view showing a first embodiment of the sample chamber of the photoacoustic cell of FIG.

FIG. 4 is an explanatory diagram showing a noise reducing action according to the present invention.

FIG. 5 is an enlarged perspective view showing a second embodiment of the sample chamber.

FIG. 6 is an enlarged perspective view showing a third embodiment of the sample chamber.

[Explanation of symbols]

 1 Photoacoustic spectrometer 4 Microphone 11 Photoacoustic cell 15 Sample chamber 16 Microphone chamber 17 Waveguide 18 Outer wall 19 Inner wall

Claims (5)

[Claims] 1. An acoustic detection means detects photoacoustic emitted from a sample by absorption of light irradiated on the sample by the measured substance in the sample, and spectroscopic measurement of the measured substance is performed based on the detected photoacoustic signal. In the photoacoustic spectroscopic measurement device, the sample chamber that hermetically seals the gas on the sample surface where the photoacoustic is generated has an outer wall portion made of a light-shielding material and a low thermal conductivity provided along the inner side of the outer wall portion. A photoacoustic spectroscopic measurement device comprising: an inner wall portion made of the light-transmitting material. 2. The acoustic detecting means is arranged laterally of the sample chamber, and the acoustic detecting means and the sample chamber are extended by a waveguide extending along a direction substantially orthogonal to the incident direction of the irradiation light. The photoacoustic spectroscopic measurement device according to claim 1, wherein the photoacoustic spectroscopy measurement device is in communication. 3. The inner wall portion is formed of a light transmissive material having a low thermal conductivity as a separate component from the outer wall portion,
The photoacoustic spectroscopic measurement device according to claim 1, wherein the inner wall portion is arranged in a nested manner on the inner side surface of the outer wall portion. 4. The inner wall portion is a coating layer formed on the inner surface of the outer wall portion and made of a light-transmissive material having a low thermal conductivity, according to claim 1 or 2. Photoacoustic spectrometer. 5. The photoacoustic spectroscopic measurement device according to claim 1, wherein the outer wall portion is a coating layer formed on the outer surface of the inner wall portion and made of a light-shielding material.