JPH11101686A - Feeble light detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make detectable a feeble light emitted from a measured sample, by receiving the light emitted from multiple light guide probes with multiple light receiving elements arranged in a shaded airtight container, and amplifying the difference between obtained light reception signals. SOLUTION: The signal light and reference light guided from two light guide probes 13, 14 are converted into two light reception signals by light receiving elements 24, 25, and the difference between two light reception signals is detected by the differential amplifier of an electronic circuit section 26. A chopper 27 having a rotary blade 27a chopping the light emitted from the rear ends 13b, 14b of the light guide probes 13, 14 and entering from translucent windows 11b, 12b respectively and intermittently feeding the light to the light receiving elements 24, 25 is provided between the translucent windows 11b, 12b and the light receiving elements 24, 25. The rotary blade 27a is driven by a chopper drive device 27b, a high-frequency AC component is added to the light passing through the chopper 27, and the 1/f noise of the light reception signals can be sufficiently reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a weak light detecting device used for measuring weak scattered light.

[0002]

2. Description of the Related Art Weak light detection technology is expected to be applied to a wide range of applications in the fields of biology and astronomy, medicine, food and nutrition. In particular, the so-called singlet oxygen, which is one of active oxygen and placed in a specific excited state, has an important role in biological defense, and at the same time, it may adversely affect living organisms, producing singlet oxygen It is important to search for substances to be removed and substances to be removed, and a detection system capable of doing so is required. Although the detection of weak light at a wavelength of 1.268 μm generated from singlet oxygen is important from an academic and clinical application point of view, it has been studied in the laboratory, but is still in practical use for clinical application. And its detection device has not been established.

Conventionally, a photomultiplier tube (PMT) has been mainly used for detecting weak light. However, the photomultiplier tube works effectively in a region of a light wavelength of several hundred nm, and is more than 1 μm. In the infrared region, the quantum efficiency is as small as a few percent or less,
Further, since it is an electron tube, its size is large, and cooling is required to reduce noise, but it is difficult to cool it to minus 80 degrees or less.

[0004] Under these circumstances, recently, a high-sensitivity semiconductor light receiving element capable of easily achieving a quantum efficiency of about 90% has been developed, and is expected as a sensor suitable for detecting weak light. ing.

[0005]

In using this semiconductor light receiving element, it is necessary to cool the light receiving element in order to reduce dark current from the light receiving element. In general,
It is known that the dark current decreases as the light receiving element cools. In addition, since noise generated from resistance and the like due to cooling is also reduced, a weak light detection system usually cools main components including a light receiving element to extremely low temperatures. By the way, such a weak light detection system often handles a living body or a part of a human body as a sample to be measured, and it is difficult to cool such a sample to be measured in the same manner as the detection device. Therefore, thermal radiation (hereinafter referred to as background light) from the sample to be measured and its surroundings often becomes a large noise source. If the wavelength of the measurement light emitted from the sample to be measured is known in advance, a considerable amount of background light can be removed by an optical filter that transmits only that wavelength, but the background light has the same wavelength range as the measurement light. , The background light cannot be removed by the optical filter.

The present inventor has been researching and developing a method for solving such a problem. However, in the weak light detecting device developed so far, light emitted from a living body or a human body,
In particular, there are many difficulties in detecting weak light emitted from any part of the human body. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a weak light detection device suitable for detecting weak light emitted from a measurement sample, which has conventionally been difficult to detect.

[0007]

A weak light detecting device according to the present invention for achieving the above object is provided with a first light-transmitting window for taking in light at a front end, and detects light incident from the first light-transmitting window. Two light introduction probes each having an optical fiber or a bundle of optical fibers for transmitting to the rear end, and the two light introduction probes being optically coupled to the rear ends of the two light introduction probes respectively. A light-shielding airtightness that includes a second light-transmitting window that receives light emitted from the ends and that blocks light other than light emitted from the rear ends of the two light-introducing probes and keeps the inside airtight. A container, a depressurizing means for depressurizing the inside of the light-tight airtight container, a cooling means for cooling the inside of the light-tight airtight container, and two of these two light-introducing probes arranged inside the light-tight airtight container in correspondence with the two light introduction probes, respectively. Light introduction probe it Two light-receiving elements for receiving light emitted from the rear end thereof, and a differential amplifier disposed inside the light-tight airtight container and amplifying the difference between the two light-receiving signals obtained by the two light-receiving elements. And a main body having the same.

Accordingly, if the background light entering the light receiving element from the two light introducing probes has the same power, the signal light from the sample to be measured is input to one light receiving element through one probe, and the two light receiving signals By taking the difference, the background light can be removed. Here, in the weak light detection device according to the present invention, each of the two light introduction probes may be provided with a tube that covers a periphery of the optical fiber or the bundle of optical fibers and through which a liquid passes. preferable. It is also preferable that the tubes of the two light introduction probes are separated from each other so that liquids having different temperatures can pass therethrough.

In the weak light detecting device according to the present invention, at least the front ends of the two light introducing probes are fixed to each other, and the two light introducing probes are connected to the two light introducing probes. The first light transmitting window of each of the introduction probes and the front end of the optical fiber or the optical fiber bundle of each of the two light introducing probes are interposed between the first light transmitting window and the first light transmitting window. It is preferable to provide a chopper for chopping light to be incident on the optical fiber bundle. Further, in the above-mentioned weak light detecting device, one of the two light introduction probes is configured to constitute one of the light introduction probes instead of including the first light transmission window. It is also a preferable embodiment to provide a reference light incidence optical system for making a predetermined reference light incident on the optical fiber or the optical fiber bundle.

In the weak light detecting device according to the present invention, each of the two light introduction probes is interposed between the first light transmitting window and the optical fiber or the optical fiber bundle. It is also preferable to include a chopper for chopping light that enters from one light transmitting window and is to enter the optical fiber or the optical fiber bundle.

Further, in the weak light detecting device according to the present invention, the main body is interposed between the second light transmitting window and the two light receiving elements, and is provided behind each of the two light introducing probes. It is also a preferable embodiment to include a chopper having rotating blades for chopping the light emitted from the end and entering the second light transmitting window and intermittently entering the two light receiving elements.

In the weak light detecting apparatus according to the present invention, it is preferable that the apparatus further comprises a first adjusting mechanism for adjusting the directions of the rear end faces of the two light introducing probes.
It is also preferable that the apparatus further includes a second adjusting mechanism for adjusting the directions of the two light receiving elements. In a preferred embodiment, the weak light detecting device of the present invention further includes a temperature adjusting means for independently applying heat to each of the two light receiving elements.

Further, in the weak light detecting device according to the present invention, either one of the first and second light transmitting windows, or both the first and second light transmitting windows, have a desired wavelength. Alternatively, one of the preferable embodiments is to comprise an optical filter for selectively transmitting light in a wavelength band.

[0014]

Embodiments of the present invention will be described below. FIG. 1 is a sectional view of a main body in one embodiment of the weak light detecting device of the present invention, and FIG. 2 is a sectional view of a light introducing probe in one embodiment of the weak light detecting device of the present invention.

The weak light detecting device 10 shown in FIGS.
Has two light introduction probes 13 and 14 and a main body 20. The two light introduction probes 13 and 14 include:
The first light-transmitting windows 11a and 12a for taking in light to the front ends 13a and 14a, and the optical fiber bundles 15 and 16 for transmitting the light incident from the first light-transmitting windows 11a and 12a to the rear ends 13b and 14b. Provided. The main body 20 has rear ends 13 of the light introduction probes 13 and 14 optically coupled to rear ends 13 b and 14 b of the two light introduction probes 13 and 14.
b, the second light-transmitting window 1 for taking in the light emitted from 14b
1b and 12b are provided.

The light introduction probe 13 of the two light introduction probes 13 and 14 is a probe for detecting signal light,
The light introduction probe 14 is a probe for introducing a reference light.
In FIG. 2, these two light introduction probes 13, 1
The front ends 13a and 14a of the 4 are connected but can be used separately. The main body 20 includes a light-tight hermetic container 21 capable of blocking light other than light emitted from the rear ends 13b, 14b of the two light-introducing probes 13 and 14 and keeping the inside airtight, and a light-tight airtight container. A compressor 22 for depressurizing the inside of the container 21 and a cooling device 23 for cooling the light receiving elements 24 and 25 placed inside the light-tight hermetic container 21.
And light introduction probes 13 and 14 inside the light-tight airtight container 21.
The light introduction probes 13, which are arranged corresponding to each,
14, two light receiving elements 24 and 25 for receiving light emitted from the rear ends 13b and 14b, and a light-tight airtight container 21.
An electronic circuit unit 26 including a differential amplifier for amplifying a difference between two light receiving signals obtained by two light receiving elements 24 and 25 disposed therein.

As described above, in the weak light detecting device 10, the light receiving elements 24 and 25 using the optical semiconductor element for converting light into an electric signal are arranged in an environment where the performance of the light receiving element can be maximized. Have been. The weak light from the object to be measured is guided by the optical fiber bundles 15 and 16 having a small transmission loss to the main body 20 where the light receiving elements 24 and 25 are arranged, where the signal is detected. Although it is possible to detect extremely weak light radiated from a living body or a human body by such a method, it is actually affected by noise temporally and spatially. At the same time as or before and after the time when the measurement was performed, at a time very close to the measurement time, measurement was quickly performed in the absence of weak light emission, the baseline (baseline) was determined, and the amount of deviation from the baseline was determined. Needs to be measured. Furthermore, it is necessary to perform the same measurement a plurality of times and average it to improve the measurement accuracy. Here, details of such a measurement method will not be described, but it is necessary to consider it in actual measurement.

In this embodiment, two light introduction probes 1
The signal light and the reference light introduced from 3 and 14 are converted into two light receiving signals by separate light receiving elements 24 and 25, respectively, and the difference between these two light receiving signals is detected by the differential amplifier of the electronic circuit unit 26. Therefore, the weaker the light from the sample to be measured, the more balanced the output signals from these two light receiving elements 24 and 25 in a state where the weak light is not detected.

It is considered that the output signals from the two light receiving elements become unbalanced due to the following two causes. (1) When the size of the background light itself entering the two light receiving elements is different. (2) When the optical and electrical characteristics of the two light receiving elements and the electronic circuit system are unbalanced. At the same time as stabilizing the ambient temperature of the device, multiple reflections caused by physical symmetry at the light guiding portion and the like pose a problem. Therefore, it is necessary to reduce the reflection at the end faces of the optical systems and adjust the parallelism between the end faces of the two optical systems. Furthermore, in order to forcibly balance, it is necessary to change the temperature of the constant temperature water for stabilizing the temperature of the two light introduction probes.

Regarding the cause of (2), the imbalance of the dark current of the light receiving element can be finely adjusted by controlling the cooling temperature of the light receiving element. Therefore, it is preferable to configure the detecting device as described above. The dark current of the electronic circuit system itself can be easily zero-balanced by electrically adjusting it in advance. In this embodiment, two light introducing probes 13 and 14 are interposed between the second light transmitting windows 11b and 12b and the two light receiving elements 24 and 25, respectively, in the light shielding airtight container 21 of the main body 20. From the rear ends 13b, 14b of the second light-transmitting windows 11b, 12
A chopper 27 having rotating blades 27a for chopping the light incident from b and intermittently entering the two light receiving elements 24 and 25 is provided. The rotary blade 27a is driven by a chopper driving device 27b. Since a high-frequency AC component is added to the light that has passed through the chopper 27, the 1 / f noise of the received light signal can be sufficiently reduced.

The first light-transmitting windows 11a and 12a may have, if necessary, a function such as an optical filter for selectively transmitting only light of a specific wavelength to be measured or a detachable light collecting mechanism. Can be. On the other hand, the second translucent window 11b,
12b is a window for taking in light and has a function of a vacuum sealing window.
b can have the function of an optical filter as needed.

In the main body 20, two light receiving elements 24,
25 to a very low temperature of 100 ° K or less, the electronic circuit section 26 including the differential amplifier to a low temperature of 0 ° C to -60 ° C, and the rotating blade 27a of the optical chopper 27 to a temperature of 0 to -60 ° C. So as to take into account the distance from the cooling head and thermal insulation. In addition, it is preferable to provide a temperature adjusting unit so as to independently apply heat to each of the two light receiving elements 24 and 25. By independently applying heat to the two light receiving elements 24 and 25 in this manner, it is possible to easily achieve zero balance of the light receiving signals from the two light receiving elements 24 and 25 when there is no signal. A specific example of the temperature adjusting means will be described in detail in the description with reference to FIG.

As described above, dew condensation may occur when the inside of the light-tight airtight container 21 is cooled. Therefore, it is necessary to control the humidity so that the atmosphere in contact with the end faces of the optical fiber bundles 15 and 16 has a humidity of 0%. is there. Therefore, the main body 20 of the present embodiment is provided with a compressor 22 which is a pressure reducing means for reducing the pressure inside the light-shielding airtight container 21 in order to prevent dew condensation inside the light-shielding airtight container 21. Further, measures are taken to prevent external vibrations from being transmitted into the light-tight airtight container 21.

In this embodiment, the light introduction probe 1
The introduction of the weak light from the optical fibers 3 and 14 to the main body 20 is performed by the optical fiber bundles 15 and 16. However, the introduction of the weak light is not limited to the optical fiber bundle, and one light Fiber may be used. The diameter of the optical fiber bundles 15 and 16 used in this embodiment is 10
mm from the end faces of the optical fiber bundles 15, 16 at the rear ends 13b, 14b of the light introduction probe.
The distance to the 4,25 surface is also about 10 mm. This one
At a distance of about 0 mm, the background light incident on the light receiving elements 24 and 25 from the end faces of the optical fiber bundles 15 and 16, the second light transmitting windows 11b and 12b, the rotating blade 27a of the chopper 27, etc. To external noise. Background light fluctuates due to slight thermal fluctuations of each of these components.
In particular, the optical fiber bundles 15 and 16 are moved by a measurement operation, and have a long length, which may be a large noise source. Therefore, in this embodiment, 2
Each of the light introduction probes 13 and 14 includes tubes 17 and 18 that cover the periphery of the optical fiber bundles 15 and 16, and the optical fiber bundles 15 and 18 are provided inside the tubes 17 and 18.
The temperature of the optical fiber bundles 15 and 16 is stabilized by circulating constant-temperature water W for cooling the optical fiber bundle 16. With this configuration, the two light receiving elements 24 and 25
When the same background light is incident on the light source, the differential amplifier of the electronic circuit unit 26 outputs the difference between the two light receiving elements 24 and 25. Therefore, even if the background light has the same wavelength component as the signal light, the amount of the background light is Can be removed.

The tubes 17 and 18 of the two light introduction probes 13 and 14 are separated from each other, and can pass different liquids from each other. The reason that the optical fiber bundles 15 and 16 can be cooled separately is that the background light power is changed by separately adjusting the cooling temperature of the optical fiber bundles 15 and 16 and the light receiving elements 24, 25 and This is because the level of the signal light including the electronic circuit unit 26 is balanced and, when there is no signal light, the output from the electronic circuit unit 26 is adjusted to be zero or nearly zero.

It should be noted that the chopper 27 and the optical filter (the first and second light transmitting windows 11) provided in this embodiment are provided.
a, 12a, 11b, and 12b) are arranged according to the minimum detection sensitivity and the detection wavelength, and may be removed if unnecessary. Next, another embodiment of the weak light detection device of the present invention will be described.

FIG. 3 is a view showing an embodiment in which a chopper is provided at the front end of the light introducing probe shown in FIG.
As shown in FIG. 3, the two light introduction probes 113 and 11
The four front ends 113a and 114a are fixed to each other. The front end portions 113a and 114a of these two light introduction probes 113 and 114 have first light transmission windows 111a and 111, respectively.
12a and the front ends of the optical fiber bundles 115 and 116 of the light introduction probes 113 and 114, respectively.
Of the optical fiber bundle 1 entering through the light transmitting windows 111a and 112a
A chopper 127 and a chopper driving device 127a are provided for chopping light to be incident on the light receiving devices 15, 116. Thus, the light introduction probes 113, 11
When the chopper 127 is provided on the front end portions 113a and 114a of the fourth unit 4, the chopper 27 on the main body 20 side in the embodiment shown in FIG. 1 may be omitted.

FIG. 4 is a diagram showing an embodiment in which a reference light incident optical system is provided at the front end of one of the two light introduction probes shown in FIG. As shown in FIG. 4, the front end portion 214a of one of the two light introduction probes 213 and 214 is not provided with a light transmitting window, and instead, the light introduction probe 214 is not provided. Is provided with a reference light incidence optical system 230 for causing a predetermined reference light to be incident on the optical fiber bundle 216 constituting the optical fiber bundle. In this manner, light of known power is incident on the light receiving element (not shown) of the main body from the optical fiber bundle 216 of one light introduction probe 214, and is used as reference light to estimate weak absolute detected power. be able to.

FIG. 5 is a diagram showing an embodiment in which each of the two light introduction probes shown in FIG. 2 has a chopper at the front end of the light introduction probe. By separating the front end 313a of the light introduction probe 313 and the front end of the other light introduction probe as shown in FIG. 5, it is possible to measure and compare objects to be measured at different places. The front end 313 of each of the separated light introduction probes 313
a between the first light transmitting window 311a and the optical fiber bundle 315,
A chopper 327 for chopping light to be incident on the light source 15 is provided.

FIG. 6 shows an embodiment in which the weak light detecting device shown in FIG. 1 is provided with first and second adjusting mechanisms for finely adjusting the parallelism between the rear end face of the light introducing probe and the light receiving element. FIG. In this embodiment, as shown in FIG.
A first adjusting mechanism 430 for adjusting the direction of the rear end surfaces 415b and 416b of the optical fiber bundles 415 and 416 of the light introducing probes 413 and 414 is provided. The first adjustment mechanism 430 includes two light introduction probes 413,
It has three adjustment screws 431 that adjustably fix the relative position between the probe holding substrate 432 that holds the rear end of the probe 414 and the top plate 421a of the light-tight airtight container 421. The three adjusting screws 431 are provided at positions corresponding to the vertices of an equilateral triangle on the probe holding substrate 432, and by rotating these three adjusting screws 431, the rear end surfaces 415b and 416b of the optical fiber bundles 415 and 416 are connected. The degree of parallelism with the light receiving elements 424 and 425 can be finely adjusted, whereby the imbalance of dark current between the two light receiving elements 424 and 425 can be finely adjusted. It should be noted that airtightness is maintained by the O-ring 433 between the probe holding substrate 432 and the top plate 421a.

In this embodiment, the second adjusting mechanism 44 provided for the same purpose as the first adjusting mechanism 430 for adjusting the directions of the two light receiving elements 424 and 425 is provided.
0 is provided. This second adjusting mechanism 440
Cooling substrate 442 on which two light receiving elements 424, 425 are mounted
And three adjusting screws 441 that adjustably fix the relative position of the light-receiving element holding substrate 443 and the light-receiving element holding substrate 443. The three adjusting screws 441 are provided at positions corresponding to the vertices of an equilateral triangle on the light receiving element holding substrate 443, and by rotating these three adjusting screws 441, the optical fiber bundle 41 is rotated.
5,416, rear end surfaces 413b, 414a and light receiving element 42
4 and 425 can be finely adjusted, whereby the imbalance of dark current between the two light receiving elements 424 and 425 can be finely adjusted.

In this embodiment, the cooling substrate 442 on which the two light receiving elements 424 and 425 are mounted is heated independently of the two light receiving elements 424 and 425 to cooperate with the cooling function of the cooling substrate. And two light receiving elements 42
Heaters 444 and 445, which are temperature adjusting means for independently adjusting the temperatures of 4,425, are provided. FIG.
Is a graph showing the relationship between the dark current of the light receiving element, the bias voltage, and the temperature of the light receiving element.

Since this measuring device has a measurement limit near a current value of 1 pA, a dark current of 1 pA or less cannot be measured, but it is clear that the dark current increases as the temperature of the light receiving element increases. Therefore, based on this principle, the first and second adjustment mechanisms 430, 4 in the embodiment shown in FIG.
Using the heater 40 and the heaters 444 and 445, while observing the output signal waveforms of the two light receiving elements 424 and 425, the dark current balance can be adjusted so as to obtain a signal waveform obtained when the apparatus is in balance. it can.

[0034]

As described above, according to the weak light detecting device of the present invention, it is possible to obtain a weak light detecting device suitable for detecting weak light emitted from a sample to be measured, which was difficult to detect conventionally. Can be.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a main body in an embodiment of a weak light detection device according to the present invention.

FIG. 2 is a cross-sectional view of a light introduction probe in one embodiment of the weak light detection device of the present invention.

3 is a diagram showing an embodiment in which a chopper is provided at a front end of the light introducing probe shown in FIG. 2;

FIG. 4 is a diagram showing an embodiment in which a reference light incident optical system is provided at a front end of one of the two light introduction probes shown in FIG. 2;

FIG. 5 shows two light introduction probes shown in FIG.
It is a figure showing an embodiment in case a chopper is provided in the front end of a light introduction probe.

FIG. 6 is a diagram showing an embodiment in which the weak light detection device shown in FIG. 1 includes first and second adjustment mechanisms for finely adjusting the parallelism between the rear end face of the light introduction probe and the light receiving element. is there.

FIG. 7 is a graph showing a relationship among a dark current, a bias voltage, and a light receiving element temperature of the light receiving element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Weak light detection apparatus 11a, 11b, 12a, 12b Light transmission window 13, 14 Light introduction probe 13a, 14a Front end 13b, 14b Rear end 15, 16 Optical fiber bundle 20 Main body 21 Light-tight airtight container 22 Compressor 23 Cooling device 24, Reference Signs List 25 light receiving element 26 electronic circuit unit 27 chopper 27a rotating blade 27b chopper driving device 111a, 112a first light transmitting window 113, 114 light introduction probe 113a, 114a front end 115, 116 optical fiber bundle 127 chopper 127a chopper driving device 213, 214 light introduction probe 214a front end 216 optical fiber bundle 230 reference light incident optical system 311 first light transmitting window 313 light introduction probe 313a front end 315 optical fiber bundle 327 chopper 413,414 light introduction probe 415,416 Fiber bundles 415b, 416b Rear end surface 421 Shielding airtight container 421a Top plate 424, 425 Light receiving element 430 First adjusting mechanism 431 Adjusting screw 432 Probe holding substrate 433 O-ring 440 Second adjusting mechanism 441 Adjusting screw 442 Cooling substrate 443 Light receiving element Holding substrate 444,445 Heater

Claims (11)

[Claims] An optical fiber or a bundle of optical fibers for transmitting light incident from the first light-transmitting window to a rear end thereof is provided at a front end of the first light-transmitting window for taking in light.
A light transmitting probe, and a second light transmitting window optically coupled to a rear end of each of the two light transmitting probes to receive light emitted from the rear ends of the two light transmitting probes; A light-shielding airtight container capable of blocking the incidence of light other than light emitted from the rear ends of the two light-introducing probes and keeping the inside airtight, a pressure reducing means for reducing the pressure inside the light-shielding airtight container, Cooling means for cooling the inside of the light-tight hermetic container, and receiving light emitted from the rear ends of each of the two light-introduction probes arranged inside the light-tight hermetic container in correspondence with each of the two light-introduction probes And a differential amplifier disposed inside the light-tight airtight container and amplifying a difference between two light-receiving signals obtained by the two light-receiving elements. Light detection device . 2. The method according to claim 1, wherein each of the two light introduction probes is
2. The weak light detection device according to claim 1, further comprising a tube that covers a periphery of the optical fiber or the optical fiber bundle and through which a liquid passes. 3. The weak light detecting device according to claim 2, wherein the tubes of the two light introducing probes are separated from each other so that liquids having different temperatures can pass through each other. . 4. The two light introduction probes, wherein at least the front ends of the two light introduction probes are fixed to each other, and the two light introduction probes are each a first light transmitting window of each of the two light introduction probes. And between the front end of the optical fiber or the optical fiber bundle of each of the two light introduction probes,
2. The weak light detecting device according to claim 1, further comprising a chopper for chopping light incident from the first light transmitting window and entering the optical fiber or the optical fiber bundle. 5. An optical fiber or an optical fiber constituting one of the two light introduction probes, instead of the one light introduction probe having the first light transmission window. 5. The weak light detection device according to claim 4, further comprising a reference light incidence optical system for causing a predetermined reference light to enter the bundle. 6. The two light introduction probes, respectively,
A chopper interposed between the first light transmitting window and the optical fiber or the optical fiber bundle, and chopping light that enters from the first light transmitting window and is about to enter the optical fiber or the optical fiber bundle. The weak light detection device according to claim 1, further comprising: 7. The second light-transmitting probe is interposed between the second light-transmitting window and the two light-receiving elements, and is emitted from rear ends of each of the two light-introducing probes. 2. The weak light detecting device according to claim 1, further comprising a chopper having rotating blades for chopping the light incident from the window and intermittently incident the light on the two light receiving elements. 8. The weak light detecting device according to claim 1, further comprising a first adjusting mechanism for adjusting the directions of rear end surfaces of the two light introducing probes. 9. The weak light detecting device according to claim 1, further comprising a second adjusting mechanism for adjusting the directions of the two light receiving elements. 10. The weak light detection device according to claim 1, further comprising a temperature adjusting means for independently applying heat to each of the two light receiving elements. 11. One of the first and second light-transmitting windows, or both the first and second light-transmitting windows, selectively transmit light of a desired wavelength or wavelength band. 2. The weak light detecting device according to claim 1, further comprising an optical filter that causes the light to be filtered.