JPH055698A - Light measuring instrument and optically measuring method - Google Patents

Abstract

PURPOSE:To restrain a quantum noise of a light source, by providing a means to convert one photon into a pair of photons and a means to separate measured data in the middle of an optical path into the optical path, detect the intensity of light, and measure optical characteristic. CONSTITUTION:One photon within a photon beam 10 emitted from a laser 100 is converted by a wavelength converting element 200 into two photons of which at least wavelengths or polarizing directions differ each other. A photon beams 21 and 22 formed by these two photons are made as a reference beam and a probe beam respectively, and both the beams are separated into two different optical paths 31, 41 by an optical path separating means 300. Measured data 400 are inserted into the optical path 41, and the photon beam to transmit the data 400 makes incident into an optical path 42. The reference beam and the probe beam to transmit the data are detected by photo detectors 502 and 501 setup at ends of the optical paths 31 and 4,2, a difference signal 601 of photoelectric currents of the detectors 501, 502 is found and input into a data processing element 700, and the optical properties of the data 400 are measured. The quantum noise is restrained by taking the difference of the photoelectric currents.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention can be applied to almost all optical measuring devices such as quality control, material inspection, pollution measurement, biological sample, and biological sample measurement in various industries. For example, inspection of raw material gas used in semiconductor manufacturing, detection of dust in the air in a clean room, measurement of optical fiber attenuation factor, detection of specific substances in biological samples with extremely low light absorption, light transmitting substances such as glass. It can be effectively used for detecting micro cracks inside.

[0002]

2. Description of the Related Art FIG. 1 shows an example of an optical measuring device used by the present inventors, which is used for absorption measurement. The light beam emitted from the light source 100 is separated into two light beams 45 and 46 by an optical path separating means 310 such as a semitransparent mirror.
The light beam 46 is incident on the sample 400 to be measured as probe light, and the light beam 45 serves as reference light. The reference light and the probe light transmitted through the sample 400 to be measured are respectively detected by high-sensitivity photodetectors 521 and 522 such as photomultiplier tubes. The output signals I ₁ and I ₂ of the photodetectors 521 and 522 are processed by the data processing unit 710 such as a logarithmic amplifier and a subtraction circuit, and a signal proportional to the amount of light absorbed by the sample is obtained.

[0003]

In the optical measurement by this device configuration, the quantum noise (shot noise) of the light source is
It is the limit noise that the noise level cannot be lowered any further. Even if a coherent light source such as a laser is used, the light intensity of the light source has a certain amount of fluctuation due to the stochastic process (spontaneous emission process) included in the light generation mechanism. The magnitude of this fluctuation is called the quantum limit of noise. This fluctuation has set the limit for noise reduction in conventional optical measurement. For example, in FIG. 1, the photodetector 521,
When the output signals I ₁ and I ₂ of 522 are subtracted, the amount of absorption is obtained. However, since there is no correlation between the quantum noises included in I ₁ and I ₂ , the quantum noises can be obtained even if they are subtracted. Does not decrease. An object of the present invention is to provide an optical measuring device capable of suppressing the quantum noise of this light source.

[0004]

In order to achieve the above object, according to the present invention, a probe beam and a reference beam are generated by simultaneously generating a probe beam and a reference beam used in optical measurement as a pair of two photons. The quantum noise is suppressed by correlating the properties related to and the quantum noise with respect to each other, and the difference of the photoelectron currents between the two is taken, and only the change of the photon state due to the interaction with the measured sample is selectively detected.

Specifically, referring to FIG.
A photon beam 10 emitted from the photon beam 10 is converted by a wavelength conversion element 200 into at least two photons having different wavelengths or polarization directions, and the photon beam 21 generated by the two photons is referred to. The light and the photon beam 22 are used as probe light, and both beams are divided into two different optical paths 31 and 41 by the optical path separating means 300, the sample 400 to be measured is inserted in the optical path 41 of the probe light, and The light beam transmitted through the measurement sample 400 enters the optical path 42. Two photoelectric detectors at the ends of optical paths 31 and 42
Reference light and probe light transmitted through the sample are detected by 501 and 502, respectively, and the two photoelectric detectors 501 and 502 are detected.
The subtraction circuit 600 obtains the difference signal 601 of the photoelectron current, which is the output of 1., and the difference signal 601 is input to the data processing unit 700 to measure the optical properties of the sample 400 to be measured.

[0006]

In order to explain the operation of the means for solving the above problems,
2 and 4 are used. 2 and 4, in order to show the mechanism of quantum noise generation, the light beam on each optical path is
Drawn as a photon train.

FIG. 4 is a diagram for explaining the principle of the apparatus configuration of FIG. Similarly, FIG. 2 is a diagram for explaining the principle of the apparatus configuration of FIG.

In FIG. 2, the output generated from the light source 100 is represented as a photon train 950. Photon train 950 like this
The beam splitter 310 distributes the light to the optical paths 45 and 46 with a probability of 50% to generate a photon train 960 and a photon train 961. Since such distribution is a stochastic process,
One photon on the photon train 950 becomes either path 45 or path 46.
It is impossible to predict which one will be assigned. Photon train
The 960 and 961 are drawn in consideration of these points.
The light beam on the optical path 45 enters the sample 400. If absorption occurs by the sample, photons will drop out from the photon train 970 representing the light beam after passing through the sample, corresponding to the absorption occurrence event. The photon shed in this way was drawn like photon 977. On the other hand, if no loss occurs in the light beam on the optical path 46, the photon train 971 becomes
Equally depicted as Photon Sequence 961.

Next, the photon trains 970 and 971 are detected by photoelectric detection. The photon train incident on the photoelectric detector 521 is
The photon train 971 is a photon train incident on the photoelectric detector 522.
Photon train 970. Photoelectric detector 521 and photoelectric detector 522
Converts these photon trains into a stream of electrons. These photoelectron currents are phenomena in which each electron passes through the conducting wire, and can be represented by a current pulse train as shown in the figure.
This state is represented by an electron pulse train 980 and an electron pulse train 981. The subtraction circuit 711 obtains the difference between these electron pulse trains to obtain an output pulse train 990. The current of the output pulse train 990 is the output current 712. By the way, since the beam splitter 310 distributes photons to two optical paths with a probability of 50%, if there is no absorption by the sample 400,
The electronic pulse 980 and the electronic pulse train 981 cancel each other out. Therefore, the current value of the electronic pulse train 990 is zero as an average value for a sufficiently long time. However, as shown in the figure, if the output current 712 is observed in a sufficiently short time, a current pulse train is observed, and the instantaneous value of the current is not zero.
This is called quantum noise (shot noise). The electron pulse train 980 extinguishes a single electron pulse 988 when there is a small amount of absorption by the sample (eg, corresponding to the event of a photon loss from the photon train 970). However, such a slight decrease in current is buried in the shot noise as described above and cannot be detected.

On the other hand, the reference light beam 21 and the probe light beam 22 in FIG.
One high-energy photon in the photon beam 10 emitted from is generated by the process of being converted into two photon pairs of low energy according to the law of conservation of energy. Therefore, when photons are present in the reference light beam 21,
There will always be photons present in the probe light beam 22 as well. As described above, such a situation is expressed by using a photon train as shown in the figure. That is, there are two photons corresponding to each photon in the photon train 901 representing the output of the laser light 100.
An image in which two photons exist at the same time is obtained like the photon train 910. If the wavelength conversion element 200 is properly selected, the polarization directions of these photon pairs will be orthogonal to each other.
Can be direction. A reference light beam 21 and a probe light beam 22 are defined corresponding to each of these polarization modes. For example, the reference light beam 21 can be made to correspond to the P polarization mode, and the probe light beam 22 can be made to correspond to the S polarization mode.

Reference light beam 21 and probe light beam 22
Is a beam with different polarization direction, the optical path separation means
If a polarization beam splitter is used as 300, it can be divided into two different optical paths. These optical paths are referred to as an optical path 31 and an optical path 41, respectively. For example, the reference light beam 21
When P-polarized, the photons in the reference light beam 21 are always transmitted and directed on the optical path 31, while the probe light beam 22 is S
Since it is polarized light, the photons in the probe light beam 22 are always reflected and travel up the optical path 41. The resulting photon train is
It is represented by photon array 920 and photon array 921. As shown in the figure, these photon trains 920 and 921 are laser light sources.
Since it is considered that they are generated simultaneously from one photon of 100, they have the same correlation as the photon pair on the photon train 910. That is, both beams have common characteristics with respect to the quantum noise of the light source.

The probe light beam 22 incident on the optical path 41
Enters the measured sample 400 and further enters the optical path 42, and is converted into an electronic pulse train 940 by the photoelectric detector 501. If there is absorption by the sample, photons will drop out of the probe light beam on path 42. This state is photon train 930
It expressed like. Here, the number of photons lost is 933. On the other hand, the reference light beam 21 that has entered the optical path 31 enters the photoelectric detector 502 without loss and is converted into an electron pulse train 941. These electron pulse trains are input to the subtraction circuit 600, and the output pulse train 950 and the output current 601 are output.

If there is no absorption by the sample 400, the electron pulse trains 940 and 941 cancel each other and no electron pulse is generated in the output. The reason for canceling each pulse is that the photons that generate these electron pulse trains are
This is because two of them were generated at the same time. This point
The present invention is different from the prior art in that the subtraction circuit 600
The shot noise derived from the photons at the output of is completely canceled at the level of each photon. Such noise suppression effect is described, for example, in Publicly Known Example 1, Hightman et al., Fujiaru Review Letters, Vol. 59, 22.
Issue, page 2555, 1987 [Heidmann et al.,
Phys. Rev. Lett., Vol. 59 No. 22, p. 2555, (198
7).], And known example 2, Wooker and Sewald,
Quantum Optics, Volume 1, p. 75, 1987
Year (JG Walker and SF Seward, Quantum Opt., Vol.1
p.75, (1989).].

Therefore, as shown in FIG.
When slight absorption (at the level of one photon) or scattering by the sample exists, the electron pulse disappears from the electron pulse train 940 in response to these absorption and scattering. The disappeared electron pulse corresponding to the lost photon 933 is referred to as an electron pulse 944. As a result, the photoelectron trains 940 and 941 are out of balance and are detected with high sensitivity.

Here, the photoelectric detector 501 and the photoelectric detector
It should be noted that unless the quantum efficiency of 502 is close enough to 1, the above effect cannot be obtained because the photon train is lost. Therefore, these detectors include, for example,
Photoelectric detectors with high quantum efficiency, such as PIN diodes, must be selected.

It should be noted that, in the above-mentioned known examples 1 and 2, although the noise suppression effect has been verified, there is no description of the configuration in which the sample is inserted only on the optical path of the probe light. Also, known example 3, Debuischert et al., Quantum Optics, Volume 1, page 3, 1989 [TD
ebuisschert et al., Quantum Opt., Vol. 1 p.3, (198
9).] Also describes the principle of the method of measuring the spread of an object using light having quantum correlation, but in this example, the measurement of the probe light attenuation and its noise suppression effect are described. Is also not mentioned.

[0017]

EXAMPLE FIG. 5 shows, as an example of the present invention, quantification of a trace amount of impurities in a material gas used for manufacturing a semiconductor, measurement of attenuation characteristics of light propagating in an optical fiber, trace amount in air in a clean room. An example in which the present invention is applied to various absorption measurements such as dust density measurement will be described. A continuous wave laser 110 is used as a light source. Examples of the continuous wave laser 110 include an argon ion laser and a continuous wave Nd: YAG.
The second harmonic of the laser or the like can be used. An optical parametric oscillator 201 is used as the wavelength conversion element. The optical parametric oscillator 201 includes a high reflectance mirror 210.
And 211 and a nonlinear optical element 250 arranged so as to satisfy the phase matching condition in the optical resonator. The non-linear optical element is, for example, various inorganic non-linear crystals (KTP, K
NbO ₃ , Ba ₂ NaNb ₅ O ₁₅ , LiNbO _3, etc.), various organic nonlinear optical materials (low-molecular-weight crystals, low-molecular-weight doped polymers), or quasi-phase matching elements in which a domain inversion structure is formed by these materials, etc. Can be used. The entrance and exit end faces of these crystals are coated with an antireflection film. At this time,
The laser light is passed through the optical isolator 11 so that the stability of the laser light is not disturbed by the reflected light of the pump light 12 incident on the optical parametric oscillator 201 on the mirror 210.
10 and the optical parametric oscillator 201 are coupled. Note that 1
3 is a mirror.

If the phase matching condition of the nonlinear optical element 250 is appropriately selected, the reference light beam 21 and the probe light beam 22 output from the optical parametric oscillator 201 are
The polarization directions of the two can be made orthogonal to each other. Therefore, when the two light beams are incident on the polarization beam splitter 301, the reference light beam 21 is transmitted and is incident on the optical path 31, and the probe light beam 22 is reflected and incident on the optical path 41. is there. That is, the polarization beam splitter 301 plays the role of the optical path separating means 300 of FIG. When the two photon beams output from the optical parametric oscillator 201 have different wavelengths, a wavelength selecting element such as a prism can be used as the optical path separating means. Since it is possible to remove uncorrelated light with different wavelengths generated from the element,
The S / N ratio is improved.

The sample 400 to be measured is inserted on the optical path 41. The probe light incident on the optical path 42 is converted to a photoelectron current signal by the photodetector 511, and the reference light incident on the optical path 31 is converted to a photoelectron current signal. Further, in order to enable suppression of quantum noise, these photodetectors 511 and 512 need to have sufficiently large quantum efficiency, so that the wavelengths of the reference light 21 and the probe light 22 are the quantum efficiency of the photodetectors 511 and 512. Is set to a high range. For example, when the second harmonic of an argon ion laser or a continuous wave Nd: YAG laser is used and the nonlinear optical crystal is used, InGaAs-PI is used.
An N, Si-PIN photodiode or the like can be used. In the data processing unit 700, for example, in the concentration measurement of the measured sample 400, the measurement data for the standard sample having a known concentration is stored in the memory in advance, and the measured data for the measured sample 400 is compared with the sample, The arithmetic processing is performed so that the density of is obtained.

The main noise sources of this optical measuring device are
It is uncorrelated light generated from the wavelength conversion means. When various inorganic nonlinear optical crystals are used as the nonlinear optical element, it is advantageous to use a phase matching condition called Type-II because the above-mentioned non-correlated light can be reduced. It is also effective to use the nonlinearity of atomic vapor instead of the nonlinear optical crystal.

The manner of signal processing, outputs the I _P of the photodetector for the probe light, and the output of the photodetector and I _R for the reference _{beam, (I R -I P) /} I R, (I R - I _P ) / (I _R + I _P )
Needless to say, various signal processing is possible.

Further, although the present invention is applied to the measurement of the absorption amount of the sample in the present embodiment, the object of measurement of the present invention is not limited to this, and the number of photons is changed by the interaction such as the interference optical system. It can be applied to anything.

As the wavelength conversion element, a substance that undergoes a cascade transition process may be used. In this case, one of the two photons produced by the cascade transition process may be used as probe light and the other may be used as reference light.

FIG. 6 shows a second embodiment in which the present invention is applied to a sample concentration measuring device. In this embodiment, a pulsed laser 120 is used as the laser. As the pulsed laser, a mode-locked Q switch Nd: YA
The second harmonic of G laser can be used. In this embodiment, an optical parametric amplifier 202 is used as the wavelength conversion element 200 in FIG. The optical parametric amplifier 202 is composed of a nonlinear optical crystal arranged so as to satisfy the phase matching condition. The above-mentioned nonlinear optical crystal is, for example, KTP, KNbO ₃ , Ba ₂ NaN.
b ₅ O ₁₅ or LiNbO ₃ can be selected. The entrance and exit end faces of these crystals are coated with an antireflection film. By using pulsed light as the excitation light source,
Since the peak power can be made sufficiently large, the conversion efficiency of the wavelength conversion element becomes sufficiently high. Therefore, when the pulsed laser passes through the crystal once,
The reference light 21 and the probe light 22 having a sufficient intensity can be obtained.
Further, since the generated photon beam does not pass through the crystal a large number of times, it is advantageous in that the requirement for the antireflection coat required for the crystal in the resonator is reduced.

As described above, by appropriately selecting the phase matching condition of the nonlinear optical crystal, the two reference light 21 and the probe light 22 output from the optical parametric amplifier 202 have their polarization directions orthogonal to each other. It is possible,
The polarization beam splitter 301 can separate the two photon beams. Optical parametric amplifier 202
When the two photon beams of the outputs have different wavelengths from each other, a wavelength selecting element such as a prism can be used as the optical path separating means, as in the above-described embodiment.

The photon beams split by the polarization beam splitter are incident on the optical path 31 and the optical path 41. Sample to be measured
400 is inserted on the optical path 41. The probe light incident on the optical path 42 is converted into a photoelectron current signal by the photodetector 511.
On the other hand, the light that has entered the optical path 31 passes through the delay element 800 and then enters the photodetector 512 as reference light and is converted into a photoelectron current signal. In order to suppress shot noise, the delay time provided by the delay element 800 is determined so that the wave packet of the pulsed light passing through the two optical paths 31 and 41 enters the photodetectors 511 and 512 at the same time. In addition, in order to suppress shot noise, these photodetectors 511, 51
It is the same as the above-mentioned embodiment that 2 needs to have sufficiently high quantum efficiency. For example, when the second harmonic of a mode-locked Q-switched Nd: YAG laser is used and the nonlinear optical crystal is used, InGaAs-PIN,
A Si-PIN photodiode or the like can be used. The operation of the data processing unit 700 is the same as that of the embodiment shown in FIG. However, it is necessary to select an electronic circuit system having sufficiently high response so that sufficient response to a high-speed optical pulse can be obtained.

FIG. 7 shows an embodiment in which the present invention is applied to an apparatus for measuring the optical activity of a sample. In FIG. 7, the laser 100, the wavelength conversion element 200, the optical path separating means 300, the subtraction circuit 600, and the data processing unit 700 are the same as those shown in FIG. 3, FIG. 5, or FIG. That is, a continuous or pulsed laser can be used as the laser 100, an optical parametric oscillator or an optical parametric amplifier can be used as the wavelength conversion element 200, and a prism or a polarization beam splitter can be used as the optical path separating means.

This embodiment shows an example in which the sample concentration measuring device is constructed by detecting the magneto-optical effect among the optical activities. Generally, in the measurement of a sample having an optical activity, the sample concentration measuring device shown in FIG. The magnetic field applying means 1000 is not necessary in the embodiment. The sample 410 to be measured is inserted on the optical path 41. The magnetic field applying means 1000 applies a magnetic field perpendicular to the optical path and having a direction having an angle of 45 ° to the polarization direction of the light in the optical path to the sample to be measured 410. The light transmitted through the measured sample 410 is converted into elliptically polarized light as a result of interacting with the sample.
Such a magneto-optical effect is called Voigt effect, and an arrangement of such a magnetic field is called Voigt arrangement. Of the probe light incident on the optical path 42, only the photon having the polarization direction equal to the component of the polarization direction of the probe light on the optical path 41 is analyzed.
It is selected by 900 and converted into a photoelectron current signal I _S by the photodetector 511. That is, the analyzer 900 serves to detect only the photons whose polarization state has not changed due to the interaction with the measured sample 410.

The light incident on the optical path 31 is converted into a photoelectron current signal I _R by the photodetector 512 as reference light. These photodetectors 511 and 512 have sufficiently large quantum efficiency. Subtraction circuit 6
00, the difference signal (I _R
By taking -I _S ), a signal proportional to the amount of change in incident light due to the Voigt effect can be obtained. In this method, the sum signal of the change in the polarization of the incident light by the sample and the attenuation of the incident light by the sample is detected. The operation of the data processing unit 700 is the same as that of the embodiment shown in FIG.

The above is the case of Voigt arrangement, but it is also possible to make the magnetic field application direction parallel to the optical path. In this case, the light incident on the sample interacts with the sample, and as a result, the polarization direction of the light rotates. Such a magneto-optical effect is called a Faraday effect, and such a magnetic field arrangement is called a Faraday arrangement. Also in this case, a signal proportional to the amount of change in the incident light due to the Faraday effect is obtained as the output of the subtraction circuit 600.

FIG. 8 shows an embodiment in which the present invention is applied to an apparatus for measuring the optical activity of a sample. In FIG. 8, the laser 100, the wavelength conversion element 200, the optical path separating means 301, the subtraction circuit 600, and the data processing unit 700 are the same as those shown in FIG. 3, FIG. 5, or FIG. That is, as the laser 100,
Wavelength conversion element 20 using continuous or pulsed laser
An optical parametric oscillator or an optical parametric amplifier can be used as 0, and a prism or a polarization beam splitter can be used as the optical path separating means 301.

In this embodiment, the pair of photons produced by the wavelength conversion element 200 are on the same optical path,
A pair of photons having different wavelengths and having polarization modes whose polarization directions are orthogonal to each other. Then, both the photon beam of wavelength lambda ₁ of the reference beam 21 and the wavelength lambda ₂ of the probe light 22,
The light is transmitted through the sample 410 to be measured having an optical activity, and the transmitted light is divided into two optical paths corresponding to the difference in polarization mode of the photon pair by the polarization beam splitter 301, and detected by photodetectors 511 and 512, respectively. In this method, the measured sample 410 is
Have optically active with respect to the probe light 22 of the wavelength lambda _2, is effective when no optical activity with respect to the wavelength lambda ₁ of the reference light 21.

In FIG. 8, since the sample 410 to be measured does not exhibit optical anisotropy with respect to the reference light 21 having the wavelength λ ₁ , the photons in the light beam 25 transmitted through the sample 410 to be measured are polarized. There is no change. When the polarization beam splitter 301 is arranged so as to transmit the photons of the wavelength λ ₁ that have become the light beam 25, the photons of the wavelength λ ₁ enter the optical path 32 and are detected by the photodetector 512.

On the other hand, if the probe light 22 having the wavelength λ ₂ is transmitted through the sample 410 to be measured and is incident on the light beam 26, the incident probe light 22 due to the optical rotatory power of the sample 410 to be measured.
A component of wavelength λ ₂ having a polarization direction orthogonal to the polarization direction of is generated. The polarization direction of this component, the wavelength lambda ₁ of the reference beam 2
Since it is parallel to the polarization direction of 1, the polarization beam splitter 3
The light passes through 01, enters the optical path 33, and is detected by the photodetector 512. Wavelength λ ₂ where the polarization state did not change in measured sample 410
The component of is reflected by the polarization beam splitter 301, enters the optical path 43, and is detected by the photodetector 511.

According to this method, in the output of subtraction of the photoelectron current, a change in the polarization state of one photon of the probe light appears as a charge amount of two photoelectrons. Therefore, the change of the signal intensity corresponding to the change of the polarization state obtained in the present embodiment is characterized by being twice as large as the change of the signal intensity obtained in the embodiment shown in FIG.

FIG. 9 (a) shows an embodiment in which the present invention is applied to an apparatus for detecting a substance having Raman activity. In FIG. 9 (a), a laser 100, a wavelength conversion element 200, an optical path separation means
300, the subtraction circuit 600, and the data processing unit 700 are shown in FIGS.
Alternatively, it is similar to that shown in FIG. That is, a continuous or pulsed laser is used as the laser 100,
An optical parametric oscillator or an optical parametric amplifier can be used as the wavelength conversion element 200, and a prism or a polarization beam splitter can be used as the optical path separating means.

Of the photon pair beams obtained from the wavelength conversion element 200, one is the probe light 22 and the other is the reference light.
21. The reference light 21 is converted into the optical path 3 by the optical path separating means 300.
Incident on 1, the probe light 22 is converted into probe light 50,
It is incident on the Raman cell 420 and generates transmitted probe light 51 and Raman scattered light 60. Of these signals, the signal selection means 430 selectively transmits only the light having the same wavelength and polarization direction as the incident light 50, that is, the transmitted probe light 51, and makes it incident on the photodetector 511. The operations of the subtraction circuit 600 and the data processing unit 700 are also the same as those shown in FIG. 3, FIG. 5, or FIG.
The attenuation due to Raman cell transmission of 50 is measured. FIG. 9 shows the relationship between the probe light frequency ω ₁ and the Raman scattered signal frequency ω ₂ .
It is shown in (b). In FIG. 9B, | e> and | g> respectively represent the excited state and the ground state of the substance to be detected, and the energy difference between these states is hΩ. Note that h is Planck's constant. As shown in the figure, the frequency of the probe light is sufficiently far from the energy region where resonance absorption of the substance to be detected occurs. In general, the Raman scattering cross section is much smaller than the resonance absorption cross section, so
The attenuation of the probe light transmitted through the Raman cell is sufficiently small.
Therefore, the Raman cell transmitted light can be detected without breaking the quantum correlation between the probe light 50 and the reference light 31.

FIG. 10 shows another embodiment in which the present invention is applied to a device for detecting a substance having Raman activity. This embodiment is different from the embodiment shown in FIG. 9A in that the laser 1 for generating the pump light 15 is used.
50, the lens 16 for adjusting the crossing angle of the pump light 15 and the probe light 50, and the probe light selecting means 430 are newly introduced, and the same components as those of the embodiment shown in FIG. 9A. , And these operations are similar.

In the present embodiment, due to the presence of the pump light 15, in addition to the transmitted probe light 52, the signal from the Raman cell 420 includes the inverse Raman signal 61, the coherent anti-Stokes Raman signal 62, the stimulated Raman signal 63, And so on. When these processes occur, the number of photons in the probe light changes, and the Raman active substance can be detected.

[0040]

Industrial Applicability According to the present invention, an extremely low noise optical measuring device can be realized, and it becomes possible to measure an extremely small amount of a substance and a weak change in optical properties.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an optical measuring device that has been conventionally used by the present inventors.

FIG. 2 is a diagram for explaining the principle of the device shown in FIG.

FIG. 3 is a diagram showing a configuration of an optical measuring device according to the present invention.

FIG. 4 is a diagram for explaining the principle of the device shown in FIG.

FIG. 5 is a diagram showing a configuration of a first exemplary embodiment of the present invention.

FIG. 6 is a diagram showing a configuration of a second exemplary embodiment of the present invention.

FIG. 7 is a diagram showing an example in which the present invention is applied to an apparatus for measuring the optical activity of a sample.

FIG. 8 is a diagram showing an example in which the present invention is applied to an apparatus for measuring the optical activity of a sample.

FIG. 9 is a diagram showing an example in which the present invention is applied to a detection device for a substance having Raman activity.

FIG. 10 is a diagram showing another embodiment in which the present invention is applied to a detection device for a substance having Raman activity.

[Explanation of symbols]

10 ... Laser light, 12 ... Pump light, 13 ... Mirror, 15
... second pump light, 16 ... intersection angle adjusting lens, 21 ...
Reference light, 22 ... probe light, 25 ... photon optical path of the wavelength lambda ₁ that has passed through the sample to be measured, 26 ... photon optical path of the wavelength lambda ₂ that has passed through the sample to be measured, 31 ... optical path, 32 ... polarizing beam splitter Photon of wavelength λ ₁ transmitted, 33 ... Photon of wavelength λ ₂ transmitted through polarization beam splitter, 41 ... Optical path,
43 ... Photon of wavelength λ ₂ reflected by the polarization beam splitter, 45 ... Light beam, 46 ... Light beam, 50 ... Probe light, 51 ... Transmission probe light, 52 ... Transmission probe light, 6
1 ... Inverse Raman signal, 62 ... Coherent anti-Stokes Raman signal, 63 ... Guided Raman signal.

Claims (1)

Claim: What is claimed is: 1. A light source, a first means for converting one photon emitted from the light source into a photon pair consisting of a first photon and a second photon, and the photon. The first photon passes through a pair of optical paths, and, for separating into a second optical path through which the first optical path for inserting a sample to be measured into the optical path and the second photon passes through. Second means, provided on the first optical path, third means for detecting the intensity of the light, and provided on the second optical path, for detecting the intensity of the light Fourth means, fifth means for canceling the quantum noise of the light source based on the output values of the third means and the fourth means, and the output value of the fifth means And an optical measuring device for measuring the optical characteristics of the sample to be measured based on the sixth means. Place 2. The optical measuring device according to claim 1, wherein the light source is a laser light source. 3. The optical measuring device according to claim 1, wherein the first means is a wavelength conversion element. 4. The optical measuring device according to claim 1, wherein the second means is a polarization beam splitter. 5. The optical measuring device according to claim 1, wherein the second means is a prism. 6. The optical measuring device according to claim 1, wherein the third means and the fourth means are photoelectric conversion elements. 7. The optical measuring device according to claim 1, wherein the fifth means has a subtraction function. 8. The fifth means, when I _R is an output value of the third means and I _P is an output value of the fourth means,
At least _{(I R -I P) / I} R or (I _R -I _P) /
The optical measurement device according to claim 1, wherein the optical measurement device has a calculation function of any one of (I _R + I _P ). 9. The optical measuring device according to claim 1, wherein the optical characteristic is measured by at least one of the following: (a) the sample to be measured is a gas, and Optical measurement of the concentration of a specific substance, (b) the measurement sample is an optical fiber, the measurement of the attenuation characteristics of light propagating in the optical fiber, (c) the measurement of the optical activity of the measurement sample , (D) measuring the concentration of a specific substance in the sample to be measured by detecting a magneto-optical effect among the optical activities of the sample to be measured, (e) optical measurement of a substance having Raman activity in the sample to be measured, Measurement for detection, (f) Measurement for detecting transmitted light of the Raman cell, wherein the sample to be measured is Raman cell. 10. The optical measuring device according to claim 1, wherein the sixth means is a data processing unit. 11. The sample to be measured is any one of a material gas used for semiconductor manufacturing, light propagating in an optical fiber, a gas containing dust and a substance having Raman activity. 1. The optical measuring device according to 1. 12. The optical measuring device according to claim 1, wherein a delay circuit is inserted in the second optical path. 13. The optical measuring device according to claim 1, further comprising a seventh means for applying a magnetic field to the sample to be measured. 14. The sample to be measured is a Raman cell, and signal selecting means is inserted in the first optical path between the Raman cell and the third means. The optical measurement device described. 15. A light source, a first means for converting one photon emitted from the light source into a photon pair consisting of a first mode photon and a second mode photon, and a photon pair of the photon pair. Second means for separating an optical path into a first optical path corresponding to the first mode and a second optical path through which the second photon passes, and provided on the first optical path, Third means for detecting the intensity of light, and a fourth means provided on the second optical path for detecting the intensity of the light,
A sample to be measured inserted on the optical path of the photon pair, and a fifth means for canceling the quantum noise of the light source based on the output value of each of the third means and the fourth means,
And a sixth means for measuring the optical characteristics of the sample to be measured based on the output value of the fifth means. 16. The optical measuring device according to claim 15, wherein the light source is a laser light source. 17. The optical measuring device according to claim 15, wherein the first means is a wavelength conversion element. 18. The optical measuring device according to claim 15, wherein the second means is a polarization beam splitter. 19. The optical measuring device according to claim 15, wherein the second means is a prism. 20. The optical measuring device according to claim 15, wherein the third means and the fourth means are photoelectric conversion elements. 21. The optical measuring device according to claim 15, wherein the fifth means has a subtraction function. 22. The fifth means, when I _R is an output value of the third means and I _P is an output value of the fourth means, at least (I _R −I _P ) / I _R or (I _R -I _P)
The optical measurement device according to claim 15, wherein the optical measurement device has a calculation function of either one of / (I _R + I _P ). 23. The optical measurement device according to claim 15, wherein the optical characteristic is measured by at least one of the following: (a) measurement of optical activity of the sample to be measured, (b) ) Measuring the concentration of a specific substance in the sample to be measured by detecting the magneto-optical effect of the optical activity of the sample to be measured, 24. The sixth means is a data processor. The optical measuring device according to claim 15. 25. The optical measuring device according to claim 15, wherein the sample to be measured is a substance having Raman activity. 26. The optical measuring device according to claim 15, wherein a delay circuit is inserted in the second optical path. 27. The optical measuring device according to claim 15, further comprising a seventh means for applying a magnetic field to the sample to be measured. 28. A single photon emitted from a light source is converted into a photon pair consisting of a first photon and a second photon, the first photon passing through the optical path of the photon pair, and the optical path thereof. Separated into a first optical path for inserting the sample to be measured and a second optical path through which the second photon passes, of the light by the first means provided on the first optical path. Detecting the intensity, detecting the intensity of the light by the second means provided on the second optical path, the output value of the intensity of each light detected by the first means and the second means A method of canceling the quantum noise of the light source based on the above, and the optical characteristic of the sample to be measured is measured based on the output value based on the processing. 29. A photon emitted from a light source is converted into a photon pair consisting of a photon of a first mode and a photon of a second mode, and the photon pair is made incident on a sample to be measured, and the photon is measured. The optical path of the photon pair emitted from the sample is separated into a first optical path corresponding to the first mode and a second optical path corresponding to the second mode, and is provided on the first optical path. By detecting the intensity of the light by the first means, by detecting the intensity of the light by the second means provided on the second optical path, each of the first means and the second means. An optical measuring method comprising: performing a process of canceling the quantum noise of the light source based on an output value, and measuring an optical characteristic of the sample to be measured based on the output value based on the process.