JP2014081345A - Sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high sensitive sensor.SOLUTION: The sensor has: a first signal source that outputs a first electromagnetic wave of frequency f1: a second signal source that outputs a second electromagnetic wave of frequency f2; a nonlinear optical crystal that allows the first electromagnetic wave output from the first signal source and the second electromagnetic wave output from the second signal source to enter; and a detector. The nonlinear optical crystal includes: a difference frequency emitting part that emits an electromagnetic wave of difference frequency f3 of the frequencies f1 and f2; a difference frequency incident part that allows the electromagnetic wave of difference frequency f3 to enter; a detection wave emitting section that emits the electromagnetic wave of frequency f2 to the detector. The first electromagnetic wave and the second electromagnetic wave allowed entering so as to interfere with each other inside the nonlinear optical crystal. The first electromagnetic wave and the electromagnetic wave of difference frequency f3 entering from the difference frequency incident part interfere with each other inside the nonlinear optical crystal. The resultant electromagnetic wave of frequency f2 is emitted from the detection wave emitting section.

Description

  The present invention relates to a sensor using, for example, a terahertz wave or near infrared light.

  Recently, development of sensors using a terahertz wave band or near-infrared light is in progress. For example, since there is vibrational excitation of molecules in these wavelength bands, terahertz waves and near-infrared light are reflected and transmitted to a target object, and the amount of absorption is measured. The composition can be examined.

  In order to realize such a sensor, a terahertz wave band and a near-infrared light generation circuit are important, and are being studied actively. Even in the case of terahertz waves, a number of generation circuits have been proposed so far, and among them, the terahertz waves can be generated easily and economically. The technology used is expected.

  In this technique, as shown in FIG. 6, the first laser beam L1 and the second laser beam L2 that are two coherent beams are incident on the nonlinear optical crystal 40, thereby generating a terahertz wave corresponding to the difference frequency. Is. Cherenkov phase matching is used as the phase matching required to generate the difference frequency. This matching method is applied when the thickness of the difference frequency nonlinear optical crystal 40 is less than half the wavelength of two incident coherent lights. This is because the light incident in the nonlinear optical crystal 40 can be regarded as a photon (charged particle). Phase matching is established by using the nonlinear optical crystal 40 having a refractive index dispersion such that the propagation speed of the photon in the crystal is slower than that of the difference frequency. By installing an optical element sufficiently thicker than the difference frequency on the nonlinear optical crystal 40, a terahertz wave is emitted.

  Since this sensor structure uses incident light of two waves, it is used as a light source for exciting a wavelength band from a terahertz wave band to a near infrared light band, which is difficult to realize with a semiconductor laser.

  The excited light source irradiates the object, detects the reflected / transmitted light with a bolometer, and measures the amount of absorption in the object, thereby examining the composition of the object in a non-destructive manner.

JP 2010-204488 A

  However, the conventional sensor has a problem that the sensitivity deteriorates due to noise generated from a heat source or the like existing in the vicinity of the bolometer.

  In order to achieve this object, the sensor of the present invention outputs a first signal source that outputs a first electromagnetic wave having a frequency f1, a second signal source that outputs a second electromagnetic wave having a frequency f2, and an output from the first signal source. A nonlinear optical crystal on which both the first electromagnetic wave and the second electromagnetic wave output from the second signal source are incident, and a detector, and the nonlinear optical crystal has an electromagnetic wave having a difference frequency f3 between frequencies f1 and f2. A difference frequency radiating section that radiates an electromagnetic wave having a difference frequency f3, and a detection wave radiating section that radiates an electromagnetic wave having a frequency f2 to the detector. Is incident so as to interfere inside the nonlinear optical crystal, and the first electromagnetic wave and the electromagnetic wave having the difference frequency f3 incident from the difference frequency incident portion interfere inside the nonlinear optical crystal, and the electromagnetic wave having the frequency f2 generated as a result thereof. Detected wave Characterized in that it is emitted from the parts.

  The sensor of the present invention does not employ a configuration in which the electromagnetic wave of the difference frequency f3 irradiated and reflected and scattered directly to the measurement object is directly measured by the detector, and once incident on the nonlinear optical crystal, the electromagnetic wave having the frequency f1. Is converted into an electromagnetic wave having a frequency f2, and the electromagnetic wave having the frequency f2 is measured by a detector. As a result, noise having an incoherent property generated from a heat source or the like is not converted into an electromagnetic wave having a frequency f2 in the nonlinear optical crystal, so that a highly sensitive sensor can be realized.

The perspective development view of the sensor of the present invention Sectional view of the sensor of the present invention Sectional view of the sensor of the present invention Sectional view of the sensor of the present invention Sectional view of the sensor of the present invention Sectional view of the sensor of the present invention Sectional view of the sensor of the present invention Sectional view of the sensor of the present invention Vector diagram representing the optical parametric effect of FIG. Vector diagram representing the optical parametric effect of FIG. The perspective development view of the sensor of the present invention Sectional view of the sensor of the present invention The perspective development view of the sensor of the present invention Sectional view of the sensor of the present invention Cross section of conventional sensor

(Embodiment 1)
Hereinafter, the sensor of the present invention according to Embodiment 1 will be described with reference to FIGS. 1a, 1b, and 1c. 1A and 1B, the sensor 1 of the present invention includes a first signal source 34 that outputs an electromagnetic wave having a frequency f1 (first electromagnetic wave) and a second signal source 35 that outputs an electromagnetic wave having a frequency f2 (second electromagnetic wave). And a second-order nonlinear optical crystal 12 to which electromagnetic waves having two frequencies f1 and f2 are input from the input unit 11, and a detector 16. Further, the nonlinear optical crystal 12 irradiates a measurement object (not shown) with a difference frequency radiation unit 13 that radiates an electromagnetic wave having a difference frequency f3 between the frequencies f1 and f2, and an electromagnetic wave radiated from the difference frequency radiation unit 13. As a result, there are provided a difference frequency incident part 14 into which the reflected electromagnetic wave of the difference frequency f3 is incident and a detection wave radiating part 15 that radiates the electromagnetic wave of the frequency f2 to the detector 16. Further, the first electromagnetic wave and the second electromagnetic wave are incident so as to interfere inside the nonlinear optical crystal 12, and the first electromagnetic wave and the electromagnetic wave having the difference frequency f 3 incident from the difference frequency incident unit 14 are The electromagnetic wave having the frequency f2 resulting from the interference inside is radiated from the detection wave radiating unit 15 and is incident on the detector 16.

  The input unit 11 refers to a region where the first electromagnetic wave and the second electromagnetic wave are input on the surface of the nonlinear optical crystal 12. The difference frequency radiating unit 13 refers to a region on the surface of the nonlinear optical crystal 12 where an electromagnetic wave having a difference frequency f3 generated by interference between the first electromagnetic wave and the second electromagnetic wave is radiated. Further, the difference frequency incident portion 14 refers to a region on the surface of the nonlinear optical crystal 12 where an electromagnetic wave having the difference frequency f3 reflected from the measurement object is incident. The detection wave radiating portion 15 is an electromagnetic wave (detection wave) having a difference frequency f2 generated by interference between the first electromagnetic wave and the electromagnetic wave having the difference frequency f3 incident from the difference frequency incident portion 14 on the surface of the nonlinear optical crystal 12. ) Indicates the radiated area. The input unit 11, the difference frequency radiation unit 13, the difference frequency incidence unit 14, and the detection wave radiation unit 15 may be arranged so as not to overlap on the surface of the nonlinear optical crystal.

  Next, operation | movement of the sensor 1 of this invention which concerns on Embodiment 1 is demonstrated using FIG. 1b. In the sensor 1, electromagnetic waves having two frequencies f 1 and f 2 are input from the input unit 11 to the nonlinear optical crystal 12. Here, the electromagnetic waves of two frequencies f1 and f2 incident on the input unit 11 are electromagnetic waves that are coherent with each other.

  For example, the two frequencies f1 and f2 may be selected so that the frequency difference | f1-f2 | between the two frequencies f1 and f2 is 1 THz or more.

  In FIG. 1b, the first electromagnetic wave of frequency f1 and the second electromagnetic wave of frequency f2 are incident inside the nonlinear optical crystal 12 so as to intersect and interfere at an angle θ2. In FIG. 1 b, the first electromagnetic wave is incident perpendicularly to the surface of the input unit 11, and the second electromagnetic wave is incident on the input unit 11 by being tilted by the incident angle φ with respect to the first electromagnetic wave.

  Since both the first electromagnetic wave of frequency f1 and the second electromagnetic wave of frequency f2 have coherent properties, signal light and idler light are generated inside the second-order nonlinear optical crystal 12 by an optical parametric effect based on nonlinear optical theory. . In the present invention, idler light is called an electromagnetic wave having a difference frequency f3. Since only the coherent light can use the optical parametric effect, the incoherent light made up of sunlight or a fluorescent lamp does not affect the difference frequency generation. That is, in the sensor 1 of the present invention, these noise sources can be removed.

  Specifically, if the angular frequencies of the electromagnetic waves having the two frequencies f1 and f2 are ω1 and ω2, the angular frequency ω3 of the generated difference frequency f3 is determined by (Equation 1) indicating an energy conservation law. The difference frequency f3 also indicates an electromagnetic wave that is coherent.

Here, h represents a Planck constant.

  The direction in which the generated difference frequency f3 is radiated is determined by (Equation 2) indicating the momentum conservation law using the wave number vectors k1, k2, and k3 of f1, f2, and f3.

  Thus, as shown in FIG. 3a, the radiation angle θ1 of the generated electromagnetic wave having the difference frequency f3 with respect to the second electromagnetic wave (assuming f1> f2) can be obtained by (Equation 3).

Here, θ2 is an angle formed by the first electromagnetic wave and the second electromagnetic wave propagating in the nonlinear optical crystal.

  Here, the first electromagnetic wave of frequency f1 is called excitation light, and the second electromagnetic wave of frequency f2 is called seed light.

  When the excitation light having the frequency f1 and the seed light having the frequency f2 intersect and interfere with each other inside the nonlinear optical crystal 12, idler light having a difference frequency f3 is generated and emitted in the direction of the angle θ1 formed with the seed light.

  For example, by selecting a laser diode in the visible light band as the first signal source 34 and the second signal source 35, an electromagnetic wave having a difference frequency f3 from the terahertz wave band to the near infrared light can be easily generated at low cost. it can. For example, if f1 is 633.8 THz (wavelength: 473 nm) and f2 is 614 THz (wavelength: 488 nm), f3 is a 19.5 THz (wavelength: 15.4 μm) terahertz wave band, and f1 is 800 THz (wavelength). : 375 nm) and f2 is 582 THz (wavelength: 515 nm), f3 becomes near infrared light of 222 THz (wavelength: 1350 nm).

  The electromagnetic wave having the difference frequency f <b> 3 generated inside the nonlinear optical crystal 12 is radiated to the outside of the nonlinear optical crystal 12 from the difference frequency radiating unit 13. The electromagnetic wave having the difference frequency f3 radiated to the outside of the nonlinear optical crystal 12 is irradiated onto the measurement object, enters the measurement object, and is reflected. At this time, a part of the electromagnetic wave having the difference frequency f3 is absorbed by the measurement object, but the amplitude of the electromagnetic wave having the difference frequency f3 reflected according to the amount of absorption decreases. Information on the measurement object can be acquired based on the amount of decrease in the amplitude of the electromagnetic wave having the difference frequency f3.

  The electromagnetic wave having the difference frequency f3 reflected by the measurement object is incident on the nonlinear optical crystal from the difference frequency incident portion 14 of the nonlinear optical crystal 12. The incident electromagnetic wave having the difference frequency f3 becomes the seed light, the first electromagnetic wave having the frequency f1 becomes the excitation light, and the idler light having the difference frequency f4 is detected in the region in the nonlinear optical crystal 12 where the two electromagnetic waves intersect and interfere with each other. As a new generation. At this time, the information on the measurement object held by the electromagnetic wave having the difference frequency f3 serving as the seed light is inherited by the generated idler light having the difference frequency f4. That is, the amplitude of the detection wave of the difference frequency f4 is also reduced according to the amount of decrease of the amplitude that the electromagnetic wave of the difference frequency f3 has received by the measurement object. This detection wave is radiated from the detection wave radiating section 15 and detected by the detector 16, and information on the measurement object is acquired from the amplitude change.

  Note that the frequency f4 of the detection wave indicates the same frequency as the frequency f2 of the second electromagnetic wave incident on the nonlinear optical crystal 12. That is, f2 = f4.

  For example, when a first electromagnetic wave having a frequency f1 is supplied by a laser diode in the visible light band (corresponding to the first signal source 34), by selecting a terahertz wave or near infrared light as the difference frequency f3, the difference frequency f4 is Visible light band. If the detection wave can be set to be in the visible light band, the detector 16 can be realized with only a photodiode, and information on the measurement object can be obtained at a low cost. Further, the detection wave is dispersed using a spectroscope corresponding to the frequency band near the frequency f4, and each of the separated light is analyzed, so that the measurement object can be detected with higher accuracy than the detection method using the photodiode described above. Information can be obtained. For example, if f1 is 633.8 THz (wavelength: 473 nm) and f3 is a terahertz wave of 19.5 THz (wavelength: 15.4 μm), f4 is a visible light band of 614 THz (wavelength: 488 nm). Further, when f1 is 800 THz (wavelength: 375 nm) and f3 is near-infrared light of 222 THz (wavelength: 1350 nm), f4 is a visible light band of 582 THz (wavelength: 515 nm).

  Only when two electromagnetic waves input to the nonlinear optical crystal 12 are coherent, an electromagnetic wave having a difference frequency between these electromagnetic waves can be generated. Therefore, incoherent light such as sunlight or a fluorescent lamp that is a noise source is different. It does not affect the generation of frequency electromagnetic waves. That is, the detection wave f4 (= f2) generated inside the nonlinear optical crystal 12 has information on the measurement object without being affected by external noise, and a highly sensitive sensor is realized. be able to.

  Since the frequency f4 of the detection wave is the same frequency as the frequency f2 of the second electromagnetic wave incident on the nonlinear optical crystal 12, the detection wave radiating unit 15 has the second electromagnetic wave to prevent the both electromagnetic waves from being mixed. It is good also as a structure which is not installed on a propagation axis (on an optical axis when electromagnetic waves are light). Thereby, it can prevent that the 2nd electromagnetic wave is radiated | emitted from the detection wave radiation | emission part 15, and the detection accuracy of the detection wave in the detector 16 can be improved. Similarly, since the frequency band near the frequency f4 of the detection wave may be selected for the first electromagnetic wave having the frequency f1, the detection wave radiation unit 15 may not be installed on the propagation axis of the first electromagnetic wave. Also in this case, the detection accuracy of the detection wave at the detector 16 can be improved.

  In addition, when the detection wave radiation | emission part 15 is arrange | positioned on the propagation axis of the 2nd electromagnetic wave which injected into the nonlinear optical crystal 12, since the energy of a 2nd electromagnetic wave overlaps with the detection wave of the difference frequency f4, it detects. It is desirable to correct the offset by the energy of the second electromagnetic wave in the device 16. In this case, the magnitude of the second electromagnetic wave input to the detector 16 may be grasped in advance.

  As shown in FIG. 1 c, at least a partial region around the nonlinear optical crystal 12 or at least a partial region around the detector 16 may have a structure covered with a light shielding material 17. By doing so, the influence of noise coming from the periphery of the nonlinear optical crystal 12 and the detector 16 can be suppressed, and a highly sensitive sensor can be realized.

  The sensor 1 according to the first embodiment has a structure in which the input unit 11, the difference frequency radiating unit 13, the difference frequency incident unit 14, and the detection wave radiating unit 15 are integrated, thereby reducing the size of the sensor. In addition, it is possible to realize a small and highly sensitive sensor without being affected by noise such as a heat source or sunlight.

  As shown in FIG. 1d, the electromagnetic wave having the frequency f3 is reflected on the surface of the nonlinear optical crystal 12 where the difference frequency radiating portion 13 that radiates the difference frequency f3 and the difference frequency incident portion 14 that the difference frequency f3 enters are opposed to each other. A reflective film 18 may be applied. Thereby, it is possible to reflect the coherent noise incident on the nonlinear optical crystal 12 from the side where the reflective film 18 is disposed, and to avoid deterioration of the sensitivity of the sensor 1. In this case, as shown in FIG. 1d, the distance d from the region where the first electromagnetic wave having the frequency f1 incident on the nonlinear optical crystal 12 and the second electromagnetic wave having the frequency f2 intersect to the reflection film 18 is the difference frequency f3. It is good also as a structure which satisfy | fills (Formula 4) with respect to wavelength (lambda) 3 of this.

Where θ2 <θ3
By satisfying (Equation 4), the phase of the electromagnetic wave having the frequency f3 directly directed to the difference frequency radiating unit 13 and the phase of the electromagnetic wave once reflected by the reflective film 18 and directed to the difference frequency radiating unit 13 are substantially in phase. Therefore, the output of the electromagnetic waves having the difference frequency can be increased.

  Further, as shown in FIG. 1d, a configuration may be adopted in which the reflective film 18 is not disposed on the propagation axis of the electromagnetic wave of f2 that is the seed light. Thereby, it is possible to prevent the seed light from being reflected by the reflection film 18 and input from the detection wave radiating unit 15 to the detector 16 and deteriorating the sensitivity of the sensor 1.

  The spot diameter of the electromagnetic wave having the frequency f2 incident on the nonlinear optical crystal 12 may be larger than the spot diameter of the electromagnetic wave having the frequency f1. Since the energy density can be increased when the spot diameter of the electromagnetic wave having the frequency f1 as excitation light is small, the electromagnetic wave having the difference frequency f3 can be efficiently generated. Moreover, it becomes easy to make it cross | intersect with excitation light by expanding the spot diameter of the electromagnetic wave of the frequency f2 which is seed light.

(Embodiment 2)
Hereinafter, the sensor of the present invention according to Embodiment 2 will be described with reference to FIGS. 2A and 2B. The sensor 20 of the present invention according to Embodiment 2 includes a first signal source 34 that outputs a first electromagnetic wave having a frequency f11, a second signal source 35 that outputs a second electromagnetic wave having a frequency f12, and a first signal source 34. A first nonlinear optical crystal 22 in which both the first electromagnetic wave output from the second electromagnetic wave and the second electromagnetic wave output from the second signal source 35 are incident from the input unit 21, and a measurement cell in contact with the first nonlinear optical crystal 22 ( A measurement region) 24, a second nonlinear optical crystal 26 in contact with the measurement region 24, and a detector 16. Further, the first nonlinear optical crystal 22 includes a difference frequency radiating unit 23 that radiates an electromagnetic wave having a difference frequency f13 between the frequencies f11 and f12 to the measurement cell 24, and the second nonlinear optical crystal 26 transmits an electromagnetic wave having the difference frequency f13. An incident difference frequency incident unit 25, an f11 electromagnetic wave incident unit 29 that receives an electromagnetic wave with a frequency f11, and a detection wave radiation unit 27 that radiates an electromagnetic wave with a frequency f12 to the detector 16 are provided. Then, the first electromagnetic wave and the second electromagnetic wave are incident so as to interfere inside the first nonlinear optical crystal 22, and are incident from the electromagnetic wave having the frequency f 11 incident from the f 11 electromagnetic wave incident part 29 and from the difference frequency incident part 25. The electromagnetic wave having the difference frequency f13 interferes with the inside of the second nonlinear optical crystal 26, and the electromagnetic wave having the frequency f12 generated as a result is radiated from the detection wave radiating unit 27. A reflective plate 28 may be disposed on a part or all of the bottom surface of the measurement cell 24. As a result, the excitation light emitted from the first signal source 34 can be reflected by the reflecting plate 28 and incident on the second nonlinear optical crystal 26, so that the sensor 20 can be realized with one excitation light source. .

  Next, the operation of the sensor of the present invention according to Embodiment 2 shown in FIGS. 2a and 2b will be described. In the sensor 20, electromagnetic waves having two frequencies f <b> 11 and f <b> 12 are input from the input unit 21 to the second-order first nonlinear optical crystal 22. Here, the electromagnetic waves having the two frequencies f11 and f12 irradiated to the input unit 21 are electromagnetic waves having coherent properties. For example, the two frequencies f11 and f12 may be selected so that the frequency difference | f11−f12 | between the two frequencies f11 and f12 is 1 THz or more.

  In FIG. 2b, electromagnetic waves having two frequencies f11 and f12 are incident on the input unit 21 of the sensor 20 so that the angle formed by f11 and f12 is θ3. Since the two input frequencies f11 and f12 have both coherent properties, signal light and idler light are generated inside the second-order first nonlinear optical crystal 22 by an optical parametric effect based on nonlinear optical theory. Here, the idler light is called the difference frequency f13. Since only the coherent light can use the optical parametric effect, the incoherent light made up of sunlight or a fluorescent lamp does not affect the difference frequency generation. That is, these noise sources can be removed, and a highly sensitive sensor can be realized.

  Specifically, when the angular frequencies of the electromagnetic waves having the two frequencies f11 and f12 are ω11 and ω12, the angular frequency ω13 of the electromagnetic waves having the difference frequency f13 to be generated is determined by Equation (5) indicating an energy conservation law. The electromagnetic wave having the difference frequency f13 is also coherent.

Here, h represents a Planck constant.

  Further, the direction in which the generated electromagnetic wave having the difference frequency f13 is radiated is determined by (Equation 6) indicating the momentum conservation law using the wave number vectors k11, k12, and k13 of f11, f12, and f13.

  From this, as shown in FIG. 3b, the radiation angle θ3 formed by the electromagnetic wave having the difference frequency f13 and the electromagnetic wave having the frequency f12 can be obtained by (Equation 7).

Here, θ4 is an angle formed by incident waves f11 and f12 propagating in the nonlinear optical crystal.

  The idler light having the difference frequency f13 is generated by the excitation light having the frequency f11 and the seed light having the frequency f12, and is emitted at an angle θ3 formed with the electromagnetic wave having the frequency f12.

  For example, by selecting a laser diode in the visible light band as the signal source of f11 and f12, an electromagnetic wave having a difference frequency f13 from the terahertz wave band to the near infrared light can be generated. For example, if f11 is 633.8 THz (wavelength: 473 nm) and f12 is 614 THz (wavelength: 488 nm), f13 is a 19.5 THz (wavelength: 15.4 μm) terahertz wave band, and f11 is 800 THz (wavelength). : 375 nm), and f12 is 582 THz (wavelength: 515 nm), f13 becomes 222 THz (wavelength: 1350 nm) near infrared light.

  The radiated electromagnetic wave having the difference frequency f <b> 13 is radiated from the difference frequency radiating unit 23 to the outside of the first nonlinear optical crystal 22. The electromagnetic wave having the difference frequency f13 radiated to the outside of the first nonlinear optical crystal 22 passes through the measurement cell 24.

  At this time, a part of the electromagnetic wave having the difference frequency f13 is absorbed by the measurement object filled in the measurement cell 24, but the amplitude of the electromagnetic wave having the difference frequency f13 reflected / transmitted is reduced according to the amount of absorption. . Information on the measurement object can be acquired based on the amount of decrease in the amplitude of the electromagnetic wave having the difference frequency f13.

  The electromagnetic wave having the difference frequency f13 may be vertically incident on the difference frequency radiating portion 23 of the first nonlinear optical crystal 22 from the inside of the first nonlinear optical crystal 22. Thereby, the propagation distance of the electromagnetic wave of the difference frequency f13 in the measurement cell 24 can be shortened, and a sensor that operates even when the output energy of the signal source is small can be realized.

  Moreover, you may implement the reflecting plate 28 in the partial surface (surface other than the area | region where the input part 21 and the difference frequency radiation | emission part 23 are arrange | positioned) of the 1st nonlinear optical crystal 22. FIG. In this case, the distance t from the point at which the electromagnetic wave having the difference frequency f13 shown in FIG. 2b is generated to the reflecting plate is equal to the wavelength λ13 having the difference frequency f13 from the intersection of the electromagnetic wave having the frequency f11 and the electromagnetic wave having the frequency f12. If the angle formed by the electromagnetic wave of the difference frequency f13 is β (not shown)

It is desirable to satisfy. By doing so, the phase of the electromagnetic wave of the difference frequency f13 directed directly to the difference frequency radiating unit 23 and the phase of the electromagnetic wave of the difference frequency f13 reflected by the reflector 28 and directed to the difference frequency radiating unit 23 are in phase and strengthened. The output of the electromagnetic wave having the difference frequency f13 can be increased.

  One of the electromagnetic waves incident from the input unit 21, here, the electromagnetic wave having the frequency f <b> 11, but the electromagnetic wave having the frequency f <b> 11 is radiated to the measurement cell 24 similarly to the electromagnetic wave having the difference frequency f <b> 13. The emitted electromagnetic wave having the frequency f11 is totally reflected by the reflector 28 provided on the bottom surface of the measurement cell 24 and is incident on the second nonlinear optical crystal 26. A part of the electromagnetic wave having the frequency f11 is absorbed by the measurement object arranged in the measurement cell 24 while propagating through the measurement cell 24. The amount of absorption is larger than that of the electromagnetic wave having the difference frequency f13. Very small. For this reason, it can be utilized as excitation light even in the second nonlinear optical crystal.

  The input unit 21 prevents the electromagnetic wave having the frequency f12 from being radiated to the outside of the first nonlinear optical crystal 22, that is, the electromagnetic wave having the frequency f12 reaching the surface from the inside of the first nonlinear optical crystal 22 is totally reflected. The incident angle of the electromagnetic wave having the frequency f12 may be set optimally. In addition, a member that reflects an electromagnetic wave having a frequency f12 may be disposed on the surface of the first nonlinear optical crystal 22. Thereby, it is possible to avoid the electromagnetic wave having the frequency f12 propagating inside the first nonlinear optical crystal 22 from reaching the detector 16, and a highly sensitive sensor can be realized.

  The measurement cell 24 may be configured to be detachable. As a result, only the measurement cell 24 can be cleaned and replaced, and a sensor that facilitates measurement work can be realized.

  The electromagnetic wave having the difference frequency f13 transmitted through the measurement cell 24 is incident on the second nonlinear optical crystal 26 from the difference frequency incident portion 25 of the second nonlinear optical crystal 26. The electromagnetic wave having the frequency f11 incident from the f11 electromagnetic wave incident portion functions as excitation light, and the electromagnetic wave having the difference frequency f13 incident in the second nonlinear optical crystal 26 functions as seed light. By making these two electromagnetic waves intersect and interfere with each other, idler light that is an electromagnetic wave having a difference frequency f14 is newly generated as a detection wave. At this time, information on the measurement object held by the electromagnetic wave having the difference frequency f13 serving as the seed light is passed on to the newly generated idler light f14. That is, the amplitude of the detection wave of the difference frequency f14 is also reduced according to the amount of decrease of the amplitude that the electromagnetic wave of the difference frequency f13 has received by the measurement object.

  Here, the frequency of the detection wave having the difference frequency f14 is the same as that of the electromagnetic wave having the frequency f12 incident on the first nonlinear optical crystal 22. That is, frequency f12 = frequency f14.

  For example, by selecting a laser diode in the visible light band for f11 and selecting a terahertz wave or near-infrared light for f13, f14 in the visible light band is generated. For example, if f11 is 633.8 THz (wavelength: 473 nm) and f13 is a terahertz wave of 19.5 THz (wavelength: 15.4 μm), f14 is a visible light band of 614 THz (wavelength: 488 nm), and f11 is 800 THz. (Wavelength: 375 nm) When f13 is 222 THz (wavelength: 1350 nm) near infrared light, f14 becomes a visible light band of 582 THz (wavelength: 515 nm).

  Here, in the inside of the second nonlinear optical crystal 26, unless two lights (electromagnetic waves) having coherent properties are used, light having a difference frequency between them cannot be generated. The influence of incoherent light can be eliminated. Thereby, a highly sensitive sensor can be realized.

  Since the frequency f14 of the detection wave is the same as the frequency f12 of the second electromagnetic wave incident on the first nonlinear optical crystal 22, the detection wave radiating unit 27 has the second frequency in order to prevent both electromagnetic waves from being mixed. It is good also as a structure which is not installed on the propagation axis of electromagnetic waves (on the optical axis when electromagnetic waves are light). Thereby, it can prevent that the 2nd electromagnetic wave is radiated | emitted from the detection wave radiation | emission part 27, and the detection accuracy of the detection wave in the detector 16 can be improved. Similarly, since the frequency band near the frequency f14 of the detection wave may be selected for the first electromagnetic wave having the frequency f11, the detection wave radiation unit 27 may not be installed on the propagation axis of the first electromagnetic wave. Also in this case, the detection accuracy of the detection wave at the detector 16 can be improved.

  For example, when a first electromagnetic wave having a frequency f11 is supplied by a laser diode (corresponding to the first signal source 34) in the visible light band, by selecting a terahertz wave or near infrared light as the difference frequency f13, the difference frequency f14 is Visible light band. If the detection wave can be set to be in the visible light band, the detector 16 can be realized with only a photodiode, and information on the measurement object can be obtained at a low cost. Further, the detection wave is dispersed using a spectroscope corresponding to a frequency band near the frequency f14, and each of the separated light is analyzed, so that the measurement object can be detected with higher accuracy than the detection method using the photodiode described above. Information can be obtained.

  Note that, as shown in FIG. 2c, at least a partial region around the second nonlinear optical crystal 26 or at least a partial region around the detector 16 may be covered with a light shielding material 31. Good. By doing so, the influence of noise coming from the second nonlinear optical crystal 26 and the detector 16 can be suppressed, and a highly sensitive sensor can be realized.

  As described above, the sensor of the present invention has a structure in which the input unit and the difference frequency radiating unit, and the difference frequency incident unit and the detection wave radiating unit are integrated with each other. A small and highly sensitive sensor can be realized without being affected by noise such as sunlight.

  In FIG. 2b, the reflection plate 28 is provided in the measurement cell 24, but the sensor may be realized by a configuration in which the reflection plate is not provided in the measurement cell 24 but is provided below the measurement cell 24. Thereby, the cost of the measurement cell 24 itself can be reduced, and the measurement cell 24 can be disposable.

  As shown in FIG. 2d, electromagnetic waves may be reflected using total reflection mirrors 32 and 33 arranged outside the measurement cell 24 instead of the reflector 28 arranged in the measurement cell 24. In this case, the electromagnetic wave having the frequency f11 or the electromagnetic wave having the frequency f12 transmitted through the first nonlinear optical crystal 22 is reflected by the total reflection mirrors 32 and 33, and can be incident on the second nonlinear optical crystal 26. Thereby, attenuation of the electromagnetic wave of the frequency f11 or the electromagnetic wave of the frequency f12 by the measurement cell 24 can be prevented, and the measurement object can be detected with high accuracy.

  The spot diameter of the electromagnetic wave having the frequency f12 incident on the first nonlinear optical crystal 22 may be larger than the spot diameter of the electromagnetic wave having the frequency f11. Since the energy density can be increased if the spot diameter of the electromagnetic wave having the frequency f11 as excitation light is small, the electromagnetic wave having the difference frequency f13 can be generated efficiently. Moreover, it becomes easy to make it cross | intersect with excitation light by expanding the spot diameter of the electromagnetic wave of the frequency f12 which is seed light.

(Embodiment 3)
Hereinafter, the sensor of the present invention according to Embodiment 3 will be described with reference to FIGS. 4a, 4b, 5a, and 5b. 4a and 4b, a sensor 30 according to the third embodiment of the present invention includes a first signal source 34 that outputs a first electromagnetic wave having a frequency f1, and a second signal source 35 that outputs a second electromagnetic wave having a frequency f2. And the nonlinear optical crystal 12 on which the first electromagnetic wave output from the first signal source 34 and the second electromagnetic wave output from the second signal source 35 are incident, and the detector 16. The nonlinear optical crystal 12 includes a difference frequency radiating unit 13 that radiates an electromagnetic wave having a difference frequency f3 between the frequencies f1 and f2, a difference frequency incident unit 14 that makes an electromagnetic wave having the difference frequency f3 incident thereon, and an electromagnetic wave having the frequency f2 as a detector. 16 and a detection wave radiating unit 15 radiating to 16. Furthermore, the sensor 30 according to the third embodiment includes a first reflective film 37 that is disposed on an outer region of the nonlinear optical crystal 12 on the propagation path of the first electromagnetic wave and reflects the first electromagnetic wave, and the first reflective film. After being reflected at 37, the first electromagnetic wave is disposed on the propagation path of the first electromagnetic wave that propagates through the inner region of the nonlinear optical crystal 12 and is radiated to the outer region, and in the outer region of the nonlinear optical crystal 12, and reflects the first electromagnetic wave. And a second reflective film 38 for allowing the first electromagnetic wave to enter the nonlinear optical crystal 12 again. The first electromagnetic wave and the second electromagnetic wave are nonlinear optically reflected from the first signal source 34 and the second signal source 35, respectively, taking into consideration the reflection angles at the first reflective film 37 and the second reflective film 38, respectively. Incident light is incident so as to interfere in the inner region of the crystal 12. In addition, the first electromagnetic wave and the electromagnetic wave having the difference frequency f3 incident from the difference frequency incidence unit 14 interfere in the inner region of the nonlinear optical crystal 12 (the first signal source 34 and the second signal source 35 so as to interfere with each other). The first reflection film 37, the second reflection film 38, and the like are disposed), and the electromagnetic wave having the frequency f2 generated as a result is radiated from the detection wave radiating unit 15.

  The electromagnetic wave having the frequency f1 radiated from the first signal source 34 enters the nonlinear optical crystal 12, propagates through the inner region of the nonlinear optical crystal 12, and is then emitted from the nonlinear optical crystal 12 to the outer region. The emitted electromagnetic wave having the frequency f1 is reflected by the first reflecting film 37 and then enters the internal region of the nonlinear optical crystal 12 again. The incident electromagnetic wave having the frequency f1 again propagates through the inner region of the second-order nonlinear optical crystal 12, and is then emitted again to the outer region and reflected by the second reflecting film 38. The electromagnetic wave having the frequency f1 reflected by the second reflective film 38 is incident again on the nonlinear optical crystal 12, and the above-described operation is repeated. By repeating this series of operations, the electromagnetic wave having the frequency f1 causes multiple reflection between the first reflective film 37 and the second reflective film 38 with the secondary nonlinear optical crystal 12 interposed therebetween. As a result, a standing wave of the electromagnetic wave having the frequency f1 is generated in the inner region of the nonlinear optical crystal 12. Thereby, even if the signal output of the first signal source 34 that radiates the electromagnetic wave having the frequency f1 is small, the electric field strength of the electromagnetic wave having the frequency f1 in the inner region of the nonlinear optical crystal 12 is enhanced. Twelve nonlinearities can be excited.

  In addition, since the electromagnetic wave having the frequency f1 is efficiently reflected by the reflection films 37 and 38 and is incident on the second-order nonlinear optical crystal 12, the cross-sectional area of the reflection films 37 and 38 is the cutoff of the second-order nonlinear optical crystal 12. It may be larger than the area. Furthermore, the reflective surfaces of the reflective films 37 and 38 may have a concave structure.

  4a and 4b, the first signal source 34 is arranged on the propagation path of the first electromagnetic wave that is multiple-reflected between the first reflective film 37 and the second reflective film 38. However, there is no need to be constrained by such an arrangement, and the first reflection film 37 and the second reflection film 38 are multiplexed using the refraction angle when the first electromagnetic wave is incident on the nonlinear optical crystal 12. It is good also as a structure which does not arrange | position the 1st signal source 34 on the propagation path of the 1st electromagnetic wave to reflect. This prevents the first electromagnetic wave from being scattered and attenuated by the first signal source 34. Moreover, it can prevent that the 1st signal source 34 fails by irradiating the 1st electromagnetic wave to the 1st signal source 34. FIG.

  5a and 5b, a part of the first electromagnetic wave is disposed between the first signal source 34 and the nonlinear optical crystal 12 and at least on the propagation path of the first electromagnetic wave (electromagnetic wave having the frequency f1). Alternatively, a configuration may be adopted in which a transmissive film 36 that transmits light and reflects part of the light is disposed. Here, the first electromagnetic wave (electromagnetic wave having the frequency f1) radiated from the first signal source 34 is incident on the nonlinear optical crystal 12 through the transmission film 36.

  At this time, the permeable film 36 is designed not to transmit the entire energy of the first electromagnetic wave but to transmit only a part of the energy. As an example of the transmission amount, a transmission amount range of about 20 to 80% can be assumed.

  The electromagnetic wave having the frequency f1 (first electromagnetic wave) transmitted through the transmission film 36 is incident on the nonlinear optical crystal 12, propagates through the inner region of the nonlinear optical crystal 12, and is then emitted from the nonlinear optical crystal 12 to the outer region. . The emitted electromagnetic wave having the frequency f1 is reflected by the first reflecting film 37 and then enters the internal region of the nonlinear optical crystal 12 again. The incident electromagnetic wave having the frequency f1 passes through the second-order nonlinear optical crystal 12 and enters the transmission film 36. In the transmissive film 36, a part of the energy of the electromagnetic wave having the frequency f <b> 1 is reflected and input again to the secondary nonlinear optical crystal 12 through the input unit 11. By repeating this series of operations, the electromagnetic wave having the frequency f1 causes multiple reflection between the transmission film 36 and the reflection film 37 with the secondary nonlinear optical crystal 12 interposed therebetween. As a result, a standing wave of the electromagnetic wave having the frequency f1 is generated in the inner region of the nonlinear optical crystal 12. Thereby, even if the output of the first signal source 34 that radiates the electromagnetic wave having the frequency f1 is small, the electric field strength of the electromagnetic wave having the frequency f1 in the inner region of the nonlinear optical crystal 12 is between the transmission film 36 and the reflection film 37. Therefore, the nonlinearity of the second-order nonlinear optical crystal 12 can be excited. At this time, in order to efficiently reflect the electromagnetic wave having the frequency f1 and enter the second-order nonlinear optical crystal 12, the cross-sectional area of the transmission film 36 is larger than that of the second-order nonlinear optical crystal 12. Also good. Further, the permeable membrane 36 may have a concave structure. 5a and 5b, the first signal source 34 does not have to be disposed on the propagation path of the electromagnetic wave having the frequency f1 that is multiply reflected between the transmission film 36 and the first reflection film 37. For this reason, it is possible to avoid the electromagnetic wave having the frequency f1 from being scattered and attenuated by the first signal source 34, and it is possible to prevent the electromagnetic wave having the frequency f1 from being irradiated to the first signal source 34 and failing.

  In addition, a part of the first electromagnetic wave emitted from the first signal source 34 and incident on the transmission film 36 is reflected by the transmission film 36 toward the first signal source 34 side. One signal source 34 may be reflected by the second reflective film 38 and input to the nonlinear optical crystal 12 through the transmissive film 36 again. Thereby, a standing wave of the first electromagnetic wave is generated in the inner region of the nonlinear optical crystal 12, and the first electromagnetic wave can be enhanced. Thereby, the nonlinearity of the nonlinear optical crystal 12 can be excited even if the output of the first signal source that radiates the electromagnetic wave having the frequency f1 is small. As a result, an electromagnetic wave having a difference frequency can be generated in the inner region of the nonlinear optical crystal 12 with an inexpensive configuration.

  5a and 5b, the second electromagnetic wave radiated from the second signal source 35 is input to the nonlinear optical crystal 12 without passing through the transmissive film 36. However, like the first electromagnetic wave, It may be configured to be incident on the nonlinear optical crystal 12 through the transmission film 36. As a result, the second electromagnetic wave can be multiple-scattered between the first reflective film 37 and the transmission film 36 in the same manner as the first electromagnetic wave, and the second electromagnetic wave can be enhanced in the internal region of the nonlinear optical crystal 12.

  Further, in the configuration shown in FIGS. 5a and 5b, the second reflective film 38 may be omitted. Even in such a simple configuration, the first electromagnetic wave can be multiple-reflected between the first reflection film 37 and the transmission film 36, and as a result, the standing wave of the first electromagnetic wave is generated in the internal region of the nonlinear optical crystal 12. Can be started. Therefore, even if the signal output of the first signal source 34 is small, the electric field strength of the electromagnetic wave having the frequency f1 in the internal region of the nonlinear optical crystal 12 is enhanced, so that the nonlinearity of the secondary nonlinear optical crystal 12 can be excited. become.

  Note that the “nonlinear optical crystal” in the present invention includes not only a crystal form but also a periodically poled structure in which the polarization of the crystal is periodically reversed.

  The electromagnetic waves radiated from the first signal source and the second signal source may be pulsed or CW (Continuos Wave).

  As described above, the sensor of the present invention can be measured nondestructively and has good sensitivity, and thus is useful for, for example, a food component analysis apparatus and a biosensor.

DESCRIPTION OF SYMBOLS 1 Sensor 11 Input part 12 Nonlinear optical crystal 13 Difference frequency radiation part 14 Difference frequency incident part 15 Detection wave radiation part 16 Detector 17, 31 Light shielding material 18 Reflective film 20 Sensor 21 Input part 22 1st nonlinear optical crystal 23 Difference frequency radiation Unit 24 measurement cell 25 difference frequency incident unit 26 second nonlinear optical crystal 27 detection wave radiation unit 28 reflector 29 f11 electromagnetic wave incident unit 32, 33 total reflection mirror 34 first signal source 35 second signal source

Claims (9)

A first signal source for outputting a first electromagnetic wave of frequency f1,
A second signal source for outputting a second electromagnetic wave of frequency f2,
A nonlinear optical crystal on which both the first electromagnetic wave output from the first signal source and the second electromagnetic wave output from the second signal source are incident;
Having a detector,
The nonlinear optical crystal is
A difference frequency radiating unit that radiates an electromagnetic wave having a difference frequency f3 between the frequencies f1 and f2, and
A difference frequency incident part for incidence of an electromagnetic wave having a difference frequency f3;
A detection wave radiating unit that radiates electromagnetic waves of frequency f2 to the detector,
The first electromagnetic wave and the second electromagnetic wave are incident so as to interfere inside the nonlinear optical crystal,
The first electromagnetic wave and the electromagnetic wave having the difference frequency f3 incident from the difference frequency incident part interfere inside the nonlinear optical crystal, and the resultant electromagnetic wave having the frequency f2 is radiated from the detection wave emitting part. Sensor characterized by. The sensor according to claim 1, wherein a spot diameter of the first signal source that outputs the first electromagnetic wave is smaller than a spot diameter of the second signal source that outputs the second electromagnetic wave. The sensor according to claim 1, wherein the detection wave radiating unit is not disposed on a propagation axis of the second electromagnetic wave. A first signal source for outputting a first electromagnetic wave of frequency f1,
A second signal source for outputting a second electromagnetic wave of frequency f2,
A first nonlinear optical crystal on which both the first electromagnetic wave output from the first signal source and the second electromagnetic wave output from the second signal source are incident;
A measurement region in contact with the first nonlinear optical crystal;
A second nonlinear optical crystal in contact with the measurement region;
Having a detector,
The first nonlinear optical crystal includes a difference frequency radiating unit that radiates an electromagnetic wave having a difference frequency f3 between frequencies f1 and f2 to the measurement region,
The second nonlinear optical crystal includes a difference frequency incident part that incidents an electromagnetic wave having a difference frequency f3;
An f1 electromagnetic wave incident part for incidence of an electromagnetic wave of frequency f1,
A detection wave radiating unit that radiates electromagnetic waves of frequency f2 to the detector,
The first electromagnetic wave and the second electromagnetic wave are incident so as to interfere inside the first nonlinear optical crystal,
The electromagnetic wave having the frequency f1 incident from the f1 electromagnetic wave incident part and the electromagnetic wave having the difference frequency f3 incident from the differential frequency incident part interfere inside the second nonlinear optical crystal, and the electromagnetic wave having the frequency f2 generated as a result. Is emitted from the detection wave radiating section. The sensor according to claim 4, wherein the first nonlinear optical crystal further includes a first electromagnetic wave radiation unit that radiates the first electromagnetic wave. The sensor according to claim 4, wherein a spot diameter of the first signal source that outputs the first electromagnetic wave is smaller than a spot diameter of the second signal source that outputs the second electromagnetic wave. The sensor according to claim 4, wherein the detection wave radiating unit is not disposed on a propagation axis of the first electromagnetic wave or the second electromagnetic wave. A first reflection film disposed on an outer region of the nonlinear optical crystal on the propagation path of the first electromagnetic wave and reflecting the first electromagnetic wave;
After being reflected by the first reflective film, disposed on the propagation path of the first electromagnetic wave propagating through the inner region of the nonlinear optical crystal and radiated to the outer region, and in the outer region of the nonlinear optical crystal, The sensor according to claim 1, further comprising: a second reflective film that reflects the first electromagnetic wave and makes the first electromagnetic wave incident again on the nonlinear optical crystal. 9. A transmission film that transmits a part of the first electromagnetic wave and reflects a part of the first electromagnetic wave is disposed between the first signal source and the nonlinear optical crystal and at least on a propagation path of the first electromagnetic wave. Sensor.

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