JP2011058892A - Observation apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily observe a subject transparent and fine as a cell, with high resolution. <P>SOLUTION: The observation apparatus 1 includes: an optical crystal 6 having a mounting surface 6a for mounting a sample A; a first irradiation system 4 for emitting first electromagnetic waves L<SB>2</SB>toward the optical crystal 6 from the side opposite to the mounting surface 6a; a second irradiation system 5 for emitting second electromagnetic waves L<SB>1</SB>; and a detection system 7 for detecting the second electromagnetic waves L<SB>1</SB>emitted from the second irradiation system 5 and reflected on the mounting surface 6a for the sample A. The first electromagnetic waves L<SB>2</SB>are pulsed terahertz waves. The second electromagnetic waves L<SB>1</SB>are pulsed electromagnetic waves having a wavelength shorter than that of the terahertz waves L<SB>2</SB>. The first irradiation system 4 and the second irradiation system 5 are arranged in such a manner that at least part of the irradiation region of the first electromagnetic waves L<SB>2</SB>and the irradiation region of the second electromagnetic waves L<SB>1</SB>overlap each other in the vicinity of the mounting surface 6a in the optical crystal 6. The detection system 7 is arranged in such a manner that its focal position matches the vicinity of the mounting surface 6a of the optical crystal 6. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an observation apparatus, and more particularly to an observation apparatus for observing a transparent sample that is difficult to observe with visible light, such as a sample such as a cell.

As a sensing technique for a transparent substance (for example, water), a sensing technique using a terahertz wave is conventionally known (for example, see Non-Patent Document 1).
This sensing technique utilizes the fact that a terahertz wave has an intensity distribution corresponding to the component distribution when the terahertz wave is transmitted through a transparent sample. In Non-Patent Document 1, a terahertz wave that has passed through a transparent sample is imaged on an electro-optic crystal by an imaging optical system. In addition, a dichroic mirror is arranged in the middle of the imaging optical system, and near infrared light is introduced onto the same optical path by this dichroic mirror, so that the introduced near infrared light is irradiated to the same electro-optic crystal. Yes. When the terahertz wave is irradiated to the electro-optic crystal, the characteristics change according to the electric field state (the amplitude and phase state of the terahertz wave). That is, sample information is recorded on the electro-optic crystal. For this reason, when near-infrared light is transmitted through the electro-optic crystal in this state, the near-infrared light is modulated during transmission. Therefore, the component distribution of the sample can be observed by detecting the modulated near infrared light.

Edited by Junichi Nishizawa, “Basics and Applications of Terahertz Waves”, published by Industrial Research Co., Ltd., April 1, 2005, p. 160-161

  However, the terahertz wave is an extremely long electromagnetic wave having a wavelength of about 30 μm to 3 mm. On the other hand, the spatial resolution of the optical system is determined by the product of the F value and the wavelength of the optical system. For this reason, in the conventional sensing technology, the spatial resolution of the imaging optical system is extremely low. That is, information with low resolution is recorded on the electro-optic crystal. Therefore, there is a disadvantage that it cannot be used for an observation apparatus for observing a sample having a fine structure such as a cell.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide an observation apparatus that can easily observe a sample having a transparent and fine structure such as a cell with high resolution.

In order to achieve the above object, the present invention provides the following means.
The present invention includes an optical crystal having a mounting surface on which a sample is mounted, and a first irradiation system and a second electromagnetic wave that irradiate a first electromagnetic wave toward the optical crystal from a side opposite to the mounting surface. And a detection system that detects the second electromagnetic wave that has been irradiated from the second irradiation system and reflected from the mounting surface of the sample, and the first electromagnetic wave is a pulse And the second electromagnetic wave is a pulsed electromagnetic wave having a wavelength shorter than that of the terahertz wave, and at least a part of the irradiation region of the first electromagnetic wave and the irradiation region of the second electromagnetic wave. The first irradiation system and the second irradiation system are arranged such that the first irradiation system and the second irradiation system overlap each other in the vicinity of the mounting surface in the optical crystal, and the focusing position of the detection system is the mounting position of the optical crystal. Provided is an observation device arranged so as to coincide with the vicinity of a surface.

  According to the present invention, a pulsed terahertz wave (first electromagnetic wave) is applied by the first irradiation system toward the optical crystal from the side opposite to the mounting surface in a state where the sample is mounted on the mounting surface of the optical crystal. ), The terahertz wave is transmitted through the optical crystal and incident on the sample on the mounting surface. A part of the terahertz wave is reflected by the sample, and is again transmitted through the mounting surface and incident on the optical crystal. Here, when the terahertz wave is reflected by the sample, it is modulated according to the refractive index and absorption distribution of the sample. The modulated terahertz wave is incident again into the optical crystal immediately after being reflected by the sample, and acts on the optical crystal to cause birefringence in the optical crystal.

  After the terahertz wave is incident on the optical crystal or at the same time as the incident, the pulsed second electromagnetic wave having a shorter wavelength than the terahertz wave is applied to the optical crystal on which the terahertz wave is incident from the side opposite to the mounting surface. When incident by the second irradiation system, the second electromagnetic wave reflected from the mounting surface of the optical crystal is modulated according to the birefringence in the optical crystal and emitted from the optical crystal. Then, by detecting the second electromagnetic wave that has passed near the mounting surface of the optical crystal by the detection system, it is possible to detect the electromagnetic wave that correctly includes information on the refractive index distribution of the sample. In this case, the imaging optical system is not included between the sample and the mounting surface, and the sample is placed close to the optical crystal at an interval equal to or less than the wavelength of the terahertz wave. While being used, the sample can be easily observed with high spatial resolution.

In the above invention, a reflection film that transmits the first electromagnetic wave and reflects the second electromagnetic wave may be provided on the mounting surface.
By doing so, only the terahertz wave is transmitted through the reflective film, and the terahertz wave modulated according to the refractive index and absorption distribution of the sample is incident on the optical crystal, and the second electromagnetic wave is incident on the sample. Without being used, it can be used only for reading information written in the optical crystal by birefringence. Thereby, it is not necessary to irradiate the sample with the second electromagnetic wave, and it is possible to observe the sample with higher resolution while suppressing the modulation received by the sample.

  In the above invention, the optical crystal is an electro-optical crystal whose refractive index changes according to the electric field state of the first electromagnetic wave, and the optical system after the detection system is reflected on the mounting surface. The polarization state of the second electromagnetic wave passing through the crystal may be detected.

  By doing so, information on the refractive index and absorption distribution of the sample is transferred to the reflected terahertz wave (first electromagnetic wave) as a change in the electric field state, and is incident on the electro-optic crystal that is incident immediately after being reflected from the sample. Transferred as a refractive index distribution. Then, when the second electromagnetic wave is transmitted through the electro-optic crystal to which the information on the refractive index and absorption distribution of the sample is transferred, the polarization state of the electromagnetic wave changes. In the detection system, by extracting the changed polarization state, the refractive index and absorption distribution of the sample can be acquired, and the sample can be easily observed with high spatial resolution.

  In the above invention, the optical crystal is a nonlinear optical crystal that performs sum frequency mixing or difference frequency mixing of the first electromagnetic wave and the second electromagnetic wave, and the detection system is emitted from the optical crystal. It is good also as detecting the electromagnetic wave mixed by sum frequency mixing or difference frequency mixing.

  By doing so, the terahertz wave (first electromagnetic wave) modulated according to the refractive index and absorption distribution of the sample when reflected by the sample is summed by the action of the nonlinear optical crystal. Frequency mixing or difference frequency mixing is performed to emit an electromagnetic wave having the frequency of the sum or difference of the terahertz wave and the second electromagnetic wave from the optical crystal. Since the emitted electromagnetic wave contains the information of the refractive index and absorption distribution of the sample contained in the terahertz wave as it is, the distribution of the refractive index and absorption of the sample can be obtained by detecting this information. The sample can be easily observed with high spatial resolution.

  The present invention also provides an optical crystal having a mounting surface on which a sample is mounted and two electromagnetic waves having the same wavelength and different intensities or polarizations toward the optical crystal, at least in a part of their irradiation regions. An irradiation system that irradiates from the opposite side of the mounting surface so as to overlap in the vicinity of the mounting surface in the optical crystal, and one electromagnetic wave that is irradiated from the irradiation system and reflected on the mounting surface of the sample is detected. The optical crystal is a non-linear optical crystal that does not generate a terahertz wave by the one electromagnetic wave and generates a terahertz wave by the other electromagnetic wave having a predetermined intensity or polarization, and the detection system Provides an observation device arranged so that its in-focus position coincides with the vicinity of the placement surface of the optical crystal.

  According to the present invention, an optical crystal can be used as a means for generating a terahertz wave, and the apparatus can be simplified because a separate means for generating is not required. In addition, as an electromagnetic wave that generates terahertz waves and an electromagnetic wave used for reading, electromagnetic waves having the same wavelength with different intensities or polarized light can be used, and the configuration can be further simplified.

  According to the present invention, there is an effect that a sample having a transparent and fine structure such as a cell can be easily observed with high resolution.

It is a whole lineblock diagram showing the observation device concerning a 1st embodiment of the present invention. It is a figure explaining the terahertz wave and near-infrared light which inject into the sample and optical crystal in the observation apparatus of FIG. It is a flowchart which shows the observation procedure by the observation apparatus of FIG. It is a figure which shows the 1st modification of FIG. It is a figure which shows the 2nd modification of FIG. It is a whole block diagram which shows the modification of the observation apparatus of FIG. It is a whole block diagram which shows the other modification of the observation apparatus of FIG. It is a whole block diagram which shows the observation apparatus which concerns on the 2nd Embodiment of this invention. It is a figure explaining the terahertz wave and near-infrared light which inject into the sample and optical crystal in the observation apparatus of FIG. It is a figure which shows the modification of FIG. It is a whole block diagram which shows the modification of the observation apparatus of FIG.

An observation apparatus 1 according to a first embodiment of the present invention will be described below with reference to the drawings.
Observation apparatus 1 according to this embodiment, as shown in FIG. 1, femtosecond pulsed light source 2 for generating the near-infrared light L _1, the near-infrared light L ₁ from the light source 2 of two A beam splitter 3 that divides into optical paths, a terahertz wave irradiation optical system (first irradiation system) 4 provided in one optical path divided by the beam splitter 3, and a near-infrared light provided in the other optical path An irradiating optical system (second irradiating system) 5; an electro-optic crystal 6 that is disposed downstream of these irradiating optical systems 4 and 5 and has a placement surface 6a on which a sample A such as a cell is placed; 6 and a detection optical system 7 that detects near-infrared light L ₁ emitted from the light source 6.

The terahertz wave irradiation optical system 4 is disposed on one of the optical paths divided by the beam splitter 3. The terahertz wave irradiation optical system 4 includes a condenser lens 8 for one light condensing of the divided near-infrared light L _1, the terahertz wave near-infrared light L ₁ that has been condensed by the condenser lens 8 (First electromagnetic wave) terahertz wave radiating element 9 for converting to L ₂ , first parabolic mirror 10a for converting terahertz wave L ₂ radiated from the terahertz wave radiating element 9 into a substantially parallel light beam, and a terahertz wave L ₂ which becomes substantially parallel light beams and a second parabolic mirror 10b for focusing on the sample a by the first parabolic mirror 10a.

The second parabolic mirror 10b, the are near the center in the through-hole 11 is provided, as described below, has been a near-infrared light L ₁ emitted from the electro-optic crystal 6, the detection optical system 7 side To pass through. In the figure, reference numeral 12 denotes a mirror.

The near-infrared light irradiation optical system 5 is disposed on the other optical path of the optical paths divided by the beam splitter 3. Near-infrared light irradiation optical system 5 includes an optical path adjusting optical system 13, a half-wave plate 14 for adjusting the polarization of the near-infrared light L _1, near which is adjusted polarization by the 1/2 wavelength plate 14 the infrared light L ₁ is focused and an objective lens 15 focused on the electro-optical crystal 6. Incidentally, near-infrared light L ₁ which passes through the 5 near-infrared light irradiation optical system is a second electromagnetic wave.
The objective lens 15 is disposed in a region S (see FIG. 2) whose focal position is close to the mounting surface 6 a in the electro-optic crystal 6.

The optical path adjustment optical system 13 includes two pairs of mirrors 13a to 13d, and a moving mechanism (not shown) moves the pair of mirrors 13b and 13c in the direction of arrow B with respect to the other pair of mirrors 13a and 13d. ). Near-infrared light L ₁ which is deflected at the mirror 13a, a pair of mirrors 13b, after being folded by being deflected twice in 13c, and is reset to the original light path by being deflected at the mirror 13d Yes. By changing the distance between the two pairs of mirrors 13 a to 13 d, thereby making it possible to adjust the optical path length of near-infrared light L _1.

The electro-optic crystal 6 is an optical crystal whose refractive index changes according to the electric field state when irradiated with the terahertz wave L ₂ , and examples thereof include ZnTe (zinc telluride). By irradiating the electro-optic crystal 6 with the terahertz wave L ₂ having the electric field state distribution, the electric field state distribution is written in the electro-optic crystal 6 as a refractive index distribution (the electric field state distribution is reflected as the refractive index distribution). When the near-infrared light L ₁ is allowed to pass through the written region S, the polarization direction of the near-infrared light L ₁ can be changed. Here, the electric field state of the terahertz wave L _2, the amplitude of the terahertz wave, and shows a state of the phase.

The mounting surface 6a of the electro-optic crystal 6, as shown in FIG. 2, is transmitted through the terahertz wave L _2, which is provided reflective film 6b that reflects near-infrared light L _1. While terahertz wave L ₂ incident from the side opposite to the mounting surface 6a of the electro-optic crystal 6 to be incident on the specimen A passes through the reflective film 6b, near-infrared light L ₁ incident from the same direction The light is reflected without passing through the reflective film 6b, passes through the electro-optic crystal 6 again, and is emitted to the outside from the same surface as the incident surface.

The detection optical system (detection system) 7 is a beam splitter 16 that branches the near-infrared light L ₁ emitted from the electro-optic crystal 6 and collimated by the objective lens 15, and the near-infrared beam branched by the beam splitter 16. a light selecting optical system 17 for selecting a near-infrared light L ₁ from among the light L ₁ having a predetermined polarization direction, an imaging lens for focusing the near-infrared light L ₁ having a predetermined polarization direction that is selected 18 and an image sensor (photodetector) 19 for photographing the near infrared light L ₁ collected by the imaging lens 18. As the image sensor 19, for example, a two-dimensional image sensor such as a CCD or a CMOS is used.

The light selection optical system 17 is a polarizer that transmits only near-infrared light L ₁ having a predetermined polarization direction (hereinafter also referred to as a polarizer 17), and a terahertz wave L ₂ is incident on the electro-optic crystal 6. near-infrared light L ₁ which is incident at non state is adjusted so as to be completely shut off. As described above, by the electric field of the terahertz wave L _2, the birefringence is induced in the electro-optic crystal 6. The electro-optic crystal 6 by passing through the, the near-infrared light L ₁ is polarized state changes occurring phase changes. Thus, the intensity of the near-infrared light L ₁ incident on the image sensor 19 of the subsequent stage through the light selective optical system 17 is adapted to change.

The operation of the observation apparatus 1 according to the present embodiment configured as described above will be described below.
In order to observe the sample A such as a transparent cell using the observation apparatus 1 according to this embodiment, the sample A is placed on the placement surface 6 a of the electro-optic crystal 6, and the pulsed near from the light source 2 is placed. emit the infrared light L _1.

Near-infrared light L ₁ branched by the beam splitter 3 and incident on the terahertz wave irradiation optical system 4 is deflected once by the mirror 12 and then condensed by the condensing lens 8 to irradiate the terahertz wave radiating element 9. Is done. Thus, the terahertz wave L ₂ is generated, after being converted into a substantially parallel light beam by the parabolic mirror 10a, it is focused on the specimen A by parabolic mirror 10b. In this case, the terahertz wave L ₂ is opposite to the mounting surface 6a of the sample A toward the electro-optical crystal 6, i.e., is incident from the lower surface, the reflection provided to the electro-optical crystal 6 and its mounting surface 6a The light passes through the film 6b and enters the sample A.

The sample A is a transparent cell or the like, but the terahertz wave L ₂ incident on the sample A is modulated by being reflected by the sample A, and an electric field state corresponding to the refractive index and absorption distribution in the sample A Having a distribution of Then, when the terahertz wave L ₂ having such a distribution of the electric field state passes through the reflection film 6b and is incident again on the electro-optic crystal 6, the electro-optic crystal 6 has an intensity distribution of the terahertz wave L _2. A corresponding refractive index distribution is generated.

The refractive index distribution generated in the electro-optic crystal 6 accurately reflects the refractive index and absorption distribution of the sample A as the sample A is closer to the sample A. Since the time during which the refractive index distribution is generated in the electro-optic crystal 6 due to the irradiation with the terahertz wave L ₂ is extremely short, it is necessary to read the information on the refractive index distribution immediately after the irradiation with the terahertz wave L ₂ .

For reading out this information, near infrared light L ₁ incident on the near infrared light irradiation optical system 5 is used. The near-infrared light L ₁ branched by the beam splitter 3 is adjusted in the polarization direction by being transmitted through the half-wave plate 14 after the optical path length is adjusted in the optical path adjusting optical system 13. Thereafter, the near-infrared light L ₁ is collected by the objective lens 15, passes through the through-hole 11 of the parabolic mirror 10 b, and then from the same direction as the terahertz wave L ₂ as shown in FIG. The electro-optic crystal 6 is irradiated. When the terahertz wave L ₂ reflected by the sample written as a refractive index distribution on the electro-optic crystal 6 a is reflected by the reflecting film 6 b provided on the mounting surface 6 a of the electro-optic crystal 6 and returns downward, reading information (near the polarization state of the infrared light L ₁ is changed).

In the figure, a region S indicated by oblique lines is a region that is written information of the distribution of the refractive index and absorption of the sample A by the terahertz wave L _2. Since the terahertz wave L ₂ based on the near-infrared light L ₁ emitted from the same light source 2 and the near-infrared light L ₁ pass through different optical paths, the pulses are simultaneously transmitted to the region S of the electro-optic crystal 6 as it is. May not pass through. Therefore, the phase of the pulse can be accurately adjusted by adjusting the optical path length by the optical path adjusting optical system 13.

As a result, almost near-infrared light L ₁ at the same time as the radiation of terahertz waves L ₂ is irradiated to the region S, it is possible to read the information of the refractive index distribution. In FIG. 2, the near-infrared light L ₁ and the terahertz wave L ₂ are drawn so as to be alternately irradiated to separate areas, but actually, at least a part of both irradiation areas S. Are irradiated so that they overlap.

In the region S, the refractive index is changed by irradiation of the terahertz wave L _2.
When the near-infrared light L ₁ that has passed through the electro-optic crystal 6 and is reflected by the mounting surface 6 a passes through the region S, the polarization state of the near-infrared light L ₁ is changed. That is, a portion of the near-infrared light L ₁ collected by the objective lens 15 is emitted downward from the electro-optic crystal 6 with the polarization state varied according to the transmission position.

The near-infrared light L ₁ emitted from the electro-optic crystal 6 is collimated by the objective lens 15 after passing through the through-hole 11 of the parabolic mirror 10 b and arranged on the optical path branched by the beam splitter 16. Is incident on the polarizer 17. Polarizer 17, in the state where the terahertz wave L ₂ is not incident to the electro-optical crystal 6 is set so as to block the near-infrared light L _1. Meanwhile, in the state where the terahertz wave L ₂ reflected by the sample is incident on the electro-optical crystal 6, by passing through the region S where the refractive index changes, near-infrared light L of a portion polarization state changed Only ₁ is passed through the polarizer 17. Thereby, the information of the refractive index distribution recorded on the electro-optic crystal 6 can be read out as the light quantity (intensity) of light.

Then, the near-infrared light L ₁ extracted in this way is collected by the imaging lens 18 and photographed by the image sensor 19, thereby obtaining an image of the sample A such as a transparent cell that cannot be observed by visible light. Can be acquired.

In this case, according to the observation apparatus 1 according to the present embodiment, the optical system is not disposed between the sample A and the electro-optic crystal 6 as in the prior art, but directly on the placement surface 6 a of the electro-optic crystal 6. Since the sample A is placed, the spatial resolution of the information written in the electro-optic crystal 6 is not limited by the optical system. In addition, since the electro-optic crystal 6 is disposed in the vicinity of the sample, it is possible to suppress the influence of a decrease in spatial resolution due to diffraction of the terahertz wave after passing through the sample. Further, the reading of the information, because of the use of short near-infrared light L ₁ than the terahertz wave L _2, there is an advantage that can be observed with high spatial resolution. As a result, even if the sample A has a fine structure such as a cell, the sample A can be observed with a simple configuration and high spatial resolution.

FIG. 3 is a flowchart showing the observation procedure.
In order to perform observation using the observation apparatus 1 according to the present embodiment, first, background measurement is performed. That is, the optical path adjusting optical system 13 is used to form a state where the terahertz wave L ₂ and the near-infrared light L ₁ do not overlap in time, or the terahertz wave L ₂ is not incident on the electro-optic crystal 6. Then, an image is acquired (step S1). Then, by adjusting the optical path adjusting optical system 13 to form a state where the terahertz wave L ₂ and the near-infrared light L ₁ are overlapped in time, to acquire the image (step S2). Finally, unnecessary information resulting from the observation environment can be removed by subtracting or dividing the image acquired in step S2 and the image acquired in step S1 (step S3). As a result, a high-quality image for imaging can be obtained. Note that the order of steps S1 and S2 may be reversed.

In the present embodiment, provided with a through hole 11 in the parabolic mirror 10b, but has led to the near-infrared light L ₁ to the objective lens 15 to be emitted from the electro-optic crystal 6, parabolic mirrors 10a is transmitted through the terahertz wave L ₂ between 10b is provided a mirror for reflecting near-infrared light L _1, it may be led to the near-infrared light L ₁ on the same optical path as the terahertz wave L _2. In this case, a Si plate or the like may be used as the mirror.
Further, although the detection optical system 7 includes the beam splitter 16 and the polarizer 17, instead of this, a polarization beam splitter having both functions may be employed.

In the present embodiment, by providing the reflective film 6b on the mounting surface 6a of the electro-optic crystal 6, transmitted through the terahertz wave L ₂ it has been decided to reflect near-infrared light L _1, instead of this As shown in FIG. 4, the reflective film 6b need not be provided. In this case, it is possible to Fresnel reflection occurs at mounting surface 6a of the electro-optic crystal 6 returns a portion of the near-infrared light L _1. Therefore, the information written by the terahertz wave L ₂ can be read by the near infrared light L ₁ as described above.

However, in this case, since a part of the near-infrared light L ₁ is incident after passing through the mounting surface 6a of the electro-optic crystal 6 to the sample A, it is preferable to irradiate the near-infrared light L ₁ This is not suitable for sample A, which is not present. In such a case, it is preferable to use the electro-optic crystal 6 having the reflective film 6b.

In each of the above embodiments, the electro-optic crystal 6 has been described as an example of the optical crystal. However, instead of this, as shown in FIG. 5, when light L ₁ and L ₂ of _two different wavelengths are simultaneously incident, the two lights L ₁ and L ₂ are sum frequency mixed or difference frequency mixed. Then, a non-linear optical crystal 6 ′ from which another light L ₃ having the frequency of the sum or difference of the frequencies is emitted may be employed.

In this way, for example, in the case of sum frequency mixing, in the observation apparatus 1 shown in FIG. 1, the nonlinear optical crystal 6 ′ simultaneously reflects the terahertz wave L ₂ reflected by the sample A and the near-infrared light L _1. 5, as shown in FIG. 5, the terahertz wave L ₂ (for example, wavelength 100 μm, frequency 3 THz) modulated according to the refractive index distribution of the sample A and the near-infrared light L that is not so modulated ₁ (for example, wavelength 800 nm) is sum frequency mixed in the nonlinear optical crystal 6 '.

Then, the sum frequency mixed light L ₃ having another wavelength (for example, wavelength 793.65 nm) including information on the refractive index and absorption distribution of the sample A is collected by the objective lens 15 and detected, thereby detecting the sample. An image of A can be acquired.
In this case, the imaging device 19, so as not to be incident near-infrared light L _1, in place of the polarizer 17 may be to provide a filter.

Further, as shown in FIG. 6, a confocal observation device 20 may be configured.
In the example shown in FIG. 6, scanners (proximity galvanomirrors) 20a and 20b that two-dimensionally scan the near infrared light L1 are provided in the middle of the near infrared light irradiation optical system 5 of the observation apparatus 1 in FIG. A confocal pinhole 28 is disposed at a position optically conjugate with the focal position of the objective lens 15. Thus, it is possible to detect only the near-infrared light L ₁ from the region S in the vicinity of the mounting surface 6a of the electro-optic crystal 6 the focal position of the objective lens 15 is arranged by the photodetector 19. Therefore, a clear image can be obtained even if the electro-optic crystal 6 itself is configured to be relatively thick.

Further, as shown in FIG. 7, a detection optical system 7 for detecting near-infrared light L _1, 1/4-wave plate 21, an imaging lens 18, the difference detection, such as a polarizing beam splitter 22 and balanced photodiodes A configuration including the vessel 23 may be adopted. For example, a Wollaston prism is used as the polarization beam splitter 22, but the polarization beam splitter 22 is not limited to this.

In this case, the quarter-wave plate 21 is adjusted so that the near-infrared light L ₁ is circularly polarized in a state where the terahertz wave L ₂ and the near-infrared light L ₁ do not overlap in time in the region S. Keep it. Then, the light that has passed through the quarter-wave plate 21 is divided into two orthogonal polarization components by the polarization beam splitter 22, and the difference detector 23 detects the intensity difference between the two polarization components. In the state where the terahertz wave L ₂ and the near-infrared light L ₁ does not overlap in time in the area S, the intensity difference detected by the difference detector 23 is zero.

In this state, when the terahertz wave L ₂ and the near-infrared light L ₁ overlap in time in the region S, the polarization state of the near-infrared light L ₁ changes, so that the two detected by the difference detector 23 An intensity difference occurs in the polarization component. By detecting this, the state of the terahertz wave near-field component, that is, information on the sample A can be obtained.

Next, an observation apparatus 30 according to a second embodiment of the present invention will be described below with reference to the drawings.
In the description of the observation apparatus 30 according to the present embodiment, portions having the same configuration as those of the observation apparatus 1 according to the first embodiment described above are denoted by the same reference numerals and description thereof is omitted.

As shown in FIGS. 8 and 9, the observation apparatus 30 according to the present embodiment is different in the electro-optic crystal 31, and thus the structure of the terahertz wave irradiation optical system 32 is different.
In the observation apparatus 30 according to the present embodiment, as the electro-optic crystal 31, _one that generates a terahertz wave L ₂ due to a nonlinear optical effect when near-infrared light L ₁ having a specific polarization state or intensity is incident is adopted. ing.

Here, the specific polarization state means a state in which the crystal axis direction of the polarization direction and the electro-optic crystal 31 in the near-infrared light L ₁ satisfies the specific condition, which will be described later half-wave plate 14, 33 can be adjusted. Further, the intensity of the near-infrared light L ₁ can be set by the intensity division ratio by the beam splitter 34.

The terahertz wave irradiation optical system 32 arranges two pairs of mirrors 35a and 35b on one optical path branched by the beam splitter 34, turns the optical path back, and then uses the other beam splitter 36 to share the same optical path as the other optical path. To join. The two mirrors 35a and 35b are provided so as to be movable in the direction of arrow C, and the optical path length is adjusted by the movement. Half-wave plates 14 and 33 for realizing different polarization states are arranged in the two optical paths, respectively, and the half-wave plates 14 and 33 are adjusted so as to enter the electro-optic crystal 31. thereby making it possible to adjust the polarization state of the near-infrared light L _1.

The operation of the observation apparatus 30 according to this embodiment configured as described above will be described below.
In using the observation apparatus 30 according to this embodiment performs observation of the sample A, the sample A is placed on the placement surface 31a of the electro-optic crystal 31, the near-infrared light L ₁ pulsed from the light source 2 Let it emit.

Near-infrared light L ₁ incident on a terahertz wave irradiation optical system 32 is branched by the beam splitter 34, a pair of mirrors 35a, is folded by 35b. At this time, the polarization state is adjusted by the half-wave plate 33 disposed in the middle of the optical path. Thereafter, the light beam is merged in the same optical path as the other optical path by the beam splitter 36, condensed by the objective lens 15, and incident on the electro-optic crystal 31.

When the near-infrared light L ₁ having a specific polarization state or intensity is incident, the electro-optic crystal 31 generates a terahertz wave L ₂ by an optical rectification effect which is a kind of nonlinear optical effect. On the other hand, if the near-infrared light L ₁ which deviates from the condition is incident terahertz wave L ₂ does not occur, or intensity of the terahertz wave L ₂ generated is very small. Therefore, the near-infrared light L ₁ incident from one optical path is used to generate the terahertz wave L ₂ , and the near-infrared light L ₁ incident from the other optical path is used to read out information on the refractive index distribution. be able to.

THz wave L ₂ generated in the electro-optic crystal within 31 irradiates the specimen A passes through the reflective film 6b, by reflecting in the specimen A, it is modulated in accordance with the refractive index distribution of the sample A. Then, the terahertz wave L ₂ thus modulated is transmitted again through the reflecting film 6 b in the opposite direction and is incident on the electro-optic crystal 31, thereby causing birefringence in the electro-optic crystal 31 and Corresponding refractive index and absorption distribution information is written.

Information is read out using the near infrared light L ₁ incident on the near infrared light irradiation optical system 5. The near-infrared light L ₁ collected by the objective lens 15 after being set to a predetermined polarization state by the half-wave plate 14 is a near-red light guided from the irradiation optical system 32 as shown in FIG. The electro-optic crystal 31 is irradiated from the same direction as the external light L ₁ . Then, in the same manner as the observation apparatus 1 according to the first embodiment, the light is written into the electro-optic crystal 31 when reflected back by the reflecting film 6b provided on the mounting surface 31a of the electro-optic crystal 31 and returned downward. Information can be read.
Thus, according to the observation apparatus 30 according to the present embodiment, unlike the first embodiment, it is not necessary to prepare the terahertz wave radiating element 9, and the configuration can be simplified.

  In the present embodiment, the single femtosecond pulse laser light source 2 is branched into two optical paths, but two separate femtosecond pulse laser light sources 2 may be used instead.

Further, in the present embodiment, as shown in FIG. 10, the electro-optic crystal 31 having a property as a nonlinear optical crystal is used. Instead, the nonlinear optical crystal 31b for generating the terahertz wave L ₂ is used. The two electro-optic crystals 31c for writing and reading information on the refractive index distribution may be bonded to each other in a laminated state. For example, the nonlinear optical crystal 31b may be a DAST crystal or a GaSe crystal, and the electro-optic crystal 31c may be a ZnTe crystal. By doing so, it is possible to detect a high-intensity and wideband signal.

In addition, as shown in FIG. 11, two near infrared lights L ₁ set to different polarization states or intensities may be combined and guided to the electro-optic crystal 31 by the optical fiber 38. In the figure, reference numeral 37 denotes a coupling lens. By doing so, there is an advantage that the electro-optic crystal 31 can be moved relatively freely and observation can be performed on the sample A that is difficult to place on the mounting surface 31a. For example, by directing near-infrared light L ₁ by the optical fiber 38 by placing the electro-optic crystal 31 to the leading end of the insertion portion of the endoscope, it is possible to perform observation in a body cavity.

  In each of the above embodiments, a moving image can also be acquired by detecting a signal continuously in time.

L ₁ near infrared light (second electromagnetic wave)
L ₂ terahertz wave (first electromagnetic wave)
A sample S area (irradiation area)
1, 20, 30 Observation device 4 Terahertz wave irradiation optical system (first irradiation system)
5 Near-infrared light irradiation optical system (second irradiation system)
6,31,31c Electro-optic crystal (optical crystal)
6 ', 31b Nonlinear optical crystal (optical crystal)
6a, 31a Mounting surface 6b Reflective film 7 Detection optical system (detection system)
32 Terahertz wave irradiation optical system (irradiation system)

Claims (5)

An optical crystal having a mounting surface for mounting a sample;
A first irradiation system for irradiating the first electromagnetic wave toward the optical crystal from a side opposite to the mounting surface, and a second irradiation system for irradiating the second electromagnetic wave;
A detection system for detecting the second electromagnetic wave irradiated from the second irradiation system and reflected on the mounting surface of the sample;
The first electromagnetic wave is a pulsed terahertz wave,
The second electromagnetic wave is a pulsed electromagnetic wave having a shorter wavelength than the terahertz wave,
The first irradiation system and the second irradiation system so that at least a part of the irradiation region of the first electromagnetic wave and the irradiation region of the second electromagnetic wave overlap in the vicinity of the placement surface in the optical crystal. Is placed,
The observation system in which the detection system is arranged so that the in-focus position coincides with the vicinity of the placement surface of the optical crystal.   The observation apparatus according to claim 1, wherein a reflection film that transmits the first electromagnetic wave and reflects the second electromagnetic wave is provided on the placement surface. The optical crystal is an electro-optic crystal whose refractive index changes according to the electric field state of the first electromagnetic wave,
The observation apparatus according to claim 1, wherein the detection system detects a polarization state of the second electromagnetic wave that passes through the optical crystal after being reflected on the mounting surface. The optical crystal is a non-linear optical crystal that performs sum frequency mixing or difference frequency mixing of the first electromagnetic wave and the second electromagnetic wave;
The observation apparatus according to claim 1, wherein the detection system detects an electromagnetic wave generated by sum frequency mixing or difference frequency mixing emitted from the optical crystal. An optical crystal having a mounting surface for mounting a sample;
To the optical crystal, two electromagnetic waves having the same wavelength and different in intensity or polarization are placed on the mounting surface so that at least a part of their irradiation areas overlaps in the vicinity of the mounting surface in the optical crystal. Is an irradiation system that irradiates from the opposite side,
A detection system for detecting one electromagnetic wave irradiated from the irradiation system and reflected from the mounting surface of the sample;
The optical crystal is a nonlinear optical crystal that does not generate a terahertz wave by the one electromagnetic wave and generates a terahertz wave by the other electromagnetic wave having a predetermined intensity or polarization,
The observation system in which the detection system is arranged so that the in-focus position coincides with the vicinity of the placement surface of the optical crystal.

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