JP2008122278A - Terahertz spectral diffraction/imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a very-high-frequency pulse transmission device capable of transmitting a high output very-high-frequency pulse to an optical fiber without deteriorating a waveform. <P>SOLUTION: This terahertz spectral diffraction/imaging apparatus is constituted of a spectrum magnifying optical fiber of a light pulse comprising a large caliber photonic crystal fiber, a dispersing compensation element and an optical fiber capable of being connected a signal producing/detecting probe head. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a terahertz spectroscopy / image apparatus, and more particularly, to a measurement / imaging apparatus using a short pulse light source.

Measurement / imaging devices using ultrashort light pulses include terahertz spectroscopy / imaging devices, multiphoton microscope devices, and nonlinear microscope devices. In these apparatuses, in order to improve measurement flexibility, a method of transmitting an ultrashort optical pulse through an optical fiber and scanning a measurement probe head coupled to the optical fiber has been developed.
When an optical pulse is transmitted through an optical fiber, the optical pulse width is widened and the optical pulse waveform is distorted due to the dispersion of the optical fiber material and the dispersion of the optical waveguide. The broadening of the optical pulse width is mainly caused by chromatic dispersion corresponding to the second-order dispersion (the group velocities of the respective wavelengths are different). The distortion of the optical pulse waveform is caused by third-order or higher-order dispersion. The smaller the pulse width of the input optical pulse or the larger the spectral width of the input optical pulse, the larger the optical pulse width and the distortion of the optical pulse waveform.

  In general, a pre-dispersion compensation method is used to correct optical pulse waveform degradation (increase in pulse width and waveform distortion) caused by optical fiber transmission. In this method, before transmitting an optical pulse, the optical pulse is previously given an amount of dispersion that compensates for the dispersion of the optical fiber to be transmitted. When this method is used, the width of the optical pulse at the time of optical fiber output is equivalent to that of the input pulse. However, when the optical pulse has a high output, a self-phase modulation effect that is a non-linear effect occurs in the optical fiber, thereby reducing (compressing) the spectrum of the optical pulse. It is known that when the spectrum decreases, the width of the optical pulse after the output of the optical fiber expands compared to the pulse width of the input pulse even if the dispersion of the optical fiber is completely compensated by pre-dispersion compensation. (Non-Patent Document 1).

The spectral compression by the above self-phase modulation effect can be qualitatively explained as follows. Since the chromatic dispersion of the optical fiber is normal dispersion (the short wavelength component is slow and the long wavelength component is fast), the anomalous dispersion of the inverse dispersion (the short wavelength component is It is chirped (fast line, long wavelength component is slow) (solid line in the left diagram of FIG. 2). Next, after being input to the optical fiber, the wavelength changes with time because of the self-phase modulation effect (the effect that the wavelength changes with time because the refractive index depends on the intensity of light. See the broken line in the left diagram of FIG. 1). Decreases with time. Since the wavelength change due to this self-phase modulation effect works in a direction to cancel the wavelength change caused by the pre-dispersion compensation, the spectrum width of the optical pulse is reduced (Δλ = Δλ ₁ −Δλ ₂ ). The greater the power of the optical pulse, the greater the reduction in spectral width due to self-phase modulation, and the spectral width of the optical pulse decreases (see FIG. 2). This decrease in spectral width results in an increase in pulse width (see FIG. 3).

Such degradation of ultrashort light pulses during optical fiber transmission results in performance degradation of terahertz spectroscopy / imaging devices, multiphoton microscope devices, nonlinear microscope devices, etc. that use ultrashort light pulses transmitted through optical fibers. In the case of terahertz spectroscopy / imaging equipment, if the optical pulse for generation / detection of terahertz electromagnetic waves deteriorates, the output of terahertz electromagnetic waves and the frequency band decrease, which degrades the signal-to-noise ratio (S / N ratio) of the terahertz spectroscopy / imaging equipment. . In the case of a multiphoton microscope apparatus and a nonlinear microscope apparatus, the spatial resolution increases as the S / N ratio deteriorates.
As a method for suppressing spectral compression due to the self-phase modulation effect in ultrashort optical pulse transmission using the above-described pre-dispersion compensation method, there is a method using a large-diameter photonic crystal fiber as a transmission optical fiber (Non-patent Document 2). ). Since the core diameter of the large-diameter photonic crystal fiber is larger than that of a normal single mode fiber, the electric field intensity of light in the core region is reduced, and the self-phase modulation effect is suppressed. Therefore, the spectral compression effect is also reduced.

  As another method, there is a method using an optical fiber for increasing the spectral width of the input pulse before the pre-dispersion compensation (Non-patent Document 3). In this case, the optical pulse from the ultrashort pulse laser is first transmitted to the spectrum expansion optical fiber, then input to the dispersion compensation element, and finally transmitted to the optical fiber coupled to the measurement probe head. Here, the dispersion compensation element performs dispersion compensation of the optical fiber before and after the dispersion compensation element. In this method, if the spectrum expansion is compensated for by the optical fiber for expanding the spectrum, or if the spectrum is expanded beyond the dispersion compensation element, the output pulse is equal to or narrower than the input pulse. A light pulse is obtained.

M. Oberthaler and R. A. Hopfel, "Applied Physics Letters", 1993, vol. 63, N0. 8, pp. 1017-1019 Lee et al., 53rd Joint Conference on Applied Physics, 23-a-M-4, 2006, p.1168 S. W. Clark et al., “Optics Letters”, 2001, vol. 26, No. 17, pp. 1320-1322 "Photonic crystal fiber (1)-Optical characteristics-" Mitsubishi Electric Industrial Time Report No. 99, 2002, pp.1-9

  In Non-Patent Document 2, a large-diameter photonic crystal fiber having a large core diameter is used in order to suppress the spectral compression effect that occurs in optical fiber transmission after dispersion compensation. By increasing the core diameter, the electric field intensity of the optical pulse is reduced, and the self-phase modulation effect that causes spectrum compression is suppressed. A large-diameter photonic crystal fiber has a feature of operating in a single mode regardless of a large diameter, which is a necessary condition for simplifying dispersion compensation. Incidentally, there is another multi-mode optical fiber (multi-mode fiber) as a large-diameter fiber. In this case, it is necessary to perform dispersion compensation for each mode, resulting in complicated dispersion compensation. The problem with the method described in Non-Patent Document 2 is that the propagation loss (particularly the bending loss) increases as the aperture becomes larger.

  For example, in the case of an ultrashort pulse titanium sapphire laser (center wavelength: 0.8 μm), the maximum core diameter is about 15 μm, and when a photonic crystal fiber having a larger core diameter is used, the propagation loss increases. Therefore, it becomes difficult to completely suppress the spectrum compression due to the limitation of the upper limit value of the core diameter due to the transmission loss. For example, when a large-diameter photonic crystal fiber with a length of 2 m and a core diameter of 15 μm is used, the output pulse width is about 200 fsec for an input pulse width of 100 fsec and an average output of 30 mW. The width is about twice the width of the input pulse (FIG. 3).

  The ultrashort optical pulse transmission device described in Non-Patent Document 3 is composed of an optical fiber for spectrum expansion, a dispersion compensation element, and an optical fiber for coupling to a measurement probe head. In this device, unlike the device described in Non-Patent Document 2, spectral compression that occurs in the optical fiber after the dispersion compensation element can be compensated by the optical fiber for spectrum expansion, and therefore there is a limit on the upper limit of the core diameter due to transmission loss. However, the problem that occurred in Non-Patent Document 2 does not occur. Non-Patent Document 3 shows that an optical pulse having a pulse width of 70 fsec and an average output of 32 mW can be transmitted with respect to an input pulse width of 75 fsec.

  As described above, Non-Patent Document 3 is suitable for transmission of a narrower pulse as compared with Non-Patent Document 2. However, the average output is not so different. In the method of Non-Patent Document 3, the reason why the power cannot be increased is as follows. In Non-Patent Document 3, a conventional single mode fiber having a small core diameter is used as an optical fiber for spectrum expansion arranged in front of a dispersion compensation element. Therefore, since the core diameter is small, the light intensity is increased and the self-phase modulation effect which is a non-linear effect occurs efficiently. Therefore, when the power of the optical pulse is increased, the spectrum width becomes very large. When the spectrum width becomes very large, higher-order (third-order or higher) dispersion compensation is required, which causes a problem that the dispersion compensation element becomes complicated. If only secondary dispersion compensation is used, tailing appears as shown in FIG. As a method of suppressing the spectrum expansion to some extent even when a high-power optical pulse is input to the spectrum expansion single mode fiber, it is conceivable to shorten the optical fiber length. However, when a power of several hundred mW or more is input, a fiber having a very short length on the order of millimeters or less is required to suppress the spectrum expansion to such an extent that high-order dispersion compensation is not required. It is not easy to perform spatial input / output of light pulses on millimeter-order optical fibers. As described above, in the method described in Non-Patent Document 3, the transmission average power is limited to about several tens of mW.

  Accordingly, an object of the present invention is to realize transmission of an optical pulse with a higher output and a narrower pulse width by raising the upper limit of the limit of the transmission power.

  As described in the above problem, in the method described in Non-Patent Document 3, a single-mode fiber having a small core diameter is used as the optical fiber for spectrum expansion. For this reason, the spectrum expansion effect due to the self-phase modulation effect is increased, so that the transmission power is limited. As a method for solving this problem, a large-diameter photonic crystal fiber is used as an optical fiber for spectrum expansion.

There are two types of photonic crystal fibers: a refractive index waveguide type and a photonic band gap type, and the large-diameter photonic crystal fiber is the former. When this optical fiber is used, the effective mode fineness (substantially the same as the core area) is large, and transmission is possible only in the single mode. The self-phase modulation effect, which is the cause of the increase in spectral width, arises from the increase in the spatial density of the electric field intensity of light. Wavelength change due to self-phase modulation effect: Δλ ₂ can be simply described by equation (1).

ここで、n₂はカー定数、P_avは平均パワー、Δtはパルス幅、a_effは実効モード面積である。この式から、自己位相変調効果を軽減するために、実効モード面積（コア面積）の大きな光ファイバを用いればよいことが分かる。

Here, n ₂ is the Kerr constant, P _av is the average power, Δt is the pulse width, and a _eff is the effective mode area. From this equation, it can be seen that an optical fiber having a large effective mode area (core area) may be used to reduce the self-phase modulation effect.

  In the conventional optical fiber, if the core diameter is increased in order to increase the effective mode area, the single mode operation condition is not satisfied. In the case of multi-mode operation, different dispersion compensation has to be performed in each mode. Therefore, when dispersion compensation becomes complicated, it becomes difficult to achieve optimum dispersion compensation.

Therefore, single mode operation is essential. There is a large-diameter photonic crystal fiber as an optical fiber that can increase the core diameter while maintaining a single mode operation. The single-mode operating condition of this fiber is that V _eff described by Equation (2) satisfies 4 or less.

ここで、Λは格子間隔(ほぼコア領域の直径に対応)、n₀は材料シリカの屈折率、n_effはクラッド領域の実効屈折率である。従来のステップ型光ファイバと異なり、コア領域を大きくする（Λが大きくなることに相当）と、コア領域とクラッド領域の実効屈折率差が小さくなるため（式（２）の√の値が小さくなることに相当）、Λの増加に伴うV_effの増加を軽減するため、広い範囲のΛでシングルモード動作条件を満足する（非特許文献４）。

Here, Λ is the lattice spacing (corresponding approximately to the diameter of the core region), n ₀ is the refractive index of the material silica, and n _eff is the effective refractive index of the cladding region. Unlike conventional step-type optical fibers, increasing the core region (equivalent to increasing Λ) reduces the effective refractive index difference between the core region and the cladding region (the value of √ in Equation (2) is small) In order to reduce the increase in V _eff accompanying the increase in Λ, the single-mode operation condition is satisfied in a wide range of Λ (Non-patent Document 4).

  If the large-diameter photonic crystal described above is used, suppression of the self-phase modulation effect and single mode operation can be realized simultaneously. If this optical fiber is used as an optical fiber for spectrum expansion of the device described in Non-Patent Document 3, the limitation of transmission power is relaxed, and transmission of ultrashort optical pulses with higher output becomes possible. Furthermore, if a large-diameter photonic crystal fiber is used for the optical fiber coupled to the measurement probe head after the dispersion compensation element, there is an advantage that the amount of spectral compression per unit length is reduced and the optical fiber can be made longer ( (Expandable range of probe head) When a large-diameter photonic crystal fiber is used as an optical fiber before and after the dispersion compensation element, an optical pulse with a pulse width of 77 fsec and an average output of 170 mW is transmitted for an input pulse with a pulse width of 100 fsec. This was confirmed by computer simulation (see FIG. 5). The core diameter of the large-diameter photonic crystal fiber used here is about 15 μm, and the length is 10 cm for the spectrum expansion fiber and 2 m for the probe head coupling fiber. The average power of the input pulse is 1.2 W, the coupling efficiency of the spectrum expansion fiber is 50%, the transmittance of the dispersion compensation element consisting of a pair of diffraction gratings is 80%, and the coupling efficiency of the probe head coupling phi is 36%. did. The propagation loss of each optical fiber was set to zero.

  According to the present invention, in an ultrashort optical pulse transmission device, an optical fiber can be transmitted with a high output and an ultrashort optical pulse without deterioration of the waveform.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

An embodiment of an optical fiber transmission type terahertz time domain spectroscopy / imaging system using the ultrashort optical pulse transmission device of the present invention will be described with reference to FIG. Here, one ultrashort optical pulse transmission device common to the probe head for terahertz wave generation / detection is used.
This system includes an ultrashort pulse laser 5 capable of emitting an optical pulse 4 having a pulse width of picosecond or femtosecond class, a large-diameter photonic crystal fiber 1 for spectrum expansion, a dispersion compensating element 2, an ultrashort An optical beam splitter 8 for branching the pulse laser pulse into a pump light pulse 6 and a probe light pulse 7, an optical mechanical chopper 9, an optical fiber 10 for transmitting the pump light pulse, and a pump light A condensing optical system unit 12 for inputting pulses to the optical fiber 10, a terahertz electromagnetic wave generating probe head 14 to which a pumping optical pulse transmitting optical fiber can be connected, and generation of terahertz electromagnetic waves in the terahertz electromagnetic wave generating probe head DC voltage power supply 15 for applying voltage to the device and transmission of probe light pulses An optical delay device 16 for making the interval variable, an optical fiber 11 for transmitting the probe optical pulse, a condensing optical system unit 13 for inputting the probe optical pulse to the photonic crystal fiber, and a probe Terahertz electromagnetic wave detecting probe head 17 to which an optical fiber for transmitting optical pulses can be connected, a current amplifying device 18 for amplifying a current signal from the terahertz electromagnetic wave detecting probe head, and a current signal synchronized with an optical mechanical chopper And a computer 20 that controls the optical delay device, captures output signal data, and performs data analysis. In the present embodiment, the arrangement is such that the terahertz electromagnetic wave pulse 22 is transmitted through the measured object 23 and the transmitted terahertz electromagnetic wave pulse is detected. However, the arrangement may be such that the terahertz electromagnetic wave reflected or scattered from the measured object 23 is detected.

  Examples of ultrashort pulse laser 5 include mode-locked titanium sapphire laser, Cr: LiSAF laser, Cr: LiSGAF laser, Cr: LiSCAF laser, Er-doped fiber mode-locked laser, Yb-doped fiber mode-locked laser, and mode-locked A semiconductor laser diode, a gain-switched semiconductor laser diode, a mode-locked semiconductor laser, or an ultrashort pulse laser in which a gain-switched semiconductor laser diode and a pulse compression device are combined is suitable.

The structure of a refractive index waveguide type photonic crystal fiber suitable for the present invention will be described in detail. The refractive index waveguide type photonic crystal fiber includes a cladding region in which air holes are periodically arranged and a core region in which one air hole is lacking. The structural parameters include air hole diameter: d and lattice spacing: Λ. Typical periodic arrangements of cladding regions include a triangular lattice arrangement and a honeycomb lattice arrangement. FIG. 7 shows the calculation results of the effective mode area: a _eff dependence of the output pulse width for various average powers. Has a frequency of up to 2TH _Z, for THz generation number μW, the pulse width of the excitation light pulse below 200 fs, the average power is required than 30 mW. In consideration of this, the a _eff of the refractive index waveguide type photonic crystal fiber needs to be 50 μm ² or more from the result of FIG. The upper limit value of a _eff is determined as follows. Refractive index waveguide photonic crystal fiber The core diameter 2a _core in the case of crystal fiber is defined as 2Λ-d. In the case of a large diameter fiber having a large a _eff , a _core ≈Λ from d / Λ << 1. The outer diameter of the fiber is about the same as that of a conventional single mode fiber (125 μm in the case of a single mode fiber), and in order to maintain the characteristics of a refractive index waveguide type photonic crystal fiber, an array of air holes of at least 2 to 3 periods is arranged. If necessary, a _core Λ≈30 μm. When approximately equal to? pa ² _core to a _eff, the upper limit of a _eff is about 3000 .mu.m ^2.

Dispersion compensation elements using one or more pairs of diffraction gratings, one using one or more prisms, one using one or more GT etalon, or a combination of these three types Is suitable. An AC voltage power supply may be used instead of the DC voltage power supply 15 for applying a voltage to the terahertz electromagnetic wave generating device. In this case, the optical mechanical chopper 9 becomes unnecessary.
As the optical delay device 16, a device constituted by a retro-reflector mirror unit and an externally controllable fine movement stage is suitable. As an alternative optical delay device, there are a device using a rotating mirror, a device using a polygon mirror, and a device that scans a retro-reflector mirror by applying an AC voltage to a piezo control actuator.
Large-diameter photonic crystal fibers are suitable as optical fibers 10 and 11 for transmitting optical pulses for pumps and probes.
Examples of the terahertz electromagnetic wave generating device in the terahertz electromagnetic wave generating probe head include a low temperature growth GaAs photoconductive antenna device, a semi-insulated GaAs photoconductive antenna device, and an InGaAs photoconductive antenna device. Each of the antenna shapes includes a dipole shape, a bow tie shape, and a stripline shape. Furthermore, a GaAs substrate, InP substrate, InAs substrate, InSb substrate, or the like may be used.
As a terahertz electromagnetic wave generating device in the terahertz electromagnetic wave detecting probe head, a low-temperature grown GaAs photoconductive antenna device is suitable.

FIG. 8 illustrates an embodiment of an optical fiber transmission type terahertz time domain spectroscopy / imaging system using the ultrashort optical pulse transmission device of the present invention. Here, two ultrashort optical pulse transmission devices are used for each of the two heads of the terahertz electromagnetic wave generation / detection probe head. In this embodiment, the large-diameter photonic crystal fiber 1 and the dispersion compensation element 2 arranged after the ultrashort pulse laser 5 in Embodiment 1 are combined with a condensing optical system unit 12 for pumping light pulses and a light pulse for probes. It is arranged in front of the condensing optical system unit 13 for use. Other components and arrangement are the same as those in the first embodiment.
In the case of this method, there are disadvantages such as an increase in the number of components and complication of the measurement system as compared with the first embodiment. However, the optical pulse transmission optical fiber 10 for the pump and the optical fiber 11 for probe optical transmission are used. Even when the chromatic dispersion is different, there is an advantage that dispersion compensation can be performed with high accuracy.

  FIG. 9 and FIG. 9 show a terahertz time domain spectroscopic / imaging system having a composite head composed of a terahertz electromagnetic wave generating probe head connected to an optical fiber, a terahertz electromagnetic wave detecting probe head, and an endoscope scope. 10 will be used for explanation. This apparatus includes a terahertz endoscope composite guide 24, a terahertz endoscope composite head 25, an endoscope guide 26, a monitor 27, and an endoscope light source 28. Others are the same as the first embodiment.

  The terahertz endoscope composite guide 24 includes a pump optical pulse transmission optical fiber 10, a probe optical pulse transmission optical fiber 11, a voltage application wire 38, a current wire 39, and an endoscope guide 26. including. The terahertz endoscope composite head 25 includes a terahertz electromagnetic wave generating probe head 14 connected to the pump optical pulse transmission optical fiber 10 and a terahertz electromagnetic wave connected to the probe optical pulse transmission photonic crystal fiber 11. An endoscope head 29 including an objective lens, a light guide, and a small CCD camera, a mirror 30, and a mirror movable stage 31 are connected to the detection probe head 17 and the endoscope guide 26.

  The light emitted from the endoscope head is reflected by the measurement object 23, and the reflected light is imaged on the imaging surface of the CCD camera by the imaging lens 32, and the imaging signal is transmitted to display the image on the monitor. By moving the mirror 30 on the mirror movable stage 31, the irradiation position of the light from the endoscope light source and the terahertz electromagnetic wave can be finely adjusted. The mirror movable stage 31 can be realized by a piezoelectric control actuator or the like.

  An embodiment relating to a multiphoton microscope apparatus using the ultrashort optical pulse transmission apparatus of the present invention will be described with reference to FIG. A multiphoton microscope is used for living body imaging and the like. This apparatus includes an ultrashort pulse laser 5 capable of emitting an optical pulse having a pulse width of picosecond or femtosecond class, a large-diameter photonic crystal fiber 1 for spectrum expansion, a dispersion compensation element 2, and an optical pulse 4. The optical pulse condensing optical system unit 33 for condensing the optical fiber 3, the optical fiber 3 for transmitting the optical pulse 4, and the optical pulse 4 emitted from the optical fiber 3 into the fluorescent substance attached measurement object 34. A light-collecting optical system unit 33 for condensing light, an optical filter 35, a photodetector 36, and an image processing device 37. A fluorescent substance is attached to the measurement object 34 in advance, and multiphoton absorption occurs due to the ultrashort light pulse. Fluorescence is emitted when electrons excited by multiphoton absorption transition to the ground level. The excitation light is cut by the optical filter 35, only the fluorescence is transmitted, received by the photodetector, and imaged.

  Here, the optical fiber 3 is suitably a large-diameter photonic crystal fiber. Examples of the ultrashort pulse laser 5 include a mode-locked titanium sapphire laser, a Cr: LiSAF laser, a Cr: LiSGAF laser, a Cr: LiSCAF laser, a fiber mode-locked laser doped with Er, and a fiber mode-locked laser doped with Yb, A mode-locked semiconductor laser diode, a gain-switched semiconductor laser diode, a mode-locked semiconductor laser, or an ultrashort pulse laser in which a gain-switched semiconductor laser diode and a pulse compression device are combined is suitable.

  An embodiment relating to a nonlinear microscope apparatus using the ultrashort optical pulse transmission apparatus of the present invention will be described with reference to FIG. Nonlinear microscopes are used for biological imaging and the like. This apparatus includes an ultrashort pulse laser 5 capable of emitting an optical pulse having a pulse width of picosecond or femtosecond class, a large-diameter photonic crystal fiber 1 for spectrum expansion, a dispersion compensation element 2, and an optical pulse 4. The optical pulse condensing optical system unit 33 for condensing the optical fiber 3, the optical fiber 3 for transmitting the optical pulse 4, and the optical pulse 4 emitted from the optical fiber 3 is condensed on the measured object 23. The optical pulse condensing optical system unit 33, the optical filter 35, the photodetector 36, and the image processing device 37. By irradiating the measurement object 23 with the ultrashort light pulse, the optical pulse 4 is converted into light having a half wavelength (second harmonic) by a nonlinear effect generated inside the measurement object. The second harmonic is selectively transmitted by the optical filter 35, received by the photodetector, and imaged. Here, the optical fiber 3 is suitably a large-diameter photonic crystal fiber. Examples of the ultrashort pulse laser 5 include a mode-locked titanium sapphire laser, a Cr: LiSAF laser, a Cr: LiSGAF laser, a Cr: LiSCAF laser, a fiber mode-locked laser doped with Er, and a fiber mode-locked laser doped with Yb, A mode-locked semiconductor laser diode, a gain-switched semiconductor laser diode, a mode-locked semiconductor laser, or an ultrashort pulse laser in which a gain-switched semiconductor laser diode and a pulse compression device are combined is suitable.

It is the figure which explained qualitatively the spectral-width reduction by the self phase modulation effect which occurs when the pre-chirped ultrashort optical pulse transmits an optical fiber. It is a figure which shows the measurement result of the average power dependence of an output pulse width and a spectrum width at the time of making single mode fiber transmission of an ultrashort optical pulse. It is a figure which shows the measurement result of the average power dependence of an output pulse width and a spectrum width at the time of transmitting an ultrashort light pulse to a single mode fiber and a large diameter photonic crystal fiber. It is a figure which shows the calculation result of the optical pulse waveform after the secondary dispersion compensation of the chirp optical pulse with a wide spectrum width. It is a figure which shows the calculation result of the input pulse waveform and output pulse waveform in the case of the ultrashort optical pulse transmission apparatus which used the large diameter photonic crystal fiber before and behind the dispersion compensation element based on this invention. 1 is a configuration diagram of an optical fiber transmission type terahertz spectroscopy / imaging apparatus using a pair of ultrashort optical pulse transmission apparatuses applied in Example 1 according to the present invention. FIG. It is a figure which shows the calculation result of the effective mode area: a _eff dependence of the output pulse width with respect to various average power. It is a block diagram of the optical fiber transmission type | mold terahertz spectroscopy and imaging apparatus using two sets of the ultrashort optical pulse transmission apparatuses applied in Example 2 which concerns on this invention. It is a block diagram of the optical fiber transmission type | mold terahertz spectroscopy and imaging apparatus using the terahertz endoscope composite head using one set of the ultra-short optical pulse transmission apparatus applied in Example 3 which concerns on this invention. It is a block diagram of the terahertz endoscope composite head applied in Example 3 according to the present invention. It is a block diagram of the multiphoton microscope apparatus applied in Example 4 which concerns on this invention. It is a block diagram of the nonlinear microscope apparatus applied in Example 5 which concerns on this invention.

Explanation of symbols

1… Large-diameter photonic crystal fiber for spectrum expansion,
2 ... dispersion compensation element,
3 ... Optical fiber,
4 ... light pulse,
5 ... Ultra short pulse laser,
6 ... Light pulse for pump,
7 ... Light pulse for probe,
8 ... Optical beam splitter,
9 ... Optical mechanical chopper,
10 ... Optical fiber for optical pulse transmission for pump,
11: Optical fiber for probe optical pulse transmission,
12 ... Condensing optical system unit for light pulse for pump,
13 ... Condensing optical system unit for probe light pulse,
14 ... Terahertz electromagnetic wave generating probe head,
15 ... DC voltage power supply,
16 ... Optical delay device,
17 ... Terahertz electromagnetic wave detection probe head,
18 ... Current amplifier,
19 ... Lock-in amplifier,
20 ... Control computer,
21 ... Mirror,
22 ... terahertz electromagnetic wave pulse,
23… Measurement object,
24 ... Terahertz endoscope composite guide,
25 ... Terahertz endoscope composite head,
26 ... Endoscopy guide,
27… Monitor,
28… Endoscope light source,
29… Endoscope head,
30 ... Mirror
31 ... Mirror movable stage
32 ... imaging lens,
33 ... Condensing optical system unit for light pulses,
34… Fluorescent substance attached measurement object,
35 ... Optical filter,
36 ... Photodetector,
37. Image processing device,
38 ... voltage application wire,
39… Wire for current.

Claims (16)

An ultrashort laser that generates ultrashort pulses with a pulse width of the picosecond or femtosecond class;
A beam splitter that splits the light emitted from the ultrashort pulse laser into two optical paths;
A first condensing unit that condenses one of the light separated by the beam splitter;
A second condensing unit that condenses the other of the dispersed light;
An optical delay device for varying the transmission time of the other split light propagating on the optical path between the beam splitter and the second condensing unit;
A probe head for generating a terahertz electromagnetic wave that receives light transmitted from the first light collecting unit and generates a terahertz electromagnetic wave having a frequency range of 0.1 to 100 THz;
A terahertz electromagnetic wave detection probe head that inputs light transmitted from the second light collecting unit and the terahertz electromagnetic wave emitted from the measured object and emitted from the measured object, and generates a current signal;
A first optical fiber connecting the first light collecting unit and the electromagnetic wave generating probe head;
A second optical fiber connecting the second light collecting unit and the electromagnetic wave detection probe head;
Photonic crystal fibers are used for the first and second optical fibers,
A dispersion compensation element for compensating dispersion of the photonic crystal fiber is provided on an optical path between the ultrashort optical pulse laser and the beam splitter, and the ultrashort optical pulse laser is provided on the input side of the dispersion compensation element. A terahertz spectroscopic / imaging apparatus characterized by using a photonic crystal fiber that expands the spectral width of the light. Each of the photonic crystal fiber used for the first and second optical fibers and the photonic crystal fiber that expands the spectral width of the ultrashort optical pulse laser has a refractive index guide having a cladding region in which air holes are arranged. ^2. The terahertz spectroscopy / imaging apparatus according to claim 1, wherein the terahertz spectroscopy / imaging apparatus is of a waveguide type and capable of propagating in a single mode in a transverse mode and having an effective mode area of 50 μm ² or more and 3000 μm ² or less. Each of the photonic crystal fiber used for the first and second optical fibers and the photonic crystal fiber that expands the spectral width of the ultrashort optical pulse laser has a refractive index guide having a cladding region in which air holes are arranged. ^2. The terahertz spectroscopy / imaging apparatus according to claim 1, wherein the terahertz spectroscopy / imaging apparatus is of a waveguide type, capable of propagating in a transverse mode in a single mode, and having an effective mode area of 50 μm ² or more and 2500 μm ² or less. Each of the photonic crystal fiber used for the first and second optical fibers and the photonic crystal fiber that expands the spectral width of the ultrashort optical pulse laser has a refractive index guide having a cladding region in which air holes are arranged. ^2. The terahertz spectroscopy / imaging apparatus according to claim 1, wherein the terahertz spectroscopy / imaging apparatus is of a waveguide type, capable of propagating in a transverse mode in a single mode, and having an effective mode area of 50 μm ² or more and 2000 μm ² or less.   2. The terahertz spectroscopy / imaging according to claim 1, wherein a photonic crystal fiber that expands a spectrum width of the ultrashort optical pulse laser is shorter than a photonic crystal fiber used for the first and second optical fibers. apparatus.   In the photonic crystal fiber for expanding the spectral width of the ultrashort optical pulse laser and the photonic crystal fiber used for the first and second optical fibers, the arrangement of air holes forming the cladding region is a triangular lattice arrangement or a honeycomb 2. The terahertz spectroscopy / imaging apparatus according to claim 1, wherein the terahertz spectroscopy / imaging apparatus has a lattice arrangement.   2. A transmission type detection arrangement in which a terahertz electromagnetic wave pulse emitted from the terahertz electromagnetic wave generating probe head is transmitted through the object to be measured, and the transmitted terahertz electromagnetic wave pulse is detected by the terahertz electromagnetic wave detection probe head. The terahertz spectroscopy / imaging apparatus described.   A terahertz electromagnetic wave pulse emitted from the terahertz electromagnetic wave generating probe head is reflected or scattered from the measurement object, and the terahertz electromagnetic wave pulse reflected or scattered is detected by the terahertz electromagnetic wave detection probe head. The terahertz spectroscopy / imaging apparatus according to claim 1. An ultrashort laser that generates ultrashort pulses with a pulse width of the picosecond or femtosecond class;
A beam splitter that splits the light emitted from the ultrashort pulse laser into two optical paths;
A first condensing unit that condenses one of the light separated by the beam splitter;
A second condensing unit that condenses the other of the dispersed light;
An optical delay device for varying the transmission time of the other split light propagating on the optical path between the beam splitter and the second condensing unit;
A probe head for generating a terahertz electromagnetic wave that receives light transmitted from the first light collecting unit and generates a terahertz electromagnetic wave having a frequency range of 0.1 to 100 THz;
A terahertz electromagnetic wave detection probe head that inputs light transmitted from the second light collecting unit and the terahertz electromagnetic wave emitted from the measured object and emitted from the measured object, and generates a current signal;
A first optical fiber connecting the first light collecting unit and the electromagnetic wave generating probe head;
A second optical fiber connecting the second light collecting unit and the electromagnetic wave detection probe head;
Photonic crystal fibers are used for the first and second optical fibers,
A first dispersion compensating element for compensating dispersion of the photonic crystal fiber on an optical path between the beam splitter and the first light collecting unit; the optical delay device; and the second light collecting unit. A second dispersion compensation element for compensating for dispersion of the photonic crystal fiber is provided on the optical path between
A terahertz spectroscopic / imaging apparatus using a photonic crystal fiber that expands a spectral width of the ultrashort optical pulse laser on the input side of the first and second dispersion compensating elements. Each of the photonic crystal fiber used for the first and second optical fibers and the photonic crystal fiber that expands the spectral width of the ultrashort optical pulse laser has a refractive index guide having a cladding region in which air holes are arranged. a waveguide type, transverse mode are possible propagation in a single mode, terahertz spectrometer imaging apparatus according to claim 9, wherein the effective mode area that is 3000 .mu.m ² or less in 50 [mu] m ² or more. Each of the photonic crystal fiber used for the first and second optical fibers and the photonic crystal fiber that expands the spectral width of the ultrashort optical pulse laser has a refractive index guide having a cladding region in which air holes are arranged. a waveguide type, transverse mode are possible propagation in a single mode, terahertz spectrometer imaging apparatus according to claim 9, wherein the effective mode area that is 2500 [mu] m ² or less at 50 [mu] m ² or more. Each of the photonic crystal fiber used for the first and second optical fibers and the photonic crystal fiber that expands the spectral width of the ultrashort optical pulse laser has a refractive index guide having a cladding region in which air holes are arranged. 10. The terahertz spectroscopy / imaging apparatus according to claim 9, wherein the terahertz spectroscopy / imaging apparatus is of a waveguide type, capable of propagating in a transverse mode in a single mode, and having an effective mode area of 50 μm ² or more and 2000 μm ² or less.   10. The terahertz spectroscopy / imaging according to claim 9, wherein a photonic crystal fiber that expands a spectral width of the ultrashort optical pulse laser is shorter than a photonic crystal fiber used for the first and second optical fibers. apparatus.   In the photonic crystal fiber for expanding the spectral width of the ultrashort optical pulse laser and the photonic crystal fiber used for the first and second optical fibers, the arrangement of air holes forming the cladding region is a triangular lattice arrangement or a honeycomb The terahertz spectroscopy / imaging apparatus according to claim 9, wherein the terahertz spectroscopy / imaging apparatus is a lattice arrangement.   10. A transmission type detection arrangement in which a terahertz electromagnetic wave pulse emitted from the terahertz electromagnetic wave generating probe head is transmitted through the object to be measured, and the transmitted terahertz electromagnetic wave pulse is detected by the terahertz electromagnetic wave detection probe head. The terahertz spectroscopy / imaging apparatus described.   A terahertz electromagnetic wave pulse emitted from the terahertz electromagnetic wave generating probe head is reflected or scattered from the measurement object, and the terahertz electromagnetic wave pulse reflected or scattered is detected by the terahertz electromagnetic wave detection probe head. The terahertz spectroscopy / imaging apparatus according to claim 9.

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