JP2003115625A - Terahertz light generating apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a terahertz light generating apparatus which can increase radiation intensity of the terahertz light generated. SOLUTION: A terahertz light generating element 1 comprises a substrate 11 as a light conductive portion, and a couple of conductive portions 12, 13 which are separately formed on the surface parallel to the XY plane of the substrate 11. At least a part of the conductive portion 12 and that of the conductive portion 13 are allocated in the Y axis direction so as to keep the predetermined interval g1. A radiating portion 2 radiates an exciting pulse beam to the predetermined radiation area of the terahertz light generating element 1. A voltage applying portion 3 applies a bias voltage across the conductive portions 12 and 13. The radiating portion 2 is configured to include a cylindrical lens 22 or the like, and to provide the radiating region which is longer in the X axis direction than that in the Y axis direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a terahertz light generating device, and more particularly to a terahertz light generating device having a terahertz light generating element using an optical switch element.

[0002]

2. Description of the Related Art A terahertz light generating element called an optical switch element is often used for generating terahertz light (for example, Smith, Auston, and Nasu (Peter.R.
Smith, David.H.Auston and Martin.C.Nuss) paper ("S
ubpicosecond Photoconducting Dipole Antennas ", IEE
E Journal of Quantum Electronics, Vol.24, No.2, p
p.255-260 (1988)), Budiort, Margolies,
Jeong, Son and Bocault (E. Budiarto, J. Margolie
s, S. Jeong, J. Son and J. Bokor) ("High-Inten
sity Terahertz Pulses at 1-kHz Repetition Rate ", I
EEE Journal of Quantum Electronics, Vol.32, No.10,
pp1839-1846 (1996)) etc.).

A terahertz light generating element called an optical switch element has a photoconductive portion and a conductive film as two conductive portions formed on a predetermined surface of the photoconductive portion and separated from each other. It is an element in which at least a part of two conductive films are arranged with a predetermined interval in the direction along the predetermined surface. In this element, even if a voltage is applied between the two conductive films, almost no current flows because the resistance value between the two conductive films (gap portion) is very high. Irradiating the gap with excitation pulsed light such as ultra-short pulsed laser light such as femtosecond pulsed laser light to generate free carriers (electrons and holes) reduces the resistance value at that moment and is applied. Carriers are accelerated by the electric field and a current flows. Terahertz pulsed light is generated by this pulsed current.

In the conventional terahertz light generating device provided with the conventional terahertz light generating element called an optical switch element, the excitation pulse light irradiation area of the terahertz light generating element is circular.

[0005]

If the radiation intensity of the terahertz light generated from the terahertz light generating device can be increased, various devices using the terahertz light (terahertz optical device), for example, a spectroscopic device, an inspection device, In an analyzer or the like, it is possible to shorten the measurement time and inspection time, expand the measurement range and inspection range, and improve S / N.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a terahertz light generating device capable of increasing the emission intensity of the generated terahertz light.

[0007]

In order to solve the above problems, a terahertz light generating device according to a first aspect of the present invention comprises (a) a photoconductive portion and a photoconductive portion formed on a predetermined surface of the photoconductive portion. A terahertz light generating element having two conductive parts separated from each other, and at least a part of the two conductive parts being arranged at a predetermined interval in a first direction along the predetermined surface; (B) an irradiation unit that irradiates a predetermined irradiation region of the terahertz light generating element with excitation pulsed light,
(C) A voltage applying section for applying a bias voltage between the two conductive sections. And in this 1st aspect, the said irradiation part is the 2nd direction along the said predetermined surface, and the length of the said irradiation area of the 2nd direction orthogonal to the said 1st direction is the said, It is configured to be longer than the length of the irradiation region in the first direction.

A terahertz light generating device according to a second aspect of the present invention is the terahertz light generating device according to the first aspect, wherein in the irradiation section, all or most of the irradiation area is the two conductive sections in the terahertz light generating element. The excitation pulsed light is irradiated so as to be a region between at least a part of the above.

A terahertz light generating device according to a third aspect of the present invention is the device according to the first or second aspect, wherein the irradiation area is substantially elliptical.

The terahertz light generating device according to a fourth aspect of the present invention is the terahertz light generating device according to any one of the first to third aspects, wherein the second region of the irradiation region is the second region of the irradiation region with respect to the length of the irradiation region in the first direction. The ratio of the lengths in the direction is 1.1 or more. The ratio is preferably 1.5 or more, more preferably 2 or more, even more preferably 3 or more, further preferably 5 or more, and further preferably 8 or more. .

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A terahertz light generating device according to the present invention will be described below with reference to the drawings.

[First Embodiment]

FIG. 1 is a schematic configuration diagram showing a terahertz light generating device according to a first embodiment of the present invention. 2 is a diagram showing the terahertz light generating element 1 in FIG.
2A is a schematic plan view thereof, and FIG. 2B is a schematic cross-sectional view taken along the line AA ′ in FIG. For ease of understanding, as shown in FIGS. 1 and 2, Xs orthogonal to each other are used.
The axes, the Y-axis, and the Z-axis are defined (the same applies to the figures described later).

As shown in FIG. 1, the terahertz light generating device according to this embodiment includes a terahertz light generating element 1, an irradiation unit 2, and a DC power supply 3 as a voltage application unit.

The terahertz light generating element 1 is shown in FIGS.
As shown in FIG.
A conductive film 12 as two conductive portions formed on one surface of 1 (a plane parallel to the XY plane in the figure) and separated from each other;
13 and 13. At least some of the conductive films 12 and 13 are arranged so as to have a predetermined gap g1 in the Y-axis direction along the plane above the substrate 11 (the upper and lower sides are shown as the upper and lower sides in FIG. 2B). There is. In the present embodiment, the conductive films 12 and 13 are entirely separated by a gap g1. This gap g1 is set to 2 mm or more, for example, 5 mm,
The substrate 11 and the conductive films 12 and 13 constitute a so-called large-diameter optical switch element.

As the material of the substrate 11, for example, a semiconductor having a high resistivity (for example, semi-insulating GaAs) can be used. As the material of the conductive films 12 and 13, for example, gold or the like can be used, and the substrate 11 can be formed by vapor deposition or the like.
Can be formed on the surface of.

In the present embodiment, as described above, the substrate 1
Although 1 itself is used as a photoconductive portion, for example, as shown in FIG. 3, a photoconductive film 14 is formed as a photoconductive portion on a substrate 11, and conductive films 12 and 13 are formed on the photoconductive film 14. You may form. In this case, for example, GaAs can be used as the material of the substrate 11 and low-temperature grown GaAs can be used as the photoconductive film 14. 3 is a schematic cross-sectional view showing another example of the terahertz light generating element 1 and corresponds to FIG. 2 (b). In FIG. 3, the same or corresponding elements as those in FIGS. 1 and 2 are designated by the same reference numerals, and the duplicated description thereof will be omitted.

As shown in FIGS. 1 and 2A, the irradiation unit 2 has a predetermined irradiation region R of the terahertz light generating element 1.
1 is irradiated with ultrashort pulsed laser light such as femtosecond pulsed laser light as excitation pulsed light. The irradiation unit 2 is
The irradiation region R1 is configured such that the length in the X-axis direction along the upper plane of the substrate 11 is longer than the length of the irradiation region R1 in the Y-axis direction. The ratio of the length of the irradiation region R1 in the X-axis direction to the length of the irradiation region R1 in the Y-axis direction is
It is preferably 1.1 or more, more preferably 1.5 or more, more preferably 2 or more,
It is even more preferably 3 or more, further preferably 5 or more, and further preferably 8 or more.
For example, the irradiation region R1 may have a substantially elliptical shape.
It is preferable for effectively utilizing the laser light and the like. This is because if the irradiation region R1 is formed into a substantially elliptical shape, it is not necessary to cut a part of the light flux of the laser light emitted from the laser light source 21 described later.

In the present embodiment, the irradiation section 2 is specifically a laser light source 21 and a cylindrical lens as a shaping optical system for shaping the cross-sectional shape of the light flux from the laser light source 21 in accordance with the irradiation region R1. 22, a concave or convex spherical lens 23, and a cylindrical lens 24.
In the present embodiment, the X-axis direction of the luminous flux of the excitation pulse light is collimated by the cylindrical lens 22 and the spherical lens 23, and the Y-axis direction of the luminous flux of the excitation pulse light is collimated by the spherical lens 23 and the cylindrical lens 24. As a result, the excitation pulsed light is irradiated onto the irradiation region R1 as a parallel light flux.
However, it goes without saying that the configuration of the irradiation unit 2 is not limited to such a configuration.

Further, in the present embodiment, in the irradiation section 2, as shown in FIG. 2, the irradiation region R1 is entirely the region between the two conductive films 12 and 13 in the terahertz light generating element 1. The excitation pulsed light is emitted.
However, the present invention is not necessarily limited to this, and for example, a part of the irradiation region R1 may be the conductive films 12 and 1.
It may overlap with 3. Further, in the present embodiment, the length of the irradiation region R1 in the Y-axis direction is shorter than the gap g1 between the conductive films 12 and 13, and the irradiation region R1 and the conductive films 12 and 13 are spaced from each other. ing. However, the present invention is not necessarily limited to this.

The DC power source 3 applies a bias voltage between the conductive films 12 and 13. The DC power supply 3 can be composed of, for example, a power supply circuit that converts AC from a commercial power supply into DC. The magnitude of the bias voltage is not particularly limited, but in order to maximize the radiation intensity of terahertz light, the magnitude of the bias voltage is
It is preferable to adjust the electric field E _bias between the two conductive films 12 and 13 so as to be the electric field strength immediately before dielectric breakdown occurs.

Here, a comparative example compared with the terahertz light generating device according to the present embodiment will be described with reference to FIG. FIG. 4 is a schematic plan view showing an irradiation region R2 of the excitation pulsed light on the terahertz light generating element 1 in the comparative example, and corresponds to FIG. 2 (a). In FIG. 4, elements that are the same as or correspond to the elements in FIGS. 1 and 2 are given the same reference numerals, and duplicate descriptions thereof will be omitted.

The terahertz light generating element 1 used in this comparative example is exactly the same as the terahertz light generating element 1 used in the present embodiment, including dimensions and materials. This comparative example is an example in which the irradiation region R2 of the excitation pulsed light on the terahertz light generating element 1 is circular, as in the conventional technique. The diameter of the irradiation region R2 is a gap g1 and the irradiation region R2 is arranged just in the region between the conductive films 12 and 13. Although not shown in the drawing, the irradiation part of the excitation pulse light used in the comparative example is different from the irradiation part 2 used in the present embodiment only in the shaping optical system, and the comparative example is also the present embodiment. Also, the laser light source 21 used is the same, and the laser light intensity per unit area of the irradiation region R2 in the comparative example is the same as the irradiation region R1 in the present embodiment.
The laser light intensity per unit area is almost the same. Further, the bias voltage applied between the two conductive films 12 and 13 in the comparative example is also the same as that of the two conductive films 1 in the present embodiment.
It is the same as the bias voltage applied between 2 and 13.

Next, the operation of this embodiment will be described in comparison with the comparative example described above.

In this embodiment and the comparative example, the conductive film 1 is used.
A direct-current voltage is applied from the direct-current power supply 3 between 2 and 13, but normally, almost no current flows because the resistance value between the two conductive films 12 and 13 (gap portion) is very high. When the irradiation unit 2 irradiates the gap portion with an ultrashort pulsed laser beam having energy higher than the band gap of a semiconductor or the like forming the substrate 11 to excite it and generate free carriers (electrons and holes), The resistance decreases and the current flows. The pulse width of the pump laser light is sufficiently short,
Moreover, this current flows only for a very short time because the lifetime of the excited carriers is short. Then, at this time, since the current changes with time, electromagnetic waves are generated. If the pulse width of the excitation laser light is sufficiently short (for example, about 100 fs or less), the frequency of the electromagnetic wave reaches several THz. This is terahertz light, which propagates to the substrate 11 side.

As described above, when the excitation pulse light is irradiated, free carriers (electrons and holes) are generated in the substrate 11 as a photoconductive portion, and the carriers are accelerated by the applied electric field E _bias. Terahertz light is generated. Electric field intensity E of terahertz light generated at this time in the distance
_THz is proportional to the time derivative of the current J flowing between the two conductive films 12 and 13, and can be expressed by the following equation 1.

[0027]

[Equation 1] E _THz ∝dJ / dt

A current J flowing between the two conductive films 12 and 13
Using the current density j and the cross-sectional area S through which the current flows,
It becomes as shown in the following Equation 2. Here, the cross-sectional area S is the product of the length of the irradiation region R in the X axis direction and the free carrier generation depth in the Z direction.

[0029]

[Equation 2] J = Sj

Further, the current density j is the mobility μ of photoexcited carriers, the density n of carriers, and the two conductive films 1.
By using the electric field E _bias applied between 2 and 13 and the electronic charge e, it can be expressed by the following Expression 3.

[0031]

## EQU00003 ## j = ne.mu.E _bias

That is, the electric field intensity E _{THz of the} terahertz light
Is dependent on the mobility μ of photoexcited carriers, the carrier density n, the magnitude E _{bias of the} electric field applied between the two conductive films 12 and 13 separated from each other, and the cross-sectional area S, It becomes as shown in the following formula 4.

[0033]

[Equation 4] E _THz ∝Sdj / dt = Sd (neμE _bias ) / dt

Assuming that the electric field E _bias applied between the two conductive films 12 and 13 does not depend on time, the electric field intensity E _THz at the far side of the terahertz light is calculated from _Equation 4, and the carrier density is It is proportional to the time differential of n and the mobility μ of the carrier, the cross-sectional area S through which the current flows, and the electric field E _bias applied between the two conductive films 12 and 13.
Now, in order to maximize the radiation intensity of the terahertz light, an electric field E applied between the two conductive films 12 and 13
_It is assumed that the _bias is adjusted to the electric field strength immediately before the dielectric breakdown occurs.

By changing the material of the substrate 11 as the photoconductive portion,
If not present, the carrier mobility μ changes over time.
It is thought to be. Also, using the same laser light source 21
Laser light intensity per unit area of excitation pulsed light irradiation area
And when the carrier density n changes with time,
Conceivable. Laser light intensity per unit area at this time
Does not saturate the generated terahertz optical radiation intensity, for example.
Adjusted to the maximum strength in a range where the element is not destroyed
It has been done. Under the above conditions, the current density j
The time derivative becomes equal, and the distant distance of the emitted terahertz light
Electric field strength E at _THzDepends only on the cross-sectional area S through which the current flows.
Will exist. Therefore, the cross-sectional area S in which the current flows
Becomes larger, the electric power of the emitted terahertz light at a far distance is increased.
Field strength E _THzGrows larger.

Comparing this embodiment with the above-described comparative example, the irradiation region R1 in this embodiment has a length in the X-axis direction longer than the length in the Y-axis direction, and the irradiation region R2 in the comparative example has an X-axis direction. Is the same as the length in the Y-axis direction, and the laser light intensity per unit area of each irradiation region R1, R2 is substantially the same. Therefore, the length of the irradiation region R1 in the present embodiment in the X-axis direction is longer than the length of the irradiation region R2 in the comparative example in the X-axis direction. As a result, since the cross-sectional area S through which the current flows is larger in the present embodiment than in the comparative example, the electric field intensity E _{THz in} the far distance of the emitted terahertz light is higher in the present embodiment than in the comparative example. growing. For example, the length of the irradiation region R1 in the Y-axis direction is set to 1/10 of the diameter of the irradiation region R2, and the irradiation region R1
If the length in the X-axis direction is 10 times the diameter of the irradiation region R2, the laser light intensity per unit area of each irradiation region R1, R2 is almost the same, but in the present embodiment, Since the cross-sectional area S through which the current flows is about 10 times that of the comparative example, an electric field intensity E _THz of terahertz light which is about 10 times that of the comparative example can be obtained.

As described above, according to the present embodiment, the electric field strength E _THz of the generated terahertz light at a distant position becomes large. Therefore, by using the terahertz light generation device according to the present embodiment, various devices that use terahertz light (terahertz light devices), for example, spectroscopic devices, inspection devices for semiconductors, medical products, foods, etc., analysis devices, imaging devices In such cases, it is possible to improve accuracy, reduce measurement time and inspection time, expand measurement range and inspection range, and improve S / N.

[Second Embodiment]

FIG. 5 is a schematic plan view showing a terahertz light generating element 31 used in the terahertz light generating device according to the second embodiment of the present invention, and corresponds to FIG. 2 (a). In FIG. 5, elements that are the same as or correspond to the elements in FIG. 1 and FIG. 2 are assigned the same reference numerals, and duplicate descriptions thereof will be omitted.

The terahertz light generating device according to the present embodiment differs from the first embodiment in that the terahertz light generating device 1 is replaced by the terahertz light generating device 3 shown in FIG.
Although not shown in the drawing, the same irradiation unit as the irradiation unit 2 in FIG. 1 and the same DC power supply as the DC power supply 3 in FIG. 1 are provided.

As shown in FIG. 5, the irradiation region R1 in which the irradiation unit corresponding to the irradiation unit 2 in this embodiment irradiates the terahertz light generating element 1 with the excitation pulse light is irradiated in the first embodiment. The part 2 is the terahertz light generating element 31.
It is exactly the same as the irradiation region R1 for irradiating the excitation pulsed light. The terahertz light generating element 31 shown in FIG. 5 is different from the terahertz light generating element 1 shown in FIGS. 1 and 2 in that the distance g2 between the two conductive films 12 and 13 is equal to the length of the irradiation region R1 in the X-axis direction. The only difference is that they are substantially the same.
The irradiation region R1 is located just in the region between the conductive films 12 and 13. Since the gap g2 between the two conductive films 12 and 13 is set smaller than the gap g1 in FIGS. 1 and 2, the electric field E _bias between the two conductive films 12 and 13 is dielectrically broken down. In the case of setting the electric field strength immediately before the occurrence of the electric field, the bias voltage applied between the two conductive films 12 and 13 in this embodiment is 2 in the first embodiment.
It is set to be smaller than the bias voltage applied between the two conductive films 12 and 13.

Also in this embodiment, the same advantages as those in the first embodiment can be obtained.

[Third Embodiment]

FIG. 6 shows an irradiation region R of the excitation pulse light from the irradiation unit with respect to the terahertz light generating element 1 used in the terahertz light generating device according to the third embodiment of the present invention.
3 is a schematic plan view showing No. 3, and corresponds to FIG. 2 (a) and FIG. 4. In FIG. 6, elements that are the same as or correspond to the elements in FIGS. 1, 2 and 4 are assigned the same reference numerals, and overlapping descriptions thereof are omitted.

The terahertz light generating device according to the present embodiment is provided with the terahertz light generating element 1 and the DC power source 3 which are exactly the same as those in the first embodiment. Similar to the comparative example, the irradiation unit 2 in FIG.
Is equipped with an irradiation unit corresponding to.

The terahertz light generating device according to the present embodiment is different from that of the first embodiment, as shown in FIG. 6, in which the irradiation unit in the present embodiment applies excitation pulsed light to the terahertz light generating element 1. The irradiation region R3 to be irradiated has a length in the X-axis direction longer than that in the Y-axis direction, but the length of the irradiation region R3 in the Y-axis direction is the conductive film 1.
The gap g1 between 2 and 13 is substantially the same, and the irradiation region R3 is located just between the conductive films 12 and 13, and the laser light source of the irradiation part in the present embodiment (the laser in FIG. 1). (Corresponding to the light source 21) emits laser light only at a higher intensity than the laser light emitted from the laser light source 21 of the irradiation unit 2 in the first embodiment and the laser light emitted from the laser light source of the irradiation unit in the comparative example. Is.

In the terahertz light generating element 1 using the optical switch element, when the intensity per unit area of the excitation pulse light with which the irradiation area is irradiated becomes higher than the predetermined intensity, the intensity of the generated terahertz pulse light is saturated and the excitation pulse light is excited. Even if the intensity of light per unit area is made higher than the predetermined intensity, the intensity of terahertz light cannot be further increased. Further, if the intensity of the excitation pulse light per unit area is too high, the element may be broken.

In the comparative example (see FIG. 4), assuming that the excitation pulse light intensity per unit area of the irradiation region R2 is the saturation intensity or the limit intensity for element destruction or the like, it is more preferable as a laser light source for the irradiation section. Even if a device that outputs a high-intensity laser beam is used, the generated terahertz light emission intensity is saturated or the element is destroyed, so that the emission intensity of the generated terahertz pulse light cannot be increased.

On the other hand, in the present embodiment, even if a laser light source (corresponding to the laser light source 21) that outputs higher intensity laser light is used, the irradiation area R3 is different from the irradiation area R2. The length in the Y-axis direction is the same, but X
Since the length in the axial direction is long, the excitation pulse light intensity per unit area of the irradiation region R3 can be suppressed to the saturation intensity or the limit intensity or less. Therefore, according to the present embodiment, when the laser light source of the irradiation unit (corresponding to the laser light source 21) that outputs a higher intensity laser light is used, the description of the first embodiment has been made. In combination with the action, it is possible to increase the emission intensity of the generated terahertz pulse light without saturating the generated terahertz light emission intensity or destroying the element.

For example, if the length of the irradiation region R3 in the X-axis direction is 10 times the length of the irradiation region R2 in the X-axis direction, the output of the laser light source of the irradiation unit used in the comparative example is When the excitation pulsed light intensity per unit area of the irradiation region R2 is the saturation intensity or the limit intensity such as element destruction, according to the present embodiment, the output of the laser light source of the comparative example is used as the laser light source 21. The electric field strength of the generated terahertz pulsed light at a distant position can be obtained without saturating the generated terahertz light emission intensity or destroying the element even when an output having about 10 times the output is used. Can be increased approximately 10 times.

[Fourth Embodiment]

FIG. 7 is a diagram showing a terahertz light generating element 41 used in the terahertz light generating device according to the fourth embodiment of the present invention, FIG. 7 (a) is a schematic perspective view thereof, and FIG. 7 (b). 7A is a schematic cross-sectional view taken along the line BB ′ in FIG. 7A, and FIG. 7C is an enlarged plan view showing a main part.

The terahertz light generating device according to the present embodiment differs from the first embodiment in that the terahertz light generating element 1 is replaced with the terahertz light generating element 4 shown in FIG.
Although not shown in the drawing, it is provided with an irradiation unit similar to the irradiation unit 2 in FIG. 1 and a DC power supply similar to the DC power supply 3 in FIG.

The terahertz pulse light generation element 41 is an example of a terahertz light generation element using an optical switch element that is not a so-called large-diameter optical switch element, and uses a dipole antenna.

As shown in FIG. 7, the terahertz light generating element 41 includes a substrate 42 and an upper side of the substrate 42 (upper and lower sides in FIG.
Shown above and below in (b). ), The photoconductive film 43 formed on the plane and the two conductive films 44 and 45 formed on the photoconductive film 43 and separated from each other. Conductive film 4
At least some of the portions 4, 45 are arranged so as to have a predetermined gap g3 in the Y-axis direction along the upper plane of the substrate 42.

The material of the substrate 42 is, for example, Si,
Ge, GaAs, sapphire, or the like can be used. The material of the photoconductive film 43 is, for example, low-temperature grown GaAs or ion-implanted silicon (RD-SOS).
Etc. can be used. Regarding the RD-SOS, the above-mentioned paper by Smith et al. (IEEE Journal of Quan
tum Electronics, Vol.24, No.2, pp.255-260 (198
It is also disclosed in 8)). As the conductive film 45, for example, a metal film such as Al or Au can be used.

In this embodiment, the conductive films 44 and 45 are made of
As shown in FIG. 7, transmission line portions 44a and 45a forming parallel transmission lines and electrode portions 4 formed at both ends thereof.
4b, 44c, 45b, 45c. The central portions of the transmission line portions 44a and 45a project inward, and a minute gap (for example, a gap of about several μm) g3 is provided therebetween in the direction along the upper plane of the substrate 42.
The portion near the gap g3 constitutes an optical switch element, and the portion near the gap g3 in the transmission line portions 44a and 45a constitutes a dipole antenna.

In the present embodiment, the irradiation region R4 in which the irradiation unit corresponding to the irradiation unit 2 in FIG. 1 irradiates the terahertz light generating element 41 with the excitation pulse light has a length in the X-axis direction in the Y-axis direction. The length is longer than the length, and the length of the irradiation region R4 in the Y-axis direction is substantially the same as the gap g3, and the irradiation region R4 is arranged in the region of the gap g3.

Also according to this embodiment, the same advantages as those of the first embodiment can be obtained.

Although the respective embodiments of the present invention have been described above, the present invention is not limited to these embodiments.

[0061]

As described above, according to the present invention,
The radiation intensity of the generated terahertz light can be increased.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a terahertz light generation device according to a first embodiment of the present invention.

2 is a diagram showing a terahertz light generating element in FIG. 1, FIG. 2 (a) is a schematic plan view thereof, and FIG. 2 (b) is FIG.
It is a schematic sectional drawing along the AA 'line in (a).

FIG. 3 is a schematic cross-sectional view showing another example of the terahertz light generating element.

FIG. 4 is a schematic plan view showing an irradiation region of excitation pulse light on a terahertz light generation element in a comparative example.

FIG. 5 is a schematic plan view showing a terahertz light generation element used in the terahertz light generation device according to the second embodiment of the present invention.

FIG. 6 illustrates a terahertz light generating element used in a terahertz light generating device according to a third embodiment of the present invention,
It is a schematic plan view which shows the irradiation area | region of the excitation pulse light from an irradiation part.

7A and 7B are diagrams showing a terahertz light generating element used in a terahertz light generating device according to a fourth embodiment of the present invention, FIG. 7A being a schematic perspective view thereof, and FIG.
FIG. 7C is a schematic cross-sectional view taken along the line BB ′ in FIG.
FIG. 4 is an enlarged plan view showing a main part.

[Explanation of symbols]

1,31,41 Terahertz light generating element 2 irradiation part 3 DC power supply (voltage application section) 11 Substrate (photoconductive part) 12, 13, 44, 45 Conductive film 14,43 Photoconductive film (photoconductive part) 21 Laser light source 22,24 Cylindrical lens 23 Spherical lens 42 board

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Toshishi Iwamoto             Tochi Co., Ltd. 770, Mitsutori, Otawara City, Tochigi Prefecture             Inside the Nikon F term (reference) 5F072 AB13 JJ04 PP10 RR10

Claims (4)

[Claims] 1. A photoconductive portion, and two conductive portions formed on a predetermined surface of the photoconductive portion and separated from each other, at least a part of the two conductive portions having the predetermined surface. A terahertz light generating element that is arranged so as to be spaced at a predetermined distance in a first direction, an irradiation unit that irradiates a predetermined irradiation region of the terahertz light generation element with excitation pulse light, and a space between the two conductive parts. A voltage applying unit that applies a bias voltage to the irradiation unit, the irradiation unit of the irradiation region in a second direction that is a second direction along the predetermined surface and is orthogonal to the first direction. The terahertz light generating device is configured such that a length thereof is longer than a length of the irradiation region in the first direction. 2. The excitation pulsed light in the irradiation section is such that all or most of the irradiation area is an area between the at least a part of the two conductive sections in the terahertz light generating element. The terahertz light generating device according to claim 1, which is irradiated with. 3. The terahertz light generation device according to claim 1, wherein the irradiation region has a substantially elliptical shape. 4. The ratio of the length of the irradiation region in the second direction to the length of the irradiation region in the first direction is
It is 1.1 or more, The terahertz light generation device in any one of Claim 1 thru | or 3 characterized by the above-mentioned.