JP2007324310A - Electromagnetic wave generator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electromagnetic wave generator capable of obtaining a high terahertz output even with normal (unamplified) femtosecond laser light. <P>SOLUTION: The electromagnetic wave generator for generating electromagnetic waves based on irradiated light includes a semiconductor substrate, a first approximately belt-like electrode provided on the substrate, and a second belt-like electrode parallel to the first electrode on the substrate. The first electrode has a sharp edge protrusion protruding toward the second electrode, and the sharp edge has an acute angle smaller than 90°. In addition, the generator includes an optical element for forming a plurality of condensing spots in a plurality of regions including the tip of the sharp edge protrusion. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electromagnetic wave generating device that generates an electromagnetic wave based on irradiated light, and more particularly to an electromagnetic wave generating device that generates a terahertz electromagnetic wave using short pulse light.

  In recent years, research and development of electromagnetic waves having a frequency of 0.1 to 10 THz, so-called terahertz waves, are active. This terahertz wave has the transparency of radio waves and the light condensing property of light, and can perform transmission analysis more safely than X-rays. Furthermore, since many materials have an absorption spectrum specific to the frequency band of 0.1 to 10 THz, the material and the material can be specified. For this reason, terahertz waves are expected to be used in fields such as security, biotechnology, medical, food processing, freshness analysis, and industrial applications.

  As a typical means for generating terahertz waves, a photoconductive switch element as shown in FIG. 16 is used (for example, Non-Patent Document 1). In this element, electrodes 102 and 103 such as gold are formed on a semi-insulating GaAs substrate 101 (or a substrate in which low-temperature grown GaAs is formed on a semi-insulating GaAs substrate). The electrodes have convex portions 102A and 103A, and these convex portions are antennas for electromagnetic wave radiation. A voltage source 104 is connected to the electrodes 102 and 103. A bias voltage is applied between the electrodes 102 and 103 by the voltage source 104. However, since there is almost no free carrier in the semi-insulating GaAs substrate 101 between the electrodes, no current flows (when there is no irradiation). When femtosecond laser light 105 (wavelength: about 800 nm, pulse width: about 100 fs) is irradiated between the electrode protrusions 102A and 103A, free carriers (electrons / holes) are generated in the irradiated spot 106, and the electrode protrusions 102A, A pulsed current flows between 103A. An electromagnetic wave is generated by this pulsed current and is emitted mainly from the back surface (the surface on which no electrode is formed) of the substrate 101. This electromagnetic wave has a frequency of 1 to 2 THz, which is a so-called terahertz wave.

  In order to improve the signal-to-noise ratio in the measurement using the terahertz wave, it is desirable that the output of the terahertz wave is high. By making the structure of FIG. 16 into an array, high output can be achieved. An example is shown in FIG. A similar structure can be found, for example, in US Pat.

  Electrodes 108 and 109 are formed on a semi-insulating GaAs substrate 107 (or a substrate obtained by growing low-temperature grown GaAs on a semi-insulating substrate). The gold electrode has five sets of convex portions (108A to E, 109A to E) and serves as five sets of antennas for electromagnetic waves. A bias voltage is applied between the electrodes 108 and 109 by the voltage source 110. When the femtosecond laser beam 111 is irradiated between the electrode convex portions 108A to E and 109A to E, free carriers (electrons and holes) are generated in the irradiated spot 112, a current flows, and a terahertz wave is emitted. The output of the terahertz wave is ideally (output per one photoconductive switch element) × (number of elements) 2.

Another conventional example (Non-Patent Document 2) is shown in FIG. Three sets of gold / chrome electrodes 121 and 122 are formed on a semi-insulating GaAs substrate 120. The voltage source 123 forms a positive potential on the electrode 121 and a negative electrode on the electrode 122. An opaque film 124 is formed between the electrode sets so as not to radiate anti-phase electromagnetic waves. The opaque film is composed of a gold / chromium film having a polyimide layer or a SiO2 layer as a spacer layer. The incident femtosecond laser 125 is enlarged to form a spot 126 and is irradiated on the entire electrode. A terahertz wave is radiated from the photoconductive switch element between the electrodes, and as a result, the radiation of the terahertz wave increases. In this configuration, the portion of the photoconductive switch element whose potential is inverted is shielded by the opaque film 124 and is not switched. As a result, a terahertz wave having an inverted phase is not output, and a high output can be obtained.
JP 2000-49402 A Masahiko Tani, Mariko Yamaguchi, Taijiro Yonekura, Fumi Miyamaru, Junji Yamamoto, Masanori Minayuki, IEICE, vol.87 No.8 718 (2004) A. Dreyhaupt, S. Winner, T. Dekorsy, and M. Helm, Applied Physics Lettetrs, vol. 86 121114 (2005)

  In the structure as shown in FIG. 17, the spot 112 must be enlarged (compared to the case of FIG. 16) in order to irradiate femtosecond laser light between the electrode convex portions 108A-E and 109A-E. In addition, the femtosecond laser is irradiated outside the photoconductive switch element region, but these do not contribute to the generation of electromagnetic waves. For this reason, with the same amount of femtosecond laser light, the light amount at the irradiation spot decreases → the number of generated carriers decreases, the pulse current decreases, the output per photoconductive switch element decreases, and the total terahertz output decreases. End up. Similar problems occur in the conventional example of FIG. In particular, in the case of FIG. 18, the region of the opaque film 124 is greatly lost, and a high-power femtosecond laser beam is required.

  On the other hand, Patent Document 1 describes that the enlarged incident light is divided and condensed on each photoconductive switch element by a lens or the like. However, it is difficult to obtain a sufficient output simply by collecting the expanded light.

  Although it is conceivable to amplify femtosecond laser light and use the laser light intensified, such an amplification device (for example, a regenerative amplification type laser device) is generally large / expensive, which is not preferable in practice.

  As a further problem, when the photoconductive switch element is two-dimensionally arranged, a region where the potential is reversed (that is, a region where the radiated electromagnetic wave is weakened) is formed. In the case of FIG. 18, this is dealt with by providing a light-shielding region. However, the existence of such an ineffective region increases the size of the photoconductive switch element and increases the chip cost.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a photoconductive switch element that can obtain a high terahertz output even with a general (non-amplified) femtosecond laser beam and has a low ineffective region and high cost performance.

  In order to solve the above-described problems, an electromagnetic wave generator of the present invention is an electromagnetic wave generator that generates an electromagnetic wave based on irradiated light, and includes a semiconductor substrate and a substantially strip-shaped first electrode provided on the semiconductor substrate. The semiconductor substrate includes a strip-shaped second electrode parallel to the first electrode, the first electrode having a sharpened portion protruding toward the second electrode, and the sharpened portion having an acute angle of less than 90 degrees It is characterized by having.

  According to this configuration, by providing a sharp pointed portion where the electric field is concentrated, carrier generation is increased and a strong pulsed current can be obtained. As a result, the terahertz output can be increased.

  Here, the first electrode has a plurality of sharpened portions arranged at a predetermined interval, and the electromagnetic wave generating device further includes an optical for forming a plurality of focused spots in a plurality of regions including the tips of the sharpened portions. An element may be provided.

  According to this configuration, the optical element can increase the light density and reduce invalid light irradiation. As a result, the terahertz output can be further increased.

  The electromagnetic wave generator of the present invention is an electromagnetic wave generator that generates an electromagnetic wave based on irradiated light, the semiconductor substrate, a plurality of substantially strip-shaped first electrodes provided on the semiconductor substrate, and the semiconductor A substrate is provided with a plurality of strip-shaped second electrodes provided alternately in parallel with the first electrode, and a light collecting element, and each of the first electrodes protrudes toward the second electrode. The sharpened portion has an acute angle of less than 90 degrees, and the condensing element irradiates a plurality of condensing spots on a plurality of regions including the tip of the sharpened portion.

  According to this configuration, the light condensing element can increase the light density and reduce invalid light irradiation. Further, by focusing the laser beam on a plurality of sharp points where the electric field is concentrated, carrier generation is increased and a strong pulsed current can be obtained. As a result, the terahertz output can be increased.

Here, the plurality of first electrodes may be positive electrodes.
The generated electrons travel to the positive electrode. By generating and accelerating electrons in the vicinity of the positive electrode, the frequency of the emitted electromagnetic wave can be further increased. That is, the output can be widened, which is useful for analysis and the like. Electromagnetic radiation due to the traveling of holes is smaller than that due to electrons, and the influence can be ignored.

  Here, the plurality of first electrodes may have the plurality of sharpened portions on one side in the same longitudinal direction, and each of the regions including the tips of the sharpened portions may constitute a photoconductive switch.

  According to this configuration, the potential direction of each photoconductive switch element is the same direction. By setting them in the same direction, electromagnetic waves having the same phase are emitted from each array element, and the output increases.

  Here, the electromagnetic wave generator may further include a film for reducing light in a region other than the plurality of focused spots.

  According to this configuration, for example, the generation of a parasitic photoconductive switch element region on the substrate is prevented by irradiating scattered light or stray light between the electrodes.

Here, the film for reducing light may have a function of reflecting light.
By forming such a reflective film, alignment between the optical condensing element and the substrate having the electrodes is facilitated.

Here, a protective film may be provided on the surface of the sharpened portion.
The surface protective film can prevent air discharge due to a strong electric field.

Here, the plurality of sharpened portions may be two-dimensionally arranged.
According to this configuration, more light output can be obtained by using a two-dimensional array.

  Here, the plurality of sharpened portions may be arranged in a matrix, and each row may be arranged so as to be shifted by a half pitch with respect to an adjacent row or each column with respect to an adjacent column.

  According to this configuration, the elements (for example, microlenses) of the light condensing elements can be arranged in a close-packed manner, and an ineffective area (such as a region where light is not condensed) between the elements can be reduced. As a result, it operates with high efficiency.

Here, the condensing element may have a plurality of cylindrical shapes.
By making each element of the condensing element into a cylindrical shape, the fabrication becomes easy.

  Here, when the main wavelength of the electromagnetic wave is λ and the refractive index of the semiconductor substrate is n, the interval between the sharpened portions may correspond to λ / 2n.

  According to this configuration, the electromagnetic wave radiated from the sharpened point resonates, and a stronger electromagnetic wave can be emitted.

  Here, each of the plurality of first electrodes has the plurality of sharpened portions on both sides in the longitudinal direction, each of the regions including the tips of the sharpened portions constitutes a photoconductive switch, and the electromagnetic wave generating device further includes: Between the first photoconductive switch group corresponding to the first side in the longitudinal direction of each one electrode and the second photoconductive switch group corresponding to the second side in the longitudinal direction of each first electrode, You may provide the time delay element which gives time delay to irradiation light.

  According to this configuration, in the substrate on which the photoconductive switch elements are two-dimensionally formed, an area that needs to be shielded is removed (because the applied electric field direction is reversed between the first conductive switch group and the second conductive switch group). be able to. That is, the useless area of the substrate can be reduced, and the cost performance is improved.

  Here, the time delay element may be formed of a light-transmitting material and have irregularities corresponding to the first photoconductive switch group and the second photoconductive switch group.

  According to this configuration, a time delay can be added by the light passing through the convex portion and the light passing through the concave portion, and the frequency can be controlled.

  Here, the electromagnetic wave generator may be capable of exchanging at least two time delay elements having different height differences of the unevenness.

  By changing the height difference of the unevenness, the outgoing electromagnetic wave can be narrowed to a specific frequency.

  Here, the electromagnetic wave generator may include the light condensing element on the convex and concave portions of the concave and convex portions.

  According to this configuration, incident light is collected and photoconductive switching can be performed efficiently.

Here, the said time delay element may have the said condensing element in the surface which does not have an unevenness | corrugation.
According to this configuration, the light collecting element can be easily manufactured.

Here, the time delay element may be formed on the semiconductor substrate.
According to this configuration, the entire apparatus can be reduced in size.

The electromagnetic wave generator of the present invention is an electromagnetic wave generator that generates an electromagnetic wave based on irradiated light, and includes a semiconductor substrate, a plurality of strip-shaped first electrodes provided on the semiconductor substrate, and the semiconductor The substrate includes a plurality of strip-shaped second electrodes provided alternately in parallel with the first electrode, and a region sandwiched between the first electrode and the second electrode constitutes a plurality of photoconductive switches. The electromagnetic wave generator further includes a first photoconductive switch group corresponding to a first side in the longitudinal direction of each one electrode and a second light corresponding to a second side in the longitudinal direction of each one electrode. A time delay element that gives a time delay to the irradiation light is provided between the conduction switch group.

  According to this configuration, in the substrate on which the photoconductive switch elements are two-dimensionally formed, an area that needs to be shielded is removed (because the applied electric field direction is reversed between the first conductive switch group and the second conductive switch group). be able to. That is, the useless area of the substrate can be reduced, and the cost performance is improved.

  The method for manufacturing an electromagnetic wave generator according to the present invention is a method for manufacturing the above-described electromagnetic wave generator, wherein a condensing element is formed by forming a resin on a substrate and heat-treating the resin. .

  This is a method for producing a condensing element by utilizing the fact that the resin is rounded by the heat treatment, and the condensing element corresponding to the sharp part can be easily formed.

(First embodiment)
FIG. 1 is a perspective view showing a configuration of an electromagnetic wave generator in a first embodiment of the present invention. This electromagnetic wave generating device is composed of a semi-insulating GaAs substrate 1, a plurality of substantially strip-shaped electrodes 2 having a sharp convex portion 5, a plurality of electrodes 3, an opaque polymer 6, and a quartz substrate 8 functioning as an optical element. Further, the voltage source 4 applies a voltage between the gold electrode 2 and the gold electrode 3 using the gold electrode 2 as a positive electrode.

  Gold electrodes 2 and 3 having a width of 10 μm and an interval of 100 μm are alternately formed on a semi-insulating GaAs substrate 1 having a thickness of 350 μm. There are 20 gold electrodes 2 and 3 with a pitch of 150 μm in the vertical direction of FIG. 1 (only three sets are shown in FIG. 1 for simplicity). The electrodes 2 and 3 are connected to a voltage source 4 and are wired so that the electrode 2 has a positive potential and the electrode 3 has a negative potential. The voltage source 4 may be a constant voltage, or may supply a pulse voltage synchronized with the incident femtosecond laser beam. The electrode 2 is formed with 20 sharp convex portions 5 having an isosceles triangle shape with a base of 10 μm and a height of 15 μm at intervals of 150 μm in both the horizontal and vertical directions (only four are shown in FIG. 1 for simplicity). )

  This interval corresponds to λ / 2 (half wavelength) of the main frequency of about 0.5 THz (main wavelength of about 600 μm) of electromagnetic waves from a normal dipole antenna, and becomes a resonance state to increase the electromagnetic waves (effectiveness of a semi-insulating GaAs substrate) The refractive index is approximately 2).

  The angle of the tip is desirably an acute angle, and is about 36 degrees in this embodiment. Accordingly, there are a total of 20 × 20 sets = 400 pieces of a plurality of photoconductive switch elements composed of the sharp convex part 5 and the negative electrode 3 (the diameter of the incident laser light is 3 mm as described below. The number is about 300). Further, an opaque polymer 6 that absorbs light in the 800 nm band is formed on the surface of the substrate 1 other than the gold electrodes 2 and 3 and the photoconductive switch element surface 7. The opaque polymer 6 can suppress malfunctions caused by scattered light and stray light and electromagnetic radiation of antiphase.

  On the other hand, 20 × 20 rows of microlenses 9 made of resin are formed on a quartz substrate 8 having a thickness of 500 μm (in FIG. 1, only 4 × 3 rows are shown for simplicity). The distance between the center of the microlenses is 150 μm in both the horizontal direction and the vertical direction. The substrate 8 on which the microlenses are formed and the substrate 1 on which the electrodes are formed are bonded with an ultraviolet curable resin (in FIG. 1, the substrate 1 and the substrate 8 are drawn separately for the sake of explanation). The shape and position of each microlens are formed so that the focal point of the incident femtosecond laser beam is in the vicinity of the apex of the sharp convex portion 5.

  Now, in the case of the prior art having only one photoconductive switch element (in the case of FIG. 16), the light emitted from the femtosecond laser device (spot diameter of about 1 mm) is reduced to about 10 μm. Therefore, the amount of incident light per unit area in the photoconductive switch element is increased to about 10,000 times that emitted from the femtosecond laser device.

On the other hand, the present invention having a plurality of photoconductive switch elements is as follows.
(1) The femtosecond laser beam 10 emitted from the femtosecond laser device with a spot diameter of about 1 mm is expanded in advance to a diameter of about 3 mm, which is approximately the same size as the photoconductive switch element, by a beam expander or the like. By this enlargement, the amount of light per unit area is reduced to about 1/10.

  (2) As shown in FIG. 2, this light is incident on the entire surface of each microlens as a spot 11. For example, the light incident on the microlens 12 is collected as a spot 14 (about 10 μm in diameter) near the tip of the sharp convex portion 5 by the condensing action (13) of the microlens. Due to this light condensing action, the amount of light per unit area increases about 200 times.

  Therefore, (1) and (2) as a total, the amount of incident light per unit area in the photoconductive switch element is 20 times larger than that emitted from the femtosecond laser device.

  On the other hand, the electric field in the vicinity of the sharp convex portion 5 is about 10 times (compared to the case where there is no sharp portion), and the electron velocity can be improved about 10 times.

Now, the radiation terahertz electric field E is approximately E = Ebσ / [σ + (1 + √ε) / η]
(For example, Justin T. Darrow, Xi-Cheng Zhang, David H. Auton, and Jeffrey D. Morse, IEEE Journal of Quantum Electronics vol. 28 1607 (1992)). Here, E _b is the bias voltage, σ is the conductivity, ε is the dielectric constant, and η is the vacuum impedance. In the case of a general femtosecond laser, the amount of light is relatively small and σ << (1 + √ε) / η, so the above equation becomes as follows.

E = E _b ση / (1 + √ε)
≒ envη / (1 + √ε)

  Here, e is the electron elementary quantity, n is the number of generated carriers, and v is the velocity.

  From the above, the terahertz wave emitted from each of the plurality of photoconductive switch elements has an electric field intensity per element of about 1/50 compared to the conventional technique (FIG. 16) having only one photoconductive switch element. (In electricity, it is only 1/2500).

However, the present invention has an effective number of 300 photoconductive switch elements. The output is 300 ² = 90000 times the radiation power per element in the coherent radiation state. Therefore, the output (power) from the all-optical switch element can be improved by about 35 times compared to the case where there is only one photoconductive switch element. As a result of the experiment, an optical output of about 30 times was obtained.

  In the case of a rectangular electrode convex part without forming a sharp convex part, the output (power) from the all-optical switch element is about 0.4 times that in the case where there is only one photoconductive switch element. It was only about. From this result, it can be seen that it is effective to form a sharp convex portion on the positive electrode as in the present invention, and to collect the incident light from the microlens there.

  Further, as shown in FIG. 3, a high resistance Si lens 15 is attached to the terahertz wave radiation side of semi-insulating GaAs. Thereby, it is possible to prevent total reflection occurring inside the terahertz wave radiation surface of the semi-insulating GaAs substrate 1. Loss caused by total reflection can be suppressed by the Si lens, and high output can be obtained.

(Second Embodiment)
FIG. 4 is a perspective view showing the configuration of the electromagnetic wave generator in the second embodiment. FIG. 5 is a perspective view showing another configuration of the electromagnetic wave generator in the second embodiment. 4 and 5 differ from FIG. 1 in that the quartz substrate 8 has a plurality of cylindrical lenses 20 and 21 in the vertical direction or the horizontal direction instead of having the plurality of microlenses 12.

  Since the cylindrical lenses 20 and 21 collect light only in one direction, the light collecting property is weak compared to the first embodiment, but the manufacturing method is easy and the manufacturing margin can be expanded.

(Third embodiment)
FIG. 6 is a perspective view showing the configuration of the electromagnetic wave generator in the third embodiment. 6 differs from FIG. 1 in that it has vertical or horizontal cylindrical lenses 20, 21 instead of having a plurality of microlenses 23 instead of the quartz substrate 8.

  The microlens 23 is directly formed on the substrate 1 on which the electrodes are formed (so-called on-chip lens). Thereby, size reduction of this apparatus can be achieved. Such an on-chip lens can be applied to other embodiments.

(Fourth embodiment)
FIG. 7A is a diagram showing the arrangement of the sharpened protrusions 5 in the fourth embodiment of the present invention. However, the light shielding layer is omitted in FIG. 7A. Moreover, FIG. 7C is a perspective view which shows the structure of the electromagnetic wave generator in 4th Embodiment. In FIG. 7A, compared with FIG. 1 of the first embodiment, the sharp convex portions 5 are arranged in a matrix and the sharp convex portions 5 of each row are adjacent to the adjacent rows, or the sharp convex portions 5 of each column. Are different from each other in that they are arranged with a half-pitch shift.

  A positive electrode 2 and a negative electrode 3 having sharp projections are formed on the substrate 1 (only three sets are drawn for simplicity). P is the pitch in the row direction of the sharp convex arrangement. I = 1, 2, 3,... The arrangement of the sharp projections on the odd lines ((2i-1), (2i + 1) lines) and the arrangement of the sharp projections on the even lines (2i) differ by P / 2 in the horizontal direction. ing. As described above, when the sharp convex portions are shifted by a half pitch between the odd-numbered row electrode and the even-numbered row electrode, the corresponding microlenses 33 are also shifted by a half pitch between the odd-numbered row and the even-numbered row.

  In order to use incident light efficiently, it is desirable that the microlens is made as large as possible and the area between the microlenses is small (the light incident on the area between adjacent microlenses (for example, the area 34) is caused by the microlens. Does not contribute to light collection). By the way, as will be described later, since microlenses are often formed by melting resin, adjacent microlenses should not come into contact (if adjacent microlenses come into contact, adjacent microlenses are combined in the manufacturing process. And it becomes one big lens). For this reason, it can be considered that the maximum radius of the microlens is almost equal to the radius when the outermost periphery of the microlens contacts. In the case of FIG. 7A, the ratio of the area of the microlens area to the entire irradiation area is about 9%.

  On the other hand, as shown in FIG. 7B, when the sharp convex portion is not shifted between the odd-numbered row electrode and the even-numbered row electrode, the microlens 35 is not shifted between the odd-numbered row and the even-numbered row. Similarly to the above, the light incident on the area (for example, the area 36) between the adjacent microlenses does not contribute to the light collection by the microlens and is invalid. In this arrangement, when the radius of the microlens is set to the maximum allowable value, the ratio of the area of the inter-microlens area (area such as the area 36 where light is not condensed by the microlens) to the entire irradiation area is approximately 22%. become. That is, as compared with the case of FIG. 7A, the area where the incident light is invalid increases three times.

  Therefore, by using a structure in which the sharp convex portion 5 is shifted by a half pitch between the odd-numbered row electrode and the even-numbered row electrode, invalid light can be reduced and high-efficiency operation becomes possible.

  In the case of FIG. 7B, the horizontal and vertical pitches of the sharp protrusions are both P, but in the case of FIG. 7B, the horizontal period is slightly smaller than P with respect to P, but the vertical period is slightly smaller than 0.87P. The effect on properties is negligible.

(Fifth embodiment)
FIG. 8 is a perspective view showing the configuration of the electromagnetic wave generator in the fifth embodiment. However, the quartz substrate 8 is omitted. This figure is different from FIG. 1 in that a SiO 2 protective film 24 is added. The SiO2 protective film 24 is formed so as to cover both electrode portions and electrodes. Since the electrode portion is also covered with the SiO 2 protective film 24, air discharge due to a strong electric field can be prevented. The microlens may be formed directly on this protective film.

(Sixth embodiment)
FIG. 9 is a perspective view showing the configuration of the electromagnetic wave generator in the sixth embodiment. This figure is different from FIG. 1 in that a highly reflective film 25 is added.

  The semi-insulating GaAs substrate 1 and the electrodes 2 and 3 are covered with a highly reflective film 25 (TiO2 / SiO2 multilayer film) that reflects incident femtosecond laser light except for the vicinity of the sharp convex part 5. For example, even if the light incident from the microlens 12 forms a spot 14 in the vicinity of the sharp convex portion, if there is a rotational deviation (θ deviation) as shown in the figure, it passes through the microlens 26 and is condensed, for example. The emitted light forms a spot 27 at a position away from the sharp convex portion. However, since the spot 27 is on the highly reflective film 25, strong reflected light is generated. Therefore, the positional deviation between the substrate 1 and the substrate 8 can be checked by the reflected light, and the manufacture becomes easy.

Next, a method for manufacturing a microlens will be described.
10A and 10B show a method for manufacturing a microlens. Resin 31 (square when viewed from above) is formed on substrate 30 (glass substrate 8 or semi-insulating GaAs substrate 1 on which an electrode is formed) using photolithography (FIG. 10A). Next, when thermal annealing is performed at about 150 ° C. for 1 hour, the resin softens and becomes hemispherical as shown in FIG. In FIG. 10A, a cylindrical lens can be obtained by forming a rectangular resin 31 as viewed from above.

(Seventh embodiment)
FIG. 11 is a perspective view showing the configuration of the electromagnetic wave generator in the seventh embodiment. 1 is different from FIG. 1 in that a glass substrate 41 is provided instead of the quartz substrate 8 and that the electrode 2 does not have a sharp projection 5. FIG. 12 is an explanatory diagram of the operation.

  Gold electrodes 2 (2a, 2b, 2c) and 3 (3a, 3b, 3c) having a width of 10 μm and an interval of 100 μm are formed on a semi-insulating GaAs substrate 1 having a thickness of 350 μm. There are 20 sets of the electrodes 2 and 3 at a pitch of 150 μm in the vertical direction of FIG. 11 (only three sets are shown in FIG. 1 for simplicity). The electrodes 2 and 3 are connected to a voltage source 4 and are wired so that the electrode 2 has a positive potential and the electrode 3 has a negative potential. The voltage source 4 may be a constant voltage, or may supply a pulse voltage synchronized with the incident femtosecond laser beam.

  Grooves (projections 42 and recesses 43) are formed on the surface of a glass substrate 41 (refractive index 1.5) having a thickness of 1 mm. The groove pitch was 300 μm, and the groove depth (height difference between the convex part and the concave part) was 600 μm. With these values, the same results as shown below can be obtained even when the pitch is 150 to 300 μm and the depth is 300 to 600 μm.

Now, an electric field is generated in the substrate 1 by the positive electrode 2 and the negative electrode 3, but the direction differs by 180 degrees for each row. That is, in FIG.
A downward electric field 44a is generated by the electrodes 2a and 3a.
An upward electric field 45a is formed by the electrodes 3a and 2b.
A downward electric field 44b is generated by the electrodes 2b and 3b.
(The same applies hereinafter)
Will occur.

  On the other hand, in the incident femtosecond laser 46, a time delay occurs between the convex portion and the concave portion due to the glass substrate 41 with the groove. The light passing through the convex part has a longer optical length by (groove depth) x (glass refractive index-air refractive index) than the light passing through the concave part. In the present embodiment, there is an optical length difference of 600 μm × (1.5−1) = 300 μm, which corresponds to a time delay of 1 psec. As can be seen in FIG. 12, the light passing through the recesses receives an upward electric field 45 (45a, 45b,...) And generates THz waves 47 (47a, 47b,...). On the other hand, the light passing through the convex portion receives a downward electric field 44 (44a, 44b,...) With a delay of 1 psec, and generates THz waves 48 (48a, 48b,...). Since the effective pulse width of the THz wave is generally less than 1 psec, the THz wave 47 and the THz wave 48 do not interfere with each other. That is, even if the directions of the electric fields 45 and 44 are reversed, THz waves generated therefrom do not cancel each other, and the total THz output (THZ wave 47 + THZ wave 48) can be increased. In addition, in this element, there is no region that needs to be shielded on the chip surface (even if the applied electric field direction is reversed), and all photoconductive switch elements to which an electric field is applied from the outside can be used (does not contribute to output). There is no unnecessary area. That is, an element with high cost performance can be realized.

  Note that the spectrum of all THz waves composed of THz waves 47 + THz waves 48 can be narrowed, or unnecessary frequency cuts can be realized by the amount of time delay of the two lights passing through the convex and concave portions. it can. Thus, the output THz energy can be collected only at a desired frequency, which is useful for analytical applications. For example, the glass substrate 41 in which the grooves 42 and 43 are formed is detachable and a plurality of glass substrates 41 are prepared. By making the depths of these grooves different from each other, it is possible to add different time delay amounts by exchanging the substrate 41.

(Eighth embodiment)
FIG. 13 is a perspective view showing the configuration of the electromagnetic wave generator in the eighth embodiment. The figure differs from FIG. 11 in that the convex and concave portions of the glass substrate 41 are cylindrical lenses.

  A condensing element of a micro cylindrical lens is formed on the surface of the groove (42, 43) of the glass substrate 41. By this micro cylindrical lens, the incident laser beam 10 (spot is enlarged and looks like 11) is condensed like a light beam 13 and becomes like an elongated spot 14, for example. Thereby, the incident laser beam 10 can be condensed only in the incident region of the photoconductive switch element, and an efficient operation can be performed.

(Ninth embodiment)
FIG. 14 is a perspective view showing the configuration of the electromagnetic wave generator in the ninth embodiment. The figure differs from FIG. 11 in that the microlens is formed on the convex and concave portions of the glass substrate 41 and the shape of the electrode 2.

  The positive electrode 2 is provided with sharp convex portions 5 on both upper and lower sides (on both sides facing the negative electrode). In addition, microlenses 9 are formed in the grooves (42, 43) of the glass substrate 41, and incident light is collected on the sharp convex portion 5. As described above, the outgoing terahertz wave can be further strengthened by providing the sharp convex portion and concentrating the light there.

(Tenth embodiment)
FIG. 15 is a perspective view showing the configuration of the electromagnetic wave generator in the tenth embodiment. This figure differs from FIG. 11 in that a microlens 49 is formed on the back surface of the glass substrate 41.

  Since the back surface of the glass substrate 41 is a flat surface (without a groove), a microlens can be formed more easily. Although the cylindrical lens is formed on the surface of the groove in the eighth embodiment, it is needless to say that the same effect can be obtained even if the cylindrical lens is formed on the back surface of the substrate as in the tenth embodiment. .

  In the above embodiment, the condensing element, the substrate on which the delay steps are integrated, and the electromagnetic wave generation substrate are described separately. However, as in the third embodiment, all may be integrated on one substrate.

  By using the present invention, a high-output electromagnetic wave generator can be realized. Use in fields such as non-destructive measurement, medicine, biotechnology, agriculture, food, and the environment can be greatly expected.

It is a perspective view which shows the structure of the electromagnetic wave generator in the 1st Embodiment of this invention. It is a figure which shows the condensing state of the electromagnetic wave generator in 1st Embodiment. It is detail drawing which shows the structure of an electromagnetic wave generator. It is a perspective view which shows the structure of the electromagnetic wave generator in 2nd Embodiment. It is a perspective view which shows the other structure of an electromagnetic wave generator. It is a perspective view which shows the structure of the electromagnetic wave generator in 3rd Embodiment. It is a figure which shows arrangement | positioning of the sharp convex part 5 in 4th Embodiment. It is a figure which shows other arrangement | positioning of the sharp part convex 5. It is a perspective view which shows the structure of an electromagnetic wave generator. It is a perspective view which shows the structure of the electromagnetic wave generator in 5th Embodiment. It is a perspective view which shows the structure of the electromagnetic wave generator in 6th Embodiment. It is a figure which shows the manufacturing method of a micro lens. It is a figure which shows the manufacturing method of a micro lens. It is a perspective view which shows the structure of the electromagnetic wave generator in 7th Embodiment. It is operation | movement explanatory drawing of an electromagnetic wave generator. It is a perspective view which shows the structure of the electromagnetic wave generator in 8th Embodiment. It is a perspective view which shows the structure of the electromagnetic wave generator in 9th Embodiment. It is a perspective view in 10th Embodiment. It is a perspective view which shows the structure of the electromagnetic wave generator in a prior art. It is a perspective view which shows the structure of the electromagnetic wave generator arrayed in the prior art. It is a perspective view which shows the structure of the electromagnetic wave generator arrayed in the prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semi-insulating GaAs substrate 2, 2a, 2b Electrode 3, 3a, 3b Electrode 4 Voltage source 5 Sharp convex part 6 Opaque polymer 7 Photoconductive switch element surface 8 Quartz substrate 9, 23, 26, 32 Micro lens 10, 12 Femto Second laser beam 11, 14 Spot 13 Condensing action 15 High resistance Si lens 20, 21 Cylindrical lens 24 SiO2 protective film 25 High reflection film 30 Substrate 31 Resin 33, 35 Micro lens maximum outer periphery 34, 36 Micro lens condensing Non-formed region 41 Glass substrate 42, 42a, 42b Glass substrate convex portion 43, 43a, 43b Glass substrate concave portion 44, 45 Electric field 46 Incident femtosecond laser light 47, 48 Emitted terahertz light 49 Back microlens 101, 107, 120 Semi-insulating GaAs substrate 102, 103, 10 , 109,121,122 gold electrodes 102A, 103A, 108A~E, 109A~E electrode protrusions 104, 110 voltage source 105,111,125 femtosecond laser pulses 106,112,126 spot 124 opaque film

Claims (20)

An electromagnetic wave generator for generating an electromagnetic wave based on irradiated light,
A semiconductor substrate;
A substantially strip-shaped first electrode provided on the semiconductor substrate;
The semiconductor substrate includes a strip-shaped second electrode parallel to the first electrode,
The first electrode has a sharpened portion protruding toward the second electrode,
The sharpened portion has an acute angle of less than 90 degrees. The first electrode has a plurality of sharpened portions arranged at predetermined intervals,
The electromagnetic wave generator further includes:
The electromagnetic wave generator according to claim 1, further comprising an optical element that forms a plurality of focused spots in a plurality of regions including the tip of the sharpened portion. An electromagnetic wave generator for generating an electromagnetic wave based on irradiated light,
A semiconductor substrate;
A plurality of substantially strip-shaped first electrodes provided on the semiconductor substrate;
A plurality of strip-shaped second electrodes provided alternately to the semiconductor substrate in parallel with the first electrodes;
A light collecting element,
Each of the first electrodes has a plurality of sharpened portions protruding toward the second electrode,
The pointed portion has an acute angle of less than 90 degrees;
The electromagnetic wave generating device, wherein the condensing element irradiates a plurality of condensing spots on a plurality of regions including a tip of a sharpened portion.   The electromagnetic wave generator according to claim 3, wherein the plurality of first electrodes are positive electrodes. The plurality of first electrodes have the plurality of sharpened portions on one side in the longitudinal direction in the same direction,
Each of the area | regions containing the front-end | tip of a sharp part comprises a photoconductive switch. The electromagnetic wave generator of Claim 3 characterized by the above-mentioned. The electromagnetic wave generator further includes:
The electromagnetic wave generator according to claim 3, wherein a film for reducing light is formed in a region other than the plurality of focused spots. The electromagnetic wave generator according to claim 6, wherein the film that reduces light has a function of reflecting light. The electromagnetic wave generator according to claim 3, further comprising a protective film on a surface of the sharpened portion. The electromagnetic wave generator according to claim 3, wherein the plurality of sharpened portions are two-dimensionally arranged. The plurality of sharpened portions are arranged in a matrix;
The electromagnetic wave generator according to claim 7, wherein each row is arranged with a half pitch shift with respect to an adjacent row or each column with respect to an adjacent column. The electromagnetic wave generating device according to claim 3, wherein the light collecting element has a plurality of cylindrical shapes. The electromagnetic wave generator according to claim 3, wherein the interval between the sharpened portions corresponds to λ / 2n, where λ is the main wavelength of the electromagnetic wave and n is the refractive index of the semiconductor substrate. The plurality of first electrodes have the plurality of sharpened portions on both sides in the longitudinal direction,
Each of the regions including the tip of the sharp point constitutes a photoconductive switch,
The electromagnetic wave generator further includes:
Between the first photoconductive switch group corresponding to the first side in the longitudinal direction of each one electrode and the second photoconductive switch group corresponding to the second side in the longitudinal direction of each first electrode, The electromagnetic wave generator according to claim 3, further comprising a time delay element that gives a time delay to the irradiation light. The electromagnetic wave generator according to claim 13, wherein the time delay element is formed of a light transmitting material and has irregularities corresponding to the first photoconductive switch group and the second photoconductive switch group. The electromagnetic wave generation device according to claim 14, wherein the electromagnetic wave generation device is capable of exchanging at least two time delay elements having different height differences of the unevenness. The electromagnetic wave generator is
The electromagnetic wave generating device according to claim 13, wherein the light condensing element is provided in the convex and concave portions of the unevenness. The electromagnetic wave generator according to claim 13, wherein the time delay element has the light condensing element on a surface having no unevenness. The electromagnetic wave generator according to claim 13, wherein the time delay element is formed on the semiconductor substrate. An electromagnetic wave generator for generating an electromagnetic wave based on irradiated light,
A semiconductor substrate;
A plurality of strip-shaped first electrodes provided on the semiconductor substrate;
A plurality of strip-shaped second electrodes provided alternately in parallel with the first electrode on the semiconductor substrate;
The region sandwiched between the first electrode and the second electrode constitutes a plurality of photoconductive switches,
The electromagnetic wave generator further includes:
Between the first photoconductive switch group corresponding to the first side in the longitudinal direction of each one electrode and the second photoconductive switch group corresponding to the second side in the longitudinal direction of each first electrode, An electromagnetic wave generator comprising a time delay element that gives a time delay to irradiation light. A method for producing an electromagnetic wave generator according to claim 3,
Forming resin on the substrate,
A condensing element is formed by heat-treating the resin. A method for manufacturing an electromagnetic wave generating device.