WO2003032451A1 - Terahertz light generator - Google Patents

Terahertz light generator Download PDF

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Publication number
WO2003032451A1
WO2003032451A1 PCT/JP2002/010365 JP0210365W WO03032451A1 WO 2003032451 A1 WO2003032451 A1 WO 2003032451A1 JP 0210365 W JP0210365 W JP 0210365W WO 03032451 A1 WO03032451 A1 WO 03032451A1
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WIPO (PCT)
Prior art keywords
terahertz light
light
irradiation
terahertz
excitation pulse
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PCT/JP2002/010365
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French (fr)
Japanese (ja)
Inventor
Hiromichi Akahori
Toshiyuki Iwamoto
Original Assignee
Nikon Corporation
Tochigi Nikon Corporation
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Application filed by Nikon Corporation, Tochigi Nikon Corporation filed Critical Nikon Corporation
Publication of WO2003032451A1 publication Critical patent/WO2003032451A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S1/00—Masers, i.e. devices using stimulated emission of electromagnetic radiation in the microwave range
    • H01S1/02—Masers, i.e. devices using stimulated emission of electromagnetic radiation in the microwave range solid

Definitions

  • the present invention relates to a terahertz light generation device provided with a terahertz light generation element.
  • a terahertz light generating element called an optical switch element
  • an optical switch element for example, Smith, Auston and Eggplant (Peter.R.Smith, David. H. Auston and Martin. C. Nuss) 's paper ("Subpicosecond Photoconducting Diole Antennas", IEEE Journal of Quantum Electronics, Vol. 24, No. 2, pp. 255-260 (1988)), Budiort, Magolies, Geong, Son and Po. Koichi (E. Budiarto, J. Margolies, S. Jeong, J. Son and J. Bokor) ("High-Intensity Terahertz Pulses at 1-kHz Repetition Rate", IEEE Journal of Quantum Electronics, Vol. 32, No. 10, pp839-1846 (1996))).
  • a terahertz light generating element called an optical switch element has a photoconductive portion and two conductive films formed on a predetermined surface of the photoconductive portion and separated from each other, and at least one of the two conductive films is provided.
  • the elements are arranged such that the portions are spaced apart from each other at a predetermined interval in a direction along a predetermined plane.
  • the excitation pulse light irradiation area of the terahertz light generating element was circular.
  • terahertz light device various devices that use the terahertz light (terahertz light device), such as a spectrometer, an inspection device, and an analyzer In equipment and the like, it is possible to shorten the measurement time and inspection time, expand the measurement range and inspection range, and improve the S / N. Disclosure of the invention
  • the present invention provides a terahertz light generation device capable of increasing the radiation intensity of generated terahertz light.
  • the terahertz light generation device includes: (a) a photoconductive portion, and two conductive portions formed on a predetermined surface of the photoconductive portion and separated from each other; A terahertz light generating element, at least a part of which is arranged at a predetermined interval in a first direction along a predetermined surface, and (b) a predetermined irradiation area of the terahertz light generating element.
  • the irradiation unit is configured such that the length of the irradiation area in the second direction along the predetermined plane and perpendicular to the first direction is equal to the length of the irradiation area in the first direction.
  • An excitation pulse light is generated so as to be longer than that.
  • the irradiation part of the terahertz light generation device generates the excitation pulse light so that the entire or most of the irradiation area is an area between at least some of the two conductive parts in the terahertz light generation element. I do.
  • the irradiation area may have a shape close to an ellipse.
  • 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 preferably set to 1.1 or more. This ratio is preferably at least 1.5 rather than 1.1. It is more preferably 2 or more than 1.5 or more, and still more preferably 3 or more than 2 or more. New More preferably, it is 5 or more than 3 or more. More preferably, it is 8 or more than 5 or more.
  • the irradiation area may have a substantially rectangular shape.
  • an opening that can adjust the size of the irradiation region can be provided in the irradiation unit.
  • the luminous flux shape of the excitation pulse light irradiated through the opening is made variable. Further, a plurality of rectangular openings having different sizes may be provided, and the irradiation area of the excitation pulse light may be controlled by switching the rectangular openings.
  • the irradiation unit may be configured to include a generation element that generates the excitation pulse light, and a light emission control unit that can adjust the irradiation intensity of the excitation pulse light.
  • the photoconductive portion may be a photoconductive layer formed on the upper surface of the substrate.
  • the photoconductive layer is preferably formed by epitaxial growth.
  • the terahertz light generating element is a large aperture light switch element or a small diameter light switch element.
  • the present invention can also be configured as an optical measurement device using the terahertz light emitting device of the above various aspects.
  • FIG. 1 is a schematic configuration diagram showing a terahertz light generation device according to a first embodiment of the present invention.
  • FIG. 2 is a diagram showing the terahertz light generating element in FIG. 1.
  • FIG. 2 (a) is a schematic plan view
  • FIG. 2 (b) is a line ⁇ — ⁇ in FIG. 2 (a). It is the schematic sectional drawing which followed.
  • FIG. 3 is a schematic sectional view showing another example of the terahertz light generation element.
  • FIG. 4 is a schematic plan view showing an irradiation area of the excitation pulse light on the terahertz light generation element in the 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 is a schematic plan view showing an irradiation area of an excitation pulse light from an irradiation unit to a terahertz light generation element used in a terahertz light generation device according to a third embodiment of the present invention.
  • FIG. 7 is a diagram showing a terahertz light generating element 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. ) Is a schematic cross-sectional view along the line VE-W in FIG. 7 (a), and FIG. 7 (c) is an enlarged plan view showing a main part.
  • FIG. 8 is a view for explaining a mask for controlling an irradiation area.
  • FIG. 1 is a schematic configuration diagram showing a terahertz light generation device according to a first embodiment of the present invention.
  • FIG. 2 is a diagram showing the terahertz light generating element 1 in FIG. 1, wherein FIG. 2 (a) is a schematic plan view thereof, and FIG. 2 (b) is along a line ⁇ — ⁇ in FIG. 2 (a).
  • FIG. 2 (a) is a schematic plan view thereof
  • FIG. 2 (b) is along a line ⁇ — ⁇ in FIG. 2 (a).
  • the terahertz light generating device includes a terahertz light generating element 1, an irradiation unit 2, and a DC power supply 3 as a voltage applying unit.
  • the terahertz light generating element 1 has a substrate 11 as a photoconductive portion and one surface of the substrate 11, that is, a surface parallel to the XY plane in the figure.
  • conductive films 12, 13 as two conductive portions formed and separated from each other. At least a part of the conductive films 12, 1 and 3 are arranged at predetermined intervals gl in the Y-axis direction along the plane above the substrate 11 (the upper and lower sides are shown as upper and lower in FIG. 2 (b)). Have been.
  • the entirety of the conductive films 12, 13 is spaced from each other by a distance gl.
  • the interval g1 is set to 2 mm or more, for example, 5 mm, and a so-called large-diameter optical switch element is constituted by the substrate 11 and the conductive films 12, 13.
  • the terahertz light generating element 1 includes a terahertz light generating element (e.g., a dipole element, a stripline element) in which the distance between the conductive films 12 and 13 is large, and In this specification, it is called a small-diameter optical switch element).
  • a terahertz light generating element e.g., a dipole element, a stripline element
  • Oguchi mysterious switch element Oguchi mysterious switch element
  • the distance between the two conductive films is several mm to several tens mm, preferably 2 mm or more and 50 mm or less.
  • the pulse light generated by the dipole-type stripline element is a point light source and not parallel light. Therefore, an optical system that converts the pulsed light into a parallel light beam is indispensable.
  • the large-mouth light switch element can be considered as an aggregate of multiple point light sources, and the generated pulse light can be treated as a parallel light flux.
  • a material of the substrate 11 for example, a semiconductor having a high resistivity (for example, semi-insulating GaAs) can be used.
  • the material of the conductive films 12 and 13 for example, gold or the like can be used and can be formed on the surface of the substrate 11 by vapor deposition or the like.
  • the substrate 11 itself is used as a photoconductive portion as described above.
  • a photoconductive film 14 is formed on the substrate 11 as a photoconductive portion.
  • conductive films 12 and 13 may be formed on photoconductive film 14.
  • FIG. 3 is a schematic cross-sectional view showing another example of the terahertz light generating element 1, and corresponds to FIG. 2 (b).
  • elements that are the same as or correspond to the elements in FIGS. 1 and 2 are given the same reference numerals, and overlapping descriptions are omitted. .
  • the substrate 11 in FIG. 3 can be formed by, for example, forming a GaAs epitaxial photoconductive layer 14 on a semi-insulating GaAs substrate.
  • the GaAs substrate can be manufactured by the well-known LEC (Liquid Encapsulated Czochralski) method and VB (Vertical Boat Method) method (also referred to as VGF method).
  • the GaAs epitaxy layer 14 is formed by an MBE (molecular-beam epitaxy) method in an atmosphere of several hundred degrees or more (250: up to 800 ° C.). This MBE method is a conventionally known film forming technique.
  • the material of the substrate 11 may be sapphire and the photoconductive film 14 may be silicon.
  • the excitation pulse light emitted from the irradiation unit 2 is irradiated as a predetermined irradiation region R1 at a location g1 of the terahertz light generating element 1 as shown in FIGS. 1 and 2 (a).
  • the excitation pulse light is an ultrashort pulse laser light represented by a femtosecond pulse laser light.
  • the irradiation unit 2 controls the shape of the luminous flux of the excitation pulse light emitted from the laser light source 21 so that the length in the X-axis direction along the plane above the substrate 11 in the irradiation area R 1 is equal to the irradiation area R Make it longer than the length of 1 in the Y-axis direction.
  • the ratio of the length of the irradiation area R 1 in the X-axis direction to the length of the irradiation area R 1 in the Y-axis direction is It is preferably 1.1 or more. It is preferable that the number is 1.5 or more, more than 1.1, 2 or more, 1.5 or more, 3 or more, 2 or more, 5 or more, 3 or more, and 8 or more.
  • the irradiation region R1 has a shape close to an elliptical shape, for example, in order to effectively use laser light or the like. This is because, if the irradiation region R1 is formed to have a shape close to an elliptical shape, it is not necessary to cut a part of the light beam of the laser light emitted from the laser light source 21 described later.
  • the shape close to an elliptical shape means a shape elongated in the X direction in which the ratio of the above dimensions XY is 1.1 or more, and can also be a shape in which a circle is flattened in the Y direction. For example, an oval shape is also included. Further, as described later, a rectangular shape elongated in the X direction with a ratio of the above-mentioned dimensions XY of 1.1 or more may be used.
  • the irradiation unit 2 is, specifically, a laser light source 21 and a shaping optical system that shapes the cross-sectional shape of the light beam from the laser light source 21 according to the irradiation region R 1, for example, a cylindrical lens 22, a concave or convex spherical lens 23 and a cylindrical lens 24 are provided.
  • the X-axis direction of the light beam of the excitation pulse light is collimated by the cylindrical lens 22 and the spherical lens 23, and the light beam of the excitation pulse light is collimated by the spherical lens 23 and the cylindrical lens 24. Is collimated in the Y-axis direction.
  • the excitation pulse light is applied to the irradiation area R1 as a parallel light flux.
  • the configuration of the irradiation unit 2 is not limited to such a configuration.
  • the irradiation area R 1 of the excitation pulse light is configured so as to cover the entire area (rectangular area) between the conductive films 12 and 13 of the substrate 11. I do.
  • Figure 8 is an example. 'The shaping optical system in FIG. 8 is configured as follows.
  • the shaping optical system has a mask 25 having a rectangular opening 26 a similar to a rectangular region between the conductive films 12 and 13.
  • the mask 25 is arranged between the substrate 11 and the cylindrical lens 24 in FIG. 1 so that the excitation pulse light is irradiated on the entire rectangular area of the substrate 11 through the opening 26 a of the mask 25.
  • the shaping optical system shown in FIG. 8 can also adjust the irradiation area R1 of the excitation pulse light to adjust the radiation intensity of the terahertz light. That is, the mask 25 has a plurality of openings 26 a to 26 d having different sizes, and one of the openings is selectively inserted into the optical path. For example, the selection of such an aperture can be controlled by an evening-let type mask switching device.
  • the evening-let type mask switching device has a mask 25 driven by a motor around a rotation center axis 27 by operation of a selection switch, and each opening 26 a to 26 d is operated by operation of the selection switch. Can be sequentially switched. This makes it possible to easily switch the radiation intensity of the terahertz light.
  • LP indicates the optical axis of the excitation pulse light.
  • the length of the irradiation region R1 in the Y-axis direction is shorter than the distance g1 between the conductive films 12 and 13, and the irradiation region R1 and the conductive film 1 2 , 1 and 3 respectively.
  • the present invention is not necessarily limited to this.
  • a part of the irradiation region R1 may overlap with the conductive films 12 and 13. That is, in the present invention, the entire irradiation region R 1 may be located in the region between the two conductive films 12 and 13 in the terahertz light generation element 1.
  • the DC power supply 3 applies a bias voltage between conductive films 12 and 13.
  • the DC power supply 3 can be composed of, for example, a power supply circuit that converts AC from commercial power into DC.
  • the magnitude of the bias voltage is not particularly limited. However, in order to maximize the radiation intensity of the terahertz light, the magnitude of the bias voltage is determined by the electric field E bi as between the two conductive films 1 2 and 1 3 It is preferable to adjust the strength so as to obtain the strength.
  • FIG. 4 is a schematic plan view showing an irradiation region R2 of the excitation pulse light on the terahertz light generating element 1 in the comparative example, and corresponds to FIG. 2 (a).
  • the same or corresponding elements as those in FIGS. 1 and 2 are denoted by the same reference numerals, and redundant description is 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 pulse light on the terahertz light generating element 1 is circular, as in the conventional technology.
  • the irradiation region R2 has a diameter g1 and the irradiation region R2 is located exactly between the conductive films 12 and 13.
  • the irradiation part of the excitation pulse light used in the comparative example differs from the irradiation part 2 used in the present embodiment only in the shaping optical system.
  • 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 that of the irradiation region R1 in the present embodiment. It is almost the same as the laser light intensity per unit area. Also, the bias voltage applied between the two conductive films 12 and 13 in the comparative example is the same as the bias voltage applied between the two conductive films 12 and 13 in the present embodiment.
  • a DC voltage is applied between the conductive films 12 and 13 by the DC power supply 3.
  • a DC voltage is applied between the two conductive films 12 and 13 (a gap portion).
  • the irradiation section 2 irradiates the gap with an ultrashort pulse laser beam or the like to excite the gap.
  • the ultrashort pulse laser beam is a pulsed laser beam having energy equal to or higher than the band gap of the semiconductor constituting the substrate 11.
  • the generated free carriers in the substrate 1 1 of a photoconductive unit (electrons and holes) by the electric field E bi the as being applied Canon Ria is accelerated Terahertz light is generated.
  • the electric field strength E THz of the terahertz light generated at this time is the time derivative of the current J flowing between the two conductive films 12 and 13. It is proportional to and can be expressed by the following equation 1.
  • the current J flowing between the two conductive films 12 and 13 is expressed by the following equation 2 using the current density j and the cross-sectional area S where the current flows.
  • 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. Therefore, the free carrier generation depth in the Z direction can be formed deeper by increasing the irradiation intensity of the excitation pulse light, so that the irradiation intensity of the excitation pulse light is adjusted to adjust the size of the cross-sectional area S. do it.
  • the electric field intensity E THz of the terahertz light can be adjusted by adjusting the irradiation intensity of the excitation pulse light by a light emission control circuit (not shown).
  • the method of adjusting the irradiation intensity of the excitation pulse light can be similarly applied to an optical filter in addition to the electric control.
  • the current density j is calculated using the mobility of the photoexcited carrier, the carrier density n, the electric field E bias applied between the two conductive films 12 and 13, and the electron charge e as follows: 3) can be expressed as
  • the generation region of the electron charge e is expanded, so that the current density j can be increased and the current J can be increased. Therefore, the electric field strength E THz of the terahertz light can be adjusted by adjusting the width of the irradiation region R1 of the excitation pulse light.
  • the electric field strength E THz of the terahertz light is the mobility of the photoexcited carrier, the carrier density n, and the magnitude E of the electric field applied between the two conductive films 12, 13 separated from each other. It depends on the bias and the cross-sectional area S, as shown in the following equation 4.
  • E THz ocS dj Zd t S d (ne E bias ) / ⁇ t ... (4)
  • E bias applied between the two conductive films 12 and 13 does not depend on time
  • E THz of the terahertz light at a distance is calculated from the carrier density n and the time derivative of the carrier mobility, the current cross-sectional area S, and the distance between the two conductive films 12 and 13. Is proportional to the applied electric field E bias .
  • two conductive films 1 2, 1 3 field E bi the as being applied between, for example as being adjusted to the electric field intensity just before the occurrence of insulation Yabu ⁇ , consider the magnitude of the electric field strength E THz.
  • the carrier mobility At changes with the same time.
  • the same laser light source 21 when used and the laser light intensity per unit area of the excitation pulse light irradiation area is equal, it is considered that the time change of the carrier density n is also equal.
  • the laser light intensity per unit area at this time is assumed to be adjusted to the maximum intensity within a range where the generated terahertz light radiation intensity is not saturated and the element is not broken.
  • the time derivative of the current density j is equal, and the electric field strength E THz of the radiated terahertz light at a distance depends only on the cross-sectional area S through which the current flows. Therefore, the larger the cross-sectional area S through which the current flows, the greater the electric field strength E THz of the radiated terahertz light at a distance.
  • the terahertz light generating element of the present embodiment will be compared with the terahertz light generating element of the comparative example described above.
  • the length in the X-axis direction is longer than the length in the Y-axis direction in irradiation region R1.
  • the length in the X-axis direction is the same as the length in the Y-axis direction in the irradiation region R2.
  • the laser beam intensity per unit area of each of the irradiation regions Rl and R2 is almost the same.
  • the length of irradiation region R1 in the X-axis direction in the present embodiment is longer than the length of irradiation region R2 in the X-axis direction in the comparative example.
  • the cross-sectional area S in which the current flows is larger in the present embodiment than in the comparative example. Therefore, the electric field strength E of the terahertz light radiated in the present embodiment is greater than that in the comparative example. THz increases.
  • the length of the irradiation region R1 in the Y-axis direction is set to be one tenth of the diameter of the irradiation region R2, and the length of the irradiation region R1 in the X-axis direction is 10 times the diameter of the irradiation region R2. Double it.
  • the cross-sectional area S where the current flows is about 10% of the comparative example.
  • the electric field intensity of the terahertz light E THz which is about 10 times that of the comparative example can be obtained.
  • the terahertz light generator according to the present embodiment is By using this, it is possible to improve the accuracy of various devices that use terahertz light (terahertz light device), for example, spectroscopy devices, inspection devices for semiconductors, medical devices, foods, etc., analysis devices, imaging devices, etc. It can shorten measurement time and inspection time, expand measurement range and inspection range, and improve SZN.
  • terahertz light device for example, spectroscopy devices, inspection devices for semiconductors, medical devices, foods, etc., analysis devices, imaging devices, etc. It can shorten measurement time and inspection time, expand measurement range and inspection range, and improve SZN.
  • the terahertz light generating device according to the second embodiment is different from the terahertz light generating device 1 of the first embodiment in that the terahertz light generating element 1 shown in FIG. The element 31 is used.
  • the terahertz light generation device according to the second embodiment includes the irradiation unit 2 and the DC power supply 3 in FIG. 1 similarly to the first embodiment.
  • FIG. 5 is a schematic plan view showing the terahertz light generation element 31 and corresponds to FIG. 2 (a). In FIG. 5, elements that are the same as or correspond to elements in FIGS. 1 and 2 are given the same reference numerals, and overlapping descriptions are omitted.
  • the distance g2 between the two conductive films 12 and 13 of the terahertz light generation element 31 is equal to the distance g2 of the terahertz light generation element 1 of the first embodiment. It is smaller than the distance g 1 between the conductive films 12 and 13, and is substantially the same as the length in the X-axis direction of the emission region R 1 of the excitation pulse light irradiated from the irradiation unit 2.
  • the irradiation area R1 is exactly the same in both the first and second embodiments.
  • the terahertz light generation element 31 of the second embodiment has the following advantages by setting the interval g2 smaller than the interval g1.
  • Two conductive films 1 2 Two conductive films 1 2,
  • bias voltage applied between the second two conductive layers 1 2, in the embodiment 1 3, first In this embodiment, the bias voltage can be set lower than the bias voltage applied between the two conductive films 12 and 13. Other advantages are similar to those of the first embodiment.
  • the terahertz light generation device includes an irradiation region of the excitation pulse light irradiated from the irradiation unit 2 of the terahertz light generation device of the first embodiment to the terahertz light generation element 1.
  • the shape of the laser was changed, and the intensity of the laser beam was increased accordingly. It is.
  • FIG. 6 is a schematic plan view showing an irradiation region R 3 of the excitation pulse light from the irradiation unit with respect to the terahertz light generation element 1 used in the terahertz light generation device according to the third embodiment of the present invention.
  • FIGS. 1, 2, and 4 the same or corresponding elements as those in FIGS. 1, 2, and 4 are denoted by the same reference numerals, and the description thereof will not be repeated.
  • the terahertz light generating device includes a terahertz light generating element 1 and a DC power supply 3 which are exactly the same as those in the first embodiment.
  • the length in the X-axis direction is longer than the length in the Y-axis direction, as in the first embodiment.
  • the length of the region R 3 in the Y-axis direction is substantially equal to the distance g 1 between the conductive films 12 and 13, and the irradiation region R 3 is disposed exactly between the conductive films 12 and 13. .
  • the intensity of the laser light emitted from the laser light source of the irradiation unit (corresponding to the laser light source 21 in FIG. 1) in the third embodiment is the same as that of the laser light source 21 of the irradiation unit 2 in the first embodiment. And the intensity is higher than the intensity of the laser light emitted from the laser light source of the irradiation unit in the comparative example.
  • the intensity per unit area of the excitation pulse light irradiating the irradiation area is higher than a predetermined intensity
  • the intensity of the generated terahertz pulse light is saturated and the excitation is performed. Even if the intensity per unit area of the pulsed light is higher than the predetermined intensity, the intensity of the terahertz light cannot be further increased. Further, if the intensity of the excitation pulse light per unit area is too high, there is a possibility that the element may be destroyed.
  • the excitation pulse light intensity per unit area of the irradiation region R2 is the saturation intensity or the limit intensity such as element rupture, etc. Even if a laser that outputs high-intensity laser light is used, the generated terahertz light radiation intensity is saturated or the device is destroyed, and the generated terahertz pulse light radiation intensity cannot be increased.
  • the irradiation region R 3 has the same length in the Y-axis direction as the irradiation region R 2 in the Y-axis direction, but has the same length in the X-axis direction.
  • the irradiation area R 2 is longer than the length in the X-axis direction. Therefore, even if a laser light source (corresponding to the laser light source 21) that outputs higher intensity laser light is used as the irradiation unit, 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.
  • the description of the first embodiment will be given.
  • the radiation intensity of the generated terahertz pulse light can be increased without saturating the generated radiation intensity of the terahertz light and without breaking the element.
  • the length of the irradiation region R3 in the X-axis direction is set to 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 above comparative example is defined as the intensity of the excitation pulse light per unit area of the irradiation region R 2 being the saturation intensity or the limit intensity such as element destruction.
  • the terahertz light generator of the third embodiment uses a laser light source having an output about 10 times that of the laser light source of the comparative example. Even if the generated terahertz light radiation intensity does not saturate or the element does not burst, the electric field strength of the generated terahertz pulse light at a distant place can be increased to about 10 times that of the above comparative example. it can.
  • FIG. 7 is a diagram showing a terahertz light generation element 41 used in a terahertz light generation device according to a fourth embodiment of the present invention
  • FIG. 7 (a) is a schematic perspective view thereof
  • FIG. 7 is a schematic cross-sectional view along the line W--W in FIG. 7 (a)
  • FIG. 7 (c) is an enlarged plan view showing a main part.
  • the terahertz light generating device is different from the first embodiment only in that a terahertz light generating element 41 shown in FIG. 7 is used instead of the terahertz light generating element 1. It is.
  • the terahertz light generator according to the fourth embodiment has the same irradiation section as irradiation section 2 in FIG. 1 (however, the power is, for example, 1/10 or less) and a DC power supply. It has the same DC power supply as in 3 (however, the applied voltage is 1/100 or less, for example).
  • 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-aperture optical switch element, that is, a small-aperture optical switch element, and uses a dipole antenna. Things.
  • the terahertz light generating element 41 is composed of a substrate 42 and a photoconductive film formed on a plane on the upper side of the substrate 42 (the upper and lower sides are indicated by the upper and lower sides in FIG. 7B). 43, and two conductive films 44 and 45 formed on the photoconductive film 43 and separated from each other. At least some of the conductive films 44 and 45 are arranged so as to have a predetermined interval g3 in the Y-axis direction along the plane above the substrate 42.
  • the material of the substrate 42 for example, Si, Ge, GaAs, sapphire, or the like can be used.
  • a material of the photoconductive film 43 for example, low-temperature growth GaAs or ion-implanted silicon (RD-SOS) can be used. RD-SOS is also disclosed in the above-mentioned paper by Smith et al. (IEEE Journal of Quantum Electronics, Vol. 24, No. 2, pp. 255-260 (1988)).
  • the conductive film 45 for example, a metal film such as A1 or Au can be used.
  • the conductive films 44 and 45 are composed of transmission line portions 44a and 45a forming parallel transmission lines and electrode portions 44b and 44c formed at both ends thereof. , 45b, 45c.
  • the central portions of the transmission line portions 44a and 45a protrude inward, and a small interval, for example, an interval g3 of about several / xm is provided between the transmission line portions 44a and 45a in a direction along the upper plane of the substrate 42.
  • An optical switch element is formed by a portion near the gap g3, and a dipole antenna is formed by a portion near the gap g3 in the transmission line sections 44a and 45a.
  • the irradiation region R4 in which the irradiation unit corresponding to the irradiation unit 2 in FIG. 1 irradiates the terahertz light generation element 41 with the excitation pulse light has a length in the X-axis direction that is the Y-axis. It is longer than the length in the direction. Further, the length of the irradiation region R4 in the Y-axis direction is substantially the same as the interval g3, and the irradiation region R4 is arranged in the region exactly at the interval g3.
  • the terahertz light generation device can be used for various measurement devices such as spectroscopy devices, inspection devices for semiconductors, medical and food products, analysis devices, imaging devices, and the like.

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  • Electromagnetism (AREA)
  • Optics & Photonics (AREA)
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  • Investigating Or Analysing Materials By Optical Means (AREA)

Abstract

A terahertz light generator comprises a terahertz light generating device (1), an irradiating section (2), and a bias power source (3). The terahertz light generating device (1) has a photoconductive section (14) and two conducting sections (12, 13) formed on this photoconductive section (14) by splitting in a first direction. A gap (g) is formed between the two conducting sections (12, 13). The irradiating section (2) irradiates the gap (g) with excitation pulse light having a flux of a predetermined shape. Its irradiation region (R1) has a shape approximate to an ellipse the length of which is longer in a second direction orthogonal to a first direction than in the first direction.

Description

明細書 テラへルツ光発生装置 本出願は、 下記の日本国特許出願を基礎とし、 その内容は引用文としてここに 組み込まれる。 ' 特許出願 2 0 0 1年第 3 0 9 1 3 3号： 2 0 0 1年 1 0月 4日出願 技術分野  Description Terahertz light generator This application is based on the following Japanese patent application, the contents of which are incorporated herein by reference. '' Patent application No. 3 2009 No. 3 2009: Application filed on Oct. 4, 2010
本発明は、 テラへルツ光発生素子を備えたテラへルツ光発生装置に関するもの である。 背景技術  The present invention relates to a terahertz light generation device provided with a terahertz light generation element. Background art
テラへルツ光の発生には、光スィツチ素子と呼ばれるテラへルツ光発生素子が、 多く用いられている （例えば、 スミス、 オーストンおよびナス （Peter.R.Smith, David. H.Auston and Martin. C.Nuss) の論文 ("Subpicosecond Photoconducting Di ole Antennas", IEEE Journal of Quantum Electronics, Vol.24, No.2, pp.255-260 ( 1988) )、 ブディオルト、 マ一ゴリーズ、 ジェオング、 ソンおよびポ コ一 （E.Budiarto, J.Margolies, S.Jeong, J.Son and J.Bokor) の論文 （"High- Intensity Terahertz Pulses at 1-kHz Repetition Rate", IEEE Journal of Quantum Electronics, Vol.32, No.10, pp l839-1846 ( 1996) ) など）。  For generating terahertz light, a terahertz light generating element called an optical switch element is widely used (for example, Smith, Auston and Eggplant (Peter.R.Smith, David. H. Auston and Martin. C. Nuss) 's paper ("Subpicosecond Photoconducting Diole Antennas", IEEE Journal of Quantum Electronics, Vol. 24, No. 2, pp. 255-260 (1988)), Budiort, Magolies, Geong, Son and Po. Koichi (E. Budiarto, J. Margolies, S. Jeong, J. Son and J. Bokor) ("High-Intensity Terahertz Pulses at 1-kHz Repetition Rate", IEEE Journal of Quantum Electronics, Vol. 32, No. 10, pp839-1846 (1996))).
光スィッチ素子と呼ばれるテラへルツ光発生素子は、 光伝導部と、 この光伝導 部の所定の面上に形成され互いに分離された 2つの導電膜とを有し、 2つの導電 膜の少なくとも一部同士が所定の面に沿った方向に所定間隔をあけるように配置 された素子である。 この素子では、 2つの導電膜間に電圧を印加しても、 通常は、 2つの導電膜間 （ギャップ部分） の抵抗値が非常に髙いため電流はほとんど流れ ない。 ギャップ部分に励起パルス光を照射して、 自由キャリア （電子と正孔） を 生成すると、 その瞬間だけその抵抗値が下がり、 印加されている電場によりキヤ リアが加速されて電流が流れる。 このパルス状の電流によって、 テラへルツパル ス光が発生する。 励起パルス光として、 フェムト秒パルスレーザ光に代表される 超短パルスレーザ光などが使用される。 A terahertz light generating element called an optical switch element has a photoconductive portion and two conductive films formed on a predetermined surface of the photoconductive portion and separated from each other, and at least one of the two conductive films is provided. The elements are arranged such that the portions are spaced apart from each other at a predetermined interval in a direction along a predetermined plane. In this device, even if a voltage is applied between the two conductive films, usually, almost no current flows because the resistance value between the two conductive films (gap portion) is very large. By irradiating the gap with excitation pulse light to generate free carriers (electrons and holes), the resistance value drops at that moment, and the applied electric field reduces the resistance. The rear is accelerated and current flows. This pulse-like current generates terahertz pulse light. An ultrashort pulse laser beam typified by a femtosecond pulse laser beam is used as the excitation pulse light.
光スィツチ素子と呼ばれる従来のテラへルツ光発生素子を備えた従来のテラへ ルツ光発生装置では、 テラへルツ光発生素子の励起パルス光照射領域は円形とさ れていた。  In a conventional terahertz light generating device provided with a conventional terahertz light generating element called an optical switch element, the excitation pulse light irradiation area of the terahertz light generating element was circular.
テラへルツ光発生装置から発生するテラへルツ光の放射強度を増大させること ができれば、 テラへルツ光を利用する各種の装置（テラへルツ光装置）、 例えば、 分光装置、 検査装置、 分析装置などにおいて、 測定時間や検査時間の短縮、 測定 範囲や検査範囲の拡大、 S /Nの向上などを図ることができる。 発明の開示  If the radiation intensity of the terahertz light generated from the terahertz light generator can be increased, various devices that use the terahertz light (terahertz light device), such as a spectrometer, an inspection device, and an analyzer In equipment and the like, it is possible to shorten the measurement time and inspection time, expand the measurement range and inspection range, and improve the S / N. Disclosure of the invention
本発明は、 発生するテラへルツ光の放射強度を増大させることができるテラへ ルツ光発生装置を提供するものである。  The present invention provides a terahertz light generation device capable of increasing the radiation intensity of generated terahertz light.
本発明によるテラへルツ光発生装置は、 （a )光伝導部と、 この光伝導部の所定 の面上に形成され互いに分離された 2つの導電部とを有し、 2つの導電部の少な くとも一部同士が所定の面に沿った第 1の方向に所定間隔をあけるように配置さ れたテラへルツ光発生素子と、 （ b )テラへルツ光発生素子の所定の照射領域に励 起パルス光を照射する照射部と、 （c ) 2つの導電部間にバイアス電圧を印加する 電圧印加部と、 を備える。 そして、 照射部は、 所定の面に沿った第 2の方向であ つて第 1の方向と直交する第 2の方向の照射領域の長さが、 第 1の方向の照射領 域の長さに比べて長くなるように、 励起パルス光を発生する。  The terahertz light generation device according to the present invention includes: (a) a photoconductive portion, and two conductive portions formed on a predetermined surface of the photoconductive portion and separated from each other; A terahertz light generating element, at least a part of which is arranged at a predetermined interval in a first direction along a predetermined surface, and (b) a predetermined irradiation area of the terahertz light generating element. An irradiation unit for irradiating the excitation pulse light; and (c) a voltage application unit for applying a bias voltage between the two conductive units. The irradiation unit is configured such that the length of the irradiation area in the second direction along the predetermined plane and perpendicular to the first direction is equal to the length of the irradiation area in the first direction. An excitation pulse light is generated so as to be longer than that.
このテラへツル光発生装置の照射部は、 照射領域の全部または大部分が、 テラ ヘルツ光発生素子における 2つの導電部の少なくとも一部同士の間の領域となる ように、 励起パルス光を発生する。  The irradiation part of the terahertz light generation device generates the excitation pulse light so that the entire or most of the irradiation area is an area between at least some of the two conductive parts in the terahertz light generation element. I do.
照射領域を楕円に近い形状としてもよい。 照射領域の第 1の方向の長さに対す る照射領域の第 2の方向の長さの比を、 1 . 1以上にすることが好ましい。 この 比は、 1 . 1以上よりも 1 . 5以上であることが好ましい。 1 . 5以上よりも 2 以上であることがより好ましく、 2以上よりも 3以上であることがより一層好ま しい。 3以上よりは 5以上であることが更に好ましい。 5以上よりも 8以上であ ることが更に好ましい。 The irradiation area may have a shape close to an ellipse. 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 preferably set to 1.1 or more. This ratio is preferably at least 1.5 rather than 1.1. It is more preferably 2 or more than 1.5 or more, and still more preferably 3 or more than 2 or more. New More preferably, it is 5 or more than 3 or more. More preferably, it is 8 or more than 5 or more.
上記照射領域を略矩形形状としても良い。 この場合、 照射領域の大きさを調整 できる開口部を照射部に設けることができる。 この開口部により照射する励起パ ルス光の光束形状を可変とする。 また、 複数の大きさの異なる矩形形状の開口部 を備え、 矩形形状の開口部を切り換えることで励起パルス光の照射領域を制御す るようにしてもよい。  The irradiation area may have a substantially rectangular shape. In this case, an opening that can adjust the size of the irradiation region can be provided in the irradiation unit. The luminous flux shape of the excitation pulse light irradiated through the opening is made variable. Further, a plurality of rectangular openings having different sizes may be provided, and the irradiation area of the excitation pulse light may be controlled by switching the rectangular openings.
上記照射部は、 励起パルス光を発生する発生素子と、 励起パルス光の照射強度 を調整できる発光制御手段を有するように構成してもよい。  The irradiation unit may be configured to include a generation element that generates the excitation pulse light, and a light emission control unit that can adjust the irradiation intensity of the excitation pulse light.
光伝導部を、 基板の上面に形成した光伝導層とすることもできる。 この場合、 光伝導層をェピタキシャル成長で成膜するのがよい。  The photoconductive portion may be a photoconductive layer formed on the upper surface of the substrate. In this case, the photoconductive layer is preferably formed by epitaxial growth.
上記テラへルツ光発生素子は、 大口怪光スィツチ素子あるいは小口径光スィッ チ素子である。  The terahertz light generating element is a large aperture light switch element or a small diameter light switch element.
本発明は、 上記種々の態様のテラへルツ光発光装置を用いた光計測装置として 構成することもできる。 図面の簡単な説明  The present invention can also be configured as an optical measurement device using the terahertz light emitting device of the above various aspects. BRIEF DESCRIPTION OF THE FIGURES
図 1は、 本発明の第 1の実施の形態によるテラへルツ光発生装置を示す概略構 成図である。  FIG. 1 is a schematic configuration diagram showing a terahertz light generation device according to a first embodiment of the present invention.
図 2は、 図 1中のテラへルツ光発生素子を示す図であり、 図 2 ( a ) はその概 略平面図、 図 2 ( b ) は図 2 ( a ) 中の Π— Π線に沿った概略断面図である。 図 3は、 テラへルツ光発生素子の他の例を示す概略断面図である。  FIG. 2 is a diagram showing the terahertz light generating element in FIG. 1. FIG. 2 (a) is a schematic plan view, and FIG. 2 (b) is a line Π—Π in FIG. 2 (a). It is the schematic sectional drawing which followed. FIG. 3 is a schematic sectional view showing another example of the terahertz light generation element.
図 4は、 比較例におけるテラへルツ光発生素子上の励起パルス光の照射領域を 示す概略平面図である。  FIG. 4 is a schematic plan view showing an irradiation area of the excitation pulse light on the terahertz light generation element in the comparative example.
図 5は、 本発明の第 2の実施の形態によるテラへルツ光発生装置で用いられる テラへルツ光発生素子を示す概略平面図である。  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.
図 6は、 本発明の第 3の実施の形態によるテラへルツ光発生装置で用いられる テラへルツ光発生素子に対する、 照射部からの励起パルス光の照射領域を示す概 略平面図である。 図 7は、 本発明の第 4の実施の形態によるテラへルツ光発生装置で用いられる テラへルツ光発生素子を示す図であり、 図 7 (a) はその概略斜視図、 図 7 (b) は図 7 (a) 中の VE— W線に沿った概略断面図、 図 7 (c) は要部を示す拡大平 面図である。 FIG. 6 is a schematic plan view showing an irradiation area of an excitation pulse light from an irradiation unit to a terahertz light generation element used in a terahertz light generation device according to a third embodiment of the present invention. FIG. 7 is a diagram showing a terahertz light generating element 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. ) Is a schematic cross-sectional view along the line VE-W in FIG. 7 (a), and FIG. 7 (c) is an enlarged plan view showing a main part.
図 8は、 照射領域を制御するマスクを説明する図 発明を実施するための最良の形態  FIG. 8 is a view for explaining a mask for controlling an irradiation area.
以下、本発明によるテラへルツ光発生装置について、 図面を参照して説明する。  Hereinafter, a terahertz light generator according to the present invention will be described with reference to the drawings.
[第 1の実施の形態]  [First Embodiment]
図 1は、 本発明の第 1の実施の形態によるテラへルツ光発生装置を示す概略構 成図である。 図 2は図 1中のテラへルツ光発生素子 1を示す図であり、 図 2 (a) はその概略平面図、 図 2 (b) は図 2 (a) 中の Π— Π線に沿った概略断面図で ある。 理解を容易にするため、 図 1および図 2に示すように、 互いに直交する X 軸、 Y軸および Z軸を定義する。 後述する図についても同様である。  FIG. 1 is a schematic configuration diagram showing a terahertz light generation device according to a first embodiment of the present invention. FIG. 2 is a diagram showing the terahertz light generating element 1 in FIG. 1, wherein FIG. 2 (a) is a schematic plan view thereof, and FIG. 2 (b) is along a line Π—Π in FIG. 2 (a). FIG. To facilitate understanding, we define X, Y, and Z axes that are orthogonal to each other, as shown in Figures 1 and 2. The same applies to the figures described later.
本実施の形態によるテラへルツ光発生装置は、 図 1に示すように、 テラへルツ 光発生素子 1と、 照射部 2と、 電圧印加部としての直流電源 3とを備えている。 テラへルツ光発生素子 1は、 図 1および図 2に示すように、 光伝導部としての 基板 1 1と、 この基板 1 1の一方の表面、 すなわち、 図中の XY平面と平行な面 に形成され互いに分離された 2つの導電部としての導電膜 12, 13とを備えて いる。 導電膜 12, 1 3の少なくとも一部同士が、 基板 1 1の上側 （上下は図 2 (b) 中の上下で示す） の平面に沿った Y軸方向に、 所定間隔 g lをあけるよう に配置されている。 本実施の形態では、 導電膜 12, 1 3の全体同士が間隔 g l をあけている。 この間隔 g 1が 2mm以上、 例えば 5mmに設定されており、 基 板 1 1および導電膜 12, 1 3によっていわゆる大口径の光スィッチ素子が構成 されている。  As shown in FIG. 1, the terahertz light generating device according to the present embodiment includes a terahertz light generating element 1, an irradiation unit 2, and a DC power supply 3 as a voltage applying unit. As shown in FIGS. 1 and 2, the terahertz light generating element 1 has a substrate 11 as a photoconductive portion and one surface of the substrate 11, that is, a surface parallel to the XY plane in the figure. And conductive films 12, 13 as two conductive portions formed and separated from each other. At least a part of the conductive films 12, 1 and 3 are arranged at predetermined intervals gl in the Y-axis direction along the plane above the substrate 11 (the upper and lower sides are shown as upper and lower in FIG. 2 (b)). Have been. In the present embodiment, the entirety of the conductive films 12, 13 is spaced from each other by a distance gl. The interval g1 is set to 2 mm or more, for example, 5 mm, and a so-called large-diameter optical switch element is constituted by the substrate 11 and the conductive films 12, 13.
本発明によるテラへルツ光発生素子 1は、 導電膜 1 2、 1 3の間隔が大きく、 数; amから数十 m程度のテラへルツ光発生素子 (たとえば、ダイポール型素子、 ストリップ線路型素子などと呼ばれる。 本明細書では小口径光スィッチ素子と呼 ぶ） に対して大口径光スィッチ素子と呼ばれる。 ここで、 大口怪光スィツチ素子 は、 2つの導電膜間の距離が数 mm〜数十 mm、 好ましくは 2 mm以上 5 0 mm 以下である。 ダイポール型素子ゃストリップ線路型素子が発生するパルス光は点 光源であり平行光ではない。 そのため、 パルス光を平行光束とする光学系が不可 欠である。 これに対して、 大口怪光スィッチ素子は、 複数の点光源の集合体と考 えることができ、 発生するパルス光を平行光束として取り扱うことができる。 基板 1 1の材質としては、 例えば、 抵抗率が高い半導体 （例えば、 半絶縁性 G a A s ) を用いることができる。 導電膜 1 2 , 1 3の材質としては、 例えば、 金 などを用いることができ、蒸着等により基板 1 1の表面に形成することができる。 本実施の形態では、 前述したように基板 1 1自体が光伝導部として用いられて いるが、 例えば、 図 3に示すように、 基板 1 1上に光伝導部として光伝導膜 1 4 を形成し、 光伝導膜 1 4上に導電膜 1 2 , 1 3を形成してもよい。 図 3は、 テラ ヘルツ光発生素子 1の他の例を示す概略断面図であり、 図 2 ( b ) に対応してい る。 図 3において、 図 1および図 2中の要素と同一または対応する要素には同一 符号を付し、 その重複する説明は省略する。 . The terahertz light generating element 1 according to the present invention includes a terahertz light generating element (e.g., a dipole element, a stripline element) in which the distance between the conductive films 12 and 13 is large, and In this specification, it is called a small-diameter optical switch element). Here, Oguchi mysterious switch element The distance between the two conductive films is several mm to several tens mm, preferably 2 mm or more and 50 mm or less. The pulse light generated by the dipole-type stripline element is a point light source and not parallel light. Therefore, an optical system that converts the pulsed light into a parallel light beam is indispensable. On the other hand, the large-mouth light switch element can be considered as an aggregate of multiple point light sources, and the generated pulse light can be treated as a parallel light flux. As a 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 can be formed on the surface of the substrate 11 by vapor deposition or the like. In the present embodiment, the substrate 11 itself is used as a photoconductive portion as described above. For example, as shown in FIG. 3, a photoconductive film 14 is formed on the substrate 11 as a photoconductive portion. Alternatively, conductive films 12 and 13 may be formed on photoconductive film 14. FIG. 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, elements that are the same as or correspond to the elements in FIGS. 1 and 2 are given the same reference numerals, and overlapping descriptions are omitted. .
図 3の基板 1 1はたとえば、 半絶縁性 G a A s基板上に G a A sェピタキシャ ル光伝導層 1 4を形成して構成することができる。 G a A s基板は、 周知の L E C (Liquid Encapsulated Czochralski)法、 V B (Vertical Boat Method)法 （ V G F法とも呼ぶ） により製作することができる。 G a A sェピタキシャル層 1 4は、 M B E (molecular-beam epitaxy)法によって数百度以上 （2 5 0 ：〜 8 0 0 °C ) の雰囲気中で成膜される。この M B E法は従来から知られている成膜技術である。 基板 1 1の材質をサファイアとし、 光伝導膜 1 4としてシリコンを用いてもよ い。  The substrate 11 in FIG. 3 can be formed by, for example, forming a GaAs epitaxial photoconductive layer 14 on a semi-insulating GaAs substrate. The GaAs substrate can be manufactured by the well-known LEC (Liquid Encapsulated Czochralski) method and VB (Vertical Boat Method) method (also referred to as VGF method). The GaAs epitaxy layer 14 is formed by an MBE (molecular-beam epitaxy) method in an atmosphere of several hundred degrees or more (250: up to 800 ° C.). This MBE method is a conventionally known film forming technique. The material of the substrate 11 may be sapphire and the photoconductive film 14 may be silicon.
照射部 2から出射される励起パルス光は、 図 1および図 2 ( a ) に示すように、 テラへルツ光発生素子 1の間隔 g 1の箇所に所定の照射領域 R 1として照射され る。 励起パルス光は、 フェムト秒パルスレーザ光に代表される超短パルスレーザ 光などである。 照射部 2は、 レーザ光源 2 1から照射される励起パルス光の光束 形状を制御して、 照射領域 R 1の基板 1 1の上側の平面に沿った X軸方向の長さ が、 照射領域 R 1の Y軸方向の長さに比べて長くなるようにする。  The excitation pulse light emitted from the irradiation unit 2 is irradiated as a predetermined irradiation region R1 at a location g1 of the terahertz light generating element 1 as shown in FIGS. 1 and 2 (a). The excitation pulse light is an ultrashort pulse laser light represented by a femtosecond pulse laser light. The irradiation unit 2 controls the shape of the luminous flux of the excitation pulse light emitted from the laser light source 21 so that the length in the X-axis direction along the plane above the substrate 11 in the irradiation area R 1 is equal to the irradiation area R Make it longer than the length of 1 in the Y-axis direction.
照射領域 R 1の Y軸方向の長さに対する照射領域 R 1の X軸方向の長さの比は、 1 . 1以上であることが好ましい。 そして、 1 . 1以上よりは 1 . 5以上、 1 . 5以上よりは 2以上、 2以上よりは 3以上、 3以上よりは 5以上、 5以上よりは 8以上であることが好ましい。 The ratio of the length of the irradiation area R 1 in the X-axis direction to the length of the irradiation area R 1 in the Y-axis direction is It is preferably 1.1 or more. It is preferable that the number is 1.5 or more, more than 1.1, 2 or more, 1.5 or more, 3 or more, 2 or more, 5 or more, 3 or more, and 8 or more.
照射領域 R 1は、 例えば、 楕円形状に近い形状とすることが、 レーザ光等を有 効に利用する上で好ましい。 これは、 照射領域 R 1を楕円形状に近い形状にすれ ば、 後述するレーザ光源 2 1から発したレーザ光の光束の一部をカットする必要 がなくなるためである。 ここで楕円形状に近い形状とは、上記寸法 X Yの比が 1 . 1以上の X方向に細長い形状を意味し、 円を Y方向に扁平した形状ということも できる。 たとえば長円形状も含まれる。 また後述するように、 上記寸法 X Yの比 が 1 . 1以上の X方向に細長い矩形形状でもよい。  It is preferable that the irradiation region R1 has a shape close to an elliptical shape, for example, in order to effectively use laser light or the like. This is because, if the irradiation region R1 is formed to have a shape close to an elliptical shape, it is not necessary to cut a part of the light beam of the laser light emitted from the laser light source 21 described later. Here, the shape close to an elliptical shape means a shape elongated in the X direction in which the ratio of the above dimensions XY is 1.1 or more, and can also be a shape in which a circle is flattened in the Y direction. For example, an oval shape is also included. Further, as described later, a rectangular shape elongated in the X direction with a ratio of the above-mentioned dimensions XY of 1.1 or more may be used.
本実施の形態では、 照射部 2は、 具体的には、 レーザ光源 2 1と、 レーザ光源 2 1からの光束の断面形状を照射領域 R 1に合わせて整形する整形光学系、 たと えばシリンドリカルレンズ 2 2、 凹または凸の球面レンズ 2 3およびシリンドリ カルレンズ 2 4を有している。  In the present embodiment, the irradiation unit 2 is, specifically, a laser light source 21 and a shaping optical system that shapes the cross-sectional shape of the light beam from the laser light source 21 according to the irradiation region R 1, for example, a cylindrical lens 22, a concave or convex spherical lens 23 and a cylindrical lens 24 are provided.
本実施の形態の整形光学系では、 シリンドリカルレンズ 2 2および球面レンズ 2 3によって励起パルス光の光束の X軸方向がコリメ一トされ、 球面レンズ 2 3 およびシリンドリカルレンズ 2 4によって励起パルス光の光束の Y軸方向がコリ メートされる。 その結果、 励起パルス光は平行光束として照射領域 R 1に照射さ れるようになっている。 もっとも、 照射部 2の構成がこのような構成に限定され るものではない。  In the shaping optical system of the present embodiment, the X-axis direction of the light beam of the excitation pulse light is collimated by the cylindrical lens 22 and the spherical lens 23, and the light beam of the excitation pulse light is collimated by the spherical lens 23 and the cylindrical lens 24. Is collimated in the Y-axis direction. As a result, the excitation pulse light is applied to the irradiation area R1 as a parallel light flux. However, the configuration of the irradiation unit 2 is not limited to such a configuration.
例えば、 整形光学系の他の変形例としては、 励起パルス光の照射領域 R 1が基 板 1 1の導電膜 1 2 , 1 3の間の全領域（矩形領域） をカバ一するように構成する。 図 8はその一例である。'図 8の整形光学系は次のように構成されている。  For example, as another modified example of the shaping optical system, the irradiation area R 1 of the excitation pulse light is configured so as to cover the entire area (rectangular area) between the conductive films 12 and 13 of the substrate 11. I do. Figure 8 is an example. 'The shaping optical system in FIG. 8 is configured as follows.
整形光学系は、導電膜 1 2 、 1 3の間の矩形領域に相似な矩形形状の開口 2 6 a を持ったマスク 2 5を有する。 このマスク 2 5を図 1の基板 1 1とシリンドリカ ルレンズ 2 4との間に配置し、 マスク 2 5の開口 2 6 aを介して、 励起パルス光 が基板 1 1の矩形領域全体に照射するようにする。 このように構成することで、 基板 1 1を構成する光伝導部の広範囲の領域に、 励起パルス光によって自由キヤ リア （電子と正孔） を生成できる。 したがって、 テラへルツ光の放射強度の増大 に寄与する。 The shaping optical system has a mask 25 having a rectangular opening 26 a similar to a rectangular region between the conductive films 12 and 13. The mask 25 is arranged between the substrate 11 and the cylindrical lens 24 in FIG. 1 so that the excitation pulse light is irradiated on the entire rectangular area of the substrate 11 through the opening 26 a of the mask 25. To With such a configuration, free carriers (electrons and holes) can be generated by the excitation pulse light in a wide range of the photoconductive portion constituting the substrate 11. Therefore, the emission intensity of terahertz light increases To contribute.
図 8に示す整形光学系はまた、 励起パルス光の照射領域 R 1を調整してテラへ ルツ光の放射強度を調整することができる。 すなわち、 マスク 2 5は、 複数の大 きさの異なる開口 2 6 a〜2 6 dを有し、 いずれかの開口が択一的に光路に揷入 される。 たとえば、 夕一レット式のマスク切換え装置により、 このような開口の 選択を制御することができる。 夕一レット式マスク切換装置は、 選択スィッチの 操作によって回転中心軸 2 7を中心にモー夕一により駆動されるマスク 2 5を有 し、 選択スィツチの操作で各開口 2 6 a〜2 6 dを順次に切換ることができる。 これによつて、 簡単にテラへルツ光の放射強度を切り換えられる。  The shaping optical system shown in FIG. 8 can also adjust the irradiation area R1 of the excitation pulse light to adjust the radiation intensity of the terahertz light. That is, the mask 25 has a plurality of openings 26 a to 26 d having different sizes, and one of the openings is selectively inserted into the optical path. For example, the selection of such an aperture can be controlled by an evening-let type mask switching device. The evening-let type mask switching device has a mask 25 driven by a motor around a rotation center axis 27 by operation of a selection switch, and each opening 26 a to 26 d is operated by operation of the selection switch. Can be sequentially switched. This makes it possible to easily switch the radiation intensity of the terahertz light.
なお、 図 8において、 L Pが励起パルス光の光軸を示す。 図 8の開口 2 6 a〜 2 6 dがそれぞれ光軸 L Pに揷入されると、 Y方向の開口長さが変化する。 しか し、 X方向の開口長さが変化するようにしてもよい。  In FIG. 8, LP indicates the optical axis of the excitation pulse light. When the openings 26a to 26d in FIG. 8 are respectively inserted into the optical axis LP, the opening length in the Y direction changes. However, the opening length in the X direction may be changed.
本実施の形態では、 図 2に示すように、 照射領域 R 1の Y軸方向の長さが導電 膜 1 2 , 1 3間の間隔 g 1より短くされ、 照射領域 R 1と導電膜 1 2 , 1 3との 間にそれぞれ間隔があけられている。 本発明は、 必ずしもこれに限定されるもの ではない。 例えば、 照射領域 R 1の一部が導電膜 1 2 , 1 3と重なってもよい。 すなわち本発明では、 照射領域 R 1の全部がテラへルツ光発生素子 1における 2 つの導電膜 1 2， 1 3の間の領域に位置すればよい。  In the present embodiment, as shown in FIG. 2, the length of the irradiation region R1 in the Y-axis direction is shorter than the distance g1 between the conductive films 12 and 13, and the irradiation region R1 and the conductive film 1 2 , 1 and 3 respectively. The present invention is not necessarily limited to this. For example, a part of the irradiation region R1 may overlap with the conductive films 12 and 13. That is, in the present invention, the entire irradiation region R 1 may be located in the region between the two conductive films 12 and 13 in the terahertz light generation element 1.
直流電源 3は、 導電膜 1 2 , 1 3間にバイアス電圧を印加する。 直流電源 3と しては、 例えば、 商用電源からの交流を直流に変換する電源回路で構成すること ができる。 バイアス電圧の大きさは特に限定されない。 しかし、 テラへルツ光の 放射強度を可能な限り大きくするため、 バイアス電圧の大きさは、 2つの導電膜 1 2 , 1 3の間の電場 E b i asが、 絶縁破壌の起こる直前の電場強度となるように、 調節しておくことが好ましい。 DC power supply 3 applies a bias voltage between conductive films 12 and 13. The DC power supply 3 can be composed of, for example, a power supply circuit that converts AC from commercial power into DC. The magnitude of the bias voltage is not particularly limited. However, in order to maximize the radiation intensity of the terahertz light, the magnitude of the bias voltage is determined by the electric field E bi as between the two conductive films 1 2 and 1 3 It is preferable to adjust the strength so as to obtain the strength.
ここで、 本実施の形態によるテラへルツ光発生装置と比較される比較例につい て、 図 4を参照して説明する。 図 4は、 比較例におけるテラへルツ光発生素子 1 上の励起パルス光の照射領域 R 2を示す概略平面図であり、 図 2 ( a ) に対応し ている。 図 4において、 図 1および図 2中の要素と同一または対応する要素には 同一符号を付し、 その重複する説明は省略する。 この比較例で用いられているテラへルツ光発生素子 1は、 本実施の形態で用い られているテラへルツ光発生素子 1と寸法や材料等も含めて全く同一である。 こ の比較例は、 従来技術と同様に、 テラへルツ光発生素子 1上の励起パルス光の照 射領域 R 2を円形とする例である。 照射領域 R 2の直径が間隔 g 1とされ、 照射 領域 R 2がちょうど導電膜 1 2， 1 3間の領域に配置されている。 図面には示し ていないが、 比較例で使用される励起パルス光の照射部が本実施の形態で用いら れている照射部 2と異なるのは、 整形光学系のみである。 また、 比較例も本実施 の形態も、 用いられるレーザ光源 2 1は同一であり、 比較例における照射領域 R 2の単位面積当たりのレーザ光強度は、 本実施の形態における照射領域 R 1の単 位面積当たりのレーザ光強度とほぼ同一となっている。 また、 比較例で 2つの導 電膜 1 2 , 1 3間に印加されるバイアス電圧も、 本実施の形態で 2つの導電膜 1 2， 1 3間に印加されるバイアス電圧と同一である。 Here, a comparative example compared with the terahertz light generation 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 pulse light on the terahertz light generating element 1 in the comparative example, and corresponds to FIG. 2 (a). In FIG. 4, the same or corresponding elements as those in FIGS. 1 and 2 are denoted by the same reference numerals, and redundant description is 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 pulse light on the terahertz light generating element 1 is circular, as in the conventional technology. The irradiation region R2 has a diameter g1 and the irradiation region R2 is located exactly between the conductive films 12 and 13. Although not shown in the drawings, the irradiation part of the excitation pulse light used in the comparative example differs from the irradiation part 2 used in the present embodiment only in the shaping optical system. In both the comparative example and the present embodiment, 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 that of the irradiation region R1 in the present embodiment. It is almost the same as the laser light intensity per unit area. Also, the bias voltage applied between the two conductive films 12 and 13 in the comparative example is the same as the bias voltage applied between the two conductive films 12 and 13 in the present embodiment.
次に、 本実施の形態の作用について、 前述した比較例と比較して説明する。 本実施の形態および比較例では、 導電膜 1 2， 1 3間には、 直流電源 3により 直流電圧が印加されているが、 通常は、 2つの導電膜 1 2， 1 3間 （ギャップ部 分） の抵抗値が非常に高いため電流はほとんど流れない。 照射部 2からギャップ 部分に超短パルスレーザ光などを照射し、 このギャップ部を励起する。 超短パル スレ一ザ光は、 基板 1 1を構成する半導体のバンドギャップ以上のエネルギーを 持つパルスレーザ光である。 このパルスレ一ザ光をギャップ部に照射すると、 自 由キャリア （電子と正孔） が生成されてギャップ部の抵抗値が下がり電流が流れ る。励起レーザ光のパルス幅が十分に短く、かつ励起キャリアの寿命が短いため、 この電流はごく短時間しか流れない。 そして、 このとき、 電流が時間変化するた め電磁波が発生する。 励起レーザ光のパルス幅が十分に短ければ、 例えば、 1 0 O f s以下程度であれば、 その電磁波の振動数は数 T H zに達する。 これがテラ ヘルツ光であり、 基板 1 1の裏面側へと伝播する。  Next, the operation of the present embodiment will be described in comparison with the comparative example described above. In the present embodiment and the comparative example, a DC voltage is applied between the conductive films 12 and 13 by the DC power supply 3. However, normally, a DC voltage is applied between the two conductive films 12 and 13 (a gap portion). ) Has a very high resistance, so little current flows. The irradiation section 2 irradiates the gap with an ultrashort pulse laser beam or the like to excite the gap. The ultrashort pulse laser beam is a pulsed laser beam having energy equal to or higher than the band gap of the semiconductor constituting the substrate 11. When this gap is irradiated with the pulsed laser light, free carriers (electrons and holes) are generated, and the resistance value of the gap decreases and a current flows. Since the pulse width of the excitation laser beam is sufficiently short and the life of the excitation carrier is short, this current flows only for a very short time. At this time, an electromagnetic wave is generated because the current changes with time. If the pulse width of the excitation laser light is sufficiently short, for example, if it is about 10 O f s or less, the frequency of the electromagnetic wave reaches several T Hz. This is the terahertz light, which propagates to the back side of the substrate 11.
前述したように、 励起パルス光が照射されると、 光伝導部としての基板 1 1に 自由キャリア （電子と正孔） が生成され、 印加されている電場 E b i as によりキヤ リァが加速されてテラへルツ光が発生する。 このときに発生するテラへルツ光の 遠方での電場強度 E THzは、 2つの導電膜 1 2， 1 3間を流れる電流 Jの時間微分 に比例し、 次の数 1で表すことができる。 As described above, when the excitation pulse light is irradiated, the generated free carriers in the substrate 1 1 of a photoconductive unit (electrons and holes) by the electric field E bi the as being applied Canon Ria is accelerated Terahertz light is generated. The electric field strength E THz of the terahertz light generated at this time is the time derivative of the current J flowing between the two conductive films 12 and 13. It is proportional to and can be expressed by the following equation 1.
ETHzocd J /d t … （ 1 ) E THz ocd J / dt… (1)
2つの導電膜 12, 1 3間に流れる電流 Jは、 電流密度 jおよび電流の流れる 断面積 Sを用いると、 次の式 2で示す通りとなる。 ここで、 断面積 Sは、 照射領 域 Rの X軸方向の長さと Z方向の自由キヤリァ生成深さとの積となっている。 従って、 励起パルス光の照射強度を増大させることにより Z方向の自由キヤリ ァ生成深さをより深く形成できるので、 断面積 Sの大きさを調整するためには励 起パルス光の照射強度を調整すればよい。 よって、 不図示の発光制御回路によつ て励起パルス光の照射強度を調整することで、テラへルツ光の電場強度 ETHzを調 整できる。 励起パルス光の照射強度を調整する方法は、 電気的制御以外に光学フ ィルターでも同様に可能である。 The current J flowing between the two conductive films 12 and 13 is expressed by the following equation 2 using the current density j and the cross-sectional area S where the current flows. 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. Therefore, the free carrier generation depth in the Z direction can be formed deeper by increasing the irradiation intensity of the excitation pulse light, so that the irradiation intensity of the excitation pulse light is adjusted to adjust the size of the cross-sectional area S. do it. Therefore, the electric field intensity E THz of the terahertz light can be adjusted by adjusting the irradiation intensity of the excitation pulse light by a light emission control circuit (not shown). The method of adjusting the irradiation intensity of the excitation pulse light can be similarly applied to an optical filter in addition to the electric control.
J = S j … （2)  J = S j… (2)
電流密度 jは、 光励起されたキャリアの移動度 、 キャリアの密度 n、 2つの 導電膜 1 2, 1 3間に印加されている電場 Ebias、 および、 電子電荷 eを用いて、 次の式 （3) で表すことができる。 The current density j is calculated using the mobility of the photoexcited carrier, the carrier density n, the electric field E bias applied between the two conductive films 12 and 13, and the electron charge e as follows: 3) can be expressed as
従って、 励起パルス光の照射領域 R 1を広げることにより、 電子電荷 eの発生 領域が広がることから、 電流密度 jを増大でき、 電流 Jを増大できる。 よって， 励起パルス光の照射領域 R 1の広さを調整することにより、 テラへルツ光の電場 強度 ETHzを調整できる。 Accordingly, by expanding the irradiation region R1 of the excitation pulse light, the generation region of the electron charge e is expanded, so that the current density j can be increased and the current J can be increased. Therefore, the electric field strength E THz of the terahertz light can be adjusted by adjusting the width of the irradiation region R1 of the excitation pulse light.
j = n e Ebias ··· ( 3 ) j = ne E bias ... (3)
すなわち、 テラへルツ光の電場強度 ETHzは、光励起されたキャリアの移動度 、 キャリアの密度 n、 互いに分離された 2つの導電膜 12， 1 3の間に印加されて いる電場の大きさ Ebias、 断面積 Sに依存しており、 次の式 4で示す通りとなる。 That is, the electric field strength E THz of the terahertz light is the mobility of the photoexcited carrier, the carrier density n, and the magnitude E of the electric field applied between the two conductive films 12, 13 separated from each other. It depends on the bias and the cross-sectional area S, as shown in the following equation 4.
ETHzocS d j Zd t =S d (n e Ebias) / ά t … （4) ここで、 2つの導電膜 1 2， 13間に印加されている電場 Ebias を時間に依存 しないと仮定すると、 テラへルツ光の遠方での電場強度 ETHzは、 式 （4) から、 キヤリァの密度 nおよびキヤリァの移動度 の時間微分、電流の流れる断面積 S、 2つの導電膜 12, 1 3の間に印加されている電場 Ebiasに、 それぞれ比例する。 今、テラへルツ光の放射強度を可能な限り大きくするため、 2つの導電膜 1 2， 1 3間に印加されている電場 E b i asが、 例えば絶縁破壌の起こる直前の電場強度 に調節されているものとして、 電場強度 E THzの大きさについて検討する。 E THz ocS dj Zd t = S d (ne E bias ) / ά t ... (4) Here, assuming that the electric field E bias applied between the two conductive films 12 and 13 does not depend on time, From Eq. (4), the electric field strength E THz of the terahertz light at a distance is calculated from the carrier density n and the time derivative of the carrier mobility, the current cross-sectional area S, and the distance between the two conductive films 12 and 13. Is proportional to the applied electric field E bias . Now, in order to maximize the radiation intensity of terahertz light as much as possible, two conductive films 1 2, 1 3 field E bi the as being applied between, for example as being adjusted to the electric field intensity just before the occurrence of insulation Yabu壌, consider the magnitude of the electric field strength E THz.
光伝導部としての基板 1 1の材質を変更しない場合には、 キャリアの移動度 At は同じ時間変化をすると考えられる。 また、 同一のレーザ光源 2 1を使用し励起 パルス光照射領域の単位面積当たりのレーザ光強度が等しいとき、 キヤリアの密 度 nの時間変化も等しいと考えられる。 このときの単位面積当たりのレーザ光強 度は、 例えば、 発生するテラへルツ光放射強度が飽和しない範囲、 かつ素子が破 壌されない範囲で最大の強度に調整されているものとする。以上の条件の下では、 電流密度 j の時間微分は等しくなり、 放射されるテラへルツ光の遠方での電場強 度 E THzは、 電流の流れる断面積 Sのみに依存することになる。 したがって、 電流 の流れる断面積 Sが大きくなれば、 放射されるテラへルツ光の遠方での電場強度 E THzが大きくなる。 If the material of the substrate 11 as the photoconductive portion is not changed, it is considered that the carrier mobility At changes with the same time. Also, when the same laser light source 21 is used and the laser light intensity per unit area of the excitation pulse light irradiation area is equal, it is considered that the time change of the carrier density n is also equal. The laser light intensity per unit area at this time is assumed to be adjusted to the maximum intensity within a range where the generated terahertz light radiation intensity is not saturated and the element is not broken. Under the above conditions, the time derivative of the current density j is equal, and the electric field strength E THz of the radiated terahertz light at a distance depends only on the cross-sectional area S through which the current flows. Therefore, the larger the cross-sectional area S through which the current flows, the greater the electric field strength E THz of the radiated terahertz light at a distance.
本実施の形態のテラヘルッ光発生素子を、 前述した比較例としてのテラヘルッ 光発生素子と比較する。 本実施の形態におけるテラへルツ光発生素子では、 照射 領域 R 1において、 X軸方向の長さが Y軸方向の長さより長い。 これに対して、 比較例としてのテラへルツ光発生素子では、 照射領域 R 2において、 X軸方向の 長さが Y軸方向の長さと同一である。 また、 各照射領域 R l , R 2の単位面積当 たりのレーザ光強度はほぼ同一である。 したがって、 本実施の形態における照射 領域 R 1の X軸方向の長さは、 比較例における照射領域 R 2の X軸方向の長さよ り長くなる。 その結果、 電流の流れる断面積 Sは本実施の形態の方が比較例より 大きくなるので、 本実施の形態の方が比較例に比べて放射されるテラへルツ光の 遠方での電場強度 E THzが大きくなる。 The terahertz light generating element of the present embodiment will be compared with the terahertz light generating element of the comparative example described above. In the terahertz light generation element in the present embodiment, the length in the X-axis direction is longer than the length in the Y-axis direction in irradiation region R1. On the other hand, in the terahertz light generating element as a comparative example, the length in the X-axis direction is the same as the length in the Y-axis direction in the irradiation region R2. In addition, the laser beam intensity per unit area of each of the irradiation regions Rl and R2 is almost the same. Therefore, the length of irradiation region R1 in the X-axis direction in the present embodiment is longer than the length of irradiation region R2 in the X-axis direction in the comparative example. As a result, the cross-sectional area S in which the current flows is larger in the present embodiment than in the comparative example. Therefore, the electric field strength E of the terahertz light radiated in the present embodiment is greater than that in the comparative example. THz increases.
例えば、 照射領域 R 1の Y軸方向の長さを照射領域 R 2の直径の 1 0分の 1倍 とし、 照射領域 R 1の X軸方向の長さを照射領域 R 2の直径の 1 0倍とする。 こ の場合、 各照射領域 R l , R 2の単位面積当たりのレーザ光強度はほぼ同一であ るにも関わらず、 本実施の形態では、 電流の流れる断面積 Sが比較例の約 1 0倍 となり、 比較例のおおよそ 1 0倍のテラへルツ光の電場強度 E THzが得られる。 このように、 本実施の形態によれば、 発生するテラへルツ光の遠方での電場強 度 E THzが大きくなる。 したがって、本実施の形態によるテラへルツ光発生装置を 用いることにより、 テラへルツ光を利用する各種の装置 （テラへルツ光装置）、例 えば、 分光装置、 半導体 ·医用 ·食品などの検査装置、 分析装置、 イメージング 装置などにおいて、 精度の向上、 測定時間や検査時間の短縮、 測定範囲や検査範 囲の拡大、 S ZNの向上などを図ることができる。 [第 2の実施の形態] For example, the length of the irradiation region R1 in the Y-axis direction is set to be one tenth of the diameter of the irradiation region R2, and the length of the irradiation region R1 in the X-axis direction is 10 times the diameter of the irradiation region R2. Double it. In this case, despite the fact that the laser beam intensity per unit area of each of the irradiation regions Rl and R2 is almost the same, in the present embodiment, the cross-sectional area S where the current flows is about 10% of the comparative example. The electric field intensity of the terahertz light E THz 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 long distance increases. Therefore, the terahertz light generator according to the present embodiment is By using this, it is possible to improve the accuracy of various devices that use terahertz light (terahertz light device), for example, spectroscopy devices, inspection devices for semiconductors, medical devices, foods, etc., analysis devices, imaging devices, etc. It can shorten measurement time and inspection time, expand measurement range and inspection range, and improve SZN. [Second embodiment]
第 2の実施の形態によるテラへルツ光発生装置は、 第 1の実施の形態のテラへ ルツ光発生装置のテラへルツ光発生素子 1に代えて、 図 5に示すテラへルツ光発 生素子 3 1を用いるものである。 第 2の実施の形態のテラへルツ光発生装置は、 図 1中の照射部 2および直流電源 3は第 1の実施の形態と同様に備えている。 図 5は、 テラへルツ光発生素子 3 1を示す概略平面図であり、 図 2 ( a ) に対応し ている。 図 5において、 図 1および図 2中の要素と同一または対応する要素には 同一符号を付し、 その重複する説明は省略する。  The terahertz light generating device according to the second embodiment is different from the terahertz light generating device 1 of the first embodiment in that the terahertz light generating element 1 shown in FIG. The element 31 is used. The terahertz light generation device according to the second embodiment includes the irradiation unit 2 and the DC power supply 3 in FIG. 1 similarly to the first embodiment. FIG. 5 is a schematic plan view showing the terahertz light generation element 31 and corresponds to FIG. 2 (a). In FIG. 5, elements that are the same as or correspond to elements in FIGS. 1 and 2 are given the same reference numerals, and overlapping descriptions are omitted.
- 図 5に示すように、 テラへルツ光発生素子 3 1の 2つの導電膜 1 2， 1 3間の 間隔 g 2は、 第 1の実施の形態のテラへルツ光発生素子 1の 2つの導電膜 1 2， 1 3間の間隔 g 1よりも小さく、 照射部 2から照射される励起パルス光の射領域 R 1の X軸方向の長さと実質的に同一である。 照射領域 R 1は、 第 1および第 2 の実施の形態ともに全く同一である。  -As shown in FIG. 5, the distance g2 between the two conductive films 12 and 13 of the terahertz light generation element 31 is equal to the distance g2 of the terahertz light generation element 1 of the first embodiment. It is smaller than the distance g 1 between the conductive films 12 and 13, and is substantially the same as the length in the X-axis direction of the emission region R 1 of the excitation pulse light irradiated from the irradiation unit 2. The irradiation area R1 is exactly the same in both the first and second embodiments.
このように、 第 2の実施の形態のテラへルツ光発生素子 3 1では間隔 g 2を間 隔 g 1に比べて小さく設定することにより、次の利点がある。 2つの導電膜 1 2， As described above, the terahertz light generation element 31 of the second embodiment has the following advantages by setting the interval g2 smaller than the interval g1. Two conductive films 1 2,
1 3間の電場 E b i as を絶縁破壌の起こる直前の電場強度に設定する場合、 第 2の 実施の形態で 2つの導電膜 1 2， 1 3間に印加されるバイアス電圧は、 第 1の実 施の形態で 2つの導電膜 1 2， 1 3間に印加されるバイアス電圧より小さく設定 することができる。 その他の利点は、 第 1の実施の形態と同様である。 1 If the electric field E bi the as between 3 is set to the electric field intensity just before the occurrence of insulation Yabu壌, bias voltage applied between the second two conductive layers 1 2, in the embodiment 1 3, first In this embodiment, the bias voltage can be set lower than the bias voltage applied between the two conductive films 12 and 13. Other advantages are similar to those of the first embodiment.
「第 3の実施の形態] "Third embodiment"
第 3の実施の形態によるテラへルツ光発生装置は、 第 1の実施の形態のテラへ ルツ光発生装置の照射部 2からテラへルツ光発生素子 1に照射される励起パルス 光の照射領域の形状を変更し、 これにともない、 レーザ光の強度を大きくしたも のである。 The terahertz light generation device according to the third embodiment includes an irradiation region of the excitation pulse light irradiated from the irradiation unit 2 of the terahertz light generation device of the first embodiment to the terahertz light generation element 1. The shape of the laser was changed, and the intensity of the laser beam was increased accordingly. It is.
図 6は、 本発明の第 3の実施の形態によるテラへルツ光発生装置で用いられる テラへルツ光発生素子 1に対する、 照射部からの励起パルス光の照射領域 R 3を 示す概略平面図であり、 図 2 ( a ) および図 4に対応している。 図 6において、 図 1および図 2、 図 4中の要素と同一または対応する要素には同一符号を付し、 その重複する説明は省略する。  FIG. 6 is a schematic plan view showing an irradiation region R 3 of the excitation pulse light from the irradiation unit with respect to the terahertz light generation element 1 used in the terahertz light generation device according to the third embodiment of the present invention. Yes, corresponding to Figure 2 (a) and Figure 4. 6, the same or corresponding elements as those in FIGS. 1, 2, and 4 are denoted by the same reference numerals, and the description thereof will not be repeated.
本実施の形態によるテラへルツ光発生装置は、 第 1の実施の形態と全く同一の テラへルツ光発生素子 1および直流電源 3を備えている。  The terahertz light generating device according to the present embodiment includes a terahertz light generating element 1 and a DC power supply 3 which are exactly the same as those in the first embodiment.
図 6に示すように、 第 3の実施の形態における照射領域 R 3は、 第 1の実施の 形態と同様に、 X軸方向の長さが Y軸方向の長さに比べて長いが、 照射領域 R 3 の Y軸方向の長さが導電膜 1 2， 1 3間の間隔 g 1と実質的に同一とされ、 照射 領域 R 3がちょうど導電膜 1 2 , 1 3間に配置されている。 第 3の実施の形態に おける照射部のレーザ光源 （図 1中のレーザ光源 2 1に相当するもの） が発する レーザ光の強度は、 第 1の実施の形態における照射部 2のレーザ光源 2 1および 上記比較例における照射部のレーザ光源が発するレーザ光の強度より高い。  As shown in FIG. 6, in the irradiation region R3 in the third embodiment, the length in the X-axis direction is longer than the length in the Y-axis direction, as in the first embodiment. The length of the region R 3 in the Y-axis direction is substantially equal to the distance g 1 between the conductive films 12 and 13, and the irradiation region R 3 is disposed exactly between the conductive films 12 and 13. . The intensity of the laser light emitted from the laser light source of the irradiation unit (corresponding to the laser light source 21 in FIG. 1) in the third embodiment is the same as that of the laser light source 21 of the irradiation unit 2 in the first embodiment. And the intensity is higher than the intensity of the laser light emitted from the laser light source of the irradiation unit in the comparative example.
光スィッチ素子を用いたテラへルツ光発生素子 1では、 照射領域に照射する励 起パルス光の単位面積当たりの強度が所定強度より高くなると、 発生するテラへ ルツパルス光の強度が飽和し、 励起パルス光の単位面積当たりの強度を上記所定 強度より高めてもテラへルツ光の強度をより高めることができない。 また、 励起 パルス光の単位面積当たりの強度が高過ぎると、素子の破壊等のおそれも生ずる。 上記比較例 （図 4を参照） において、 照射領域 R 2の単位面積当たりの励起パ ルス光強度が飽和強度または素子の破壌等の限界強度であるとすれば、 照射部の レーザ光源としてより高強度のレーザ光を出力するものを用いても、 発生するテ ラヘルツ光放射強度が飽和したり素子が破壊されたりして、 発生するテラへルツ パルス光の放射強度を増大させることができない。  In the terahertz light generation element 1 using an optical switch element, when the intensity per unit area of the excitation pulse light irradiating the irradiation area is higher than a predetermined intensity, the intensity of the generated terahertz pulse light is saturated and the excitation is performed. Even if the intensity per unit area of the pulsed light is higher than the predetermined intensity, the intensity of the terahertz light cannot be further increased. Further, if the intensity of the excitation pulse light per unit area is too high, there is a possibility that the element may be destroyed. In the above 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 such as element rupture, etc. Even if a laser that outputs high-intensity laser light is used, the generated terahertz light radiation intensity is saturated or the device is destroyed, and the generated terahertz pulse light radiation intensity cannot be increased.
本実施の形態のテラへルツ光発生装置では、 照射領域 R 3は、 その Y軸方向の 長さは照射領域 R 2の Y軸方向の長さと同一であるが、 X軸方向の長さは照射領 域 R 2の X軸方向の長さよりも長くしている。そのため、照射部のレーザ光源（レ —ザ光源 2 1に相当） としてより高強度のレーザ光を出力するものを用いても、 照射領域 R 3の単位面積当たりの励起パルス光強度を、 上記飽和強度や上記限界 強度以下に抑えることができる。 したがって、 本実施の形態によれば、 照射部の レーザ光源 （レーザ光源 2 1に相当） としてより高強度のレーザ光を出力するも のを用いた場合、 第 1の実施の形態に関する説明で述べた作用と相俟って、 発生 するテラへルツ光放射強度が飽和したり素子が破壌されたりすることなく、 発生 するテラへルツパルス光の放射強度を増大させることができる。 In the terahertz light generator of the present embodiment, the irradiation region R 3 has the same length in the Y-axis direction as the irradiation region R 2 in the Y-axis direction, but has the same length in the X-axis direction. The irradiation area R 2 is longer than the length in the X-axis direction. Therefore, even if a laser light source (corresponding to the laser light source 21) that outputs higher intensity laser light is used as the irradiation unit, 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 a laser light source (corresponding to laser light source 21) that outputs a higher-intensity laser beam is used as the laser light source of the irradiation unit, the description of the first embodiment will be given. In combination with the action, the radiation intensity of the generated terahertz pulse light can be increased without saturating the generated radiation intensity of the terahertz light and without breaking the element.
例えば、 次の条件で説明する。  For example, the explanation is given under the following conditions.
(1) 照射領域 R 3の X軸方向の長さを照射領域 R 2の X軸方向の長さの 10倍 とする。  (1) The length of the irradiation region R3 in the X-axis direction is set to 10 times the length of the irradiation region R2 in the X-axis direction.
(2) 上記比較例で用いられている照射部のレーザ光源の出力を、 照射領域 R 2 の単位面積当たりの励起パルス光強度が飽和強度または素子の破壊等の限界強度 とする。  (2) The output of the laser light source of the irradiation unit used in the above comparative example is defined as the intensity of the excitation pulse light per unit area of the irradiation region R 2 being the saturation intensity or the limit intensity such as element destruction.
上記 （1)、 (2) を条件とすると、 第 3の実施の形態のテラへツル光発生装置 では、 比較例のレーザ光源の出力の約 10倍の出力を持つレ一ザ光源を使用して も、 発生するテラヘルツ光放射強度が飽和したり素子が破壌されたりすることな く、 発生するテラへルツパルス光の遠方での電場強度を、 上記比較例のおおよそ 10倍に増大させることができる。  Given the conditions (1) and (2) above, the terahertz light generator of the third embodiment uses a laser light source having an output about 10 times that of the laser light source of the comparative example. Even if the generated terahertz light radiation intensity does not saturate or the element does not burst, the electric field strength of the generated terahertz pulse light at a distant place can be increased to about 10 times that of the above comparative example. it can.
[第 4の実施の形態] [Fourth embodiment]
図 7は本発明の第 4の実施の形態によるテラへルツ光発生装置で用いられるテ ラヘルツ光発生素子 41を示す図であり、図 7 (a)はその概略斜視図、図 7 (b) は図 7 (a) 中の W— W線に沿った概略断面図、 図 7 (c) は要部を示す拡大平 面図である。  FIG. 7 is a diagram showing a terahertz light generation element 41 used in a terahertz light generation device according to a fourth embodiment of the present invention, FIG. 7 (a) is a schematic perspective view thereof, and FIG. 7 is a schematic cross-sectional view along the line W--W in FIG. 7 (a), and FIG. 7 (c) is an enlarged plan view showing a main part.
本実施の形態によるテラヘルツ光発生装置が第 1の実施の形態と異なる所は、 テラへルツ光発生素子 1に代えて、 図 7に示すテラへルツ光発生素子 41が用い られている点のみである。 図面には示していないが、 第 4の実施の形態のテラへ ツル光発生装置は、 図 1中の照射部 2と同様の照射部 （ただし、 パワーはたとえ ば 1/10以下） および直流電源 3と同様の直流電源 （ただし、 印加電圧はたと えば 1/1 00以下) を備えている。 テラへルツパルス光発生素子 41は、 いわゆる大口径の光スィッチ素子ではな い光スィツチ素子、 すなわち小口径光スィツチ素子を用いたテラへルツ光発生素 子の一例であり、 ダイポ一ルアンテナを利用したものである。 The terahertz light generating device according to the present embodiment is different from the first embodiment only in that a terahertz light generating element 41 shown in FIG. 7 is used instead of the terahertz light generating element 1. It is. Although not shown in the drawing, the terahertz light generator according to the fourth embodiment has the same irradiation section as irradiation section 2 in FIG. 1 (however, the power is, for example, 1/10 or less) and a DC power supply. It has the same DC power supply as in 3 (however, the applied voltage is 1/100 or less, for example). 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-aperture optical switch element, that is, a small-aperture optical switch element, and uses a dipole antenna. Things.
テラへルツ光発生素子 41は、 図 7に示すように、 基板 42と、 基板 42の上 側 （上下は図 7 (b) 中の上下で示す。） の平面上に形成された光伝導膜 43と、 光伝導膜 43上に形成された互いに分離された 2つの導電膜 44， 45とを備え ている。 導電膜 44， 45の少なくとも一部同士が、 基板 42の上側の平面に沿 つた Y軸方向に所定間隔 g 3をあけるように配置されている。  As shown in FIG. 7, the terahertz light generating element 41 is composed of a substrate 42 and a photoconductive film formed on a plane on the upper side of the substrate 42 (the upper and lower sides are indicated by the upper and lower sides in FIG. 7B). 43, and two conductive films 44 and 45 formed on the photoconductive film 43 and separated from each other. At least some of the conductive films 44 and 45 are arranged so as to have a predetermined interval g3 in the Y-axis direction along the plane above the substrate 42.
基板 42の材質としては、 例えば、 S i、 Ge、 G a A sまたはサファイアな どを用いることができる。 また、 光伝導膜 43の材質としては、 例えば、 低温成 長 G a A sまたはイオン注入シリコン （RD— SOS) などを用いることができ る。 なお、 RD— SOSについては、 前述したスミスらの論文 （IEEE Journal of Quantum Electronics, Vol.24, No.2, pp.255-260 (1988)) にも、 開示されてい る。 導電膜 45としては、 例えば、 A 1や Auなどの金属膜を用いることができ る。  As the material of the substrate 42, for example, Si, Ge, GaAs, sapphire, or the like can be used. Further, as a material of the photoconductive film 43, for example, low-temperature growth GaAs or ion-implanted silicon (RD-SOS) can be used. RD-SOS is also disclosed in the above-mentioned paper by Smith et al. (IEEE Journal of Quantum Electronics, Vol. 24, No. 2, pp. 255-260 (1988)). As the conductive film 45, for example, a metal film such as A1 or Au can be used.
本実施の形態では、 導電膜 44 , 45は、 図 7に示すように、 平行伝送線路を 形成する伝送線路部 44 a, 45 aと、それらの両端に形成された電極部 44 b, 44 c, 45 b, 45 cとを有している。 伝送線路部 44 a, 45 aの中央部分 が内側に突出し、 その間に基板 42の上側の平面に沿った方向に微小な間隔、 例 えば、 数/ xm程度の間隔 g 3が設けられている。 この間隔 g 3の付近の部分によ つて光スィッチ素子が構成され、 また、 伝送線路部 44 a， 45 aにおける間隔 g 3の付近の部分によりダイポールアンテナが構成されている。  In the present embodiment, as shown in FIG. 7, the conductive films 44 and 45 are composed of transmission line portions 44a and 45a forming parallel transmission lines and electrode portions 44b and 44c formed at both ends thereof. , 45b, 45c. The central portions of the transmission line portions 44a and 45a protrude inward, and a small interval, for example, an interval g3 of about several / xm is provided between the transmission line portions 44a and 45a in a direction along the upper plane of the substrate 42. An optical switch element is formed by a portion near the gap g3, and a dipole antenna is formed by a portion near the gap g3 in the transmission line sections 44a and 45a.
第 4の実施の形態でも、 図 1中の照射部 2に相当する照射部がテラへルツ光発 生素子 41に励起パルス光を照射する照射領域 R4は、 X軸方向の長さが Y軸方 向の長さに比べて長い。 また、 照射領域 R 4の Y軸方向の長さは間隔 g 3と実質 的に同一とされ、 照射領域 R 4がちょうど間隔 g 3の領域に配置される。  Also in the fourth embodiment, the irradiation region R4 in which the irradiation unit corresponding to the irradiation unit 2 in FIG. 1 irradiates the terahertz light generation element 41 with the excitation pulse light has a length in the X-axis direction that is the Y-axis. It is longer than the length in the direction. Further, the length of the irradiation region R4 in the Y-axis direction is substantially the same as the interval g3, and the irradiation region R4 is arranged in the region exactly at the interval g3.
本実施の形態によっても、 第 1の実施の形態と同様の利点が得られる。  According to the present embodiment, advantages similar to those of the first embodiment can be obtained.
以上、 本発明の各実施の形態について説明したが、 本発明の特徴を損なわない 限り、 本発明はこれらの実施の形態に限定されるものではない。 産業上の利用可能性 The embodiments of the present invention have been described above, but the present invention is not limited to these embodiments as long as the features of the present invention are not impaired. Industrial applicability
本発明によるテラへルツ光発生装置は、 例えば、 分光装置、 半導体 ' 医用 .食 品などの検査装置、 分析装置、 イメージング装置など各種計測装置に利用できる。  The terahertz light generation device according to the present invention can be used for various measurement devices such as spectroscopy devices, inspection devices for semiconductors, medical and food products, analysis devices, imaging devices, and the like.

Claims

請求の範囲 The scope of the claims
'光発生装置は、 'The light generator is
光伝導部と、 この光伝導部の所定の面上に形成され互いに分離された 2つの導 電部とを有し、 2つの導電部の少なくとも一部同士が前記所定の面に沿った第 1 の方向に所定間隔をあけるように配置されたテラへルツ光発生素子と、  A photoconductive portion, and two conductive portions formed on a predetermined surface of the photoconductive portion and separated from each other, and at least a part of the two conductive portions is a first conductive portion along the predetermined surface. A terahertz light generating element arranged at predetermined intervals in the direction of
前記テラへルツ光発生素子の所定の照射領域に励起パルス光を照射する照射部 と、  An irradiation unit that irradiates a predetermined irradiation area of the terahertz light generation element with excitation pulse light,
前記 2つの導電部間にバイアス電圧を印加する電圧印加部とを備え、  A voltage application unit for applying a bias voltage between the two conductive units,
前記照射部は、 前記所定の面に沿った第 2の方向であって前記第 1の方向と直 交する第 2の方向の前記照射領域の長さが、 前記第 1の方向の前記照射領域の長 さに比べて長くなるように、 前記励起パルス光を発生する。  The irradiation unit may be configured such that a length of the irradiation region in a second direction along the predetermined plane and which is orthogonal to the first direction is the irradiation region in the first direction. The excitation pulse light is generated so as to be longer than the length.
2 .  2.
請求項 1記載のテラへルツ光発生装置において、  The terahertz light generator according to claim 1,
前記照射部は、 前記照射領域の全部または大部分が、 前記テラへルツ光発生素 子における前記 2つの導電部の前記少なくとも一部同士の間の領域となるように、 前記励起パルス光を発生する。  The irradiation unit generates the excitation pulse light such that all or most of the irradiation region is a region between the at least some of the two conductive units in the terahertz light generation element. I do.
3 .  3.
請求項 1または 2記載のテラへルツ光発生装置において、  The terahertz light generator according to claim 1 or 2,
前記照射領域は楕円に近い形状である。  The irradiation area has a shape close to an ellipse.
4 . Four .
請求項 1〜 3のいずれかに記載のテラへルツ光発生装置において、  The terahertz light generator according to any one of claims 1 to 3,
前記照射領域の前記第 1の方向の長さに対する前記照射領域の前記第 2の方向 の長さの比が、 1 . 1以上である。  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 1.1 or more.
5 .  Five .
請求項 1または 2記載のテラへルツ光発生装置は、  The terahertz light generator according to claim 1 or 2,
前記照射領域は略矩形形状である。  The irradiation area has a substantially rectangular shape.
6 .  6.
請求項 1または 2記載のテラへルツ光発生装置において、 前記照射部は、 前記照射領域の大きさを調整できる開口部を備える。 The terahertz light generator according to claim 1 or 2, The irradiation unit includes an opening that can adjust a size of the irradiation area.
7 . 7.
請求項 6記載のテラへルツ光発生装置において、  The terahertz light generator according to claim 6,
前記開口部は、 複数の大きさの異なる矩形形状の開口部を備え、 前記矩形形状 の開口部を励起パルス光の光路に切り換えて挿入することにより、 励起パルス光 の照射領域を制御する。  The opening has a plurality of rectangular openings having different sizes, and the rectangular opening is switched to the optical path of the excitation pulse light to be inserted therein, thereby controlling the irradiation area of the excitation pulse light.
8 .  8.
請求項 1記載のテラへルツ光発生装置において、  The terahertz light generator according to claim 1,
前記照射部は、 励起パルス光を発生する発生素子を有し、 励起パルス光の照射 強度を調整できる発光制御手段を有する。  The irradiating section has a generating element for generating the excitation pulse light, and has a light emission control means capable of adjusting the irradiation intensity of the excitation pulse light.
9 .  9.
請求項 1〜8のいずれかのテラへルツ光発生装置において、  The terahertz light generator according to any one of claims 1 to 8,
前記光伝導部は、 基板の上面に形成した光伝導層である。  The photoconductive portion is a photoconductive layer formed on the upper surface of the substrate.
1 0 .  Ten .
請求項 9のテラへルツ光発生装置において、  The terahertz light generator according to claim 9,
前記光伝導層はェピタキシャル成長で成膜される。  The photoconductive layer is formed by epitaxial growth.
1 1 . 1 1.
請求項 1〜 1 0のいずれかのテラへルツ光発生装置において、  The terahertz light generator according to any one of claims 1 to 10,
前記テラへルツ光発生素子は大口怪光スィツチ素子である。  The terahertz light generating element is a large mysterious light switch element.
1 2 .  1 2.
請求項 1 ~ 1 0のいずれかのテラへルツ光発生装置において、  The terahertz light generator according to any one of claims 1 to 10,
前記テラヘルツ光発生素子は小口怪光スィツチ素子である。  The terahertz light generating element is a forehead light switch element.
1 3 .  13 .
請求項 1〜 1 2のいずれかのテラへルツ光発光装置を用いた光計測装置。  An optical measurement device using the terahertz light emitting device according to claim 1.
PCT/JP2002/010365 2001-10-04 2002-10-04 Terahertz light generator WO2003032451A1 (en)

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JP5835795B2 (en) * 2011-09-13 2015-12-24 株式会社Ｓｃｒｅｅｎホールディングス Inspection method and inspection apparatus
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JPH10311789A (en) * 1997-05-13 1998-11-24 Nikon Corp Photometer

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JPH10311789A (en) * 1997-05-13 1998-11-24 Nikon Corp Photometer

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