WO2012056784A1 - Antenne photoconductrice et procédé de production d'une onde térahertz - Google Patents

Antenne photoconductrice et procédé de production d'une onde térahertz Download PDF

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Publication number
WO2012056784A1
WO2012056784A1 PCT/JP2011/067867 JP2011067867W WO2012056784A1 WO 2012056784 A1 WO2012056784 A1 WO 2012056784A1 JP 2011067867 W JP2011067867 W JP 2011067867W WO 2012056784 A1 WO2012056784 A1 WO 2012056784A1
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WO
WIPO (PCT)
Prior art keywords
electrodes
voltage
antenna
photoconductive antenna
terahertz wave
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Application number
PCT/JP2011/067867
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English (en)
Japanese (ja)
Inventor
黒柳　和良
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浜松ホトニクス株式会社
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Publication of WO2012056784A1 publication Critical patent/WO2012056784A1/fr

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/28—Investigating the spectrum
    • G01J3/42—Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
    • G01N21/3581—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using far infrared light; using Terahertz radiation

Definitions

  • the present invention relates to a photoconductive antenna used for spectroscopic measurement using, for example, a terahertz wave, and a terahertz wave generating method using such a photoconductive antenna.
  • This type of photoconductive antenna generally includes an electrode formed on a semiconductor layer.
  • This electrode has an antenna portion that forms an antenna region for generating or detecting terahertz waves, and a pad portion that is provided at an end of the antenna portion and is electrically connected to an external power source.
  • a photoconductive antenna used for spectroscopic measurement a multi-electrode type photoconductive antenna provided with a plurality of electrodes has been used in order to increase the generation efficiency of terahertz waves (for example, Patent Document 1 and Non-Patent Document 1, 2).
  • Non-Patent Document 1 in order to prevent the polarity of the generated terahertz wave from being reversed for each electrode and canceling the output, the light shielding is performed to block the pump light between every other electrode. A mask is placed.
  • the dead area that does not contribute to the generation of the terahertz wave is formed by the light shielding mask, and the ratio of the dead area to the element area cannot be overlooked. As a result, the generation efficiency of the terahertz wave cannot be sufficiently obtained. There is a fear.
  • the light absorption layer is separated from the substrate on which the crystal has been grown, and every other electrode is separated when this is attached to another insulating substrate.
  • the process of manufacturing the photoconductive antenna element is complicated.
  • the separation part between the electrodes becomes a dead area, the generation efficiency of the terahertz wave may not be sufficiently obtained as in the case of Non-Patent Document 1.
  • the arrival time of the pump light incident on each electrode is adjusted by making the pump light incident on a glass plate having unevenness in a stripe shape, thereby forming a dead area.
  • the polarity of the generated terahertz wave is reversed for each electrode, and the output is prevented from being canceled.
  • this configuration has a problem that the difference in arrival time of pump light incident on every other electrode must be realized by the glass thickness.
  • 1 ps in the time domain corresponds to an optical path length difference of 300 ⁇ m.
  • an optical path length difference of 300 ⁇ m is formed between air having a refractive index of 1.5 and air having a refractive index of 1.0
  • the distance between the electrodes in the photoconductive antenna is about several tens of ⁇ m, and a glass plate having a high aspect ratio of the order of several tens of ⁇ m ⁇ several mm is required to realize a larger optical path length difference. In practice, it is difficult to produce a glass plate.
  • the present invention has been made to solve the above-described problems, and an object thereof is to provide a photoconductive antenna that can reduce a dead area with a simple configuration, and a terahertz wave generation method using such a photoconductive antenna.
  • a photoconductive antenna is a photoconductive antenna that generates or detects a terahertz wave, and includes a semiconductor layer and a plurality of electrodes arranged at predetermined intervals on the semiconductor layer.
  • the electrode is connected to the antenna unit, which forms an antenna region for generating or detecting a terahertz wave, and from the external power source so as to gradually increase or decrease in order of electrode arrangement. And a pad portion to which a voltage is applied.
  • this photoconductive antenna In this photoconductive antenna, a voltage from an external power source is applied to the pad portion of each electrode so as to gradually increase or decrease in the order of electrode arrangement. Thereby, it is possible to prevent the polarity of the generated terahertz wave from being reversed for each electrode and canceling the output.
  • this photoconductive antenna since there is no conventional light shielding mask or electrode separation part, there is no dead area except for the electrode itself, and the generation efficiency of terahertz waves can be sufficiently secured. Further, since the polarity of the terahertz wave is adjusted by adjusting the voltage applied to each electrode without using a glass plate for forming the optical path length difference, the configuration can be simplified.
  • a voltage distribution circuit that distributes a voltage from an external power supply to the pad portion so as to gradually increase or decrease gradually in the electrode arrangement order is preferably provided. In this way, the voltage between the electrodes can be freely set with a single power source.
  • the voltage distribution circuit is preferably configured by resistors connected between the electrodes.
  • the voltage distribution circuit can be configured with a simple configuration.
  • the voltage distribution circuit is constituted by Zener diodes connected between the electrodes.
  • the voltage applied to each electrode by the Zener diode can be limited to a desired value.
  • a capacitor is connected in parallel to the Zener diode. In this case, noise generated in the Zener diode can be removed by the capacitor.
  • the terahertz wave generation method includes a semiconductor layer and a plurality of electrodes arranged on the semiconductor layer with a predetermined interval, and the electrodes form an antenna region for generating or detecting terahertz waves.
  • this terahertz wave generation method a voltage from an external power source is applied to the pad portion of each electrode of the photoconductive antenna so as to gradually increase or decrease in the electrode arrangement order. Thereby, it is possible to prevent the polarity of the generated terahertz wave from being reversed for each electrode and canceling the output.
  • this terahertz wave generation method it is not necessary to provide a conventional light shielding mask or a separation part between electrodes in the photoconductive antenna, and it is possible to eliminate the dead area excluding the electrode itself in the photoconductive antenna. Therefore, the generation efficiency of the terahertz wave can be sufficiently secured. Further, since the polarity of the terahertz wave is adjusted by adjusting the voltage applied to each electrode without using a glass plate for forming the optical path length difference, the configuration of the photoconductive antenna can be simplified.
  • the electrodes in the order of arrangement and apply a different voltage to the pad portion for each group.
  • the intensity distribution of the generated terahertz wave can be made uniform corresponding to the intensity distribution of the pump light.
  • one electrode located on the center side may be set to the ground potential, and a voltage from an external power source may be applied to the pad portion so that the electrodes located on both ends have the maximum positive voltage and the maximum negative voltage, respectively. preferable.
  • the maximum and minimum values of the voltage applied to the photoconductive antenna can be suppressed. Thereby, generation
  • a signal generator as an external power source and apply a modulation voltage from the signal generator to the pad portion.
  • a modulation element for modulating the pump light becomes unnecessary.
  • the dead area of the photoconductive antenna can be reduced with a simple configuration.
  • the generation efficiency of the terahertz wave can be sufficiently improved.
  • FIG. 1 is a diagram showing a configuration example of a spectroscopic measurement system to which a photoconductive antenna according to the present invention is applied.
  • the spectroscopic measurement system 1 uses a laser light source 11 that emits a femtosecond pulse laser.
  • the laser light L emitted from the laser light source 11 is split into pump light L1 and probe light L2 by the beam splitter 12 in the middle of the optical path.
  • the pump light qualified through the beam splitter 12 enters the terahertz wave generating antenna 16 through the mirror 13, the chopper 14, and the condenser lens 15.
  • the laser beam L reflected by the beam splitter 12 enters the terahertz wave detection antenna 21 through the mirror 17, the retroreflector 18 that can move in the optical axis direction, the mirror 19, and the condenser lens 20.
  • the terahertz wave T generated by the terahertz wave generating antenna 16 is incident on the terahertz wave detecting antenna 21 by the parabolic mirrors 22 and 23 and causes a correlation action with the probe light L2.
  • a voltage from a DC voltage source (external power source) 24 is applied to the terahertz wave generation antenna 16, and a lock-in amplifier 25 is connected to the terahertz wave detection antenna 21.
  • a time correlation waveform between the terahertz wave T and the probe light L2 is obtained, and the waveform is Fourier-transformed by the computer 26, whereby the terahertz wave T Is obtained.
  • FIG. 2 is a plan view showing a first embodiment of a photoconductive antenna that constitutes the terahertz wave generating antenna 16 and the terahertz wave detecting antenna 21.
  • the photoconductive antenna 31 is a multi-electrode element in which a plurality of electrodes 33 are formed on the surface of a semiconductor layer 32.
  • the semiconductor layer 32 is a GaAs layer epitaxially grown at a low temperature (200 ° C. to 300 ° C.) by MBE on a semi-insulating GaAs substrate, for example, and is formed to have a length of about 10 mm, a width of about 6 mm, and a thickness of 1 ⁇ m to 10 ⁇ m. Yes.
  • the electrode 33 is an ohmic electrode such as AuGe / Au.
  • the electrode 33 includes a linear antenna portion 34 that forms an antenna region A where the terahertz wave T is generated and detected, and a pad portion 35 connected to an end portion of the antenna portion 34.
  • six-stage electrodes 33 are formed on the surface of the semiconductor layer 32, and the antenna portions 34 having a width of about 6 ⁇ m form strip lines with an interval of about 20 ⁇ m.
  • the pad portion 35 has a rectangular shape with a length of 800 ⁇ m and a width of 800 ⁇ m, for example, and is arranged on one side of the surface of the semiconductor layer 32.
  • FIG. 3 is a diagram showing a voltage distribution circuit 36 to the photoconductive antenna 31.
  • the DC voltage source 24 is connected to the electrode 33 of each stage of the photoconductive antenna 31 by a voltage distribution circuit 36 via a pad portion 35 (not shown in FIG. 3).
  • stage will be about several hundred Mohm.
  • the resistance value is reduced to about 1 M ⁇ , depending on the intensity of the pump light L1.
  • a voltage of several tens V for example, 10 V to 50 V
  • the voltage from the DC voltage source 24 is applied to the pad portion 35 of each electrode 33 so as to gradually increase or decrease in the order of arrangement of the electrodes 33.
  • the polarity of the generated terahertz wave T can be prevented from being reversed for each electrode 33 and the output being canceled.
  • this photoconductive antenna 31 since there is no conventional light shielding mask and separation part between the electrodes, there is no dead area except for the electrode 33 itself, and the generation efficiency of the terahertz wave T can be sufficiently secured. Further, since the polarity of the terahertz wave T is adjusted by adjusting the voltage applied to each electrode 33 without using a glass plate for forming the optical path length difference, the configuration can be simplified.
  • FIG. 4 is a diagram showing a voltage distribution circuit to the photo conductive antenna according to the second embodiment of the present invention.
  • the photoconductive antenna 41 according to the second embodiment is different from the first embodiment in the configuration of the voltage distribution circuit 46 to the electrode 33 in each stage. That is, in the photoconductive antenna 41, the voltage distribution circuit 46 is configured by connecting the resistors 47 connected between the electrodes 33 and 33 to the single DC voltage source 24.
  • the resistance value of the resistor 47 between the electrodes 33 and 33 may be a value sufficiently smaller than the resistance value of the electrode 33 when the pump light L1 is incident. As described above, when the distance between the antenna portions 34 and 34 is about 20 ⁇ m, the dark resistance of the electrode 33 in each stage is about several hundreds M ⁇ , and the resistance value when the pump light L1 is incident on the antenna region A is 1 M ⁇ . Decrease to a degree. Therefore, if the number of stages of the electrodes 33 is n, the resistance value of each resistor 47 may be 100 k ⁇ , for example.
  • the generation efficiency of the terahertz wave T can be sufficiently secured with a simple configuration as in the first embodiment.
  • the voltage distribution circuit 46 configured by the connection of the resistor 47 eliminates the need to prepare the DC voltage source 24 according to the number of stages of the electrodes 33, and the single DC voltage source 24 applies the voltage to the electrodes 33 of each stage. Can be set freely.
  • FIG. 5 is a diagram showing a voltage distribution circuit to the photo conductive antenna according to the third embodiment of the present invention.
  • the photoconductive antenna 51 according to the third embodiment is further different from the first embodiment in the configuration of the voltage distribution circuit 56 to each electrode 33. That is, in the photoconductive antenna 51, the voltage distribution circuit 56 is configured by connecting the Zener diode 57 connected between the electrodes 33 and 33 to the single DC voltage source 24, respectively. Each Zener diode 57 is connected in parallel with a capacitor 58.
  • the generation efficiency of the terahertz wave T can be sufficiently secured with a simple configuration as in the first embodiment.
  • the voltage applied to the electrode 33 at each stage can be limited to a desired value by the voltage distribution circuit 56 configured by connecting the Zener diode 57. Further, noise generated in the Zener diode 57 can be removed by the capacitor 58.
  • FIG. 6 is a diagram showing a voltage distribution circuit to the photo conductive antenna according to the fourth embodiment of the present invention.
  • the photoconductive antenna 61 according to the fourth embodiment is further different from the first embodiment in the configuration of the voltage distribution circuit 66 to each electrode 33. That is, in the photoconductive antenna 61, the electrodes 33 at each stage are divided into groups (two groups of G1 and G2 in this embodiment) in the order of arrangement, and different voltages are applied to each group by the voltage distribution circuit 66.
  • the voltage that can be applied to each electrode group can be set individually, so that the terahertz wave T generated corresponding to the intensity distribution can be set.
  • the intensity distribution can be made uniform.
  • FIG. 7 is a diagram showing a voltage distribution circuit to the photo conductive antenna according to the fifth embodiment of the present invention.
  • the configuration of the voltage distribution circuit 76 to each electrode 33 is the same as that of the first embodiment.
  • the voltage from the DC voltage source 24 is applied to the pad part 35 so that the one electrode 33 located at the ground is at the ground potential and the electrodes 33 located at both ends have the maximum positive voltage and the maximum negative voltage, respectively.
  • the generation efficiency of the terahertz wave T can be sufficiently secured with a simple configuration as in the first embodiment.
  • the maximum value and the minimum value of the voltage applied to the photoconductive antenna 76 can be suppressed, the occurrence of discharge or the like can be avoided.
  • the pad portion 35 is arranged on one side of the surface of the semiconductor layer 32, but the position of the pad portion 35 is not particularly limited, and for example, the semiconductor layer 32. It may be arranged alternately on one side and the other side of the surface.
  • the pump light L1 modulated by the chopper 14 is intermittently incident on the terahertz wave generating antenna 16.
  • the chopper 14 is removed from the spectroscopic measurement system 1 and the DC voltage source 24 is used instead. You may make it apply the modulation voltage from a signal generator to the pad part 35.
  • the voltage modulation waveform in this case may be a rectangular wave having a modulation period t 0 of about 0.01 ms to 0.1 s, for example, as shown in FIG.
  • a sine wave modulation waveform may be used.

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Abstract

L'invention vise à proposer une antenne photoconductrice apte à réduire les zones blanches et présentant une structure simple, ainsi qu'un procédé de production d'ondes térahertz qui utilise cette antenne photoconductrice. A cet effet, l'invention concerne une antenne photoconductrice (31) dans laquelle une tension provenant d'une alimentation électrique continue (24) est appliquée à des parties pastilles (35) d'électrodes (33) de façon à augmenter ou réduire progressivement l'ordre d'agencement des électrodes (33). Ainsi, la polarité des ondes térahertz (T) qui sont produites varie légèrement pour chaque électrode (33) et on peut empêcher que les ondes térahertz ne soient inversées pour différentes électrodes (33) et annulent la sortie. Dans l'antenne photoconductrice (31), aucun masque conventionnel d'interception de la lumière n'est prévu, ni aucun élément de séparation entre les électrodes ; de ce fait, il n'existe pas de zones blanches autres que les électrodes (33) elles-mêmes et l'efficacité de la production des ondes térahertz (T) peut être assurée. Par ailleurs, aucune dalle de verre n'est utilisée pour obtenir des différences dans la longueur des trajets optiques et les polarités des ondes térahertz (T) sont ajustées par ajustement de la tension appliquée aux électrodes (33) ; la structure peut donc être simplifiée.
PCT/JP2011/067867 2010-10-27 2011-08-04 Antenne photoconductrice et procédé de production d'une onde térahertz WO2012056784A1 (fr)

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JP2010241108A JP5384463B2 (ja) 2010-10-27 2010-10-27 光伝導アンテナ及びテラヘルツ波発生方法
JP2010-241108 2010-10-27

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN109632840A (zh) * 2018-12-17 2019-04-16 深圳市华讯方舟太赫兹科技有限公司 太赫兹显微成像系统及成像方法

Families Citing this family (2)

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Publication number Priority date Publication date Assignee Title
KR101420226B1 (ko) * 2012-11-23 2014-07-18 한국전기연구원 비파괴 검사를 위한 고출력 테라헤르츠 신호원 기반 실시간 검출 및 영상 장치
NL2015262B9 (en) 2015-08-04 2017-04-10 Univ Delft Tech Photoconductive antenna array.

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2000049402A (ja) * 1998-07-27 2000-02-18 Hamamatsu Photonics Kk テラヘルツ波発生装置
JP2007316044A (ja) * 2006-05-26 2007-12-06 Junichi Nishizawa フォトキャパシタンス法を用いたテラヘルツ光センシングシステム
JP2007324310A (ja) * 2006-05-31 2007-12-13 Osaka Univ 電磁波発生装置

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2000049402A (ja) * 1998-07-27 2000-02-18 Hamamatsu Photonics Kk テラヘルツ波発生装置
JP2007316044A (ja) * 2006-05-26 2007-12-06 Junichi Nishizawa フォトキャパシタンス法を用いたテラヘルツ光センシングシステム
JP2007324310A (ja) * 2006-05-31 2007-12-13 Osaka Univ 電磁波発生装置

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN109632840A (zh) * 2018-12-17 2019-04-16 深圳市华讯方舟太赫兹科技有限公司 太赫兹显微成像系统及成像方法

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