光电导天线产生太赫兹电磁波的研究
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摘要
由于THz波处于电磁波谱的特殊位置,因此在物体成像、环境监测、医疗诊断、射电天文、卫星通讯和军用雷达等方面具有十分广阔的应用前景和重大的研究价值。但目前THz源所产生的THz电磁波的功率都比较小,极大的制约了THz技术的发展。
本文主要围绕THz电磁波的特性、产生方法及检测技术,研究了产生THz电磁波的光电导方法、电光取样技术以及提高THz辐射功率的问题。
用电光取样的方法对经过Si_3N_4钝化的半绝缘GaAs光电导偶极天线及其裸片进行了一系列的对比实验,并采用蒙特卡罗的模拟方法对GaAs光电导体内的光生载流子在偏置电场作用下的输运过程进行模拟。实验表明,在相同的触发光能下,较高的偏置电场作用于光电导天线,天线体内的光生载流子由于受到较大的外加电场力作用,将产生较高功率的太赫兹波。在相同的偏置电场下,太赫兹波功率将随光能增加而增加,但由于空间电荷电场屏蔽作用,太赫兹波功率的增长并不按光生载流子数目增长的平方关系增长,大孔径光电导天线能够承载更多的载流子,因而可以产生比小孔径光电导天线功率更高的太赫兹波。如果屏蔽效应被忽略的话,载流子寿命与入激光脉冲对大孔径产生和辐射太赫兹波有非常重要的影响,即载流子的捕获时间越长或入射激光的波长越短,太赫兹波辐射的强度就越大。
在建立计算模型的过程中,考虑到载流子寿命以及触发光脉冲的宽度等因素会对THz辐射产生影响。故通过改变参数,根据实验模拟结果归纳出这些因素对THz辐射的影响。这对用光电导偶极天线产生大功率THz辐射的发展具有十分重要的指导意义。
Based on the special position in electromagnetic spectrum, THz is widely used in many fields, such as imaging, environment supervising, medical diagnosis, radio astronomy, satellite communications and military radar and so on. But lacking in high-power THz source has seriously blocked the technology progress of THz.
Based on THz wave characteristics, the methods of generation and detection of THz wave, the technology of electro-optic sampling and improving the power of THz radiation have been investigated.
The semi-conductive GaAs dipole antennas are passivated by Si_3N_4 and the bare antennas experiments are contrasted. The carriage principle of carriers biased by DC field in GaAs photoconductive has been simulated by Monte Carlo. The out-coming THz power can be improved in condition of photoconductive antennas biased by higher DC electric field with the same laser energy. The reason is that the carriers inside antennas are affected by stranger electric force. The power of THz wave will increase with the more laser energy in the same bias electric field. Because of the shielding affection of space charge, the increasing of the THz power is not according to the square of the number of photoconductive on carriers. The large aperture can bear more carriers, so that the THz power of large aperture antennas is higher than that of small-bore antennas. In condition of neglecting the shielding affection, the life of the carriers and the laser play important role in radiation of THz wave. The longer the trapping time of carriers, the higher the power of THz radiation. Meanwhile, the shorter the wavelength of incident laser pulse, the higher the power of THz radiation.
During the process of building the model, because the life of carriers and the pulse width of laser are taken into account in the model, these factors on the impact of THz radiation have been summarized by changing the parameters. It is important to design the new experiments to generate high-power THz radiation by using of photoconductive dipole antenna.
本文主要围绕THz电磁波的特性、产生方法及检测技术,研究了产生THz电磁波的光电导方法、电光取样技术以及提高THz辐射功率的问题。
用电光取样的方法对经过Si_3N_4钝化的半绝缘GaAs光电导偶极天线及其裸片进行了一系列的对比实验,并采用蒙特卡罗的模拟方法对GaAs光电导体内的光生载流子在偏置电场作用下的输运过程进行模拟。实验表明,在相同的触发光能下,较高的偏置电场作用于光电导天线,天线体内的光生载流子由于受到较大的外加电场力作用,将产生较高功率的太赫兹波。在相同的偏置电场下,太赫兹波功率将随光能增加而增加,但由于空间电荷电场屏蔽作用,太赫兹波功率的增长并不按光生载流子数目增长的平方关系增长,大孔径光电导天线能够承载更多的载流子,因而可以产生比小孔径光电导天线功率更高的太赫兹波。如果屏蔽效应被忽略的话,载流子寿命与入激光脉冲对大孔径产生和辐射太赫兹波有非常重要的影响,即载流子的捕获时间越长或入射激光的波长越短,太赫兹波辐射的强度就越大。
在建立计算模型的过程中,考虑到载流子寿命以及触发光脉冲的宽度等因素会对THz辐射产生影响。故通过改变参数,根据实验模拟结果归纳出这些因素对THz辐射的影响。这对用光电导偶极天线产生大功率THz辐射的发展具有十分重要的指导意义。
Based on the special position in electromagnetic spectrum, THz is widely used in many fields, such as imaging, environment supervising, medical diagnosis, radio astronomy, satellite communications and military radar and so on. But lacking in high-power THz source has seriously blocked the technology progress of THz.
Based on THz wave characteristics, the methods of generation and detection of THz wave, the technology of electro-optic sampling and improving the power of THz radiation have been investigated.
The semi-conductive GaAs dipole antennas are passivated by Si_3N_4 and the bare antennas experiments are contrasted. The carriage principle of carriers biased by DC field in GaAs photoconductive has been simulated by Monte Carlo. The out-coming THz power can be improved in condition of photoconductive antennas biased by higher DC electric field with the same laser energy. The reason is that the carriers inside antennas are affected by stranger electric force. The power of THz wave will increase with the more laser energy in the same bias electric field. Because of the shielding affection of space charge, the increasing of the THz power is not according to the square of the number of photoconductive on carriers. The large aperture can bear more carriers, so that the THz power of large aperture antennas is higher than that of small-bore antennas. In condition of neglecting the shielding affection, the life of the carriers and the laser play important role in radiation of THz wave. The longer the trapping time of carriers, the higher the power of THz radiation. Meanwhile, the shorter the wavelength of incident laser pulse, the higher the power of THz radiation.
During the process of building the model, because the life of carriers and the pulse width of laser are taken into account in the model, these factors on the impact of THz radiation have been summarized by changing the parameters. It is important to design the new experiments to generate high-power THz radiation by using of photoconductive dipole antenna.
引文
[1]Peter H.Siegel.Terahertz Technology[J].IEEE TRANSACTIONS ON MICROWAVE THEOR3AND TECHNIQUES,2002,50(3):910-928.
[2]Bradley Ferguson,张希成.太赫兹科学与技术研究回顾[J].物理,2003,32(5):286-293.[3]Markelz A Q Roitberg A,Heilweil E J.Pulsed terahertz spectroscopy of DNA bovine serum albumin and collagen between 0.1 and 0.2 THz[J].Chem..Phys.Lett.,2002,320:42-48.
[4]Nagel M,Bolivar P H,Brucherseifer M,et al.Integrated THz technology for label-free genetic diagnostics[J].Appl.Phys.Lett.,2002,80:154-156.
[5]Wu L,Zhang X C,Auston D H..Terahertz beam generation by femtosecond optical pulse in electro-optic materials[J].Applied Physics Letter,1992,61(15):1784.
[6]Mickan S,Abbott D,Munch J,et al.Analysis of system trade-offs for terahertz imaging[J].Microeletronics Journa,2000,31:503.
[7]Jiang Z P,Zhang X C.Free-Space Electro-Optic Technologies[J].THz Sensing and Imaging Technology.2001,33:161.
[8]Zhang X C.The Encyclopedia of Imaging Science&Technology[J].Imaging Technology&Systems Section,2002,2:1993-1404.
[9]Chen Q,Jiang Z P,Xu G X et al.,Near-field terahertz imaging with a dynamic aperture[J].Opt.Lett.,2000,25(15):1122-1124.
[10]Menikh A,MacColl R,Mannlla C A et al..Terahertzboisensing technology:frontier and progress [J].Chemical Physics and Physical Chemisty,2002,56(32):854-856.
[11]K.Rudeger,Tredicucci,Alessandro,et al..Terahertz semiconductor-hetero structure laser[J].Nature,2002,417:156-159.
[12]Liu H C,Wachter M,Ban D,et al..Effect of doping concentration on the performance of terahertz quantum-cascade lasers[J].Appl.Phys.Lett.,2005,87(14):1102.
[13]S NishizaWa et al..New application of terahertz time-domain spectrometry(THz-TDS)to the phonon-polariton observation on ferroelectric crystals[J].Phys.Med.Biol.,2002,47:3771-3776.
[14]Bradley Ferguson,张希成.太赫兹科学与技术研究回顾[J].物理,2003,32(5):292.
[15]W Shi,W L.Jia,L.Hou,et al..Terahertz Radiation from Large Aperture Bulk Semi-insulating GaAs Photoconductive Dipole Antenna[J].Chinese Physics Letters,2004,21(9):1842-1844.
[16]N.Froberg,M.Mack,B.B.Hu,X.C.Zhang,and D.H.Auston.500 Ghz electrically steerable photoconducting antenna-array[J].Appl.Phys.Lett.,1990,58(5):446-448.
[17]N.Froberg,B.B.Hu,X.C.Zhang,and D.H.Auston.Terahertz radiation from a photoconducting antenna array[J].IEEE J.Quantum.Electron.,1992,28(10):2291.
[18]Nan M.Froberg,Bin Bin Hu,Xi-Cheng Zhang and David H.Auston.Terahertz Radiation from a Photoconducting Antenna Array[J].IEEE JOURNAL OF QUANTUM ELECTRONIC,1992,28(10):2301.
[19]赵尚弘,陈国夫,赵卫等.THz射线产生技术及应用最新进展[J].激光技术,2000,24(6):352-353.
[20]J.T.Darrow,X.C.Zhang,and D.H.Auston.Power scaling of large-aperture photoconducting antennas[J].Appl.Phys.Lett.,1991,58:25-27.
[21]S.G.Park,A.M.Weiner,M.R.Melloch,C.W.Siders,J.L.W.Siders,and A.J.Taylor.High power narrow band Terahertz generation using large aperture photoconductors[J].IEEE J.Quantum.Electron.,1999,35(8):1257-1268.
[22]G.Rodriguez and A.J.Taylor.Screening of the bias field in terahertz generation from photoconductors[J].Opt.Lett.,1996,21:1046-1048.
[23]洪胜富,齐正中.短脉冲雷射激发兆赫兹辐射技术及其应用[J].物理,2001,23(2):323-324.
[24]Hattori T,Tukamoto K,Nakatsuka H.Time-resolved study of in-tense terahertz pulses generated by a large-aperture photoconductive antenna[J].Jan.J.Appl.Phys.,2001,40(8):4907.
[25]Q.Wu,X.C.Zhang.Free-Space Electro-Optic Sampling of Terahertz Beam[J].Appl.Phys.Lett.,1995,67:3523.
[26]Q.Wu,X.C.Zhang.Design and Characterization of Traveling-Wave Electro-optic THz Sensors[J].J.Select.Topics Quantum Electron,1996,2:693.
[27]Q.Wu,X.C.Zhang.Free-Space Electro-Optic Sampling of Mid-Infrared Pulses[J].Appl.Phys.Lett.,1997,71:1285.
[28]S.Kono,M.Tani,P.Go and K.Sakai,et al..Detection of up to 20 THz with a low-temperature grown GaAs photoconductive antenna gated with 15 fs light pulses[J].Appl.Phys.Lett.,2000,77:4104.
[29]S.Kona,M.Tani and K.Sakai,et al..Ultrabroadband photoconductive detection comparison with free-space EOS[J].Appl.Phys.Lett.,2001,79:898.
[30]A.Nahata,A.S.Weling,and T.F.Heinz.A wideband coherent terahertz spectroscopy system using optical rectification and electro-optic sampling[J].Appl.Phys.Lett.,1996,69:2321.
[31]D.T.F.Marple.Refractive index of ZnSe and CdTe[J].J.Appl.Phys.,1964,25:539.
[32]J.T.Darrow,X.-C.Zhang and D.H.Auston.Power scaling of large-aperture photoconducting antennas[J].Appl.Phys.Lett.,1991,58(1):25.
[33]A.Bonvalet,M.Jofre,J.L.Martin and A.Migus.Generation of ultrabroadband femtosecond pulses in the mid-infrared by optical rectification of 15 fs light pulses at 100 MHz repetition rate[J].Appl.Phys.Lett.,1995,67(20):2907.
[34]Minwoo Yi,Kang Hee Lee,Inhee Maeng,Joo-Hiuk Son,R.D.Averitt,and Jaewook Ahn.Tailoring the Spectra of Terahertz Emission from CdTe and ZnTe Electro-Optic Crystals[J].Japanese Journal of Applied Physics,2008,47:202-204.
[35]J.A.Valdmanis,G.Mourou,and C.W.Gabel.Picosecond electrooptic sampling system[J].Appl.Phys. Lett.,1982,41:211.
[36]J.A.Valdmanis and G.Mourou.Subpicosecond electrooptic sampling:principles and applications[J].IEEE Journal of Quantum Electronics,1986,22:69-78.
[37]M.Born and E.Wolf.Principles of Optics[M].Pergamon,1987:334.
[38]G.Gallot and D.Grischkowsky.Electro-Optic Detection of THz Radiation[J].opt.soc.Am.-B,1999,12:486.
[39]G.Mourou,C.V.Stancampiano,and D.Blumenthal.Picosecond Microwave Pulse Generation [J].Appl.Phys.Lett.,1981,38:470.
[40]G.Mourou,C.V.Stancampiano,A.Antonetti,and A.Orszag.Opto-electronic vivaldi transceiver[J].Appl.Phys.Lett.,1981,39:295.
[41]王少宏,许景周,汪力,张希成等.THz技术的应用及展望[J].物理,2001,30(10):612-614.
[42]陈敏,肖体乔,徐洪杰.超短THz脉冲在随机散射介质中的传播[J].物理学报,2003,11:16.
[43]Toshiaki Hattori,Kazuhiro Egawa,Shin-ichi Ookuma and Taro Itatani.Intense Terahertz Pulses from Large-Aperture Antenna with Interdigitated Electrodes[J].Jpn.J.Appl.Phys.,2006,45:422.
[44]Han P Y,Cho G C,and Zhang X C.Materials for terahertz science and technology[J].Opt.Lett.,2000,25:242.
[45]G.S.Smith.An Introduction to Classical Electromagnetic Radiation[M].U.K.Cambridge University Press,1990,28:1607.
[46]贾婉丽,纪卫莉,施卫.半绝缘GaAs光电导开关产生太赫兹波电场屏蔽效应的二维Monte Carlo 模拟[J].物理学报,2007,56:2042.
[47]施卫,贾婉丽,纪卫莉,刘锴.光电导开关工作模式的蒙特卡罗模拟[J].物理学报,2007,56:6334-6636.
[2]Bradley Ferguson,张希成.太赫兹科学与技术研究回顾[J].物理,2003,32(5):286-293.[3]Markelz A Q Roitberg A,Heilweil E J.Pulsed terahertz spectroscopy of DNA bovine serum albumin and collagen between 0.1 and 0.2 THz[J].Chem..Phys.Lett.,2002,320:42-48.
[4]Nagel M,Bolivar P H,Brucherseifer M,et al.Integrated THz technology for label-free genetic diagnostics[J].Appl.Phys.Lett.,2002,80:154-156.
[5]Wu L,Zhang X C,Auston D H..Terahertz beam generation by femtosecond optical pulse in electro-optic materials[J].Applied Physics Letter,1992,61(15):1784.
[6]Mickan S,Abbott D,Munch J,et al.Analysis of system trade-offs for terahertz imaging[J].Microeletronics Journa,2000,31:503.
[7]Jiang Z P,Zhang X C.Free-Space Electro-Optic Technologies[J].THz Sensing and Imaging Technology.2001,33:161.
[8]Zhang X C.The Encyclopedia of Imaging Science&Technology[J].Imaging Technology&Systems Section,2002,2:1993-1404.
[9]Chen Q,Jiang Z P,Xu G X et al.,Near-field terahertz imaging with a dynamic aperture[J].Opt.Lett.,2000,25(15):1122-1124.
[10]Menikh A,MacColl R,Mannlla C A et al..Terahertzboisensing technology:frontier and progress [J].Chemical Physics and Physical Chemisty,2002,56(32):854-856.
[11]K.Rudeger,Tredicucci,Alessandro,et al..Terahertz semiconductor-hetero structure laser[J].Nature,2002,417:156-159.
[12]Liu H C,Wachter M,Ban D,et al..Effect of doping concentration on the performance of terahertz quantum-cascade lasers[J].Appl.Phys.Lett.,2005,87(14):1102.
[13]S NishizaWa et al..New application of terahertz time-domain spectrometry(THz-TDS)to the phonon-polariton observation on ferroelectric crystals[J].Phys.Med.Biol.,2002,47:3771-3776.
[14]Bradley Ferguson,张希成.太赫兹科学与技术研究回顾[J].物理,2003,32(5):292.
[15]W Shi,W L.Jia,L.Hou,et al..Terahertz Radiation from Large Aperture Bulk Semi-insulating GaAs Photoconductive Dipole Antenna[J].Chinese Physics Letters,2004,21(9):1842-1844.
[16]N.Froberg,M.Mack,B.B.Hu,X.C.Zhang,and D.H.Auston.500 Ghz electrically steerable photoconducting antenna-array[J].Appl.Phys.Lett.,1990,58(5):446-448.
[17]N.Froberg,B.B.Hu,X.C.Zhang,and D.H.Auston.Terahertz radiation from a photoconducting antenna array[J].IEEE J.Quantum.Electron.,1992,28(10):2291.
[18]Nan M.Froberg,Bin Bin Hu,Xi-Cheng Zhang and David H.Auston.Terahertz Radiation from a Photoconducting Antenna Array[J].IEEE JOURNAL OF QUANTUM ELECTRONIC,1992,28(10):2301.
[19]赵尚弘,陈国夫,赵卫等.THz射线产生技术及应用最新进展[J].激光技术,2000,24(6):352-353.
[20]J.T.Darrow,X.C.Zhang,and D.H.Auston.Power scaling of large-aperture photoconducting antennas[J].Appl.Phys.Lett.,1991,58:25-27.
[21]S.G.Park,A.M.Weiner,M.R.Melloch,C.W.Siders,J.L.W.Siders,and A.J.Taylor.High power narrow band Terahertz generation using large aperture photoconductors[J].IEEE J.Quantum.Electron.,1999,35(8):1257-1268.
[22]G.Rodriguez and A.J.Taylor.Screening of the bias field in terahertz generation from photoconductors[J].Opt.Lett.,1996,21:1046-1048.
[23]洪胜富,齐正中.短脉冲雷射激发兆赫兹辐射技术及其应用[J].物理,2001,23(2):323-324.
[24]Hattori T,Tukamoto K,Nakatsuka H.Time-resolved study of in-tense terahertz pulses generated by a large-aperture photoconductive antenna[J].Jan.J.Appl.Phys.,2001,40(8):4907.
[25]Q.Wu,X.C.Zhang.Free-Space Electro-Optic Sampling of Terahertz Beam[J].Appl.Phys.Lett.,1995,67:3523.
[26]Q.Wu,X.C.Zhang.Design and Characterization of Traveling-Wave Electro-optic THz Sensors[J].J.Select.Topics Quantum Electron,1996,2:693.
[27]Q.Wu,X.C.Zhang.Free-Space Electro-Optic Sampling of Mid-Infrared Pulses[J].Appl.Phys.Lett.,1997,71:1285.
[28]S.Kono,M.Tani,P.Go and K.Sakai,et al..Detection of up to 20 THz with a low-temperature grown GaAs photoconductive antenna gated with 15 fs light pulses[J].Appl.Phys.Lett.,2000,77:4104.
[29]S.Kona,M.Tani and K.Sakai,et al..Ultrabroadband photoconductive detection comparison with free-space EOS[J].Appl.Phys.Lett.,2001,79:898.
[30]A.Nahata,A.S.Weling,and T.F.Heinz.A wideband coherent terahertz spectroscopy system using optical rectification and electro-optic sampling[J].Appl.Phys.Lett.,1996,69:2321.
[31]D.T.F.Marple.Refractive index of ZnSe and CdTe[J].J.Appl.Phys.,1964,25:539.
[32]J.T.Darrow,X.-C.Zhang and D.H.Auston.Power scaling of large-aperture photoconducting antennas[J].Appl.Phys.Lett.,1991,58(1):25.
[33]A.Bonvalet,M.Jofre,J.L.Martin and A.Migus.Generation of ultrabroadband femtosecond pulses in the mid-infrared by optical rectification of 15 fs light pulses at 100 MHz repetition rate[J].Appl.Phys.Lett.,1995,67(20):2907.
[34]Minwoo Yi,Kang Hee Lee,Inhee Maeng,Joo-Hiuk Son,R.D.Averitt,and Jaewook Ahn.Tailoring the Spectra of Terahertz Emission from CdTe and ZnTe Electro-Optic Crystals[J].Japanese Journal of Applied Physics,2008,47:202-204.
[35]J.A.Valdmanis,G.Mourou,and C.W.Gabel.Picosecond electrooptic sampling system[J].Appl.Phys. Lett.,1982,41:211.
[36]J.A.Valdmanis and G.Mourou.Subpicosecond electrooptic sampling:principles and applications[J].IEEE Journal of Quantum Electronics,1986,22:69-78.
[37]M.Born and E.Wolf.Principles of Optics[M].Pergamon,1987:334.
[38]G.Gallot and D.Grischkowsky.Electro-Optic Detection of THz Radiation[J].opt.soc.Am.-B,1999,12:486.
[39]G.Mourou,C.V.Stancampiano,and D.Blumenthal.Picosecond Microwave Pulse Generation [J].Appl.Phys.Lett.,1981,38:470.
[40]G.Mourou,C.V.Stancampiano,A.Antonetti,and A.Orszag.Opto-electronic vivaldi transceiver[J].Appl.Phys.Lett.,1981,39:295.
[41]王少宏,许景周,汪力,张希成等.THz技术的应用及展望[J].物理,2001,30(10):612-614.
[42]陈敏,肖体乔,徐洪杰.超短THz脉冲在随机散射介质中的传播[J].物理学报,2003,11:16.
[43]Toshiaki Hattori,Kazuhiro Egawa,Shin-ichi Ookuma and Taro Itatani.Intense Terahertz Pulses from Large-Aperture Antenna with Interdigitated Electrodes[J].Jpn.J.Appl.Phys.,2006,45:422.
[44]Han P Y,Cho G C,and Zhang X C.Materials for terahertz science and technology[J].Opt.Lett.,2000,25:242.
[45]G.S.Smith.An Introduction to Classical Electromagnetic Radiation[M].U.K.Cambridge University Press,1990,28:1607.
[46]贾婉丽,纪卫莉,施卫.半绝缘GaAs光电导开关产生太赫兹波电场屏蔽效应的二维Monte Carlo 模拟[J].物理学报,2007,56:2042.
[47]施卫,贾婉丽,纪卫莉,刘锴.光电导开关工作模式的蒙特卡罗模拟[J].物理学报,2007,56:6334-6636.