Phase-stable electromagnetic pulses in the THz frequency range offer several unique capabilities in time-resolved spectroscopy.However,the diversity of their application is limited by the covered spectral bandwidth.In...Phase-stable electromagnetic pulses in the THz frequency range offer several unique capabilities in time-resolved spectroscopy.However,the diversity of their application is limited by the covered spectral bandwidth.In particular,the upper frequency limit of photoconductive emitters-the most widespread technique in THz spectroscopy-reaches only up to 7 THz in the regular transmission mode due to absorption by infrared-active optical phonons.Here,we present ultrabroadband(extending up to 70 THz)THz emission from an Au-implanted Ge emitter that is compatible with mode-locked fibre lasers operating at wavelengths of 1.1 and 1.55μm with pulse repetition rates of 10 and 20 MHz,respectively.This result opens up the possibility for the development of compact THz photonic devices operating up to multi-THz frequencies that are compatible with Si CMOS technology.展开更多
Plasma waves play an important role in many solid-state phenomena and devices.They also become significant in electronic device structures as the operation frequencies of these devices increase.A prominent example is ...Plasma waves play an important role in many solid-state phenomena and devices.They also become significant in electronic device structures as the operation frequencies of these devices increase.A prominent example is field-effect transistors(FETs),that witness increased attention for application as rectifying detectors and mixers of electromagnetic waves at gigahertz and terahertz frequencies,where they exhibit very good sensitivity even high above the cut-off frequency defined by the carrier transit time.Transport theory predicts that the coupling of radiation at THz frequencies into the channel of an antenna-coupled FET leads to the development of a gated plasma wave,collectively involving the charge carriers of both the two-dimensional electron gas and the gate electrode.In this paper,we present the first direct visualization of these waves.Employing graphene FETs containing a buried gate electrode,we utilize near-field THz nanoscopy at room temperature to directly probe the envelope function of the electric field amplitude on the exposed graphene sheet and the neighboring antenna regions.Mapping of the field distribution documents that wave injection is unidirectional from the source side since the oscillating electrical potentials on the gate and drain are equalized by capacitive shunting.The plasma waves,excited at 2 THz,are overdamped,and their decay time lies in the range of 25-70 fs.Despite this short decay time,the decay length is rather long,i.e.,0.3-0.5μm,because of the rather large propagation speed of the plasma waves,which is found to lie in the range of 3.5-7×10^(6)m/s,in good agreement with theory.The propagation speed depends only weakly on the gate voltage swing and is consistent with the theoretically predicted 1/4 power law.展开更多
基金The support by R.Bottger and the Ion Beam Center(IBC)at HZDR is gratefully acknowledged.
文摘Phase-stable electromagnetic pulses in the THz frequency range offer several unique capabilities in time-resolved spectroscopy.However,the diversity of their application is limited by the covered spectral bandwidth.In particular,the upper frequency limit of photoconductive emitters-the most widespread technique in THz spectroscopy-reaches only up to 7 THz in the regular transmission mode due to absorption by infrared-active optical phonons.Here,we present ultrabroadband(extending up to 70 THz)THz emission from an Au-implanted Ge emitter that is compatible with mode-locked fibre lasers operating at wavelengths of 1.1 and 1.55μm with pulse repetition rates of 10 and 20 MHz,respectively.This result opens up the possibility for the development of compact THz photonic devices operating up to multi-THz frequencies that are compatible with Si CMOS technology.
基金funding from the Adolf Messer Stiftungthe Friedrich-Ebert Stiftung+5 种基金the Rosa Luxemburg Stiftungthe EU-funded action H2020-MSCA-ITN-2015-ETN CELTAfunded by the Deutsche Forschungsgemeinschaft(DFG project RO 770/40)support via the BMBF projects 05K16ODA,05K16ODC,05K19ODA,and 05K19ODBfunding from the Swedish Research Council(grant no.2017.-04504)funding from the Academy of Finland(grant nos.325810,312297,320167,and 314810).
文摘Plasma waves play an important role in many solid-state phenomena and devices.They also become significant in electronic device structures as the operation frequencies of these devices increase.A prominent example is field-effect transistors(FETs),that witness increased attention for application as rectifying detectors and mixers of electromagnetic waves at gigahertz and terahertz frequencies,where they exhibit very good sensitivity even high above the cut-off frequency defined by the carrier transit time.Transport theory predicts that the coupling of radiation at THz frequencies into the channel of an antenna-coupled FET leads to the development of a gated plasma wave,collectively involving the charge carriers of both the two-dimensional electron gas and the gate electrode.In this paper,we present the first direct visualization of these waves.Employing graphene FETs containing a buried gate electrode,we utilize near-field THz nanoscopy at room temperature to directly probe the envelope function of the electric field amplitude on the exposed graphene sheet and the neighboring antenna regions.Mapping of the field distribution documents that wave injection is unidirectional from the source side since the oscillating electrical potentials on the gate and drain are equalized by capacitive shunting.The plasma waves,excited at 2 THz,are overdamped,and their decay time lies in the range of 25-70 fs.Despite this short decay time,the decay length is rather long,i.e.,0.3-0.5μm,because of the rather large propagation speed of the plasma waves,which is found to lie in the range of 3.5-7×10^(6)m/s,in good agreement with theory.The propagation speed depends only weakly on the gate voltage swing and is consistent with the theoretically predicted 1/4 power law.
